[RCSE] new product announcement (a little belated)
for sport flying the electric. I like to launch into a shallow climb at about 1/2 throttle, get my right hand back on the transmitter and check that everything is trimmed and stable, then smoothly open the throttle to full while simultaneously rotating to a max performance climb angle. This gets the model to Hi-start altitudes in about 10 seconds, and to winch-launch heights in about 20-30 seconds. There is theoretically enough juice in the battery for about a dozen climbs like this, although I've never actually succeeded in running the battery completely out in any of my test flights. Of course both the sailplane and electric versions still have all the parts for the builder's choice of V-tail or two different sizes of conventional tail. It still has the wide root chord for a big visual footprint that makes it easier to see at high altitudes and for beginners. It also still has the same great handling and extremely strong dynamic stability, and the long tail moment that helps it display lift so effectively. That long tail also provides novice fliers with plenty of visual cues to help them master the fine art of controlling pitch attitude. The sailplane version typically weighs 26 to 28 ounces, for a wing loading of 5.18 to 5.58 oz./sq.ft. without ballast. Low speed performance is excellent as you might expect, but so is range and penetration. One of our customers described it as having ...the same float, but twice the range of some of its wooden 2-meter competitors. The electric version is of course heavier, but still lighter than some 2-meter pure sailplanes. My personal prototype, with the MP Jet 28/20-7 outrunner, 14-9.5 CAM prop, CC Phoenix 35 ESC, 2-cell 2000 mah 15C rated Li-poly motor battery and a separate 270 mah NiMH pack to power the radio (it's a good idea to use a separate radio battery on models that are capable of extended soaring flights) only weighs 37 ounces, for a wing loading of only 7.37 ounces per square foot. At that weight it has a very nice blend of low speed thermalling ability and high speed penetration. We have more details and photos of both versions posted on our website. If you're thinking about trying a 2-meter sailplane and/or electric sailplane, you might do well to take a look. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com/ RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
Re: [RCSE] Re:wing alignment
Chuck Anderson brings up a very good point: ...I ignore wing root alignment. I align the wings at either the inboard end of the ailerons or at the polyhedral break for RES models On a propeller blade the aerodynamic center is at the 75% radius, i.e.: 3/4 of the way out from the prop's axis to the tip of the blade. The blade angles are measured at this radius during final assembly of the prop. This is where most of the thrust is centered on the blade, so it's good for the performance issues. It's also well outboard on the blade, where most of the bending moments are generated, so it's also good for addressing vibration issues. On a wing, we have a contradiction to deal with in this regard. For roll trim, we should measure well out on the wing, like Chuck recommends. However, the bulk of the lift on a wing is generated in the center, so for performance issues the roots are probably more critical. On the other hand, the ailerons are out near the tips, so the airfoil distortion (and related performance losses) introduced by aileron deflection is related to roll trim. This raises the priority of the outboard measurements again. Ideally we need to consider the alignment along the entire wing. The consensus I see in all of this is that we should probably check incidences at the root, mid-span and tip, and then split the differences to get all of those as close as possible. Of course the problem with that approach is that you'll spend so much time getting the wings mounted that you'll never finish the model! Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
[RCSE] New product announcement - Li-poly battery mounting kit
After all the recent controversy about safety issues with Li-poly batteries, we got to thinking about what we could do to help the situation. One piece of very good advice is to remove the battery from the airplane before charging, and then charge it in a fireproof container of some sort. I used to put the battery in a covered Pyrex dish, but lately I've been following Fred Marks' advice and sticking the battery in our oven. However, the key to all of this is having an efficient way to remove and reinstall the battery. I personally do not like hook-and-loop fasteners such as Velcro for this purpose. They're bulky, can be relatively heavy, and really are not all that secure, especially at the G forces that some of our more aerobatic Roadkill Series models can pull with a 3-cell pack. Some of the things I do with the Triplane, the Ryan ST or some of the others currently in development could quite conceivably pull a battery loose from a piece of Velcro. Tape is lighter and more secure, but is definitely not very convenient for removing and reinstalling the battery. Instead, we came up with a neat little laser-cut plywood plate that glues or tapes to the battery. The ply plate has keyhole slots in it for slipping onto two small screws. Just loosen the screws half a turn each, and you can slip the battery off of the screws through the keyhole slots in the plate. After charging, just slip the plate back into place and tighten the screws back down. Quick, simple, light and very secure. The mounting kit is designed to adapt to a variety of battery sizes, up through about 1200 mah 3-cell packs. The big factor is the amount of weight you can safely support with the mounting plate; with enough additional mounting plates you can probably support larger batteries. The mounting kit includes CAD-drawn instructions, the battery mounting plate, two screws and a pair of plywood plates to glue to the model to hold the screws if the surface you're mounting to is something that won't hold screws by itself, such as balsa. Retail price is $1.25 plus shipping, and dealer inquiries are welcome. The mounting kit can probably be used for convenient mounting of other types of components as well, such as small servos. I'll leave that up to your ingenuity. For more info, photos and ordering, please visit the Products section of our website. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
[RCSE] Subject:
Anker Berg-Sonne writes: Aerodynamically the X tail is most efficient because no surfaces work against each other... Well, that's debatable, especially when you consider the cases of combined control inputs of simultaneous rudder and elevator. However, the case for intersection drag is a little more clear cut. Inside corners generate intersection drag. A V-tail has only one inside corner, a T-tail and a Conventional tail each have two, and a Cruciform tail has four. The case for an X-tail will depend on the specific details of the particular tail design in question, but could be as bad or even worse than a Cruciform tail's. As someone who has designed with all major types of tails, including considerable experience with V-tails, and with models that are available with the builder's option of V-tail or conventional tail, I can say with confidence that the aerodynamic differences between the tail types are extremely small, if the tails in question have been designed properly. The main advantages of the V-tails over other types in actual practice are in the areas of structural efficiency and durability. For models, those advantages can be considerable, if the tail is designed to take advantage of them. This subject has been thoroughly thrashed over many times in the past, almost as much as the Downwind Turn and the Skeeter threads. Some of the results of those discussions can be found in the Ask Joe and Don section of our website. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] Props to spin or not to spin
, the profile losses could exceed the flat-plate drag of a stopped prop. Like I said, no one size fits all answer. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] Nostalgia
Tony Estep asks: ...Here's a question that illustrates the inherent paradoxes of a nostalgia event: There's a certain cutoff date after which planes aren't legal. Does that date advance by one year each year? If not, why not? This was hashed out thoroughly on this forum a few years ago. Apparently the 1980 date was picked specifically to exclude the Sagitta. It was felt that the Sagitta heralded a major shift in the performance and overall capabilities of R/C sailplanes, and allowing it would totally outclass the older designs, as well ad blurring the differences between the type of flying in the Nostalgia class and the existing modern classes. It would be something like setting up a Nostalgia HLG class with the cutoff date set specifically to preclude discus launching (now there's an interesting idea!). For this reason the date was set at 1980, and it will stay at 1980, or so I am told. I can see arguments on both sides of this issue. However, the fact remains that it was set up that way for a specific reason, with apparently a fair amount of forethought behind it. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
[RCSE] Re: LiPoly
us, the unloaded voltage should never go below about 2.7 volts per cell. It's safe to run them down to about 2.3 volts under load in an electric-powered airplane, since the voltage will jump back to 2.7 when you close the throttle. We use a programmable Electronic Speed Control (the Castle Creations Pixie 7-P is our favorite for these applications) and set its voltage cutoff function in keeping with these numbers, but in actual practice we've found that it's really not necessary unless you're going to do a lot of thermalling. The rpm of an electric motor depends on the voltage you feed it, and the power absorbed by a propeller is proportional to the cube of the rpm. When the battery voltages starts to drop, the power absorbed by the prop declines rapidly with it, and even with a 3-cell pack we've found that there aren't enough watts absorbed by the prop to sustain flight long before the battery voltage is low enough to endanger the cells. If you're planning to be WAAYYY high in a thermal at the end of the flight, it could be an issue, but for any sort of low-altitude motoring around sport flying the plane should naturally tell you to land when the batteries still have an adequate margin left, if your battery and motor system are reasonably well matched to the airplane. We simply use good equipment and reasonable care and prudence when using and when re-charging these batteries. The horror stories are not something to completely disregard, but not a big prohibitive risk either. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
[RCSE] Dyneema - Ultra High Strength Polyethelene Fiber
Jimmy Andrews asks: I wonder if anyone has tried this fiber. The claims on the website are amazing. They claim has a higher strength to weight ratio, a higher Tensile Modulus, a higher abrasion resistance and flex life, better light stability, and chemical resistance, than Kevlar. In addition to the problems Scobie mentioned, the other BIG problem with Spectra/Dyneema is cold flow. If you subject it to a steady load, it relaxes or creeps. All plastics do this to some extent, but polyethylene fiber is in a league by itself with regard to this. A wing of a full-scale aircraft made from this stuff would develop elliptical anhedral just from sitting in the hangar with its own weight pulling down on it. Back when we were developing the 2-meter Chrysalis, I tried some cable-actuated, spring-opened, cable-closed spoilers for it. The Spectra line I used was nice and slippery and ran nicely through its guide tubes, but relaxed so much every night just form the tension from the springs that every morning the spoilers would be halfway open. Later I tried it for pulling some dihedral into the wings of a LiteStik to get better roll response. It worked OK right after I installed it, but the next morning, most of the extra dihedral was gone. It was after this that I developed the polyhedral mod for the LiteStik. Much better roll response, less drag, less stress on the wing roots, doesn't take any longer to install, and the dihedral is still there the next morning, as well as every morning after that. Spectra (or its equivalents) has its place, but if there is a need for something with dimensional stability, Spectra is usually not a good choice. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] Dyneema, Spectra
Mark Mech writes: There was a similar fiber available in cloth from a British source, I think it was called Dynel or something similar. The home built boat community liked it for the final layer on the bottom of the boat. It was so abrasion resistant that you could beach the boats with very little wear. This would probably be good on the skid area of slopers.. Dynel was something else, a form of Dacron if I remember correctly. It was also a bad idea for primary structure in composite construction, but for an entirely different reason. The basic idea in a fiber composite is to have some strong, stiff fibers to carry the loads, and some sort of matrix material to hold the fibers in position. The key is that the fibers must be much stiffer than the matrix material or else the matrix does all the work and the fibers are along for the ride. For example, consider concrete reinforced with steel rods. The concrete holds the rods in position, but the much stiffer steel rods do most of the work of carrying the loads. Now imagine concrete reinforced with rubber rods. Perhaps the rubber rods are indeed capable of carrying quite a bit of load, but by the time you stretch them far enough to start carrying that load, the concrete has long since cracked and crumbled away. The matrix tried to do all the work, the fibers didn't do their job, and the matrix (and therefore the structure) failed. This was the problem with Dynel. It's less stiff than epoxy, so the epoxy tries to do all the work. It would actually be stronger to use just epoxy by itself, at least you'd have a greater amount of epoxy in the same total volume. I remember a seminar by Burt Rutan I attended years ago. Someone asked him his opinion of the Dynel/epoxy used in the KR-2 homebuilt (which fortunately just used the composite for the outer shell for shape, but used wood for the primary load-bearing structure). His comment was that The Dynel is a great way to hold the epoxy in place while it cures. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
RE: [RCSE] Altitude braggers
Sheldon, On this particular aircraft there is an Avionics bay that is not pressurized (at least that's what I think he called it). At any rate, yes, we would have to place the ALTi2 in an unpressurized area of the aircraft to get anything close to meaningful. I don't think it would do much good to check the cabin pressure ya' know G. I mean, what the heck, at least it'll be fun...Much more interesting than discussing whether we should or should not list planes that win at contest along with the placement of the winners, what constitutes a soaring team (pilot+plane, pilot+timer, timer+plane,pilot+?, etc), or who's the latest dealer to bash. BWG Before we decide that there's nothing good to come of it, let's at least try it and see what we find out...Hmmm??? A bit of knowledge might be somewhat revealing... The point is that an unpressurized area of a plane is still not going to be at the same pressure as the static pressure outside. The Sundowner is not pressurized. The altitude readings when measured from the alternate static source in the cabin not only are inaccurate, but the inaccuracy varies with things like airspeed, and whether or not a little four-inch-square window is open or closed. I'm sure your device is a very accurate measurer of whatever pressure is fed to it. However, trying to measure altitude from the pressure inside the fuselage is going to be inconsistent from one flight condition to another, and from one airplane to another. Even little things such as the seal of a hatch or the taping of the wing roots could alter the numbers. To be really useful, the device needs to have a fitting to attach a tube to, and that tube needs to run to properly positioned static ports. It's easy to generate very impressive looking numbers. Generating accurate numbers usually requires considerably more work. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] potential frequency problems
While we're on the subject of radio interference from high-powered electrical devices, I have a related question. We have two horses. Both of them are BIG (one Clydesdale, one Belgian-Clydesdale). Savannah, our Belgian-Clydesdale (she looks similar to Big John in the Tim Allen - Kirstie Alley movie For Richer or for Poorer) is extremely intelligent, as is typical of draft breeds. A little TOO intelligent. In the winter when the grass is scarce, she's quite adept at finding the weak spots in any fence. She walks down mesh fence, figures out how to defeat barbed wire, and can go under a chest-high hi-tensile wire, or even between two hi-tensile wires (one higher and one lower). She's bigger and stronger than a Volkswagen, and extremely clever and resourceful, better in that category than most dogs I've worked with. In the interest of keeping her from wandering the neighborhood roads in the wee hours of some icy winter morning, I'm getting ready to install our last resort, an electric fence (pretty powerful one too, strong enough to stop a really big horse). However, I fly quite a bit in the back yard and in the pastures, around, across and over where the electric fence will be, with all sorts of radios including some ultra-micro single conversion radios. Does anyone have any actual experience with flying in close proximity to an electric fence? What sort of interference can I expect from it, and if there are problems, are there any solutions short of turning it off while I'm flying? Savannah is smart enough to figure out if the sight of one of my toys overhead means the fence is shut down. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] And now for something interesting...
Simon, Would it not make more sense to just wait for the results instead of panning it? THEY CLAIM a 30% reduction in induced drag. Unless the baseline design they're comparing to is really awful, there simply isn't 30% worth of improvement there to be made, not without making substantial increases in wing span. A wing makes lift by grabbing chunks of air and shoving them down. Assuming you're using the air the wing grabs reasonably efficiently to begin with (i.e.: a spanwise lift distribution that's reasonably close to elliptical), the only way to make a substantial improvement in induced drag for a given amount of lift is to grab a bigger chunk of air. To get a 30% reduction in induced drag, you would need to increase the effective span by approximately 20%. It's simple physics. Do you really believe that they can grab a chunk of air that's 20% bigger in diameter by making wingtips that look like curly fries? In addition, that wingtip has a hole with all the flow distortions associated with that, two inside corners at the inboard end of the hole that also disturb the flow over the upper surface of the wing in that region, and that little vane creates additional inside corners with more interference drag, and a whole bunch more whetted area, all of which eats away some of whatever induced drag benefits it might have. In addition, they add mass at what's one of the worst possible places to add mass, degrading the dynamic stability and handling and probably needing a bigger tail to compensate. As far as the tips being removable for test, unless they have conventional tips to replace them, they're testing a reduced span conventional layout against an increased-span winglet design. Not exactly a valid comparison. There are folks out there trying to tell us that if we install their little piece of modified window screen in our car's carburetor, it will get 30% better gas mileage. Those claims are also obviously bogus, even a rudimentary knowledge of physics will tell you that. If the folks promoting these new wingtips had claimed a few percent instead of 30%, it might be more believable. In any case, they have claimed an unbelievable (and I chose that word very carefully) improvement, and they need to substantiate it. The easiest way to make a 30% improvement in induced drag is to make a 30% reduction in weight for a given span. That's very do-able, and entirely in keeping with the laws of physics. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] shrinkable polyesters
I heard years ago that the heat-shrinkable films were bi-directionally stretched during manufacturing. When you apply heat, they want to return to their original dimensions, which is where the massive amount of shrink comes from. Without this pre-stretching, they would not shrink as much. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
[RCSE] Re: Micro Slopers?
Ryan Flowers writes: ... I was thinking something of a micro sloper with ... one aileron only (so as to not overload the hs-50) We don't have anything in production at the moment that fits your requirements, although I have some ideas I'm hoping to fit into the schedule one of these days. You might take a look at Dave Robelen's Kestrel design in the downloadable plans section of the R/C Microflight website at www.rcmicroflight.com However, I think your one aileron requirement is WAAYYY pessimistic with regard to the capabilities of an HS-50, particularly if you're planning to link both ailerons to the same servo (so that they can counterbalance each other's lift forces). We used an HS-50 on each flaperon for our old Wizard four-servo HLG, as well as the old Monarch CX and the Spectre VR with no problems, including for slope flying. The flaperons on the Wizard were about 24 span each and about 3 chord, with max travels of about 3/4 up and 1/2 down. As long as you make the aileron horn long enough and the servo arm short enough that you're using the full travel of the servo to get the full travel of the control surface, an HS-50 will handle an amazingly large surface. Folks also use them for Speed 400 pylon racers with ailerons on both wings (certainly as fast as your sport sloper is likely to be) with no trouble. It's only if you waste the servo's capabilities by setting up a way-too-sensitive control linkage, and then expecting the transmitter programming to reduce the travels, that you're likely to create a problem. A fancy transmitter is no substitute for good design and building practices! Take the time to get an efficient linkage setup, then use the transmitter programming for fine-tuning only. Your efforts will be rewarded with better use of the servo torque, less sensitivity to slop and better resolution. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
[RCSE] Re: Aileron ship dihedral
Dave Seay asks: Ok, now that Model Aviation published that article supporting increased dihedral in full house ships, who's going to start manufacturing wing rods at 10 to 15 degrees? We had a 10 degree carbon wing rod of our own design and manufacture in our old 2-meter Monarch quite a few years back. It also had some interesting anti-split features that worked quite well. However, although it was not all that difficult to manufacture, it was just enough of a nuisance item (not enough profit in it to make it worth the time and trouble) that we switched to one of Don Richmond's excellent aluminum rods. He did make it special with the 10 degree bend for us. As far as the myth about ailerons needing minimal dihedral, we disproved that one many years ago with our old Monarch 'CX', the last of the wood-wing Monarchs. It had 3 wide full-span flaperons, all the way to the tips, and the exact same polyhedral setup that the 2-channel Monarch 'C' used. Hands-off stability was the same for both versions, the roll rate of the 'CX' using ailerons alone (no rudder input) with no differential was about the same as for the 2-channel 'C' with rudder alone. If the ailerons are designed so that they are sufficiently efficient, there is little or no trouble with adverse yaw, and therefore no trouble with large amounts of dihedral. With rudder added to the aileron, the roll rate of the 'CX' was in the Pitts Special category. The overall handling and stability of the 'CX' were excellent. However, it used the same older series of airfoils as all the other wood-wing Monarchs (as well as the 2-meter Monarch), which limited the launch height and high speed performance. The production costs of making pre-sheeted wood-skinned wings was way too high, and the work of making all those flaperons was asking a bit too much of our customers. We found that certain brands of C/A accelerator could cause cracking in the special fittings we made to couple the inboard and outboard flaperons across the polyhedral breaks. We also found that we could make a glass-skinned wing more consistent, cheaper and lighter than we could make a pre-sheeted balsa skinned wing. The net result of all of this was the replacement of the Monarch 'C' with the Monarch 'D' and 'D-lite', and the replacement of the 'CX' with the Wizard. The 2-meter Monarch was replaced with the 2-meter Monarch 'D', and eventually the 2-meter Spectre. ...and who's going to buy them? That's the real problem. If you folks don't buy something in sufficient quantities for the manufacturer to cover their material, labor and especially their overhead costs, and still make a reasonable and fair profit, it sooner or later ceases to be produced. Even the folks who do this for fun and don't expect to make any money at it sooner or later learn that there's an awful lot about the kit business that simply isn't fun, especially when they realize that they're shipping money out of their own pocket out the door with each kit. Just like certain laws of physics, there's just no way to get around certain laws of economics. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
Re: RE: [RCSE] Flexible covering for twisting wings?
Tord writes: The famous Friese aileron is pretty much a recessed Junkers' aileron, = forcing the air to pass in a roundabout manner over the surface, compared to the = original. Well, not exactly. The main feature of the Frise aileron (named after its British inventor) is its leading edge design and the resulting drag behavior. The hinge is aft of the leading edge of the aileron, and can be located vertically in a variety of locations, typically somewhere between the lower surface and the upper surface. In at least some cases I've seen, the gap at the upper surface is sealed (which is why it is not a variation of the Junkers flap). Unlike the Junkers flap, the lift-increasing effects of a slot on the upper surface are not an inherent part of the Frise design. When the aileron is deflected downwards, the nose of the Frise aileron moves upwards into a cavity in the wing. However, when the aileron is deflected upwards, the nose of the aileron sticks out below the lower surface of the wing, creating drag. This helps cancel out adverse yaw, and also (since this drag force is acting below the hinge line) acts as a aerodynamic counterbalance to reduce loads on the control stick. By comparison, a Junkers flap may or may not exhibit these properties. The Frise aileron has lower stick forces than a conventional aileron (not a factor for most R/C models, since we're using servos to move the ailerons; also, aerodynamic aileron counterbalances like this don't help the servos unless both ailerons are tied to each other with a common linkage, not driven separately by separate individual servos). Frise ailerons may have more authority than a conventional aileron setup that uses differential to combat adverse yaw (a lot of the ailerons' control authority comes from the downward-moving aileron, and the use of differential reduces that downward deflection). On the negative side, the hinges and their supporting structure as well as the structure of the wing trailing edge and aileron leading edges for a Frise aileron are more complicated. A Frise aileron will also probably have more drag than a conventional simple-hinged set of ailerons set up with differential, and/or using rudder to combat adverse yaw. I have tried Frise ailerons, with and without upper surface slots, on a variety of models, mainly powered ones. They're a fair amount of work to build, but look nice when they're done. They work OK, but getting the right amount of compensation for adverse yaw could require some extra tweaking, which is inherently more complicated to do than with a simple adjustment of differential. In fact, a better approach is usually to get a nominal amount of compensation from the Frise effects, then fine-tune the rest of the adverse yaw out by using differential adjustments. I don't recommend them for gliders, since they're fundamentally based on using added drag to help control the airplane, which is a no-no on most sailplanes. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
Re: [RCSE] Lost workspace
Andrew Mileski writes: Alex Janssen found a solution:all it required was his wife's permission: http://isoar.ca/~andrewm/rc/bot/images/alex_janssen-5.jpg GREAT photo! My only question is, considering the high calorie content of most of the items being used to aid construction, did the model turn out overweight? ;-) Seriously though, I faced the same problem when I was in college, living in the dorms. I bought a 7' x 18 Luan mahogany hollow door and laid it on the bed for building, then leaned it up against the wall when I needed the bed for other things like sleeping. It worked fine, although I did get very good at keeping track of all pins, X-acto knives and blades, C/A bottles, etc.! Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
Re: [RCSE] vendor bashing
Don A. writes: Don, unhappy people usually vote with their feet... Unhappy vendors vote with their feet, too. I have no problem with bringing problems to light and getting them fixed. The problem I have here is a matter of degree and of attitude. I'm on several other forums as well, and with few exceptions they manage to get problems exposed and resolved quickly, efficiently and politely, and without weeks upon weeks of one-sided public floggings, and they do it without an immediate assumption of guilt and willful negligence with regard to the accused party. If you've noticed a shortage of posts to this forum by me in recent months, it's because it's much more pleasant to invest my time in those other forums. I suspect there are other former and present members of RCSE who feel similarly. It is possible to resolve problems peacefully, and without vengefully attempting to make a public example out of someone. If you verbally pin someone up against a wall and publicly threaten them with major harm, you can expect them to get defensive. That is usually not the most effective way to solve a problem or dispute. More importantly, you can also expect that any other innocent bystanders who observe you doing this will feel at least a little apprehensive about doing any future business with you. This is true regardless of whether you're a vendor or a customer. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
[RCSE] Re: model aerodynamics
B Yen asks: I'm looking for a website which describes model-aircraft design: - wing shape, area, amount of dihedral - tail size - angle of incidence (main wing stabilizer) - length of fuselage... You can find much of what you're looking for in the Ask Joe and Don section of our website: www.djaerotec.com There are over 300 articles in AJD on a wide variety of aviation-related subjects. Just type the topic you're interested in into the search engine and it will give you a list of links to AJD articles that discuss that topic. The method of relating tail size and tail moment arm is called tail volume coefficients. There are several AJD articles that discuss these, how to calculate them, how to equate them to V-tails and other tail types, and their relationship to static and dynamic stability. BTW, for all the magazine columnists, club newsletter editors, etc., out there, you are welcome to use anything you find in AJD in your publications. All we ask is that you include proper acknowledgement of where you found it, and that you not take anything so out of context that it alters the meaning, or otherwise puts words in our mouths. If you need something re-worded to fit the context of where you plan to use it, just let us know and we'll work with you. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
Re: [RCSE] Joe Bridi Tercel - Will it Fly
Bob Massmann writes: I have the Flipper which is very similar. My first HLG was also a Bridi Flipper, very similar to the Tercel. If I remember correctly there were some differences in the shape of the tail, but otherwise they were almost alike. Low speed handling was great, but range and L/D was a bit lacking. The other problem was the bulkhead at the leading edge of the wing, the one that the wing's leading edge dowel plugged into. That whole area of the fuselage structure was very poorly designed, and essentially had all the wing loads transferred across the grain of the balsa instead of parallel to the fibers. Anything less than a perfect landing would break some part of that structure. I'd recommend at least adding some fiberglass tape and epoxy around that area. The other culprit from a performance standpoint was the short wingspan. Stretching it out to a full 59 would significantly help performance. The Zephyr was a very similar model from that same era, and also had a short wingspan. Most of the Zephyr flyers I knew had added some additional rib bays to the wing to stretch it out to the full 59. Besides the shortage of range and penetration, the other quirk involved the Eppler 205 airfoil. It has a mush mode of separated flow and high drag that develops well above the final stall break. If you don't pay close enough attention and let it get too slow, it will sneak into a mush that will require a lot of altitude to fully recover from. A skillful pilot can use this almost like spoilers for glide path control on landing, but most of the time it's a nuisance and a trap for the unwary. Joe Hahn scratch built a 2-meter scaled-up version of the Flipper that flew quite well. My second HLG was a Vertigo. Foam wings with balsa skins, heavier, more legs, but couldn't thermal nearly as well in the small, weak lift we get around here. About that time I was also reading the part in The Old Buzzard's Soaring Book about how you could make an airplane heavy and fast and search better, or keep it very light and thermal well but not search as far. It was presented in the book from an either/or point of view. It was quite clear to me that the Flipper and the Vertigo represented classic examples of the two schools of thought, and that in the widely spaced, small diameter, very weak lift typical of this area, neither approach was getting the job done. Joe, who worked downstairs from me in another department of the same company, was coming to similar conclusions with his own HLG experiments. We questioned why it had to be either/or; couldn't we come up with a model that could do both? We also noticed that the state of the art in HLG's at that time (1992) seemed to be based on scaling down larger models, airfoils, planforms, structures and all, to HLG size, rather than looking at the unique demands of HLG's on their own merits. We started comparing notes and collaborating on designs, and six fuselages, seven tails, eight wings and about 150 hours of computer work later we had the first Monarch. Shortly after that, Bob Massmann, one of our friends in the DARTS club, hung up his Flipper for one of our first kits. I still have my Flipper, and about an afternoon's work could make it airworthy again. It was a sweet handling airplane for its time, but I don't really have any desire to go back. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
RE: [RCSE] tip aileron theory (was 6 servo+stylus)
Stefan Smets asks: Ok, I'll ask the stupid question then :-) : The only stupid question is one that you should have asked, but didn't! ;-) or to fly flatter turns (although I'll never understand why anyone would do that) I would guess to lose less lift in the turn ? Sometimes I try to level the wings a bit while turning by cross-controlling the ailerons the other direction than the turn. I've even read about that in different magazines. Judging from what you wrote, there is something wrong with that ? There's a difference between using crossed controls and having an uncoordinated turn. I've flown a number of full-scale aircraft where I found it was necessary to use crossed controls (top aileron plus bottom rudder, typically) in order to keep the ball centered. Two that come to mind a re a 7AC Aeronca Champion, and a Schweitzer 2-22. In a turn there are a lot of unsymmetrical things happening to various parts of the airplane. In particular, the airflow is now curved (the amount of which and the significance of that curvature depends on the aircraft in question, its flying weight, and the details of the turn being flown), and the local airspeeds along the wing are different. In a good HLG, it's possible that the airspeed at the outboard wingtip could be twice the airspeed at the inboard tip. This means that the inboard tip's Reynolds number is half that of the outboard tip, and it also needs to develop four times the lift coefficient of the outboard tip! At the same time, the lower airspeed can reduce its parasite drag in comparison to the outboard tip. The net result of all of this can, in some cases, result in the airplane wanting to roll into a steeper bank angle (overbanking tendency), while at the same time yawing toward the outside of the turn. A combination of aileron towards the outside of the turn (top aileron; this increases both the camber and the angle of attack of the inside wingtip so that it can make that extra lift coefficient needed to balance the extra airspeed of the outboard tip), and enough into-the-turn (bottom) rudder deflection to counteract the yaw is needed to balance these effects. Without these crossed control inputs, the airplane will not fly a coordinated turn. Note, this phenomenon may or may not exist for a particular aircraft and flight condition. I've flown other aircraft that did not need these control inputs. It all depends on how the various factors and forces add up. The bottom line is that you should use whatever control inputs are needed to make your airplane straighten up and fly right! Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
RE: [RCSE] How does one calculate parameters for the perfect poly
I guess it's probably time to reveal some more secrets. Tom Clarkson asks: Lastly on the topic of boom length, I am having a hard time making the empirically observed behavior fit with the way things should work. We have two identical fuses and tail groups except one has a 2 longer boom length. The shorter one turns better and tighter using all of the test wings at different EDAs. So, I am trying to figure out what could be going on because it does not make sense given the previous comments on this topic. First of all, be careful here. Damping has to do with what happens when you're changing something, such as rolling into or out of a bank. Other factors come into dominance when you're in a steady state condition, such as straight and level flight, or a constant diameter, constant bank angle turn. The other thing that seems to be inadequately covered or even missing altogether from these discussions and analyses is the curvature of the airflow while in a turn. The airplane is flying in a curved path, and therefore the relative wind at the tail is not coming from the same direction that it's coming from at the wing, or at the nose. You can see this in a full-scale sailplane that has both a ball-slip indicator on the instrument panel, and a yaw string taped to the front of the canopy. In a really tight turn, particularly with a light wing loading, the tail end of the yaw string will point a little bit towards the outside of the turn when the ball-slip indicator is perfectly centered. This makes perfect sense if you consider that the ball tells when the turn is coordinated (and therefore the wings are lined up with the airflow at their location), but the yaw string, located out on the nose, well ahead of the wings, is seeing a distorted flow due to the curvature of the turn. Likewise, in a tight but coordinated turn with the local airflow perfectly aligned with the wing, the airflow at the tail will be blowing inward and upward. From a control standpoint, this has the same effect as holding some top rudder and down elevator. The tighter the turning radius in comparison to the size of the model, and the longer the tail moment, the more pronounced this effect becomes. On a good HLG design, it's not uncommon to see differences in the direction of the airflow at the wing vs. the direction at the tail of 10 to 15 degrees or more in both pitch and yaw. It's an important enough effect that I've included it in my own design programs as one of the major parameters I consider when designing the tail assembly. On airplanes that normally make big, wide turns, this effect is often negligible. Not so on a good HLG! Another consideration: 2-channel (non aileron) HLG's need a little top rudder in a turn to yaw the airplane a little to the outside. This increases the angle of attack of the inside wingtip, increasing its lift coefficient and counteracting the loss of lift it sees due to its lower airspeed in a turn. Since the length of the tail moment arm influences how much angular difference there is between the local flow at the wing vs. at the tail, the tail moment arm can be adjusted to give just the right amount of outward yaw necessary to keep the turn balanced. If you have too much tail moment, not only will the damping make it difficult to roll crisply in and out of a turn, but the curvature of the flow during the turn will constantly be trying to make the airplane level out again. Yes, you can add more rudder to counteract this, but eventually you will run out of rudder. The airplane with a shorter tail moment will get to a tighter circle before it runs out of rudder. However, since damping is proportional to the square of the tail moment, the loss of damping from the short tail moment will make it more difficult to keep the short-tailed airplane steady in the turn, even though it has the same tail volume coefficient as the long-tailed airplane. The same tail volume coefficient will give it about the same static stability, but the shorter tail moment will give it less dynamic stability. You need to have the right amount of BOTH of those if you want the airplane to handle well. Unfortunately, the amount of yaw required, and the amount of yaw caused by the airflow curvature both change as you change bank angle. Therefore, you will probably have to tune the tail moment for your typical turn, and accept the need for some pilot inputs for turns with less or with more bank angle than that. Airplane design almost inevitably involves some compromise. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
Re: [RCSE] spar-sizing calculations
Skye Malcolm writes: It seems to me that you're on the right track with the steel rods. You = might see if you can find one tempered. ... There are several different ways to harden different types if steels. One is by heat treating. The typical process is to heat it above the temperature where all the alloying elements go back into a solid solution (dissolve) in the iron (typically around 1500 degrees F for garden-variety hardenable steel alloys), then quench (rapidly cool) the part so that some of the alloying elements get caught in harder types of microstructures (such as martensite), since they don't have time to revert back to their fully-annealed types of microstructures (typically ferrite for plain-carbon alloys). The resulting fully hardened part is extremely hard but very brittle. Even dropping it on the floor could result in shattering (that's also why they have a warning on hammers to not hit the hardened face against another piece of hardened steel, it could shatter and send splinters of itself into various soft and fragile things, such as your eyes). Fully hardened alloys also often have very high internal stresses. In some cases, just letting it sit around for a while in that state could result in microcracking. For this reason, it is normal practice to temper a part after quenching. The part is re-heated to something less than the quench-hardening temperature (typically around 700 to 900 deg. F for common steel alloys, with the higher temperature resulting in a softer final part), then slowly cooling back to room temperature. The alloy loses some of its hardenss but gains back enough ductility to eliminate the brittleness. Another type of hardening is work hardening. The alloy is mashed, stretched, or otherwise physically abused, which causes the buildup of physical stresses and microstructure changes in the material that have essentially the same effect as heat treating. In the case of music wire, the alloy is AISI 1060 steel (that means it's an iron-carbon, or plain carbon alloy, with a carbon content of 0.60%). It is drawn through a series of dies to work it down from the initial ingot diameter to the final desired wire size. Each time it gets pulled through a die, it gets work hardened. After a few steps it's been cold-worked so much that it's just about fully hard and has lost almost all its ductility. It is then annealed (slowly heated and then SLOWLY cooled) to make it soft again, and then the drawing process is continued. They use the minimum number of annealing steps, so that the wire at its final diameter is nearly fully hard, about the same hardness as the best you could get from it by heat treating. It's quite brittle at that point, which is why music wire can crack and snap if you bend it and then try to straighten it. It's already been subjected to about all the work hardening it can stand, and if your bending back and forth imposes more on it, it says ENOUGH!! At that hardness it's also close to about the same hardness and strength as most tool steels, which is why it will leave nice semi-circular dents in the jaws of your diagonal cutters if you try to use them to cut it. This also means that going to a heat-treated version of some other alloy (with a few very exotic exceptions) is not likely to get you any significant improvement in bending strength. You might get some improvements in toughness, but the hardness and strength (and therefore the bending load at which it gets bent) is not likely to see much improvement. The stiffness of all steel alloys is nearly identical, so the tip deflection due to elastic bending (i.e.: bending from which it can still spring back to its original shape) will not be changed in any case. About the only thing you can do that will significantly improve the bending strength of the rod is a diameter change. Also you might try shortening the rod instead of lengthing it. At some = shorter length this will theoretically put more stress into the wing rod = sleeves... This will increase the stresses in the connections between the joiner rod and the wing spars, but it will not change the stresses in the joiner rod itself in the middle. There are a certain number of inch-pounds bending moment created by the lift forces and the length of the wing panels, and the center of the joiner rod has to absorb that amount of bending moment, irregardless of how long the joiner is. The only thing that matters at that center point in the rod is the amount of bending moment, the size and shape of the joiner's cross-section, and the properties of the joiner's material. If your joiner is tearing up its sockets in the wing roots, a longer joiner could help. If your joiner is bending in the middle, the best fix is to get a fatter joiner. RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
[RCSE] Re: cg questions again.
Bill Johns asks: I would think that each airfoil has an optimum cg, right? I would think that planform influences how one determines the cg relative to any airfoil. IE: a 7037 might be optimum at for instance 40% of chord [I'm pulling that out of the air (no pun intended) I don't know what it actually is], but planform might influence where at the root chord one actually balances to. Is this correct? Well, yes and no. C/G is a function of almost everything in the entire design. In our experience, the airfoil can have some influence on the C/G, but it's really one of the weaker influences. We've gone through quite a few different airfoils and planforms on the Monarchs and Wizards over the years, and found that planform changes have a surprisingly small but significant influence, but airfoil changes have a very minor influence. Tail volumes and moment arms are one of the biggest factors, and even fuselage shapes can have a significant effect. The other consideration is that C/G also influences yaw stability, not just pitch, and on some designs (particularly flying wings), finding a C/G that satisfies both yaw and pitch requirements simultaneously can become a rather tricky problem. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com/ RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED]
[RCSE] Re: Public Apology - Part 1.5
Gabe Baltaian writes: If any of you reading this don't know what CS tubing is, well... it's only the best, lightest, clearest and just basically Clearly Superior Heat-Shrink Tubing available. You can see more about it at: http://nyblimp.com/cs.htm I got a sample of this stuff from Gabe at last year's Toledo show, and I can attest to his statement above. It's wonderful stuff, and I've found quite a few uses for it. My favorite is for mounting servos, particularly on small, weight-sensitive models. Just cut off the mounting lugs and "shrink-wrap" the servo in a piece of Gabe's tubing so that the edges of the shrunken tubing wrap around the corners of the servo case a little (so the servo can slip out of the tube). Now put four dots of slow cyano-acrylate on one face of the shrink-tube-covered servo, and just stick the servo in place in the model. C/A sticks very well to Gabe's tubing (which is not always the case with some other brands of tubing). If you need to get the servo out, just slice through the shrink tube acros the middle of the exposed face, spread the tubing open and pull out the servo. If you did a clean job of this and the loads on the servo aren't too high (such as on an HLG or one of our "Roadkill Series" profile indoor/backyard models), you can reinstall the servo by slipping it back into the split shrink tube mount and then taping the spilt closed with a small piece of Scotch tape. For something with more load on it, just peel the remains of the split shrink tubing out of the model, and reinstall the servo using a fresh piece of tubing. The servos in my Spectre 2-meter are installed this way (including the flap servos, and the tape has performed very well. I also use it on my "Roadkill" prototypes for installing receivers, ESC's and batteries. I used to wrap my servos in paper tape and then C/A them in, and had major problems with the tape delaminating, releasing the servo. Since I started using heat shrink tubing, I have yet to have one come loose except when I wanted it to! Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] A note of interest for the F3J guys.
Jim Bacus writes: It may turn out that the new generation of lightweight (low 50oz range) US TD ships may work very well in certain conditions. You mean, something like about a 120" ship that weighs around 45-49 ounces, has an extremely wide speed range, great handling, and that has been demonstrated to be strong enough for a two-man F3J tow WITH a stake? I just happen to know of such a plane. It's already in production and available, and doesn't cost nearly as much as most of the hollow-molded ships. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: Who is this Reynolds dude?
Date: Sun, 04 Feb 2001 19:25:43 -0500 From: Clifford Schwinger [EMAIL PROTECTED] To: RCSE [EMAIL PROTECTED] Clifford Schwinger asks: I have been seeing a lot of references being made to the "Reynolds Number" recently. Could someone please explain to me - in simple terms - what this number is and what it means when a sailplane has a small "Rn" vs. a large "Rn". From what my feeble mind has figured out so far, the "Rn" has something to do with the increasing difficulty of an airplane to fly as it gets smaller? 2-meter sailplanes have a higher Rn than an rchlg? An rchlg has a higher Rn than a ffhlg? Does the Rn explain why I can't build a glider with a 1" wingspan? How does one compute the Rn for an airplane? If I have a sailplane with a 1.5 meter wingspan is the Rn for that plane "set in stone" or can you do something with the geometry or weight of the plane to vary the Rn and make it fly better? Does anyone know of any websites that have a clear explanation of the Rn? There are quite a few articles in the "Ask Joe and Don" section of our website that discuss the nuances and implications of Reynolds numbers. It is such a significant factor that there are quite a few articles where it makes at least a cameo appearance. Just type "Reynolds" into the Ask Joe Don search engine and you'll get a big list of articles to browse on the subject. One article that discusses the number itself is at: http://www.djaerotech.com/dj_askjd/dj_questions/hlgairspeed.html BTW, I have built FF gliders with wingspans as small as 5/8", and kites (scale models of Monarch butterflies, complete with all the black lines and white spots) with 3/8" spans, both of which flew successfully. However, the max L'd's are definitely lower than what is possible at larger sizes. Reynolds number (or "Re" in engineering shorthand) is air density times length (usually wing chord) times speed, divided by air viscosity. It's a numerical measure of what modellers call "scale effect". It gets smaller as you go up in altitude, slower in airspeed, or smaller in chord. At sea level standard day conditions it's: Re = 778 * Chord (in inches) * Speed (in MPH) In general, decreasing Re means that your drag will increase, and your max lift coefficient will decrease. Airfoils designed for one Re will generally not work well at a substantially different Re. However, it is possible to design airfoils with reasonably good efficiencies at very low Re's (as we did for our Spectre series), although it becomes increasingly difficult, especially at Re's below about 100,000. Below that number, things really get squirrely, and most of the traditional ways at analysing airflow tend to quickly get into serious trouble. Most of the commonly available airfoil codes generate mostly garbage below that number, and most wind tunnels aren't significantly better. In my experience, at very low Re's, what is more important than the software you're using is your experience and skill in properly interpreting its outputs. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: Goop Adhesive Technique
Robert Buxton asks: Picking the lists brains for the best way to use GOOP adhesive to plant two JR241 servos in the fuselage of a Carbon D-Lite**... I've tried using masking tape between the servo and the glue, with poor results. The tape seems to split in half along its thickness after a while, resulting first in some funny changes in trim and control throw, followed the servo coming loose completely. Yes, it was a good brand of mnasking tape, but maybe not the same as what other people have used. What works for me is shrink tubing, like what's used to wrap battery packs. Just shrink a ring of it around the servo (make sure it wraps a little bit around the corners to guarantee that the servo can't slip out the end), scuff the surface a little with some medium sandpaper, then Goop or C/A the outer surface of the shrink tubing to the fuselage. If you ever need to remove the servo, slit the shrink tubing. Once the servo is safely out, it's fairly easy to peel the shrink tubing and glue residue out, then just use a new piece of shrink tubing to install the new servo. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] Profiles for swept wings
Greg Nuspel asks: I was looking at the process of cutting swept wing cores. It would be preferable to not have to put the core on the table at the swept angle. I would like to be able to calculate the airfoil coordinates required if the blank is cut with it laying parallel to the table edge. I have looked at calculating the different cord lengths which is easy but the actual airfoil points become quite complicated. Does any of the existing software handle this calculation? You need to increase both the thickness AND the camber by 1/cos(sweep angle). The program we use, Eric Sanders' CompuFoil (www.compufoil.com) does this, and Chuck Anderson's program might do it as well. In CompuFoil, just go to the "Modify" pull-down menu, and the "modify camber" and "modify thickness" are the first two items on the menu. However, you really don't need to bother with modifying the templates at all. Just cut the core blank with the correct sweep on the root and tip ends, make your templates match the finished chords, then nail the templates to the ends of the core blank. Set the core blank on your foam cutter with the trailing edge parallel to the edge of the cutter, just as with an unswept panel. Yes, the wire will be sliding across the template at an angle. As long as the template is smooth, reasonably stiff, and adequately held against the end of the core, this will NOT be a problem. I've cut MANY cores for swept wings this way with no trouble. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: Looking for formula to figure tail area?
[EMAIL PROTECTED] asks: I need formula or guide to figure out tail area. I know it must have relationship to fuselage length as well... There's an article in the "Ask Joe and Don" section of our website that discusses exactly this. The URL for that specific article is: http://www.bright.net/~djwerks/askjd/tailvolumn.html but while you're in AJD you might want to browse through some of the other articles as well, you'll probably find some other useful information as well. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: FLUTTER ON HLG CHRYSALIS
Patrick Quarterman asks: I built a V-tail Chrysalis and am having trouble with flutter in the tail on launch. I pretty much followed the plans so no variations to worry about. I just had another person ask the same question through our website. This problem occurs occasionally, and this is virtually ALWAYS the result of looseness and/or springiness in the ruddervator control linkages. Make sure that the pushrods are as straight, light and stiff as possible, and also check for holes in the servo arms and the control horns that are a loose fit for the pushrod wire. For the servo arms, you may need to replace the arm or drill a new hole in between the existing holes to get a tighter fit. On the control horns back at the ruddervators, you can plug the old hole with cyanoacrylate, then re-drill the hole. Also check for slop in the control surface hinges (too much space in the hinge between the aft edge of the stabilizer and the leading edge of the ruddervator can cause this), and for too soft a mounting for the servos. If the pushrod is flexing, try to minimize or eliminate any bends in the rod. If it's flexing in the middle, try adding a support, slightly forward or aft of the middle of the rod (having the unsupported segments of the pushrod slightly different in length is better than supporting it exactly in the middle), loose fitting around the rod so it keeps it from bowing to one side, but leaves it free to slide back and forth. Generally the hole the pushrod runs through in F3 is enough of a support (assuming you didn't make that hole so big that it doesn't restrain the pushrod flex), but in stubborn cases a second support mid-way down the tail boom can help as well. Whatever you do, make sure that the linkages for both ruddervators match each other. If they don't, then the two ruddervators won't move the same distance when given the same command. Every time you give it an elevator command it will also inadvertently get an unwanted rudder command mixed with it, and vice versa. Contrary to one of the other comments on this thread, the pushrods have an excellent stiffness to weight ratio compared to music wire or Kevlar pull-pull cables. There's an article in "Ask Joe and Don" on our website that analyses this in depth. It turns out that although the Kevlar pull-pull system is the lightest, it also has the worst stiffness to weight ratio; the conventional wood+wire pushrod (assuming you have the holes in the servo arm and control horn fit properly, and the pushrod is straight and well-supported enough that it doesn't flex) is actually the best of the three. David Enete's comments about launch technique are very appropriate, and apply equally well to just about any other HLG as well. Pulling down on the model at the end of the throw does not add any useful energy to the throw, and puts enormous stresses on the wings, in addition to exciting any flutter tendencies that may be present. As far as Kris Harig's comments about wing flutter, that is generally the result of using the wrong covering material and/or not having it shrunk properly, along with exciting it with bad throwing technique as described by David Enete. We went to a lot of extra trouble in the design of the Chrysalis to eliminate the need for any D-tube sheeting on the leading edge, since this is a very common problem area for a great many beginners. However, as a result, the wing does rely on the covering for quite a bit of its torsional stiffness. If you use a lightweight covering such as lightweight Ultracoat, lightweight Oracover, or Micafilm on the wing, especially on the inboard panels, or if the covering is applied loosely, the torsional stiffness will not be high enough and the wing is likely to flutter on launch. Regular weight Ultracoat or Oracover, or regular or transparent Monokote work fine. Of these, the stiffest and lightest in our experience seems to be transparent Monokote, although Ultracoat and Oracover are somewhat tougher. We've had good results with all of those three. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: 2 meter Spectre reports??? - You may want to also consider the 2M Dartar
Sal DeFrancesco writes: ...Once you drop in area you need to have a...(big snip)... The high aspect ratio and small chords will just not pull hard enough on a typical contest winch...(etc., etc) Seems like we have a number of folks here (mostly our competitors) who seem to have all sorts of opinions about why our Spectre series "can't possibly work", even though they've never actually seen one of them fly yet. I think that if you check with folks such as Rob Glover (who actually have them), you'll find a different opinion. Let me tell you all a little story about Sal and our products. Back in late '92, Joe and I had just frozen the design of what became the original Monarch HLG. We developed it for ourselves, because we'd been disappointed with the other RCHLG's we'd tried. We originally hadn't even considered the possibility of making kits, but after the amount of time and effort and expense we'd invested, and the indications of interest from some of the other DARTS members, we thought about making a few kits just to try to recoup some of our investment. Then we thought "Well, as long as we're doing that, maybe that NSP company up in Vermont be interested in selling a few?" We called Sal, and he replied "Send me one and I'll let you know you if I like it." We finally got one finished for him and sent it to him a little after Christmas. He was of course tied up at the time and didn't have time to put a radio in it just then, but he did call us, with all sorts of advice questions, like "I think there's too much dihedral", and "What's with the weird airfoils?" and "Why that strange flat fuselage" and "That tail moment is too long." We replied "Sal, just FLY it, and THEN tell us what you think." A couple weeks later he had a chance to put a radio in it and give it a few tosses. He was immediately back on the phone to us, with the message "DON'T CHANGE ANYTHING!" In all fairness to Sal, he isn't shy with his opinions, but he is willing to be open minded and see for himself. He does have a 2-M Spectre on order, and I fully expect that when he flies it he will be very pleasantly surprised. As usual. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] Does Altitude cause bad air?
Glenn R. Whitcomb asks: ...Does high altitude affect lift and the way gliders fly? In addition to the increase in true airspeed caused by the lower air density, as discussed by Oliver Wilson, and the associated increase in sink rate and turning radius, there is also a decrease in Reynolds number. This usually reduces the max lift coefficient, and increases drag. The reduction in air density causes an increase in speed, but since lift is proportional to the square of the velocity, that speed increase is inversely proportional to the SQUARE ROOT of the air density change. Meanwhile, since Reynolds number is LINEARLY proportional to density (and because air viscosity at our altitudes is approximately constant with altitude), the change in Reynolds number follows a linear function. Therefore, the increase in airspeed due to the thinner air at higher altitude cannot compensate completely for the loss of air density, and the Reynolds numbers go lower. This usually hurts performance over the entire operating envelope, althoiugh the exact extent of that loss depends on how well the design of the specific model in question handles the decrease in Reynolds numbers. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
RE: [RCSE] Decalage (was: Stab size)
Chris Bruner writes, in regard to Mark Drela's post, ...Decalage refers to the incidence of the tail relative to the wing, and DOES affect the handling (note that if you compensate with elevator, you've not changed the decalage). Too much decalage requires too much nose weight and makes the airplane handle like a snowplow, to use Thornberg's term... The key point here is that in order to change the decalage and NOT exactly cancel it out with the opposite elevator required to keep the model in trim in pitch, you have to change the C/G. The change in handling is due to the C/G change, NOT the decalage change. Looking at it from a "control theory" standpoint, handling is primarily related to dynamic effects, not steady-state effects. One of the main points that is made in the very first classes of undergrad-level vibrations and control theory fundamentals courses is that for reasonably linear systems (as Mark pointed out), a steady-state force change (such as the direct effects of incidence or decalage changes) does NOT significantly change the dynamic characteristics of the system. If you're seeing a significant change in handling qualities, it is due to some side effect that, although it might have been triggered by the decalage change, was not directly due the decalage change itself. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: HL Gap Seal Tape?
Tom Clarkson asks: Anyone have any ideas on how to make super light gap seal tape for the underside of ailerons on handlaunch gliders?... We have found that good gap seals can be very important in some flight modes if you want to get the most out of your airfoil. Fortunately, simple but effective gap seals are easy to make. I like to use scotch tape seals for this. Cheap, light, doesn't overload the servo, conforms to the surface and can be formed to follow the deflections of a control surface. They do wear out eventually, but they're cheap and easy to replace. Get some 1/2" wide scotch tape, 3-M 600, or other similar tape. Pull out a strip of it long enough for the gap you're trying to seal plus a little extra. Use two short pieces of tape (one at each end) to tape this strip STICKY SIDE UP to a cutting board. It should be snug and straight, but not stretched tight. Now tape another strip (again STICKY SIDE UP) right alongside the first one, their edges butting together along their entire length, but not overlapping. Now take a third piece and CAREFULLY lay it sticky side down, exactly centered over the butted edges of the first two tapes so that 1/4" is on one tape and 1/4" on the other. You get ONE try at this, so do it right. I find it usually works best to hold the piece of tape stretch out over the approximate final location, lower one end into position, then (keeping the tape stretched so it doesn't sag in the middle and get stuck prematurely!) carefully lower the other end into position. Use a no. 11 X-acto knife, single-edge razor blade, piece of broken mayonnaise jar, or other very sharp implement of your choice, to slice the tapes into two pieces along the line formed by the butted edges of the first two tapes. Voila! You now have two complete gap seals, with a 1/4" wide strip of sticky-one-side tape for the attaching half, and a double thick and non-sticky 1/4" wide strip to form the wiper half. Cut it loose at the ends, carefully lay it in place on the model and rub the sticky side down onto the model's surface. You can also deflect the control surface away from the gap seal, then rub along the edge of the gap to form a bend in the gap seal that will keep it pressed against the control surface during moderate control deflections. It takes less time to do than it does to describe. I also use these on the ruddervators of my personal 2-M Spectre (the one in the photos on our website you can see one of these gap seals on the right ruddervator in the photo labelled "Close-up of the V-Tail (Top view)") to save weight in the tail. It works fine on any surface of an HLG, including flaperons, and should be OK for tail surfaces on most models. However, I wouldn't recommend them for flaps and ailerons of 2-meter and larger models, those tend to see a lot of abuse during landings. For those applications the sturdier conventional gap seals are probably a better choice. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] V tail
Yiu Kwong Chan writes (again!!): Using V tail to perform rudder or elevator function have low efficiency problem. For those who knows maths (assuming 90 degree V example) It takes two(0.7) units...(big snip of same analysis we've heard from him before)... Y.K., the problem here is that you're ignoring the fact that those two 0.7 units each of lift force are each being generated by a tail panel that has greater span than the conventional fin/rudder you're comparing it to. Induced drag is proportional to the square of that span. Yes, the total lift force being generated is somewhat greater, but it's being generated with much greater efficiency. The net result is that the total drag is about the same for both tail types, with some small variations either way depending on design details (sometimes in favor of the V-tail). Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Effects of different ballast types on radio range
Joe and I finished our flight tests on the Spectre 2-meter a little early this afternoon, so we did some ground investigations of the effects of steel BB's and of lead shot on radio range. We were concerned that a large mass of conductive metal pellets (and magnetic too in the case of steel BB's) in close proximity to the antenna where it goes past the ballast compartment on the way to the tail might have some adverse effects. The test method has a significant effect on the results. In general, for the conditions most like flight operations (ground test, but with the rubber ducky Tx antenna unrestricted), it appears that the steel shot does reduce range significantly, although the resulting range may still be adequate. If you plan to fly at long distances you might want to avoid steel ballast. Lead ballast (the large-size split-shot fishing sinkers from the sporting goods section at Meijer's) does not seem to reduce the ground range significantly when using the rubber ducky antenna on Joe's JR transmitter, the only major problem was my sore feet from having to walk so far for two sets of tests. If anyone else has investigated this question, we'd like to hear from you. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] Heavy Boomerang - Elevon issues
Dan Borer writes: ...If the rules state 'no resin coated' whatevers, then that means they will not be tolerated--PERIOD. The rules are to create an even and safe field; they are not there to be ignored. I've been listening to this thread as a reasonably objective bystander. I'm now going to do something that I'm sure I will regret later, and stick my nose into something that I don't think I know all the details about. Of course that's how we learn, by asking questions. Oh, well, here goes... If I remember correctly, one of the other posts to this thread mentioned that the rules outlawed COMPOSITES (not "resin coating") in the tail surfaces, meaning fiberglass/epoxy, carbon fiber/epoxy, etc.. Technically speaking, resin coated elevons as I understand them (i.e.: they are epoxy smeared onto the wood, no glass cloth involved) are not composites in that sense. They are merely wood painted with epoxy, as opposed to painting it with Varathane, or butyrate dope, or Sears all-weather latex. It's essentially just another kind of paint. Would KB Superpoxy, Hobbypoxy paint, Black Baron, or Rustoleum's epoxy-based stove and refrigerator paint be therefore illegal as well? They're all ways of applying epoxy resin to wood. In fact, virtually all modern paints are based on some sort of resin, so that if the rules really do specifically outlaw "resin coating", then they essentially outlaw virtually all paints, not just epoxies. The other point that someone else pointed out was that the rules actually say that "nothing within an inch of the leading edge can be hard or reinforced." It seems to me that most of the aircraft in question have elevons that are further aft of the leading edge than that, and therefore are not involved in that rule in the first place. Dan, Jerry, et. al., if as Dan stated, "The rules are to create an even and safe field", then there should be a fairly clear and obvious explanation that shows why this particular rule is necessary, and exactly how it provides those "even and safe field" benefits it claims. Otherwise it's just another unnecessary rule. So far I haven't heard anything from the pro-rule camp in this little flame war that clearly explains why this is a good rule in the first place. All I've heard so far in this rule's favor boils down to little more than "Because I said so!" As a reasonably unbiased (other than the fact that I don't like unnecessary rules that don't provide any observable benefits) observer in this debate, I'd like to hear a logical explanation of this. That explanation should also deal clearly with why this supposed hazard is an issue now, where it apparently hasn't been an issue in the past at other similar events. If it's really a significant hazard, then there must be some logical explanation why other organizers of similar events in the past haven't needed to make an issue of it. To assume otherwise would be to assume that all of those other organisers were either uneducated with the realities of their events, or were being intentionally stupid. Have we recently learned something new that suddenly identifies a new or previously unrecognized hazard, or a hazard that is peculiar to your event and not to other seemingly similar events? If such an explanation exists, then I'd bet that other organizers of similar events will see the wisdom in this rule and adopt it for their events as well. I'm sure you had some reason you believed that this rule was necessary. What is it? OTOH, if there is no such explanation, then it seems to me that someone is just being hasty and arbitrary, without really concentrating on that goal (as stated so clearly by Dan) when they formulate all these new rules. If it's your event, that's your privelege, but it doesn't make your event better if you do that. If you clutter your event with arbitrary and unnecessary rules, folks will choose to spend their precious recreational time at someone else's event. So, which of those situations is it? Inquiring minds would like to know! Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: 3 cell or 4 cell ?
eceivers and these servos seem to be "current hogs". In summary, for the rather miserly needs of Hitec and Berg components, 50 mah 3-cell packs seem to be the best for Mosquito class models. 2-servo 1.5 meter HLG's also do well for us on 3-cell 50 mah or 110mah packs, and for our current 4-servo models we generally recommend 3-cell 110 or 150 mah batteries. Other models, including our older Wizards with the short flaperon horns and stiffer flaperon hinge layups, need more torque from the servos. For these you may need 150 mah cells and/or 4-cell packs. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.bright.net/~djwerks/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
