[RCSE] Re: Incidence and Decalage (long)
Computing best decalage for desired speed and trim is actually fairly involved. I know of no one good reliable simple formula that you can use to calculate decalage (angular difference between wing and horizontal stab) for all sizes and types of soaring gliders. If you pressed many designers they would probably have to admit to you that a fair amount of empiricism (read flight trimming) is typically involved in setting up decalage on a new design. Decalage is effected by many other glider design parameters including designed range of speeds, CG location, Airfoil pitch moment, wing's drag moment, wing downwash angle of air at tailplane, etc. A variety of approaches to computing decalage are possible. These methods vary in their reliability and difficulty. Method 1 - Best Approach - Plane Geometry Software If you are lazy and want to get the right answers I would suggest you investigate some very fine glider design software called "Plane Geometry". You can do all the necessary calculations on paper to get a good estimate of decalage (but it is an arduous and error prone process). For routine work it is much easier (and less error prone) to use a computer program to do the grunt work for you. Blaine Rawdon (a rather gifted professional aerodynamicist and active aeromodeler) has written a truly excellent Excel spreadsheet that greatly simplifies the process of accurate soaring glider design. Plane geometry is very helpful for answering questions like optimum decalage, best fuselage deck angle (angle the wing mounts on the fuselage for minimum drag), tail length and tail surface sizing for best performance and handling, control surface sizing to achieve known good effective response from control surfaces, etc.. I know of no other single tool that provides as much excellent information as Plane Geometry (initially, you may be a little overwhelmed with the amount of information Plane Geometry provides. You can begin by only using the parameters you need and over time learn more about more exotic parameters and use them when you need them). Michael Shellim has a fine review of Plane Geometry on his web page that should give you a good idea of how the interative process of using the design tool works. You can view Mike's informative page at http://www.rc-soar.com/hardsoft/planegeo.htm Plane Geometry's results for decalage, fuselage deck angle, and stabilizer geometric incidence are the most reliable of any of the calculational methods I have tried. Plane Geometry is easily worth the approximately US$20 which it costs if you design model gliders. One thing that Plane Geometry does not do is predict the performance of a proposed glider design (Plane Geometry does not have a database of airfoil polars/performance). You must use other tools to identify an airfoil/wing design that should have good Lift/Drag, sink rate, etc. Plane Geometry will help you implement that design by providing vital design information like decalage, CG range, tail sizing for stability/performance, etc. Plane Geometry focuses on the design issues of conventional gliders with tailplanes (cruciform and V-tail). Design Problems relating to tail less gliders (flying wings) and canards are not directly covered by Plane Geometry. Decalage Method 2 - Designers rule of thumb (Good starting point for an estimate of decalage but less accurate/reliable than Plane Geometry Software) Almost every thing else affects decalage at least a little (CG location, airfoil pitch moment, wing's drag moment, downwash angle of air at tailplane) so the final setting is often a matter of trimming rather than computation. For thermal soarers trimmed for good performance at speeds near maximum lift to drag 5 to 6 degrees from the zero lift angle of attack of the wing is usually a good starting point for an initial guess of decalage. For example, the zero lift angle for RG15 is approximately -2.52 degrees so a beginning suggestion for decalage for an RG15 thermal soarer would be somewhere around 2.48 degrees. Decalage Angle (RG15 thermal soarer) = AoA~ -2.52+ 5 degrees = 2.48 degrees Note: Decalage for slope racing gliders is typically a little different than for thermal soarers. I would suggest adding 3 degrees to the airfoil zero lift angle as a designers guess for the decalage (thermal gliders are tuned for optimum performance at speeds near those for optimum Lift/Drag while racers are trimmed for performance at high speed and typically require a little less decalage than soarers when trimmed that way). Example (Slope Racer) Decalage Angle (S2062) = AoA~ -2.03 + 3 degrees = 1 degree The decalage for a racer needs to be small to preserve the speed range of the glider. Typically very small angles (= 1 degree) are involved which are difficult to measure and to build accurately. This desgner's rule of thumb is a surprisingly good initial guess of a value of decalage but you will have to typically resort to flight trimming to get final
[RCSE] Selectable Tx FM frequency shift polarity
FM radios modulate the base carrier in frequency (slightly increasing and decreasing the frequency of the carrier) to transmit information to receivers and servos. The polarity of the shifting of the carrier is different for different manufacturers. It would be nice to use one transmitter with all styles and manufactures of FM receivers. I would be grateful to know if any FM computer transmitter offers the feature of switchable frequency shift sense (selectable FM shift polarity). Does anyone know of a manufacturer making a transmitter having this feature? __ Get Your Private, Free Email at http://www.hotmail.com RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Fiberglass Mold Surface Coat
I would be grateful to know of a source for fiberglass mold surface coat (sometimes a special hard epoxy is applied to the surface of a fiberglass mold to improve wear and durability). There is one product listed in "Aircraft Spruce and Specialty Company" catalog but I am uncertain if it is appropriate for model fuselage mold fabrication. Thanks for any leads! __ Get Your Private, Free Email at http://www.hotmail.com RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Liftroll.xls Question for John Hazel
Discussion in rec.models.rc.soaring usenet group reveals that enthusiastic local Liftdistribution software "experts" do not understand (at least in a satisfying intuitive way) why the "Local Cl" graph tends to peak up when local chord become narrow and decrease when local chord become large (the situation at the root of strongly tapered wings). It is clear that this is the way that Liftroll responds but it is not quite clear and intuitive why this is. Could you provide us an insight as to why Local Cl increases as local chord gets smaller (tips) and decreases when local chord is larger (root)? Does the expression that gets plotted on the Local Cl graph include local chord as a term in the denominator (thereby making the plotted expression larger when local chord is smaller)? Is there some other interesting (and intuitive) reason why the Local Cl graph has this behavior? __ Get Your Private, Free Email at http://www.hotmail.com RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Flying Wing?
The DAW Schweizer 1-26 you are currently flying is a rather nice versatile slope glider when properly trimmed (especially if the glider has been built with ailerons and reduced dihedral of about 2 degrees). If the glider was built with rudder/elevator and standard recommended polyhedral it tends to exhibit some tendency to get blown over in strong winds/crosswind landings on the slope. I have had good results with the straight dihedral aileron equipped Schweizer HLG penetrating in rather strong winds up to about 25 mph. I might suggest you consider examining the trim of your glider before you dump it in favor of a flying wing or other aircraft. Consider 1) Check the CG to make sure it is at the manufacturers suggested location (the Schweizer tends to build up mildly tail heavy). 2) Check the decalage (relative angle between the chord line of the wing and the chord line of the horizontal stab) such that it is approximately 1.5 degrees. Foamy airplanes tend to get tweaked when crashed or carried in a vehicle and they get knocked out of trim. It is also possible to warp the EPP fuselages when assembling using strap tape. Check to see the the aft portion of your fuse lies flat when placed against a flat surface (if not it is an indicator that the fuse is warped/tweaked and you need to correct the problem using a monocoat iron/heat gun bending the part in a direction opposite the warp while applying heat). When properly adjusted the DAW Schweizer has one of the widest performance envelopes (light lift to very strong wind conditions) of any EPP foamy glider. The improvement resulting from getting the decalage set correctly is significant. If you have too much positive incidence set in the horizontal stab it will reduce the high end speeds that the glider can operate at. Schweizer 1-26 gliders built for the slope can benefit from slight reduction of the decalage to no more than 1.5 degrees as this will preserve the wide speed range the glider can fly at. The best flying of the EPP foam flying wings in my opinion is the CSD Boomerang. This is a rather agile glider designed for combat but is tuff enough for intermediate flight training. If you decide not to work further on improving your DAW Schweizer this would be a glider to consider (it flies in light lift and also fine in quite strong winds). Best wishes! __ Get Your Private, Free Email at http://www.hotmail.com RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] Re: best airfoil and layout for speed and turns on slope ?
There are some really fine experienced designers (which I will not mention for fear of leaving someone out) that tend to lurk in RCSE and the F3F mailing list. My hope is that a few of them will join this discussion and offer nice suggestions. I will offer the following two wing designs in an effort to be of help (and possibly take some flack and learn something from my friends). For all around balance I am not aware of a better airfoil than RG15 for the F3F course. You can experiment with thinner lower cambered airfoils like HQ10/08, RG14, or SD6062 which indeed are marginally faster on the straights but tend to lose it in the turns. I would suggest you consider the following two wing designs Wing One - Aspect Ratio 13.4 RG15 Root with SD7003 Tips Root Chord 21 cm (8.3") Root Panel Length 50.8 cm (20") First Break Chord 20 cm (7.9") Mid Panel Length 38.7 cm (15.25") Second Break Chord 15 cm (5.9") Tip Panel Length 27.3 (10.75") Tip Panel Chord08 cm (3.15") This wing uses RG15 for Root, First Break, and Second Break airfoil - Tip airfoil is SD7003 which performs a little better than RG15 at very low reynolds numbers and should make the wing slightly faster than a straight RG15 wing. No geometric washout (twist)is used in this wing but the difference in airfoils between the root and tip yeilds about .8 degrees of aerodynamic washout and should improve handling and reduce the tendency of tip stall. This wing rather closely approaches elliptical lift distribution but in my opinion has tips that are too small and will cause more drag and handling problems then a slightly larger tip (a very small chord tip suffers higher profile drag and stalls at a reduced angle of attack because it is operating at very low reynolds number). For speed and F3F I would compromise on a slightly lower Aspect Ratio and slightly wider chord tip and live with the slightly reduced lift efficiency. Wing Design Two - AR=12.95 - Slightly larger Tip Chord RG15 Root with SD7003 Tips Root Chord 21 cm (8.3") Root Panel Length 50.8 cm (20") First Break Chord 20 cm (7.9") Mid Panel Length 45.7 cm (18") Second Break Chord 15 cm (5.9") Tip Panel Length 20.3 (8") Tip Panel Chord10.8 cm (4.25") RG15 is used for Root, First Break, and Second Break Airfoils - SD7003 used for the Tip. The lift distribution of this wing is not quite as good as for Wing One but the improved handling indicated by the local lift distribution charts and the improved reynolds number that the Tip operates at should make this wing faster and easier to fly. No geometric washout (twist) is used on this wing but as in Wing One the use of diferent airfoils produces an aerodynamic washout of about 0.8 degrees which should help reduce the tendency to tip stall. Best wishes with your project. I must be beautiful to soar in Norway (during the months when the sun shines)! From: [EMAIL PROTECTED] Hi fellows. I intend to make a wing, designed for speed and turns on slope i.e. F3F 1) What airfoil will be best suited for this? 2) Below you are able to consider my new wing layout IM not sure Help and Comments are Highly Welcome. WS 236cm (92-92 inch) Chord 1 (root) 21cm (8.3) (max due to fuselage pylon support ) Chord 2 20cm (7.9) Chord 3 15cm (5.9) Chord 4(tip) 08cm (3.15)(washout 1,5 ?) regards Kjell-AAke Alfredsen, City of Tromsoe Norway 69degree of latitude north Up here at the top of the earth; from the 21november until 21jan the sun disappear and a small amount of daylight is visible At a part summertime the sun shines all the night and day and we fly at all hours around the clock. __ Get Your Private, Free Email at http://www.hotmail.com RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
