Re: [RCSE] The perfect platform or Not....
There is/was a school of thought that you decrease camber toward the tips to reduce lift and vortex to decrease drag. What this does to overall efficiency is questionable to me, but I am only an amateur aerodymanicist. I expect that you increase "effective" wing load due to sacrifice of tip lift in trade for reduced vortex. I wonder which one wins? If you stay away from stall speeds you might never notice a plane has a tip stall tendency - not to infer that the Sharon has one. If you are using camber flaps that drop equally accross the wing, you may be increasing camber more at the tips than at the center due to geometry and getting the best of both worlds anyway. Hope I can sleep tonight instead of thinking about this one. Tom Koszuta Western New York Sailplane and Electic Flyers Buffalo, NY - Original Message - From: "John Erickson" <[EMAIL PROTECTED]> > The Sharon has a 7037 at the root, transitioning to a RG-15 at the tips. > Seems totally backwards; more camber at the root than at the tips. This is > aerodynamic washin unless there is some twist in the molding process. > > The alternative is to blend the airfoils to get aerodynamic washout and > > decreased stall speed at the tips. 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] The perfect platform or Not....
Thomas, I'm still trying to figure out how the Sharon 3.7 does it. The Sharon's flew beautifully this last weekend in Phoenix. Great plane for the "mid" winds and thermal cycles they had at the contest. The Sharon has a 7037 at the root, transitioning to a RG-15 at the tips. Seems totally backwards; more camber at the root than at the tips. This is aerodynamic washin unless there is some twist in the molding process. JE -- Erickson Architects John R. Erickson, AIA > From: "Thomas Koszuta" <[EMAIL PROTECTED]> > Date: Tue, 8 Feb 2005 15:30:49 -0500 > To: > Subject: Re: [RCSE] The perfect platform or Not > > You can only optimize a wing with one airfoil for one speed. You then > either need to compromise for good performance at more than one speed or > accept the poor performance at other speeds. The old floaters are good > examples of this. This is one of the reasons that camber flaps are so > popular. > > The alternative is to blend the airfoils to get aerodynamic washout and > decreased stall speed at the tips. Martin Simons book describes this by > using more camber at the tips, then using geometric washout to bring the > aerodynamic AOA back to the same value. I have taken to this by using > something like SA7035 at the root (2.5% camber) and SA7038 at the > tip(3.25%camber) with the SA7036 and SD7037 between and washing the whole > wing out. It is a near continuous twist to about 0.75 degreees - the > approximate 0.75 degree (estimate) difference in zero lift angle. 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] The perfect platform or Not....
As for a web page bits and pieces at different times... The most current page is: http://www.rasdoc.com/splinter/solar2004.htm The collection of related pages (Many Many really outdated) http://www.rasdoc.com/splinter At 01:32 PM 2/8/2005, you wrote: >I can use LiftRoll to adjust twist to make it look like an elipse or not, but how do I generate the comparison number from my origional post, IE wing 1 will have min sink of 1 fps and wing 2 will have minimum sink of X fps? You don't necessarily want an elliptical lift distribution in a real-world model, since that might result in turning behaviour that is a little scary at times if your airfoil selections aren't correct. You're really looking to optimize cruise here, right? (ie min power setting for level flight). Look into the power factor calculation available from xfoil/profili. Flight power is proportional to CD/CL^1.5, but remember that CD is the total airframe drag coefficient, so working with the airfoil Cd along isn't going to give you the full picture. >How do I use LiftRoll to get a wing Cd, Cl given a polar Cl, Cd? Very simple...you can't. It's not designed to be able to give you this information, since at no point does it incorporate actual airfoil data. >In LiftRoll is av/mx Cl the Cl I want to optimize for? That's a planform efficiency number, giving you a measure of how "aggressive" the planform design is. Real-world meaning: a high efficiency number will require a more competent pilot, since upon reaching stall more of the wing will "let go" at the same time. Compromising this measure will result in a model that's easier to fly over a wide range of conditions. >How do I go about guessing an AOA? (Again from the airfoil polar? ) Don't bother...I've already made a sheet that will calculate it for you (overall Cd, wing drag, tail drag etc). You need to know the weight of the model (assuming you're calculating a level flight condition, ie weight=lift required) and you need access to the airfoil polar data from Profili/Xfoil at the appropriate Re# Go to the following link to download the sheet...based off of LiftRoll about 3 yrs ago: http://www.soarcalgary.com/Extras/Articles/Sailplane%20Design%20Spreadsh eet/ Did you have a webpage for your solar project? I've been curious how it was coming along, but the few searches I ran never came up with the webpage that I seem to remember seeing once upon a time. Hope that helps, Adam Adam Till Mechanical Engineer 403-270-9200 (ext 154) 403-270-0399 (Fax) UMA Engineering Ltd. 2540 Kensington Road NW Calgary AB, Canada T2N 3S3 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 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] The perfect platform or Not....
>I can use LiftRoll to adjust twist to make it look like an elipse or not >but how do I generate the comparison number from my origional post, >IE wing 1 will have min sink of 1 fps >and wing 2 will have minimum sink of X fps? Beats me. I suspect that the spreadsheet is not capable of that level of precision. Bill 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] The perfect platform or Not....
Well, I changed the file names long ago and I forget exactly what they used to be. However, the newer sheet has the input data shown in COLOR (red,black,yellow,white) while the older one does not. Personally, I've not had any reason for the newer sheet's complexity. I'm thinking the two have are just LiftRoll and LiftDist. They're fairly old. I've had the first sheet for about six years. Bill Swingle 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] The perfect platform or Not....
>I can use LiftRoll to adjust twist to make it look like an elipse or not, but how do I generate the comparison number from my origional post, IE wing 1 will have min sink of 1 fps and wing 2 will have minimum sink of X fps? You don't necessarily want an elliptical lift distribution in a real-world model, since that might result in turning behaviour that is a little scary at times if your airfoil selections aren't correct. You're really looking to optimize cruise here, right? (ie min power setting for level flight). Look into the power factor calculation available from xfoil/profili. Flight power is proportional to CD/CL^1.5, but remember that CD is the total airframe drag coefficient, so working with the airfoil Cd along isn't going to give you the full picture. >How do I use LiftRoll to get a wing Cd, Cl given a polar Cl, Cd? Very simple...you can't. It's not designed to be able to give you this information, since at no point does it incorporate actual airfoil data. >In LiftRoll is av/mx Cl the Cl I want to optimize for? That's a planform efficiency number, giving you a measure of how "aggressive" the planform design is. Real-world meaning: a high efficiency number will require a more competent pilot, since upon reaching stall more of the wing will "let go" at the same time. Compromising this measure will result in a model that's easier to fly over a wide range of conditions. >How do I go about guessing an AOA? (Again from the airfoil polar? ) Don't bother...I've already made a sheet that will calculate it for you (overall Cd, wing drag, tail drag etc). You need to know the weight of the model (assuming you're calculating a level flight condition, ie weight=lift required) and you need access to the airfoil polar data from Profili/Xfoil at the appropriate Re# Go to the following link to download the sheet...based off of LiftRoll about 3 yrs ago: http://www.soarcalgary.com/Extras/Articles/Sailplane%20Design%20Spreadsh eet/ Did you have a webpage for your solar project? I've been curious how it was coming along, but the few searches I ran never came up with the webpage that I seem to remember seeing once upon a time. Hope that helps, Adam Adam Till Mechanical Engineer 403-270-9200 (ext 154) 403-270-0399 (Fax) UMA Engineering Ltd. 2540 Kensington Road NW Calgary AB, Canada T2N 3S3 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] The perfect platform or Not....
You can only optimize a wing with one airfoil for one speed. You then either need to compromise for good performance at more than one speed or accept the poor performance at other speeds. The old floaters are good examples of this. This is one of the reasons that camber flaps are so popular. The alternative is to blend the airfoils to get aerodynamic washout and decreased stall speed at the tips. Martin Simons book describes this by using more camber at the tips, then using geometric washout to bring the aerodynamic AOA back to the same value. I have taken to this by using something like SA7035 at the root (2.5% camber) and SA7038 at the tip(3.25%camber) with the SA7036 and SD7037 between and washing the whole wing out. It is a near continuous twist to about 0.75 degreees - the approximate 0.75 degree (estimate) difference in zero lift angle. I built a 10 foot set of wings like this and it was a nice flyer. I used the same templates to make a 2M. I hope it flies just as well. The base assumption of LiftRoll and Lift3Span is a single airfoil accross the wing. I think it is based on a sd7037, but I may have this confused with something else. If you are designing strictly for minimum sink to be at the lowest possible, then don't worry about what it will do at 60 mph when the Cl is 0.3 instead of 1.0. Use LiftRoll to make sure you aren't designing in a deadly tip stall. This is another compromise with efficiency. I do not know how to estimate the actual performance numbers of these complex section wings. I bet that we would be entering the world of finite element analysis and other fun methods. Tom Koszuta Western New York Sailplane and Electric Flyers Buffalo, NY I can adjust the planform twist to get eliptical lift distribution at one AOA It is then off at a different AOA. 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] The perfect platform or Not....
Wing design is very complex. Folks make careers out of doing it. I hadn't noticed ;-) I'd suggest getting a copy of a spreadsheet written by John Hazel called something like Liftroll. It's a good way to play with the basic aspects and make reasonable choices of span, twist and chord. The basic principles are consistent local Cl's across the span with an elliptical distribution of lift across the span to minimize induced drag. I've played with LiftRoll, but a couple of things escape me I can adjust the planform twist to get eliptical lift distribution at one AOA It is then off at a different AOA. (as expected for a rectangular platform) So how do I convert this non-eliptical lift distribution to a drag number for comparison. I can use LiftRoll to adjust twist to make it look like an elipse or not, but how do I generate the comparison number from my origional post, IE wing 1 will have min sink of 1 fps and wing 2 will have minimum sink of X fps? Paul In General: Min sink is when (Cl ^(2/3) /Cd) is maximized. How do I use LiftRoll to get a wing Cd, Cl given a polar Cl, Cd? In LiftRoll is av/mx Cl the Cl I want to optimize for? How do I go about guessing an AOA? (Again from the airfoil polar? ) If you can't find John's spreadsheet, I can forward either the simpler earlier version or a more involved later version. If I can figure out how, I could just put it on my website. Bill Swingle Janesville, CA 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] The perfect platform or Not....
If you can't find John's spreadsheet, I can forward either the simpler earlier version or a more involved later version. If I can figure out how, I could just put it on my website. Sorry to intrude upon someone else's conversation here, but I was not aware there was a "more involved later version." Which version would that be? Is it LiftDrag or is there a later version of the old LiftRoll? Thanks. RVC 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] The perfect platform or Not....
Wing design is very complex. Folks make careers out of doing it. I'd suggest getting a copy of a spreadsheet written by John Hazel called something like Liftroll. It's a good way to play with the basic aspects and make reasonable choices of span, twist and chord. The basic principles are consistent local Cl's across the span with an elliptical distribution of lift across the span to minimize induced drag. If you can't find John's spreadsheet, I can forward either the simpler earlier version or a more involved later version. If I can figure out how, I could just put it on my website. Bill Swingle Janesville, CA p.s.. Don't sweat the tips. "The most important thing about tips is simply the distance between them." - Phil Lontz 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
[RCSE] The perfect platform or Not....
I've asked around this question in the past, but the answers or my brain have all missed the mark a little bit... So I'll be more specific: Given two wings, same span, same area, same weights 1)A a square tip wing aspect ratio of 12 10 degrees simple dihedral. Twist optimized for a single most efficient point 2)A perfect elliptical wing with perfect elliptical lift distribution aspect ratio 12 10 degrees simple dihedral, or simple polyhedral with a flat center. Twist optimized for a single most efficient point I want to optimize minimum sink (climb actually but minimum sink is a good stand in) If wing 1 sinks at 1 ft/sec Will wing 2 sink at .95 or .5 or The tradeoff I'm trying (presently unsuccessfully) to weigh is for my solar plane, a non square wing really ads to the complexity of the power conversion and cell packing density. I can exactly quantify how much weight and power a non square wing costs me. What I can't currently quantify is the loss of efficiency for a well designed square wing. (McCready's Pathfinder/helios were square so I can't be too far off ;) 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
