In Soaring FAQ on Web page: http://www.geocities.com/Athens/3171/soar-faq.htm#589884 I read about aspect ratio (AR). Can author (I do not know who is) of this text (or someone else) help me with equations to calculate the optimum AR according to text. Any help will appreciated. Thanks Brane V. Here I quote the text: A few days ago I sent out a critical reply to a discussion on aspect ratios. I did not however provide any insight or answers. I apologize and will make amends now. Many people have asked for value of the best AR, instead of technical jargon. So I wrote a program that looks at all of the drag components and optimizes AR for a Maximum L/D condition. NOTE: The optimum AR depends highly on flight condition (High lift, low lift etc.), so I picked max L/D as a good overall optimization point. First a quick discussion on the optimization process, (without longequations) Cd=Cdp+Cd(vortex)+Cd(lift dependent viscous), Where Cdp is the parasite drag and is a function of (Re#, wing thickness, and skin friction coefficient). Cd (vortex) is the inviscid vortex drag and is a function of (lift coefficient, Aspect Ratio and inviscid wing efficiency (e inv)). The Last term is the lift dependent drag coefficient and is a function of (Cdp and lift coefficient) For best L/D Cdp=Cd(vortex)+Cd(lift dependent) (a fact, trust me). Combining these equations and balancing RE# effects with AR effects, an optimum AR can be determined. Here are some results. Starting assumptions: Velocity=35ft/s, Average chord = 8", e inv = 0.98, Weight =6 lbs. Results: OPTIMUM AR =12.5, corresponds to 100" span NOTE: overall wing efficiency at this condition (e = Oswalds efficiency factor) is 0.8 Using the same method and calculating optimum AR for a full-size glider Starting assumptions: Velocity = 90ft/s, Average Chord =4 ft., weight =1000# (I made these numbers up, I don't know how accurate they are) Results: Optimum AR = 25, wing efficiency =0.74 These results clearly indicate that as RE# decreases, optimum AR also decreases, which is why Full-size AR are not efficient at model RE#'s. Also wing efficiency decreases as AR increases, due to viscous effects. These last two facts are what I previously posted without the explanation. NOTE: These are approximate values, I used numerical CD methods to approximate the drag components. Accuracy could be improved by using wind tunnel drag data for your specific airfoil. (If you have the data available at your desired RE#) Well I hope this helps. If anyone would like a better explanation and the governing and optimizing equations, then e-mail me your mailing address, and I will be glad to send it to you. So why believe me? I am an Aerospace Engineer for NASA Ames Research Center, where I am a Test Manager at the National Full-Scale Aerodynamics Complex. I am also completing a masters degree this march, specializing in applied aerodynamics. End of quote. --== Sent via Deja.com http://www.deja.com/ ==-- Share what you know. Learn what you don't. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
