Hi folks, Hoping someone can give me a hand with the particularities of proper stab/fin airfoil design. I remember understanding the concepts behind it at one point, but I've since forgotten, and would appreciate a refresher (the archives for these lists didn't help I'm afraid).
I'm designing a new aerobatic model, and after some investigation have decided to try some of the Eppler sections that were presented in the March 2001 issue of S&E Modeller. When Dr. Eppler was writing about the E175, he said: http://groups.yahoo.com/group/xfoil/files/E175/ "Also, when I calculated the flapped case for the rudder chord of the 1/3 scale Swift at 50%, I clearly noticed a turbulator is necessary on both sides of the section at 35% chord. You must be aware of this fact, as I am afraid that the landing control may become very difficult without the turbulator" Well, frankly...I don't see it. I tried running a few test cases, and I see a marked decrease in the lift/drag ratio with the addition of the turbulator. Maybe my Reynolds number is too high? (300K) I've included the output I get for the section in flapped condition (6 degrees) with and without the turbulators in the following folder: Could some kind soul explain to me how best to optimize a stab or fin airfoil for a particular Re#? I'm not really interested in the full-flying variety at this point, but am willing to learn anything new if you'd like to share those concepts as well. In a related manner, I've been doing some reading on F3A pattern models, and have noticed that even though their manoeuvre speed is about 80 mph, they tend to truncate the wing airfoils they use so that the wing has a thick TE (2-3mm sometimes on a 19" chord). This apparently results in a dampening effect much like exponential. When I simulate this, I get a slight increase in max lift at a corresponding increase in drag at low Cl, but I can't rationalize an "exponential" effect. I've even heard of flared TE's on F3A rudders, which apparently help the models keep a heading on an upline (my guess is that this works much the same way as a double gurney flap). Is this a case of an airfoil actually needing a turbulator, as Dr. Eppler describes? Finally, regarding the location of hingelines, my typical approach in the past has been to run a variety of flapped conditions using a single value for degrees of deflection, and then to choose the case with the best lift/drag ratio. If this is different at for the tip and root of the stab, I've drawn a line perpendicular to the fuse centerline and aligned the hingelines to give me an overall stab planform. Is this method sound? Thanks for any help you can offer, 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
