On Friday 18 February 2005 17.12, [EMAIL PROTECTED] wrote: > Generally speaking higher aspect ratio with either a fixed span or area > will equal a reduced wing chord. This will result in reduced reynolds > numbers which equals reduced performance for most all airfoils > *** > > Yes, but also .... what's happening (for a fixed wing span) is a trade off > between wing loading and induced drag. Re (at least for DLG chords and up) > is a variable but not the dominant one. >
I think Martin Simons "Model Airplane Aerodynamics" is a good source for info about this, not least appendix #1! A practical, high AR wing, is by default heavier (if having the same area), than a low AR wing, which makes the gain with a high aspect wing smaller than expected, even though it has lower drag. Also, when talking constant area, and small models, the lower efficiency of small chord wings comes into effect. Also mechanical matters affect the calculations, as narrow wings are more flutter-prone than low AR wings! Thus, as we are talking equal wing area, short wings are light, affecting minimal sink, while good glide ratio, equals low L/D, but the longer they are the faster they have to fly, to maintain good Reynold's numbers! If I remember correctly, your wings were all balsa sheet, thus approximately the same weight no matter what Aspect Ratio they have. The reason that AR about 7 are optimum, is that longer wings have too small AR to be efficient, while shorter have too big induced drag! In the real world high aspect ratio wings are perfect, as long as you can build a strong enough wing, but they will be default be heavy! But if you have a motor the calculation gets more difficult, as a lot of induced drag during take-off and landing, due to short span, can be compensated by brute power. At cruise speed and straight flight long wings are not that helpful, unless the engine can be throttled back efficiently! So a motorglider has very low useful load, but excellent fuel economics! Good luck, Tord 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
