wings question

[TJay]

I was wondering has anybody left the wings at the 12 foot mark, and forgot about the 2 foot extension, shorten the lift struts a bit by moving them in on the spar, I thought that would be a good way to keep the under camber wing and speed up the plane a few mph. just thinking here.

[avidflyer]

With the Avids, the wings could be built as speedwings and removable extentions were made to slip in and go to full length as one wanted. That is what I would do if it was me. I wouldn't change the struts, on the Kitfox 3, 4, and later, the struts are longer than the model 1 and 2 by about a foot with the same length wing. Also, on later then the earliest Kitfoxes, the spars were about 14' long. Jim Chuk

[jtpitkin06]

Aerodynamics can be a strange duck. If shortening the wing two feet makes it go faster, then why not shorten it 4 feet and go faster still? We all know it doesn’t quite work that way. No free lunch here. The speed gain with shorter wings is so small you will hardly notice a difference on a cross country trip.


With less wing area you can theoretically go faster providing you have enough power. At the same time your climb rate will probably drop off.
Let’s suppose with shorter wings you can gain 5 knots over your normal cruise speed of 80 knots. An 80 nm trip would previously take you 60 minutes. With the clip wing you might be able do it in 56.5 minutes if you could do 85 knots the whole way. Your climb rate is less so you must factor in more time at climb speed instead of cruising speed. The net result is very little gain. Maybe 2.5 minutes per hour. Some owners report zero gain at heavier weights.


Sometimes there are surprises in performance with wing area. One pilot decided his KR2 was a bit fast on landing and he wanted to shorten the landing distance. He added two 18 inch extensions to his wings to lower the stall speed and would just accept the drop in cruise. To his amazement the cruise speed went up at the same time. You don’t always get the results you expect.


Kitfox builders with removable extensions can report just how much benefit they do or do not get with the shorter wings. I would say fly the Kitfox as a low and slow airplane for what it is. Enjoy the scenery and don’t worry about a few knots.


John Pitkin
Greenville, TX