A much faster Kitfox?

[Slyfox]

not sure what my prop is 70 or 72. I called and ask for and got one. have to go measure. it's perfect in my opinion. I like to slip hard as well, that's how come I can do the 10ft off the numbers for a base turn and to slow down more on the home stretch I flatten the wings and keep in the hard full rudder until I have the right speed to touch down, than I let go of the rudder and full stick back ya baby. gotta love that fox

[SWeidemann]

Getting back to the faired in fuselage bottom to enclose the landing gear, does anyone know of drawings, plans or a parts modification available? (For a retro-fit or new build).

Thanks much,

Skot

[Slyfox]

I personally have thought of doing this. would like to hear more. also the fairing on the rear horizontal brazes sound good as well. now I have the nice cowl for the front of the radiator, haven't put it on yet either. too much time flying not enough time to do things I guess.

[Kurt.A]

I think this is a great idea. Anything that reduces drag certainly has to help fuel economy which means more flying time, more accessories etc. With my limited knowledge of aerodynamics I do have a question. What effect does reduced drag have on stall speed? Does it remain the same speed? Will the warning indicators prior to stall change?

[PapuaPilot]

Kurt,

Reducing drag will not affect the stall speed. Without going deep in the aerodynamics the only real factor on a Kitfox would be the weight.

A plane with less drag will be harder to slow down for landing.

[HighWing]

Kurt,

Reducing drag will not affect the stall speed. Without going deep in the aerodynamics the only real factor on a Kitfox would be the weight.

I thought on this thought. The guy I helped modify his Avid reported on the effects of the mod. He had presented his elevator with a set of full size drawings that I followed while doing the mod. He reports that it increased elevator area by 30% and reduced stall apeed by 8 mph. Lots of talk in the past on the Kitfox sites on increasing elevator authority so as to be able to do a true three point landing. Increasing elevator area might be the best solution.

[PapuaPilot]

High Wing,

The increased area of the elevator didn't change the stall speed. It only helped to get more pitch authority and a greater angle of attack (i.e. to slow down).

Stall speed is a function of weight, wing area, air density and coefficient of lift. Here is the stall speed formula: V = sq root (W/(1/2p x S x Cl_max))

Where:
V = Stall speed
p (rho) = air density
S = wing area (Ft2)
Cl max = Coefficient of lift at stall
W = weight

In the case of your friend's Avid nothing in the stall formula changed. The wing area and Cl max (the lift of the airfoil at the max angle of attack - determined in wind tunnel testing) didn't change. Stall speed assumes that the wing is an its maximum angle of attack. The Avid simply could not achieve the needed angle of attack to stall the wing due to an undersized elevator.

Like I said in the first reply, the only thing on a Kitfox that can change the stall speed is the weight of the plane. A heavier plane will have a higher stall speed. The other factors are part of the aircraft's design (wing area and type of airfoil). We can't do anything about the air density, it is the mass of the air molecules. Don't get this confused with density altitude. They are not the same and is a whole other topic.

I purchased the larger elevator that is being used in the current production Kitfox for my Model 5 for the very reason you stated. I have a heavier engine and was told by John McBean that I would run out of elevator in the flare. The only other way to keep the elevator effective is to keep a little power in so there is prop wash over the elevator, which will only make you come in faster. I want elevator authority so as to be able to fly STOL landings and bought the larger elevator.

[HighWing]

I think I understand your point, but still have a question or two. Are you suggesting that when we complete the POH we do some math and enter a number on the performance page under the stall speed heading? When I did my Phase I, I took the airplanr to altitude and did several stalls at different throttle settings. Those are the numbers I put in the POH. My friend did the same and now with the larger elevator he finds the numbers 6 mph lower. What do you suggest he put in his POH?

[PapuaPilot]

I haven't done any Phase 1 testing so it's hard to know what to say. I think you would have to put the numbers that you found during the flight testing.

[PropellerHead]

Could it be that, with the smaller elevator, your friend was just running out of elevator authority and not really stalling?

What about some rigid fairing attached directly to the landing gear legs? Maybe leave a little gap to account for gear movement?