Vne for KF model 4/1200

[jrthomas]

You're probably right DesertFox4 about the windshield thickness. I just figured the airfoil tail surfaces might be less likely to flutter at higher speeds. I do remember that the Speedster called for a thicker windshield. I suspect we're both right. James Thomas

[avidflyer]

Just as a comparison, the Avid MK IV had a VNE of 135. They never did use any wood ribs in the tail feathers on the Avids. Avid wings are 2' shorter than the standard Kitfox 4. I have noticed the .060" thickness windshield start to buckle in at about 100 MPH though. JImChuk

[Av8r3400]

My IV-1050 stated 125 mph.

My IV-1200 Classic has listed 140.


I agree with Steve, it is all about the windshield. The earlier kits had a thin (.062"?) Lexan (polycarbonate) sheet the w/s was made from. This would begin to stove in at around 115-120 mph. The later kits had a thicker piece (.087'?) or the molded acrylic piece from LP Aeroplastics which was much more rigid.

[WISDAN]

Is the 140 mph for the standard wing span Larry?

[Av8r3400]

I don't know that the wingspan has any effect on the VNE.

[av8rps]

FYI:

Denney Aerocraft Company Model 4 brochure from June of 1992 lists VNE for standard Model 4 at 125 mph, and 145 mph for the Model 4 Speedster.

There is however mention in the brochure about the Speedster having a thicker windshield for the higher airspeeds it flew at (which was advertised with a cruise of 125 and top speed of 135. fwiw, I flew that plane and can verify it actually did those numbers or more, and all on a wood 3 blade GSC prop no less!)

[av8rps]

Relative to this discusssion, it is my opinion that maximum structural cruising speed is much more important to the everyday Kitfox pilot than VNE.

The Vno is 98 mph for my Model 4 -1200. When dealing with lots of turbulence I adhere to that number like religion as it is a lot more likely exceeding that airspeed number will potentially cause structural damage to your Kitfoxes airframe

Ironically, my Kitfox is the first plane I have ever owned that I had to pay so much attention to that number, as my other planes aren't fast enough to get close to their Vno number. And even though my Kitfox is a float plane, there are times I have to work to keep it under that number