What is factory Vne on Model-4 and Speedster ???

[rogerh12]

Howdy;
What is the Vne on the Model-4-1200 and Speedster type, as defined by Kitfox? Is there a difference between the two versions? What is the typical physical limiting factor that established this factory specified Vne? Are these Vne's at all flexible upwardly, too conservative, or is that just a crazy concept to bring up?
I guess this last question has to due more with a temporary overspeed during a dive in smooth air, not a sustained overspeed in cruise or through turbulence in a long decent.
Thanks
Roger

[Av8r3400]

My IV Classic-1200 has a Vne of 145 mph.

My IV-1050 has a Vne of 125 mph.

My understanding of the limiting factor was the windshield. The earlier planes used a thinner material that would begin to stove in above 125 mph. The later kits had a thicker material supplied. I don't know this is the only reason, though.

The IV-1200 has two counter weights on each flapperon. The 1050 only has one (of twice the mass). This may have been to prevent a twisting flutter in the flapperon to start?

I have a molded plexiglass (LPAeroplastic) windshield on my 1050, so it has never been a concern for me. I also have one for my 1200 now, too.

[HighWing]

Roger,
I tried to verify the numbers with my collection of documents but couldn't find anything and the Kitfox Aircraft site doesn't have the IV specs posted, but my memory tells me that the Vne of the IV kit as delivered was 125 MPH. The Speedster was 135 MPH.

All the talk then to now indicated that the difference was totally dependent on the windshield thickness. The long wing IV had the windshield thickness at 3/32" - .090" Lexan whereas the Speedster had 1/8" - .125".

The .125 Lexan caused problems because Lexan that thick doesn't like to be bent to the tight radius at the door posts and would readily craze requiring frequent replacement. Typical fabrication guides place a minimum cold formed bend radius of .125" Lexan at 12.5"

As a side note, the .090 will craze as well (9" minimum bend radius) and some went to the .060" - I did. It would oil can a bit approaching red line but not at the typical cruise speeds.

[Geowitz]

The official Skystar Kitfox "Pilots Operating Handbook" that came with my kit says...

Model 4-1050 - 125mph
Model 4-1200 - 125mph
Model 4 Speedster - 140mph

Ditto on the windshield comments.

[rogerh12]

Once I asked the designer of the Zenith line, how the Vne was determined on his planes. He said it was just a speed that they tested the plane too, and not a speed at which anything above would cause permanent damage (the the G-rating on a wing). So I asked what speed would cause permanent damage to my 601HDS, and he said he didn't know, and remarked that they have not calculated the damaging Vne speed, or even test the plane to determine this "True Vne" speed.

So I was wondered if the Kitfox had a "True Vne", something to be avoided at all cost, so I could mark it on my Airspeed indicator as a double red line. And also wondered what would get bent first, which sounds like the wind screen. (Easy enough to see bending, so who needs a redline on the indicator anyway !!!)

Thanks for the input guys
Roger

[DesertFox4]

(Easy enough to see bending, so who needs a redline on the indicator anyway !!!)

The DAR signing off on you airworthiness certificate.

[jdmcbean]

POH - Published numbers: VnE
Model IV-1050: 125 MPH
Model IV-1200: 125 MPH
Model IV Speedster: 140 MPH Speedster had the Acylic windshield

Early Model 4-1050 actually had 95 MPH published but was changed by SkyStar later on. Speculation was a carry over from the Model 3.

[Geowitz]

There ya go.

[rogerh12]

Since my new Airspeed indicator stops at 130 mph, I will just use 125 as my marked Nne. I doubt my Porsche powered plane will go much faster than 100 mph anyway, with a climb prop attached (beats 95 mph anyway).
Roger

[HighWing]

I finally found what I was looking for. See attachment.

One note, though, I guess we will have to agree to disagree about the availability of the acrylic windshield in 1992.