Kitfox 4 fin size?

[SkySteve]

Jim,
Thanks for the correction.

[tommg13780]

Steve,

I did the rudder mod to a model 2 by purchasing a model 4 rudder from Kitfox aircraft and modifying it to fit the existing model 2 hinges. Also we went with a balanced (Cub style) kind of birds beak which confines the work area to the rudder only. The existing model 2 rudder was cannibalized to get the hinges transplanted and the birds beak over top of the vertical fin.

This modification corrected the Yaw neutral characteristic and improved rudder authority by a large margin. Major components were the new rudder at approximately $400 and about $400 in professional tig welding. Cover and paint was done by myself and considered incidental cost. Well worth the expense and effort.

[avidflyer]

There is a guy on the AvidFoxFlyers site that just enlarged the rudder on his Kitfox 3. Really doesn't look like that much work if one has access to someone who can weld and bend tubing. He probably had about $50-$60 worth of new tubing in this remodel. I do like the idea of the birds beak over the top of the verticle stabilizer the way you show Tom. For another $20-$25 or so of tubing, that could be added on to the original. JImChuk

[David47]

The "birds beak" you refer to is an aerodynamic horn balance. As the added area is forward of the rudder hinge line it will change the characteristics of the rudder hinge moments, which is reflected in the pilot forces you apply. In short, when you add a horn balance, it will change the rudder forces you need to apply for the same rudder angle. From memory, adding a horn will lower the rudder forces required for the same rudder angle.

[dholly]

Jim did not add the balanced rudder design because the height of his plane on his trailer would have been too tall for his storage building opening. He also could not lower the tail support on the trailer to provide extra clearance without the wing tips interfering with his tow vehicle. In short, to add a taller vertical stab/rudder, he would have been forced to make costly alterations to his building or trailer. Hopefully, the extra chord alone will provide a significant improvement in slow flight rudder authority and I anxiously await his pirep.

The other comments raised on his AFF forum build thread regarding this mod is that you may need to 1.) reposition flaperon counter balance weights to prevent interference with wing folding and 2.) strengthen the V.S. side rudder post to better handle the increased forces the larger rudder imparts. One member who enlarged his rudder slipped a reinforcing tube into his rudder post.

[firesteve]

Cheers guys, I must admit I had no idea that the hinge design had been changed!

[TJay]

I do think the hinges that Jim posted are only for the 1200lbs Model If you find a Kitfox 4 1050 rudder they should match the early birds,

[Av8r3400]

The 1050 rudder is shorter than the 1200 (with the goofy hinges).

That was the first mod I did to the Mangy was to cut off those rod-end style hinges.

[av8rps]

Might just be me, but I kind of like the earlier, shorter rudder style of the Model 4 -1050 and the earlier model 1-3's. I'm sure the taller fin will handle slightly better than the shorter verical, but after flying a bunch of these type planes over the years, it seems they all fly a bit different anyhow. So I just adjust myself to the particular flight characteristcs (which also keeps my feet from getting lazy...). Plus, if you are concerned about weight and an inspector ok'ing changes I'd just stick with what it came with. Again, that's just my opinion. But I think all the early airplanes flew pretty well, albeit differently than later models. Although there is more to the improvements in later models than just the change to the vertical. The control system mixers are hugely different, which provided differential to ailerons in the Model 4, which in my opinion is probably the biggest change between models.

Oh, and for a bit of trivia, did you know the vertical on early Kitfoxes was styled from a P-51 tail? Yup, just look at the profile of the early Kitfoxes and you'll see it. So if you change over to the newer tail you will lose that fun little bit of early Kitfox identity / history.

Plus, if you keep the standard vertical you'll end up being a better pilot

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[DesertFox4]

" Oh, and for a bit of trivia, did you know the vertical on early Kitfoxes was styled from a P-51 tail."

For a little bit more Kitfox trivia, so was the 7 Super Sport's vertical stabilizer.