Prop/ground clearance

[Allen Sutphin 705]

Had the tail raised this evening to level (dang the tail is high) getting ready for fuel flow test and noticed the prop clearance is at a min. What do most of you guys have for clearance in a level attitude, for those that have even checked? I am running a 70" 2 blade and may have to shorten it a bit.

[Willja67 144]

I have the book "Landing Gear Design for Light Aircraft" by Ladislao Pasmany, on page 7(attached below) he summarizes FAR 23 that says ( for certificated aircraft at least) that your minimum ground clearance with landing gear statically deflected in the takeoff position should be no less than 9".  So load the plane up to max gross lift the tail to takeoff position and see how much clearance you have. 

If you operate from rough strips you will want more clearance. 

Edited 12 Aug 2019 by Willja67

[Allen Sutphin 705]

Tail position for take off in a Kitfox is probably not fuselage level. According to the manual, level for a Fox fuselage with the underside of the floor level, which puts the tail about 8 1/2' in the air. I've never seen one take off in that position. Wheel landings, are another story.  Sitting tail down I have 18" clearance, fuselage level I have 7". When I got it  also had a 70" 3 blade/Subaru combo. So according to that I need to do something to gain 2" prop clearance. Bigger tires, longer gear, or shorter prop. Another clue that it wasn't flown much if any.

Edited 12 Aug 2019 by Allen Sutphin

[1avidflyer 1983]

Allen,  I just went and looked at your plane when you put the wings on so I could see how big your tires were.  They don't look especially small.  More like the standard size they would have come with in a factory kit.  It wouldn't have been unusual for Kitfoxes to have 70" props either, so what is different about yours?  Does the Hirth gearbox not go up as high as others or does the engine sit lower?  I would be reluctant to cut the prop down unless I knew it was to big power wise.  Better to get a set of the Nanco 22" tires if you ask me.  About $100 for the pair on ebay.  Then again, what is the mission of the plane.  If you never intend to leave paved strips, prop clearance is less of an issue.  If you intend to do back country flying then it's a different story.  But like I said, why do you have the problem and others don't.  I had a 70" prop on my Kitfox 1 with 582, and thought I had enough clearance.  JImChuk

PS  just looked at your pictures of the plane, and it looks like the prop spinner is in the center of the cowl for up and down. 

[Allen Sutphin 705]

Right now I have no idea!  Engine does sit lower than a 582. 22" tires are probably the easiest cure. And I was planning on going to them anyhow, sooner or later. The current tires are the stock 20" Nanco's.  Evidently the cowling came from NSI with the engine  so may be a tad different as far as center since the NSI used a centerline gearbox. I rarely use paved strips. This Fox has been a PITA all the way since everything firewall forward had to be custom built. But so far, all the issues have been solved with a little effort and this will work out somehow, too. Not a project for the faint of heart. It has become a challenge.