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Kitfox Highwing gear on an Avid???

11 posts in this topic

Posted (edited)

Hi all,  I'm picking up a Highwing bush gear from someone who never used it, and was going to put it on my Avid MK IV.  Got to thinking, and reading and realized the wheels will sit further back on the Avid then they did on the Kitfox.  Has anyone used the Kitfox gear on an Avid, and if so, what are your thoughts.  Also, what has been your thoughts on the Highwing gear on what ever plane it was on.  Any bent fuselages?JImChuk

Edited by 1avidflyer

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Posted

Yes, bent the fuselage twice with it before I gave up and moved on to my current gear.  The wheel position was not an issue but the cabane will not fit, the Avid mounts set a little wider than the Kitfox.  The first time I had Lowell leave the top bar of the cabane split in the center and spread the cabane which kind of worked but the second go around I built the cabane to fit the MK IV fuselage.

So the bottom line for me is I would not use that gear again.  The gear will be just fine if you baby the plane and don't fly as close to the edge as I do.  Maybe with the mod suggested by Leni it would be ok but I am over that style of gear just not forgiving enough for my flying style.  I can say the workmanship is excellent.  I will be happy to answer any other questions you may have.

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Posted

What do you think caused the damage?  Did the springs bottom out?   Do you think it was a weaker set up than the stock bungee gear over all?  I've thought it would have helped to tie the cabane to the seat truss in the center.  What are your thoughts on that?  What modification of Leni's are you referring to? Thanks,  JImChuk

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Posted

I have the Highwing gear on a kitfox and the only improvement I could see other than a better Spring setup ,would be to have the wheels about 4 inches further back.If you can make it fit ,it will be great improvement on the original gear.

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Posted

I do believe that the springs bottomed out. I don't know if it is weaker than the stock bungee gear but I would choose the wide bungee gear over the Bush type spring gear knowing what I know.  The mod I am referencing uses a spring from a snowmobile and an extended slot. Connecting  the cabane to the seat truss may help but don't know for sure.  One thought would be to use the gear legs and build Cub style struts to replace the the spring struts.  Those use the hoop style bungees.  The gear I built uses the Roberts Rage gear uses one hoop bungee and one air shock on each strut.  The downside is the cost is high.  I picked mine up at half price but they were still pricey.  The Cub style should be reasonable to build but I don't know what the cost of the bungee hoops would be.

i know there are some out there that are using this gear and are happy with them but the design is not suitable to my style of flying.  There have been many fuselages damaged with this gear so I know I am not the only one that has had problems and I will not be the last.  There are several ldeas for improvement on this site.

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Posted

NLappos just installed a set on his Avid MK4 but it needed a slight modification on the cabane which Lowell is familiar with.

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Posted

Ya, I talked with Lowell today.  Maybe I'll get a new cabane from him that fits the Avid rather than modify the one that fits the Kitfox.  Looks like the Avid width is 1/2" more than the Kitfox.   JImChuk

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Posted (edited)

I installed Lowell's Highwing gear and have flown it now for about 3 hours. It is a charm, stable and very low ground loop tendency, a marked improvement on the Avid original gear. During normal landings the spring compresses less than 1/2". The landings feel smooth and not harsh.  Lowell had to widen the cabane by 7/8" because the Avid is that much wider than the KF. It fits perfectly.

I attach a quick analysis of the gear (I am an aerospace engineer). note the sketch is not to scale, but the angles and dimensions are accurate. It says:

1) the gear is good to 4 g's and 12 ft/sec

2) the spring is not too stiff

3) If you make the spring weaker (less spring rate lb/in) then the gear gets weaker and damages the airplane at a lower landing sink rate.

IMG_0640.JPG

gear analy.jpg

Edited by nlappos
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Posted

Thanks for the info Nick.  Just one question though.  If I'm reading this right, in the upper left corner of your drawing, you show weight at 600 #   My plane weighs right at 600 lbs.  Of course when I add fuel and my fat butt, it goes up from there.  Add someone else, and we will get up to a maximum of 1150 gross weight.  But then I got thinking, well there are two landing gear, if each one does 1/2 the weight, that's close to the 600lb you mention.  I'm confused.  Just for comparison, it would be interesting to see the numbers on a bungee gear.  I'm imagining that would have to involve real drop tests though, cause how else could one accurately  figure the stretch and movement  in the bungees.  Thanks for getting my brain working (or at least moving) this morning.  :-)  I wonder how close some of my landings come to that 3.8 Gs you show???   I never set the ELT off anyway.  :lmao:Well not lately anyway..... JImChuk

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Posted

Yes, the 600 is half of 1200, because there are two gear! My MGW is 1150 but I rounded up.

I agree, you have to work the bungee spring rate which is hard, because it is all scrunched up in there and probably not linear at all. The rest of the Avid geometry is easy to analyze. I bet the bungee gear is dandy at this too, it is just a bit too narrow and therefore not as stable on the ground.

4 g's is a pretty hard whack, and involves 12 feet per second landing sink rate, which is 50% higher than Cessnas have to meet. I have hit the ground at 4 g's in experimental helicopters, it is not easily forgotten! 

 

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Posted

I have installed a G-meter in my Catalina...and a usual soft / good landing on a hard runway shows 1.3-1.5 G (remember there is NO shock absorption on the Cat besides the tires).

A hard/bad landing will show about 1.9- 2.1 G's

Hope that helps a bit..

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