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MODIFYING UNDERCAMBER TO KITFOX 4 RIBS

4 posts in this topic

Posted (edited)

If you looked at my post about KITFOX RIBS, then you have seen the drawings comparing the Eppler undercambered ribs to the Harry Riblett Kitfox 4 ribs.

If you use the Harry Riblett modification as shown in VGs ON BOTTOM, then you would have a problem getting the bolt into both your rear strut fittings and the rear jury strut fittings, causing you to:

1. change the rear strut fitting to make it taller, which would:

A. Change the incidence of the wing, or

B. Shorten your rear strut,

C. This would change position of flaperons, controls length, etc.

Neither of these are areas I want to start changing!

2. make your rear jury strut fittings longer - a simple thing to do.

By modifying the undercamber profile to match the Kitfox 4 ribs, as shown in the attached photos, you will do 2 simple things:

1. cut off and move your trailing edge about 1 to 1 1/2 inches forward, and

2. make your rear jury strut fittings longer.

IMO, this is the easier change to make.

Hopefully, this mod will erase the 90mph wall that the undercamber hits, and it will eliminate the nose-down force produced by the undercambered ribs, while not hampering stol performance.

I estimate that the new 1/8 x 1 x 38 inch capstrips from Spruce cost me about $52, less what VGs would cost, and I can always add VGs later if I want to.

This is just a crude workup - I used gorilla glue on the wood dowels on this, but you could use aluminum tubing for the spacers, and I intend to use 9460 epoxy to attach all of this.

Someone may have a better way, or a suggestion to make this better, and you can feel free to post your ideas here.

I am going to try to attach 3 photos - the first two are a mod for the hanger ribs. I did not want to cut these because of the black area which shows the cutout on my ribs - I just trimmed the lower cap off and added an aluminum angle to each side to glue fabric to, and the last is a non-hanger rib, and I cut the end off and will move the trailing edge forward as shown.

I plan on using clear-tape or Saranwrap on the ribs to fill up the spaces with a can of foam, unless someone has a better idea - I can make a mess with a can of foam!

Thanks for reading - hope this helps someone.

EDMOpost-399-0-93199600-1376945730_thumb.jpgpost-399-0-08206200-1376945776_thumb.jpgpost-399-0-87618500-1376945809_thumb.jpg

Edited by Ed In Missouri

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Posted

Are both of these the same post Ed? I can delete the one without the pics if it is.

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Posted

Are both of these the same post Ed? I can delete the one without the pics if it is.

Yes Joey - I didn't realize one didn't have photos - Please delete it for me.

Thanks,

EDMO

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Posted

After due consideration of what a mess I would make with a can of instant foam, I decided to abandon the idea that Harry Riblett had suggested to change the rib profile. I spent about 2 hours making the 1/4 inch thick plywood rib web strips that are needed to support the new ribcaps for the Kitfox 4 profile on the bottom of the wing. These are now glued to the caps on the underside of one of my wings. I will add the caps to these after cutting the new profile aft of the rear spar to relocate the trailing edge.

Thanks Leni - the KISS principle at work!

EDMO

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