Kitfox Mk2 wing rebuild

18 posts in this topic

Posted

Hi everyone,

I will soon be rebuilding the wings from my Mk2 Kitfox and wondered if there are any fixes or mods I could incorporate to make it fly better ?
I have read about optima wing kits and sticking a plastic former on the front spar and speed wing conversion but I don't know exactly what this involves.
My aircraft is currently registered as a 3 axis microlight so I have to keep within the rules for stall speed etc.

Also, I have noticed that in my 4 wings, I have 2 types of spar, one is an aluminium extrusion tube with a central section (like 2 back to back capital D's), this runs all the way along the wing.

The other type is an aluminium tube with an insert inside it to mimic the one piece extruded one, the insert starts just before the lift strut attachment point and runs to the end of the wing.

Any ideas which one is better ?


Any ideas or input would be really helpful.
Cheers,
Skelly.

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Posted

Sounds like a standard Model 2 wing spar. About all of them had the spar insert. Only mod I would make is to reinforce the rib tails per the manual.

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Posted

For a while Kitfox went with the aluminum extrusion for the wing spars.  Late Kitfox 1s and Kitfox 2s had it.  When the Kitfox 1 used that type of spar, the gross weight was raised from 850 to 950 lbs.   On a tube spar, it much depends on what the stiffener is like.  The later Kitfox models used a .058" spar, and had the gross weight at something like 1400 lbs.  The .065 spars are used up to 1550 gross weight.  Like I said, it all depends on the stiffener.  My understanding is the stiffener was always centered on the lift strut attachment point.  I wouldn't doubt that the extruded spar makes for a stiffer wing.  I think either one will work though if you stay with the 950 goss weight.  Rib tail reinforcement is a good idea like Allen said.  Actually I think it may be required in your country.  The plastic leading edge that Kitfox 4 and later use is actually part of the rib design. It may not do much for the undercambered wing like the Kitfox 2 has.  JImChuk

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Posted

I´m also rebuilding my wings for my KF 2, i have bought new spars and inserts from Kitfox and i hope tu use most of the materials from the old wings. I´m rebuilding because of damage to the spars.

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Posted

Interesting stuff,

I looked down my spars on my orange wings th/at have the separate insert and was quite shocked to see that the stiffener web is not vertical where you would expect  it to offer max strength.

I don't know who built it that way but I'm glad I never flew in it.

The spars on my blue wings are the one piece extruded type but both front spars are damaged, the 2nd spars seem good though, 

I measured the twist on these wings at 1.5 inches.

I have 6 brand new full length one piece spars so I should be able to use some of those to fix up my blue wings.

I'll try and post some photos.

@Peter_se how much wing twist are you using ?

Cheers,

Skelly.

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Posted (edited)

Hi Skelly,

 

I'm looking at doing exactly the same mods on my mk2 also, I'm not far from you on the Norfolk/Lincolnshire border. If we get our heads together we may be able to share the hassle of the 'mod' process with the LAA, not to mention the costs!!

PM me your details, I'm having trouble with the site not allowing me to send you a message or contact me at stevelyden1974@gmail.com

 

Kind regards, Steve

Edited by Firesteve
spellig!!
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Posted

Sorry but I missed your post, I will go by the twist in my original build manual that is 1” 3/4 

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Posted

All good,

@Firesteve Are you keeping yours as a microlight ?

I will be doing my wings exactly as the book says as I'm hoping to keep it in the microlight category.

I may be after some long wing ribs if you know of any going spare.

Cheers,

Skelly.

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Posted

Hi Skelly,

I'm looking into the possibility of installing a 912 and still keeping it within the microlight category. I think it can be done with careful positioning of certain components and removal of any unnecessary items. I'm looking into the removal of the under-camber on the wings as with the 'optima' mod but keeping the wing length the same, hopefully keep the stall under the required limit. Eurofox seem to manage it and after all there is not a great deal of difference in the airframe. I'm investigating wider undercarriage also along with a few other mods including increasing the vertical stab and rudder. New cowlings made to fit the Jabiru but these will now have to be modified if the 912 goes in!

DSC_0245.JPG

DSC_0269.JPG

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Posted

Hi Steve,

Cool project,

Looks like you are slightly more ahead with it than I am with mine.

A couple of things to consider:

(Bear in mind here that most of my knowledge refers to the kitfox mk2)

Are you sure that fitting a 912 is a good idea ?

Will the airframe handle the weight ?

Will you have to stick a church roofs worth of lead in the tail to get the C of G right ?

Will this combined weight put it out of the microlight category ?

Dont forget that any extra weight added will lessen the payload.

You could end up with a SSDR before you know it.

Have you considered a Jabiru 1600 ?

Are the wing mods a good idea ?

I believe your aircraft has a VNE of 1000 mph, this will not change no matter what you do to the wings.

I'll message you my number,

Cheers,

Skelly.

 

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Posted

There is one other in the UK with a 912 fitted, it is registered as a group A but I think it is down to the 'Optima' wing mod it has on it.

I have always liked the 912 and have a friend with lots and lots of spares so it seems the obvious option to me. My '2' had a Jabiru 2200 fitted along with a 6lb lead weight in the tail! It seems to have been a bit of a 'stick it on' and fly it installation, nothing wrong with that but I think with a little time and careful calculation as to where to fix items to the airframe I should be able to make it work.

BSGG weighed 525lb with the Jab fitted, with two people at 86kg it only left enough room for 28ltrs of fuel to remain under MAUW, if I can achieve that with a 912 I would be more than happy!!

100mph is more than enough for me, it would be nice to be able to have a set of non-under camber wings to put on if a bit of touring was on the cards. To be honest I would register it as SSDR if I thought I could get away with it but its just too heavy!!

G-FOXZ is the UK based Mk2 with a 912 fitted.

0607693.jpg

23463507013_87b176dc0f_b.jpg

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Posted

I am intrigued as to what the optima wing mod is ?

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Posted

Golf Golf looks cool in black.

Just to add to the mix,

I have a KFM112M engine in mine, 54kg dry and 65 hp.

Should be ok without any lead in the tail.. hopefully...

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Posted (edited)

Hi Dusty, the 'Optima mod' as it is so called here in the UK (who knows why) but basically involved removing the under camber but inserting foam packers or the addition of plywood spar extensions to flatten the underside. Remove one bay from the end of each wing to shorten the wingspan.

Only done here if you want a group A aircraft as it takes the stall speed threshold above the required standard here in the UK to registered as a microlight.

Edited by Firesteve
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Posted (edited)

I figure if the weight and balance requires weight to be added to the tail I will extend the vertical stab along with the horizontal and increase the cord. I figure larger surfaces have to be preferable to dead weight doing nothing! The cowlings on BSGG with the Jab had to be extended by four inches, you can see it on the photograph above. When I removed the cowlings to see how the mod had been done I was taken back by the weight, 6.3kg (13.88lb)!!!! a mass of bodged on glass fiber was used to achieve the extension of the nose. The carbon fiber alternatives I made come in at 2.6kg (5.73lb) all saved weight at the pointy end!

 

Edited by Firesteve
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Posted

So FOXZ is a kitfox mk2 with a 912 and still a microlight ?

Interesting...

Skelly.

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Posted

Not a microlight anymore, group A but I think that is down to the wing modifications not the weight. Interestingly even as a group A it still has the weight limitations the same as ours, that is 950lb MAUW. I need to have a chat with the owner and see how he has achieved this.

 

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Posted

Interesting stuff,

Please keep us posted,

Cheers

Skelly.

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