Wing rib modifications

[EDMO 1078]

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 to clear-tape or use Saranwrap on the spaces and fill with a can of foam, like Riblett suggested, unless someone has a better idea. I can make a mess with a can of foam!

Thanks for reading - hope this helps someone.

EDMO

Edited 20 Aug 2013 by Ed In Missouri

[akflyer 1427]

Ed,

 

I would make a plywood web to fill the void, or even look at using 6MM depron to do it.  This is not a structural component, it just needs to help it hold shape,  My only concern would be the foam melting when I hit it with the poly tac or poly brush.  You shouldn't have an issue using the stewarts system.

 

[EDMO 1078]

Ed,

 

I would make a plywood web to fill the void, or even look at using 6MM depron to do it.  This is not a structural component, it just needs to help it hold shape,  My only concern would be the foam melting when I hit it with the poly tac or poly brush.  You shouldn't have an issue using the stewarts system.

 

Leni,

I think the foam, and exposed wood on the ribcaps should be covered with urethane or spar varnish to seal it. Had not thought about the POLY products melting it.

The thought of cutting out about 30 identical plywood parts does not thrill me - If I could find a laser-cutter to do it, that would be a lot better.

Thanks,

EDMO

I found a local laser-cutter - now just got to get a price. They also do metals, so probably going to get my flap hangers done there too. I have the 1/4 inch plywood to make the rib mods.

EDMO

Edited 20 Aug 2013 by Ed In Missouri

[EDMO 1078]

Leni,

I think the foam, and exposed wood on the ribcaps should be covered with urethane or spar varnish to seal it. Had not thought about the POLY products melting it.

The thought of cutting out about 30 identical plywood parts does not thrill me - If I could find a laser-cutter to do it, that would be a lot better.

Thanks,

EDMO

I found a local laser-cutter - now just got to get a price. They also do metals, so probably going to get my flap hangers done there too. I have the 1/4 inch plywood to make the rib mods.

EDMO

Well, no luck on laser-cutter: They can only do thin balsa - Got to start cutting on bandsaw.

EDMO

[Av8r_Sed 82]

I've been led to believe that a water jet can cut the type of plywood for our ribs.  Do you have anyone in your area with a CNC waterjet?

[EDMO 1078]

There is a machine shop in St. Louis that I have used that has a water jet. I will probably have my flap and aileron hangers cut there - I don't think I want my plywood submerged in water, especially since they have chemicals in the water there. And, they want too much money for the initial computer setup for a small job.

I will bite the bullet and spend a day on the bandsaw.

EDMO

Edited 24 Aug 2013 by Ed In Missouri

[Av8r3400 1179]

You're better off to make a jig and use a router.  That is how Avid and Kitfox used to make them.

 

Using a water jet does not mean the workpiece is submerged in water.  There is a water tank below the workpiece to "catch" the jet after it cuts.

[EDMO 1078]

You're better off to make a jig and use a router.  That is how Avid and Kitfox used to make them.

 

Using a water jet does not mean the workpiece is submerged in water.  There is a water tank below the workpiece to "catch" the jet after it cuts.

I did that for the ribs initially - Lots of waste for a thin part tho.

I watched the water jet cut out some metal parts - the water was milky, and believe it had soluble oil in it. They want too much to make initial setup anyway. I can get close enough with bandsaw and belt sander to make them a close match to my pattern - It aint rocket science!

EDMO

[EDMO 1078]

Here are two photos showing the modified undercambered ribs to the profile of Riblett ribs with leading edge extensions finished.

EDMO

[TJay 1041]

where did you get the kitfox 4 wing template I would like to play around with that mod too. also I see the kitfox 4 has a truss design in the rib web, where yours and mine don't do you think that was changed for a reason. and why the leading edge extension? what do you think it will add to performance. Thanks

[EDMO 1078]

TJay,

I posted a drawing on this section of a Kitfox 5/4 rib overlaid with a Kitfox 2 rib, with my extensions, and the modification lines I made.

There is a yard-stick in the photo, so you can print it, take it to a copy shop and have it enlarged to actual size.

My leading extension is to balance the Subaru engine and nose gear and heater to the short fuselage, and the longer flaps and ailerons I am making.

I don't know about the part you mentioned - but just look at some of the spaghetti-thin webs in other planes that are flying and compare.

EDMO

[TJay 1041]

great thanks and have a nice thanks giving

[marksires 484]

Ed,

A couple of things - don't use the 'can' foam for anything you want to hold it's shape.  that stuff doesn't fully set for a very long time and continues to slowly expand.  It is a urethane based foam, so the chemicals probably won't hurt it after it sets, but I'd test a sample to be sure.  You can get pour foam that will set quickly and not continue expanding, but it is not cheap like the can stuff.

 

Also, don't ever hotwire any urethane based foam - it gives off cyanide gas when you do, and you've had enough chemicals inhaled already!

 

The thick PVC foam at home depot, up to 2" thick, is easy to shape with a hot wire.  We use what are basically the big blocks of that stuff used for dock floats as the core of the wings on the composite airplane I have plans for.  We make a template using pressboard, stick one to each end of the block with nails, then run the hotwire over the template.  Slow going if the block is big, but it is the fastest, easiest, most accurate way to shape PVC foam (but not Urethane!)  And no foam mess from sanding, routing or cutting.

Mark

[EDMO 1078]

Mark,

Thanks for posting the info - We covered most of it in AMT school - I believe that the canned foam is advertised "Not for aircraft use", and think it can cause corrosion. There is no foam in my plans - the ailerons and flaps are planned with a combination of aluminum and wood ribs and covered with .025 sheet and rivets where not glued.

EDMO

[marksires 484]

Ed,

Ok, I just read all the way through your post from August, and you mentioned filling some spaces with can foam.  Just wanted to make sure you had moved on from there!

Mark

[EDMO 1078]

Mark,

Thanks for looking out for my mistakes in writing / thinking - I knew that was wrong about the canned foam, and I know that some others have used it - donno if they will pay a price for that in the future?

Happy Turkey Day,

EdMO

[EDMO 1078]

TJay,

     I did have to make taller rear jury strut attachment fittings - the strut fittings should be OK. 

EDMO

[Tree top pilot 13]

I am really liking that set of spars. There's a lot of nice things with that design. I bet the die for that was slightly high priced.... Nice looking wings ! Still wanting to form a set of ribs out of aluminum.....I know they can be made lighter. Lots of ideas and not enough time... I should have started earlier in life with all the airplane stuff....

 

I had spoken with another engineer in my area about making the ribs from 6061 T-0 and then having them heat treated. After we looked at some CAD models and there would be a need for compression struts...but allowed the use of cables for sail/anti sail bracing and tube trailing edge. Could CNC the rib die and form ribs with rubber block in press ready to phosphate and rivet in place.... We estimated that would come out to a completed wing near 25 lds ready for fabric. The flaperon hinges would also be T-6....flaperons made up of aly ribs and .018" 2024 sheeting. Round tube wingtip of T-6. Basic profile and lighter weight....unless parts were all carbon composite.....

 

Ed... that water that looked milky was the abrasive that is suspended in the water to aid in the cutting action. I know a guy out west that has one in his shop...said he needed that machine 20 years ago for the time it saves his shop. No slag to clean up or hardened edge to grind beyond....and doesn't warp the metals from heat of CNC torch - laser - plasma cutting. Says it takes just enough pressure to keep the parts from wiggling around to hold them in place when cutting.

Edited 18 Dec 2014 by Tree top pilot

[EDMO 1078]

I would use the T6 and not worry about the heat treatment. SkyPirate on here showed me the very nice set of aluminum ribs that he made at home without any machinery - Looked real nice when all assembled for his ultralight he was building. I have enough problems to deal with without making another set of ribs!

EdMO