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Material for making ribs ?

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Posted

Hey guys I have a new friend {Dan Tanner} that has found me and is seeking help with a basket case he bought. He picked up a Kitfoxlite2 that has been abused a lot and needs to build new wings. After talking a bit and looking at pix our wings are very similar. He wants to make a new ribs and wanted to know where to get the wood. Dan said the people at Kit fox had the ribs in stock at a premium.  After looking at my wings we couldn't figure out what kind of plywood was used to make my ribs. Marine ply?  They show 5 very distinct plys under the epoxy sealer. He said Mr. Kit fox told him that was not aircraft plywood as it needed to have 10 or 12 plys for 1/4" or it would not be strong enough. We looked at ACSpruce has the material - over $200 of wood just to get enough material. Is it worth it?  Dan has in-laws with CNC router tools to make the parts. We are wondering what else is out there...I told him to try Airdale but that didn't work. I told him to sign up here as there is a great bunch of guys and lots to learn.

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Posted (edited)

The material you want is either 1/4 inch or 6mm (Finland Birch) plywood as sold by Spruce - Mine was in 5 foot squares, but haven't checked the book for smaller pieces.   It has a lot of plies, and is a lot stronger and harder than the other plywoods with less plies.

Kitfox wanted $78 EACH for ribs the last time I checked.  It is a lot cheaper to make your own.

The ribcaps are also sold by Spruce - to get the best price, you measure what lengths you want them to cut it, and total up the combined lengths, and you buy the total length.

I didn't have CNC - just a hole saw and a jig saw and sand belt, and built my own fixtures to hold them while the glue set up - You want the capstrips to set at a true 90 degrees to the rib.

I used the 1mm to cover my extended leading edges.

Hope this helps.

EdMO

Just got to thinking, the Kitfox Lite may have used 5mm or 3/16 in same plywood? 

But, I didn't know they made a Lite2.

EDMO

Edited by Ed In Missouri

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Posted (edited)

Another name for the ply is 'Baltic Birch'. It's very similar to aircraft ply but a lot cheaper to buy.

 

I've used it on various car restorations and it's very nice stuff to work with. You'd need to find a specialty wood dealer..,not the kind of thing HD sells.

Edited by ABF

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Posted

Might try looking at a fine cabinet shop if you have one locally they often carry wood like this. would probably save quite a bit on shipping too if you could find it locally.

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Posted

One of the guys on this site duplicated the Kitfox ribs out of aluminum for an ultralight he was building.

SkyPirate, have you got any photos of your fixture and the ribs you made?

EDMO

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Posted (edited)

According to John Larsen, "Avid originally used a 9 ply about 6mm plywood made in Finland at great expense. Kenny Schreader, when he ran Sky Raider, went to US cabinet grade maple veneer 7 ply which was 5/16 as I recall. I have not heard of any Sky Raiders falling out of the sky due to faulty plywood. The shrunken fabric holds the wing together, so use a plywood you feel comfortable with."

IIRC, KF 1-3 used aviation grade Mahogany 9-ply w/ 90*degree ply layup for rib webs, and either aviation grade Spruce or Birch 5-ply for cap strip material. If you opt out of the oem or ACS aviation grade rib or cap strip material, seek out Grade 1 or AA Marine birch ply as it will have 90*degree ply orientation, higher quality sanded face veneer, no core voids plus a fully waterproof structural adhesive. Birch is also stronger than mahogany or spruce, I used a 1/8" Marine grade birch 5-ply for my floorboards sourced from a local specialty lumber yard, it would probably work fine as cap strip material too.

Just a thought, what if you used a waterproof glue and carefully laminated together two layers of locally sourced 1/8" Marine grade birch 5-ply ie., less expensive than the ACS rib material but more than adequate strength wise? Don't recall what it cost but it wasn't terribly expensive and no shipping cost.

Edited by dholly

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Posted (edited)

We were taught at Aviation school that aircraft plywood is 45 degree ply and not 90 like standard plywood. :huh:

My Kitfox 1 and 2 ribs held up just fine until they hit something - whatever they were made of.

EdMO

Edited by Ed In Missouri

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Posted (edited)

Ed,

As I understand it, "aircraft grade" ply as defined by MIL-P-6070B spec requires cross banding plies at 90* to grain and edge. However, I believe plywood grading overall is primarily dependent on bonding adhesive and procedure. That is considered most critical because wood does not have a fatigue life limit and if properly preserved and stored, will last indefinitely. Adhesive, however, can deteriorate with time and must be suitable for the application i.e. non-elastic, not corrosive to the wood fibres, not subject to fungal attack etc. Also, strict adherence to manufacturer recommended shelf life, mixing instructions, spreading requirements, pot life, clamping requirements, temperature and humidity limitations, gap filling properties etc, etc. come into play. All of this is important because in forming the joints the adhesive does not bind one wood surface to the other, rather, each surface is individually bound to the glue. In wooden structures the strength of the glue line must be greater than that of the wood, whereas in adhesive bonded metal structures the glue line will most likely be weaker than the metal. Bonding adhesives for plywood are generally classified as:

‘A Bond’ (WBP) - a water and heat proof glue line produced from phenolic resins that will not deteriorate under extreme conditions (WBP - Water Boil Proof adhesive, must withstand 3 hours of boiling in water). It is readily recognisable by its black color. Type A bond is always specified for exterior, aircraft, marine and structural plywood.

‘B Bond’ - produced from melamine fortified urea formaldehyde resin and suitable for limited exposure.

‘C&D Bond’ – is produced from urea formaldehyde resin and suitable for interior use only.

Most common A Bond adhesive used in aircraft and marine grade plywood construction is Hot Press Thermoset Phenol Formaldehyde Resin (Tego-film), although Resorcinol Formaldehyde Novolac Synthetic Resin Glue, Urea Formaldehyde Synthetic Resin Glue, Type 2 Hot Press Urea Resin Glue or Araldite AW 134 Epoxy Resin based adhesives are also used to lessor degree.

Note: "Baltic Birch" multi-ply all birch w/ solid inner plies is often described by sellers or considered synonymous with aircraft grade plywood, but is not true aircraft grade when constructed with cold curing acid catalysed phenolics, urea-formaldehyde resin, melamine fortified urea-formaldehyde resin or casein milk and animal protein derivised adhesives. Beware import plywood quality if not stamped certified, seek plywood from US mills manufacturing with domestic cores and domestically cut veneers if possible.

Without getting more wonky, in general I think it would be safe to say:

Aircraft grade ply is cross grain hot glued under pressure with waterproof structural glue and cannot have voids in the inner layers. Can be WBP or better. Minimum 5-ply for 1/8", 7-9 ply better. Aircraft grade uses all top quality plies of the same species. Also aircraft plies are “balancedâ€, that is with an odd number of plies with the same amount of fibers in the crossed direction to minimize warping. WBP ply is best for structural uses like rib web.

Marine grade ply is cross hot glued under pressure with waterproof structural glue and can have minor voids in the inner layers, but all voids must be filled, making it much stronger than lesser grades of plywood. Marine grade can be WBP or better, also min. 5-ply for 1/8". Marine grade is often denser (therefore, heavier) than aviation grade.

Cabinet grade ply does not require structural waterproof glue, will have voids in the inner layers where you cannot see them, making the plywood weaker. Often with cabinet grade plywood the back side will have voids that have been filled. Can be as few as 3-ply, however, the lesser grades of ply with voids and lower quality internal veneers are not consistent in strength and weight and are not suitable for structural applications in aircraft.

Tip: For a less expensive but still very strong alternative to aircraft grade birch with little weight penalty, look for a marine grade Okoume ply. Okoume ply made in France by Joubert is the highest quality marine plywood available today and is certified by Lloyd's of London to be manufactured to the BS (British Standard) 1088. My local specialty lumber shop carries full 4'x8'x6mm (1/4") sheets of Grade AA Joubert marine grade Okoume ply for $81.55.

Edited by dholly
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Posted (edited)

Thanks for the info Doug,

      I know things have changed since I was taught by Korean War Vets - I think they had just approved FPL-16 at the time, and printed in the books as an alternate to the old glues.  Maybe a young someone can find out how long my Finnish Birch and Kitfox ribs lasted someday after I am long-gone.

EDMO

Edited by Ed In Missouri

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Posted

Lol, the Luan skin ply off a 10 y.o. hollow core closet door from Bargain Outlet would probably outlast me. McBean understandably has to cover his ass on part and material sales so no surprise there.

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Posted (edited)

We have certainly been taught that "MIL-SPEC is the 'APPROVED' material" - but being "experimental", we can use anything from cardboard to I-beams - to each his own.   Kit Manufacturers may have a little more responsibility for their product, but the final liability is with the builder.

EDMO

Edited by Ed In Missouri

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Posted

Thanks for all the info on plywood ! 

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Posted

I thought I had posted this once, but it disappeared somehow:

I stated that Govment Specs and methods may be 40 or 50 years behind the technology.  

I think that a carbon fiber laminate would be far superior to any plywood ribs.

EDMO 

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Posted

OK I decided to start all over from square one with the wings. Making enough stuff for 4 wings is easier than just 2 helping another. So we got up an order for AS and went router bit shopping. A Local Klingspor wood shop had a nice selection of bits- we picked up the solid carbide downward chip ejection with roller bearings. Ply wood came in- 5 ply for capstrips and 10 ply for ribs. Dust flew....and piled up outside.....reminded me of snow. Now we are set. I have a full set of new ribs and falsies for the aileron and flaps. All new steel parts are also in the works....everything new. Now that I have been getting a little better health wise....I now have to find another place of employment. Guess I was "downsized" or just plain phased out. Never the less I will tinker with this as I can and share results. I made all the master templates and metal fixtures for the parts being made. At this rate I may want to start building airplanes....It's not like I don't have the equipment to. That's just fine . Something else to cloud my thoughts.

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post-341-0-66076900-1411334283_thumb.jpg

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Posted

Looks good.  Maybe you want to make up some ribs for Avids, especially the ones with the long tails for flaperon attachment.  Might find a bit of a market for them...??? Maybe even just the part of the rib that's behind the rear spar with cap strip running about 1' forward of that top and bottom.   Seems that it's not at all unusual to break the rib tails off in a crash that doesn't damage the rest of the wing very much.   Jim Chuk

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Posted

I would love to see the control system you have for that.  It looks like your not going to use flaperons?  I would seriously dig a set of ribs that use the USA35B airfoil and separate flaps and ailerons.  I can put the cap strips on myself, but having the ribs CNC cut would be worth some money to me.

 

:BC:

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Posted (edited)

I wondered about the shape of the ribs myself, glanced at the earlier posts, and thought they were for a Kitfox single seat (UL like).  Now I reread a bit closer and he says they are for a Kitfox lite 2.  Wasn't that a two seater that was supposed to be an ultralight trainer?  If my memory is right, it was like a 1050 gross weight Kitfox 4.   I thought those used the flaperons just like the other Kitfoxes, I wasn't sure about that for the single seater.  Looks like a lot more wing behind the rear spar than the regular Kitfox wings.  Wonder how that effects the CG??  I guess now I have more questions...  Any answers???  :-)  Jim Chuk

 

They do look nice though!

Edited by Jim Chuk

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Posted

Kitfox Lite Squared was intended to go hand in hand with the Kitfox Lite (103 legal ultralight) as the trainer.  

 

The Lite Squared was a Model IV-1200 sold with lightweight fabric and stripped down panel and fixtures.  I believe it was sold with a Rotax 503 as the recommended motor.

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Posted

Great workmanship Tree top pilot!

Jim - As far as I know, KF Lite and Lite Squared both used flaperons. I think those are Ridge Runner ribs which begs the question... does Dan plan on using RR wings with flaps on his KF Lite Squared?

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Posted

I made my own patterns for ribs and tails for the Avid Stohl profile, and used a router with a bearing what they call a laminate trimmer to cut them out , no need to use a fancy CNC program. Anymore all plywood interior or exterior plywood will pass the water and heat tests, they are using better glues today. Aircraft plywood was mainly special due to the lack of defects, as a trial run I cut up a sheet of underlayment and as thin as the wood that is left is if there was  void I would have found it, No voids, Gorilla glue will tear the wood apart before the joint so it is useable newer materials are out doing the strength and quality of the old.

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Posted

I watched Kitfoxes CNC machine at work at the factory yesterday it's a pretty impressive set up.

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Posted

If I were turning them out as fast as Kitfox I would be using CNC too, But with a laminate trimming bit I was able toturn out 4 wings worth of ribs in a day by myself. That included making the patterns. I have heard that CNC programming hass gotten easier since I last did any about 30 years ago, but in the old days this rib pattern was quicker to make by hand than it would have been to write the program. There are times when I think about making my own CNC lathe or possibly a small mill just to be able to make some small parts.

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