Would you use expanded foam sheets for wing ribs?

[turboplanner]

You guys might be interested in the book "Civilization One" by Christopher Knight and Alan Butler (http://www.amazon.com, about $10.00)

 

It covers how Alexander Thom discovered the megalithic yard, and how that was transferred with amazing accuracy from the south of England to Scara Brae in Scotland using a pendulum.

 

It has a fantastic photo of Newgrange in Ireland which looks like it was built a couple of years ago, but was accurately measuring the solar system 1000 years before the Egyptian pyramids were alleged to be built (that's another story in another book.)

 

It shows how both the Imperial and Metrics systems were derived from the same source!

 

I'm not sure whether they'd accept an Australian section while it has poofteenth in it though.

 

 

[Old Koreelah]

Damn! the inexorable march of standardisation! Looks like even "tad", a "touch", "smidge" and "poofteenth" will have to be defined, measured, converted to fractions of the wavelength of krypton and accepted by the ISO!

 

(Meanwhile, thanks for the idea, turboplanner, I'll have to get a copy of "Civilization One".

 

Lyle

 

 

[Guest Mark Mac]

Very interesting topic. I have mobs of klegecell (PVC foam with 75kg/m3 density) left over from another project and used some of it in a sandwich with 1.5mm hoop pine ply. Mobs of stiffness, and pretty light. but I have no idea of the numbers.

How about making two ribs, one per the original drawings, and one per the new method, then do crush/twist/bend tests in as many geometries as you think might answer your question. Use scales and weights to provide some objective measurements, then 'voila' you have an answer to then take to your wing prototype, and then do it again.

 

 

[Aero28]

Hello All, I would like to add my bit to this discusion , The pic has 30mm wide foam ribs with .6 ally cap strips top and bottom. Sikaflex bonds the cap strips to the foam and pop rivits on the front and rear spars. The plane in my avatar has foam ribs.

 

 

 

[old man emu]

It is interesting that Aero28's ribs are 30mm thick when made from blue styrofoam. I assume that these have been cut from a thick sheet of foam, probably 100mm thick. There is no side covering attachd to the ribs. The foam I am looking at has expanded PVC foam between stiff plastic sheeting. I think that the plastic sheet would give the sheet a good deal of rigidity.

 

I also notice that Aero28's ribs don't have lightening cut-outs. That would add to the resistance of teh rib to vertical forces. I must compare the weight of ribs cut from foam and plywood to see if there is any weight saving, which ultimately was one of the reasons I was looking to using the sheet.

 

OME

 

 

[Aero28]

The foam comes in sheet form and is actually building insulation for walls, I think 25 and 30 mm thick. Dow Corning product. Each one of those ribs weighs 230 gramms with the cap strips. You don't really need to worry about lateral/sideways strength with ribs as the covering top and bottom takes care of that so would think that sandwich panel would be overkill.

 

Cheers

 

 

[Bozz50]

Just came across this subject. There is a little red rocket out there in Aus somewhere ( single seater, low wing) called a Starlite. Its wings were constructed using a single wooden spar which used 1" extruded polystyrene ribs (blue foam) and a 1/16" or 1/32" skin of ply over the entire wing. The fuselage was made from Pre-Preg fibreglass sandwiched foam which was vacuum bagged and baked in an oven. Very light & very strong. Same fuselage construction as the Lanceair. I believe it was even produced by the same people in The States. It was based in Caloundra near Brissie about 15 years ago. I remember Rowan, the owner, had problems with people squeezing the leading edge of the wing to see what it was made of. Several people cracked the thin plywood skin by doing this.

 

The wings (main spars overlapped from each wing) slotted into the fuselage and had two 1/2" pins which locked them in place like some gliders. One wing was the thickness of the spar, more forward than the other. I have video & plans of it if anyone needs more info. It runs a Rotax 447 and does 100 mph on 2 gallons/hr.

 

Link with pics: http://www.homebuiltairplanes.com/forums/sale-wanted/5580-starlite-aircraft-sale.html

 

So yes . . . extruded polystyrene foam is a valid & proven wing rib building material.

 

 

[damkia]

Most fiberglass aircraft today use composite methods (noting that this is a construction method not material). all it amounts to is as previously covered using two or more different materials layered together to give the benefits of all materials to the composite structure.

 

All Lancairs are composite structures from the spinner to tailfin, with the addition of metal components embedded into fiberglass honeycomb sandwich at appropriate points, so called "hard points". In short there is nothing wrong with using composite materials for the wing ribs, it has been done many times. Even the A380 has a composite wing - bonded aluminium to honeycomb to aluminium. You just need to make sure the edge to edge compressibility will withstand the forces that the wing skin will be exerting on it, and the outer lamination's adhesive is suitably strong to resist separating from the inner core.

 

One well known product that is accepted as a composite is the cement and steel mix that goes into today's major infrastructure projects. The cement is good under compression, and the steel is good under tension. The composite material (reinforced concrete) gets the benefit of both.

 

Boeing used to supply the Australian manufacturer of Lancairs with their composite materials that were almost out of date. If you know anyone in the industry it may not be that difficult to obtain the correct stuff, or you could try a company that supplies to the aviation industry (Jabiru?) for some offcuts. At least then you have the right stuff with known properties.

 

An interesting aside is that balsa wood has been used by some early homebuilt designs as the core in composites.

 

Polystyrene foam is used on the Glassairs and all of the Rutan "X-eze" designs, freeform bent and covered with fiberglass or cut/shaped and covered with glass.

 

 

[Thirsty]

Lots of large model aircraft use solid core foam wings with either ply or balsa sheeting then a coat of light glass fibre. Not sure how that would translate to a full size aircraft but I've seen some very large models using this construction method.

 

 

[corvairkr]

The mighty KR will be celebrating its 40th birthday this year using this technique:super hero:

 

http://www.dubigefen.50megs.com/photo_8.html

 

jason

 

 

[winsor68]

The mighty KR will be celebrating its 40th birthday this year using this technique:super hero:http://www.dubigefen.50megs.com/photo_8.html

 

jason

That build log is brilliant... Great photos.

 

 

[corvairkr]

That build log is brilliant... Great photos.

Yeah Win Dubi is doing a beautiful job its very neat .

 

jason

 

 

[winsor68]

Check out this build log of the first SD-1 in Australia. Foam ribs again...

 

https://picasaweb.google.com/116021783417882855184/ConstructionOfSD1Minisport76?authuser=0&authkey=Gv1sRgCJz-kvLen87x-wE&feat=directlink#

 

 

 

[corvairkr]

How cool is that !

 

jason

 

 

[winsor68]

How cool is that !jason

It is being built locally to where I live too! Going to be nice to see this machine flying.

 

 

[Guest ozzie]

The lazair wing is made up of foam ribs 25mm wide with ali cap strips glued on and 12mm fibreglass tape cross wrapped around the rib. Inside the D cell foam nose ribs are stationed every 18 inches or so. As the wing covering is transparent the ribs are painted with a water based paint. If you are using foam ribs and are covering with conventional methods be very carefull with MEK etc. it will send your foam straight to the ozone layer.