Peter Sripol is at it again...

[Turd Ferguson]

I mean those who think that...a homebuilt should be designed by at least one Boeing engineer, that Lycoming and Continental are the only engines you should use to power an aircraft, that if you dream of building a homebuilt you are far better off buying a used Piper or Cessna, the cruciform shape is the only valid form for aeroplanes, wooden airplanes are dangerous because the glue won’t last 300 years.I have heard these and similar opinions espoused so many times on this forum.

On the contrary, I can't recall ever seeing these and/or similar opinions espoused - not in HBA anyway. If so I'd have to scratch my head and wonder "What part of HBA do they not understand?"
In other aviation forums what you say is true. But here? Perhaps you could provide a cut & paste example?

Homebuilding is the last bastion of innovation in light aviation, the large manufacturers have given up on this sector, the cost of flying has gone through the roof. I believe that all dreams of flight should be encouraged, everything from model airplanes, gyros, powered parachutes, trikes et al.

Agree, which is why I support any kind of flying / plane building / aircraft ownership / activity and have done so for the past 40 yrs, even if I am not motivated to personally participate in that segment.

 

[proppastie]

back to technical .....do we have a number for shear strength for that white foam he used?....while we are at it how about the blue foam seems like many like

 

[karmarepair]

back to technical .....do we have a number for shear strength for that white foam he used?....while we are at it how about the blue foam seems like many like

We are not sure if he used EXPANDED Polystyrene or EXTRUDED Polystyrene foam. The Extruded is much more homogenous, and has structural properties nearly double the Expanded (call it 80% higher). If I were building wings the way he has, I'd use 2 pcf Extruded (the lightest commonly available, in sheets up to 4 inches thick and 8 inch thick billets, available from, among others http:/www.aircraftspruce.com/catalog/cmpages/polystyrene.php and STYROFOAM SMALL CELL | Aircraft Spruce A useful comparison between XPS and EPS here http://xpsa.com/wp-content/uploads/2020/05/Comparison_of_XPS_and_EPS_Foam_Insulation-US.pdf

Some mechanical properties for "Foamular" XPS here http://www.foamular.com/assets/0/144/172/174/bf64ec70-16f1-4748-abc7-c9dee5100987.pdf

EPS ("Beadboard"):

Density (pcf)	Stress @ 10% Compression (psi)	Flexural Strength (psi)	Tensile Strength (psi)	Shear Strength (psi)
1.0	13	29	31	31
1.5	24	43	51	53
2.0	30	58	62	70
2.5	42	75	74	92
3.0	64	88	88	118
3.3	67	105	98	140
4.0	80	125	108	175

 

[tr7v8]

But surely all the foam is doing is giving an overall rib outline, beam strength comes from the aluminium tube spars. I've built model aircraft wings this way. Home cut polystyrene foam, wooden leading & sub training edge & covered in film. The thing you've linked to is predominately sales puff about thermal efficiency & homogenous characteristics both irrelevant in this context.

 

[pictsidhe]

But surely all the foam is doing is giving an overall rib outline, beam strength comes from the aluminium tube spars. I've built model aircraft wings this way. Home cut polystyrene foam, wooden leading & sub training edge & covered in film. The thing you've linked to is predominately sales puff about thermal efficiency & homogenous characteristics both irrelevant in this context.

The air loads still need to get to the spar(s)

 

[cluttonfred]

Like I said before, I think there is real potential to use this sort of full-span foam rib in combination with plywood skins to create a short cut to the lightweight strength of a geodetic structure without all the little sticks. Foam over the spars and a CNC-cut plywood lattice over the foam, the plywood cut away as much or as little as needed for strength. Here's a simple two-spar geodetic wood wing from a Fisher Dakota Hawk:

Ignore the wingtip framing for now, just imagine the main and rear spars running the full height of the rib profile with top and bottom surfaces beveled to match the airfoil. Glue Peter's full-span foam ribs forward of the main spar and between the two spars, then glue the plywood lattice (left solid sheet at the leading edge or anywhere more strength is required) over the foam top and bottom. I could even see leaving slots for spruce capstrips in the foam rib and adding them and the plywood spar web using the rib as a jig. You might still need a couple of compression struts between the two spars but basically the wing structure is done except for fabric covering.

 

[poormansairforce]

I once figured that XPS foam for my Minimax wing would weigh about 30 lb each.(not going to use EPS like Peter) If you hollow it out you might be able to get rid of 30 to 40% of that. My Minimax wings with ailerons weren't that much heavier than his and they were way stronger/more durable. The biggest place he saved weight was with the film covering. Put lattice/plywood on there and it gets worse.

 

[TFF]

He did not want the ailerons. What he did with ailerons would be a whole different mess of beans. I think he understands where and why. His next project might just be more advanced wings. He has never expressed elegant engineering as his driving force. Get R Dun is his. He probably has better lift transfer to his spars compared to every wood wing ever made. He is probably over engineered there.

 

[Michael Silvius]

Like I said before, I think there is real potential to use this sort of full-span foam rib in combination with plywood skins to create a short cut to the lightweight strength .......

Matthew:
Someone sent me this a long time ago.....



A couple other interesting images from a Pik 26 build... that could also be skined with thin ply as in a Tailwind.

 

[Protech Racing]

RE the 2 post above this /

No diagonal/drag strength. Take every other rib and add some angle inside of the spar box to prevent the structure from paralleling.

You can use paper over the solid foam but it dents easy. Works fine tho and paints with latex well.

 

[cluttonfred]

Sorry, but to which post are you responding?

No diagonal/drag strength. Take every other rib and add some angle inside of the spar box to prevent the structure from paralleling.

You can use paper over the solid foam but it dents easy. Works fine tho and paints with latex well.

 

[Pops]

I was building large RC model foam wings with spruce spars and covering with poster board back in 1970.

 

[karmarepair]

The thing you've linked to is predominately sales puff about thermal efficiency & homogenous characteristics both irrelevant in this context.

I was having a hard time finding mechanical properties of EXTRUDED Polystyrene foam on short notice; what I posted was the best I could find. I encourage you to find a better reference, or synthesize the information into a more coherent comparison.

The foam is transmitting the distributed aerodynamic loads into the spar, resisting the drag loads, and the SLIGHT torsion created when yaw input turns the whole wing into an aileron via the yaw-roll coupling induced by the relatively high dihedral angle.

 

[BBerson]

His rigid foam and vinyl wing should have a great deal more torsion rigidity compared with say an Aeronca wing with just fabric.

 

[Speedboat100]

His rigid foam and vinyl wing should have a great deal more torsion rigidity compared with say an Aeronca wing with just fabric.

Did you see the tail feathers fluttering in the video?

 

[stanislavz]

Matthew:
Someone sent me this a long time ago.....

View attachment 103771

A couple other interesting images from a Pik 26 build... that could also be skined with thin ply as in a Tailwind.
View attachment 103772View attachment 103773

Same done on Cri-cri with aluminium skin 0.002 / 0.5mm, need rib each 45 / 90 mm. Ribs were made from 6mm klegecell 100 (density 100kg/m3)

And for comparison of full foam wing, even at 45mm spacing, weight was equivalent to 6/45 * 100 13 kg/m3 foam..

For comparision - extruded come from 35 kg/m3, expanded from 15 kg (packing foam) to same 30 kg per m3

 

[karmarepair]

Did you see the tail feathers fluttering in the video?

I don't recall seeing how they were built. Time stamp from the videos showing that, anyone?

 

[Speedboat100]

It is in the mk 4 rebuilt video.

 

[BBerson]

All tails "shake" from prop blast. It isn't "flutter".

 

[Speedboat100]

Well nevertheless 2 inch oscillation is still called aeroelastic vibration...generally known as flutter.