Peter Sripol is at it again...

[Michael Silvius]

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.

The Tailwind has no diagonal bracing, the plywood sheathing carries the torsional load. Same with the Pik 26 wing in the two photos I posted.
In the case of the sketch none is needed as the solid foam caries the torsional load. Peter used no diagonal bracing on his and it was not even solid foam.

 

[Michael Silvius]

Another one to look at is Marvin Barnard's Flying Squirrel. Foam and FG carry the loads there

http://www.flysquirrel.net/prototype.html

 

[Protech Racing]

I'm doing the same. Sheet the flat bottom between the spars. Set the upper ribs on the sheet. Stiff and drag controlled.
My spars are at 28% and 90% tho.

 

[stanislavz]

Peter used no diagonal bracing on his and it was not even solid foam.

Peter have two spars. And no aileron.

 

[karmarepair]

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

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

There are TWO videos on this plane. The first is about the fuselage and the empennage, and he taxis around with the Vitorazzi running.

He hadn't built the wings yet. The first video shows the steel tube forward fuselage, and the poplar "stick built" warren truss aft fuselage and empennage, which is fabric covered (I'm betting Oratex). Put another way, the controversial Vinyl Wrap over Foam construction is NOT used on the horizontal stabilizer. Initially, the brace wire (singular, per side) for the horizontal stabilizer ran from the rudder post to the AFT spar of the H.S. And in the FIRST flight in the SECOND video, it pretty clearly flutters. About 8 minutes into the SECOND video you can see where he added another brace wire to each side, from the LE of the rudder to the FWD spar of the H.S.

 

[karmarepair]

Another one to look at is Marvin Barnard's Flying Squirrel. Foam and FG carry the loads there

http://www.flysquirrel.net/prototype.html

View attachment 103803

Marvin is using EXTRUDED Polystyrene foam here. Higher mechanical properties than EXPANDED Polystyrene foam for the same density.

 

[BBerson]

Ah, ok, he said it fluttered. The video I saw must have been a shorter video without that segment or I didn't notice.

 

[Michael Silvius]

Marvin is using EXTRUDED Polystyrene foam here. Higher mechanical properties than EXPANDED Polystyrene foam for the same density.

Yea but the point that Protech Racing raised was about the need for diagonal bracing.
I contend that no diagonal bracing is required in Peter's plane, the PIK 26, Tailwind or the Flying Squirrel. Torsional loads are carried bythe solid blocks in case of that sketch I posted, and similarly by cored foam in the case of Peter's plane. And in the case of the PIK, TW and FS by the skin.

 

[karmarepair]

Yea but the point that Protech Racing raised was about the need for diagonal bracing.
I contend that no diagonal bracing is required in Peter's plane, the PIK 26, Tailwind or the Flying Squirrel. Torsional loads are carried bythe solid blocks in case of that sketch I posted, and similarly by cored foam in the case of Peter's plane. And in the case of the PIK, TW and FS by the skin.

You and I are in complete agreement on these points.

The only questions in my mind are 1) IF Peter used EXPANDED PolyStyrene, if it's strong enough to take the Drag and Torsion loads, and 2) how long the vinyl will last.

 

[Michael Silvius]

You and I are in complete agreement on these points.

The only questions in my mind are 1) IF Peter used EXPANDED PolyStyrene, if it's strong enough to take the Drag and Torsion loads, and 2) how long the vinyl will last.

I am sure that for his application Peter did the math and concluded expanded polystyrene it was strong enough.
How long will it last? well, I think someone here recently mentioned that Peter builds disposable airplanes. He is really experimenting to see what can be done.
That said I know the guys in Argentina building the Facil are using expanded polystyrene (something they call Tergopol down there) for their ribs and it appears to be holding up well.

https://www.facebook.com/groups/326514714191777/media

 

[stanislavz]

That said I know the guys in Argentina building the Facil are using expanded polystyrene (something they call Tergopol down there) for their ribs and it appears to be holding up well.

Write him to add layer of fiberglass on each side of his foam, it will add only 500-800 grams per wing, will give structural ribs.. By testing it with sandbags - eps works only in compression, but in real life - you have load on top skin only, and eps works on tension.. Eps and tension are not friends.

 

[Michael Silvius]

Write him to add layer of fiberglass on each side of his foam, it will add only 500-800 grams per wing, will give structural ribs.. By testing it with sandbags - eps works only in compression, but in real life - you have load on top skin only, and eps works on tension.. Eps and tension are not friends.

So far there are about two dozen of these MS FACIL aircraft. None has fallen out of the sky yet. Due to the limited supply of materials and punitive import costs they are built entirely out of locally sourced materials. MIG welded 1025 tube. Agricultural irrigation pipe spars. Tergopol ribs. Greenhouse plastic sheeting for covering. Fiat or Renault engines for power. Leading edge cuff is quite large as you see and made out of fiberglass and polyester resin over a mold and then glued onto the wing. I am fairly certain Miguel Scheinin did the math and knows the numbers.

 

[stanislavz]

So far there are about two dozen of these MS FACIL aircraft. None has fallen out of the sky yet.

Better late than sorry. I would still insist on it. This kind of load on eps - tension is not being tested with sandbags.

 

[BBerson]

Sandbags do load the inner face of the foam in tension. Kind of hard to simulate flight loads exactly with sand bags. Any testing is more than most do.

 

[stanislavz]

I was able to find more eps mechanical properties

https://www.researchgate.net/profile/L_Landro/publication/223681186/figure/fig9/AS:596045658591234@1519119767201/EPS-tensile-strength-as-a-function-of-density.png

Whole publication.

https://www.researchgate.net/publication/223681186_Deformation_mechanisms_and_energy_absorption_of_polystyrene_foams_for_protective_helmets

And as written in publication - eps is brittle by nature.

 

[Vigilant1]

I was able to find more eps mechanical properties

https://www.researchgate.net/profile/L_Landro/publication/223681186/figure/fig9/AS:596045658591234@1519119767201/EPS-tensile-strength-as-a-function-of-density.png

Whole publication.

https://www.researchgate.net/publication/223681186_Deformation_mechanisms_and_energy_absorption_of_polystyrene_foams_for_protective_helmets

And as written in publication - eps is brittle by nature.

That study is a good find, thanks for posting it. It contains info on EPS that is hard to find. I've been thinking about lightweight under-seat energy absorption using EPS, and the crush data in their graphs is perfect.

I'm a bit surprised that the tensile strength of EPS is as high as they show. If someone is using the very low density EPS sheets from the hardware store (approx 1.8 lbs per cu ft = approx 30g/L), the tensile strength of .45 MPa (65 psi) is higher than I would have guessed. I wonder how a real EPS rib in a real airplane subject to vibration, flexing, heat, lots of repeated load cycles, etc would perform. XPS would seem less prone to brittle fracture and resultant tensile failure over time, but that's just a guess and not real data.