Peter Sripol is at it again...

[TFF]

Peter is building disposable airplanes. He does not care if the covering is permanent as long as it stays on in flight. He has built four airplanes in four years and bought a fifth. They are disposable because he likes playing with things. Everyone looking for the perfect plane are always left behind. One and done seems to never get built. He and Mark Stull would have been a force.

 

[Topaz]

Peter is building disposable airplanes. He does not care if the covering is permanent as long as it stays on in flight. He has built four airplanes in four years and bought a fifth. They are disposable because he likes playing with things. Everyone looking for the perfect plane are always left behind. One and done seems to never get built. He and Mark Stull would have been a force.

This. As the apparent poster child for "one and done seems to never get built," I admire what he's accomplished, in the same way I admired Mark Stull's record of building so many new and different airplanes. The flip side is that the engineering here seems on the "thin" side, just like it was with Mark, and I fervently and genuinely hope that doesn't come to bite Peter.

The best approach is probably somewhere "in between."

 

[Victor Bravo]

He mentions that he has "aero friends" who have brought some engineering ability to the table and checked over his work. I think this may be an intentional understatement.

Making a big deal on camera that he had (a bunch of high-end Boeing engineers, or such) do all the calculations for him would change the game for the viewers. It would become something too obvious, and not have any risk.

If I had a youtube channel showing how to do cool things with explosives, and I said that I had an ex-Navy EOD and movie SFX friend with 50+ years of experience (I do) making sure I didn't get hurt... I would have X number of subscribers.

If I said that I was experimenting with explosives, and I should be safe enough "because Bubba the 80 year old drunken miner from Hillbilly County Arkansas was gonna learn me how to do it reeeeal safe" - I'd have 10X subscribers.

 

[rotax618]

Unlike cars most sport airplanes are not exposed to the sun for long periods, generally being hangared. It is the UV that destroys most plastics & paints. Some owners of sailcloth covered ultralights have used water based house paint to greatly extend the life of the covering - perhaps that method is a possibility.

 

[rotax618]

There are literally hundreds of amateur designs that haven’t been checked by a “grown up” that have been flying since the Wright Brothers. I agree that most people lack the necessary skills to accomplish this, but you don’t have to be a “Boeing Engineer” to design and build a successful lightweight airplane, a good understanding of the principles of flight and a knowledge of materials and structures is required.

 

[billyvray]

It is good to see the step change improvements in his designs. The welded tube fuselage, while not necessary for what he's doing, is a good choice for potential crash protection. I really like the wing design intent. The foam is quick to be cut out and does good work. I would think it needs a bit more aluminum ladder bracing, but not excessive. The vinyl wrap is a great idea. Belite used that over foam cored wings also, but I think he also had a wrap of polyester fabric too.

 

[ToddK]

It is good to see the step change improvements in his designs. The welded tube fuselage, while not necessary for what he's doing, is a good choice for potential crash protection. I really like the wing design intent. The foam is quick to be cut out and does good work. I would think it needs a bit more aluminum ladder bracing, but not excessive. The vinyl wrap is a great idea. Belite used that over foam cored wings also, but I think he also had a wrap of polyester fabric too.

My first thought was a couple of tubes for compression, and a layer of BID (?) fiberglass and that would be a pretty dang stout wing.

 

[Victor Bravo]

I believe the hot wired foam "continuous rib" is doing the same actual job as the rib batten tubes (that are simply slid loosely into pockets in sewn ultralight sails) were doing previously on ladder type UL wings.

Which means (to my uneducated guess) the foam shapes and peel 'n' stick vinyl are plenty plenty plenty strong for the job they are doing.

 

[proppastie]

Fantastic :....Peter if you have the time I am sure all of us would like to see more details....hot wire the wing, where can I get that motor?, how many/weight of batteries, what is the controller?

 

[cluttonfred]

That wing is particularly interesting, basically full-span expanded extruded polystyrene ribs in top and bottom halves. Presumably they are hot-wired, are there any other easy ways to create those shapes?

 

[Vigilant1]

Here's a video of him cutting the wings foam for a previous airplane of his (this one with poplar trusses)

(1:20 through 2:05)
He used thin plywood templates (cut with ajigsaw?) on each end of the 42" long sections and cut them solo using a hot wire on a PVC frame/bow. Looks like he fed the wire through each blind section by first boring a path using a length of EMT heated with a torch. After removing the hot-wired cuts, the foam weighed 55% less. The foam in this wing weighed less than 5 ounces for each foot of span, so less than 8 lbs if we had a 25' span wing. On this plane, he says he planned to cover the wing in 3/4 oz fiberglass cloth.

I don't know how well this would work for a plane with higher wing loading or higher dynamic aero pressures.

 

[Vigilant1]

Here's a video of him cutting the wings foam for a previous airplane of his (this one with poplar trusses)

I just noticed--it sure looks like he's using expanded polystyrene (EPS, aka "beadboard") foam for the wing core in this previous design. I sure can't see why he'd use that rather than extruded polystyrene (XPS).

 

[rotax618]

Its half the weight

 

[Vigilant1]

Its half the weight

Some is, some ain't.

1) Yes, the most readily available (in home improvement stores, etc) EPS has a lower density than the most commonly available XPS

2) XPS is stronger than EPS of (almost) equivalent weight:
..........................Density.........compressive strength................flexural strength
EPS Type II: 1.5 lb/cf.................15-21 psi.....................................35 psi
XPS Type IV: 1.55 lb/cf..............25 psi............................................50 psi

Other:
The XPS most commonly used for wing cores is, I believe, 2.2 lb/cf Type VII. It has a compressive strength of 60 PSI and flexural strength of 75 PSI.

EPS is available at densities lower than any XPS. The lightest EPS is 1 lb/cf, has a compressive strength of 10-14 psi and flexural strength of 25 psi.

Maybe Peter's choice was based on cost or availability. Or, maybe an equivalent weight of very light EPS could be carved into a thicker beam, giving more rigidity than a thinner XPS beam.

Having worked with both a little, I don't think I'd want to use EPS for this.

 

[rotax618]

I believe EPS is or was used for Jabiru wing cores

 

[TFF]

The foam is only for simplicity. It’s back to him not building the end all be all; to him it’s number 4. Not number 6; no escape. Cheap foam means there is budget for 5,7,8,9... because it’s continuous or is probably more supportive than a dozen 1/4” Spruce ribs like in a regular wing covered in fabric.

Now it’s time for someone to take that idea, build an integral spar and drag spar with a hard outside surface. Mature the idea.

 

[Vigilant1]

Mature the idea.

That's why we are comparing foam types. Input?

 

[BBerson]

He load tested the foam with sand bags to about 5g.

 

[Vigilant1]

He load tested the foam with sand bags to about 5g.

Maybe that was a different plane, or a different video?

In the video on Post 31, he loaded sandbags until he got to 2.5G (approx 10:30 in that video)

In the video in the OP, he loaded sandbags until he got to a little less than 4 Gs (approx 5:50 in that video)

Also, with the minimalist skin in his newest design, the wings won't have much resistance to twisting. That's probably not a problem for him in his application: the twin struts help a lot, plus his low speed, and no flaps or even ailerons. But, it would be a consideration in a conventional cantilever wing.

 

[BJC]

Keep in mind that Peter is not designing an HBA to be useful or even replicated. He is providing entertainment on YT as a business venture. He is very good at that.

This is not a criticism of Peter; it is just a reminder of what the videos are. I suspect that he is doing quite well for himself, and may very well own a Citation a few years.


BJC