Building An Ultralight Out Of Foam In A Basement

[Peter Sripol] is something of a legend in the DIY RC aircraft crowd. He’s friends with Flite Test, and there he built an enormous RC cargo plane that could easily carry a small child aloft. Now, [Peter] is aiming a bit higher. He’s building an ultralight — a manned ultralight — in his basement. It’s made out of insulation foam.

Yes, this ultralight is constructed out of insulation foam, but you can think of that as just a skin. The real structure here comes from a wooden frame that will be fiberglassed. The design of this aircraft is an electric, twin-engine biplane. The relevant calculations have already been done, and [Peter] is already flying an RC scale model of this craft. So far, everything is not as sketchy as it could be.

As with any, ‘guy builds an airplane in his basement’ story, there must be a significant amount of time dedicated to the legality, practicality, and engineering of said plane. First off, the legality. [Peter] is actually building an ultralight under Part 103. The certifications for a Part 103 ultralight are much more lenient than the next step up in FAA-certified aircraft, a light sport or experimental aircraft. An ultralight is not required to have an airworthiness certification, and pilots of ultralights are not required to pass any tests of aeronautical knowledge or hold a medical certificate. Yes, legally, any moron can jump in an ultralight and fly. Think about that the next time someone brings up the Part 107 ‘drone’ certification.

Next, the practicality and engineering. [Peter]’s plane can weigh a maximum of 254 pounds, and should not be capable of more than 55 knots in full power level flight, while having a stall speed that does not exceed 24 knots. This is slow for a Cessna, but just about right for the gigantic remote-controlled planes [Peter] has already built.  A few years ago, [Peter] built a gigantic remote-controlled cargo plane out of what is basically foam board and a few aluminum tubes. The construction of [Peter]’s ultralight will be a highly refined version of this. He’s using foam insulation sheets for the body of the fuselage, reinforced with plywood and poplar struts. This foam and wood build will be wrapped with carbon fiber and fiberglass sheet, epoxied, and hopefully painted with flames on the side.

The use of poplar is a bit curious for an ultralight aircraft. For the last hundred years, the default wood for aircraft has been either spruce or douglas fir. The reason for this choice is the strength to weight ratio; spruce and douglas fir have the highest strength to weight ratio of any other wood. Poplar, however, is ultimately stronger and available at his local home improvement store, even though it does weigh a bit more. If [Peter] can keep the weight down in other areas, poplar is an excellent choice due to cost and availability. The video (below) is unclear, but we can only hope [Peter] has read up on the strength of aircraft frames and the orientation of the grain of each structural member.

This is the first video in what will be an amazing build series, and [Peter] hopes to get this thing up in the air by September. If you’re concerned about [Peter]’s safety, he’s also put up a GoFundMe page for a parachute. [Peter]’s going to fly this thing if you complain or concern troll or not, so donate a dollar for the parachute if you’re that concerned.

32 thoughts on “Building An Ultralight Out Of Foam In A Basement

  1. Insulation foam covered in fiberglass is very popular with many home built aircraft. The Long-Ez and variants, the KR-2, Quickie, Velocity, and many more. Spars made of fiberglass are the key to giving the wing strength. Hotwire to shape the foam into aerodynamic shapes is easy and repeatable.

    1. Years ago, I spoke to a professional boat builder about using insulation foam (specifically Styrofoam and no-name clones of such) and he advised strongly against it. He said that those foams off-gas for years and this results in delamination – the glass-epoxy releases from the foam and significantly reduces strength over time. He recommended sticking with foams rated as core materials.

      What type of insulation foam is used in these aircraft?

      1. There are a lot of types, but extruded polystyrene (XPS) is common in the US. The difference is that “styrofoam” – those stuck-together beads that everyone’s seen in coolers etc. is supplied as granular pellets saturated with a “blowing agent” – typically pentane – that is expanded into a mold with heat (the heat volatilizes the agent and the little beds “puff” like popcorn). That pentane may be what your friend was referring to – it’s either been replaced in most applications or is in the process of going there. XPS is the same polymer but is produced differently, in a sheet-production facility using a different blowing agent.

        The blowing agent in a sheet production system may be something much simpler – much closer to one of the R-xxx refrigerants/aerosol propellants. Because it’s going to be incorporated into a house there are some pretty strict standards about reactivity, VOC and outgassing – no bueno if it makes people sick both in the factory or at home, or causes the shower stall to come apart.

        Here is a commercial site (I have no connection to this) about the agents used in sheet XPS: http://bit.ly/2vxr6p2

      2. Same problems with surfboards. People thought epoxy was better due to leaking and delamination of older fiberglass techniques. The epoxy boards would ding and dent to hell and back if you just looked at them. Some manufacturers/shapers had issues while others suffered less, I guess because of their choice of foam core as you mention. Pretty cool project and hope he survives the test flights :D

      3. (I accidentally clicked report, sorry, I hope your post isn’t removed)

        The most recent recommendation for foam that I have found:

        Blue Styrene: Dow Chemical Co. Brand F.B. Styrofoam 2 lbs/ft² ±0.2 lbs/ft² density. Cell size 1.4 mm to 2.4 mm.

        That is the wing foam used in the Long-Ez and similar types (Cozy, Velocity, Quickie). http://www.aryjglantz.com/2015/09/right-wing-foam-cores.html

        Of course the aircraft are “composite” so they composed of different foams for different parts. Pour foam and urethane foam for non-structural parts (fairings and such) to H45 Divinycell for the fuselage sides.

        1. You do realise that familiy relations work very differently in different parts of the world, right? He is very overt about his Thai background and the restaurant his family owns.

  2. This will fly ok. He obviously read up quite a bit, mentions static testing with 2000 lbs on the wings, etc. If it passes static it will be strong enough. Great work so far.

    1. “If it passes static it will be strong enough.”

      Yeah, against static load, but not necessarily for fatigue loads.

      Take a piece of fiberglass and static test it to 2000 lbs. Then load it up with 200 lbs and start shaking. It breaks. What gives?

  3. “… can weigh a maximum of 254 pounds, and should not be capable of more than 55 knots in full power level flight, while having a stall speed that does not exceed 24 knots. ”

    Hmm, does any humongous, only slightly heavier than air, craft with slightly negative buoyancy in air, but also with an aerodynamic lift, pass as an ultralight, or the regulations correctly specify mass instead of weight? Asking for a friend …

    1. It’s my understanding that the weight limits apply to the deflated balloon or blimp. I know there are balloons that make the unpowered weight limit (155 pound), of both cloudhopper and basket designs; dunno if there are powered blimps making the 254-pound limit, but it should be possible.

      It does raise an interesting question on the threshold of powered vs. unpowered. If one builds a hot air balloon and finds it creeping over the 155-pound mark, can one make it a legal powered ultralight by hanging a CPU fan, or an RC motor and prop, off one side?

  4. I wish [Peter] the best of luck with this endeavor. But if it fails, expect to see the (hopefully not too) tragic results to appear on the Discovery and/or National Geographic Channel in yet another of their ubiquitous “found footage on the Web” programs that make up Soooo much of their content these days (the lazy bastards). Yeah, we all HATE that crap from Discovery and NatGeo. Again, good luck [Peter], please be careful…

    1. Download the flight simulator X-Plane, there is a plane builder, design your plane, fly it.
      It calculates realistic values depending on the geometry, airfoil…
      Btw: The Velocity aircraft was conceived on that simulator…

  5. This isnt the first time someone from the Flite Test family has done foam board manned flight. The FT hosts did the Redbull Flutag a few years back so powered flight seems like an obvious next step. Hope Peter is planning on releasing the plans when hes done like the rest of the FT designs! My MiniArrow works so well, I look forward to building one of these too : )

  6. This is not so unusual as a group endeavor. Japan hosts a “Japan International Birdman Rally” over Lake Biwa every year where anyone can build a man-carrying ultralight and fly it, albeit once, off a dock for distance and entertainment value. Some are serious contenders sponsored by universities and clubs and some are little more than costumes put on by individuals, but all eventually end up in the lake to great applause by the audience. Other countries do this too with the first I believe having been done in the UK in 1971. The ultralights can be unpowered gliders or man-powered, never motored. Only a few make it close to the opposite end of the lake without a dunking. I could be wrong, but I don’t believe anyone has gotten seriously hurt flying these contraptions. Peter’s device may be unusual in that it could be reusable if he succeeds in flying it more than once…

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