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.

49 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:

        1. the problem is not the pentane , extruded styrofoam is simply not gasoline resistant! it dissolves like sugar in that stuff as sugar does in water, second: foam cores more and more become an issue when you search around for delamination, not bcs styrole gasses out forever, but ncs the designers are undereducated and don,t calculate the local stresses on the binding areas🤷‍♀️that simple! we in construction learn this in tje second semester! even PU foam cores delaminate simply bcs the guys or girls designing so desperately witj fiberglass( heavy) and carbon laminates( heavy as such, but not bcs of the carbon…but bcs epoxy soaks i to tje foam and epoxy is heavier than water🤷‍♀️and needs a minimum thickness, so it,s useless under compression….the rest is taken by foamcores , low rated G loads or you need very thick wingroots…🤷‍♀️that easy! ) …and so on…and so on…
          his airpkane flys, yes…it simply shows that we all are restricted without any real reason but that Governemnets hate us to fly, they all fear terrorism…it started with ww1…anyone can build an airplane, it,s actually cheaper amd easier to do than a good sailing yacht( i tried both, and gave up…what for? it.s outlawed since 2019 almost everywhere…) …if you use foamcores you need to know the stressload distripution running thourgh the airfoil area, and most let that out…and so the stresses on the binding surfaces are too much and the foam comes loose…or it.s simply not propable of taking changin intervall loads…like many poor aluminium alloys..they stress out pver time and get cracks…wood holds up the longest, uless it starts to get moldy/ rotten…)
          he prooves that it.s easy and simpke🤷‍♀️the lifespan of his plane is short anyways, he built anotherone later…underpowered again bcs electric propulsion is a lie! Tesla now needs Uranium and powerplants to feed his cars, that.s. surely very eko friendly…and millions of km of new copper cables for charging stations…🤷‍♀️all that is powered by fossile fuels for the engines, trucks and machinery to dig the ores, coal for processing amd so basically all a lie, not eko friendly at all🤷‍♀️at the contrary, as it doubles the need for ores and metals and fossile fuels for producing all that stuff, so combustion engines are lighter, need thereby less fuel at the emd amyways, don.t need extra mewly built faciluties and infrastructure and so on…electric propulsion is a lie! 🤷‍♀️itls harmful to the environment, just when you consider charging losses of 20% every time sou use any kind of batterie, production and twice the weight 🤷‍♀️all he proves is that it can be done…when you use 2 cheap RC 160 ccm engines they hold on for 50 hrs u til they need a rebuild amd then you have 16-20 hp easily🤷‍♀️and not 5-8🤷‍♀️his one had merely 5 kw! wtf? ….so don.t be delusional….what the FAA does seemingly not like is his cool approach and lack of care…they want aviation to be taken seriously…but Peter proves it.s as easy as any task once you know the basics…
          foam cores are great for low stress constrcution amd no gasoline or other solvents coming there…imagine a gasoline tank is filled and some fuel trickles into the foam core, a death sentence! we already have 50%+ on firts flight failures! the UK fights against it with stronger controls! the EU basically outlawed anything that is jot an Experimental amd most other countries world wide imply military control on aviation…🤷‍♀️bcs drug and gun dealers use any old gum airplane found in the woods or somewhere with lost certification amd such and still föy for years with them and transport their goods! 🤷‍♀️on the other hand homebuilts according to design drawings have endless problems with cracks and details…simply bcs many designers don,t semm to know how to calculate stresses and forces…🤷‍♀️it.s ridiculous, when a construction comapny shrugs off a collapsing house…hmm? but with airplanes itls a daily treat? crazy! take care! no styrofoam! and yes, the old “specialists”in the EU clubs who have piwer over homebuilders use 50 yrs old wire cutting styrofoam techniques! crazy! middle ages! old hippie methods? and those control by law what i do and i have to pay them? sorry…for 6-10 k on cotrol and same for licensing, and another time for the PPL and still 6 for the bird…plus 4 for oppressd instrumentations nobody needs…sorry….i can fly with a boight ticket or book a cruiser every month for a trip and have no extra costs but served meals🤷‍♀️when you use foam use PU…! it.s resistant to most solvents, has similar configurations according to data, needs to be sprayed or shaped in molds( so you need this extra step…🤷‍♀️from cans or 2 componenets) and is not good for wire cutting…) …
          take care, and blue skys! 🤷‍♀️

      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).

        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. it.s used everywhere and the blue one seems to have a soecific desity and strength…but still soluble in gasoline and other solvents! not heat resistant…when you park the bird in the Arizona sun and have a dark paintjob done, it basically evaporates inside and weakens! it.s still common practize in the EU homebuilt clubs that control the homebuilders under “advice”/ force by the authorities…bcs they seem to tjink tjise old guys know their trade…yes, somehow…seemingly on 1980 ies levels🤷‍♀️but take toms of money for controls…
          try to build a mold and spray PU foam of needed desity/stress strength etc into it🤷‍♀️off course you jeed some foul or wax to take it out…some build that way…or you foam a block and cut all out…and so on…it.s still primitive amd many companies just before covid pisted NEW videos about their crude building processes! 🤷‍♀️others are addicted to carbon laminates…why? bcs carbon is lighter than glass…and has high strength, but you forget that epixy is stull heavy! and it is mot good for pressure loads as a thin laminate…and delamination recently became an issue on airliners too! 🤷‍♀️some hidden repirts can be found…simply designers seem not to have any clue or education about stress loads in a stringer…and wings or fusellages are basically complex stringers…so a foam core wrapped in a hogh strength skin only good for srtess but no compression has a big flaw…the foam core is too weak on the outer regions🤷‍♀️but everyone ignores this…so others laminate two wing skins, embedd a stringer out pf wood but better aluminium and glue it all togetehr…🤷‍♀️as long as the aluminium is not tired of chnaging stress loads( and all aluminium tires out….) it works…foam is hood for low loads spread over wode areas, damping flutter and vibrations and insulation against temp. and noise…🤷‍♀️it can take wide soread pressure loads and even stress, yes…but VERY LOW…so the area between the laminate and the foam simply misses a transition zone bcs no such material exists or is used, as it would be heavier amd thereby the whole idea is useless🤷‍♀️basically easy! ask a civil ingenieer abozt construction, they will laugh at the idiocies done at airpkanes amd cars🤷‍♀️don.t ask architects, thise are just designers…artists! no technicians! 🤷‍♀️so when we bust the bubble i should ask how many thousand deaths are going on account of those experts still using styrofoam and then the investigations wonder why aurplanes decompose in blue sky🤷‍♀️hmm? use PU, epoxy, wood and well approved metals…forget styrofoam! it even evaporates under isulation fassades on houses on the hot sunny surfaces…it stinks for years! it burns like gas on fires! be careful…it melts when it becomes hot…don.t use styrole or styrene or however it is called regarding what chemical stage of priduction is wuoted…🤷‍♀️

      4. I purchased an already built skypup ultralight in 1992. I had been a hang glider pilot for years, but hang gliding required a trip to the mountains and half the time it wasn’t soarable which meant a couple of 10 minute sled runs from the launch site to the landing site.

        I have put hundreds of hours on the skypup. Mine has a Rotax 277 engine which is slightly overpowered and makes it a little nose heavy. The Styrofoam brand insulation has not degraded much if at all over time. The foam is strong in compression and the thin aircraft plywood laminated to it is strong in tension. They form a very strong structure. The article is incorrect about it being covered with fiberglass. The outside only… is covered with fabric.

        I got back from a skypup flight one day and a person with a hangar near ours had given my wife a ride in his Piper Tripacer. My wife said that we needed an airplane that she could go flying in too. I always joke that I am the first man in the history of aviation whose wife said, “We need an airplane.”

        We purchased a Piper Cherokee and the Skypup hasn’t got much use since that time.

        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.

    1. well, crowdfunding is easier than carreer….others waste their life with work, many simply collect money for free and call it a society or club….an old parachute costs some mere hundred dollars….he flys at 10 m hight…on 5-8 hp🤷‍♀️the parachute is useless! just another delusional heavy crap added to the bird! like those batteries…and heavy motors….one 8 hp RC engine with 160 ccm weights 8 lbs…inkl. minimal mufflers…🤷‍♀️so , tell me anyone if his electric propulsion is reasonable or safe…one RC engine with low service life costs less than 1k, expensive ones cost 2…🤷‍♀️no extra weight..and as his batteries just hold for 15 minutes or such…since ww1 its. proven that combustion engines need about 200-250g of fuel per HP /hour….netto! and you only need full throttle on takeoffs and harsh maneuvers…crusing needs less than 75%…many fly on 50%… his UÖ for safe flight would need a minimla power rate of 1:7(hp:kg) so less than 20.25 is idiotic….i played it through amd calculated it during cofid a hundred times, inkl. that idiotic foam core ideas…🤷‍♀️atbthe end i returned to combustion engines, wood, aluminium and epoxy/polyurethane….🤷‍♀️and i don,t use fabric! sorry…too heavy! idiotic! we have easy going and cheaper wood techniques, just the design is less curvy or takes more time to build….
      most make one mistake, when they add a stress loaded part instead of an unstressed part( replacing fabric skin for plywood) they still fuck in hundreds of diagonal struts…AND add the fabric on top…and so on…🤷‍♀️bcs they have no education amd knowledge about whta they are doing, just rules of thump…
      it works with boats, bcs water is heavy, but itls idiotic with airpkanesbcs air is light…so it needs higher speeds for more lift and/or bigger wing areas…for what? 🤷‍♀️check on Goat Gliders…slow and low flying on youtube, there is a guy who does it,..and as ULs are asked for slow flight anyways, why using naca 64xx🤷‍♀️it,s for fast flight…and yes, i went through all options and all calculations…🤷‍♀️took me a whole year! take care…
      and yes, asking for money bcs he is broke and wants to fly is low! 🤷‍♀️the FAA grounded him bcs he showed his private parts on a vid( by accident?dunno.ö.who cares..ö)

  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. he read a lot…but still his knowledge does hardly hit20% of the mechanics involved…that.s why he is stuck and lateron built “destruction battle cardboard planes” , but his work ( hobby!) shows what is possible amd that authorities tell lies to keep people off from doing stuff…and that many stuff was left out for speed and power…aviation was always about profut and warfare….🤷‍♀️slow airplanes, lightweight and cheap….no money to make! 🤷‍♀️so his constructions show that possibly anything can fly🤷‍♀️bcs he builds in real size! nit some 20″ models and RNs are different on those..ö🤷‍♀️so his stuff had some worth, yes…his methods….crude! his birds…short lived bcs they will fall apart within 2 yrs or simply become a hazzard when binding surfaces and joints weaken in no time…but who cares…
      a parachute for a dead person bcs he does not even know he can.t deploy it within such short falling distances is useless to sponsor…sorry🤷‍♀️but, nice ry…we all need money for free! his motors were free! his batteries free! what else🤣🤷‍♀️i want 2 ums 16 hp radials for free too, each is 2,8-3,2k…and i want the same rules for ULs where i live or a free visa to fly in the US too…yes….we all can want…but realuty sucks!

  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?

    2. good wuestion…but as far as i remember there is a passus against airships…in such cases they need to be weight without gas…🤷‍♀️and your question shows how outdated and uneducated the lawmakers thinkings have been…bcs a well made law takes such into considerations….weight or mass….🤷‍♀️yes, the weight of an airship is basically zero when swimming in the ocean of the atmosphere🤣cool….Hindenburg was an UL? 🤔no, there is a paragraph against it!

  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…

      1. As I understand it, X planes builder and flight characteristics are based on the plank method and are not as accurate as XFLR5 for design analysis. Though it may be adequate, I’m not technically an engineer

  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 : )

    1. 00 yrs ago there were no regulations! so everoyne dould build and fly freely! ( i.m so envious! 🤬) so what plqns do you need? 🤷‍♀️if you can.t even that then don,t even start! you would possibly die…

  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…

      1. well wood has the best weight to strength ratio, holds endlessly when kept from rotting amd can be glued amd nailed togetehr,,,,no other material can that….basically you could build wing ribs from willow branches cut with your pocket knife amd use some epoxy or pu glie and get all the ribs for just the glue…and have nice walks along the woods amd lakes or parks🤷‍♀️check the dimensions…basically this was done 120 yrs ago! they used baskets as fusellages! bending wings made from willow and ash! 🤷‍♀️so what?

    1. no, we are compkaining on the öqck of sophistication amd mass overpraise which is not rectified by the results and methods…! pls don.t dump us as trolls…we are warning and asking why certain stuff was done so crudely, why everyone hypes idiotic electric propulsion and keeps the environmental destruction needed for all the materials and uranium ore ozt of the equation, why we still see”sooo wel done” styrofoam construction when hundreds of ULs fall out of the sky, why we have so many rules without any sense but on the other hand nobody changes the hazzardous methods called provem and reliable! 🤷‍♀️he did a great job for someone with such lack of information/knowledge…i even got my firts ideas from him…now 2 yrs later and hundreds of hours of research i know better…sorry….the best stuff he explains is the balance! 🤷‍♀️and he shows what is possible against the maistream….the rest is kinda dangerous🤣

  7. I have seen all your videos and I think you got a great start of something fun I was wandering where you got your plans from and the name of the plane I was thinking of maybe trying to use the same plane but add a few more motors for vertical take off ?

    1. Peter designed the plane himself from scratch, and a lot of making it up as he went along. He has decided not to release the plans as the plane is not a good performer due to being higher weight versus his intended results. You can see all the build and flight videos on his youtube channel. He is in the midst of building his 2nd attempt at a scratch built ultralight now. It is with aluminum frame, with the same foam core fiberglassed flying surfaces. videos on youtube

  8. I watched all of the videos available of both projects. Peter obviously learned a lot about aeronautics through the construction and flying of RC planes, a luxury that the Wright Brothers didn’t have. And with all of the modern materials and so much work being done by so many experimental builders over the years there is a wealth of information out there. Probably the hardest thing Peter had to do was to wade through all of the misinformation available by naysayers who are “expert armchair engineers” with degrees from the academy of negativity. Great job Peter. Weight seems to be your worst enemy in reality. But you succeeded! You’re second design looks much improved though you need to redesign the gear and tweak the weights and balances. Even given that there was an abundance of information and materials to work with since flight first began in America, you are still a pioneer. You have contributed to experimental and ultralight aviation and advanced our pool of knowledge. There will be a handful of people touched by your videos that will become aviators and innovators because of you! And just like you, they will put their time, money, and lives on the line to turn their dreams into realities. Seeing that your parents are both supportive of your dreams enough so as to put their fears for your life and safety aside and allow you to experiment with life, I’m guessing that they are also dreamers who have built their dreams into realities. I’m building my second plane in the garage now. The first was a plans built, two seat wood and fabric strut braced high wing with a converted Volkswagon (Revmaster). The new one is a one off parasol single place with a half VW engine. It’s wood, composite and fabric. Best of luck Peter and thank you for your enthusiasm and your contribution to experimental aviation! You are an encourager to others!

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