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Thread: Structural honeycomb Panels

  1. #1
    Registered User KC135DELTA's Avatar
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    Structural honeycomb Panels

    Hello guys, long time no talk.

    Would Aluminum structural honeycomb panels used over a limited true structural frame (both being load bearing) be a legit way to build a lightweight but very strong aircraft structure capable of taking high surface loads? Such as high speed turns and aerobatics. Here's what I had in mind:


    Maybe not so dense with the supports but you get the idea. The interior voids would probably be filled with a lightweight foam for increased rigidity.

    Has this been done? Is it overkill?

    danke

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    Re: Structural honeycomb Panels

    You are asking an extremely broad question that isn't really easy to answer. The very simplistic answer to your rather hard question is "yes it has been done." Look at a Grumman Yankee as it uses the honeycomb panels if I remember correctly. But the devil is in the details and depending on the design of the structure it may or may not be sufficient and would require a complete analysis and tradeoff study with more conventional methods to know the answer for what you have in mind.

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    Super Moderator orion's Avatar
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    Re: Structural honeycomb Panels

    Structural honeycomb panels are an excellent candidate for aircraft construction in all three markets: Kit, one-off or even certified production. I'm currently working on two projects that utilize these materials for much of the airframe and the benefits are quite impressive not only from the standpoint of strength and durability but also from the standpoint of construction.

    The material is quite applicable to many of the structural components in an airframe and at this point I can see only two or three negatives, although they're not detrimental to the cause. One is weight: You really don't want to use a skin any thinner than about .020", which simply means that much of the applications will end up weighing about the same as if you used a material that's about .040" thick (actually more than that if you add in the core and the adhesive). Fortunately the airframe is a relatively small percentage of the gross weight so for most conventional applications the extra weight is readily accounted for in the initial design steps.

    The second disadvantage of the sandwich sheets is simply that it is difficult to do anything other than flat structures. There are ways to incorporate rounded corners but overall, you'll end up with a relatively squarish looking airplane. If aesthetics is your goal then this may not be the right choice.

    And the third issue is cost. Airframe appropriate sheets (4' x 8') will most likely cost in the $900 to $1,100 neighborhood. By airframe appropriate I mean that the sheets are fabricated using methods that will provide the material with durability and dependable quality. You do not want to use the commercial materials. The sheets will need aircraft quality and alloy skins; they will have to be fabricated using a hot press (no room temp materials); and they will have to use honeycomb cores with a cell size no larger than 1/4" (1/8" is better).

    And all this holds true for the composite sandwich sheets also except that the costs will most likely be higher.

    The picture below is of a test fuselage I built using some surplus glass/honeycomb panels. All the components are built of the sandwich sheets including the two turtledecks.
    Attached Thumbnails Attached Thumbnails Structural honeycomb Panels-facet-fuselage.jpg  
    "To live is to learn; to learn is to live" (author unknown)

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    Registered User BBerson's Avatar
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    Re: Structural honeycomb Panels

    Barnaby Wainfan did a forum at Oshkosh a few years ago about building with honeycomb panels.
    Of course, he likes flat panel "faceted" airplanes.
    BB

  5. #5
    Registered User Jan Carlsson's Avatar
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    Re: Structural honeycomb Panels

    The BD-17 is using same method.
    see BedeCorp - BD-17 Nugget

    Jan

  6. #6
    Registered User KC135DELTA's Avatar
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    Re: Structural honeycomb Panels

    Quote Originally Posted by orion View Post
    Structural honeycomb panels are an excellent candidate for aircraft construction in all three markets: Kit, one-off or even certified production. I'm currently working on two projects that utilize these materials for much of the airframe and the benefits are quite impressive not only from the standpoint of strength and durability but also from the standpoint of construction.

    The material is quite applicable to many of the structural components in an airframe and at this point I can see only two or three negatives, although they're not detrimental to the cause. One is weight: You really don't want to use a skin any thinner than about .020", which simply means that much of the applications will end up weighing about the same as if you used a material that's about .040" thick (actually more than that if you add in the core and the adhesive). Fortunately the airframe is a relatively small percentage of the gross weight so for most conventional applications the extra weight is readily accounted for in the initial design steps.

    The second disadvantage of the sandwich sheets is simply that it is difficult to do anything other than flat structures. There are ways to incorporate rounded corners but overall, you'll end up with a relatively squarish looking airplane. If aesthetics is your goal then this may not be the right choice.

    And the third issue is cost. Airframe appropriate sheets (4' x 8') will most likely cost in the $900 to $1,100 neighborhood. By airframe appropriate I mean that the sheets are fabricated using methods that will provide the material with durability and dependable quality. You do not want to use the commercial materials. The sheets will need aircraft quality and alloy skins; they will have to be fabricated using a hot press (no room temp materials); and they will have to use honeycomb cores with a cell size no larger than 1/4" (1/8" is better).

    And all this holds true for the composite sandwich sheets also except that the costs will most likely be higher.

    The picture below is of a test fuselage I built using some surplus glass/honeycomb panels. All the components are built of the sandwich sheets including the two turtledecks.
    Not going to lie Mr. Orion. I LOVE what you have pictured there. That's almost exactly what I had in mind. If you don't mind me asking, what are the dimensions and weight of the fuselage you have there?

    Thankyou, Once again much appreciated. I sometimes wonder what us knuckleheads would be doing on this board without your expertise.

    Regards,

    Drew D.

  7. #7
    Super Moderator orion's Avatar
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    Re: Structural honeycomb Panels

    Quote Originally Posted by KC135DELTA View Post
    Not going to lie Mr. Orion. I LOVE what you have pictured there. That's almost exactly what I had in mind. If you don't mind me asking, what are the dimensions and weight of the fuselage you have there?
    That fuselage (called the Facet) was an experiment to see if such construction was even feasible. The name came from the shape that the outside skin took on a a result of the kerfing of the inner skin. The large curves (aft turtledeck) were kerfed on about 1" centers and the small curves were cut on 1/2" centers. The result was a series of narrow facets on the outside of the curvature.

    Once cut, the panels were put into a wooden framework where they took on the final shape and glass was laid in on top of the kerfed areas to re-establish the sandwich. After that cured, the wooden frameworks were assembled (they were designed so they piloted off of each other) and the cockpit and tailcone pieces were joined. Once the that cured the two turtledeck pieces were removed from their jigs and assembled to the bottom canoe.

    The whole assembly was then removed from the jigs and glassed over with two layers of 7781 glass, using Hysol EA9412 epoxy. The interesting thing was that once the glass was applied and the whole thing got primed and sanded, the kerfs pretty much disappeared so it took on the smooth surface you see in the picture.

    The glassing of the inner skin was done right on the part so unfortunately the channels formed by the cuts absorbed a lot of resin, which of course ended up being somewhat of a weight penalty. I probably should have wetted-out the fabric on a table and then placed into the part so that there was no excess to flow into the cavities.

    Once all set up, additional reinforcement was added so that the firewall mounts had a load distribution path into the shell. This was 6" wide unidirectional built up to just short of 1/4" thick that extended from the firewall to the vertical tail post. In other words, this was a beefy build.

    The fuselage was about fourteen feet long, although I don't recall the specifics. Once it got to the shape you see there the overall weight was probably around a hundred pounds, give or take a bit. But keep in mind, this was a single place designed to take full sized engines (to IO-360) so it had a lot of structural capability.

    But the project did not evolve into an actual aircraft - this was purely an exercise whose purpose was to see if such an airplane was feasible on an amateur level. Once it got to this stage I received a bunch of other work so had no time to devote to it. Furthermore, I needed the floor space so eventually it got cut up and scrapped.

    But it did prove that this approach was feasible and it did deliver a phenomenally strong structure. The two project I'm working on now have sort of evolved from this idea. One of these is all aluminum and is being designed for a company in Texas (American Aviator, Inc.) - they should be able to start in on their prototype within the next couple of weeks.

    The other project is part time and is similar in scope but larger, and is based on composite materials.

    Quote Originally Posted by KC135DELTA View Post
    Thank you, Once again much appreciated. I sometimes wonder what us knuckleheads would be doing on this board without your expertise.
    Thank you - you make me blush.
    "To live is to learn; to learn is to live" (author unknown)

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    Re: Structural honeycomb Panels

    Furthermore, I needed the floor space so eventually it got cut up and scrapped.
    Next time auction it off on the "for sale" section .
    (I realize the liability would probably stop you, just being facetious)

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    Re: Structural honeycomb Panels

    That is the same construction as the CFM Shadow's fuselage.

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    Registered User wally's Avatar
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    Re: Structural honeycomb Panels

    A lot of the big planes I hang around use honeycomb for some portion of the flight surfaces. They seem to work pretty good. Well, except for the B-58A years ago. I used to see them on the ramp with big chunks of trailing edge elevon honecomb just gone!

    A bit of a chore to make repairs on. That might be a consideration on a small plane constructed using honeycomb panels. The big boys also do compound curve panels with a bonded honeycomb center. Like flaps on DC-10/MD11. Other places they are sometimes used is floors, galley panels and of course the lavatory.

    You can also get - or used to get - panels made with outer sheets of aluminum or one side aluminum, the other fiberglass and having a core of end-grain balsa. Available in various skin thickness and overall thicknesses.

    A major dificulty is in attaching two pieces to make a corner that is strong, light, not complicated to build, and a smooth transition around the corner. One way is to route out the core of each piece and bond some sort of curved filler in place.

    Oh, you might need to get a little hammer to do "tap testing" of the honeycomb panels too. It can disbond internally and not be visible from either side. By tapping you can tell where it is disbonded and where a repair is needed. A serious problem on something like an engine thrust reverser or 30 foot high rudder.
    Good luck!
    Wally

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    Registered User Birdmanzak's Avatar
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    Re: Structural honeycomb Panels

    Best "tap tester" I've ever used is a 50 cent coin (Australian). It's a similar size to the US half-dollar, but about 35% heavier (thanks, Wikipedia!).

    The US coin would do a fine job. Good enough to sign a 767 inspection off with, anyway. Cheap, too.

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    Registered User berridos's Avatar
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    Re: Structural honeycomb Panels

    I will use aluminium honeycomb in the firewall of my kr2s bonded with firerestistant fibres.

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