Aluminum Tube & Gusset Airbike / Legal Eagle / Parasol Thread

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Victor Bravo, Oct 8, 2019 at 7:02 AM.

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  1. Oct 9, 2019 at 6:25 AM #41

    Victor Bravo

    Victor Bravo

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    OK, I will have to take that as gospel, since I have zero personal skill/experience with actually setting up or cutting parts this way. My only experience was watching someone design bulkhead parts on CAD before he water cut them (for my Cessna landing gear re-design project), and it took a long time designing each part to fit each individual location. So I thought if you could create a universal gusset there would be some huge savings.

    If that is not the case in reality, then so be it, we'll take that idea out back and napalm it. Or, to quote Goldfinger... "goodbye, Mr. Bond..."

    On to the next idea:

    I think that (unlike some of the Baslee style structures) this T'n'G fuselage should judiciously use some 4130 strap fittings that are riveted to the tubes where highly stressed bolts will go. Wing attach, landing gear attach, cabane struts, etc.

    Some of the ultralight style aircraft use all aluminum for this, but I believe that steel is likely a better choice for bolt loads. Attaching a steel strap fitting or "finger patch" type fitting to aluminum tube, using rivets, will require some gen-u-wine engineering calculations (to be sure you're in bearing failure and not in shear failure).

    So I would guess that the number of fasteners needs to be higher, to reduce the load on each fastener (because the difference in material stiffness could load the fasteners unevenly as the flight load is applied)???

    I'm guessing there would b e a lamination of two or three thinner steel straps to "taper" the thickness - to me that sounds like it is going in the right direction. Any input or volunteer effort from our HBA engineering brain trust?
     
  2. Oct 9, 2019 at 6:40 AM #42

    mcrae0104

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    Universal gussets are child's play... :)
    [​IMG]
     
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  3. Oct 9, 2019 at 2:49 PM #43

    Aerowerx

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    Rethink this.

    The tail boom is attached to the pod with a 4-sided structure. Bad idea. Why do you think all truss structures are made of triangles? Because the triangle is inherently stable. A 4-sided structure is not and can bend at the joints. There is an infinite number of 4-sided figures with the same sides. Only one triangle with the same sides.

    Also, the piece sticking out in front is cantilevered? The joint just above the wheel takes all the stress and would have to be tremendously strong.

    And isn't this thread about the METHOD, and not a particular design?
     
  4. Oct 9, 2019 at 2:55 PM #44

    Vigilant1

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    If you are the thread purity policeman (again), why did three of four paragraphs in your post deal with something other than "the method"? Focus, people! No wandering!!
     
  5. Oct 9, 2019 at 2:57 PM #45

    Aerowerx

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    Italian Erector Set???:)

    Maybe so, but this does not allow for an infinite number of joint designs. You would still have to design the structure to fit the gussets instead of the gussets to fit the structure.
     
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  6. Oct 9, 2019 at 3:41 PM #46

    litespeed

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    I am for the double gusseted tube idea with square tubing. Way stronger than just a single one. I have often wondered why this is rarely done? The extra gussets and rivets are worth the weight penalty and the strength increase should be substantial.

    If aimed at a sensible weight, not 254lbs, we could make a cheap but strong aircraft.
    The gusset and tube can be very strong as a cabin if done right. Safety should be a primary concern should the ground rush up and smite thee. The ability to design in a light stiff and collapsible crush zone ahead of the pilot should be considered. If done well a design can be far more crashworthy than others. No you can't try poke holes in granite at vne but the ones most pilots get caught at- low level and slowish. The machine should not be very fast, so landing/takeoff/speeds in circuit should be survivable.

    Their are a few ways to give a bit of crash compression but any should start with the idea of the cabin must stay in shape, no flexing and snapping back in shape. Anything outside the cabin is disposable in a crash and used to reduce g loads on the pilot. That means it should get crushed and deflect away its forces, break off or generally send its load around the perimeter of the frame.

    Getting rid of g loads when it all goes to hell is a great survival strategy. I am more than willing to pay the extra in weight, time and dollars to get a more robust and mistake friendly machine.
    No ballistic chute can help down low but good design can. A lot cheaper as well.

    I know we were talking simple and basic quick build but, if we address pilot protection as part of the initial design, it will influence choices made.

    A double firewall with compression zone and back angled towards the rear can do wonders and cost little.
    The same with the seating and a compression zone mounted seat. Not real hard to do if designed from the start.

    Make sure the gear will take a hammering from drop loads to absorb very hard landing etc but mounted to tear off in shear from a crash.

    A dash well away from flailing arms and knees would be nice. A side stick is nice as well, to save been impaled on one.

    Oh also a fuel system that does not dump it load in fast stops.

    Cheers
     
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  7. Oct 9, 2019 at 4:10 PM #47

    Vigilant1

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    +1. And how does this relate to "the method"?
    1) Designing to keep the occupants safe in typical crash scenarios is something best done early in the design stage.
    2) Designing tube junctions that can take loadings from other-than-the-usual direction is something to consider when designing the gussets/saddles. And designing some selected junctions/tubing sizes for loadings above "design + 1.5 FOS" may result in significant payback in safety.
    3) If "the method" can be used to construct a craft that protects the occupant(s) in a badly dropped-in landing, a noseover, or an excursion into the trees-- and do it with minimal extra weight --why not do that? Wouldn't that be the best approach?
     
    Last edited: Oct 9, 2019 at 4:42 PM
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  8. Oct 9, 2019 at 4:45 PM #48

    FritzW

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    I think the basic "design 101" stuff can be assumed. It should be safe, it shouldn't catch fire, it shouldn't fall apart, etc.

    Going back to post #1. It sounds like the thread is about the method AND the design ("TnG airplane that fulfills the mission of an Airbike, Legal Eagle, et al.") ...actually this thread is a spin off of the TnG Airbike that started on the Monotube thread.

    The problem is: we've proven on several threads that it's impossible to design an airplane by committee. The only thing to do is toss around ideas about method, configuration, design and see what floats to the top.
     
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  9. Oct 9, 2019 at 5:11 PM #49

    Aerowerx

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    Square tubes will have the same problem as angles. It will twist when you try to bend it, particularly in compound curves, like the lower longeron in most tube and fabric designs.

    I tried it with square wood longerons, back when I was trying to build. I didn't like the idea of all that built in stress from forcing it to not twist. Round is the way to go.
     
  10. Oct 9, 2019 at 5:38 PM #50

    litespeed

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    I agree square is not ideal if bends are substantial for the length. However its very stiffness and large areas for gussets and rivets make it ideal for a very strong cabin. It can be bent gently and roller dies are best for tighter bends. The ability to do easy strong gussets on the flat surfaces is the big bonus. It can mean the big important part of the aircraft can be easily built and aligned on a flat surface. All the gussets can be double up or triple in needed areas to spread loads. And it can then even be metalized with a skin riveted to the outside. The rest being can be what ever suits your taste.

    The rest of the airframe can still use round tube if required. Having a main structure of square tube and a light round tube and cloth to suit tastes on the outside.

    Square tube has been done with success before and can suit a CNC world quite well.
     
  11. Oct 9, 2019 at 5:54 PM #51

    proppastie

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    IMG_20170703_203431.jpg IMG_20170703_204006.jpg IMG_20170703_204655.jpg
    kind of late to re-think this..... 52# mostly 7075-t6 just tubes gussets nuts bolts, wing attach, actual weight, does not include engine mount, wheels, skid,seat, canopy, stick pulleys,
     
    Last edited: Oct 9, 2019 at 6:05 PM
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  12. Oct 9, 2019 at 6:11 PM #52

    proppastie

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    yes....one reason it is 52#....designed to 6G ultimate....7075-t6 is very strong.

    The lower aft tube mounts the engine...triangular layouts I did were more weight, however obviously there are a very large number of possible designs, and perhaps your design will be better.
     
  13. Oct 9, 2019 at 7:43 PM #53

    Aerowerx

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    I suppose you could use square tube for the cockpit area and stick round tube inside it extending back for the fuselage.

    The problem, in my experience, is in trying to make a square wood longeron conform to a nice compound curve. It wants to twist. When I built the sides flat, with a simple curve, and then tried to bend them there was a lot of force required.

    I know there are ways to bend square tubes in simple curves, but what about the compound curves?
     
  14. Oct 9, 2019 at 8:27 PM #54

    Victor Bravo

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    Square tube is not the right materials for this IMHO. Maybe one or two parts that specifically benefit from it enough that it justifies the cost and greatly reduced selection of wall thicknesses.

    However, considering that round tubes can be riveted very easily and reliably to flat sheet gussets (at the tangent point), and they come in thin wall sections, cheaply, and are reasonably corrosion resistant, and are fairly good in compression... a quickly built near-minimalist airplane for chronic cheapskates is a pretty good case study for 6061-T6 round tube.
     
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  15. Oct 9, 2019 at 9:55 PM #55

    Aerowerx

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    Just wondering about something....

    Earlier on in this thread there was a discussion as to fish-mouthing the tubing at the joints was needed, or just cut it square.

    In a welded tube fuselage the tubing has a fish-mouth to enable a tight fit before welding. And isn't the weld what provides the strength to the joint, and transfers the forces from one tube to another?

    In a rivet tube and gusset joint aren't the rivets what provides the strength? In which case the ends of the tubes don't need to be a snug fit. Am I right in this?
     
  16. Oct 9, 2019 at 10:01 PM #56

    ScaleBirdsScott

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    With the riveted tube the rivets do provide all the strength in keeping the members together. The problem is that if you only have one gusset plane and the rivets in line on a tube/whatever on that one plane, then it's possible for the tube to rock or wiggle left and right along those rivets. The ways to prevent this are to fishmouth the tubes tight so that they have a snug fit and physically resist movement, or have at least one other contact plane (and preferrable perpendicular or anything but parallel to the first plane) with more rivets so that they prevent the tube from rocking around one point. In such a setup, yes, the tubes don't need to touch at all, but you don't want too much gap or you need gussets with enough stiffness not to flex/buckle/etc.
     
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  17. Oct 9, 2019 at 10:09 PM #57

    Rockiedog2

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    I like work on it a few years behind closed doors and when way far along show it to the troops then. And sit back and watch em pick it apart. Great fun!
     
  18. Oct 9, 2019 at 10:14 PM #58

    Rockiedog2

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    I especially like the test fixture in the first pic. I got an ancient small dozer that works good for a deadman.
     
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  19. Oct 9, 2019 at 10:16 PM #59

    ScaleBirdsScott

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    Ouch, I can feel it.

    I hope something starts to come from this thread, I've got far far too many irons in the fire right now to spend any serious mental power on designing something like this at the moment. Way too many. I need to put some irons out just to keep all of them from melting into slag.

    But I hope something starts to come from this. All I ask is that it better look awesome. Better look way rad.
     
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  20. Oct 9, 2019 at 10:29 PM #60

    FritzW

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    ...you gotta keep new ideas running through your head all the time or your brain turns to goo
     

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