Hi,Is the plywood aviation grade ?
Incorrect. If I were relying only on the end-bonds, you would be correct. But the structural pieces are sandwiched between two pieces on ply. On the inside is the 1.5mm template, and on the outside, a full 3mm sheet. Those structural pieces aren't going anywhere...That's not quite correct. Even with your "built in gusset", the gluing area isn't as much as a gusset glued on the side. But more importantly, gussets on the side load the glue joints in shear, which is what you want for a good glue joint. Your method loads the joints in tension, which is not good.
The difference is in (1) precision of fit (2) build time. For example, I cut out the entire fuselage (ie both sides) in just over 4 and a half hours. That was yesterday's job. Today, I will glue them all together. Since this is my first plane using this method, I fully anticipate some hiccups and SNAFUs - but essentially we're talking hours, not days to build a side. And I'm pretty darn certain that my joints will be about as close as is possible to manufacture. Actually, to within a tenth of a millimeter accuracy.Other than being cut from 3/4" ply, not solid wood, how is this method any different than a traditional stick, filler and ply joint?
Hi. The cabin area is reinforced with a 3mm ply doubler on the inside, as shown below.Yes, that lower rear corner if the cockpit cut-out is very heavily-loaded.
An engineering analysis might suggest using a solid sheet of plywood in that corner. Alternately, you could glue doublets inside or outside of the cockpit will. Outside doublets will create little drag at Flying Flea airspeeds.
Do you mean the base of the seat? Because every other corner is clearly radiused. But consider - the seat base and back are separate pieces, so no stress risers possible.May I also suggest radiusing the inner corners to reduce stress-risers?
Actually, I'm going to be using 3mm ply bulkheads throughout bonded to every structural member. That's 12 bulkheads in total (all with suitable cut-outs, of course)Finally, you may need to glue in a plywood seat back and bottom to transmit twisting loads around the cockpit. The seat-back bulkhead will need holes large enough for access to control cables, etc. but can be cut from remarkably thin plywood.
This is very kind of you to say. Thank you. The proof of the pudding is in the eating, of course, but I'm reasonably confident that this will all work as planned.Finally, a big Thank You for developing a new method for scratch-building airframes. Your new method best utilizes the software and CNC routing skills of the young generation of “hackers” and “makers.” A day or two using CNC tools at their local “maker space” will save them hundreds of hours in their home shop.
You are headed in the right direction.
Hi,An abbreviated, yet useful, test:
Connect three routed struts in a triangle. Connect three conventional solid wood struts of equal volume and lengths. Orient both on a bench and press down from one apex toward the opposite side. Compare the two for strength. Is one more easily broken? How does it break? Where does it break?
The scale of the test triangles should equal the largest triangle of the actual fuselage to be most informative.
Ah... OK. I didn't realize you had a skinned structure. You kept saying "template", which usually means a disposable layout aid, not part of the structure. If you have plywood skin throughout on both sides, that's a lot better.Incorrect. If I were relying only on the end-bonds, you would be correct. But the structural pieces are sandwiched between two pieces on ply. On the inside is the 1.5mm template, and on the outside, a full 3mm sheet. Those structural pieces aren't going anywhere...
Think of it this way: instead of having to cut a million little corner reinforcing blocks and gluing them in place (and good luck with getting the angles to mate perfectly) I simply include them in each structural piece. QED.
I was just trying to point out that your method was similar structurally. Some of ;the others missed that you were skinning both sides.The difference is in (1) precision of fit (2) build time.
Hi,We can no longer keep up with Duncan's build process.
1) Draw frame on Etch-a-Sketch.
2) Pin down & cut Plywood bones.
3) Superglue-Epoxy profile-siding.
4) Post pictures of HBA gloating.
Hi,The HM 14 was a sit in rather than sit on fuse, the one I built was insufficiently stiff in torsion, I had to double the top longerons to stiffen it up. Your sit on flea will have much less torsional strength, with two lifting surfaces at each end and a rudder applying a large torsional force to the fuselage, to my eye the seat area DLAR (doesn’t look about right).