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rtfm

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How on earth is that done? One piece for the top and another for the bottom? With just a glue line holding top and bottom together?
 

TFF

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Memphis, TN
Fabric attachment? Glue and rib stitching or old fashioned needle and thread sewing a sleeve and then rib stitched.
 

rotax618

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Evans Head Australia
An elliptical wing generally requires a laminated bow to give perimeter form the the wing, the ply leading edge is glued to the laminated bow....
7F1B351C-77BE-4731-A66C-BDC777E1BCE1.jpeg
 

rtfm

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Yes, fabric would do it, but I'm covering my wings with 1.5mm plywood. Makes curved surfaces difficult. I could abandon the idea of a single piece of plywood reaching back to the spar, and take a look at two separate pieces (on on top and the other on the bottom, meeting at the LE piece). But that only provides a very small glue area at the LE.

View attachment 109128
An elliptical wing generally requires a laminated bow to give perimeter form the the wing, the ply leading edge is glued to the laminated bow....
View attachment 109133
Ah - got it. Thanks. (PS Nothing like a pen and paper...)
 

Victor Bravo

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rtfm, covering the elliptical wing is EASY. Don't even think twice about it. The easiest way is to sew a simple envelope that exactly matches the curved shape of the wingtip, and slide the "giant sock" over the wing. This takes ten minutes on a sewing machine, and saves three hours of wrestling with the fabric if you used the "blanket method".

Look up videos of covering wings using an "envelope", and you will see it. It's a no-brainer, and the curved wingtip is the perfect situation where you get a big advantage using the envelope method versus the blanket method.
 

rtfm

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Hi,
A number of things...
  1. First, digitally remastering the HM293 fuselage would not be possible. Sure, you could cnc cut the bulkheads, but the rest of the fuselage is made up of 15mm square spruce sticks. There's no way to digitise these without cutting them from 15mm ply (building in the corner reinforcements). Actually, bending the 15mm ply would be a Herculean task, but if one cut three 5mm ply sides, one could bend these over a former, bond them together and they'd form a rather neat airframe.
  2. The comfort of a sit-in fuselage is moot. If that's your thing, then fine. But in Queensland, where the winter day temps rarely get below 20 deg C (about 70 F), and the average summer day temps are in the early 30's (about 90 F) a sit-on fuselage is the way to go.
 

rtfm

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Not all XPS foams are born equal.
I (unthinkingly) followed the online consensus and ordered 10 sheets of 20mm Dow Chemicals Blue foam for my ribs. Then, due to one of my (VERY rare) balls-ups, I went looking for some more (at about $100/sheet, mind). What I did find, however, were quarter sheets of 30mm XPS as stocked by Bunnings hardware store - for $12.90 each. This stuff is chalk and chees when compared with the DOW Blue foam.

For example, I have to cut 25mm holes in the ribs to accommodate the building jigs (25mm stainless pipes). When comparing these cut out plugs, I was astounded to find that the much-vaunted Dow Blue foam was (by comparison with the Hardware store XPS) soft and insubstantial. I could easily crush the blue foam plugs between my thumb and forefinger. Not so the Hardware store XPS. Solid as a rock under the same thumb-pressure. This stuff is HARD...

Dow Chemicals blue foam crush test (very scientific)
1617934969514.png

The hardware store XPS crush test - no perceptible crushing at all...
1617935065188.png
 

rtfm

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Oh - the weight penalty for using the hardware store XPS (bearing in mind that these blanks are 30mm thick compared to the Dow blue foam's 20mm) is all of 12g (less than half an ounce). This is the stuff I'm talking about:
1617935761529.png

Guess what I'm using for the Fleabike ribs?

Oh, and speaking of ribs, I cut the rear wing ribs out this morning (five sheets of Bunnings XPS) - it took me all of 17 minutes.
 

rtfm

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Finally, I spent the rest of the morning making the jig for the wing panels. Each panel is only 1250mm wide (front wing) and 1000mm wide (rear wing). I've built in two aligning holes in each rib so that I can thread the ribs onto 25mm stainless pipes, which will be held in place by the jigs.

Taking a break now, but hopefully I'll be able to post some photos later this afternoon so that you can see what I'm talking about.

Duncan
 

rotax618

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Evans Head Australia
I cover the shell with a single layer of 6gm/m2 glass cloth using 3 coats of water based urethane floor finish, the urethane floor finish has the consistency and appearance of milk, it hardly adds any weight and with the glass cloth gives a hard smooth shell that sticks strongly to the foam. you could double the strength of your ribs if you used the same technique.
 

rotax618

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As for digitizing the HM295, I really should have said re-design and simplify an already simple aircraft.
The fuselage could have a simple rectangular cross-section, it would still require stringers but they could be pre-glued to the CNC’d sides and bottom before bending around the 3 or 4 CNC’d bulkheads. The outer wing panels don’t need to be elliptical they could be trapezoidal with the same span and perhaps a little more area.
The ribs could be CNC’d out of thin ply or foam, the leading edge D could be hot wire cut from foam and light glass covered.
Just an idea - not detracting from your fine effort Duncan, just another way of looking at a the same problem.
 
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