Badland F2 kit

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Victor Bravo

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Fiberglass springs are available. Google fiberglass leaf spring. Also there was a guy named George Sychrovsky who made glass springs for the Hi-Max, which should be very usable for your plane.
 

Peer Ebbighausen

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Thanks Galapoola and VB. That took me down a bit of a rabbit hole!

I found George's website, and may contact him.

In the meantime, I may see if I can find a way to calculate how much "spring" I need (even if I stick with steel), considering the gross weight of the UL.
 

Victor Bravo

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Laying up a flat leaf spring using glass and carbon would not be a particularly difficult process. Bend a sheet of aluminum or plastic to the shape or bend of the spring you want. Take some strips of wood, or foam, or clay and put them on this curved form 1.5 or 2 inches apart. Put a layer of glass in, then fill the trough with carbon strips or rods, then another layer of glass. Let it cure out in the sun inside a black garbage bag for several hours, then take it out of the mold and cut it to final length. Then post-cure it at a little warmer temperature.
 

Peer Ebbighausen

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Not a bad idea...I may give this a shot down the line. It sounds like it could be a fun project. Thanks VB.
 

Victor Bravo

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If Sychrovsky will sell you a pre-made leaf spring that will work, at a price equal or less than three or four hours of your time is worth, then IMHO buy it and move on with building the aircraft.

It's biting off enough to build an airplane form the kit. Adding to that workload by scratchbuilding and designing new components is a whole order of magnitude more, that has the potential to slow you way down.

Ask me how I know this so well.... :mad:
 

robust

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Laying up a flat leaf spring using glass and carbon would not be a particularly difficult process. Bend a sheet of aluminum or plastic to the shape or bend of the spring you want. Take some strips of wood, or foam, or clay and put them on this curved form 1.5 or 2 inches apart. Put a layer of glass in, then fill the trough with carbon strips or rods, then another layer of glass. Let it cure out in the sun inside a black garbage bag for several hours, then take it out of the mold and cut it to final length. Then post-cure it at a little warmer temperature.
It is impossible to make a spring from carbon fiber. Carbon fiber has a high modulus of elasticity and low elongation. Therefore, it has low energy absorption. The largest energy absorption of fiberglass. Only you need to choose the right thickness and width. Poor manufacturing technology will cause fiberglass delamination.
 
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Peer Ebbighausen

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Excellent point, VB. It's likely I will order one from Sychrovsky, and call it a day. I think I've already bitten off enough to keep me busy for a very long time.

I'm slowly fitting bits together, and will post some pics as soon as I get a moment. In spite of being home pretty much 24/7, it's amazing how little free time there seems to be!
 

ScaleBirdsScott

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I feel like if it comes with the steel tail spring its probably best to leave it unless you can validate the change with the designer. At least wait until the thing is done with what the kit includes before swapping things out.

Its possible the steel spring is simply for cost or ease of specification. But isn't it also possibly a W+B issue where an extra bit of weight in a robust tail spring was deemed better than adding an expensive spring that has certain tradeoffs and then a lead weight?
 

Victor Bravo

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Yeah, Scott is right. Don't buy anything yet.

Besides, it will be a while before you need the spring. The airplane may be nose heavy, tail heavy, or perfectly balanced when everything else is done. If you bought a glass spring and it turns out you need weight in the tail, it will have been a waste.

I'm assuming you have good e-mail or text access to Chris Deuel and he is willing to spend XYZ amount of time answering questions. So perhaps you can ask him if it is highly likely you need the heavier spring in the back, or whether he specified the steel spring for any particular reason.
 

Peer Ebbighausen

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I have been chatting with Chris about it, actually. He had ordered a bunch of the composite springs from George and should be receiving them within days.

My (purely speculative) concern with this spring is it has so little flex. Could it (as a result) transfer the shock to the air frame, rather than absorb it, or is this not a valid concern?

At any rate, I'll hold off for now as I work out the landing gear and controls. Thanks!
 

b7gwap

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Per springs: in the words of my college physics professor, “everything is a spring.” Some materials make better springs than others. We should perhaps define what we mean when we call something a spring. Most springs in mechanical terms refer to a device that will deform when stressed and return more or less to its original shape when the stress is removed. Yes there will be some loss of energy (absorption), but generally the duty of reducing the acceleration of the deflection (damping) belongs to a device called a shock absorber (Which can also take many forms). CFRP and GFRP can both make excellent springs at an excellent stiffness to weight. If you also want damping function, neither metal nor composite alone will give you much. But steel and CFRP have very high fatigue strength. (Lots and lots of cycles) Most airplane tailwheel gear function as springs. If you hit the tail hard, it will bounce.
 
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