aluminum tube strap design/construction techniques

[Michael Miles]

Hi folks:

Anybody here with experience using aluminum tube strap ultralight design/construction techniques as in the green eagle ppg (http://www.greeneagleppg.com/models/)? I'm hoping to use similar techniques with a powered parachute frame I've developing and would appreciate pointers as I progress.

My first question would be about the material for the strap (the tubing is 6061). How is it formed and can it be done with hand tools?

Thanks, Michael

[rdbenterprise]

Hi folks:

Anybody here with experience using aluminum tube strap ultralight design/construction techniques as in the green eagle ppg (http://www.greeneagleppg.com/models/)? I'm hoping to use similar techniques with a powered parachute frame I've developing and would appreciate pointers as I progress.

My first question would be about the material for the strap (the tubing is 6061). How is it formed and can it be done with hand tools?

Thanks, Michael

2024 is used for the strap portion in this type of construction. It is softer, and can be bent and formed without brittleness developing.

[Dana]

2024 is used for the strap portion in this type of construction. It is softer, and can be bent and formed without brittleness developing.

Uh, no... in most tempers 2024 is considerably harder and stronger than 6061.

[Bill Berson]

The video shows Velcro strap construction: https://m.youtube.com/watch?v=O7LNAPTiGfg

[Michael Miles]

Thanks for replies folks. Bill, I'm talking about the aluminum brackets that are used to hold together the frame parts, not the velcro for the prop guard. You can see them as black (mostly) u-shaped bands in these pictures holding the green tubes together: https://www.picclickimg.com/10/!B0h1Lpg!2k~$(KGrHqYOKjoE)NLnO2uoBM,t,h(G)!~~_1.JP G?set_id=880000500F

https://www.planetppg.com/pagepics/Green_Eagle/GE_PICT0089web.jpg

They are obviously flat aluminum bent in a U-shape; question is how are they bent, with what techniques and tools?

Michael

[Bill Berson]

Just make a small press form with 12" scrap two by fours about 1" apart (screwed down to plywood) on the floor.
With a 24"X 1" pipe just step on the pipe and press the strap into the slot. Might need a 7/8" pipe or other size for spring back, just experiment.

[Michael Miles]

OK, so you're basically saying the flat strap can be bent into a U-shape without compromising the structural integrity of the aluminum?

[Bill Berson]

OK, so you're basically saying the flat strap can be bent into a U-shape without compromising the structural integrity of the aluminum?
Yes.
Look up the bend radius allowed for the particular alloy. Aircraft Spruce has this info in the catalog.
It will give the bend radius allowed for the thickness. For example, it might require a radius two times the sheet thickness for alloy 2024-t3. Check for cracks on the edge after bending with a 10X magnifying glass.

[Michael Miles]

Thanks Bill - I found the Aircraft Spruce info here: https://www.aircraftspruce.com/catalog/mepages/aluminfo.php

Would using stainless steel straps be an option too? Much more resilient and probably easier to bend. Part of the design is the energy absorbtion during a crash (twisting and absorbing before failure). I think the nominal frame tube diameter is 1-5/8 inch with 1/8 inch walls.

[Bill Berson]

Aluminum is easier to bend, drill, etc. Straps are pretty good at twisting without breaking no matter what the material.
No need to use something stronger than needed. Do some sample twist tests to destruction, if desired.