Ahtreb

[DynaSoar]

Outside, this bird is hardly suprising. It's essentially a Big Bertha clone. It has a slightly different nose is all. The lack of a visible nose/body joint isn't a fault of the photo or technique in hiding joint lines. There isn't one. As always, that's a 1/2 meter T-square for scale.

 

[wwattles]

You've got a motor hook, so obviously you're not using rear-ejection. So how are you slowing the descent of this little gem?

WW

 

[DynaSoar]

This is the Ahtreb (Bertha backwards, for now obvious reasons) in recovery configuration.

The engine mount is a piston that runs the full length of the body and slides on coupler tube guides. The parachute (18" mylar) is centered on the engine/piston tube, held against the aft piston guide with a centering ring, and the shrouds looped through a centering ring inside the forward piston guide. A slice of coupler tube is glued inside the main body in such a way as to (1) act as an engine block by keeping the mount from sliding forward and (2) preventing the forward guide from ejecting all the way out of the body. Obviously the order of assembly had to be worked out carefully.

Packing the chute is a lot easier than it looks. A piece of paper is wrapped around the chute/shrouds, the piston is pushed halfway in, and the paper is allowed to unroll and pulled out.

 

[Fore Check]

Neat! I hope it works according to plan!

 

[DynaSoar]

Originally posted by Fore Check
Neat! I hope it works according to plan!

Nose first recovery ("prang" to the Brit crew) isn't new, but doing it on purpose isn't normal. The body does pop off fairly easily if I blow into the engine tube.

Weather ghods willing, as they haven't been for some time, I'll try it at CATO next weekend, along with the Lamp. I'm betting this thing won't drift far.

 

[fehskens]

Very clever design. Are you doing anything to vent the ejection gases when the recovery piston is fully extended? If you don't you may discover that the ejection gases will make thrir own vent.

len.

 

[DynaSoar]

Originally posted by fehskens
Very clever design. Are you doing anything to vent the ejection gases when the recovery piston is fully extended? If you don't you may discover that the ejection gases will make their own vent.

len.

As the famed philosopher Simpson said, "D'oh!"

I'd thought about vents, but only in terms of expansion due to the piston coming aft. Since the main tube became open aft at that point, I decided it wasn't necessary.

I just got out the drill and put a hole through the tube wall, through the top end of the lug to keep it somewhat hidden. Hopefully it's big enough to vent enough gas to prevent a self-venting event, but not so large as to let in enough air pressure during boost that it blows the ejection tube.

Thanks Len!

 

[DynaSoar]

Originally posted by DynaSoar
As the famed philosopher Simpson said, "D'oh!"

I'd thought about vents, but only in terms of expansion due to the piston coming aft. Since the main tube became open aft at that point, I decided it wasn't necessary.

I just got out the drill and put a hole through the tube wall, through the top end of the lug to keep it somewhat hidden. Hopefully it's big enough to vent enough gas to prevent a self-venting event, but not so large as to let in enough air pressure during boost that it blows the ejection tube.

Thanks Len!

Here it is just starting to do its business.