Astron Sprite question

Ok, well, I don't know what happened to the first post, but that seems to be entirely gone now. So I'll repost my question:

Why is the the ejection gas port on the Astron Sprite below the top of the engine hook? It seems like the motor case would block the port and prevent it from working, unless there's something I'm missing. Was the fit of the Series III engine into a BT30 tube loose enough that it allowed enough flow past? It seems like a neat design, but this is the case, without the original tube size or intended motors available the design would have to be modified to build now. I'd actually like to downscale it to a BT5 and use a mini engine, and the ring tail could be a BT60.

By this, I'm referring to the original Sprite from the '60s, not the modified version that came later that used the mini engine instead of the Series III. I'm trying to discern how the original design was intended to work.

I believe the motor casing was supposed to slide back on ejection, and be caught by the long hook to make the rocket tumble. The port is where it's at to vent the ejection after the motor moves back a bit to prevent it from shooting right out of the rocket.

The original Astron Sprite used Series III motors, which were an inch shorter than a conventional 18 mm motor. And yes, the motor slides out the back and is retained by the extended motor hook for "tumble" recovery.

I've flown mine on a mini in an Estes adapter casing.

OK, that makes sense. I was picturing it using a suitably shortened hook (like for a mini engine), and thus the engine was in a fixed location. This makes more sense. So, one could potentially still achieve the same effect with a mini engine on a BT5 size tube, using the 2.75" hook. Or, for that matter, upscaled to BT50 with a C11/D12 using an 3.75" hook... Thanks.

There are some very nice examples of originals and upscales in the gallery.

https://www.rocketryforum.com/showthread.php?15652-Estes-(Astron)-Sprite-Gallery

Nice instructions and rationalization here:

https://www.spacemodeling.org/jimz/estes/k-15.pdf

It's pretty amazing; the difference between the Estes instructions of old and the ones today.

kjohnson said:

The port is where it's at to vent the ejection after the motor moves back a bit to prevent it from shooting right out of the rocket.

Click to expand...

That's why the hole is there!
The same with the Scout, the ejection charge gasses have to exit out somewhere.
Years back it did have a Sprite where the engine did eject and didn't get stopped by the standard flat engine hook.
The Scout engine hook was thicker round wire with a longer bent end on the low (engine stop) side.

EXPjawa said:

So, one could potentially still achieve the same effect with a mini engine on a BT5 size tube, using the 2.75" hook.

Click to expand...

If you look at the Fliskits Tumbleweed you will see that it is basically exactly that..

BobH48 said:

If you look at the Fliskits Tumbleweed you will see that it is basically exactly that..

Click to expand...

thanks for pointing that out, I didn't realize that was available.

One thing that helped the old Astron Sprite work was that the original Series III "Short" engines had really heavy casings, so that there was a substantial weight shift backwards at ejection. One trick to replicate that is to use a sawed off expended standard (18 mm) casing as your adapter. Just cut 1" off the nozzle end of the expended casing, leaving a 1 3/4" long adapter. The mini engine will fit tightly as is. If it's too tight, unpeel a little paper from inside the dead casing, and if it's too loose, add masking tape to the live mini engine. The engine hook was 2 3/4" long, so you can use a standard engine hook, but it needs to be bent substantially inward to retain the engine at ejection. I'm embarrassed to admit I haven't bouth an Estes kit in kinda some years, but I recall the hooks have extra metal for a sort of "handle" at the end, and you may have to clip that off, or down, anyway, to match the original.

The Estes hook now have the thumb tab, but most of the other ones on the market do not. Either way, it isn't really a problem. What I was thinking was cutting down a plastic 13-18mm motor adapter to house a mini engine. But using an 18mm motor case might be better, since its one piece. No risk of it popping apart during transition or hooking properly.

EXPjawa said:

But using an 18mm motor case might be better, since its one piece. No risk of it popping apart during transition or hooking properly.

Click to expand...

I've made shorty engines like this quite a few times, for flying in Sprite and Firefly clones, works great! Semroc used to sell shorty casings for this too. The FlisKits tumbleweed is a nice little kit too, with laser-cut fins. I've flown it on an A3-4T and recovered - they key is bright alternating colors, so it can be seen tumbling. Don't take your eyes off it!