Rainbow Dash, or my first Mach rocket.

Erica · Nov 23, 2016

Hello everyone.

This is my first post on this forum under my proper name, previously I posted on here under JBrocketman, though not very often. My name is Erica Bradley, and I am the TRAR prefect for Reno, an avid flier, and I'm slowly working towards my level three.

Currently I'm examining possible improvements on a rocket that I put up at XPRS 2016. It was designed to be my first mach rocket, and I was putting a lot of things about it on faith, but now I'd like to make some good modifications to it so that it's a better all around rocket, and might actually get past mach 1 this time.

In my only flight of this rocket so far, I got much more altitude than I had anticipated (7600') but only mach .9

On it's first flight, the motor chuffed several times, losing just that extra bit of impulse I needed. Turns out the Aerotech H268-R had trouble with the grains being too tight in the liner, I'll make sure to fix that next time. Check out the flight takeoff picture though! Courtesy of my wife.

So a few things I already plan on doing are:
Carve a boattail out of the aft fiberglass of the rocket to streamline the rear end, replace the kevlar strap with kevlar cord, change the style of the nosecone bulkhead to allow a GPS tracker inside of it, use a dremel to remove some of the extra fiberglass in the motor mount, and maybe shorten it a little more to remove more weight from the body.

I'm also thinking about removing the knurled section of the aft closure of my motor, and shortening the rear of the rocket even more, then making the boattail section remove even more weight and go all the way down to the diameter of the motor.

This was originally a hawk mountain Raptor kit which I've shortened by about a foot, made dual deploy (streamer and x form chute) and made a set screw retention system for the motor, instead of using an aft end retention.

When I have some time I will be adding more detailed pictures of the current state of the rocket, how it's put together now.

Does anyone know whether the Altus Metrum Easymini has an automatic mach delay? It's something I definitely should have checked ahead of time, but I haven't had much luck with the user manual in figuring it out. Another question for rocketeers better than I, with such short fins, is fin flutter a big enough risk that I should thicken my fillets to account for the possibility? I've never hit mach 1 with anything before, and I want to do it right.

Thanks for reading, I look forward to your comments.

Nytrunner · Nov 23, 2016

Out of curiosity, what are you using to form the tube into a boat tail?

Erica · Nov 23, 2016

I would be using a dremel and marked angles to work it down, and then end with a sandpaper scrub down to smooth it out. I work with a dremel constantly since I haven't been able to afford a lathe or drill press yet. Though I'm possibly getting a new job soon so here's hoping!

OverTheTop · Nov 23, 2016

Does anyone know whether the Altus Metrum Easymini has an automatic mach delay?

IIRC the Altus Metrum elecronics uses Kalman filtering in the processing algorithm and is immune to pressure fluctuations around Mach 1 causing problems. As such, "Mach delay" or "Mach lockout" is not needed.

I have personally flown a TeleMega to Mach 1.8 without any problems (and many times to just on Mach 1). The static ports were quite close to the NC as well, which would have presented the baro sensor more challenging data.

Erica · Dec 1, 2016

Okay, so my wife and I just got back from a San Francisco whale watching tour (no whales, lots of seagulls, and insane weather) and recovered from the flu so I can finally start posting things again! First off, here's RD close up:

I was wrong about her size, she's in fact three feet long.

So the portion I'm considering turning into a boat tail is the following, the bit that covers the aft motor closure and has been blackened by the first flight. I would chop that off and shape the section forward of it to slope in towards the motor.

Finally, to show the rockets full construction, I've got it all taken apart.

Description of parts, you can see the booster section, set screw to retain the plugged motor, then the piston and streamer as the drogue, then the altimeter bay (A sled, friction fit with a set screw to retain in the altimeter bay) and the main parachute bay which holds a piston and small x form parachute.

I think the strap style kevlar just takes up too much room, it is strong sure but it doesn't compact well and requires a lot of folding or coiling to keep it out of the way. Thus wanting to replace it with cord style kevlar.

The nosecone is currently empty, and I want to put a GPS chip from Altus Metrum in there, have positive tracking on it that way.

What do you all think? Oh, and in case any of you spotted it, the altimeter bay coupler was in fact too small for the outer body so I wrapped it in a D&D character sheet I wasn't using!

Thank you!