Monday, May 25, 2015

Announcing another single-use rocket

Here is my first build of the year: a 4-stage, 29mm rack rocket that I am calling  the 4-F Club. A 'full load' would be four Estes F15's. I call it single-use because I have a poor track record of recovering small rockets that fly as high as this one will.

The nose is an Apogee PNC, the body is LOC tubing, the spars are basswood and the fins are balsa. Recovery will be via a caution-tape streamer. I have the parts and assembly has begun.

Here is a sim that I ran to check stability. I didn't bother to fake a 4th stage as I mainly wanted to find the cp/cg relationship. I added a mass object to account for the mass of the bottom motor. It should be plenty stable and, as expected, a -8 delay is warranted.

The top two sims have an E16-8 in the sustainer and the next two have an F15. Top and bottom are with no wind and the middle two are with 8-14 mph, which is more in line with my launch site weather.

The only issue I see is the speed off the pad. Estes claims that an F15-0 can lift a 19 oz rocket, based on the initial thrust spike. However, if you use the typical rule of thumb by using the average impulse, then the rocket is way too heavy. The good news is that a TRF user had success with a similar rocket, which weighed an ounce or so less. Still, based on the sims, I think a long rail will be safer that a short 1/4" rod, so I will add buttons.