Almost a blog post

Rocketdork · Post by **Rocketdork** » Tue Sep 12, 2006 9:06 am

This is just too interesting (to me) not to share...its almost blog material, but I wanted to post it here too...

I guess you all know that I am "into" rockets, some of you may not know that I also make my own motors. Last weekend I tested one of the motors I made...the test was good. This time we tested a 6 grain 75mm motor. The same formula as the stuff we have done before. A graph of the data is in the link. Thrust is in Newtons (4.45N per pound force) Max thrust was 635 lbs force.

Just a couple of observations from the data. Big spike in pressure and thrust in the middle of the burn. I am speculating that this is due to a void in the grain. Density numbers from the casting sessions have been good. Around 95% of theoretical range.

A bit of erosive burning at the beginning of the burn. I may just leave this in, but I may not. If i decide to take it out, I'll increase the core a 1/16th of an inch, that should resolve that.

Pressures are a bit higher than I want, so I'll increase the nozzle throat a bit and run a bit lower KN.

I got better than expected ISP for this burn. Bigger motors tend to have better ISP numbers, but this is higher than I would attribute to that. I suspect that my load cell calibration was a bit off. All of my test equipment is hand built by me. The load cell and load cell amp are custom pieces that I made. I am still perfecting the amp circuit.

I've got a movie of the firing, but its in .mov format, and I can't edit it right now. I may be able to get it done in the next few days, but I don't know for sure.

This static firing is in preperation for BALLS this year. Our little group of 4 people will be flying this and other motors at the event. I plan a commercial 2 grain 75mm motor (AMW L700), a 2 grain 75mm of my own formula, a 3 or 4 grain 75mm of my own formula.

One of my friend plan a commercial "M" motor for a certification flight on Friday, followed by a 5 grain 75mm of my formula if the cert is successful.

Another friend plans a two stage flight of a 6 grain 75mm in the booster, 5 grain 75mm in the sustainer for around 25K ft. Several 54mm flights (4 grain and 7 grain)

The other friend is planning several hybrid flights, including a 2 stage hybrid flight. His motor is unique and is patent pending! They come in around the large J to small K in total impulse.

Can't wait to get down there and fly. There should be some amazing stuff. One of the guys I know is planning a "Q" class flight. The motor is amazing...Total impulse 133000 NS, max thrust about 5200 Lbs burn time of 7.5 seconds...average impulse is 17500 N.

baldy · Post by **baldy** » Tue Sep 12, 2006 11:01 am

eeeerm, what he said

Post by **bio** » Tue Sep 12, 2006 11:22 am

This is what happens when many of the forum users are engineers

Post by **miftah** » Tue Sep 12, 2006 5:12 pm

I really want to understand this. Just like I wish people understood some of the cool things I do with AfterEffects. Unfortunately most genius goes unnoticed.

Rocketdork · Post by **Rocketdork** » Tue Sep 12, 2006 6:26 pm

so ask questions...

I don't even know what AfterEffects is, or what it does...

mudflap · Post by **mudflap** » Tue Sep 12, 2006 7:52 pm

I like pie.

Deater · Post by **Deater** » Tue Sep 12, 2006 9:56 pm

mmmm ya, French silk pie.