Launch Test 107

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I wanted to do a test of my new launch rail before the Prelude Rocket flight next month. Just to make sure there aren't any unforeseen problems. So I broke out the old rebuilt fiberglass rocket for another flight. I used the electronics module from the Cosmo 2 rocket, as it had both my home brew altimeter and a back up timer in it. This flight is going to use a very light propellant load, so a single parachute will be used for recovery. I had to sort of cram the larger main chute in the piston below the nose cone, the area was designed to hold a smaller drogue, I sure hope the chute doesn't get stuck in there!

The flight has a predicted apogee of only 1,126'. I really wanted to use an erythritol propellant load, but I would have had to make a very long, thin web grain due to the slow burn rate of KN/ER propellant. So I opted to use standard KNO3 and sugar. It's been so long since I cast some regular KN/SU I almost forgot what it was like. I'm glad I found the propylene glycol to thin the propellant, after it was melted it was so much thicker than the KN/ER propellant. But the propylene glycol thinned it out to a reasonable level.

The rocket had to sit for over a week, the weather has been terrible, wet and rainy, then cold and windy. Finally a decent day to fly. So I loaded the motor in the rocket, hooked up my trailer and headed out to the launch site.

Here's the new launch rail mounted on a trailer. I had the old boat trailer and no longer a boat. So I built a small deck on the trailer. The launch rail is mounted to the trailer bed with hinges so it folds down for transport and to load a rocket. When tipped up I have two turn buckles to hold the rail in place.

I was a little closer than I should have been here, so I sort of half hid behind the van for some protection. Once everything was ready, all clear, then the countdown. 5,4,3,2,1 and ignition! In the picture above the rocket nose is about to leave the top of the rail.

And away we go! I didn't notice anything unusual about the liftoff. The rocket seemed to jump right off the tower into a nice straight flight.

It was a low enough flight that I could watch the rocket all the way to apogee, just after the rocket arched over and started to go nose down the home brew altimeter fired the deployment charge, and out came the chute.

Here you can see the UFO that dropped by to watch the launch. OK, so it's only a sun flare in the camera lens, but it looks cool.

And here's the rocket after another safe landing. My, this rocket has seen a lot of flights.

Once home I downloaded the altimeter data into my PC. The data indicated an apogee of 2,009', that's significantly higher than expected. First of all I forgot to trim my propellant grains, I had intended to use only .8 pounds of propellant, and I used nearly 1 pound instead. I should have looked at my notes before I loaded the motor, but it really didn't matter. So I ran the new numbers into my flight simulation software, using an Isp of 125, and the altitude at apogee, I ended up with a Cd of about .61 for the rocket. That's not too bad for a crusty old bird like this. I'm sure the Cd would have been over .7 had I used launch lugs.

Once home I washed off the trailer and the launch rail. I was a bit worried about how much damage the exhaust would cause at liftoff. As it turns out, there was only about a 3 inch area directly under the nozzle where the paint was blistered off. I think I'll tack some sheet metal in that spot to help reduce wear. I'm more comfortable launching the Prelude from the rail now. I really wanted to get a launch under my belt before launching a large rocket from the rail. Mission accomplished, next launch will be the Prelude.