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You may wonder why I would go for an altitude attempt for the first flight using xylitol based propellant. That's easy, xylitol based propellant lends itself much better to a longer, larger motor. The propellant is slow burning with a good Isp, but to get adequate thrust a fairly long motor is required.
The rocket electronics consists of a homemade altimeter with a homemade timer as back up for apogee deployment. An FRS radio for crude data transmission and RDF location after landing, and a personal alarm used as a sonic locator to aid in locating the landed rocket. Recovery consists of a 29" drogue and an 80" main chute, both deployed from the upper body tube by means of a PIRM2.
If you read the Cosmo 2 page, I mentioned the inhibitor layer had disbonded in some areas. I did cast a new set of grains, but they really should have a few more days to cure. So I went through the grains and applied epoxy to areas that had problems. The area of the grains that did show problems was small, maybe 5% of the surface area, and that was only on about 4 or 5 of the 8 grains. So I doubt if that would have created a problem anyway, but I felt better about using these grains after I had applied the epoxy to them.
I spent a lot of time on this project, I guess that's true of any scratch built rocket and motor, then throw in scratch built electronics and the time increases even more. With that in mind, I look at the odds of a successful flight. There are really only two outcomes; 1) A successful flight, defined as a rocket that is recovered in flight worthy condition. 2) An unsuccessful flight, defined as a lost, damaged or destroyed rocket.
A few thing I like to do to increase the odds in my favor:
Here are the pre launch numbers on the rocket:
Propellant Weight: 3.659 pounds
Total Motor Weight: 6.3 pounds
Rocket (no motor) weight: 8.2 pounds
Lift off weight: 14.5 pounds
As it stands software predicts a flight to about 7,500' and a maximum velocity of mach .92. Of course the maximum altitude assumes a totally vertical flight path, no wind and a nice smooth body finish. None of which are likely to occur. (I really need to get some 2 oz. fiberglass cloth as a sanding veil.) So if this flight makes it to 6,500 to 7,000' I'll be happy. As for the speed, that's pretty much a given unless I have a faster than expected burn, in that case the rocket could actually reach mach 1. Regardless, I'll be in the transonic speed range, (transonic is the point where the rocket isn't going mach 1 or greater, but certain surfaces of the rocket have supersonic air flow across them). The transonic region of flight is the most demanding time on a rocket, so this should be a good test of the construction techniques I'm using.
I've been watching the weather forecast with great interest for the past several days. We've been having a lot of rain and weather systems rapidly rolling through as of late. There appears to be a one day hole in the inclement weather, so now I've been watching the wind forecast the last two days, an early morning launch looks promising, I'm set for a dawn launch. T - 8 hours...
Launch Day:
Except for loading the motor the rocket was assembled the night before launch, as I was planning for a dawn launch to minimize wind drift. Bill showed up almost on time and we set out at about 5:30 am for the launch site. There was a heavy dew and the ground was still wet from the previous days rain, but we set up regardless as the sun was rising to clear blue skies and very light wind.
We had the pad set up, the controller and wires ready. I turned on the FRS tracking radio, then turned on the power to the timer and altimeter. Just as I was getting ready to connect the leads to the motor igniter there was a loud pop inside the rocket. I knew right away the PIRM2 charge had fired. So much for a dawn launch. We took the rocket off the launch rail, and loaded it back in my van to head home. There's going to be a great video here, as soon as I take the time upload it. I had set up a second camera on a tripod to record the launch from a different angle, this camera was recording, I forgot all about it. Jumped in the van and headed home, squinting into the rising sun, I drove straight over the video camera. As luck would have it, the camera survived, can't say as much for the tripod though. So it was looking like a real poor start to the day.
Once home I broke down the rocket and tried to find the problem with the altimeter. I spent about 2 hours testing it, and couldn't find the problem. It was working fine again. So I thought, and I thought, then finally it dawned on me. I must have loaded the flight software in without running the read software first. The read software needs to be run to reset the eeprom on the altimeter. So I reassembled the rocket, reloaded the deployment charges and Bill and I headed back up to the launch site. Needless to say the wind had picked up some by now, but it still wasn't too bad. Bill and I reset everything and prepared for launch. Just in the nick of time another friend of mine and his son showed up to see the launch.
All those hours of testing the xylitol propellant, all those hours working on the altimeter, all those hours building the rocket. Everything was now on the line, the next few seconds would tell the story.
Bill was at the launch controller.
All clear. 5,4,3,2,1 and ignition!
Liftoff!
Click here for a must see video of the boost portion of the flight.
Click Here for a slightly longer version in a standard Windows Media File.
And my what a liftoff it was! The rocket blew off the pad like nothing I've ever launched before. It happened so fast, there really wasn't even time to think about it. A few seconds after liftoff I heard the FRS radio transmitting the tones from both the altimeter and the timer. Everything seemed nominal. We all lost sight of the rocket as it coasted to apogee. Then the welcome sound of the apogee deployment was heard through the FRS receiver, then we all saw the puff of smoke high in the sky, then you could see the rocket descending under the drogue. My friend drew my attention away from the descending rocket as a ball of fuzz drifted over our heads, he thought it was one of the parachutes torn from the rocket. It wasn't, but after the fuzz incident we all lost sight of the rocket. I could still hear tones from the transmitter, then the sound of the main deployment could be heard. When the large main chute deployed at 700' we again sighted the rocket, a long way away at this point. In the end the rocket landed some 3/4 mile from the launch site.
The adventure of finding the rocket was now at hand. Radio contact had been lost when the rocket landed, and it had drifted into a rough area where there were no roads for 2 miles. So we circled the area as best we could by road, to no avail. So I set out on foot with two FRS receivers. After about a 1 mile walk, I picked up a faint signal. After another 1/2 mile or more of walking, I decided the rocket had landed in a shallow valley with a creek running through it. After some more cat and mouse work with the FRS radio, I decided the rocket was on the OTHER side of the creek. So I left all my equipment at the bank, and tried forging the creek. When the fast flowing stream reached my neck, I decided to go back.
I could kind of see something just on the other side of the stream, but wasn't certain if it was the rocket.
Here's a picture I took from the wrong side of the stream. Doesn't look like it should be that deep does it? The red arrows are what I thought were the parachutes.
In the mean time Bill was wandering aimlessly somewhere else, as I tried to guide him to my location with my FRS radio. I finally told Bill to head back to the van, pick me up, and we'd make our way from the other side of the stream. So I walked the 1/2 mile back to the road, Bill picked me up and we drove to an access point on the other bank of the stream. Then walked the 1/2 mile back out to where I thought the rocket was.
Low and behold there she was. Not 50' from the water!
I guess I used up all my bad luck earlier in the day. I could just picture the rocket landing in the stream!
As it turns out, the landing was picture perfect. Not a scratch on the rocket. So Bill and I headed back to the van, almost exhausted from over 2 hours of plodding through muddy fields, I was never the less, elated. Perfect boost, perfect deployment, and now the rocket was back safe in my arms.
Once home I downloaded the flight data into my PC. Peak altitude was recorded as 6,621', just about where I expected it.
My first flight of the Cosmo 2 rocket using a xylitol based propellant was a great success. What a day, my was that fun!
The FRS radio played a huge role in locating the rocket after it landed, I doubt I would have found it, or at least it would have taken many more hours of searching without it. The battery life on the FRS was also a concern of mine. As it turned out, the radio continued to transmit for some three hours after launch, until I remembered to turn it off once back home with the rocket, with the batteries still going strong.
The "personal alarm" sonic locator also worked. I could hear it on the ground from over 1 mile up. Unfortunately, the battery life was limited, and when the rocket was found the once loud alarm was only a sparrows chirp.
The only discrepancy I found in the flight was the descent time. Assuming a 29" flat sheet parachute with a descent rate of 52.77 fps, from an altitude of 6,621' to 700' (main deploy), leaves a descent time under drogue of 112.2 seconds. The actual time under the drogue chute was 147 seconds, then assuming the altimeter fired at 40' below apogee, you could take another second off the expected descent time or add another second to the actual descent time. So 148 seconds under the drogue times descent rate of 52.77 fps leaves 7809.9' under drogue plus 700' of main and drogue leaves an altitude of about 8,509' based on descent time. So I'm not sure what to make of that, either the altimeter reported a somewhat lower altitude than the rocket really reached, or the descent rate calculator I used is off a lot. I've run the pressure readings from the altimeter through several different programs and I'm pretty confident of the numbers from the altimeter. So I'm left wondering about the software I'm using for descent rate. Not a big deal but perhaps I should look for some new software or formulas for calculating descent time/rate.