It was sometime in the summer of ’98 that I thought about really going for high altitude. I’d flown a couple of high altitude single stage rockets to over 10,000 feet and wanted to do something different this time. There were many vehicle options, but few motor choices. After confirming that a 75mm motor would be available, I decided on a narrow diameter two-stage bird that would give maximum altitude.
The rocket was to use Aerotech’s new 75mm L1120 in the booster and another new Aerotech motor, the 54mm K700 in the sustainer. The ‘L’ and the ‘K’ are both "full" motors with a combined total impulse of 7680 N-Sec. The goal was to fly it at Medicine Wheel 4 in Alberta.
The only way to transport this beast by car was to have it in modular sections. This would also ensure easy access to all components during construction and assembly. I chose Loc 3" cardboard tubing for the airframe because it was light and fairly inexpensive. A friend of mine was gracious enough to spend a whole Saturday helping me fiberglass over 11 feet of the airframe tubes. Over 6 layers of epoxy soaked 9.7oz glass cloth were wrapped over the tubing. It was then tightly bound in flagging tape and left to cure. The sanding process was not fun, it involved four sweaty hours with both a random orbit and belt sander. When finished the tubes looked great though and were strong enough to stand on horizontally without any bending.
I was still at the drawing board for other components. After fiddling around with VCP on the computer, I came up with a fin design that allowed for a generous stability margin for both the booster and sustainer. After verifying the center of pressure calculations by hand I started fabricating the fins. I found some thin 1/16" fiberglass sheeting at the industrial plastic store, which was a perfect base for fins. The sheeting was cut into the shape of the fins, covered on each side with 4 layers of fiberglass cloth, and pressed against glass to cure. I then started shopping for the interstage parts. After looking at a few other two-stage projects, I decided to use protruding steel rods in the interstage coupler and hollow aluminum arrow shafts in the sustainer as the receiving tubes. I made the mistake of buying the arrow shafts first, which led to over 3 hours of filing to get the steel rods to slide nicely inside (oops!). The rods and arrow shafts were to be mounted using centering rings - so I made some templates with Autocad to drill holes exactly 120 degrees apart. The steel rods and arrow shafts were epoxied into their respective rings and then glued into the airframe tubing.
After hearing many horror stories about altimeters deploying when passing through Mach, I opted to use timers. I decided on an Adept single channel timer for the booster, and a four channel Adept timer for the upper stage payload. Since the entire rocket was modular, building the payload and electronics sections was fairly easy. Both timers and their batteries were mounted on pieces of plywood with brass tubing glued on the back. They then slid over two ¼" threaded rods in the electronics bays and were fastened down with lock washers and nuts. A coupler with a bulkhead was placed over the eletronics for protection. Deployment charges and eyebolts (for shock chord attachment) were mounted on the bulkhead. Four-strand telephone wire was used through all bulkheads to connect the electronics to the charges. This wire was also run alongside the upper stage’s 54mm motor mount tube to facilitate upper stage ignition.
Everything was coming together nicely, and most aspects of the design had been finalized. It was time to attach the fins. After some generous sanding, the laminated fiberglass fins were tacked to the booster and sustainer using 5-minute epoxy. Large fillets were made on either side of the fins with cold cure epoxy. Once set, the area was again sanded and "wet-out" with epoxy. A piece of glass cloth was cut to size and was laid over one fin, across the body tube and over another fin. The process was repeated twice, and the fins were solidly attached. Many more hours were spent sanding and priming the rocket prior to its inaugural flight.
A project of this size and complexity required constant testing and calculation. The first flight was done in Moses Lake, Washington. The computer predictions called for an altitude of 7,600 feet. The motors of choice were an Aerotech J800 in the booster and an I211 in the sustainer. These motors would reasonably test the launch vehicle and launch tower as well as the electronics and timing of events. We left Vancouver at 4am and arrived in Moses Lake around noon. I spent the next five hours prepping the bird while a couple of friends and my dad set up the launch tower. I was exhausted when everything was finally together and just managed to squeeze in under the wavier deadline. Everyone stayed to watch the flight - the pressure was mounting. The countdown hit zero and the J800 fired up imediately lifting the 10-lb beast skyward. A couple of seconds passed and the charge in the interstage coupler fired, seperating the sustainer. From our vantagepoint it looked like the booster actually coasted past the sustainer. "Come on, any time now!" Nothing, no I211 ignition. By this time the sustainer had arced over and was coming in ballistic. There was a 20 second delay on the two drogue chutes. I had my fingers crossed. The upper stage was approx 200 feet above ground when both drogues emerged from the mid-section and promptly shredded. That was to be expected, as they were flimsy Loc chutes with shroud lines tacked to the canopy edge. However they did manage to prevent serious damage to the sustainer. It suffered a small crack in one fin, which was easily repaired. The booster came down without a scratch. Post-flight analysis revealed that the sustainer ignitor had fired, but not lit the I211. Prior to the flight it was suggested that I use fast-thermalite with my electric match to light the I211. The problem wasn’t a big concern, as I knew I could make a beefier ignitor with slow- thermalite for the next flight.
With less than one month prior to the Medicine Wheel 4, it was the final stretch. The fin was repaired and the rocket was given a black finishing coat and some stripes. I ran many different timing sequences through the computer for upper stage ignition and chute deployments. I purchased new parachutes from Trajectory Hobby Supply in Manitoba. They were custom made and shipped to my door very quickly. I received my Dr. Rocket 75mm and 54mm hardware from HPRT in Edmonton. I purchased over 80 feet of 1" tubular nylon for shock chord. All the components were assembled and packed into the vehicle. The fit was tight, but manageable. All systems were go. The computer predicted an altitude around 20,000 feet and a top speed of 1200 mph!
The end of May rolled around quickly. A friend of mine, John and myself drove through the night from Vancouver to Medicine Hat. We then drove back to Calgary to pick up my dad, who flew in from Vancouver. After a short five hour sleep we made our way to the Suffield base and attended the launch briefing. The Saturday weather did not look promising. Once at the site, it didn’t take long to realize that we weren’t going to get a chance to fly that day with the low cloud ceiling. The launch tower was set up and placed in the field with the far pads. We were all pretty dissapointed, as we had to head back to Vancouver by noon on Sunday. We arose Sunday to promising skies. There were a few blue patches out there. Once at the launch site we knew this was our chance. It took a mere two hours to get the beast flight ready and get it in the tower, thanks to the help of many people.
We placed a video camera on a tripod around 30 feet from the launch tower to capture the liftoff. A gracious spectator volunteered to follow the flight with another camera. As the countdown commenced, the moment of truth drew near. The button was pushed and the L1120 roared to life. The bird left the tower very quickly, much faster than I expected. The L shut down and the K700 fired up, sending the upper stage screaming straight as an arrow into a patch of blue sky. Unfortunately the blue patch of sky was bordered by a puffy white cloud, which made the sustainer hard to track. Meanwhile, the booster was on its way back to earth and touched down just behind the car line. There was still no sign of the sustainer. The sustainer drouge x-form chute deployed at 33 seconds from liftoff, and the main chute was to deploy at the 5minute 20second mark. John had his watch timer counting down so we would know when to watch for the ejection puff. The next several minutes were tense to say the least. No one had a track on the sustainer, and we were all looking in the same direction under the clouds. Just before John’s timer hit the 5minute 20second mark, he said to me "We’re all looking the same way, it could be coming down in the opposite direction". As soon as he said it I looked back towards the pads and the sustainer was floating down in the blue patch of sky. The watch timer went off and we saw a puff from the payload section. The nose cone popped off but the main chute failed to deploy - probably because it was packed so tightly in the cramped space. The touchdown was less than 300 feet from the pads. It was too bad that I didn’t have the extra money for an altimeter so we could confirm that the rocket set a Canadian High Power altitude record. With such a straight flight it must have come pretty darn close to the 20k-foot prediction - but we’ll never really know.
The vehicle was pretty toasty when it came back, but nothing I didn’t expect. Part way through construction I realized which components would cause minor problems, but that was okay because I could only afford to fly it once! The one abnormality that occurred was the ejection of the booster motor casing. Post-flight revealed that the radiant heat from the L motor melted through the 1/16" steel music wire that was retaining the motor casing. Because of its enormity, the motor case was easily found in the field.
The most enjoyable part of this project was overcoming the hurdles. Solving the engineering problems was truly rewarding in the end, and I have gained valuable insight for subsequent projects. Hopefully I’ve provided others with some interesting information, and with hope. Go for it - anything is possible.
Without many people this project would never have flown. Thanks to Don Rolls, my old high school shop teacher for the limitless use of everything from the metal lathe to the belt sander. Thanks to my dad for all the great pictures, and letting me put 3600 Km’s on his car in a single weekend. Thanks to Vince for making sure we lifted off into that little patch of blue.
Cheers,