F A S T E R , L O U D E R , A N D M U C H M O R E D A N G E R O U S ~ P A R T O N E
Q: What sort of propulsion do you use, and how did you decide on it?
A: We use a hybrid rocket motor system. The system uses normal asphalt roofing tar as fuel,(it's easy to melt and pour the fuel grains)and nitrous oxide as an oxidizer. An igniter and a small piece of an Estes model rocket engine (or other slow-burning ignitables such as sparklers) is placed in the forward end of the motor. When the flammable material is ignited, a valve is opened about a second later, which allows the nitrous oxide to be injected into the rocket motor. This causes the normally hard-to-burn tar to burn at temperatures up to 3000 degrees farenheit; that's when the fun begins.
We chose this system because the hybrid motor can be stopped simply by closing the oxidizer valve, a handy feature if you see your rocket bike racing towards a brick wall or something else you do not want to hit. This motor system we used many times on the rocket canoe, and I felt it was safe enough to sit on top of. We have never seen this system fail catastrophically. The worst thing that has happened is nozzle failure, and this just shoots out sparks. A hybrid motor can also be throttled.
A lot of manned projects used the decomposition of hydrogen peroxide to make thrust. This just makes steam and no flame, which is kinda dull, if you ask me. I like the fire and the smoke. To me, that's what rockets are all about.
Q: That's what I call hard-core attitude! Does it make a lot of noise, too?
A: The rocket motor we used makes a very loud hissing noise. We are never running at optimum conditions because the temperature of the nitrous varies, which causes the feed pressure to vary; this is a pressure fed system, nitrous oxide being its own pressurant. It always seemed to me, because of this, that every motor firing sounded a little different, like the motor had a short and violent life of its own. We are firing motors in very primitive field conditions. I have heard some hybrids with minor combustion instabilities sound like a very
loud and angry frog croaking or sorta like the big electric gatling guns used on A-10 tank killers. This is not what you want, but it sure sounds cool- good enough for exibition stuff.
Q: I presume that the rocket motor is machined stainless steel. Aside from that, this would seem to be a pretty cheap form of manned rocketry. About how much did it cost to get your bike up and firing?
A: Here is where you might call the guys with the white jackets- it was schedule-80 gas pipe for the engine on your cover. Here in Memphis, we are really working out of the garbage can, we will probably not run that system again because it has received criticism from those that are rightly concerned about safety. This was our test boiler-plate motor from Rocket Propulsion of Memphis Hybrid Motor Test Program. Currently we (Tim Pickens, Mark Wells, G. May) are working on a new motor that has 160 pounds of thrust, 60 pounds more than the one you have seen , that has all stainless steel components. It will also look better.
The second part of the question about cost, I am not sure- probably 20 dollars for the motor, maybe 200 dollars in the valves, hoses, and switches, which were aerospace surplus from NASA auctions.
Q: You're getting a hundred pounds of thrust out of a $20 gas pipe motor and $200 worth of surplus plumbing and electrical bits? That's amazing! What kind of power curve does the current motor deliver, and how fast do you expect the bike to go with 60 more pounds of thrust?
A: The thrust curve is almost neutral, the thrust varies little with a single-port fuel grain. As to how fast it will go, it went about 30 mph in three seconds on the hundred- pound motor. We will have to watch our speed on this one. We are also making a throttle valve, basically a ball valve controlled by a linkage.
Q: Zero to 30 in 3 seconds is pretty impressive! Is 3 seconds the actual burn time, or is 30 MPH the top speed at maximum thrust, with a longer actual burn time?
A: Three seconds was pretty close to the burn time. We had plenty of fuel left, the run was limited to our small nitrous tanks on the bike, I believe they were 900 cc each and we had two of them. The rocket bike has been disassembled to use some of the components for the new and more powerful bike. We have a much larger nitrous tank and bigger motor. I am real excited about the new bike. I must give Tim Pickens most of the
credit for making the boy's dream of a rocket powered bicycle a reality. I wanted to do it, he wanted to build and design, and I wanted to be first to ride it. Tim and I have made a good team of two, we don't argue much, we naturally want to do things the same way. Tim takes a common-sense approach to rocket motors-design for overkill: build a powerful motor, build it rugged, build it simple, and make it easy to work on, kinda like the Russians. We are just getting started; the rocket bike is only the beginning.
Q: I like the Russian comparison; it's pretty tough to beat simple, sturdy, and cheap. In your pages about Tim Pickens' projects, you have a photo of him with a rocketbike he built. It looks fairly similar to yours except his had an acrylic/nitrous hybrid motor. Was the decision to use roofing tar as fuel for your rocketbike based on his experience with the other fuel, and that tar is a superior fuel; or is it just that tar's cheaper? And what form was his acrylic in? I envision a length of plexiglas tubing when I hear the word.
A: Asphalt is a cheap and easy hybrid fuel, and a good performer for the cost. The acrylic fuel is kinda pricey and has to be machined. I have heard of people using a roll of salami as a fuel grain, but it is probably a poor performer.
The rocketbike in the photo with Tim is the same bike, the only difference is, it had the low-powered acrylic-nitrous motor. We took this motor off and put the asphalt motor on and all the plumbing and valves remained the same. Basically Tim and I put that bike together in a weekend, Tim already had most everything we needed laying around including the motor. The acrylic fuel grain, basically, is a rod of solid acrylic with a hole drilled thru the center to allow a surface for combustion.
As for how far the bike went in 3 seconds, I can't tell you because I don't remember, I just remember it was a rush. We do have the run on video, I need to make copies of it, everyone we have showed it to has got a kick out of it.(Sometimes I get told I am a candidate for the Darwin awards).
Q: Would you run us through the pre-ignition sequence of a rocketbike run, and then describe the experience following ignition?
A: The oxidizer tanks are filled with nitrous oxide until a white fog appears from the vent valves, then the valves are closed. The ignitor wires are tied together to prevent accidental ignition. Once the rider is in position he unties the ignitor wires and hooks them to the electric ignition system, which on this bike had a button on the left handle bar. The rider is ready to go, and is sitting on top of a motor most everyone else would hide behind a bunker from (probably wisely). The rider pedals just a few times to get a little stability before the motor lights(we will do standing starts when I get more practice) then the rider pushes the button to ignite the ignition charge, then a split second later pushes the button on the right handlebar that electrically opens a valve, then you're off. You kind of get the feeling you are a jet plane on a runway fixing to fly.
Q: You've mentioned that you find nitrous hybrid rockets much more amusing than Hydrogen Peroxide rockets, which only emit steam, with no spectacular flames. Aside from that, what do you think of the performance of the N202 rockets, as used by ETE, the Swiss guys, on their bike? They claim something like 200 KPH.
A: The Swiss guys have got it going on-they are hardcore- really are kicking our butts (us Americans) when it comes to these type of manned rocket projects, we used to do a lot back in the sixties and seventies-Blue
Flame, Spirit of America, all kinds of exhibition dragsters, now we have almost nothing that is pushing men with rocket motors except a government boondoggle space shuttle, and a few amateur projects who are working out of the garbage can. The X-Prize is at least about six years old now, and none of the contestants have really done much except build pretty webpages. I am wondering what happened to "The Rocket's Red Glare" that America once had, are we now scared of things that make fire and smoke and offend the peace and quiet of lazy days? I am doing what I can, but I am not doing enough. I salute the Swiss.
Q: At least the E-mail link on your site works. If ETE's ever starts working, we'll interview them 8-). It's good that you're applying rocketry to the bicycle format. People, especially kids, can really relate to the concept of a rocket-propelled bike. The trick in this, as in most cases, is to expose as many people as possible to the sight of a rocketbike blasting off. The post-WWI barnstorming pilots performed that role in increasing aviation consciousness in the American public. By the time WWII came along, the US had a highly-developed aviation infrastructure in place, because aviation had been deeply popularized here.
BR&K is working toward the formation of an international sanctioning body, the IBRKA. It would promote the creation of local kustom bicycle shows and associated 1/8th-mile bike drag races. There would be many benefits to this, as outlined in theIBRKA Manifesto. I think rocket bike runs would be a terrific conclusion to that sort of event. It would seem, based upon your experience, that it's feasible that rocket propulsion might be added to the classes. Simple and cheap rocket motors readily fall into our concept of ideal bike drag racing. Is it realistic to envision a rocket bike event on a street in front of a suburban school? Is it possible for high school kids to get into this, especially if a kit of components could be bought? Or, do you think rocket biking is inherently too hazardous to the audience and riders for runs in that sort of setting?
A: This question is the toughest for me to answer.
I have been building and firing hybrid rocket motors for about four years now. It took me 3 years to get comfortable enough to test fire them without standing behind a barrier. I still stand behind a barrier if I don't plan on riding on what it's pushing against. So far, I have only seen one get real ugly, and that was a flight-weight hybrid, not the boilerplate- type motors we are using for bikes and canoes.
I believe a rocketbike event could be done with minimum risk. There is however, always a risk. I would also like to add that it is acceptable or people would not do it, to get hurt playing high school football, and I know there has to be some High School kid killed(probably more than one each year) playing football. I like football too, but I have no illusions about it. When I played in the fifth and sixth grade that was some of the most fun I had as a kid. But I was little and knew my physics, when I got older and weighed more so would the other kids and when we clashed it would hurt worse and worse and because we had more inertia when we hit. I was too chicken to continue playing, I could see myself getting hurt, plus I was bored with it, and something of a rebel. I would rather ride wheelies on my bike instead of going to practice
If the high schools would have a good teacher take on the project of building and designing a hybrid motor with the students and the parents were behind it, man I would probably try to impersonate a high school student to be a part of that program. Who knows though, if a motor was tested many times, everyone might be just happy enough to have done that, and might think putting it on a bike is just too scary. If someone got hurt though, lawyers would be all over this. I could not be the one to promote this, even though I think it would be good. There are many students in High School who are lion-hearted but do not play sports; I bet there are many who would have liked to take Dennis Tito's place on his ride into space. Maybe one day there will be rocket clubs in schools that will not be using Estes motors. It was a dream I had long ago as a student.
Q: You've just completed the first run on the new bike; how did it go?
A: I do not have the numbers on the bike and acceleration, but Phillip May, an engineer friend of mine, said it could go faster than I wanted to go. This bike, we will probably not run much over 50 MPH because it is just not built for it. We will do quick burns with fast acceleration to put on a show. Maybe we will build another bike that could go faster. On the new bike we got only 32 MPH on it the first time out. There are a few restrictions in our plumbing that need to be removed to get the necessary thrust that we calculated. I am patient, it is like running a car at the track: you have to go out a few times to get the bugs out. The effort was kind of rushed. I am glad we went out and did it, even though it was not perfect, I want to stay close to rocket motor firings, and not get scared by it because I stayed away from it too long.
Q: As a grown-up, the idea of sitting on a rocket would be fairly scary to me, also. The natural instinct would be to hide behind something thick and a good distance away. Being aware of the possibilities, and still climbing into the saddle is pretty impressive to us. Thanks a lot for sharing with us, Glen.
Editor's Note: We are extremely sad to have to report that Glen May was killed in an accident at Scaled Composites, Mojave, CA July 27, 2007, while working on the SpaceShipTwo project. Glen was a fine person, a dedicated rocketeer, and a good friend of BikeRod&Kustom. He will be missed greatly by his friends and family. Our eulogy to Glen may be found here.