Welcome everyone. Due to the recent surge in activity on the website I though it would be best to take the time to post a FAQ (frequently asked questions) and try to explain some of the things that we get emails and general questions about. I hope this helps to answer some questions of our site viewers.

Jet Bike FAQ

Q: Why build a jet bike at all?

A: The jet bike was conceived as a way to test the potency of a larger home made jet engine. Since jet engines are reaction type engines, they need long stretches of running room to get up to speed. Some of the original ideas for testing the engine were to mount it on a go-cart, or a small pond fishing boat. While both can be fun, I felt the need for long, smooth running surfaces would be essential. Where better to find such surfaces than Americas highways. Yes, your tax dollar at work will provide some of the testing surfaces of the bike.

Q: What do you mean reaction engine?

A: A jet engine is actually a reaction engine. The thrust produced by the engine works to propel the engine in the opposite direction. This is based on Newton's laws of motion. For every action there is an equal and opposite reaction. To illustrate the principle I will give an example. Imagine you are standing on a skateboard. If you throw a brick behind you, you will roll forward a little. Similar to firing a gun, with the recoil effect. If you were to keep throwing bricks, you would slowly accelerate. Throw bricks faster and you will accelerate faster. Since the real purpose of the jet engine is to move vast quantities of air, the effect is the same. Air has mass, therefore it has weight. The weight of air per cubic foot is .07608 pounds at 62 degrees Fahrenheit and 14.7 PSI (atmospheric pressure). Simply said, throw enough air, and you will be throwing a substantial weight. You will get a reaction. Don't believe me? Look up in the sky. See those airplanes? They believe me!

Q: What will the top speed of the bike be?

A: The top speed of the bike is theoretically limitless. Note that I said theoretically. Reaction engines will continue to accelerate indefinitely while they are being operated. We do live in the real world though. (OK, some of us do anyway!) In the real world, there are factors acting against the bike that will limit its top speed. These factors include weight of the bike and the weight it is carrying, rolling resistance, road resistance, and air resistance.

The weight of the bike and its contents will have an effect from gravity that holds it to the ground. They also have the effect that the objects will want to stay in the current state of motion. As you know, it is hard to push a car by hand from a stopped position. It can be done however, and once the car is rolling it is easier to keep it rolling. Say hello to Mr. Newton again! He said Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. That means objects in motion want to stay in motion, and objects at rest want to stay at rest. Since another of Mr. Newton's laws says that F=ma (F=force, m=mass, a=acceleration which works out to 'Force = mass x acceleration' for all of those who did not pay attention in school. You know who you are!) we can work out that the jet bike will accelerate at an exponential rate. Once moving, it will be easier to keep the bike moving. It will also be easier to accelerate it to a faster speed. Since the actions are continually taking place, the bike will be propelled faster, the faster it goes. To give an example that may put this in to perspective I offer the following, though it is not based on any actual testing. Lets say that the finished bike (remember this is hypothetical!) takes 20 feet to achieve a speed of 5 mph (miles per hour) from a stopped position. The bike would then reach a speed of 10 mph in the next 10 feet, and 20 mph in the next 5 feet. Although these numbers are not real world numbers, they do serve to illustrate the point.

Remember as I said before, these calculations rely on real world conditions. In our world there are factors which greatly affect the movement of any object. The primary force we are concerned with is friction. Friction is a resistance to motion caused by contact with a surface. (It can also be the resistance of a wife who says you have spent too much on the jet bike this month!) It is everywhere and acts on the bike in ways that are not apparent at first. The friction in the wheel bearings, or rolling resistance, of the bike will slow things down a bit, although not much at all. The main problems will be the air resistance and the road resistance. The air, as we learned earlier, has mass. Because of this we have to cut through the air efficiently. This is why I chose to use the bike with its aerodynamic plastic body panels or fairings. These will allow the air to slide around the bike more smoothly and will cut down on the air resistance. The road resistance will be the friction between the tires and the road surface. A larger tire has more surface in contact with the road at any given time and will therefore have more resistance. As the tires want to grip the road, they also do not like to let go as the wheel is rolling. Think of it like bubble gum on your shoe. While not much resistance is generated, every bit slows the bike down. Again, the bike excels here. Motorcycle tires have a rounded profile and also are much larger in diameter than go cart tires. The patch of rubber making contact with the road on the bike tires is considerably less than a go cart tire and will make less resistance. In perspective, a bike tire has a contact patch on the road of about 2 inches wide, and 4 inches long. A go cart tire will have a patch about 8 inches wide and 6 inches long based on the shifter kart tires that most other builders use. Obviously the bike will have less resistance than most other vehicles.

So the top speed of the bike is theoretically limitless. As for the real top speed...... I don't know. I will be more than happy to get the bike up to 100 MPH in the quarter mile drag race. Would you want to drive such a small bike much faster than that? One day I will strap on my leather riding suit and take her out for a speed run. I don't think the tires will be good for more than about 150 MPH though, as they are smaller than larger bikes obviously. Don't you feel smarter having read all of that?

Q: What kind of fuel does the engine use?

A: Ahh, an easy question. I'll give you all a break on this one and try to make it a short explanation. The engine will run on any fuel that is combustible. Testing is being done on propane, as it is much easier to use since it does not require pumps and other associated gear during the tests. I will be running the engine on diesel fuel during actual runs though. For those interested in a few more facts about the fuel, read on. You may skip to the next section if you would rather not be bothered by things such as fuel.

Diesel, kerosene, and Jet-A fuel are all pretty much the same thing. They provide the most bang for the buck in these engines and are fairly safe to use. These fuels must have certain conditions to be able to be burned. They must either be heated to the point of volatility, run through a wick of some sort, or vaporized to achieve combustion. This makes them much safer than say gasoline, which has a much lower flash point. They also produce the most heat output per unit of any of the commonly available fuels. Since the engines rely on the ability to heat and expand gasses this is a plus. The engines can be run on gasoline, but I do not recommend it for safety's sake. Other fuels I have seen run in these engines are used motor oil, bio diesel, and used cooking oil. Yup, they are pretty forgiving engines. Aren't you glad you read all that!

Q: What is an afterburner?

A: An afterburner is simply another combustion chamber on the engine. Its purpose is to expand the gasses leaving the engine even further to produce more thrust. They work by providing fuel to the unburned oxygen leaving the engine to expand the air and force it through a nozzle. The amount of fuel used by an afterburner is immense, and is why they are used mainly for take off on military jets or when they need to accelerate faster. It will not really be used on the street for the operation of the bike, but will be used on the dragstrip They do spit out lots of flames and heat up so quickly that the metal will glow white hot. Temperatures of 2000 F are possible with afterburners, so they are not the safest thing to have right under your rear end!

Q: How will you keep from melting the bike and yourself?

A: Heat shielding methods are going to be employed in the bike in the form of ceramic coating, heat wrap, and heat shielding material. The ceramic coating is sprayed on and baked to provide a high heat coating that will keep all of the heat moving through the engine and pipes and right out the rear. Think of the ceramic tiles on the space shuttle and you will know that this stuff works. Wrapped around all of the hot parts will be a special high temperature "bandage" to keep the heat contained even further. The heat shields will be placed on the inside of all of the body panels to keep the damaging heat away from the plastic parts. This combined with the insulating trapped air between the panels and the hot pipes will keep things within limits.

Q: Why do you use the basic stamp?

A: The basic stamp is a microcomputer which is quite powerful. It is being used to keep an eye on the engine since it would be hard to read all of the gauges while driving. Some of the things it will monitor will be ambient air temp, combustor temp, exhaust gas temp, and oil temp. It will also detect fuel, oil, and compressor pressures. There are many other things it keeps an eye on, but the main thing is that it will be able to detect an unsafe condition, alert the rider, and shut off the engine when necessary. A necessity when you realize that the rider sits right above spinning wheels of death in the turbine. One little mistake and you could be singing falsetto for the rest of your life. Our thanks goes out to the team at Parallax for making it all possible!

Q: How many miles to the gallon will the bike get?

A: It should read more like how many gallons to the mile will the bike get. These engines are hungry beasts to say the least. I am not building this bike to be fuel efficient. I do believe that in the world today we should be looking at vehicles which make better use of the reserves of fuel we have, but this bike is not designed to be an everyday driver. The bike will be for exhibition purposes on dragstrips for the most part. Motor sports will always use vast amounts of fuel, and the primal reaction of an individual attending a racing event is worth the fuel expenditure. I will be happy if the 2 1/2 gallon tank will run the bike for 15 minutes. Before anyone feels the need to send me dirty emails about fuel efficiency, please re-read the above. It is for exhibition. Go buy a hybrid car and let racers be racers. Also take a look at the fuel consumption of jet airliners.

Q: How does the engine hook to the rear wheel?

A: Put simply, it doesn't. It uses thrust to move the bike. There is simply not enough room in the frame to put in a shaft turbine or transmission. There are ways to do it though, and the simplest of all is to use another turbine section connected to a gearbox to extract the power from the moving air and convert it to rotational energy. If I build another jet bike in the future I will use this technique.

Q: How much thrust does the engine produce?

A: As the engine is not completed yet, there is no way to tell. We are estimating that the engine will produce between 50 to 60 pounds of thrust while running at top speed. The afterburner should bring the totals up quite considerably. Although there is no way to tell right now, we are hoping to see a total of between 100 - 150 pounds of thrust when all is said and done. To put this in perspective, imagine tying 100 pounds of weight to a long rope and attaching the other end to the bike. Throw the weight off a cliff and see how fast it accelerates you toward the edge of the cliff. (I am not actually recommending this, and anyone who does so does it at their own risk. I will also call them a lot of really bad names which depict their intelligence) If you get the idea, it will push the bike along and accelerate it nicely. I have friends who have achieved 80 MPH on go carts with similar engines. With my lower resistance, as stated previously, I hope to achieve higher speeds.

Q: Do you have plans for the bike or engine?

A: Why yes I do have plans for both of them. I am going to ride them! In actuality I do have plans for what I have built, but they are for shop purposes only. I am not currently selling plans or completed engines. Although this may change in the future, it is not the case right now. Please do not email me asking to purchase plans or engines. If I have any to sell later I will make it known on the website.

Q: Why have sponsors?

A: The costs associated with building a project of this scope can rise quite quickly. Because of this we have tried to obtain sponsors whose products we have used before, or that we believe will be the best for the particular purpose. We do not solicit sponsors to get parts that we wouldn't use. We solicit sponsors based on the quality and suitability of their products for the jet bike. We are fortunate to have some sponsors who have contributed to the project simply because they believe in our work. All of our sponsors are appreciated, and without them the progress would be much slower, if we could finish at all. Potential sponsors can contact us directly to speak with us about opportunities.

Q: What is Bad Brothers?

A: Bad Brothers is a company set up to manufacture accessories for sportbikes and pocketbikes. Some of the products include custom racing setbacks for large bikes, and custom billet nitrous systems for pocketbikes. We were looking to do a fun project for quite a while and thought the jet bike would fit the bill.

Q: What tools do you use to make the bike?

A: The basic tools we use in the shop are milling machines, lathes, drill presses, grinders, saws, cut-off wheels, sanders, welders, lots of clamps, hammers, you name it. Most of our tools are from Harbor Freight Tools. They have great prices, and the tools are pretty good. Anyone can afford to get the tools they need from them, so stock up your garage now by going to have a look at www.harborfreight.com

They turned us down for sponsorship by the way, so feel free to drop them a line to let them know where you heard about their tools and what they missed out on. Who knows, maybe they will pick us up after all!

Q: How do I get started building my own?

A: Join a good users group such as www.turbinebuilder.com or the Yahoo Groups DIYGas Turbines message group. Both of these places have excellent resources for the aspiring builder. Just use caution when attempting a project such as this. Jet engines can be very dangerous. They produce lots of heat and noise, and have bits moving at supersonic speeds. Not for the faint of heart. You can also find practical information in these very pages to help you along the way. All DIY jets are unique however, and are based around the turbo the builder will be using. If you are serious, consult with others on the groups on how to select a suitable turbocharger before doing anything else. Be sure to let them know what you want to engine for, i.e.. a go cart, or just to build a small one to see what it is like. Expect to spend some cash on it. It does take lots of time and money to truly do it right.

If there are any other questions not addressed here, feel free to drop me a line and I'll do my best to answer them. While I do not know everything, I have good resources to find the information and I will try to present it in an easy to understand format. Thanks for reading.

Russ W. Moore