BRK: For this question we return to the sports bar: Among the many fine plan-sets offered on your site is one I find especially intriguing- the Gluhareff Propane-fueled Pressure Jet Engine, with thrust ratings up to 130 pounds. One of the considerations of HPV use in urban areas is the need for being able to insert oneself quickly into the traffic stream. My earlier thoughts on the subject involved the use of a 2-stroke engine, or an electric motor as a pedal-assist. However the thought of a JATO (Jet-Assisted Take-Off) bike is extremely appealing (not to mention muy cool). Since the Gluhareff engine looks to be cheap to build, and would appear to be fairly lightweight, do you think that a jet-propelled XR2 would be a viable concept? RQR: Funny you mention the jet engine. Just a few days ago, I received a photo from a fellow who recently tested a conventional bicycle powered by a 20-pound-thrust Gluhareff jet. |
RQR: It's a little difficult to explain the strength of this stuff in a way that's intuitive. But once you've handled a piece of foam-core composite, its enormous strength-to-weight ratio becomes very obvious. I'll give it a try on the explanation. First, imagine that you have a thin piece of sheet metal, say 1 foot square, and only about as thick as a sheet of copy paper. If you clamped onto the metal along the top and bottom edges (so the metal was under a tension load), you could lift a car with it. In other words, the metal doesn't stretch very easily, even though it's very thin. And it's just as strong in the opposite direction; when it's under a compression load (in the edgewise direction) for example. And in fact, if you tried to compress the metal edgewise, it would simply oilcan and bend, but it would not actually compress and become shorter. But you could bend it with just a little pressure across the middle. Now imagine that you have two of these sheet metal squares and you glue them together with a piece of 1-inch-thick foam between them. If you tried to bend that sandwich "composite," you'd be trying to force the metal to stretch on one side and compress on the other side of the foam core. Keep in mind that the foam is holding the sheet metal pieces apart from each other and is not allowing them to oilcan. So the only way the sandwich structure can bend is if the metal on the outside of the bend stretches and the metal on the inside of the bend compresses. It would be a very difficult part to bend. Now imagine that instead of overlaying the metal onto a piece of 1-inch thick foam, you overlay it onto a piece of 6-inch-thick foam. You could drive a truck over the resulting sandwich structure and it wouldn't bend. So the greater the separation between the outer and inner skin, the stronger the composite piece becomes. But weight wouldn't be much greater because you've only added foam. The foam itself is not very strong at all, but it does the job of holding the outer and inner skin in place so the skin can't oil-can, which forces it to carry loads in the edgewise direction. And this is the reason for the extremely high strength-to-weight ratio of a foam-core composite structure. So if the material is so light and strong, why don't they build cars out of it? Well, pretty soon they will. At my former company, Quincy-Lynn Enterprises, we pioneered the automotive application of fiberglass-over-foam composite in the early '70s. Practically every automobile on my website is built that way. Today, the big carmakers are working on volume production methods for this type of composite. And the Hypercar being promoted by Amory Lovins (of the Rocky Mountain Institute) is designed around a foam-core composite. Some of the most advanced homebuilt aircraft are now built using this type of construction method. I can't say enough about foam-core composites. And it's the perfect system for the do-it-yourselfer because you don't need a mold. |
BikeRod&Kustom Interview: Robert Q. Riley Page Two |
RQR: Continued The reason for the custom-made fork on the XR2 is that it provides total control over packaging and steering geometry, which wouldn't exist if we used an off-the-shelf repair fork. The fork design even lets the builder experiment with different amounts of trail before permanently welding the blades to the crown. So handling can be dialed-in to suit even the "most" discriminating cyclist. But I think this discriminating cyclist fellow may be getting unfairly nailed. When I was in the business, people bought bicycles mostly on the basis of price. So it's a real pleasure for me to see the superior design and craftsmanship that goes into today's machines. And most of it wouldn't exist if it weren't for folks who were willing to pay for something better. This new level of appreciation has also opened the way for the XR2. If I had done something like this 15 years ago, I doubt that it would have been anywhere near as successful as it is today. |
Frame & Seat: Carbon Fiber Cloth.............................................$122.50 Vinylester Resin....................................................$35.00 Urethane Foam.....................................................$65.00 Metal Steering Housing.........................................$25.00 Bottom Bracket Shell (rear).................................$16.00 Tandem Bottom Bracket Shell (front)....................$25.00 ----------------------- Total for Frame and Seat..................................$288.50 Steering Tube, Fork & Rear Stays: Universal Joint ......................................................$25.00 Bearings for rear stays...........................................$15.00 Tubing and Plate for steering tube, fork & stays.....$35.00 Cut fork & stay plates to shape............................$100.00 Welding................................................................$50.00 Machining...........................................................$300.00 ----------------------------------- Total for Special-Made Parts......................... $525.00 TOTAL..................................................................$813.50 |
BRK: That seems pretty reasonable to me, considering that most people who'd venture building their own bike from scratch probably have boxes full of bike parts squirrelled away. I certainly do, and I'm not exceptional that way. Having studied your plans pretty thoroughly, I can say that it wouldn't take a huge amount of time to build an XR2. So someone could end up with a state-of- the-art, good-looking LWB recumbent for under a thousand bucks and a few weeks' spare-time labor. That's what I'd call a real bargain; especially considering that you can spend twice or three times as much for an uglier, heavier, and clunkier off-the-shelf machine. You mentioned earlier that your technical section of the manual covers all the considerations for custom-modifying the frame to suit the builder's needs and desires. I think that's very valuable information to include for a project of this type. Creative home-builders sometimes tend to play a little fast and loose with plans. In the case of homebuilt aircraft this can have tragic consequences; in the case of a recumbent bike it can lead to having to do the whole thing over again. You anticipate common modification urges, point out the do-not-exceed dimensions and the logic behind them. This is very commendable, and is not covered in most plan-sets I've seen. |
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RQR: It's a little difficult to explain the strength of this stuff in a way that's intuitive. But once you've handled a piece of foam-core composite, its enormous strength-to-weight ratio becomes very obvious. I'll give it a try on the explanation. First, imagine that you have a thin piece of sheet metal, say 1 foot square, and only about as thick as a sheet of copy paper. If you clamped onto the metal along the top and bottom edges (so the metal was under a tension load), you could lift a car with it. In other words, the metal doesn't stretch very easily, even though it's very thin. And it's just as strong in the opposite direction; when it's under a compression load (in the edgewise direction) for example. And in fact, if you tried to compress the metal edgewise, it would simply oilcan and bend, but it would not actually compress and become shorter. But you could bend it with just a little pressure across the middle. Now imagine that you have two of these sheet metal squares and you glue them together with a piece of 1-inch-thick foam between them. If you tried to bend that sandwich "composite," you'd be trying to force the metal to stretch on one side and compress on the other side of the foam core. Keep in mind that the foam is holding the sheet metal pieces apart from each other and is not allowing them to oilcan. So the only way the sandwich structure can bend is if the metal on the outside of the bend stretches and the metal on the inside of the bend compresses. It would be a very difficult part to bend. Now imagine that instead of overlaying the metal onto a piece of 1-inch thick foam, you overlay it onto a piece of 6-inch-thick foam. You could drive a truck over the resulting sandwich structure and it wouldn't bend. So the greater the separation between the outer and inner skin, the stronger the composite piece becomes. But weight wouldn't be much greater because you've only added foam. The foam itself is not very strong at all, but it does the job of holding the outer and inner skin in place so the skin can't oil-can, which forces it to carry loads in the edgewise direction. And this is the reason for the extremely high strength-to-weight ratio of a foam-core composite structure. So if the material is so light and strong, why don't they build cars out of it? Well, pretty soon they will. At my former company, Quincy-Lynn Enterprises, we pioneered the automotive application of fiberglass-over-foam composite in the early '70s. Practically every automobile on my website is built that way. Today, the big carmakers are working on volume production methods for this type of composite. And the Hypercar being promoted by Amory Lovins (of the Rocky Mountain Institute) is designed around a foam-core composite. Some of the most advanced homebuilt aircraft are now built using this type of construction method. I can't say enough about foam-core composites. And it's the perfect system for the do-it-yourselfer because you don't need a mold. |
BRK: For this question we return to the sports bar: Among the many fine plan-sets offered on your site is one I find especially intriguing- the Gluhareff Propane-fueled Pressure Jet Engine, with thrust ratings up to 130 pounds. One of the considerations of HPV use in urban areas is the need for being able to insert oneself quickly into the traffic stream. My earlier thoughts on the subject involved the use of a 2-stroke engine, or an electric motor as a pedal-assist. However the thought of a JATO (Jet-Assisted Take-Off) bike is extremely appealing (not to mention muy cool). Since the Gluhareff engine looks to be cheap to build, and would appear to be fairly lightweight, do you think that a jet-propelled XR2 would be a viable concept? RQR: Funny you mention the jet engine. Just a few days ago, I received a photo from a fellow who recently tested a conventional bicycle powered by a 20-pound-thrust Gluhareff jet. |
I wouldn't expect much speed from 20 pounds of thrust. But consider that it takes only 130 pounds of push to get Tri- muter up to 75 mph. It weighs 850 lb, |
and is nowhere near as efficient as the XR2. Just as a guess, I'll bet the XR2 could easily break 200 mph with a full fairing and a 130-pound-thrust jet engine for power. What a ride that would be. And just to show you what a nice guy I am, you can go first and have all the glory. If everything works out okay, I'll take the second run. |
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BRK: Fantastic! You build it and I'll strap it on. I think I went to different schools together with that jet-bike guy, too. About how much would it cost to build the jet engine? RQR: If you did all the work yourself (except for machining the injection nozzle), I would say that you could build a jet engine for under $1000. And it wouldn't matter much whether it was a 20- or a 130-pound-thrust engine. The 130 is larger than the 20, but the architecture is the same. |
BRK: Thanks, that was a very lucid explanation-much better than "Uh... internal leverage?" As you mentioned earlier, a surface-filled and painted XR2 frame weighs about six pounds. Could you project the curb weight of a typical, finished one, assuming that normal bike wheels and components are used? RQR: The prototype weighs 31 pounds, but it's a bit overweight compared to one that would be built from the plans. That's mainly due to the prototype's steel steering tube, and an excess amount of Bondo on the seat. Plans specify an aluminum steering tube with lightening holes, and we give a technique for building the seat that will keep the amount of Bondo to a minimum. With our seat, we started off doing it wrong, then revised it and covered all the sins with a liberal coating of Bondo. So if we were to build another one exactly according to the plans, the finished machine would weigh in at about 29 pounds. And that's based on a frame that is considerably over-built. The number of lay-ups specified in the plans assumes the builder will do a marginal job of it. If the carbon fiber is well applied, he could cut back on the number of lay-ups. There are a couple of other ways to remove weight without sacrificing strength. First of all, you can switch to a natural finish and save at least 1-1/4 pounds. The frame weighed only about 4-3/4 pounds before we applied Bondo and paint. It's also perfectly okay to drill lightening holes in the headpiece, the two bottom bracket shells, and the metal steering housing before laminating them into the frame. In fact, the only real purpose of the metal steering housing is to provide a round form over which to apply the carbon fiber. But once the carbon fiber is in place, the extra strength that comes from the metal housing is unnecessary. The carbon fiber itself is plenty strong enough to support the steering tube by itself. (The steering tube fits inside the steering housing and does the actual steering.) And we didn't use the lightest bicycle components on the prototype. So a builder's choice of components can have a big impact on the final weight of the XR2. Interestingly, those carbon fiber wheels on the prototype didn't result in a lighter machine. The overall weight of the carbon fiber wheels (9-speed cassette on the rear wheel) was virtually identical to a set of aluminum wheels with a Sachs 3 x 7 internal-geared hub and 7-speed cassette at the rear. So I'd put the weight range at about 30 pounds on the top end and about 25 pounds on the bottom end |
© 2000 Erik Hunter |
BRK: I'm not saying that I've run out of questions, but the rest of them are even weirder than the last one. So this might be a good time to stick a fork in it. I'd like to thank you for a really enjoyable interview, and for making it possible, through your plan-sets, for ordinary folk to achieve the exaltation and pride which accompany the building of advanced machinery. The finest gift you can give someone is the opportunity to feel super-human, and you've done that for vast numbers of people. May you live long and prosper, and continue to have maximum fun with your work. |
RQR: Your comments remind me of a phone conversation I had a couple of years ago, which I'd like to share. A fellow called me and said that he had bought one of my car plans many years ago, and that it had changed his life. He went on to explain that he had dreamed of becoming a school teacher, but had given up on the idea because he felt it was beyond his abilities. But when the plans arrived he said: "Here was someone who was telling me that I could actually build a whole car. And from the plans, I could see that I could actually do it! So if I could build a car, I could certainly become a school teacher." So he decided on the spot to go for his dream, and today he is a high-school shop teacher. Wow! Can you imagine how it feels to hear something like that? It's beyond words to describe. You'll never get that from looking at trendlines and counting dollars. So many thanks to you for the opportunity to talk about it. And I'd like to compliment you on your excellent interviewing style. It has been a real pleasure. |
So figure about $800 to $850 to get to a place where you're ready to start bolting on standard bicycle parts. Don't ask me for a total cost because the price of bicycle parts can vary from one extreme to the other. We paid $500 for those fancy carbon fiber wheels on the prototype, and you can buy a whole bicycle for that. The most economical way would be to buy a used bicycle and strip the parts from it. You'll still have to purchase a few more parts. But a used bicycle can supply about 80 percent of the parts you will need to finish your XR2. |
RQR: The cost of building the XR2, exclusive of off-the-shelf bicycle parts, breaks down as follows: |
BRK: That was pretty much a rhetorical question, merely an excuse to show the picture. I can't imagine anyone actually finding fault with it. The only thing nicer than a carved and polished aluminum fork is one drilled full of lightening holes. Mmmm! I find it mighty tasty. That's a good point about the discriminating cyclist opening the door for the XR2. People are more used to spending serious money for hi-tech bikes, nowadays. I realize that it's pretty tough to come up with an average price for a complete bike, because most builders will use salvaged parts. But, can you give us a rough estimate as to how much the frame and associated custom-made parts would cost for materials? And machining, under the assumption that most builders would take the stock and drawings to a machine shop for cutting, milling, etc? |
great amount of weight, as it usually entails brazing sheet metal in the opening and adding Bondo fairing, as in lowrider bikes. With a laid-up-composite-in-mold form, typical of commercial composite products, extra cloth and resin would be needed in the flat area, to avoid "oil-canning" (flexing). This should not be necessary with the composite-over-foam process used in XR2 ( as well as many homebuilt aircraft). I take advantage of this attribute of the process quite often in my own work. However, when clients ask me why the thing is so light, yet rigid and strong, I usually mumble something about "internal leverage" or whatever. Would you mind explaining to me, and our audience how this actually works? |
Being Kustom Krazy, as soon as I went through the plans, I immediately started thinking about what I would do to personalize it. The attached image is a piece of Photoshop futzing with which I was toying. The principal modification is to leave out the opening beneath the steering tube, for greater surface area for Kustom graphics. With a metal-tube bike frame, a modification such as this would normally add a |
