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#1
January 12th 04, 05:15 AM
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In article ,
Mike Borgelt wrote: On 11 Jan 2004 14:39:20 -0700, (Mark James Boyd) wrote: In article , Mike Borgelt wrote: I've come to much the same conclusion as Mike. I'd use a single more powerful turbine (maybe the 1500) instead of 2, but the numbers seem to work for even fairly short fields. The heat on the tail scares me though. Hmmm...how do we get rid of the glider tail?  The guys with the Silent don't seem to have a problem with the heat on the tail - the two AMT 450 turbines seem to be mounted parallel to the centerline. If this still worries you a V tail as on HP gliders or the Salto is the easy answer. I've never seen a turbine airplane design that allows the hot exhaust to reach a control surface of the aircraft. The fact that the Silent flew a few times in this configuration is not convincing to me. If the owner would put it on a stand in a hangar and run it for an hour with his face right in front of the rudder/stab, I'd change my tune. I don't have any hard facts or figures, but my intuition sets off some warning flags here... I first thought of using the AMT1500 but when you do the numbers two AMT450s (and soon the XP versions with about 10% more thrust) are quite adequate for a 400kg glider. The larger engine isn't for more thrust than two engines, but just for the lower complexity of using one engine. Two engines are best used in aircraft with high wing loading that carry passengers through turbulence. Two engines in a light-wing loaded aircraft is just unneccesary, IMHO. Engine failure is a non-issue due to the glide ratio, and the reliability of turbines. The added weight, wiring, two starters, fuel lines, etc. seem silly if a single turbine can be used instead. Great for motorising motorless gliders as the weight in the fuselage is minimal. Convert part of the water tanks/bags for jet fuel.60Kg(75liters) will give you one hour. Figuring out how to manage fuel from two tanks is a minor complexity, and being able to dump fuel should ensure one doesn't fly "chinese style" (won weeng lo). It does seem using the fuel as ballast is an excellent feature, but I'd want to really think hard about fire dangers. Perhaps use less flammable fuel? I guess there is quite a variety of fuel choices available... Now look at a Sparrowhawk One AMT 450 will self launch this adequately. Two smaller engines may still be optimum for slightly increased thrust and engine out capability. More power than adequate = better. One can always throttle back for fuel savings. I suspect the designers used two engines instead of one because the 1500 may not be readily tested/ available rather than due to the need for redundancy. Again, I've flown some twins and they have their uses; a powered glider isn't a good match for two turbine powerplants (just overkill/expense)... Hope the Windward Performance guys have a plan to increase production because if this works they might be swamped by customers. The Sparrowhawk may be ideal for this application, but other light gliders also have comparable potential. And I personally would want to see a competitor which could taxi well. A self-launch glider which has trouble taxiing is less interesting to me personally than something more flexible. Besides, the noise may get one banned from the gliderport and forced to use a gasp towered airport... ;P 
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#3
January 12th 04, 04:58 PM
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Mike Borgelt wrote:
As for complexity of two jet engines compare with a horrible, heavy, noisy vibrating two stroke with reduction drive and propeller, complex and heavy extend /retract mechanism, heat issues if the engine is buried in the fuselage and complex operating procedures with very limited climb speed range. Look at the prices being charged for these contraptions. Typical self-launchers are rpm limited to about 70-75 knot cruise, which is painfully slow when flying into a 30-40 knot headwind while trying to reach a wave. As a result, I often don't attempt to fly our best winter waves, since it'd an hour+ to reach them. Being able to cruise at 100+ knots would cut the transit time in half. -- ----- change "netto" to "net" to email me directly Eric Greenwell Washington State USA
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#4
January 12th 04, 04:41 PM
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Mike Borgelt wrote:
As for complexity of two jet engines compare with a horrible, heavy, noisy vibrating two stroke with reduction drive and propeller, complex and heavy extend /retract mechanism, heat issues if the engine is buried in the fuselage and complex operating procedures with very limited climb speed range. Look at the prices being charged for these contraptions. Compared to a two-stroke, four jet engines is an improvement. But again, IMHO, one jet engine of the same power is better than more engines in light wing-loaded aircraft. The complexity of pilot management, and the extra workload to manage the feeding and maintenance is the downside. And redundancy is, I believe, notional. I'd rather run out of gas and then switch to a full tank than run out of gas on one engine and then, a few seconds later, run out of gas on the other side. I hope we can agree as gentlemen to disagree on this one... I'm strongly in favor of a single turbine engine for this application. I've never seen a turbine airplane design that allows the hot exhaust to reach a control surface of the aircraft. The fact that the Silent flew a few times in this configuration is not convincing to me. If the owner would put it on a stand in a hangar and run it for an hour with his face right in front of the rudder/stab, I'd change my tune. I don't have any hard facts or figures, but my intuition sets off some warning flags here... You can easily then cant then out a little if you want. Problem solved(and a good argument for two engines) I just don't know how large the heat cones are out of these engines, so I can't really agree or disagree...I don't think I can solve this one from an armchair... Given you will have only an electric fuel pump you are going to want two anyway even for one engine. You already have two fuel tanks. You might want two batteries as well to be sure of getting a start when about to land out. Each of two smaller engines is lighter and simpler to swing out than one larger one. This looks one one of those issues where the "obvious" solution isn't so obvious on reflection. The cost of the engines seems to scale roughly with thrust so it is dollars per Newton you pay for. The smaller engines also have thousands of hours operating history which is worth a lot. And I *love* the idea of engine out capability plus with two you really aren't going to fail to get at least one running to avoid an outlanding. Out of gas is out of gas, period. Turbines get more reliable as they get larger, and are lots more reliable than anything with a prop. The reliability card simply has negligible meaning in this context. And again, the cost isn't the acquisition or fuel costs, it's continuing cost... I figured on one tank in each wing anyway and jet fuel is much less flammable than gasoline anyway. The fuel is slightly less flammable but the heat danger is much greater than a pure glider (of course). My point is just that if one has a choice, maybe use the least flammable fuel? You can still fill up with Jet A if needed... And I'm also emphasizing that I think the fire risk is really something to pay attention to and minimize by design... Yes and the redundancy is really nice to have. If the glider was not capable of climbing on one I'd agree with you that one engine is desirable but what is the point of designing around an engine that isn't readily available with lots of operating history? Completely true. If we MUST use two because of marketing/availability/testing reasons then fine. Two in the hand is better than none in the bush. But accepting a sub-optimal design instead of making some extra phone calls means somebody else is gonna compete with you later, at a better price offering reduced maintenance/complexity... The packaging of two is also easier. Boy I gotta strongly disagree with that. Installing, testing, wiring, instrumenting, fueling, operating, shutting down, diagnosing in flight, etc. for two engines is wholly different than one. There's a reason 727s have three crewmembers instead of one, and it isn't because of the complexity of the passengers or so the Captain can take a nap... I've seen and heard the R/C model jets fly. They aren't that noisy at all. Two smaller engines over the wingroots actually shields the people on the ground from much of the noise. My comment about noise meaning you may get banned from the gliderport was tongue in cheek. Here's the that should have been there...Taxiing is still going to be problematical but then very few existing self launchers taxi well(as opposed to Stemme's, Katanas etc and even they would have trouble at our airport. I've got some time in the Jet Caproni about 20 years ago and I wasn't that impressed. When I last flew in it 10 years ago the owner had figured it out and it was good. We are talking the same sort of thrust weight for a 400Kg glider(most 15/18m gliders) with two AMT 450's. Mike Borgelt Yes, I'd very much like to see taxi capability. A short wingspan and light weight like a Sparrowhawk is excellent for this turbine. The extra stuff to make it taxi well would sell it to the biggest market, "power pilots," with the best success. Mark Boyd
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#5
January 12th 04, 09:47 PM
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#6
January 13th 04, 12:30 AM
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Mike Borgelt wrote:
Yes, I'd very much like to see taxi capability. A short wingspan and light weight like a Sparrowhawk is excellent for this turbine. The extra stuff to make it taxi well would sell it to the biggest market, "power pilots," with the best success. You would need to check the fuel consumption at reduced power. You might get a nasty surprise. The taxi to the strip might have fuel consumption comparable to driving an M1A2 the same distance. I can easily live without the taxi ability. I'm looking forward to the Ventus Ca17.6TJ(that's TwinJet) I love being able to taxi in my ASH 26 E, but the alternative is to push a 850 lb glider to the end of the runway. If it were a turbine powered SparrowHawk, it'd be less 200 pounds, and pushing it down to the end wouldn't be any worse than just walking down there. Seriously, it is so much easier to push, it's not an issue, it's just walking. I could do without the taxi ability to avoid carrying a large of amount of fuel to do the taxi. About 80% of my flights have only one engine use, a climb to ~2000' agl. The rest have another engine start, and 15% have a typical run time of less than 10 minutes. About 3% can be as much as 20 minutes additional run time, and the last 2% haven't exceeded 40 minutes (total of 45 minutes for the flight). I can easily avoid that 2% and be happy with 30 minutes of fuel at climb power. What do these things use for fuel? Do we need to land at airports with Jet A to refuel? Or a town with a hobby shop and model airplanes? -- ----- change "netto" to "net" to email me directly Eric Greenwell Washington State USA
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#7
January 13th 04, 02:38 AM
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Eric Greenwell wrote:
I love being able to taxi in my ASH 26 E, but the alternative is to push a 850 lb glider to the end of the runway. If it were a turbine powered SparrowHawk, it'd be less 200 pounds, and pushing it down to the end wouldn't be any worse than just walking down there. Seriously, it is so much easier to push, it's not an issue, it's just walking. I could do without the taxi ability to avoid carrying a large of amount of fuel to do the taxi. An excellent point. A reflective vest and one could simply walk the glider to the runway. About 80% of my flights have only one engine use, a climb to ~2000' agl. The rest have another engine start, and 15% have a typical run time of less than 10 minutes. About 3% can be as much as 20 minutes additional run time, and the last 2% haven't exceeded 40 minutes (total of 45 minutes for the flight). I can easily avoid that 2% and be happy with 30 minutes of fuel at climb power. Assuming sustained flight may only require 10-20 lbs of thrust at best L/D, fuel consumption may be quite low when used as a turbo. On the other hand, full power may provide startling (redline) speeds with 80-200 lbs of thrust and a 400# gross weight. What do these things use for fuel? Do we need to land at airports with Jet A to refuel? Or a town with a hobby shop and model airplanes? Jet A, and some other stuff. I think they may burn just about anything: castor oil, alchohol, melted margarine, autogas, avgas, jet A, diesel, etc. The real problem is if the fuel has contaminants (margarine may be a BAD idea). Don't quote me on the fuels they use, but the turbine principle seems to have few fuel restrictions in theory... Eric Greenwell
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#8
January 13th 04, 02:31 AM
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Mike, Let's face it: you just WANT two engines. It isn't a matter of design or complexity or fuel or cost; you just WANT two little turbines on your glider. It looked really cool and it sounds neat and you want TWO. Nothing wrong with that... :P Mike Borgelt wrote: Even the jet Caproni was fly by wire for engine management. These engines already come with automatic electronic controls. Not a heck of a lot of complexity. They simply are not available yet. Two smaller turbines are and have some advantages and I beleive aren't likely to cost significantly more than one large one. solved(and a good argument for two engines) plus with two you really aren't going to fail to get at least one running to avoid an outlanding. AMT450 or the AMT1500/1700. Redundancy may indeed be very nice to have. The little engines are used in R/C models. Obviously the heat issues are solvable. Yes and the redundancy is really nice to have. If the glider was not capable of climbing on one I'd agree with you that one engine is desirable but what is the point of designing around an engine that isn't readily available with lots of operating history? Until he has a customer have an engine failure right after takeoff. The packaging of two is also easier. We are talking something that weighs 5 pounds. Installing and mounting it isn't that difficult. Check out the model jet websites. Mike Borgelt You would need to check the fuel consumption at reduced power. You might get a nasty surprise. The taxi to the strip might have fuel consumption comparable to driving an M1A2 the same distance. Two gallons per mile? $4 to taxi to the runway? I'm fine with that. My whole premise in this design was that 1/5 of the fuel efficiency of a two-stroke is worth the enormous other benefits (including 1/5 the parts count for the engine). Wasting fuel is a feature, not a disadvantage in my mind. $10 extra a launch in fuel is better than sending the testy ASH-26 engine back to the factory for six months (talk to Bill Gawthrop).
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#9
January 13th 04, 04:26 AM
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"Mark James Boyd" wrote in message news:4003668d$1@darkstar... Mike, Let's face it: you just WANT two engines. It isn't a matter of design or complexity or fuel or cost; you just WANT two little turbines on your glider. It looked really cool and it sounds neat and you want TWO. Nothing wrong with that... :P Dude, let's face it, logging multi-engine turbine time _is_ cool! Tim Ward
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#10
January 13th 04, 05:00 AM
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Mark James Boyd wrote:
$10 extra a launch in fuel is better than sending the testy ASH-26 engine back to the factory for six months (talk to Bill Gawthrop). Puhleease... I'm sure Bill is testy about his engine (six months is too long, I think), but the engine used in the ASH 26 E has a very good record, at least equal to the Solo used in the other gliders (a better record, in my opinion). -- ----- change "netto" to "net" to email me directly Eric Greenwell Washington State USA
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