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#2
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Peter:
"Peter Holm" wrote in message om... Itīs been a while and I have been rather busy, but I nevertheless didnīt want to let pass the deadline for responding. (John Clear) wrote in message ... (cut) Do a search on 'Turbo Raven'. Wayne Handley's site doesn't appear to have video, but there is probably some out there. Unfortunately, the Turbo Raven was only flown for one season. http://www.waynehandley.com/archive.html John Besides you, there has been one other person answering to my mailbox. And that answer referred itself to the Turbo Raven as well. But I havenīt yet found any video of that aircraft. In fact, it seems to me as if that aircraft has been the only dedicated turboprop aerobatic aircraft that was ever flown. And that there is nothing today. Am I wrong on that? The first that I saw was a turbo Great Lakes, sponsored by Mennen (the aftershave company.) It used smoke that smelled like the aftershave, and did a vertical S ontakeoff. That was in the eaarly 1970's as best as I remember. The Turbo Raven flew for a short time before the crash. There is a turbo Sukohi that Ihave seen photos of, but I haven's seen it live. Just in case that I am right: I know that a turboprop airplane can easily cost twice as much as a piston plane of the same size. But this fact could only explain a relative rareness of turboprop airplanes among aerobatic planes. What it cannot explain is their (next to?) absence, since experience shows that if there is a will there is a way, and some or another team of people should always be able to adquire one of these planes. Just a SWAG, but I would think that the Turbo Raven cost about 6 times what a good Edge 540 would cost. Sponsorship before construction would be important. If I extrapolate by scale from what I have frequently seen with model aircraft (which tend to have a much higher power to weight ratio than full scale aircraft), an aerobatic turboprop plane should be able to execute a sustained torque roll at 10 or 15 feet above ground. And that ought to be an absolutely awsome sight! Has anybody ever done that? Doins so would be betting one's life and airplane on no wind gusts, absolutely no pilot miscalculation, and no aircraft / engine problem. I have seen the Turbo Raven hover, descend vertically, then ascend vertically. Scary to watch. But now I think that - sadly - I will never get to see that, and I am starting to wonder why. Rich and foolish is not a combination that survives long. I know that piston engines can have certain advantages under certain conditions: For example, when it comes to propulsion on a solid surface (greater range of rpmīs), or when it comes to the transportation of large amounts of goods at a minimal price on a liquid medium (fuel eficiency). But when it comes to airplanes, I can see that turbo engines are employed either next to exclusively (commercial/military airplanes) or at least frequently (private/business airplanes), exept in the case of crop dusters - and aerobatic airplanes. Now I can understand that turbo crop dusters make little sense, but how about in the case aerobatic airplanes? Turb crop dusters make lots of sense for large scale application, are numerous, ane are profittable. Therefore, my question is (always assuming that my basic assumption above is correct): Is there a rational reason for the next to absence of turboprop planes among aerobatic aircraft, or is this absence perhaps due to some sort of stubborn romanticism? Cost is a rational reason. Turbine engines are not allowed in international aerobatic competition. Peter BJC |
#3
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Is there a rational reason for the next to absence of turboprop planes
among aerobatic aircraft, or is this absence perhaps due to some sort of stubborn romanticism? There are actually a number of tubro powered aerobatic planes, think for example of the PT-6 trainers. For competition aerobatics however which includes lots of gyroscopic forces, there are I believe concerns about the long shafts in those engines and the huge gyroscopic forces at work. That would limit them to sportsman stuff .. which is quite a restriction for a $1,000,000 + airplane. I suspect also the time required to spool up/down the power is an issue. Peter |
#4
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Power reaction is not such an issue for a single-shaft engine. My engine can
go from 10-90% torque in one second, no problem. However, you did hit on the larger problem: Very high gyroscopic forces. Although the spinning mass is not very large, my engine turns at 43,500rpm. That's loads of gyro. I have to be very careful not to snap against the engine or I might just loose it. BTY, I fly aerobatic helicopters, so there's a larger gyroscope to deal with, but it "flies"... "Peter Ashwood-Smith C-GZRO" wrote in message om... Is there a rational reason for the next to absence of turboprop planes among aerobatic aircraft, or is this absence perhaps due to some sort of stubborn romanticism? There are actually a number of tubro powered aerobatic planes, think for example of the PT-6 trainers. For competition aerobatics however which includes lots of gyroscopic forces, there are I believe concerns about the long shafts in those engines and the huge gyroscopic forces at work. That would limit them to sportsman stuff .. which is quite a restriction for a $1,000,000 + airplane. I suspect also the time required to spool up/down the power is an issue. Peter |
#5
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"nametab" wrote in message k.net...
Power reaction is not such an issue for a single-shaft engine. My engine can go from 10-90% torque in one second, no problem. However, you did hit on the larger problem: Very high gyroscopic forces. Although the spinning mass is not very large, my engine turns at 43,500rpm. That's loads of gyro. I have to be very careful not to snap against the engine or I might just loose it. BTY, I fly aerobatic helicopters, so there's a larger gyroscope to deal with, but it "flies"... "Peter Ashwood-Smith C-GZRO" wrote in message om... (cut) There are actually a number of tubro powered aerobatic planes, think for example of the PT-6 trainers. Where and when do they fly? For competition aerobatics however which includes lots of gyroscopic forces, there are I believe concerns about the long shafts in those engines and the huge gyroscopic forces at work. That would limit them to sportsman stuff .. which is quite a restriction for a $1,000,000 + airplane. (cut) Because you are flying such a large gyroscope, I wonder if you might not be overestimating the gyroscopic forces produced by turboprop engines. Because in distiction to what Peter Ashwood-Smith is saying above, small turboprop motors only appear to have a long rotor shaft. In reality they have two shafts mounted separately one behind the other: The (single) rotor shaft and the power shaft (with the reduction gears in front of the latter). I can really speak competently only about model aircraft turboprops. And the weight ratio of rotor shaft weight/total aircraft weight should be at least equal if not higher in model aircraft than in real aircraft. Besides, microturbine rotor shafts rotate at speeds typically between 120.000 and 200.000 rpm. And in model aircraft, the guroscopic forces from the rotor shaft are considered to be negligible. I donīt see how this could be due to some sort of scaling effect. So in order to put an end to all of this speculation, I think what would really be needed here is the testimony of a pilot who has actually flown aerobatics with a turboprop plane. One additional question for you out of interest: Do you believe that aerobatic turboshaft helicopters are relatively more abundant than aerobatic turboprop planes? And if yes, why would that be so? After all, this appears to be contradictory since the pilot of an aerobatic turboshaft helicopter ought to have to deal with much higher gyroscopic forces than the pilot of an aerobatic turboprop plane. Peter H. |
#6
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The reason the only aerobatic helicopters (if you can say that) are turbine
powered, is merely power. Where can you get 600 HP out of an engine that weighs less than 300lbs.? We need loads of HP and turbines deliver that. With that said, the turbine does act as a large gyro, however the rotor is about 5x stronger than the engine. It's just that the engine mounts are not made to take those loads. It's assumed that the helicopter will not normally snap around like you can get in aerobatics. That's why we have to be careful about it. "Peter Holm" wrote in message om... "nametab" wrote in message k.net... Power reaction is not such an issue for a single-shaft engine. My engine can go from 10-90% torque in one second, no problem. However, you did hit on the larger problem: Very high gyroscopic forces. Although the spinning mass is not very large, my engine turns at 43,500rpm. That's loads of gyro. I have to be very careful not to snap against the engine or I might just loose it. BTY, I fly aerobatic helicopters, so there's a larger gyroscope to deal with, but it "flies"... "Peter Ashwood-Smith C-GZRO" wrote in message om... (cut) There are actually a number of tubro powered aerobatic planes, think for example of the PT-6 trainers. Where and when do they fly? For competition aerobatics however which includes lots of gyroscopic forces, there are I believe concerns about the long shafts in those engines and the huge gyroscopic forces at work. That would limit them to sportsman stuff .. which is quite a restriction for a $1,000,000 + airplane. (cut) Because you are flying such a large gyroscope, I wonder if you might not be overestimating the gyroscopic forces produced by turboprop engines. Because in distiction to what Peter Ashwood-Smith is saying above, small turboprop motors only appear to have a long rotor shaft. In reality they have two shafts mounted separately one behind the other: The (single) rotor shaft and the power shaft (with the reduction gears in front of the latter). I can really speak competently only about model aircraft turboprops. And the weight ratio of rotor shaft weight/total aircraft weight should be at least equal if not higher in model aircraft than in real aircraft. Besides, microturbine rotor shafts rotate at speeds typically between 120.000 and 200.000 rpm. And in model aircraft, the guroscopic forces from the rotor shaft are considered to be negligible. I donīt see how this could be due to some sort of scaling effect. So in order to put an end to all of this speculation, I think what would really be needed here is the testimony of a pilot who has actually flown aerobatics with a turboprop plane. One additional question for you out of interest: Do you believe that aerobatic turboshaft helicopters are relatively more abundant than aerobatic turboprop planes? And if yes, why would that be so? After all, this appears to be contradictory since the pilot of an aerobatic turboshaft helicopter ought to have to deal with much higher gyroscopic forces than the pilot of an aerobatic turboprop plane. Peter H. |
#7
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In article ,
Byron J. Covey wrote: Just in case that I am right: I know that a turboprop airplane can easily cost twice as much as a piston plane of the same size. But this fact could only explain a relative rareness of turboprop airplanes among aerobatic planes. What it cannot explain is their (next to?) absence, since experience shows that if there is a will there is a way, and some or another team of people should always be able to adquire one of these planes. Just a SWAG, but I would think that the Turbo Raven cost about 6 times what a good Edge 540 would cost. Sponsorship before construction would be important. Larry Ellison, CEO of Oracle, and owner of many big boy toys, is also a fan of aviation. The story goes that he was talking with Wayne Handley and Sean Tucker after some airshow, and they hatched the idea of the Turbo Raven. Cost isn't much of an issue for Larry Ellison, since he is way up there on the various 'richest people' lists. Another post mentioned the difference between aerobatics and competition aerobatics. The T-6A and various other trainers are aerobatic turboprops, but they don't have to worry about staying in the competition aerobatic box, which is quite tiny. The cost of a turboprop, and the size of the box are probably the main reasons they aren't used on competition planes. The maintenance requirements on the turboprop would probably also be an issue. The Turbo Raven was just a show plane, in the same category as the jet powered Waco. Fun to watch, but totally ridiculous. John -- John Clear - http://www.panix.com/~jac |
#8
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Turbines are not more difficult to maintain. In fact the maintenance is much
lower on a turbine (on a per-hour basis). The cost of the overhaul is quite different though! However, the TBO is much better for a turbine. Overhaul on my turbine is about US$235,000 but I get 3000 hours out of it. It's quite a bit more expensive than other turbines, but you still are in the US$100,000 zone for an overhaul of a 600hp+ engine. How much would a 600hp piston engine cost to overhaul? "John Clear" wrote in message ... In article , Byron J. Covey wrote: Just in case that I am right: I know that a turboprop airplane can easily cost twice as much as a piston plane of the same size. But this fact could only explain a relative rareness of turboprop airplanes among aerobatic planes. What it cannot explain is their (next to?) absence, since experience shows that if there is a will there is a way, and some or another team of people should always be able to adquire one of these planes. Just a SWAG, but I would think that the Turbo Raven cost about 6 times what a good Edge 540 would cost. Sponsorship before construction would be important. Larry Ellison, CEO of Oracle, and owner of many big boy toys, is also a fan of aviation. The story goes that he was talking with Wayne Handley and Sean Tucker after some airshow, and they hatched the idea of the Turbo Raven. Cost isn't much of an issue for Larry Ellison, since he is way up there on the various 'richest people' lists. Another post mentioned the difference between aerobatics and competition aerobatics. The T-6A and various other trainers are aerobatic turboprops, but they don't have to worry about staying in the competition aerobatic box, which is quite tiny. The cost of a turboprop, and the size of the box are probably the main reasons they aren't used on competition planes. The maintenance requirements on the turboprop would probably also be an issue. The Turbo Raven was just a show plane, in the same category as the jet powered Waco. Fun to watch, but totally ridiculous. John -- John Clear - http://www.panix.com/~jac |
#9
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#10
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The Australian Roulettes fly the PT-6 as well as a few other countries
I can't think of at the moment. Brazil perhaps? But one has to remember, what aerobatic teams do, and what happens in an aerobatic competition aren't identical. The competition box is one size for all competitions, 1000 square meters. Changing it would require sancitioning from the FAI. But creating different sized boxes for different aircraft neutralizes the spirit behind the competition. Airshows on the other hand, boxes are determined mainly by the venue. One of the reasons you don't see many more turbine GA aircraft is partly due to the lack of certified small turbines. There is a growing number of turbine homebuilts. Comp Air and Lancair being two that offer kits designed for them. I've also seen an article on a turbine RV-4 in Sport Aviation not too long ago. As time goes on, cheaper and smaller turbines will probably have a greater presence in the GA market. Don't know what the economics are though, how much does a hot section cost compared to overhauling a piston engine? And what does that translate to per hour costs? No need to get hostile over all this, Holm. Turbines are not the end-all, be-all of aviation. Jets, turboprops and pistons all have thier strengths and weaknesses. And their appropriate application. Aviation pistons right now are just at the top of thier game when it comes to hardcore aerobatic aircraft. And you wouldn't put a piston in a commuter airliner. -j- |
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