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#21
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Turbo prop question
"Bertie the Bunyip" wrote in message .. . "muff528" wrote in news:SMuRj.25645$TS5.1624@trnddc08: "Bertie the Bunyip" wrote in message ... "muff528" wrote in news:krtRj.968$lc6.775@trnddc04: "Bertie the Bunyip" wrote in message .. . wrote in news:e508d435-db20-4b21-9c9b- : On Apr 25, 4:37 am, Bertie the Bunyip wrote: wrote in news:de5298d4-778b-475f-9321- : On 25 Apr, 11:53, Frank Olson wrote: Bertie the Bunyip wrote: Chris W wrote in news:74gQj.67968$y05.19485 @newsfe22.lga: I was channel surfing the other day and caught the tail end of some show about rich people and their planes. Anyway the pilot of this one single engine turbo prop said there was no mechanical connection between the prop and engine. How can that be? It's a free turbine. Most modern turboprops use that system. There's a seperate turbine that runs the prop geabox. He's technically incorrect since that turbine is part of the engine... Bertie Rich people. More money than brains.- Hide quoted text - I'm not in disagreement with Bertie, wouldn't dare, but it "could be" electric drive, hydraulic drive. Nah, not on a turbine. These are used in other vehicles. Most cars in the US use an automatic transmission that includes a torque convertor for example. I am sure that it is in this case a free turbine - gas drive - that connects to a propellor - gas-gas drive. http://www.gasgas.com/index.shtml Yeah, almost all modern turboprops use this system. Some of the older ones, like the RR Dart or the Allisons were gear driven off the main turbine, but this is all but abandoned these days. In fact, even "jets" are really just ducted fan turboprops with the fan driven by a turbine in the exhaust. Bertie The Garrett TPE 331 is still a fixed turboprop. Lots of those flying, especially on some upscale kitplanes. Isn't the Swearingen Merlin powered by those, too? http://www.aircraftenginedesign.com/pictures/TPE331.gif Dan Yeah, Garret are one of the holdouts. They're on alot of airplanes. the Metro, the turbine commanders. I think there's a Walter that's in th esame class being used on quite a few airplanes as well. The Pratts are all free turbines, AFAIK. The older ones are centrifugal engines with a revese flow, that is, the intake is on the back and they exhaust in front, which is why the PT6 's have those stovepipes just behind the prop, and the newer 120 and newers are axial with the air coming in the front and the fire going out the back. The 120 has a prop brake with which you can stop the prop while the engine is running ( on the ground) and use the engine for an APU. Bertie Amazing how after a while you can tell the difference between the Pratts and the Garretts from the ground while the plane is at 13,500 ft above you. Many times we had a Twin Otter with Pratts and a Casa 212 with Garretts flying on the same day and you could tell which was on jump run just by the sound. I just assumed it was because of the different methods of coupling the props to the powerplant. !!! I don't think I could except by seeing the airplane. Yeah, you get tuned in to any engine you're familiar with, though, don't you? Bertie Yeah, I think the fact that they were flying within a few minutes of each other all day makes the comparison easier. The main difference seems to me to be the "loudness" of the beat freq. generated by slightly "out-of-sync" props, especially when the "cut" occurs just before exit time. The Garretts sounded "gutsier" for lack of a better term and the beat frequency amplitude was much greater than the PT6's. Even during the climbout to jump altitude the Garretts seemed to sound more authoritative. But that brings up another question that I have wondered about. For a twin, for example, does the force of the atmosphere pushing against the props have an "equalizing" effect on the propeller speeds of turbine-coupled props on slightly out-of-sync engines? I would intuitively think that such a moderating effect would account for differences in beat sounds between them and direct-coupled twins which were a few rpm's out. Well, I've only flwon one type with the turbine directly geared to the prop and it was a single lever operation which meant you were altering the power as well as the prop pitch whne you mover the lever. it had no autosynch so you did it the old fashioned way and it was out of synch a good bit of the time. I can't remember hat we had in the King Airs I flew, but the PW120 had an autosynch so that might account for it. Bertie Thanks, I never thought of propellers as such complex devices. Dan's link to Hartzell was pretty informative. TP |
#22
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Turbo prop question
"muff528" wrote in
news:REvRj.11461$Rk6.9130@trnddc07: "Bertie the Bunyip" wrote in message .. . "muff528" wrote in news:SMuRj.25645$TS5.1624@trnddc08: "Bertie the Bunyip" wrote in message ... "muff528" wrote in news:krtRj.968$lc6.775@trnddc04: "Bertie the Bunyip" wrote in message .. . wrote in news:e508d435-db20-4b21-9c9b- : On Apr 25, 4:37 am, Bertie the Bunyip wrote: wrote in news:de5298d4-778b-475f-9321- : On 25 Apr, 11:53, Frank Olson wrote: Bertie the Bunyip wrote: Chris W wrote in news:74gQj.67968$y05.19485 @newsfe22.lga: I was channel surfing the other day and caught the tail end of some show about rich people and their planes. Anyway the pilot of this one single engine turbo prop said there was no mechanical connection between the prop and engine. How can that be? It's a free turbine. Most modern turboprops use that system. There's a seperate turbine that runs the prop geabox. He's technically incorrect since that turbine is part of the engine... Bertie Rich people. More money than brains.- Hide quoted text - I'm not in disagreement with Bertie, wouldn't dare, but it "could be" electric drive, hydraulic drive. Nah, not on a turbine. These are used in other vehicles. Most cars in the US use an automatic transmission that includes a torque convertor for example. I am sure that it is in this case a free turbine - gas drive - that connects to a propellor - gas-gas drive. http://www.gasgas.com/index.shtml Yeah, almost all modern turboprops use this system. Some of the older ones, like the RR Dart or the Allisons were gear driven off the main turbine, but this is all but abandoned these days. In fact, even "jets" are really just ducted fan turboprops with the fan driven by a turbine in the exhaust. Bertie The Garrett TPE 331 is still a fixed turboprop. Lots of those flying, especially on some upscale kitplanes. Isn't the Swearingen Merlin powered by those, too? http://www.aircraftenginedesign.com/pictures/TPE331.gif Dan Yeah, Garret are one of the holdouts. They're on alot of airplanes. the Metro, the turbine commanders. I think there's a Walter that's in th esame class being used on quite a few airplanes as well. The Pratts are all free turbines, AFAIK. The older ones are centrifugal engines with a revese flow, that is, the intake is on the back and they exhaust in front, which is why the PT6 's have those stovepipes just behind the prop, and the newer 120 and newers are axial with the air coming in the front and the fire going out the back. The 120 has a prop brake with which you can stop the prop while the engine is running ( on the ground) and use the engine for an APU. Bertie Amazing how after a while you can tell the difference between the Pratts and the Garretts from the ground while the plane is at 13,500 ft above you. Many times we had a Twin Otter with Pratts and a Casa 212 with Garretts flying on the same day and you could tell which was on jump run just by the sound. I just assumed it was because of the different methods of coupling the props to the powerplant. !!! I don't think I could except by seeing the airplane. Yeah, you get tuned in to any engine you're familiar with, though, don't you? Bertie Yeah, I think the fact that they were flying within a few minutes of each other all day makes the comparison easier. The main difference seems to me to be the "loudness" of the beat freq. generated by slightly "out-of-sync" props, especially when the "cut" occurs just before exit time. The Garretts sounded "gutsier" for lack of a better term and the beat frequency amplitude was much greater than the PT6's. Even during the climbout to jump altitude the Garretts seemed to sound more authoritative. But that brings up another question that I have wondered about. For a twin, for example, does the force of the atmosphere pushing against the props have an "equalizing" effect on the propeller speeds of turbine-coupled props on slightly out-of-sync engines? I would intuitively think that such a moderating effect would account for differences in beat sounds between them and direct-coupled twins which were a few rpm's out. Well, I've only flwon one type with the turbine directly geared to the prop and it was a single lever operation which meant you were altering the power as well as the prop pitch whne you mover the lever. it had no autosynch so you did it the old fashioned way and it was out of synch a good bit of the time. I can't remember hat we had in the King Airs I flew, but the PW120 had an autosynch so that might account for it. Bertie Thanks, I never thought of propellers as such complex devices. Dan's link to Hartzell was pretty informative. On the fixed shaft turboprops they're extremely complex. All sorts of gadgets on them to keep them under control. on the old Allisons the most common reason for shutdown by far was a prop problem of one type or another. but giving your observation about the Garret vs PW it's probably due to the Garret fineing off as the throttles close as opposed to the Pratts where they do, but not so much... Bertie |
#23
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Turbo prop question
On Apr 28, 9:03*pm, Bertie the Bunyip wrote:
"muff528" wrote innews:REvRj.11461$Rk6.9130@trnddc07: "Bertie the Bunyip" wrote in message . .. "muff528" wrote in news:SMuRj.25645$TS5.1624@trnddc08: "Bertie the Bunyip" wrote in message ... "muff528" wrote in news:krtRj.968$lc6.775@trnddc04: "Bertie the Bunyip" wrote in message . 130... wrote in news:e508d435-db20-4b21-9c9b- : On Apr 25, 4:37 am, Bertie the Bunyip wrote: wrote in news:de5298d4-778b-475f-9321- : On 25 Apr, 11:53, Frank Olson wrote: Bertie the Bunyip wrote: Chris W wrote in news:74gQj.67968$y05.19485 @newsfe22.lga: I was channel surfing the other day and caught the tail end of some show about rich people and their planes. *Anyway the pilot of this one single engine turbo prop said there was no mechanical connection between the prop and engine. *How can that be? It's a free turbine. Most modern turboprops use that system. There's a seperate turbine that runs the prop geabox. He's technically incorrect since that turbine is part of the engine... Bertie Rich people. *More money than brains.- Hide quoted text - I'm not in disagreement with Bertie, wouldn't dare, but it "could be" electric drive, hydraulic drive. Nah, not on a turbine. These are used in other vehicles. Most cars in the US use an automatic transmission that includes a torque convertor for example. I am sure that it is in this case a free turbine - gas drive - that connects to a propellor - gas-gas drive. http://www.gasgas.com/index.shtml Yeah, almost all modern turboprops use this system. Some of the older ones, like the RR Dart or the Allisons were gear driven off the main turbine, but this is all but abandoned these days. In fact, even "jets" are really just ducted fan turboprops with the fan driven by a turbine in the exhaust. Bertie * * * * The Garrett TPE 331 is still a fixed turboprop. Lots of * * * * those flying, especially on some upscale kitplanes. Isn't the Swearingen Merlin powered by those, too? http://www.aircraftenginedesign.com/pictures/TPE331.gif * Dan Yeah, Garret are one of the holdouts. They're on alot of airplanes. the Metro, the turbine commanders. I think there's a Walter that's in th esame class being used on quite a few airplanes as well. The Pratts are all free turbines, AFAIK. The older ones are centrifugal engines with a revese flow, that is, the intake is on the back and they exhaust in front, which is why the PT6 's have those stovepipes just behind the prop, and the newer 120 and newers are axial with the air coming in the front and the fire going out the back. The 120 has a prop brake with which you can stop the prop while the engine is running ( on the ground) and use the engine for an APU. Bertie Amazing how after a while you can tell the difference between the Pratts and the Garretts from the ground while the plane is at 13,500 ft above you. Many times we had a Twin Otter with Pratts and a Casa 212 with Garretts flying on the same day and you could tell which was on jump run just by the sound. I just assumed it was because of the different methods of coupling the props to the powerplant. !!! I don't think I could except by seeing the airplane. Yeah, you get tuned in to any engine you're familiar with, though, don't you? Bertie Yeah, I think the fact that they were flying within a few minutes of each other all day makes the comparison easier. The main difference seems to me to be the "loudness" of the beat freq. generated by slightly "out-of-sync" props, especially when the "cut" occurs just before exit time. The Garretts sounded "gutsier" for lack of a better term and the beat frequency amplitude was much greater than the PT6's. Even during the climbout to jump altitude the Garretts seemed to sound more authoritative. But that brings up another question that I have wondered about. For a twin, for example, does the force of the atmosphere pushing against the props have an "equalizing" effect on the propeller speeds of turbine-coupled props on slightly out-of-sync engines? I would intuitively think that such a moderating effect would account for differences in beat sounds between them and direct-coupled twins which were a few rpm's out. Well, I've only flwon one type with the turbine directly geared to the prop and it was a single lever operation which meant you were altering the power as well as the prop pitch whne you mover the lever. it had no autosynch so you did it the old fashioned way and it was out of synch a good bit of the time. I can't remember hat we had in the King Airs I flew, but the PW120 had an autosynch so that might account for it. Bertie Thanks, I never thought of propellers as such complex devices. Dan's link to Hartzell was pretty informative. On the fixed shaft turboprops they're extremely complex. All sorts of gadgets on them to keep them under control. on the old Allisons the most common reason for shutdown by far was a prop problem of one type or another. but giving your observation about the Garret vs PW it's probably due to the Garret fineing off as the throttles close as opposed to the Pratts where they do, but not so much... Bertie- Hide quoted text - - Show quoted text - Here are a few numbers for you (taken from my Flight Safety big book on the Twin Commander 1000). This airplane uses the Garrett TPE331-10 engines with 1000 shaft horsepower, flat rated back to 800 hp. The 800 hp are available up to 18,000 ft. Naturally, this means these airplanes climb like scalded cats (3000+ fpm.) The engine has all the turbines on a single shaft which runs at 41,730 rpm maximum. Cruise rpm is 96-100%. This shaft is geared down by a planetary gear reduction with 26:1 ratio, giving a max prop rpm of 1591 rpm. Engine rpm is pretty much controlled by propellor blade angle. A Beta mode (reverse thrust) is available for ground use only. No question about it, they are very loud. Even in ground idle mode, the prop rpm is 65% of max. One always receives the Twin Commander salute (index fingers in both ears) from anybody standing around on the ramp. One advantage of the single shaft design is fuel efficiency. The airplane cruises at 300+ knots true at 26,000 ft on 80 gph after a maximum gross weight takeoff of 11,700 lbs. Try that in your P&W turboprop. ;-) Beside the Twin Commanders, these engines are also used in the Mitsubishi MU-2. TBO on the engines is 5,000 hours with a hot section inspection at 2500 hours. K l e i n |
#24
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Turbo prop question
Here are a few numbers for you (taken from my Flight Safety big book
on the Twin Commander 1000). This airplane uses the Garrett TPE331-10 engines with 1000 shaft horsepower, flat rated back to 800 hp. The 800 hp are available up to 18,000 ft. Naturally, this means these airplanes climb like scalded cats (3000+ fpm.) The engine has all the turbines on a single shaft which runs at 41,730 rpm maximum. Cruise rpm is 96-100%. This shaft is geared down by a planetary gear reduction with 26:1 ratio, giving a max prop rpm of 1591 rpm. Engine rpm is pretty much controlled by propellor blade angle. A Beta mode (reverse thrust) is available for ground use only. No question about it, they are very loud. Even in ground idle mode, the prop rpm is 65% of max. One always receives the Twin Commander salute (index fingers in both ears) from anybody standing around on the ramp. One advantage of the single shaft design is fuel efficiency. The airplane cruises at 300+ knots true at 26,000 ft on 80 gph after a maximum gross weight takeoff of 11,700 lbs. Try that in your P&W turboprop. ;-) Beside the Twin Commanders, these engines are also used in the Mitsubishi MU-2. TBO on the engines is 5,000 hours with a hot section inspection at 2500 hours. K l e i n Yes!.........LOUD...........That's the word I was looking for! :-)) Always a treat to get on a Casa load and watch runway rapidly drop away through the open tailgate when the pilots decided to do a "high-performance" takeoff. With 23-24 people sitting toboggan-style on the floor the only outside view is through the tailgate. TP |
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