ak907 From United States of America, joined Mar 2012, 36 posts, RR: 0 Reply 2, posted (3 months 2 weeks 5 days 7 hours ago) and read 3227 times:
Yes actually, but like cornutt said, it's not much. Usually around 5% or so. It is actually listed in the type certificate of that engine, and is included in the shaft horsepower output of the engine. They use a formula to convert thrust into horsepower, and add both together under "equivalent shaft horsepower".
For example a PT6-114A has a shaft horsepower of 675hp, and exhaust thrust of 124 lbs. Add both together using a formula and they come up with an equivalent shaft horsepower of 725hp.
Mir From United States of America, joined Jan 2004, 19715 posts, RR: 56 Reply 6, posted (3 months 2 weeks 5 days 5 hours ago) and read 3129 times:
Quoting Aesma (Reply 5): The PT6 is an interesting example since it's usually installed "backwards" so I always thought the exhaust thrust was very little.
The exhaust is still ejected in a backwards direction, so it does contribute to the overall thrust in a very small way.
-Mir
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bomber996 From United States of America, joined Aug 2005, 364 posts, RR: 0 Reply 7, posted (3 months 2 weeks 5 days 3 hours ago) and read 3087 times:
I remember hearing during a cockpit visit in a PSA Airlines DO-328 that the exhaust from the engine contributed to something like 25% of the total thrust of the engine. Then again, I was a lot younger than I am today and I may be over exaggerating that number.
Starlionblue From Hong Kong, joined Feb 2004, 15871 posts, RR: 66 Reply 8, posted (3 months 2 weeks 4 days 22 hours ago) and read 2973 times:
Quoting Mir (Reply 6): Quoting Aesma (Reply 5):
The PT6 is an interesting example since it's usually installed "backwards" so I always thought the exhaust thrust was very little.
The exhaust is still ejected in a backwards direction, so it does contribute to the overall thrust in a very small way.
The PT6 actually reverses flow four times, as the combustors have airflow reversed compared to engine airflow. PW wanted a really short engine with a simple prop installation I guess.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Dufo From Slovenia, joined May 1999, 752 posts, RR: 4 Reply 9, posted (3 months 2 weeks 4 days 17 hours ago) and read 2842 times:
Official figures for GE CT7-5A installed on Saab 340A tell that the engine produces 1735 SHP and 1800 ESHP. The difference between these two numbers is the jet propulsion.
I seriously think I just creamed my pants without any influence from any outside variables.
Spacepope From Vatican City, joined Dec 1999, 2739 posts, RR: 1 Reply 10, posted (3 months 2 weeks 3 days 20 hours ago) and read 2480 times:
IIRC, even piston engines, such as the RR Merlin (specifically when installed in later Spitfires), gained a not-insignificant amount of thrust from the exhaust flow. Enough to boost the top speed by exhaust stack design.
aviaponcho From France, joined Aug 2011, 230 posts, RR: 4 Reply 11, posted (3 months 2 weeks 3 days 20 hours ago) and read 2458 times:
Hello
On the electra 501-D13's
Thrust from the propeller was 3460 Hp (8000 lbsf) and thrust from the exhaust 290 hp (726 lbsf)
So that's not insignifiant.... that's 8%
It remain to see how this evolved in new designs... as efficiency goes up, residual thrust can go down, isn't it ?
KELPkid From United States of America, joined Nov 2005, 5932 posts, RR: 4 Reply 14, posted (3 months 2 weeks 3 days 13 hours ago) and read 2277 times:
As I understand it, on both the Cessna 208 Caravan and DeHavilland Twin Otter, the thrust put off by the jet pipes is not so insignificant when the aircraft is equipped with floats. That thrust basically guarantees that as long as the engine(s) are burning, the aircraft will be moving on the water (apart from putting the prop(s) in beta). On a regular (non turbo-prop) float plane, when water taxiing, putting the throttle to idle usually lets the aircraft coast to a stop, where it is only affected by wind and water currents.
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
Scooter01 From Norway, joined Nov 2006, 1155 posts, RR: 8 Reply 16, posted (3 months 2 weeks 3 days 3 hours ago) and read 2122 times:
A bit off topic, since this thread seems to be about fixed wing aircraft.
When the first Agusta Bell 204B helicopters came to Norway in the spring of '62, they were equipped with the Bristol Siddeley Gnome H.1000 engine where the exhaust exited sideways, like on this Dutch machine:
The owners were apparently not quite happy with the performance, and the machines were sent back to Italy at the end of '63 to be re-engined with the Lycoming T-53 -with a straight-back exhaust. After the conversion I remember it was talk of a significant improvement of forward airspeed, but I cannot recall how much.
Scooter01
"We all have a girl and her name is nostalgia" - Hemingway
vikkyvik From United States of America, joined Jul 2003, 8223 posts, RR: 28 Reply 17, posted (3 months 2 weeks 2 days 13 hours ago) and read 1948 times:
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Quoting KELPkid (Reply 14): As I understand it, on both the Cessna 208 Caravan and DeHavilland Twin Otter, the thrust put off by the jet pipes is not so insignificant when the aircraft is equipped with floats. That thrust basically guarantees that as long as the engine(s) are burning, the aircraft will be moving on the water (apart from putting the prop(s) in beta). On a regular (non turbo-prop) float plane, when water taxiing, putting the throttle to idle usually lets the aircraft coast to a stop, where it is only affected by wind and water currents.
That's just a function of your total thrust versus drag, though. Doesn't have any special dependence on the exhaust, unless I'm missing something.
I'm assuming props at idle throttle still have some forward thrust.
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Starlionblue From Hong Kong, joined Feb 2004, 15871 posts, RR: 66 Reply 18, posted (3 months 2 weeks 2 days 10 hours ago) and read 1894 times:
Quoting vikkyvik (Reply 17): I'm assuming props at idle throttle still have some forward thrust.
Assuming you mean the actual propeller here, it depends on the pitch capability of the prop. Certainly on a GA plane with a constant speed prop the prop's pitch cannot go all the way to zero so you will still have thrust.
On airline class turboprops you tend to have reverse ("beta") so you can go to zero pitch (and beyond) and thus zero thrust.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
vikkyvik From United States of America, joined Jul 2003, 8223 posts, RR: 28 Reply 19, posted (3 months 2 weeks 1 day 19 hours ago) and read 1753 times:
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Quoting Starlionblue (Reply 18): On airline class turboprops you tend to have reverse ("beta") so you can go to zero pitch (and beyond) and thus zero thrust.
True, but I was just talking about idle throttle, not prop pitch (assuming they're separate).
"Two and a Half Men" was filmed in front of a live ostrich.
KELPkid From United States of America, joined Nov 2005, 5932 posts, RR: 4 Reply 20, posted (3 months 2 weeks 1 day 18 hours ago) and read 1743 times:
Quoting vikkyvik (Reply 17): That's just a function of your total thrust versus drag, though. Doesn't have any special dependence on the exhaust, unless I'm missing something.
I'm assuming props at idle throttle still have some forward thrust.
In a turboprop, probably not much...rememer that there is a prop hub that is constantly adjusting blade pitch to maintain propeller RPM. Unless that RPM is really, really low, the prop will have to be at a really fine pitch to allow it to spin with the engine at a relatively low power setting (i.e. ground idle or slightly above it). On a PT6, I would imagine that the condition lever is not set for flight while taxiing...which lowers the engine's idle RPM.
Quoting Starlionblue (Reply 18): Assuming you mean the actual propeller here, it depends on the pitch capability of the prop. Certainly on a GA plane with a constant speed prop the prop's pitch cannot go all the way to zero so you will still have thrust.
A constant-speed prop, even with the prop lever at the firewall, is going to turn at fairly "normal" RPM's on the ground while taxiing, because although the prop hub might be striving to turn the prop at maximum RPM, the engine just isn't providing the power to it, and the hub has physical limits on just how fine it can make the prop pitch
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
dw747400 From United States of America, joined Aug 2001, 1244 posts, RR: 1 Reply 21, posted (3 months 2 weeks 1 day 12 hours ago) and read 1677 times:
Quoting KELPkid (Reply 20): On a PT6, I would imagine that the condition lever is not set for flight while taxiing...which lowers the engine's idle RPM.
It depends on the specific installation. On a King Air C90 with four bladed props, even with the condition levers at ground idle, we have enough static thrust to start rolling at all but max gross. We spend a lot of taxi time with the props in beta to keep from wearing down the brakes. I haven't flown the three bladed C90, but I'm told it has much less static thrust and thus doesn't need beta to keep it from accelerating.
I discussed this with a C-130 pilot once; he informed me that they had considerable excess thrust at idle at light weights, but at high takeoff weights the idle power wouldn't keep them moving.
Quoting vikkyvik (Reply 19):
True, but I was just talking about idle throttle, not prop pitch (assuming they're separate).
I can't speak for every installation, but all I've seen or flown use throttle to control beta/reverse. Your prop control sets RPM, your throttle sets how much power you are producing and what direction that thrust is directed.
Starlionblue From Hong Kong, joined Feb 2004, 15871 posts, RR: 66 Reply 22, posted (3 months 2 weeks 1 day 10 hours ago) and read 1658 times:
Quoting vikkyvik (Reply 19): Quoting Starlionblue (Reply 18):
On airline class turboprops you tend to have reverse ("beta") so you can go to zero pitch (and beyond) and thus zero thrust.
True, but I was just talking about idle throttle, not prop pitch (assuming they're separate).
Ah. Sorry I had brainfart there. You mean the thrust from the core. Well certainly since there is airflow through the engine you'd have some thrust.
Also interestingly the thrust lever goes from controlling thrust in normal range to controlling pitch in beta range.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
ZKSUJ From New Zealand, joined May 2004, 6937 posts, RR: 10 Reply 24, posted (3 months 1 week 2 days 10 hours ago) and read 1261 times:
Quoting flylku (Thread starter): I was on a Dash 8 tonight and it got me wondering, are there any turboprop aircraft where the turbine exhaust adds meaningfully to thrust?
The Dash 8 has about 120hp thrust from the exhaust (or jet thrust as I like to call it) Not where near enough to power the aircraft though as previous posters have mentioned
25 DiamondFlyer: There are also piston powered aircraft that have reverse capability. -DiamondFlyer
26 DashTrash: Beta and reverse are different (Dash 8 anyway). DH called "beta", "disc". I don't recall what blade angle range was in disc, but reverse was availabl
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