Prop speeds
Can someone tell me roughly the operating range for prop speeds on a turbo prop aircraft? My Google search gives me every detail known to man except prop speeds.
Much obliged |
any... to just under speed of sound... :D
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Prop speeds
Sorry, I should have said rotational speeds
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well thats probably still true. Tip speeds get close to and sometimes through the speed of sound - boeing stearmans make the rasping noise they do because of the tips going supersonic. A 90" prop on something like a king air is describing a path about 7 metres round and at 2200 rpm thats ..um M0.78.
Saturday afternoon maths of course.. Do you mean just rpm? if so, no idea, google is your friend http://www.enhanced.aero/pdf/performance_raisbeck.pdf (might be talking rubbish.. am sitting here watching the F1) |
Q400: 850 to 1020 rpm. The smaller ones up to 1200 rpm.
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Prop speeds
Gentlemen
Many thanks, just what I was looking for. Theres always an answer if you ask the right bloke. Boslandew |
Safelife, just clarifying something, but I presume you mean the smaller Dash 8s? And not smaller turboprops in general - because the Kingair I fly is around 2200 rpm, not 1200
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Just to add another, larger diameter turbo-prop to the mix.
The Lockheed P3 Orion, and therefore the Electra props are constant speed (in flight) at 1,021 rpm, with an 11 foot diameter prop if I recall! Though the Electra had square-tipped and the Orion round-tipped prop blades. |
L410: 2080 max (takeoff), 1900 climb, 1700 cruise
Saab340: 1380 max, 1230 climb and cruise |
Homebuilts powered by Volkswagen engines typically have a 3300 RPM redline.
However if you wanted to generalize: Large Turboprop airliners (30 plus seats): prop RPM range 800-1200 Small Turboprops.................................................. .....1700-2200 Pistons engines ........................................................1800-2700 |
The BIIIG pistons had even slower-turning props.
For example - P&W R-4360-4 Max crankshaft RPM = 2700 Reduction gear ratio = 0.425 Resulting prop RPM = 1148 Other R-4360s had gear ratios as low as 0.333, for prop rpm = 900. |
DH8D:
maximum (takeoff/go around) 1020, as has been mentioned; climb power 900, cruise power 850 (also useable for climb and landing; brings some reduction in noise and performance). DH8C: Maximum 1200, intermediate setting 1050, cruise 900 rpm. Also on this series, 900rpm is allowed for climb and landing with some performance penalty but noticeably less cabin noise. NK-12 powered turboprops (Tupolev 95, An-22): 700rpm, which results in supersonic tip speeds due to the large propellers. Still seems to be efficient though. |
IIRC (five years have passed) ATR 42-300 with PW120 and Hamilton 14SF5 four bladed props used 100% for takeoff and approach, 86% detent for climb and 77% for cruise when out of icing conditions, 100% being 1200 RPM. We could set RPM anywhere between detents and often used 92% for cruise in icing conditions as it was less noisy than 86%, increase in consumption was minuscule and cruise speed (250 KTAS) not affected.
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Prop speeds
Many thanks for the further info. As an ex-rotary man I had thought that cruise rpm would have been about 2000 as with piston engines, say DC3. An eye-opener to see rpm as low as 850.
Boslandew |
Looked through a couple old manuals, both the P&W 1830-94 and Wright 1820-80 have 16/9 reduction gears. So if the engine is turning 2050 rpm in cruise, the prop is turning about 1150 rpm. I know R985s don't have a reduction gear and judging from the sound R1340s don't either.
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R-1340 prop speeds
There are both direct-drive and geared (3/2) versions; the direct-drive model is much more common. The geared version (R-1340-AN-2) was built primarily for large blimps, with oversize prop for low-speed efficiency.
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Prop speeds
The logical question has just occurred to me. Why should turboprop rpm be half that of a piston engine on a comparable type, say DC3 against DH8C.
Probably not a good comparison of types but I hope you get the point I'm trying to make |
Why should turboprop rpm be half that of a piston engine on a comparable type, say DC3 against DH8C. i think the extreme was a lockheed starliner where the engine turned the props via a .355 gearing so prop speeds were something about 750-800rpm in cruise . |
Aerobat
Probably didn't use precise enough terms. According the Pilots Notes Once had, the DC3 Prop turns at about 2000 RPM plus or minus a bit in the cruise, nearly twice that quoted below for, say, the Q400. Have I missed something? |
No, the DC-3 CRANKSHAFT turns ~2000 rpm (that's what the cockpit tach shows).
The prop turns 56.25% of that speed, or 1125 rpm - because of the gearing ratio. |
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