Redfox From United Kingdom, joined Sep 2003, 172 posts, RR: 2 Posted (6 years 5 months 1 day 6 hours ago) and read 8088 times:
Can anyone help with the propeller RPM of a Spitfire or other Warbird aeroplane. I wish to know if the engine is geared toward the prop i.e. 2,500engine rpm may yield 5,000 prop rpm. Is the engine just linked directly to the engine as a light aeroplane (C152).
I would like to know the take off, cruise and taxy propeller RPM.
SlamClick From United States of America, joined Nov 2003, 10019 posts, RR: 76 Reply 1, posted (6 years 5 months 1 day 6 hours ago) and read 8074 times:
Cannot give you the numbers you seek but I can tell you that most, if not all, are geared. However, they are geared DOWN and not UP.
Engines have optimum RPM ranges and so do propellers, but the ideal for the prop is probably always lower than that of the engine. I watched this airplane do its airshow routine at Reno yesterday . . .
. . . and did hear some numbers related. The announcer said that this engine is run at 2500 RPM throughout the show and the prop is geared down to run at 800 RPM. (It also has three black blades and one white blade so it looks even slower than that. Now that is probably extreme. This beauty is over-engined. That is an R-4360 in it, nearly twice the size of the original R-2800.
I would expect a V-12 as seen in Spitfires, Mustangs and the like, to turn maybe 2500 on the crankshaft and 1200-1500 on the propeller. That is just an educated guess and I'd surely welcome correction from anyone who knows. The Merlin engines from these planes are used in unlimited racing hydroplanes where they turn over four thousand with the prop geared UP, maybe 3:1 and as much as 200 inches of manifold pressure with nitrous oxide injection. They also blow up like a hand grenade after a few minutes of this. (Quicker if the prop comes out of the water.)
edit: Too bad you didn't ask this question last week. I walked the pits at the Reno Air Races on monday and could have asked any number of Mustang crews this question about the Allison and the Merlin engines. Unfortunately I don't intend to visit the pits again this year.
[Edited 2005-09-16 15:53:23]
Happiness is not seeing another trite Ste. Maarten photo all week long.
LeanOfPeak From United States of America, joined Oct 2004, 509 posts, RR: 1 Reply 2, posted (6 years 5 months 1 day 5 hours ago) and read 8065 times:
FWIW, most modern unlimited hydroplanes run turboshaft engines. I don't believe there is an unlimited still running a Merlin. There is said to be one that runs an Allison, however.
Many WWII aircraft had direct drive, i e engine and prop running the same RPM with the prop essentially bolted to the drive shaft. Then again, there were those with reduction gearboxes.
Bear in mind that these aircraft with few exceptions all had constant speed propellers. In other words, RPM is not the measure of output power it is in your fixed-pitch light aircraft.
Cheers,
Fred
[Edited 2005-09-16 17:17:09]
I thought I was doing good trying to avoid those airport hotels... and look at me now.
SlamClick From United States of America, joined Nov 2003, 10019 posts, RR: 76 Reply 4, posted (6 years 5 months 1 day 4 hours ago) and read 8041 times:
Check this site: http://www.bcam.net/engines/merlin.htm
It will take you directly to a picture of the Rolls-Royce Merlin engine as installed on the Spit. You can see the prop shaft projecting from a casing that appears to house a reduction gear train of approximately 1:2 ratio. You can see that the lower gear in that casing seems to be splined to the nose of the crankshaft.
There is also a like to a similar picture of an Allison V-1710 as found on some Mustangs, P-40s etc. The reduction appears about the same.
Every radial engine I've ever seen up close has a planetary reduction box integral to the engine. Click on the Wright R-3350 for example and note the round extension from the center of the engine which houses this gear set.
Happiness is not seeing another trite Ste. Maarten photo all week long.
FredT From United Kingdom, joined Feb 2002, 2179 posts, RR: 29 Reply 5, posted (6 years 5 months 1 day 4 hours ago) and read 8037 times:
I think you better listen to SlamClick and not to me.
I have been ransacking my mind to come up with an example of a direct drive WWII aircraft of the more powerful variety, and come up with nothing except the nagging suspicion that perhaps this is one of those cases where what you think you "know" isn't based on facts at all.
Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
Jetlagged From United Kingdom, joined Jan 2005, 2327 posts, RR: 15 Reply 6, posted (6 years 5 months 1 day 1 hour ago) and read 8014 times:
For the Griffon engined Spitfire XIV:
Normal takeoff power setting was +7 psi boost.
Maximum takeoff power was 2,750 RPM / +12 psi boost.
Normal climb setting was 2,600 RPM / +9 psi boost.
For cruise, boost was set to +7 psi and speed controlled by adjusting RPM.
On approach rpm was set to 2,400 (-5 psi boost), increasing rpm and boost as flap and gear were extended.
Minimum RPM allowed in flight was 1800.
The above numbers come from the Pilots Notes for the Mk XIV.
For the Merlin engined Spitfires the numbers were similar, but I don't have the details to hand at present.
All RPMs are engine RPM, as the pilot had no propeller RPM indication, apart from seeing it turning (or not) . Propeller gear reduction ratio was around 2:1, so divide by 2 to get an approximation to prop RPM.
The unlimited Reno racers are highly modified so their performance and data will differ from wartime production aircraft
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Timz From United States of America, joined Sep 1999, 6181 posts, RR: 8 Reply 9, posted (6 years 5 months 23 hours ago) and read 7991 times:
Another gearing question: as we all know, most P-38 props were handed, but Gunston once said that Allison prop rotation could be reversed by added or removing an extra gear. So, did the two engines on a P-38 rotate the same way?
SlamClick From United States of America, joined Nov 2003, 10019 posts, RR: 76 Reply 11, posted (6 years 5 months 23 hours ago) and read 7978 times:
Quoting Timz (Reply 9): So, did the two engines on a P-38 rotate the same way?
As far as I know, the engines - yes, but the props rotated in opposite directions. Oddly enough they rotate so that the descending blade is outboard. This has the effect of giving it two "critical" engines rather than none.
Apparently it has enough power that this is not a problem. One can reduce power on the good engine at just about any point in the flight envelope. I've heard many tales of Tony LeVier's demonstration of this to squadron pilots.
Happiness is not seeing another trite Ste. Maarten photo all week long.
Timz From United States of America, joined Sep 1999, 6181 posts, RR: 8 Reply 12, posted (6 years 5 months 20 hours ago) and read 7952 times:
Another question: does the crankshaft on a geared engine usually turn the same direction as the prop? Or are some engines same-rotation and others opposite?
Starlionblue From Greenland, joined Feb 2004, 14992 posts, RR: 69 Reply 13, posted (6 years 5 months 18 hours ago) and read 7940 times:
Quoting SlamClick (Reply 11):
As far as I know, the engines - yes, but the props rotated in opposite directions. Oddly enough they rotate so that the descending blade is outboard. This has the effect of giving it two "critical" engines rather than none.
I know I'm going to feel stupid when this is explained but "critical engines"? Huh?
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
HaveBlue From United States of America, joined Jan 2004, 1936 posts, RR: 1 Reply 14, posted (6 years 5 months 17 hours ago) and read 7930 times:
Starlion I'm going to take a stab at this, as I only fly singles. IIRC its like this... take a Seminole for example. You have 2 engines, both rotating the same way. If the number two, or starboard, engine quits, the #1 engines spiraling slipstream is coming in contact with the rudder of the aircraft, thereby giving you more rudder authority than if your #2 is the flying engine, in which case the spiraling slipstream is actually going further away from the aircraft and thereby giving you less rudder authority.
Since the descending blade on #1 is close to the fuselage, the airflow against the tail is better than the #2, where the airflow from the further out descending blade is traveling more or less away from the tail.
So the #2 engine is critical, as in it will be much harder to compensate for the asymmetrical thrust with only that engine turning.
2H4 From United States of America, joined Oct 2004, 8897 posts, RR: 66 Reply 15, posted (6 years 5 months 17 hours ago) and read 7917 times:
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Regarding critical engines, P-factor also comes into play. When the angle of attack is higher (at low speeds, for example), the airflow is not parallel to the airplane's longitudinal axis. Relative to the fuselage, the relative wind (airflow) flows several degrees upward.
Now, assuming both engines are turning clockwise when viewed from the cockpit, the descending propeller blade on each engine will be taking a larger bite out of the air than the ascending propeller blade. As the right side engine places the descending blade further away from the fuselage, it would produce more yaw (than the left engine) if it were the only operating engine.
Here's a great example:
Now, because the right engine would produce more yaw than the left during single engine ops, the left engine (in this example) is considered the critical engine. In other words, you'll have a more difficult time handling the airplane if the left engine fails.
And that's the best I can do with my limited knowledge of multiengine ops. If anyone spots any inconsistancies, please correct me.
Buzz From United States of America, joined Nov 1999, 697 posts, RR: 29 Reply 16, posted (6 years 5 months 7 hours ago) and read 7893 times:
Hi FredT, Buzz here. You were wondering about a direct drive engine... how about a T-6 /Harvard? The R-1340 engine (600 hp) is direct drive.
On the R-2800 engines the Reduction Gear ratio was about 50%, the crankshaft would produce about 50% more power strokes per revolution than a direct drive engine. On the dash 21 (P-47 Thunderbolt) engine it was 16:8 ratio. On most other R-2800 engines the ratio is 16:9, 16 revolutions of the engine give 9 revolutions of the prop. The numbers have no common multiple, it's a vibration control function.
The R-1830 of the C-47, and R-2800, and that R-4360 are geared engines, notice how large the nose case is - where the "crankshaft" and the prop meet.
I haven't worked on Wright engines, i'm trying to think if the R-1820 (B-17, T-28, S-2F) is geared or not. It sure has a short nose case... the crankshaft might have a direct connection to the prop. And i've only had my tools on a Merlin engine a couple times, so i don't know what Takeoff Power is on that kind of engine.
Takeoff RPM on the big radial engines seems to be 2700 -2800 RPM on the R-1830 and R-2800. Wright engines turn a few hundred RPM less, they have larger diameter jugs (keep your mind out of the gutter!) so they need a little more time to "fill up". The "pointy" engines: V-12 Allisons and Packards and Rolls engines seem to spin faster than the Big Radials. But at the Reno Air Races the 2 types of engine seem to go equally fast when driven to insane extremes.
And they all use a constant speed prop, so the RPM isn't what determines the thrust... manifold pressure ... throttle, is a measure of how much "thrust" the engine is delivering. As the throttle is opened, the prop blades take a bigger bite of air to keep the RPM constant.
A good web site for more Big Engine Stuff is The Aircraft Engine Historical Society.
g'day
Pilotpip From United States of America, joined Sep 2003, 2996 posts, RR: 14 Reply 18, posted (6 years 4 months 4 weeks 17 hours ago) and read 7823 times:
HaveBlue,
For a single driver you did a pretty good job with the explanation. However, the seminole has counter rotating props so that there is basically not a critical engine in an aerodynamic sense. Both props descend towards the fuselage so that the thrust lines of both are basically on the same point near the wing root. After the aerodynamic part, you can count the engine that will affect you in the most adverse manner. IE: You only have one alternator(all the seminoles I have flown have two) and the engine that it is on just quit.
It has always amazed me that on higher powered twins if you have an engine failure on takeoff at or below blueline you will likely have to REDUCE power to have a good chance of surviving. No wonder so many people have driven into the ground head first in barons and 310s. It's counter-intuitive.
Buzz, your knowledge continues to amaze me. Welcome to my respected users list!
FredT From United Kingdom, joined Feb 2002, 2179 posts, RR: 29 Reply 19, posted (6 years 4 months 4 weeks 13 hours ago) and read 7807 times:
V1 must be above Vmc, meaning you shouldn't have to reduce power to maintain directional control once you are past V1.
On the other hand, experience shows that the chances of most light twin pilots doing things just right are slim, and that the tolerances for doing things slightly wrong are small...
Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
SlamClick From United States of America, joined Nov 2003, 10019 posts, RR: 76 Reply 20, posted (6 years 4 months 4 weeks 6 hours ago) and read 7780 times:
Quoting FredT (Reply 19): On the other hand, experience shows that the chances of most light twin pilots doing things just right are slim, and that the tolerances for doing things slightly wrong are small...
Well said.
It is really sad to watch this happen over and over. Someone has enough money for a light twin, but not the humility to subject himself to a brutally honest instructor, or without the will to face certain realities about what will happen if one quits.
Happiness is not seeing another trite Ste. Maarten photo all week long.
Erj-145mech From United States of America, joined Oct 2001, 306 posts, RR: 1 Reply 21, posted (6 years 4 months 3 weeks 4 days 3 hours ago) and read 7673 times:
Slamclick, just for the record, that Corsair is an F2G, the R-4360 is the original engine for that airframe. The sliding canopy is standard on the F2G also, not on the F4U or FG-1 series.
The museum that I used to work for sold that airframe and engine to the present owner.
Gt1 From United States of America, joined Feb 2001, 132 posts, RR: 0 Reply 22, posted (6 years 4 months 1 week 1 day 15 hours ago) and read 7546 times:
My compliments to all the posters, very impressive knowledge. I really enjoyed reading this post. I had never heard of "critical engine", since I've worked heavy jets my whole career. Great stuff, thanks very much.
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From United Kingdom, joined Sep 2003, 172 posts, 
From United States of America, joined Nov 2003, 10019 posts, 
. Propeller gear reduction ratio was around 2:1, so divide by 2 to get an approximation to prop RPM.
From Greenland, joined Feb 2004, 14992 posts, 
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