 | Contra rotating Propellers| Technical Discuss Contra rotating Propellers in the World War II - Aviation forums; Joe: That's a very good explanation of the "critical engine" I had heard
the term before but ... |
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08-07-2007, 11:15 AM
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#16 | | Older Than Dirt
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Country:  | Joe: That's a very good explanation of the "critical engine" I had heard
the term before but Wikipedia explains it so even I can understand it.
Is that why they say, "never turn into a dead engine" ?
Charles
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08-07-2007, 11:32 AM
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#17 | | Senior Member
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| Counter (or contra) rotating prop on the same axis, either driven by 1 or 2 engines, also have the advantage of allowing shorter blades and so to reduce the tip speed (vs a single prop configuration designed to handle the same power)
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08-07-2007, 11:33 AM
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#18 | | IP/Mech THE GREAT GAZOO
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Originally Posted by ccheese  Joe: That's a very good explanation of the "critical engine" I had heard
the term before but Wikipedia explains it so even I can understand it.
Is that why they say, "never turn into a dead engine" ?
Charles | Yep - and as in WW2, today the biggest killer of (GA) pilots is lack of proficiency when performing emergency engine out procedures on twin engine aircraft - I've ranted about this on earlier threads.
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08-07-2007, 07:16 PM
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#19 | | Senior Member
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Originally Posted by FLYBOYJ | Losing your critical engine sucks. I would always hate it when they failed my left engine (critical) in the C-12B... standing on the damn rudder gets old REAL quick.
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08-22-2007, 07:20 AM
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#20 | | Junior Member
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Originally Posted by FLYBOYJ | Well, the P38 didn't have a critical engine because it didn't have a better performing engine (inboard turning) of the two. Pfactor is the result of an an effective AOA change of a tilted prop disc. Tip a prop disc back . . . say, ten degrees . . . and maintain its horizontal direction and the down going blade has a higher angle of attack (pitch) than the up going blade. This has the effect of moving the thrust line from the prop axis horizontally towards the down going blade. Whether this is towards or away from aircraft centerline determines how much rudder (drag) is required to maintain neutral yaw. With both engines running the inboard wing sections would have a higher effective AOA than the outboard sections (spiral slipstream affect) which would help stalls start inboard where they should. With the surplus of power the P38 had as well as reasonable yaw control this was seen as a good compromise. The P82 adopted the same approach initially but stall performance was so benign North American switched the engines so both engines gave superior single engine performance.  | |
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08-22-2007, 07:40 AM
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#21 | | IP/Mech THE GREAT GAZOO
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Originally Posted by chuter Well, the P38 didn't have a critical engine because it didn't have a better performing engine (inboard turning) of the two. Pfactor is the result of an an effective AOA change of a tilted prop disc. Tip a prop disc back . . . say, ten degrees . . . and maintain its horizontal direction and the down going blade has a higher angle of attack (pitch) than the up going blade. This has the effect of moving the thrust line from the prop axis horizontally towards the down going blade. Whether this is towards or away from aircraft centerline determines how much rudder (drag) is required to maintain neutral yaw. With both engines running the inboard wing sections would have a higher effective AOA than the outboard sections (spiral slipstream affect) which would help stalls start inboard where they should. With the surplus of power the P38 had as well as reasonable yaw control this was seen as a good compromise. The P82 adopted the same approach initially but stall performance was so benign North American switched the engines so both engines gave superior single engine performance. | OK...........
As stated, the P-38 did not have a critical engine.............
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08-22-2007, 04:35 PM
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#22 | | Junior Member
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Country: | . . . uhhh . . . wow . . . it was the middle of the night.
-- I was near the end of my work shift (A320 C-checks). -- | |
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08-22-2007, 05:30 PM
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#23 | | IP/Mech THE GREAT GAZOO
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Originally Posted by chuter . . . uhhh . . . wow . . . it was the middle of the night.
-- I was near the end of my work shift (A320 C-checks). -- | been there, done that - 737s, DC-9s - where do you work?
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08-24-2007, 07:20 AM
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#24 | | Junior Member
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I work at a "Major Carrier's" maintainance base on the field (the only one). Continuing rumors (rumors are now hitting the press) we are to be sold . . . happy days :/ . . . are taking their toll here. On the flip side I start a one week vacation today. WOOHOO. | |
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08-24-2007, 09:28 AM
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#25 | | IP/Mech THE GREAT GAZOO
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Originally Posted by chuter SFO
I work at a "Major Carrier's" maintainance base on the field (the only one). Continuing rumors (rumors are now hitting the press) we are to be sold . . . happy days :/ . . . are taking their toll here. On the flip side I start a one week vacation today. WOOHOO. | I did heavy iron maintenance for a while - I hated it. SFO - probably United? My father in law retired last year from United...
Have a great vacation....
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08-24-2007, 02:28 PM
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#26 | | Senior Member
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Originally Posted by FLYBOYJ I did heavy iron maintenance for a while - I hated it. SFO - probably United? My father in law retired last year from United...
Have a great vacation.... | Small world . . . my father-in-law also retired from United, but about 5 years ago. Got out just before they declared Chapter 11 . . . used to fly 747-400's international (mostly Hong Kong, Beijing and Okinawa). My brother used to work at the MOC in Oakland, and my wife used to work at Central Res in SF. Weird . . . | |
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08-25-2007, 05:14 PM
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#27 | | Senior Member
Join Date: May 2007
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Country:  | Found this interesting schematic showing the contraprop workings of the Koolhoven FK 55 in a 1944 Dutch aircraft encyclopedia. Maybe someone can translate some of the labelling.  | |
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08-26-2007, 12:17 AM
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#28 | | IP/Mech THE GREAT GAZOO
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Originally Posted by SoD Stitch Small world . . . my father-in-law also retired from United, but about 5 years ago. Got out just before they declared Chapter 11 . . . used to fly 747-400's international (mostly Hong Kong, Beijing and Okinawa). My brother used to work at the MOC in Oakland, and my wife used to work at Central Res in SF. Weird . . . | Wow! pretty weird! Are you guys on the "buddy pass" gravy train as my father in law likes to call it? I use his passes more than any one in the family - he doesn't care, as long as they all get used up before the end of the year.
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08-31-2007, 07:24 PM
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#29 | | Member
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Country:  | Hi Graeme
Thanks for posting that, I never heard of the Aircraft itself, but it's interesting that the engine is also behind the pilot in a layout like that......tough on him if he has to go through anything though.
I heard it said that with a propeller plane the engine makes a hole and you follow through, with a Jet YOU make the hole, the engine follows you! | |
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08-31-2007, 07:40 PM
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#30 | | IP/Mech THE GREAT GAZOO
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Originally Posted by Seawitch Hi Graeme
Thanks for posting that, I never heard of the Aircraft itself, but it's interesting that the engine is also behind the pilot in a layout like that......tough on him if he has to go through anything though.
I heard it said that with a propeller plane the engine makes a hole and you follow through, with a Jet YOU make the hole, the engine follows you! | And with a turbo-prop?!?!? 
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