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BrettInLJ · August 30th, 2005, 16:46

[ QUOTE ]
Would like a little more info or better understanding then what I already know about the following:

When you lose an engine you lose 50% of your power and 80% of your performance. I have seen this explained two ways:
1. Using numbers that explain thrust horsepower avialable and thrust horsepower required. I don't want to teach off this method because I think those numbers are just pulled out of the air somewhere, i cant prove where they came from.

2. I have been telling students that we loss so much performance because we gain so much drag from the control inputs needed to counter the yawing and rolling tendencies. This makes sense and is easily understood.
Im just looking for a little more info or understanding, if there is any?

Secondly, could someone give me a good explination on lateral stability (specifically dihedral)?

Thanks

[/ QUOTE ]

It is about numbers, but here is an intuitive way to think about it. Think of performance as the excess thrust you have vs. what you have to move (the mass of the aircraft with drag). Forget pounds, drag, bhp, etc. and lets just think about generic units.

If you need to move 1000 and each engine supplies 1300 you have 2600 moving 1000, which is 1600 to spare. If an engine quits you have 1300 moving 1000 which is 300 to spare. The amount to spare is your performance, so as you can see you have about 80% less to spare with only one engine.

August 30th, 2005, 16:46	#3
BrettInLJ Senior Member Join Date: Jun 2002 Location: Home:SFO Work:MSP Posts: 1,035	Re: A little help [ QUOTE ] Would like a little more info or better understanding then what I already know about the following: When you lose an engine you lose 50% of your power and 80% of your performance. I have seen this explained two ways: 1. Using numbers that explain thrust horsepower avialable and thrust horsepower required. I don't want to teach off this method because I think those numbers are just pulled out of the air somewhere, i cant prove where they came from. 2. I have been telling students that we loss so much performance because we gain so much drag from the control inputs needed to counter the yawing and rolling tendencies. This makes sense and is easily understood. Im just looking for a little more info or understanding, if there is any? Secondly, could someone give me a good explination on lateral stability (specifically dihedral)? Thanks [/ QUOTE ] It is about numbers, but here is an intuitive way to think about it. Think of performance as the excess thrust you have vs. what you have to move (the mass of the aircraft with drag). Forget pounds, drag, bhp, etc. and lets just think about generic units. If you need to move 1000 and each engine supplies 1300 you have 2600 moving 1000, which is 1600 to spare. If an engine quits you have 1300 moving 1000 which is 300 to spare. The amount to spare is your performance, so as you can see you have about 80% less to spare with only one engine.