A little help

[FOD]

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

[JEP]

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


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Try this thread - click here

[BrettInLJ]

[ 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

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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.

[flyguy]

It obviously also depends on the power loading of the aircraft. 80% is just a general number applicaple to the average light twin.

[B767Driver]

[ 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.

[ QUOTE ]


Sure you can prove them. Compute the all engine rate of climb. Then compute the single engine rate of climb. Then divide the single engine rate of climb by the all engine rate of climb. Should be about an 80% loss of climb performance for a typical light twin.

Simple as that.

[BoilerPilot2007]

C - cowl flaps
C - CG aft
C - critical engine inop
P - power (full on operating engine)
S - sea level
G - gear
F - flaps
W - windmilling prop
G - ground effect
G - gross weight
T - takeoff max weight
B - bank (5 deg into op. eng.)

Pronounced: Russia's (CCCP'S) Greatest Feat Was Germany's Greatest Tactical Blunder

[seagull]

FOD, drop your #2 explanation, it's wrong, that accounts for only a very small portion of the loss of performance. The example of using just units to explain the excess thrust issue was very good and simple to understand.