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Engine nacelles high or low..??

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Old 08-18-2019, 11:43 AM
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canardlover
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Default Engine nacelles high or low..??

Howdy all multi engine lovers: I am currently designing my first tri-motor plane and need to pick your brains on the placement of wing engine prop axis in relation to the wing chord line. In other words: should the engine(s) be placed high or low on the wing..? It is known that in an engine-out situation the plane does not only yaw towards the dead engine but will also bank towards the dead engine further aggravating the situation (see attachment #1)So my question for you is this: is there a “neutral point” where prop axis (high/low) vs. wing chord line will give minimal wing lift change at engine-out..??Or to phrase it differently: How low can you hang your engine(s) without a detrimental wing lift reduction.? (see attachment #2)
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Old 08-20-2019, 06:56 PM
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ps2727
 
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It is true that in an engine out situation you get yaw and roll. The majority of the roll is because of the yaw.
When you have some dihedral or leading edge sweep any yaw will produce a rolling moment. This is how we are able to fly 3 channel models with only rudder to manage turning.
To maintain control with an engine out you must control the yawing moment with rudder. If the rudder is correct the roll moment will be minimized or go away completely. While your concern for engine placement is valid it is a minor concern in comparison to zeroing out any side slip.
I modified a trainer into a twin in order to learn multi flying. Flying a twin on one engine was not difficult if proper rudder was used.
Just my opinion....
Best of luck on you design!

Paul
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Old 08-21-2019, 04:54 AM
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canardlover
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Paul, thanks for your reply and yes, rudder is certainly imperative to handle the engine out situation and I plan to have ample rudder area with a very strong linkage and servo. Admittedly, most of my ships can only knife-edge in one direction - when I pull rudder, sloppy "snake" linkages prevent knife-edging when I push rudder.
I have read much of the available material on RCU regarding twins and will follow advise from e.g. Ed Moorman about ample "toe-out" on the wing engines. However, engine placement high/low on the wing is seldom treated. I`m intrigued by the Custer CCW-5 which seems to imply that the propeller slipstream is creating more lift when the prop axis is above the wing chord line.

Last edited by canardlover; 08-22-2019 at 12:36 AM. Reason: added pictures
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