Several ME questions

[cookmg]

Hi all.

1) How do Flaps affect control? I have read that they improve control by reducing the the thrust moment of the operative engine. I have also been told that they hurt control due to uneven lift created due to accelerated slipstream. Which wins? What about cowl flaps? Do they significantly affect control? As far as performance is concerned: Do cowl flaps improve performance by keeping the engines cool, or do they hinder performance due to the obvious drag?

2) How does spiraling slipstream on a conventional twin affect the impact of the critical engine?

3) For the MEIs out there, in what order do you present the ground material and why? For the MEI checkride?

Thanks!

Mike

 

[avbug]

How do flaps affect control? That depends on the airplane. One thing that flaps do is reduce stall speed, which often means placing your minimum controllable speed (Vmca) higher than stall speed.

The specifcs of how flap application affects a given airplane depend on the airplane.

Spiraling slipstream is not nearly the factor on a conventional multi engine airplane, that it is on a single engine centerline thrust propeller driven airplane. P factor/assymetrical thrust is a bigger issue, due to it's moment or distance from the longitudinal axis of the airplane.

Present what material?

 

[wxman]

Flaps and Vmca - basically, flaps reduce Vmca by reducing the P-factor for a given airspeed. Think of it this way... if you are flying along at 120KIAS, straight-and-level, and you deploy approach flaps, you will have to lower your pitch attitude to maintain your airspeed. Lower pitch results in reduced P-factor. This is very similar to how ground effect reduces Vmca. P-factor.

As for the spiralling slipstream - it is not much of a factor in a conventional twin-engine airplane, due to the location of the engines.

In presenting ground material to a multi-engine student, it goes something like this: 1) aircraft systems; 2) limitations and FAR 23 stuff; 3) normal procedures; 4) engine-out aerodynamics; 5)engine-out procedures and maneuvers; 6) IFR procedures; 7)emergencies and procedures; 8) review. Since I am away from my office right now, I'm just listing these things off the top of my head. It should be pretty close, however.

 

[PA31Ho]

When it comes to spiraling Slipstream, like the other replies said, it's not much of a factor, however it does a little. This slipstream from the left engine slams into the left side of the vertical stab. and counteracts the yawing moment caused by the loss of the right engine. Now, if the engines are not counter rotating and you have failure of the left engine, the slipstream from the right engine wouldn't counteract the yawing moment because the airflow from the right engine would not be anywhere near the verticle stab.

Hope this helped.