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Engine failure in multi

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Active member
Dec 4, 2001
Got my ME rating 3 years ago and haven't used it since :(
I'm sure I understand the 9 factors, etc, etc.... but I don't remember a good explanation of the following.
It doesn't make sense. I go through my whole Private, Insturment, Commercial, CFI, CFII (and twin, except engine failure) training under the impression that if the ball is centered, I'm coordinated. But wait a second.....Kill an engine in a conventional twin and the EVERY authority on multi-operations says that the rules change completely. All of a sudden, the way to stay coordinated is to fly what I had previously considered a sideslip (wings slightly banked, ball "split into the operating engine")

According to the FAA's Airplane Flying Handbook, some light twins will see as much as a 300 fpm increase in descent rate by holding wings level/ball centered. The way to hold coordinated flight is bank 2 degrees into the operating engine and center the yaw string with the rudder. (ususally end up with the ball slightly out of center)

Why the discrepency between the ball and yaw string? I can't remember it from my twin training. Theres a lot of experienced pilots on this board, how does it affect the aircraft you fly?

The only explaination I've recieved is that the rudder is creating a lateral force in the direction of the dead engine and it causes the sideslip. Last I heard, the rudder creates a torque around the Center of Mass that counters the torque effect of the operating engine. They cancel each other out. (the books say this creates a net sideslip towards the inop engine. . .HUH??)

whats the deal? Why can't I trust the ball to give me accurate coordination info with an engine failure?
If the above question doesn't make sense, I'll rephrase.

You need to fly uncoordinated in a twin to eliminate the sideslip, which, as you recall, introduces a lot of drag. Banking into the good engine eliminates the slip, and therefore the drag, giving you the best single engine performance possible.

The info the coordination ball is giving you is accurate. You simply need to be doing something else!
Eliminating sideslip during s/e ops

Great explanation, Timebuilder. Short and to the point.

You answered your own question, actually, when you said you were under the impression that the ball should always be centered, even in a twin, EXCEPT engine failure. That changes the rules.

Possibly another way to view it is that your thrust is unbalanced with an engine out, which is not the same as a single. Unless, of course, you're flying a push me-pull you Cessna Skymaster or a Do-336. :D
A good way to look at is that when you have your given angle of bank set in to eliminate slip you apply enough rudder to keep the yaw string centered. This will give you a uncentered inclinometer because you will be straight and level with a bank angle in. The ball will roll to the wing low side when in coordinated flight.
I forgot to mention.....
A good way to find out what your inclinometer should look like when flying engine out properly is to go out with both engines and put your airplane into a 5 degree bank (or whatever you like to use when single engine). Apply enough opposite rudder to get no heading change. The amount that the ball is off to the wing low side is the amount that should be seen when in coordinated single engine flight. Yes, you will be cooridinated in single engine flight.
Remember that 5 degrees is only a certification target. In reality, the required angle of bank will vary, and is often slightly less than 5 degrees. In some cases, at higher power settings in certain aircraft, it's slightly more.
Why the discrepency between the ball and yaw string?

You've just deflected the rudder (ball centered) to stop the yaw and roll however, now you have a deflected rudder which is causing a sideslip. While sideslipping along, the relative wind is striking the vertical stab. and rudder combination at a decreased AOA. Also, the relative wind is flowing into the "side" of the vertical stab. thus blocking some of it from flowing over the rudder(It's striking the side of the whole plane too). Both of these things reduce rudder effectiveness. By banking toward the op. engine you are now producing a horizontal component of lift, "from the wing", the AOA of the rudder is increased and the relative wind is inline with the vertical tail which increases rudder effectiveness (decreasing VMC). As far as the ball displacement, it will be displaced more with the critical engine inop. Assuming it's a conventional twin. I hope this helps...As far as the control issue goes any way. This explanation is a lot easier with a diagram... Anyone have any thing else to add?
Let me address one small point possibly overlooked. You mentioned the torque of the dead engine counteracted by torque around the center of mass by the rudder. This is not an accurate way to view the situation. The failure of an engine produces yaw to one side, yaw produces roll to a certain degree which is where you find yourself when you lose the engine. You push rudder to correct for it. Rudder produces yaw, not torque, unless you want to view it as torque around the vertical axis which in my opinion is usually considered yaw.

It really is much better to look at the vector diagrams or some other visual diagram. Basically there is no opposite force to balance the horizontal force of the rudder input you are using to stop the assymetrical thrust of the one good engine. So, we use the small horizontal lift force created by the 3-5 degrees of bank to balance that and give us equal horizontal forces. The other explanations of why the ball ends up being slightly off are good.

One instructor gave an example of your twin sitting on a frozen pond. If only one engine is developing power and you apply opposite rudder to counteract (as if you are flying straight and level with ball centered) you would see your airplane sliding slightly sideways on the ice as it went forward.

I don't know if any of this helps but I hope you get it figured out. I know how it can be when you just can't get something to make sense in your own mind.
The methods discussed so far are correct for small twins and work great but larger aircraft are flown much differently than your typical seminole. Jets that use spoilers for roll control would be in serious trouble if you were trying to counter rolling tendencies with aileron/spoiler. It decreases the performance and increases sink rate big time because the spoiler on the operative engine side is sticking up in the air causing a lot of drag and loss of lift. The big boys use mostly rudder with a a continued takeoff above V1 to counter the engine failure. You'll also see that the ball is centered in flight, if it has a ball.

In the BE1900 when I was practicing V1 cuts, it took an incredible amount of aileron to counter the rolling tendency. Almost full scale aileron deflection at such low speeds was amazing and I think is common with V1 cuts in a lot of turboprops. Even turboprops a lot of times, you'll see the ball centered and not much bank in flight once you get your speed up. Remember the slower you go the greater the bank and rudder deflection you need to maintain the zero side slip condition.

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