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## Sideslip in Multi engine with one engine inoperati

• Spinrecovery
• Topic Author

### Spinrecovery created the topic: Sideslip in Multi engine with one engine inoperati

If an engine failure occurs and the aircraft is banked toward the operating engine without any rudder application, the resultant of the operating engine thrust force and the horizon component of lift will cause
a. A decent and turn towards operating engine
b. A slip toward the operating engine.
c. A climb and turn towards the failed engine.
d. A slip towards the failed engine.
The correct answer is B. but I think the answer should be D because one engine is producing thrust while the other is not producing any. Therefore, even though you bank toward the operating engine the aircraft still yaws toward the dead engine due to asymmetrical thrust, drag from windmilling propeller on the dead engine, and no rudder input. Please enlighten me.
Cheers

• Mister W

### Mister W replied the topic: Sideslip in Multi engine with one engine inoperati

I had to read the question a couple of times to see where it was coming from. I think it is referring to what is happening to the turn itself after a failure of an engine.
With the failure of the outside engine and usual basic problem occurring, the aircraft will now enter a slipping turn. Slipping towards the operating engine.

Lets look at it the other way. Same turn, this time the inside engine stops. The aircraft will now enter a skidding turn. Skidding towards the operating engine.

To visualize this, use a model (or your hand). Place it in a banked attitude for a turn. Then, yaw it towards a failed engine and see what type of turn you end up with a know that it will be towards the live.

D is technically correct when you talk about the effect of an engine failure in a multi engined aeroplane and the resulting change in direction of the relative airflow. I used to tape a piece a string to the nose of the trusty ol' Seminole and Seneca to demonstrate this. The string indicates a slip towards the dead and we are using rudder and in some cases a bit bank towards the live to get going straight again and maintaining control.

Hope this helps.

Regards,
Mr W.

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 702

### John.Heddles replied the topic: Sideslip in Multi engine with one engine inoperati

A few thoughts, if I may ..

a. A descent and turn towards operating engine

Descent ? probably. Turn to the operating engine ? depends on the strength of the couples so, maybe yes, maybe no.

b. A slip toward the operating engine.

Definitely.

c. A climb and turn towards the failed engine.

Climb ? probably not. Turn to the failed engine ? depends – see (a)

d. A slip towards the failed engine.

There is no force in the setup to cause this so, no.

It follows that (b) is the sensibly correct alternative so run with it.

The usual sequence of events with an engine failing is –

(a) Rudder input on the operating engine side to oppose the asymmetric yawing couple. Note that this ALSO results in a lateral rudder force which creates a sideslip toward the failed engine side. (Along the way, power goes up, configuration changes are made, etc.)

(b) If the speed is anywhere near Vmc, input 5 degrees bank to the operating engine side immediately. This creates a balancing sideslip toward the operating engine which reduces the actual Vmc. Unless otherwise stated, assume that the OEM book Vmc is based on 5 degrees toward the operating engine side.

Continued flight wings level or, much worse, bank the other way, results in a significant increase in actual Vmc and, historically, has been the causative factor in more than a few hull losses.

Note that 5 degrees relates to an initial low speed failure and is a handling, rather than a performance (read climb) consideration. Once the control concerns have been sorted out and speed increased, best climb will require around 3 degrees bank toward the operating engine to balance the slip-associated drag.

(c) If the speed is well above Vmc bank requirements, and terrain avoidance is not super critical, the pilot may elect to continue wings level, accepting the sideslip-related reduction in climb performance to achieve a reduced workload. Indeed, for some aircraft (usually in the jet fraternity) ADI limitations with small bank angles may dictate wings level flight once the initial handling problems have been sorted out.

Engineering specialist in aircraft performance and weight control.