Might as well add my 2c...
Originally Posted by
KC10 FATboy
In multi-engine prop aircraft, you learn day one that you don't fly them with asymmetric thrust and in a coordinated (ball centered) side-slip. You should be banking 2-3 degrees into the good engine with about 1/2 ball displacement into the good engine.
Here's why ...
1. You increase drag because the deflection of the fuselage and rudder with respect to the relative wind increases.
Agree, but this is a landing scenario. Minimizing drag is not a high priority.
Originally Posted by
KC10 FATboy
2. Unfortunately, because of the greater yawing moment due to the asymmetric thrust, you must deflect the rudder more so than if you were flying with symmetric thrust. Due to the sideslip, rudder deflection is parallel to the relative wind now and that makes it is less effective. The net result is that you need to use more rudder than otherwise necessary. You must counteract the yawing moment from asymmetric thrust and the natural weather vaning into the wind.
3. Since rudder authority is reduced (due to he relative wind being parallel to the rudder deflection), VMCA is going to increase. Depending on the type of aircraft, this could be very significant.
VMCA is based on TOGA thrust. I seriously doubt you would be anywhere near that for the technique being discussed.
Originally Posted by
KC10 FATboy
4. The relative wind striking the fuselage/tail on the reduced engine side, increases the yawing moment. This adds to the rudder problem. (see #2)
The effect should be much less than what you would experience on rotation from a V1 cut with the same crosswind, and we know the airplane can handle that.
Originally Posted by
KC10 FATboy
5. Extra drag is produced because of the rudder deflection and fuselage being deflected into the wind. (drag is increasing, but you are reducing power on an engine???)
Landing. Drag reduction not priority.
Originally Posted by
KC10 FATboy
6. Stall tendencies can be masked or changed because the airflow over the wing (on the side with the engine that has been increased) is partially blocked by the fuselage.
No worse than kicking out crab with rudder
Originally Posted by
KC10 FATboy
7. But the biggest reason I don't like this technique is this. If you suddenly lose the higher thrusted engine, you are going to instinctively push up the power on the remaining engine. When you do, and you have that rudder deflected into the once high powered engine, the increased yawing moment and associated roll is going to prove dangerous.
This I can agree with. Its a case of risk management - whats your biggest threat for that approach, is it the crosswind, or is it engine failure in the flare?
Originally Posted by
KC10 FATboy
In a normal crab to forward-slip landing, you aren't as susceptible to an engine failure. In my current aircraft, the manufacturer recommends the crab to forward-slip procedure. Even the autopilot uses this method when flying autoland approaches. Even if you lose an engine at 50 feet or below, the autopilot can still autoland.
Agree that this is not an approved procedure, and that the autoland does not use it. However in my current aircraft (A330) the autoland crosswind limit is only half of the demonstrated 40kts.