Aerodynamics: banking into a max performance climb

[photofly]

Here's your aerodynamics question for the day.

If an engine fails on a twin, to maintain a straight flightpath it's customary to apply rudder towards the live engine, and fly with a small bank towards the same side ("raise the dead"). You could instead keep the wings level, and avoid turning by using more rudder towards the live engine, but that would involve flying with a slip angle, therefore increased drag and reduced performance.

In a single engine aircraft at low speed and high angle of attack, like in a maximum performance climb, there's an asymmetry in thrust which we call asymmetric disc loading or "p-factor". (For US engines you get more thrust on the right side of the prop disc.) We train to maintain wings level and counteract the yaw from the asymmetric thrust with rudder.

For maximum performance, shouldn't we do as we do in a twin with a failed engine on the left side, and input a slight bank towards the right (for a US engine) and reduce the right rudder input?

[Colonel Sanders]

Is there an underlying assumpting that a single
is symmetrical? Because it isn't ... the Lyc/TCM
engine will typically be mounted pointed right and
down and there is often a twist in the vertical fin,
etc.

Anyways, I suppose we could tape a piece of yarn
below the windscreen (like a glider or twin) to tell
us when we aren't really sideslipping, but that's not
going to work very well with a single

[photofly]

Is there an underlying assumpting that a single
is symmetrical? Because it isn't ... the Lyc/TCM
engine will typically be mounted pointed right and
down and there is often a twist in the vertical fin,
etc.

True, but those tricks are designed to minimize rudder input and slip in cruise flight.

If we want to squeeze maximimum performance in a slow climb, when those tricks aren't enough, we should dip a wing, shouldn't we?

[5x5]

Perhaps if single engine aircraft had the engine mounted on a wing instead of the centreline, then we would fly them like an engine out twin.

Here's one to discuss if your thing is aircraft design and aerodynamics -

[Steve Pomroy]

For maximum performance, shouldn't we do as we do in a twin with a failed engine on the left side, and input a slight bank towards the right (for a US engine) and reduce the right rudder input?

Strictly speaking, yes. But (a) you would need to know how much bank or how much ball offset, otherwise you might not accomplish much and might even overcorrect to the point of making things worse; and (b) it probably wouldn't make much difference, at least a low altitudes where you have a reasonable amount of excess power.

I wrote about this back in September here: http://www.flightwriter.com/2012/09/step-on-ball.html. A little excerpt:

The aircraft can be flying in a slip with no lateral accelerations (and therefore no ball indications). This is because yawing moments (for example from the engine) are balanced by a force applied at the rudder. This force doesn't just yaw the aircraft, but also pushes it laterally. This lateral push is cancelled by an equal and opposite lateral push due to the slip. Multi-engine pilots will be familiar with this, as it is an important consideration after an engine failure (it is, in fact, the reason why we "raise the dead").

In a single-engine aircraft at low speeds and high power settings, there is lots of yaw induced by the engine, so lots of rudder force is required. At the same time, the lateral drag caused by a slip is reduced by the low speed. So balancing these two (and thus centering the ball) can require a large slip angle. This is one (of several) of the reasons why an aircraft is more prone to spinning when it stalls power-on.

Cheers,
Steve
http://www.flightwriter.com
http://www.skywriters.aero

[single_swine_herder]

Google "Zero sideslip angle."

It's quite instructive.

[dr.aero]

photofly...

Anyways, I suppose we could tape a piece of yarn
below the windscreen (like a glider or twin) to tell
us when we aren't really sideslipping, but that's not
going to work very well with a single

I've thought the exact same thing as you and I've done what CS said: tape a piece of yarn to the windscreen. With the ball centred and wings level I couldn't really see anything but the yarn going straight up the windshield indicating there was no slip.

Like CS said, the engines are offset, the vertical stab is offset, and sometimes the wings are mounted at slightly different angles of incidence. If you were to build a plane with everything mounted with no offset, I think you'd be able to notice a slight slip with wings level and the ball centred in a climb - but it'd be VERY small in my opinion.