Engine failure in multi

[SIGman]

It helps clarify my confusion, I guess...

1. Am I understand that the ball (inclinometer) gives us "coordination" information but not necessarilly "slip" information? I've been taught and been teaching my students that they are the same thing. I thought coordinated = zero sideslip. No? not in a half busted twin? why?

2. Speedtree...you said what I said, I think. The operating engine (producing thrust) and inop engine (producing drag) produces a rotational force (torque) around the vertical axis (yaw). (this yaw also creates roll, I know)

We use rudder to create a rotational force (torque) around the vertical axis (yaw) to counter the engine failure. How much is required depends upon our KIAS and at least the "9 factors."

3. How do we fly the plane then? We have talked about (I assume) flying the aircraft at (or close to) Vmc. And have determined how to maintain the best CONTROL at Vmc. How about best perfomance at Vyse and Vxse? Same, Same??

Thanks for your responses and patience,
D

 

[DoinTime]

1. Am I understand that the ball (inclinometer) gives us "coordination" information but not necessarilly "slip" information? I've been taught and been teaching my students that they are the same thing. I thought coordinated = zero sideslip. No? not in a half busted twin? why?

Because your inclinometer is calibrated to give you coordination during wings level straight flight or coordinated banked turns. When you are in straight flight with wings banked (single engine operation) your inclinometer will always be wrong. I saw years ago an add-on adjustable inclinometer that you could calibrate yourself. You could set it for up to a 10 degree angle of bank. When you were single engine you would just adjust it to whatever angle of bank was appropriate and it would give accurate info. Pretty neat....haven't seen one since.

 

[Timebuilder]

You wrote:
1. Am I understand that the ball (inclinometer) gives us "coordination" information but not necessarilly "slip" information? I've been taught and been teaching my students that they are the same thing. I thought coordinated = zero sideslip. No? not in a half busted twin? why?

The meaning of the ball's position changes because it is responding to the inputs which became necessary during the single engine operation. The use of bank, which by the way reduces the rudder deflection from the initial amount, is the reason that the sideslip is being eliminated, and the ball wasn't designed to respond to this set of conditions. So, according to the turn coordinator, as designed, you are uncoordinated, but according to the airplane, which is the more meaningful indicator, you are coordinated because you have responded to the changing circumstances with changing control inputs, and eliminated the sideslip.


2. Speedtree...you said what I said, I think. The operating engine (producing thrust) and inop engine (producing drag) produces a rotational force (torque) around the vertical axis (yaw). (this yaw also creates roll, I know)
We use rudder to create a rotational force (torque) around the vertical axis (yaw) to counter the engine failure. How much is required depends upon our KIAS and at least the "9 factors."

The dead engine is responsible for yaw, and your first response is to apply rudder. The dead engine also creates roll as the lift is reduced on the side of the dead engine as induced airflow stops.
Flying this way, without banking into the good engine and keeping the ball centered, produces the performance robbing sideslip.


3. How do we fly the plane then? We have talked about (I assume) flying the aircraft at (or close to) Vmc. And have determined how to maintain the best CONTROL at Vmc. How about best perfomance at Vyse and Vxse? Same, Same??


We fly the airplane at blue line, or Vyse. Due to the factors, Vmc may indeed be lower than the red radial line, but I wouldn't go exploring that! Vmc is a useful guide to avoid a roll when low and close to terrain when density altitude is higher than your single engine climb ceiling. This means that you are in a controlled descent, and maneuvering to avoid objects as you prepare to set it down following your engine failure. The survivability of this scenario depends largely on avoiding the upside-down landing. Staying above Vmc is the way to avoid that rollover. How do you avoid this set of woeful circumstances? Good preflight planning is the answer. There are days when five or ten miles of clear, flat terrain would be necessary at the departure end of your runway to ensure a safe climb after an engine failure following takeoff on a warm day, or a controlled descent to an off-field landing on a hot day.

In other words, you can choose to not put yourself in a situation that doesn't allow you to safely climb after a failure and circle to land. Keep it on the ground whenever you can, following a failure. I was told this old chestnut once: it is better to go through the fence at 70 knots than to go through a barn at 150 knots.

I recommend these two FAA publications as required reading for my multi students:

FAA-P8740-19, Flying Light Twins Safely

FAA-P8740-25, Always Leave Yourself an Out


Think first, and then fly.
The fact that you are asking these questions is great. Good luck!

 

[avbug]

The inclinometer is in no way "calibrated." The closest that may be said an inclinometer comes to calibration is ensuring that the ball sits in the center when the wings are level on the ground, and that's a maintenance function of installing the instrument properly. Otherwise, there is no "calibration."

"Coordination" means using the controls of the airplane in such a manner that the airplane does what you want it to do. The common use term refers to keeping the skid ball in the center of the inclinometer, but this is erroneously applied. One coordinates the controls to make the airplane perform as desired. For passenger operations, the controls are generally coordinated such that the skid ball stays centered, but many operations require otherwise.

Note the purpose of the name "inclinometer." This is simply a primitive device which tells you which way something is leaning. In flight, we use it in conjuction with force vectors, intuitively; that is, the ball is acted upon by various forces in flight aside from gravity. When those forces are not acting on the ball in the inclinometer, it simply shows which way the airplane is tipped, or inclined, as gravity takes over.

A "dead" engine has little or no positive torque (often negative torque). Torque is manifest as a rolling tendency, proportional to the power produced by the engine, to a degree. It is not a yawing tendency.

"Coordination" has nothing to do with zero sideslip. It has everythign to do with making the airplane do what you want it to do. If the ball of the inclinometer is not centered, the airplane is not necessarily "uncoordinated." In the case of a multi-engine airplane with zero sideslip due to bank during an engine-out situation, the ball won't be centered, but this doesn't mean the airplane isn't "coordinated." It is coordinated. However, because the airplane is banked and isn't slipping or skidding, the ball will be course of gravity head downhill...typically a half to a full ball width in many light twins.

Imagine a single engine airplane in knife-edge flight. It is flying level, at a constant altitude, and is not turning, is not slipping, or skidding. Where is the skid ball? In the case of a left wing low knife-edge (90 degree bank), the ball is at the far left of the instrument. There it sits until acted upon by some other force than gravity. A similiar condition exists when operating engine out with a bank into the "good" engine in a multi engine airplane.

You teach side slips and forward slips. When coordinating the controls using opposite aileron and rudder (hard to accept the fact that cross controlling is coordinating, isn't it??) to slip, you'll notice that the skid ball is displaced opposite the rudder. That is, apply right rudder and left aileron to slip, you'll find that the ball moves off center to the left. Intuitively we know that to center the ball, we need only "step" on it, or use left rudder.

Imagine performing a side slip using a crosswind on final. A strong 90 degree crosswind is blowing, and you're banked into the wind to prevent drift. Where is your skid ball now? You're in a similiar situation to what you would be with an engine out on the downwind side of the airplane with respect to path over the ground (it's illustrative, not a perfect example). Aerodynamically there are differences, but by stopping your movement to the side, you will find that the ball of the inclinometer is off-center to the low side, much like a bank into a good engine in a multi engine airplane. Again, there are some differences aerodynamically, and this example, poor though it may be, is for illustrative purposes only.

Typically in large turbojet aircraft, the ball, when available (not found in all aircraft) is kept centered. However, not in all. I've flown several large types which required bank into the good engine(s) during engine-out work. The requirements vary with the airplane, not necessarily the size or powerplant. There are many large airplanes that are flown exactly as a seminole or other light twin.

 

[Timebuilder]

"Yea, wha he say."

 

[sstearns2]

.....

All engine out training in twins should be done with a piece of string taped to the center of the windshield.

The best way to look at this is to draw a basic top view of a conventional twin and draw the forces on it. Good engine thrust, airframe drag at the CG, and the force being generated by the vertical tail. Study this picture and you'll see that your flying sideways if you don't have any lift from the wing projected to oppose the force from the vertical tail.

The ball is centered if your wings level and your heading isn't changing. The ball just happens to have a close relationship to angle of sideslip in a centerline thrust airplane.

Scott

 

[DoinTime]

The inclinometer is in no way "calibrated." The closest that may be said an inclinometer comes to calibration is ensuring that the ball sits in the center when the wings are level on the ground, and that's a maintenance function of installing the instrument properly. Otherwise, there is no "calibration."

AVBUG...You contradict yourself here. Ensuring that an instrument that relies on being properly installed to give the desired results is in every way "calibrated." If it did not need to be "calibrated" you could bolt it on in any old way and get the desired effect.

Typically in large turbojet aircraft, the ball, when available (not found in all aircraft) is kept centered

What aircraft do not have a ball? or a digital representation of a ball (as in a glass cockpit)? A slip/skid indicator is required for IFR ops you know. 91.205.d.4

 

[avbug]

There is no calibration standard for an inclinometer. How many pounds of force, degrees of sideslip, g loadings, degrees of bank, or other measurement is given by ball displacement? Simply because an inclinometer ball rests at the low part of the glass at rest on the ground, doesn't make it calibrated. The inclinometer isn't calibrated. Ensuring that the item is properly installed isn't calibrating it. No mechanic calibrates an inclinometer. You won't find instructions or standards anywhere for calibrating an inclinometer. No manufacturer has standards or instructions for continued airworthiness for inclinometer calibration. Sticking it on the panel so it's straight is NOT calibration.

Not all large airplanes fly IFR, and not all large airplanes, or small ones for that matter, are bound by the minimum instrumentation spelled out in the FAR. Think about it.