Critical Engine Question.

[Hckey2477]

I understand that the critical engine is the engine that has the thrust line closest to the fuselage (correct me if that is incorrect). I also know that it is the engine that would mostly effect the performance and handling of the aircraft if failed.

But how do you actually determine which engine has the thrust line closest to the fuselage? Is this stated in the Ops. Manual? Thanks for the help.

[mojo6911]

There are a few ways to determine critical engine. We teach PAST:

P-Factor
Accelerated Slipstream
Spiraling Slipstream
Torque

The Airplane Flying Handbook discusses it in detail.

[madmax]

The downward rotating prop has the greatest thrust, so the engine with the downward prop closest to the fuselage is Critical.

[germb747]

For airplanes that have clockwise-rotating propellers, you can see that the left engine has a thrust line closer to the fuselage, since most of the thrust is being developed by the descending blade. Some airplanes have counter-rotating props to compensate for this--thus there is no critical engine. There can, however, also be a critical engine from a systems standpoint

[Chewie von Nubbins]

Originally Posted by mojo6911

There are a few ways to determine critical engine. We teach PAST:

P-Factor
Accelerated Slipstream
Spiraling Slipstream
Torque

The Airplane Flying Handbook discusses it in detail.

Not true. The critical engine is the engine that is still running after the MEI pulls one of the two of your engines. It is critical because if you decide to feather the good one in a fit of panic, a nice patch of field might be in your future. Hope things are still going well for you there Morgan. Need to catch up.

Oh yeah.....forgot the <sarcasm> tag.

[mojo6911]

Originally Posted by madmax

The downward rotating prop has the greatest thrust, so the engine with the downward prop closest to the fuselage is Critical.

Very good stuff on Wikipedia, mostly from the Airplane Flying Handbook:

http://en.wikipedia.org/wiki/Critical_engine

[Matt13C]

Originally Posted by madmax

The downward rotating prop has the greatest thrust, so the engine with the downward prop closest to the fuselage is Critical.

So, if I was on a twin, both props spin clockwise (looking head on), the prop on the right wing would be the critical engine?

[Hckey2477]

So with the spiraling slipstream, it would be the engine that the slipstream doesn't cross the fuselage? Thanks for the Diagram, that helps.

[Chewie von Nubbins]

Originally Posted by Matt13C

So, if I was on a twin, both props spin clockwise (looking head on), the prop on the right wing would be the critical engine?

haha...actually, your dislexic example would indeed work. If you were looking head-on and both props spun clockwise (which would actually be spinning counter-clockwise, in reality) the right engine would be critical.

All examples referring to this are assuming that you are viewing the engines from the pilot's seat...which would be viewing it from the back of the plane, instead of head on.

[Matt13C]

Originally Posted by Chewie von Nubbins

haha...actually, your dislexic example would indeed work. If you were looking head-on and both props spun clockwise (which would actually be spinning counter-clockwise, in reality) the right engine would be critical.

All examples referring to this are assuming that you are viewing the engines from the pilot's seat...which would be viewing it from the back of the plane, instead of head on.

HA HA yeah, after I posted I realized I used multiple perspectives for no apparent reason. But, you understood what I was getting at, whatever works.

So that is the critical engine because if it goes out P-factor increases substantially over having the other engine go out? It seems everything else would be the same regardless of which engine went out. That might be my lack of a Multi engine rating speaking though.

Thanks

[E6BAV8R]

Originally Posted by Matt13C

So, if I was on a twin, both props spin clockwise (looking head on), the prop on the right wing would be the critical engine?

With a conventional twin, where the props are spinning clockwise as if sitting in the airplane, the left-engine is always the critical engine.

Most training environments have a twin that has counter-rotating props, where the left engine spins clockwise and the right engine spins counter-clockwise, to where both engines are creating thrust at the same arm (distance from the fuselage), which essentially gets rid of a critical engine.

[Matt13C]

Originally Posted by E6BAV8R

With a conventional twin, where the props are spinning clockwise as if sitting in the airplane, the left-engine is always the critical engine.

Most training environments have a twin that has counter-rotating props, where the left engine spins clockwise and the right engine spins counter-clockwise, to where both engines are creating thrust at the same arm (distance from the fuselage), which essentially gets rid of a critical engine.

Thanks.

Is there a critical engine when flying jets? I am guessing that if you were flying a 747 and lost an outer engine you would get excess thrust from the opposite side that could cause same yawing, correct?

[Baronpilot244]

Good discussion!

I sometimes wish the Baron I fly had counter rotating props - engine out procedures in that airplane can be a lot of work!

BP244

[Wolfy]

Originally Posted by Matt13C

Thanks.

Is there a critical engine when flying jets? I am guessing that if you were flying a 747 and lost an outer engine you would get excess thrust from the opposite side that could cause same yawing, correct?

Anytime you lose an engine in a multiengine airplane, you're going to have substantial yaw. (As long as it's not center line thrust, like a 337). The term critical engine is really a misnomer. From an aerodynamic standpoint, losing either engine has a very similar effect, it's just one is more pronounced. "More critical" is really more accurate.

[Flyin_bryan]

Originally Posted by Wolfy

Anytime you lose an engine in a multiengine airplane, you're going to have substantial yaw. (As long as it's not center line thrust, like a 337). The term critical engine is really a misnomer. From an aerodynamic standpoint, losing either engine has a very similar effect, it's just one is more pronounced. "More critical" is really more accurate.

the dreaded 7 engine approach...

[mojo6911]

Originally Posted by Wolfy

The term critical engine is really a misnomer. From an aerodynamic standpoint, losing either engine has a very similar effect, it's just one is more pronounced. "More critical" is really more accurate.

Not really. The definition of critical engine is the engine, if lost,that most adversely affects the performance and handling of the aircraft. Obviously losing either engine will adversely affect it.

[Wolfy]

Mojo, I think we're saying the same thing there. I just mean the word "critical", meaning essential or indispensable, is a little misleading. It seems to imply the other isn't critical, isn't of importance. The term confused me a little bit when I got my multi engine rating and I thought I'd help if anyone else had the same problem.

[JulietBravo]

Originally Posted by Flyin_bryan

the dreaded 7 engine approach...

haha, love it! One of our professors here talks about his days flying the B-52 and it took him and his Copilot a half hour to realize they lost an engine after take-off. He said he didn't notice any decrease in performance and eventually realized it when he had more time to check the gauges.

[typhoonpilot]

Originally Posted by Matt13C

Thanks.

Is there a critical engine when flying jets? I am guessing that if you were flying a 747 and lost an outer engine you would get excess thrust from the opposite side that could cause same yawing, correct?

One answer that is given for this question is this:

Critical engine below Vr is the most outboard upwind engine because of the combined effect of assymetric thrust and weathervaning, making control of the aircraft more difficult while still on the ground. After Vr ( once airborne ) the critical engine is the most outboard downwind engine because of the combined effects of assymetric thrust and crosswind induced drift which make tracking the extended centerline more difficult.


Typhoonpilot

[LoadMasterC141]

Originally Posted by mojo6911

There are a few ways to determine critical engine. We teach PAST:

P-Factor
Accelerated Slipstream
Spiraling Slipstream
Torque

The Airplane Flying Handbook discusses it in detail.

I am a fan of PAST too....Read about it in the AFH. Understand that the P and S are YAW tendencies, while the A and T are Roll.