Critical Engines
 

If all propellers spun clockwise would every propeller driven engine have a critical engine? Or is this predominant on mostly light twins?

You obviously need to read up on this stuff. Do yourself a favor and read the material.

It is a twin engine thing. And there are no propeller driven engines (unless it is windmilling), there are however engine drive propellers. :)

I have read the material. I have been studying twin engine aerodynamics however this is a legitimate question. Not every airplane has a critical engine; understood. I am not asking a hypothetical question either. Take a Dash 8 for instance would a Dash 8 have a critical engine if both engines operated clockwise? A Dash 8 and a PA-44's aerodynamics are highly different (i.e high wing vs low wing; perhaps higher torque; etc). That's what I am asking. Do all twin engine aircraft (assuming both propellers operated clockwise) have a critical engine? I understand why there is a critical engine and how we come to the conclusion I am just trying to fully understand this principle.

And touche' ASpilot2Be. I meant engine driven propellers!

If both engines are turning the same direction then yes there is a critical engine. It doesnt matter if there is a low wing or high wing. The PA-44 does not have a critical engine because it has counter rotating props.

The main principle you should be looking into is P-factor. If you lose the left engine you have to pitch up to substitute for the loss of lift to maintain altitude. When pitching up you are increasing the the angle of attack of the descending blade, which creates more of a "bite". The arm is longer from the longitudinal axis to the descending blade on the right engine and shorter on the descending blade of the left engine. This increase in P-factor and longer arm on the right side is what makes the left engine critical whenever both propellers spin clockwise. There are three other factors that contribute to the left engine being the most critical to lose, but P-Factor is the main one to conecentrate on. Hope this Helps!

Keep it simple brother.

Unless you have counter-rotating propellers you have a critical engine which will always be the right engine. At least I've never heard of both props running counter-clockwise. If that were the case though the left would be critical.

You have it mixed up. The "critical engine means the engine whose failure would most adversely affect the performance or handling qualities of an aircraft". Clockwise= Left engine critical.

Correct me if I'm wrong but on European built airplanes isn't the critical engine usually the right engine? ASpilot2be I know the PA-44 does not have a critical engine however my question was assuming that all props rotated clockwise only.

I would suggest paying an instructor to teach you this..there's a difference between studying the material and getting everything all confused, in which case the instructor is going to have a lot of your misunderstandings to correct...

To stay on subject though, left engine for conventional twins. Usually training twins (Seminole, Dutchess, etc) have counter-rotating props..hence eliminates what makes a critical engine, "critical"

Why don't they just put counter rotating props on everything? Goes back to what I learned in private ground school..what makes an airplane fly? Money

A dash 8 has its props spinning two different ways precisely so it doesn't have a critical engine. Otherwise there would be no reason to justify the expense of making the engines/props differently.

I think you guys are confused as to what my question was actually asking. I understand why there is a critical engine, that not every plane has a critical engine. The only question I had is ASSUMING that every propeller spun clockwise (and only clockwise) would every plane have a critical engine? If you read any multi engine hand book or even the King Multi engine ground school no where in there does it refer to heavy multi engine airplanes. I am merely trying to verify that if every propeller did in fact spin clockwise that every airplane would in fact have a critical engine.

Ohh okay, like water spinning the opposite way in the toilet down south.:D

Unless the Europeans designed both engines as counterclockwise rotating, then no the right engine is not critical.

Remember the only reason we have a "critical" engine is because when you lose that engine the other engine creates the largest effect on control and performance.

Remember to read your PAST acronym.

Pfactor
Accel slipstream
Sprial slipstream
Torque

Yes, every airplane would have a critical engine. It comes down to basic aerodynamics. Last I checked aerodynamics effect airframes the same, large or small. :D

In response to another comment about P-Factor being the most important factor in determining the critical engine. I must disagree. Accelerated lift can play a large factor in determining the critical engine as well.

Good luck studying for you Multi!

Um, well, you realize the asymetrical thrust (P-factor) across the propeller blade at high AOAs IS what CAUSES the asymetrical lift (accelerated slipstream) in back of prop right?, and a rolling moment a little greater to the left with the left engine dead than to the right with the right engine dead....

Lots of the time when I was teaching this people would often confuse "critical engine" with "reasons why an airplane rolls and yaws towards the dead engine". They are different things. Airplanes yaw and roll due to asymetrical thrust, windmilling prop (prop a/c only), loss of accelerated slipstream (prop only), and the outside wing yawing and generating more lift. No matter what engine fails, these always happen and they always cause a yaw and roll to the dead engine.

This is one of those subjects where you can ask 10 MEIs and get 10 different, not-wrong answers. The examiner on my MEI ride loved the PAST acronym..however, all the FAA pubs (Airplane Flying Handbook, Flying Light Twins Safely, etc) on multi-engine flying name P-factor as the cause of a critical engine.

P-factor, longer moment arm on the descending blade. Correct. Another thing to remember is you lose 50% of your available horsepower, but you generally lose 80% of your performance. That running engine, if you're not good at maintaining in balance, will just take you to the scene of the accident. Long time MEI.

The British did have a counter clockwise rotating engine, the Rolls Royce Dart, thus making the right engine the critical engine. Either way they spin leaves you with a longer moment arm on the critical engine, and asymmetric disc loading (P-factor).

You're absolutely right, I should have thought through the thought process completely before making myself sound dimwitted!

Dash-8? Not the bombardier dhc-8.