multiengine instrument: dead engine questions

[Donsa320]

MauleSkinner: Thank you for this post. It is informative. The problem with wind tunnel tests as I know them is that the results are always an extrapolation. They may be accurate and they may not. But they are usually an indication of the truth.

A couple of more thoughts. In large airplanes we usually are a long way from VMC when operating with an engine out. The faster one is going, the less the engine out yaw is. That said, there was a C-130 accident in the last decade or so in which engines 1 and 2 were at flight idle on a trainig flight and a missed approach was conducted. The trainee was flying while the IP was working with ATC and was not paying close attention to the control inputs. The trainee was holding heading with only aileron inputs and the airspeed decayed until the ineviable roll-over occured. I believe they hit a motel.

In all of the large 2, 3 and 4 engine airplanes I've flown, engine out yaw was only countered with rudder. The near accident at SFO in which a B-747 nearly hit a hill after take-off, with the loss of #4 after V1, was attributed to insufficient use of the rudder by the flying pilot (the F/O). It seems that their simulator training allowed copius amounts of aileron to be used to control heading. This was forthwith changed!

But again, large airplanes are flown differently than light twins which have much less surplus power with an engine out.

BTW, I take exception to the professor's advice to use copious bank if flirting with VMC. The only safe thing to do is reduce power and accept the contolled forced landing, instead of the stall with yaw which will occur shortly.

 

[MauleSkinner]

BTW, I take exception to the professor's advice to use copious bank if flirting with VMC. The only safe thing to do is reduce power and accept the contolled forced landing, instead of the stall with yaw which will occur shortly.

I would agree with that statement, under "normal" circumstances...but say a prop doesn't feather for you...Vmc goes up, stall speed doesn't change much. You're light enough that you have some performance available to keep climbing...Vmc went up because of reduced weight, but stall speed went down. This might be a good situation to increase bank angle and keep flying.

As with most everything in aviation, there are no hard-and-fast answers...and when the situation occurs, you don't have time to pour a cup of coffee and consider your options, so you do the best you can. If "the best you can" turns out good, it was the right decision.

Fly safe!

David

 

[Donsa320]

I would agree with that statement, under "normal" circumstances...but say a prop doesn't feather for you...Vmc goes up, stall speed doesn't change much. You're light enough that you have some performance available to keep climbing...Vmc went up because of reduced weight, but stall speed went down. This might be a good situation to increase bank angle and keep flying.

As with most everything in aviation, there are no hard-and-fast answers...and when the situation occurs, you don't have time to pour a cup of coffee and consider your options, so you do the best you can. If "the best you can" turns out good, it was the right decision.

Fly safe!

David

Ah, but VMC is usually determined with the propeller windmilling, no? But I agree, never say never, but the good professor made a bad statement if it had to stand alone. IMHO.

DC

 

[A Squared]

A Squared, I can not respond to the Navy pilot who commented in the other thread about the 300 FPM increase in ROC by zero side slip because I just don't really know all the facts about the report. Maybe this was done on a hot summer day with thermals and the results are invalid. Maybe he was mistaken or maybe he was ordered to make the particular airplane look better so as to get a big government contract. Who knows? I do wonder why the Navy would even do such tests as that is not the kind of work that they usually do, to the best of my knowledge.

The flights in question were a part of the syllabus at the Navy Test Pilot School, so I think it is safe to assume that
a) The USN Test Pilot School is aware of how thermal activity might influence climb performance data. and

b) They were not trying to fake performance numbers to please the congressman form the district in which the plane was made. I'm sure that Skiddriver, if he were reading this thread, would appreciae your slight on his integrity though.

So in the end, the results of this referenced test just are not entirely believable to me.

Seeminly for no other reason than because it conflicts with your belief

Therefore, if you will, I would you like to hear your comments on the Boeing questions and the single engine analogy question in my prior post.

Sure, as I've already stated, I really don't have any idea why Boeing might not mention it in their manuals. Perhaps, like I suggested it was a choice to make emergency procedures simpler and more fool proof at the expense of performance. But that is merely speculation

As for your single engine analogy, I don't know. It seems like it could be a way of simulating the situation, except that the yaw string would be pretty much meaningless due to propeller slipstream...but then, it could have a dissimilarity for reasons that haven’t occurred to me (or to you) .

The problem with wind tunnel tests as I know them is that the results are always an extrapolation. They may be accurate and they may not.

True, but the results come from wind tunnel tests *and* flight tests. I don’t have the details of exactly how Mr. Byington determined which data, but then, neither do you. To dismiss it as you do as meaningless because it is wind tunnel data, is an unwarranted assumption. A 100 fpm improvement in climb is not as impressive as a 300 fpm improvement, but neither is it negligible.

 

[MauleSkinner]

Ah, but VMC is usually determined with the propeller windmilling, no? But I agree, never say never, but the good professor made a bad statement if it had to stand alone. IMHO.

DC

Key word "usually" ...as I posted in another thread http://forums.flightinfo.com/showthread.php?t=81913
we have a King Air that has been modified...it publishes Vmca at 92 knots. For this modified airplane, autofeather is required to be operational, as a windmilling propeller raises Vmca to 99 knots.

Note that takeoff performance is predicated on a "decision speed" and rotation at 95 knots, which makes the 99-knot figure kinda ugly

Anyway, this is one case (and I'm sure there are others) where Vmca is based on a feathered prop.

As to the good professor's statement standing alone, well, probably blame me for pasting it out of context.

Fly safe!

David

 

[RefugePilot]

Just a few quick responses here. I dont have time to read through the whole thread because I just came here to research critical altitude for a checkride tommorow.

I was having trouble with this single engine under the hood a week ago. The simple answer I had was look at the ball, step on that rudder and put the ailerons in that direction, then go to cleaning everything up. As soon as I started doing that my single engine approaches became much smoother.

The reason to make your turn towards the good engine is because every degree of bank towards the good engine raises Vmc by I think 3 degree. I remember that as it was one of the things I blanked on for my MEI ride.

With single engine it is a trade off between control vs performance. Less than 3 degrees bank towards good engine means control goes down and Vmc goes up, more than 5 means performance goes down, and so does the plane or airspeed.

 

[MauleSkinner]

Just a few quick responses here. ...

The reason to make your turn towards the good engine is because every degree of bank towards the good engine raises Vmc by I think 3 degree. I remember that as it was one of the things I blanked on for my MEI ride.

The "turn" towards the good engine is actually a "bank"...and it "lowers" Vmc, usually by a number of "knots" probably specific to the airplane make and model.

I'd suggest responding a little more slowly

Fly safe!

David

 

[RefugePilot]

The "turn" towards the good engine is actually a "bank"...and it "lowers" Vmc, usually by a number of "knots" probably specific to the airplane make and model.

I'd suggest responding a little more slowly

Fly safe!

David

Sorry I wasn't clear but I meant "turn" as in a circling to land approach, which would be acheived by "banking" the aircraft. I was assuming most people here already new how to turn an aircraft. Part of this thread was asking why you are supposed to turn towards the good engine if you have a choice, and the responses I saw(did not read all of them), said there is no reason to turn towards the good engine.

I passed my checkride today, so I now have time to read entire posts before responding. I can also go back and read about the big 0-sideslip debate.

 

[MauleSkinner]

Sorry I wasn't clear but I meant "turn" as in a circling to land approach, which would be acheived by "banking" the aircraft. I was assuming most people here already new how to turn an aircraft. Part of this thread was asking why you are supposed to turn towards the good engine if you have a choice, and the responses I saw(did not read all of them), said there is no reason to turn towards the good engine.

I passed my checkride today, so I now have time to read entire posts before responding. I can also go back and read about the big 0-sideslip debate.

Sorry...I didn't realize that Vmc was decreased by turning the aircraft.

 

[A Squared]

Sorry...I didn't realize that Vmc was decreased by turning the aircraft.

ZZZiiiizzzzzz .... ( the sound of irony sailing right over someone's head)

 

[MauleSkinner]

ZZZiiiizzzzzz .... ( the sound of irony sailing right over someone's head)

Huh...I thought it was sarcasm

 

[MauleSkinner]

Sorry...I didn't realize that Vmc was decreased by turning the aircraft.

Now that I think about it, assuming a constant level of sideslip, a turn into the good engine probably increases Vmc a little...you've got the adverse yaw of the ailerons requiring additional rudder...if you're AT Vmc, you haven't got enough rudder to make the turn. If you're just above Vmc, you have the additional rudder to make the turn, but that's all.

Once you're stabilized in a coordinated turn, it generally still requires a little bit of rudder pressure into the turn, so again, you're requiring more rudder than "straight-ahead" Vmc.

The good news is that if you do indeed start to lose directional control, it's taking you back towards "straight-ahead" flight before you roll over. You've got a little time to get the aircraft back under control.

In the same situation with a turn into the dead engine, you'd be decreasing Vmc by a small amount, but you'd have to increase Vmc in order to roll out of the turn. If you start to lose directional control there, things will probably only get worse.

Interesting... (well, to my pea-brain, anyway). I think the aerodynamic nuances of this could get pretty complex. Kinda makes me want to never be maneuvering near Vmc.

A Squared...what sound did that make? (hopefully not "BBUZZZZZ...thank you for playing!"

Fly safe!

David