multiengine instrument: dead engine questions

[A Squared]

My point has always been that it is not as significant as it is supposed to be. It's simply an over-rated performance enhancement technique and many people believe that it will boost performance as much as 300 FPM. Maybe 10 FPM or possibly 50 to 75 FPM or even 100 FPM by placebo effect, but not 300 FPM.

Yeah, that's just it, you keep dodging the fact that the navy test pilot guy in the other thread had a measured 200-300 fpm increase in climb, in a General Aviation aircraft.

SO your insistence that it's 10 fpm or maybe 75 fpm but never 300 fpm is just patently false. It *is* possible on some aircraft under some conditions to get an increase of several hundred FPM.



Clumping litter, congratulations on your new rating.

 

[clumpinglitter]

Thanks, guys!

-Christine

 

[UndauntedFlyer]

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. So in the end, the results of this referenced test just are not entirely believable to me. Seeing is believing and even seeing can be wrong because of unknown outside factors. It’s not just the report of one person on this point that would convince me of a 300 FPM gain in any GA aircraft. But I will keep his report in mind because what I and everyone want is the truth about "zero side slip."

Now, A Squared, you know that I have always have great respect for your knowledge and your posts on FI, and that is why you are a valued member of this Board. 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.

Thank you all FI members.

Your comments and questions are always appreciated.

UndauntedFlyer

 

[MauleSkinner]

Just as an FYI...I acquired some BPPP training material which, naturally, has information specific to the Baron models...I'm not saying it proves anything one way or the other, but it does put some very specific information into the equation.

A few quotes (all emphasis/punctuation is theirs):

*The bank angle is critical; too much or too little can cause loss of control at speeds well above Vmca!
*There is NO instrument in the aircraft to indicate the proper bank angle!
*A yaw string attached to the nose of the plane will provide the proper information on bank angle.
*An increase in altitude...lowers Vmca without significantly changing the stall speed, indicating that for most all light twins, there is some weight/altitude combination where Vmca and Vs are the same. For the sameple, this crossover occurs at half fuel, mid CG and 3000 feet--the exact conditions at which most multi-engine Vmca training demonstrations are performed.
*DECREASING the bank angle AWAY from the good engine INCREASES Vmca AT THE RATE OF 3 KNOTS PER DEGREE OF BANK ANGLE.
*If the pilot inadvertently or instinctively tries to hold the wings level in an engine out situation, Vmca CAN INCREASE AS MUCH AS 20 KNOTS. THE AIRCRAFT COULD BE UNCONTROLLABLE AT SPEED AS HIGH AS Vyse. This situation WILL EXIST if the pilot tries to maintain heading with the ball centered!

Additionally, a Prof M.R. Byington of ERAU conducted flight and wind tunnel tests on a Crusader, a Seminole, and a 58 Baron, with a 3-foot length of yarn as a yaw string and a "large inclinometer" in the cockpit, at a 5000' density altitude. Results for the Baron include:
1 degree into the DEAD engine--0 ft/min climb
Zero bank--50 ft/min climb
2.7 degrees into the good engine--150 ft/min climb, yaw string centered, ball about .7 out of center
5 degrees bank into the good engine (max allowed by FAR for Vmca demo)--75 ft/min climb
7.5 degrees into the good engine--0 ft/min climb, but no rudder force required. Vmc is "vanishingly low", and he recommends this configuration if you're flirting with Vmca rollover.

Exactly how that would translate to an engine-out climb after takeoff from a 1000-ft D.A., I don't know...obviously the total climb numbers would increase across the board, but would the INCREASE change?

Well, now you know as much as I do

Fly safe!

David

 

[UndauntedFlyer]

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.

 

[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