Myth Busting - Engine Inop Performance

[MauleSkinner]

Its just so little difference that its not enough to worry about and can not be see on the VSI or a yaw string.

Climb rate aside, if you're saying that you can't see a noticable change in a yaw string with half-ball change in slip, you're doing something wrong.

David

 

[UndauntedFlyer]

Maulskinner: Thanks for your interest in this thread. Regarding the yaw string, I went out one time years ago with a camera to try to make a slide to use in my FIRC class on this subject. I was trying to get a photo to look something like the ones in the text books on this subject. But it just didn't work. There was so little change that in order to get something to use I had to fake it with a BIG cross-controlled forward slip. Of course to use that slide would have been a lie so I stopped perpetuating the Myth about all of this great enhancement in performance with the ball half-out vrs. in the center. It is truly overrated, not that the concept isn't true, but just that this whole business is greatly over done. And in the end, a lot of people believe it because of what they have read and then they teach this as something that is important. But really, if a person truly goes out and feathers an engine and then holds Vyse in smooth air you'll see that any performance enhancement is very minimum if can really be detected at all. It is so slight that if you want to see an increase in performance you probably will, and if you want to see no change you probably will see that too. So in the end, the answer is negligible change. This is my experience on this subject.

 

[NoPax]

Zero-Sideslip - ie banking into the operative engine will KILL YOU in an MU-2.
Half a ball deflection costs about 400fpm (or so I was told by an MU-2 veteran)

Varies with different types of airplane.

 

[MauleSkinner]

This is my experience on this subject.

Obviously, the rest of our experience disagrees.

David

 

[skiddriver]

Last post on this

Last post on this subject.

First, I have to ask, does anyone really think that there is no sideslip just because Dauntless' string didn't show one in his installation. The installation of aircraft test instrumentation is a science unto itself. Sideslip measuring vanes are not installed on the top of the nose of an aircraft due to the localized airflow effects there; they are installed in free air at the end of a pitot-static test boom. Dauntless' experience notwithstanding, in the described flight condition, there is a sideslip, and it does have an effect on performance.

When I said that the effect was small, when I review my data card from the flight, it had a 200 to 300 FPM positive effect, as measured on a sensitive (instrumentation grade) IVSI. This is one-time test day data in a specific aircraft. A "real" test program would have referred this data to test conditions and would have been conducted across a spectrum of conditions to achieve generalized data. If you are already at a significant positive rate of climb, 200 to 300 FPM added is probably not significant. If you need the climb rate, it may be. In any case, I believe, and have both the theoretical basis (as in having computed the partial differentials to prove the concept) as well as test data (taken in an instrumented aircraft) that show that there is a positive effect in the blended solution of arresting rotation with the rudders, and banking into the good engine approximately 3 degrees. This effect is going to vary between aircraft and given conditions of the day.

Dauntless, you'll probably think I'm being facetious, but I'm not. If you are interested in being a test pilot, contact the National TPS. You can buy yourself a seat there and will actually learn what it takes to conduct a valid test program. http://www.ntps.edu/

 

[A Squared]

When I said that the effect was small, when I review my data card from the flight, it had a 200 to 300 FPM positive effect, as measured on a sensitive (instrumentation grade) IVSI.

Hmmmm, I'm thinking that 200 fpm might be just what I need to make the difference between going *down* 100 fpm, and going *up* 100 fpm. Me, I'll take 100 fpm up over 100 fpm down any day. Undaunted can continue arguing the merits of 100 fpm down if he wants, it will be a tough sell.

 

[UndauntedFlyer]

Skiddriver: You are providing some good information about certain high performance military aircraft but have you done any tests on GA aircraft such as this thread discusses? I mean planes like the Seminole, the C310, the Baron or a C421?

I have never said that your tests are wrong, only than the performance enhancements and so small on GA aircraft that it isn't worth getting all wrapped up in thinking this will help a lot because I know it doesn't.

Also, do you have any idea why all this zero side slip is never mentioned in the FM for large 2-engine or 4-engine airline equipment? No one says nor does the FM say anything about this technique for engine failure at V1 at max GW when performance is very critical.

 

[A Squared]

Skiddriver: You are providing some good information about certain high performance military aircraft but have you done any tests on GA aircraft such as this thread discusses? I mean planes like the Seminole, the C310, the Baron or a C421?

Uhhhhhh, the U-21 of which he speaks is a king air 90. Not knocking the king air, but it's hardly a "high performance military aircraft"

So the answer woud be, yes, he has done tests in GA aircraft.

 

[minitour]

Hmmmm, I'm thinking that 200 fpm might be just what I need to make the difference between going *down* 100 fpm, and going *up* 100 fpm. Me, I'll take 100 fpm up over 100 fpm down any day. Undaunted can continue arguing the merits of 100 fpm down if he wants, it will be a tough sell.

Yep...100fpm in a light twin on one engine can be very exciting considering the alternatives.

-mini

 

[Skygod]

On the airbus, lose an engine on takeoff and the slip-skip indicator changes to become a beta target, and when centered with the rudder this results in best climb performance.

Don't know about Boeing, but seems Airbus trusts test pilots and their 'placebo.'

 

[A Squared]

Yep...100fpm in a light twin on one engine can be very exciting considering the alternatives.

Yes, in a engine out situation in a light twin, 100 fpm *up* could be cause for intense jubilation.

I guess I don't really get what undaunted's beef is. We all agree that using rudder and bank to achieve zero sideslip isn't going to press you down in your seat and flatten your eyeballs in thier sockets with the increase in performance, but we all (including undaunted) agree that there is *some* increase in performance. Undaunted appears to me to be advocating *not* teaching pilots about this small performance edge which might save thier a$$ some day. Why, is beyond me.

Think about it this way; say a pilot wth whatever reason (high, hot, overloaded, or just poor performing light twin) finds himself in a position where he's slowly losing altitude with one engine feathered. Consider two ways the scenario could play out.

1) he bores along, wings level, losing altitude gradually until he crashes into a schoolyard, spreading dismembered little bodies across the playground.


2) He banks slightly into the live engine and gets the slight performance boost he needs to clear the top of the swingset, and slowly gain enough altitude to bring it around and put it back on the pavement.


I am at a loss for understanding why Undaunted seems dead set against teaching pilots that option 2 might exist.

 

[UndauntedFlyer]

All members who have made posts on this subject have made good points and as ASquared says, we all really agree. And I have many times agreed that at least trimming to a half ball is easier on the trim and on my leg if that is the only force behind the rudder. There in lies the greatest PRACTICAL advantage of zero side slip with an engine inoperative, less rudder force.

My general complaint is that in GA zero side slip is an over emphasis to where multi students think that ball out of center is always an objective when an engine is inop, it is not. If it is needed, give it a try, why not? It may be a performance enhancement tool to some small degree that could be important sometimes as an "ace in the hole" that theoretically will do some good. As I have said, this technique does not hurt anything with regards to performance. So what the heck, try it before you hit the trees? I would too, why not try anything at that point?

The only real problem is people who I have referenced before in this thread, who try to identify a dead engine with the ball out of center. This has happened several times in my examining work. The situation is the pilot corrects for the engine failure with all aileron and then has to use the wrong (opposite) rudder. Then the student incorrectly tells me which engine is out because "dead foot dead engine" is wrong here. When I ask why the ball is out of center he tells me that it's not suppose to be in the center. This is a training problem.

Also, as I have mentioned here too, I see students trying to fly a 1-engine ILS's and desperately trying to hold the GS/LOC and the airspeed which is hard enough, but to complicate things he is also trying to keep the ball out of center. Of course, when going down hill at partial power there is no need for this at all.

I also talk to people before I fly with them and almost all tell me that the zero side slip technique will enhance performance 3j00- 500 feet per min. When I fly with them they are surprised when it actually reveals no enhancement what so ever, or so slight an enhancement that it is immeasurable. Yes, maybe I am a victim of placebo effect too.

This all tells me that there is, in general, too much emphasis on this element of engine out multiengine knowledge.

To me this whole thing is mostly an over done concept, almost a myth with SOME TRUTH behind it.


Thank you for all your comments on this thread.

 

[infiniti757]

Does any one have any actual numbers for GA twins and their SE performance?

 

[stupidwork]

there is a faa hand out or ac with a list of se climb perf. i cant refence it now because im at home and the paper is at work... but it dose list a dozen or so GA multi engine aircraft. i think its title is "leave your self an out".
wait found it....http://maxwellaeroclub.com/Always Leave Yourself An Out.pdf

 

[100LL... Again!]

The issue is not so much that banking is unnecessary as much as that the whole issue is trained very rote in most cases I have experienced.

Not enough real correlation is being achieved.

I will agree that once performance issues are no longer a concern, wings-level works just fine. (I.E on the ILS).