multiengine instrument: dead engine questions

[clumpinglitter]

...but unfortunately Undaunted's experience seems to override the rest of ours

David

My instructor and I taped a yaw string to the Duchess the other day, but after we took off, it just hung down instead of going up over the windshield. I think the end of the string caught on something. Pissed me off.

-C.

 

[UndauntedFlyer]

In my limited experience, the yaw string does do a good job of displaying zero side slip.

I believe you will find that the yaw string does show yaw just as it is supposed to do. If you are flying with an engine inoperative and windmilling plus using bank and no rudder correction the yaw string will show lots of side-slip yaw. But if the failed engine is feathered (or set to zero thrust) and you're holding heading with the ball in the center or whether it's off one-half ball width while still holding heading, the displacement of the yaw string is almost nothing from one situation to the other and neither situation has the yaw string more aligned with the longitudinal axis than the other as can be seen.

 

[SPilot]

UndauntedFlyer, thanks for your reply.

I rest my case.

But I have tried it, and noticed better performance with 5 degree bank and offset ball, compared to wings level and ball centered.

I have however not tried to compare performance just with or without offset ball, using 5 degrees of bank in both cases.
And also with the string on the windshield, I've not attempted to look for any difference between ball centered and ball offset, but I have noticed significant difference on the string between banking and wings level.
On the Seneca I flew, the string was sort of "sticky" because of moisture combined with dirt and bugs on the windshield, so it was difficult to see small differences (it took a large change in yaw to convince the string to rip loose and move).

In any case, the minor difference in performance is not all that interesting during practical flying. I'm probably not able to fly the airplane with such extreme precision during an emergency anyway.

 

[UndauntedFlyer]

I have not tried to compare performance just with or without offset ball.

That is the whole point of the yaw string test and your instructor didn't do it?

Of course the 5 degrees of bank would only be along with the ball at half-scale deflection. And that would be compared with the ball centered and the wings almost level level or the airplane would be turning. And in this test you will see that there is no measurable change in the yaw string. The point being that zero side slip is not all that it is supposed to be in terms of greatly reduced drag. In reality all that it will do is give your leg a rest. The performance enhancements are minimum if they can be seen at all.

Personally, I file all reports of greatly enhanced performance as a result of "zero side slip" configuration under the title of placebo effect.

 

[gkrangers]

I believe you will find that the yaw string does show yaw just as it is supposed to do. If you are flying with an engine inoperative and windmilling plus using bank and no rudder correction the yaw string will show lots of side-slip yaw. But if the failed engine is feathered (or set to zero thrust) and you're holding heading with the ball in the center or whether it's off one-half ball width while still holding heading, the displacement of the yaw string is almost nothing from one situation to the other and neither situation has the yaw string more aligned with the longitudinal axis than the other as can be seen.

I can't be positive as its been over a month since I've done this now, but I do know at times there would be a considerable difference between ball centered and setting up for zero side slip, in our Duchess.

Could depend a lot on the airplane and the way the string is attached perhaps.

I know you have far more experience than I, just stating what I've observed.

I'm not talking performance differences, just centering the string along the longitudinal axis of the aircraft.

 

[nosehair]

Keep in mind that a small, insignificant performance improvement in a small training airplane may convert to a larger, more impressionable performance improvement in a larger engine airplane.

 

[minitour]

Keep in mind that a small, insignificant performance improvement in a small training airplane may convert to a larger, more impressionable performance improvement in a larger engine airplane.

...and sometimes a small, insignificant (100fpm) performance improvement in a small training airplane may be the difference between a controlled crash and staying airborne.

-mini

 

[gkrangers]

...and sometimes a small, insignificant (100fpm) performance improvement in a small training airplane may be the difference between a controlled crash and staying airborne.

-mini

I would call 100fpm significant. Anyone know, lets say on average or at standard atmosphere how much improvement zero side slip gives in a Duchess, Seminole, or anything really ?

 

[A Squared]

Personally, I file all reports of greatly enhanced performance as a result of "zero side slip" configuration under the title of placebo effect.

Ummm yeah, it's just "placebo effect" RIghty, last time we discussed this, the guy who was a Navy Test pilot, the one who had actually done extensive test profiles on this, with a highly instrumented aircraft, and his systematic, carefully measured flights under controlled conditions showed a significant increase in climb (not sprctacular, but significant) yeah that was probably "placebo effect"

OK, undaunted, I'm going to get personal here for a moment.

Look. You bring a lot of good things to this forum, a great deal of experience, an enthusiasm for General Aviation, the perspective of an actual examiner, and you've sparked some interesting discussions. That's all good. But for some reason, you have a bug up your a$$ because you think the zero sideslip concept is a myth. That's fine as far as it goes. I, like you, believe that dogma should be challenged, and I'll be the last to claim that everything in an FAA text is true. However there comes a time to admit that you are in fact wrong. The time for you to admit that you are wrong was when a trained, navy test pilot showed you from his flight test records in GA twin with test instrumentation that the zero sideslip concept actually *DID* yield performance improvements. Yet, unbelievably, you insist that there is no value to "zero sideslip" that it's all "placebo effect" .

I gotta ask, what is wrong with you? why do you keep tilting at this windmill when you've been shown to be wrong? Do you think that your casual dicking around in a duchess with a string tied to the windshield is more accurate than a trained test pilot flying specially instrumented aircraft through a carefully planned test sequence? Or are you just so convinced of your omniscience and omnipotence, that nothing anyone says or does (even trained test pilots) will make any difference to you?

Sorry for getting personal. Like I said, I do think you contribute some positive things to this forum, but your "just say no to zero sideslip" campaign is not a positive contribution.


FOr those of you scratching your heads wondering what the deal is here, take a look at this thread.

http://forums.flightinfo.com/showthread.php?t=74012

Take a look at Skiddriver's posts. He's the test pilot. Notice how Undaunted goes from saying that performance increases from zero sideslip is a myth at the begining of the thread to conceding that the performance improvements exist. Now, for some reason he's back to insisting that they are due to "placebo effect" I don't get it. All I can say is that I would point out to Undaunted Flyer that this foolishness undermines his credibility on other subjects.

 

[Metro752]

i woulda failed my multi checkride if Al was my DE. i was flying around half the checkride in a zero side slip condition

 

[Donsa320]

zero side slip

I have a Beechcraft Safety booklet which suggests that to obtain zero side slip, one should use a 1/2 ball width displacement if the critical engine has failed and 1/4th ball width if it is the other engine. Since the Be-76 is counter rotating, 1/4th ball width should do it for either engine.

I only do a little ATP preping now and I insist that to identify a failed engine, center the ball and decide which foot you are not using. Lordy, it only takes a second or two. After things are under control then start playing with a wing down.

That 5 degree bank thing is another peeve. That figure is the maximum that the manufacturer is allowed to use to determine VMC. Use it and you may find yourself sinking. Vxse and Vyse need less bank than that if you want to climb. VMC is not necessarily going to allow a climb at all. Vxse and Vyse may not either at Denver.

DC

 

[minitour]

I would call 100fpm significant. Anyone know, lets say on average or at standard atmosphere how much improvement zero side slip gives in a Duchess, Seminole, or anything really ?

When I did the drag demo during my MEI training (that I still haven't gotten to complete the flight portion of the checkride on), it was pretty significant.

The instructor wanted me to see in all configuration settings what a difference it made. We started with flying wings level ball centered...then tossed gear, then flaps. Three words came to mind, "oh f& me"

Let the ball out a bit and bank a touch...things get better....clean it up...hey...we're climbing...not much, only 50-100 fpm but that was in a semen-hole at 7k too...so I'll take it.

-mini

 

[UndauntedFlyer]

Spilot: With all due respect, what you have written here is really not correct. First, when an engine fails it is most important to increase to full power, level the wings, center the ball and hold heading. The ball needs to be centered in order to be sure of just which engine has failed using the dead foot dead engine method. Allowing the ball to be displaced during this procedure can result in a misidentification of which engine has failed. Second, once the inoperative engine is determined and secured then the "zero side slip" technique may be used if you think that will enhance performance. Personally my experience is that the "zero side slip" technique doesn't do much of anything for performance but it does give your leg a rest. And finally, you have indicated that by attaching a yaw string to the windshield that this will show how important it is to use "zero side slip." This statement makes me wonder if you have ever really done this yourself or just looked at drawings in manuals. I have personally done this yaw string test many times and it really shows no difference in deflection with an engine out (feathered) and the ball centered or with the ball displaced half a ball width.

Placebo effect is a very powerful influence.

The points I am trying to make here in this post are just three things. I am sure no one has any exception with the first point about how to identify the failed engine. If there are those that take exception lets discuss that.

The second point I make is that the zero side slip doesn't make much of a difference in performance but it does definitely give your leg a rest to let off on the rudder pedal. What I am saying is that it definitely does then make some difference as I have always said, but it is very little as compared to the claims I sometimes hear or read with boasts of about 300 FPM increases in ROC. I will say now that that kind of increase in performance just does not happen in any light twin as a result of the zero side slip technique. I will say that based on the many times I have personally done this in several models of light twins the performance enhancements are so small that I can not see them clearly enough to be conclusively positive that there is a change. Yes, I will always agree that aerodynamically there must be a performance enhancement but my position on this is that it is very small. And anecdotally there will always be those who will claim the 200 to 300 FPM increases in ROC but I just think that those who make such claims mean well but that they were not patient enough to really wait for the comparative results. And to really do this test it must be done in the very early hours of the morning when there are no thermals.

Now my last point is the yaw string point. Again let me say that there is a difference in a yaw because there must be, and any scientific instrument would have to show it. But my point is that it is so slight that it can not be seen on a single yarn yaw string taped to the nose of a typical light twin. I have seen these drawings of the aerodynamics of zero side slip and while I agree totally with the concept, the drawings all show a yaw string example of 20 and 30 degree displacements. That is just not so. The real number may be just 2 or 3 degrees which is so small that it can not be seen on a crude yarn yaw string.

Now the part of my posts about placebo effect is my own explanation as to why some people report the stunning results of zero side slip enhancements on performance and the yaw string displacement between ball centered and one-half deflection, when my tests show so little change.

So in the end, rather than listen to me or others further discuss this, why doesn’t one of our board members that seem to indicate that they are regularly flying the BE-76 in training, or any light twin, just go out one morning very early with a 2 foot piece of yarn yaw string taped to the nose in front of the windshield and climb to 3 or 4000 feet and then feather an engine for a test. Then just slow down and pitch to hold blueline with full power on the operating engine. Hold this configuration for several minutes and note the ROC and yaw string position with the wings level ball centered. Then just let off on the rudder to a one-quarter or one-half ball width deflection while still holding heading and note the results after allowing a few minutes for the airplane to re-stabilize. I think that in this case there will be very little if any noticeable changes. Yes, there must be change as I know there must be but my point is that it is very little change. (I recommend that this test be done over an airport and that the fuel be at about one-half or one-fourth tanks to improve performance for the safety of this test.)

Yes, I will also say that if I lost an engine and wanted to climb I would use the zero side slip technique because it definitely will not hurt performance and it must help somewhat. Of course it can not hurt anything and it is easier on your leg, so why not use it?

And regarding flight tests that I administer and applicant’s knowledge on this subject, everyone is supposed to know about zero side slip because that is in the FAA reference books and as I have said it is true. Applicants are only responsible for what is in the FAA references and the POH for their airplane and are not held responsible for what I write on FI or write any where else.

What I write here is for those to read that want to here my opinions based on my experience. I share these opinions and experiences for anyone to listen to or hear about and I believe that everything I write is correct even though it may not always be in alignment with everything else that is printed. Might I be wrong about something? No doubt that can be. But what I write about my experience is as correct as what I observe. Could my observations be incorrect? I suppose so but I have seen the same thing over and over.

Now I do sometimes take exception to some things that I see printed on various subjects, but my complaint here on this subject has always been with the amount of performance enhancement stated in books, and not that it doesn’t exist. For example, you may have noticed that in the 1980 edition of the FAA Flight Training Handbook (p.237) it says that there may be as much as a 300 FPM increase in ROC in typical light twins by using the zero side slip configuration. And now in the latest FAA Airplane Flying Handbook which superseded the FTH, in the multiengine section it no longer makes such a claim because it just wasn't so. Also in the new AFH on page 12-23 it shows an example of zero side slip and pictures a yaw string with about 30 degrees deflection. Again this just isn't so.

I do hope that someone will go out in a typical light twin and make the in-flight test as shown above and report back with a post on this thread. Is there a 300 FPM increase? And is there a 30 degree yaw string change? Not by my tests. How about yours?

Your further questions or comments are always welcome.

Undaunted Flyer

 

[A Squared]

I sometimes hear or read with boasts of about 300 FPM increases in ROC. I.........And anecdotally there will always be those who will claim the 200 to 300 FPM increases in ROC but I just think that those who make such claims mean well but that they were not patient enough to really wait for the comparative results.

Right, the guy in the other thread, the guy who is/was a navy test pilot. the one who went to the trouble to dig up the performance numbers from the test flights he did in flight test school, The guy who reported a difference of 200-300 fpm in his test flights? that guy? Yeah, I'm sure he was just "boasting", it was just "anecdotal" and he "means well" but just wasn't
"patient" enough.

 

[UndauntedFlyer]

As a point of interest, as I have previously mentioned in the thread on this subject (previously referenced), no Boeing Flight Manual says anything about configuring for zero side slip for engine out performance following an engine failure at V1 at max GW. This would certainly be a performance situation where ROC is most critical and at a bare minimum. Boeing with their data show no need to do anything different than keep the wings level and climb straight out. If there would be an increase of 300 FPM by just letting off on the rudder that would be in the manual. It is not. FYI.

 

[A Squared]

As a point of interest, as I have previously mentioned in the thread on this subject (previously referenced), no Boeing Flight Manual says anything about configuring for zero side slip for engine out performance following an engine failure at V1 at max GW. This would certainly be a performance situation where ROC is most critical and at a bare minimum. Boeing with their data show no need to do anything different than keep the wings level and climb straight out.

That is interesting.

If there would be an increase of 300 FPM by just letting off on the rudder that would be in the manual. It is not. FYI.

THat is not necessarily true.

You're jumping a very long way to an assumption. Perhaps the performance gain is negligible, on the other hand, perhaps Boeing, as a matter of policy, has chosen to meet thier performance requirements without taking advantage of the increased performance, possibly for the purpose of making engine out procedures simpler and eliminating the possibility of a pilot banking the wrong way in the heat of the moment, aggrevating the situation. Perhaps they don't use zero sideslip for some other reason that is not obvious.

I don't know why they don't use it, and more to the point *you* don't know why. For you to say that the fact Boeing doesn't call for this technique proves that it has no benefit is a stretch.

 

[UndauntedFlyer]

That is interesting.

I don't know why they don't use it, and more to the point *you* don't know why. For you to say that the fact Boeing doesn't call for this technique proves that it has no benefit is a stretch.

I did not say now or ever that it has no benefit nor did I say that Boeing says it has no benefit. (Boeing makes no comment on this in any Boeing jet manual that I know of) In fact I have continuously said that "zero side slip" does have a performance benefit. 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.

300 FPM is a MAJOR enhancement in performance. I find it hard to believe that if there was that much of a gain that it wouldn't be even mentioned in the flight manuals for the 737, 747, 757, 767 or the 777. And as far a difficulty in a takeoff and climb situation following an engine failure, letting off on the rudder pedal just a bit while holding heading with few degrees of opposite bank is not demanding for the pilot at all and is really a little easier than wings level in my opinion. That's why I have said it is good technique for that situation, it is easier to do, it's easier on the leg, and it definitely doesn't hurt anything because it will enhance performance slightly. But as far as a 300 FPM gain in a typical light twin or any other twin, no way based on my experience and common sense, and as I have mentioned, remember that the 300 FPM number has even been removed from the FAA pubs on this subject.

Really though, if you think about it from a common sense point of view, how could just half a ball width on the inclinometer really have much of an effect on slip stream or on performance? If you use what is well known from your common single engine experiences and think about it, you’ll see that it can’t be true that there is such a bragged about boost in performance. How about this, take any single engine airplane and do the opposite. What I mean is just let the plane go from a ball centered (zero side slip) configuration in the single engine airplane to a half ball width deflection (slight side slip) configuration with opposite bank to hold heading. What does that do to performance? Does that really make a difference that can be noticed, either on performance or on a yaw string? Certainly not. Oh I’m sure it does make a “DIFFERENCE” but, like the twin, it’s on paper (mostly academic) and not really a noticeable difference. Of course a really huge 2-ball width deflection would increase drag noticeable. But just a half a ball width, give me a break, that’s not enough to notice anything. Is this a valid analogy? ASquared: Yours and other FI board members comments on the above analogy would be appreciated. Is it valid? Your thoughts please.

But let's also see what our board members may say on the ME question if one of them goes out in a twin and does the “zero side slip” test as I have described in the previous post about this.

Board Members: Your help is needed if you are interested. And please try to to do the test early as described and to be objective. Your results will be valuable to this thread and all mankind.

Remember, "One small step for a man, one giant leap for mankind."

Here is you chance.

Thank you.

Undaunted Flyer

 

[clumpinglitter]

But let's also see what our board members may say on the ME question if one of them goes out in a twin and does the “zero side slip” test as I have described in the previous post about this.

Board Members: Your help is needed if you are interested. And please try to to do the test early as described and to be objective. Your results will be valuable to this thread and all mankind.

I'd perform the test, but I passed my ME checkride yesterday, and I won't be renting that spendy Duchess for a while. But I'll be doing some ME practice in a sim -- maybe I'll try it then. I'm all for helping mankind.

-C.

 

[UndauntedFlyer]

I'd perform the test, but I passed my ME checkride yesterday, and I won't be renting that spendy Duchess for a while. But I'll be doing some ME practice in a sim -- maybe I'll try it then. I'm all for helping mankind.-C.

Clumpinglitter:
Congratulations on your new MEI rating. Your offer for the sim is nice but I'm afraid that won't tell us anything. In fact it may only confuse the issue. Maybe you can get some of your colleagues to participate in the offer to help mankind.

UndauntedFlyer

 

[Amish RakeFight]

I'd perform the test, but I passed my ME checkride yesterday, and I won't be renting that spendy Duchess for a while. But I'll be doing some ME practice in a sim -- maybe I'll try it then. I'm all for helping mankind.

-C.

Congratulations on passing the ME instrument rating. That can be a tough one.