ft

Milt,
I certainly will consider that a small win. I'm not sure if you meant that it should be a small win for me though...

Just recently, you stated:
You base your case on there not being any horizontal force at the tail sans sideslip?

Now:
And voila! Now you base your argument on a horizontal force sans sideslip!

I hope to be going to Dunnunda over the next few years. Am I getting a cold one for this?

I am still puzzled though... as to how you seem to have interpreted something I wrote as building on separating the rudder/fin from the rest of the tail?

I'll check your most recent post later. Yes, this is certainly addictive!

Cheers,
Fred (still waiting)

SR71

It is absolutely possible to have zero sideslip and non-zero bank.

Take an axis-symmetric cylinder whose longitudinal axis is aligned with the velocity vector i.e., \alpha & \beta = 0.

Rotate it about this axis and tell me you still believe what you affirm to be true is the case Milt...

People are still confusing the axes systems involved in this problem.

Aerodynamics isn't sensitive to \phi.

The state vector includes six fundamental variables none of which is \phi!

The mathematics never lies.

Keith.Williams.

OK MIlt, I think we are finally getting somewhere.

To quote from your most recent post.

"Your situation 1 is now real close to how it happens except for that increased use of rudder. Before you put on that extra rudder we were balanced having arrested the yaw.
So now you go and spoil it all by changing the rudder. The tiniest bit either way will unbalance us again. But if all you want to do is go along your original track/course then by all means use a little rudder to do a slow flat turn to do just that. It is only 2 or 3 degrees anyway. Having turned to the new heading you must return to balance again by returning the rudder to its precise original anti yaw position. Remember if you change CAS or thrust or drag you unbalance and there will be a changed rudder deflection to regain balance."

I did not say that this manoeuvre was a good idea nor that it is easy to achieve, but simply that it is possible. Now let's be clear about it, we are talking about a situation in which the aircraft is sideslipping to the left. YES or NO?


And:

"Situation 2. Yes that is what we do to get the rudder back close to centre. Usually about 5 degrees thank you which gives us enough horizontal component of lift to cause us to sideslip to the desired extent.."

And isn't this sideslip to the right? YES or NO?

Unless I am mistaken we now have agreement that it is possible to sideslip either to the left or to the right with a left engine out, depending on the combination of bank angle and rudder.

Now we can get back to my original argument.

If we can sideslip left and we can sideslip right, then presumably we can gradually change from slipping left to slipping right. And at some point during the manoeuvre we will not be slipping at all.

If you look at the situation you will see that this will occur with a slight bank towards the live engine. This means that it is possible to have zero sideslip when banked towards the live engine in asymmetric flight.

ft

SR71,
going offtopic for a moment here... I'm curious about the peculiar convention you're using for mathematics here. Where does it stem from, with the \backslashes etc? Never seen anything like it before.

Any pointers to explanations, advantages and historical background? Frankly, I find it rather opaque but I'm always willing to learn something new.

Regards,
Fred

SR71

Fred,

No problem. The syntax originates from the days of my doctorate studies.

LaTeX is the de facto standard syntax for the communication and publication of scientific documents. A lot more versatile than anything MS can come up with...

LaTeX is based on the idea that it is better to leave document design to document designers, and to let authors get on with writing documents.

You can check the WWW for numerous references to the project but try here first:

The LaTeX Project

ft

Gah! Horrible flashback! Yes, I did write in LaTeX (with the horrible formatting of the logotype) way back when... aaaagh!

Never thought anyone would try writing raw LaTeX in a forum though. You're a deeply disturbed person! It's not exactly intended to be human-readable...

Hey, how about converting to PostScript?

Cheers,
Fred

john_tullamarine

Milt,

What jolly good fun this all is ...

Cap 56 - "If the force from the rudder/fin (they work together) is equal to the the force from sideslip caused by the bank, while at the same time you balance the moment from the live engine, you have zero slip straight flight."

Milt - " .. you have cancelled out the sideforce due to the bank caused sideslip. Now we have no sideforce to counter the yaw being rapidly developed by the live engine. We are turning into a frisby again. "

Cap 56 addressed the need to keep the moment balance - hence no frisbee excitement. A more appropriate observation would have been that the requirement to maintain zero slip (once obtained) is to maintain a nil residual lateral force and nil moment imbalance.

One should observe that a zero slip condition is likely to be approximate and than there will, in all likelihood, be random minor excursions into a slip regime .. but the general point still remains... or are you simply being pendantic on this point of semantics ?


"Absolutely impossible to have zero side slip with bank applied. The very reason we put on bank in the first place was to generate that indispensable sideforce to counter the yaw and allow us to get the rudder close to centre."

Generally accepted for symmetric thrust .. but the crux of the discussion for a thrust asymmetry. Again, why is there a need to seek the Holy Grail of near zero rudder deflection ?


"Having turned to the new heading you must return to balance again by returning the rudder to its precise original anti yaw position. Remember if you change CAS or thrust or drag you unbalance and there will be a changed rudder deflection to regain balance."

Can not the pilot play with bank-related forces in addition to, or in lieu of, rudder-generated forces ?


Fred,

First shout is on me during your forthcoming trip ...

SR71,

Why don't you come along also and at least we will outnumber Milt.

Milt,

You stir the pot superbly well, good sir.

Milt

John Tullamarine


Our worthy moderator has raised 6 points for clarification concerning the complexities of asymmetric handling.

Rather than repeat them item by item which would make this a lengthy rendition I ask participants and other parties of interest to refer back to JT's post hoping that it is not now on a separate page. Damn just saw that it is on the previous page.

Item 1.
In seeking a comprehensive definition of sideslip the term "normal to the vertical axis" was included only for completeness knowing full well that the sharp minds viewing the post would likely be critical of a definition which only related to our strictly horizontal determinations. We well may have to defer to our aerodynamics potentate whoever that may be for the absolute precise definition. Let us agree for now on the simple version applicable to the horizontal.

Item 2.
Don't think that quote was mine but I recall I did respond to it. To have "skidding zero rudder deflection" we must necessarily have bank to cause the skid. The skid is creating the force to stop yaw. Use of rudder to reduce the skid changes the force and immediately puts us back into unbalance. There is NO way to go with rudder and stay in balance unless we readjust the bank angle.

Item 3.
Answered by Item 2 above I believe and I think you have answered your own question correctly. We do play with the bank angle to readjust our rudder position. For any bank angle there will be a precise rudder position for balance. You cannot change one without changing the other as you have said in Item 4..

Item 4.
Airflow directions? That's a curly one and I think too complex for a definitive statement. Instinct from experience tells me that the variations to sideslip as we vary our relationship between bank and rudder will be so infinitesimal that we can confidently say there will be insignificant change in the small range of bank angles of any worthwhile use. Somewhere in there may well be the minimum drag combination we want but then the flatness of the drag curve here may mean that it is of no consequence. We are now into the realms of instrumented flight test or wind tunnels. Would be great to hear from someone who has been there.

Item 5.
The statement is applicable to any condition of balanced flight. Of course we often change the drag vector but usually take care to balance one side of an aircraft with the other. If we install a drag producing device on one side only we have a total drag line offset from the fore and aft axis. We have then created an inability for that aircraft to be able to fly balanced directly in line with its fore and aft axis. If the delta drag is small then the sideslip to compensate will be minuscule and indiscernible to a pilot but it will be there nevertheless. Where it is very discernable though is when we have an engine out causing a large drag line offset.

Item 6.
Why is it that one cannot input rudder to achieve the force desired? John that is precisely what we do. The force desired is that which makes up the total from the tail to offset the yaw. It is a precise amount to achieve balance. Move the rudder that nat's whisker (or should it be gnat's?) either way and you go into unbalance. And yes the same with elevators and ailerons. For any balanced condition there will be a precise position/angle for both. We try to trim to those positions.

What now ? Strong coffee maybe !

Ohhhhhhhhhh now I have a whole new set of items from JT amongst others all waiting with baited breath !

Watch this space.


Keith.Williams

We have been consistently trying to handle an asymmetric twin with its left engine shut down whilst being flow by a succession of terribly mixed up pilots .

In your last post you say " we are talking about a situation in which the aircraft is sideslipping to the left. YES or NO?"

A huge NO NO NO Keith. We are sideslipping to the RIGHT to generate that sideforce to oppose the yaw to the LEFT. They balance out don't you see?

Then "And isn't this sideslip to the right? YES or NO?"

YES by banking into the live right engine.

Now , having recognised your incorrect perceptions above, you will clearly see that there is no way we can get to a condition of zero sideslip.

You must now be my first disciple.! or do I have to prepare more sermons.?

Have you ever flown asymmetric?


SR 71

Cannot see the path of your proposed logic SR 71.

You have blinded me with science to the extent that I am unable to achieve a decode.

Put it in the simple terms directed at the asymmetric twin which is fast running out of fuel!!

Milt

Just made 3 separate posts which have somehow become merged.

Perhaps this is what happens with PPRuNe when the same poster post consecutive posts.

Well back to the slipping and skidding and yawing and endeavouring not to lose control.

That right engine continues to run sweetly.

Milt

ft Fred

Ref your last post.

Sorry don't know who won what?

You say now "You base your case on there not being any horizonatal force at the tail sans sideslip?"

Sorry again I have lost track of the specific 'case' to which you are referring. Suffice to say - I hope we are remaining strictly in the horizontal plane.

Yes - no horizontal force at the tail without sideslip. Rudder is integral with the tail. Bank or rudder angle or offset drag will each cause sideslip seperately of together in our balanced flight circumstances.

Hey fair go Fred

My quote is quite specific in saying that under normal horizontal circumstances the application of some rudder will cause sideslip which generates our side force.
Where is this horizontal force without sideslip that you are now attributing to me? when you say

"And voila! Now you base your argument on a horizontal force without sideslip!" The only ones I know in this forum are thrust and drag. (Oh --- please ignore the horizontally resolved component of thrust not aligned with the line of drag; let's keep it simple.)

The prospects for a cold one or two Dunnunda are most welcome.

There may be a few wanting to suss out the rebel who undertook to thoroughly question some long established beliefs. I have been doing this ever since my first aerodynamics lecturer tried to convince his class that an aircraft made a balanced turn under the influence of rudder alone. He had nil or little flying experience.

Do we progress?

Milt

John Tullamarine

John you presume too much.

At no time have I agreed to the impossible. The impossible is to have zero sideslip under conditions of asymmetric straight balanced flight.

We can't even get close to zero sideslip. Maybe 2/3 degrees for our typical twin. Don't think you will pick it with a yaw string. The SIDE force on the tail is ALL that is stopping us from being that frisby. And at Vmca we are using the total sideforce the tail can muster. There is none left.

Why seek near rudder deflection as in the banked case?

Keeps the flight deck tidier!!! Also we may have run out of rudder trim and that leg is objecting . Real reason is to give us wider options of using over-riding rudder control should we need to use it in a turn or to cope with turbulence or to stay further away from fin stall if this is significant or ---- whatever happens. Penalty may arise from fact that we have had to replace the lift we are using for the sideslip. This and the increased sideslip needed to zero out the rudder we now have adds to total drag.

I really do not know the combination for min drag. It will of course vary with different aircraft and differing directional stabilities.

So someone has come up with the 'rule of thumb' that 5 degrees bank is the best average. But you wouldn't need anywhere near that bank angle for someting like the Concord because the tail's sideforces will vary approximately with the square of the CAS. Slow down to Vmca at low altitude in a Concord with an outer shut down and the others at take off power and you may well benefit from the 5 degrees of bank. My WAG (Wild Arsed Guess) for a Concord's raw Vmca so afflicted would be about 140 Kts in that the engines are fairly close inboard.

I said "Concord's raw Vmca" as I have taken off the 2 seconds do nothing time which allows for the reaction time of the less than average pilot.

Are you there Bellerophon for comments on a Concord's Vmcg and Vmca for a failed outer.?

John - a get together would be a memorable ocassion but I am already considerably outnumbered.

Keith.Williams.

Helo again Milt,

You have convinced me (and I suspect a good many other readers) of only one thing:

None there so are blind who those as see will not (anag)

ft

To recap:

I asked you to falsify my presented scenario of straight non-slipping flight, as you claim it cannot happen. This scenario builds on the horizontal component of stabiliser force. Your reply was:

In other words, you claimed there’s no horizontal force generated at the stab without sideslip. In return, I point out that if you deflect the rudder there will most certainly be a horizontal force even though there’s no sideslip.

Then you counter (?) with:
My good man! I do believe you are contradicting yourself slightly!

And this leaves me with my example of straight, non-slipping flight with asymmetrical thrust still unfalsified. And while it is unfalsified, there is non-slipping asymmetrical straight flight.

Regards,
Fred, patiently waiting

(BTW, my definition of slip, for the purpose of this discussion, would be “the angle between the projections of the aircraft x axis and the flight path vector on the horizontal plane”)

Mad (Flt) Scientist

Assuming we're talking about civil certified aircraft here, there's something that should be clarified in a previous post...

There is no such thing.

14 CFR 25.149 (to amdt 25-84 if we're being precise) has no requirements for reaction time in determining Vmc (=Vmca), nor Vmcg. In fact a 2 second reaction time for the latter test would be mightily exciting.

I believe the confusion is arising from the takeoff speeds requirements, 14 CFR 25.107(a)(2) to be precise, which requires that V1 be not less than Vef plus a time interval for pilot reaction, and also 14 CFR 25.107(a)(1) which requires that Vef be not less than Vmcg. Together these paragraphs require that V1 be not less than Vmcg plus a reaction time (2 seconds) BUT that is a reaction to begin aborting the takeoff, not a reaction to keep the aircraft on the runway. That is assumed to be a great deal faster than 2 seconds. (And is shown to be so during normal Vmcg tests)

The only variations which can be applied to the Vmc values are airspeed indication corrections (the technical analysis will be completed with fully corrected speeds, but information for crew will be "indicated" speeds).

john_tullamarine

I was wondering how long it would take for a member of the sandpit to take Milt to task on that one ..

A minor point to add to MFS' post.

The 2 second accel-stop pause and have a brief coffee requirement came in at FAR 25 A/L 42. There is no retrospective requirement so aircraft to older frozen design standard amendments remain a bigger problem for line pilots in ASDA-limiting situations.

Milt

Raw Vmca.

Apolgies to all who considered Raw Vmca to be a formalised term.

It is my way of saying that most of the certified speeds for aircaft types have a buffer to give us a reaction time. None of us can react intantaneously and succeed at what I have called my Raw Vmca. Without that buffer you are instantaneously right at the edge of losing it.

For those who consider there is no buffer and then realise that they need around 2 seconds to identify the culprit engine and follow through with appropriate actions (and that will be most of us) then you had better add YOUR 2 seconds to the published IAS/CAS. Your pilot not in command will certainly appreciate you doing just that. So will you if you are down the back.

My mention of the 2 seconds was to cause readers of the thread to ponder their predicament if no buffer exists.

Not having been involved with the determination of Vmcaes/Vmcges for a decade or two I am temporarily outdated on current certification flight tests. The buffer is a judgement made by the TPs who have a responsibility to you for safe operation.

Tinstaafl

From Milt
(my emphasis)


I don't think any of us think this is possible. As far as I can see all 'zero sideslip' supporters specify that some angle of bank towards the live engine will be necessary, albeit not much.

Milt

Vmcg and Vmca Speeds and Safety Factors

Some research on this subject since my recent post indicates that the old 2 second delay stipulation has been overtaken by civil type certification guidelines for TPs . The 2 second do nothing is still considered for special circumstances.

The following are my summaries which are presented as a stimulus for your further considerations and mental preparedness should you be suddenly faced with the non blessed event.

In the determination of Vmcg, recovery should be achievable by the average pilot within the confines of a 30 feet diversion from centre line.

In the determination of Vmca, recovery should be achievable by the average pilot within a 20 degree change of heading.

These allowances embrace your reaction buffer which will only be enough if you maintain your skill and intuitive reflexes.

I decry the fact that simulators cannot quite substitute for the real thing in this critical area of flight and blame the bean counters for taking simulation too far.

When was the last time you experienced Captains had one pulled on you on a training flight and how was it?

ft

Tinstaafl,
aaaah, a change of position! Missed that one.

In previous episodes of the 'Yawing, slipping and sliding about' miniseries:
Add 'balanced' into the mix and it's a whole new ballgame (pun unintentional). Cunning, Milt, very cunning indeed!

Cheers,
Fred

newcrew

thanks a ton to all who replied

well belive i am pretty clear wrt the issues re turning and zero sideslip / minimum drag...

the other thing i was interested to know was if any other types had a sideslip indicator fitted ? (concorde style)

anybody know (pictures ?)

thanks

cheers