I'll make one quick observation related to RBS, in reference to helmet fire's originating post.

Good explanation throughout that post. I agree with your theory, but there are some parts where you haven't explained through. For example, you said, "Because the stall interrupts the blade’s climb, it can no longer reach its pre stall height over the tail boom, hence the tip path plane is lower at the rear when in retreating blade stall.".

I agree that interrupting that climb would change the tip path plane, but nothing you said indicates that the disk maintains it's orientation, other than lower at the rear (ie it doesn't tilt to the left or right). It doesn't go on to explain why the tip path rises in the front. I'd almost expect the front to be even lower since the blade starts it's forward sweep from a lower position.

I can answer these questions. The interrupted lift on the left side of the disk acts similiar to inputting aft cyclic. Whatever explanation you want to give at this point will fill in the blanks I have above. I prefer an aerodynamic explanation that talks about rotational dynamics, but I do find the gyroscopic precession explanation legible even though in most rotors it is not completely accurate.


Matthew.

Thanks Heedm, good point.
You said: >>The interrupted lift on the left side of the disk acts similar to inputting aft cyclic. Whatever explanation you want to give at this point will fill in the blanks I have above.<<

I agree, it does act similarly (I think) to aft cyclic but I would like to avoid reference to a different cyclic position because it introduces more variables. Perhaps I should have explained it thus:

As the stall causes the blade to reach a reduced high point over the tail, the tip path plane can effectively be now thought of as lower at the rear than the pre stall condition. As the system attempts to align the rotor mast perpendicular to the tip path plane, the lower rear blade position will manifest itself as a fuselage pitch up, i.e. the nose pitches up.

How does that sound?

Lu,
A POSTCARD FROM THE COLONIES

Things down here in the Colony are going well, a woman was burned at the stake for being a witch, and a few thousand arrived by prison hulk for stealing bread.

There was also a public whipping for a guy teaching gyroscopic precession, down here in the colonies, we frown on that.

The kangaroos are causing trouble in the main square and the Koalas fall out of the trees because their gyroscopes don't work well.

We got a letter from the old country and things are still pretty glum there, no talk of precession at all, even in the pubs, only aerodynamics.

At least the beer is cold.

Farewell from the Colony :D

helmet fire, your explanation seems sound.

However, I still don't see how it explains the disk rising at the front. Does the disk rise at the front? I don't know.

Matthew.

Sorry Lu,
We havn't been called a Colony for quite some time

Frank Robinson's post explained why the swashplate links are rotated 18 degrees away from where Lu would like them to be in the Robbie.

Lu maintains that a cross coupling exists that will make the R22 rotor tilt in a diferent direction than what it is commanded to do. Ho-Hum we've been through this.

Helicopter pilots understand that the rotor takes 1/4 turn to respond to a cyclic input(90 degrees).
Those with an engineering backround know that this lag can be altered by such things as delta3 or pitch-flap coupling, offset flap hinges, etc. Lu does not buy it.

But here is the kicker:
Let's assume that Lu is right somehow, and the R22, with its 18 degree mis-rigged head will have the rotor tilt slightly left and forward in response to strictly forward stick....

Even if this were true, I believe that the cross coupling error would be a momentary event.
In other words, when the cyclic is moved, the rotor would respond as Lu suggests, but then would quickly wobble around to the correct orientation.
The controls can be rigged with 90, 72, 63 or whatever degrees and the rotor will still follow the plane of the swashplate.

The swashplate tilts exactly in the direction that the cyclic is pointed, right?
The rotor disk must be perfectly parallel to the swashplate or it will see a cyclic pitch change.
If the rotor disk is not parallel to the swashplate, it will re-orient itself until it gets there. If there is a gamma angle of 72 degrees instead of 90, it will take a few revolutions of the rotor for the disk to get settled down, but the rotor will always wind up parallel to the swashplate.

I found ammunition to support this idea at :
http://www.cartercopters.com/pressrel30.html

They have spectacular photos of a prop spinner disintegrating in flight.
Down lower on the page it talks about their delta 3 rotor head and how it has a momentary rotor response in the wrong direction.

Floyd

[ 11 August 2001: Message edited by: Floyd Dan ]

[ 11 August 2001: Message edited by: Floyd Dan ]

GET YOUR ACT STRAIGHT OLD MAN.

Yopu announced it as "The ultimate arbitration" intending to get the end all answer from Nick Lappos, and you didn't like his answeer, so you ran to hide behind Ray Prouty, whom you claimed called you out of the blue when in fact you called him.

No one knows just what you told him, but one thing is certain, he wasn't given all the FACTS, and you likely DIDN'T understand his response.

And you have never accepted anything presented to you here. You didn't in the above statement as well, round and round it goes ... Have at it with the rest of them.

I guarentee that it will end up like any other LZ thread ...

[ 11 August 2001: Message edited by: RW-1 ]

No, you didn't. You announced to all "I just received a call from Ray Prouty", someone to whom you have placed disagreements with in the past. You made no mention that you called him, etc.

You ran to him because your arbitrator didn't live up to your expectations,period.

You removed the thread after I made mention to this, that you would never live that thread down, and you still will not.

Plain and simple, the thread was to be your end all, but it didn't go that way, anyone here who read it can be witness, and you needed to give the possible comment from Ray the only weight you had left on that thread, otherwise it was over.

Let's get something straight here, now your arrogance says that the forum will die without you, another demanted theory, did you tell them that at JH before they booted you? JH is still there. Some wish you would fade away and PPRUNE rotorheads will not suffer at all, will not fade away, but can get on with business instead of constantly trying to educate one LZ. Why not do what normal newbies/wannabies do? Lurk. You are close to the ground anyway, it should be normal for you.

When, not if (for reasons given again and again by everyone) you finally decide that you were incorrect, then we all can move on I'm movin on now, for I have some weather flying to do this PM ... But I predict you will still play the semantic game until that has been exhausted as well.

You are not worth anyone's time, you have to resort to wind up's to get a response at this point.

[ 12 August 2001: Message edited by: RW-1 ]

To heedm, you said:
>>However, I still don't see how it explains the disk rising at the front. Does the disk rise at the front?<<

No, the disc does not rise at the front per se, in fact this is the reason I try to avoid comparing the pitch up to aft cyclic. The term “rotor disc” should never be thought of as a solid entity (sorry Lu), rather it should be thought of in terms of individual blades. The term is used purely for simplicity of description and ease of understanding. (I believe this was one of the points you were alluding to in your excellent description of gyroscopic precession.) Accordingly, when the rear blade no longer climbs as high in RBS as it did in the pre stall, there is no corresponding effect on the height of the front blade because the disc/tip path plane is not solid. The effect is that the tip path plane (again not a solid entity as such) is lowered at the rear without being heightened at the front. Hence the aircraft attempts to realign itself with the new tip path plane by pitching nose up.

Hope that helps. Please bear in mind that I am no aerodynamics expert, so I may be going off on a tangent.

To Lu,

I note that you continue to avoid discussion on specific points by diverting discussion. Until you can keep it on track, I do not think you will be able to achieve your stated aim of being able to understand some of the POF discussed on the forum. An example?

You said on the “vote” thread, Page 3 post 5: >> Here is the way I would teach it and actually it is the way I teach it<< and then you went on to describe your method.

In post 7 on the same page, I dissected your statement to show you where your understandings are incorrect and in need of flapping to equality/cyclic feathering understanding.

Your response to that was in post 8 on the same page, and I quote:

>>To: Helmet Fire
I do not teach it that way.<<

Lu, can you not see the contradiction from what you said in post 5? Why do you deflect the discussion to irrelevant details such as wether or not you do/don’t teach it that way rather than try and benefit from the explanations offered? You did not acknowledge that any points were even made.

For example, you have avoided any response to my opening posts on RBS, and on which parts of your understanding are flawed. Even in your new explanation of how you “really” teach it you are mixing concepts. You said:

>>In a retreating blade stall condition the right side of the disc is generating more lift than the left side. It is this differential of lift that causes the disc to raise 90-degrees later and the disc flaps back.<<

This is not true Lu. The disc does not raise at the back, the rear blade is just unable to climb as high as it did in the pre stall condition, creating an apparent lowering of the tip path plane at the rear of the disc. Flap back is a completely different phenomena unrelated to this discussion, rather it is applicable to changing of airspeeds over the disc and flapping to equality/cyclic feathering (see explanation by Arm out the window on gyroscopic thread). This use of incorrect terminology is continued in your repeated reference to pitch instead of Angle of Attack, amongst other things. Unfortunately, the incorrect usage hints at a lack of understanding of application, so you might want to tighten up your terminology, and I am using US terminology here.

You continued by saying: >>However it is not instantaneous [ie the stall] so the disc will become unstable and the lift differential will generate a left rolling moment.<<

As stated in the posts above (that you ignored), the disc does NOT become unstable. The disc cannot be thought of as a solid entity. As pointed out above by ShyT, only sections of an individual blade enter and leave the stalled state during its revolution through the retreating side. Perhaps it is semantics, but I would say that even the individual blade is not “unstable” in this condition. It was bought to your attention in previous posts on this thread that the blade does not suddenly drop, etc (you ignored this too).
Lastly, you finish your explanation with:

>>Shortly thereafter the rolling moment will manifest itself by causing the disc to flap back due to gyroscopic precession.<<

Flap back is not related to this discussion, as per above (see Arm out the window’s explanation on flapping to equality/cyclic feathering). I will not go into the gyroscopic bit as I do not full understand the dynamics of gyroscopes, but in my original post, I had a go at describing recovering from RBS. In that description I noted that you get a pitch down in the absence of a rolling moment. I note that you ignored it too.

There is not a difference of opinion being discussed here (Mr Prouty and Ft Rucker teach flapping to equality and cyclic feathering), so please do not divert the conversation by saying its just a difference of opinion. You will never develop in your knowledge if you cannot start from sound first principles.

A disclaimer: I am no expert, and some of you will no doubt see flaws in my explanations, so dig in, I am here to learn too. I need a drink now…..

Lu,
Your reputation has been slaughtered by your own words, your way of understanding is flawed by the fact that you, as an unqualified person, cannot accept PROVEN theory of EXPERTS in their field. You persist with "ive been teaching it this way" and " this is what i was told" and " One guy at so and so said .....".

LU, GIVE IT A REST and get on with your real job, you are reducing this forum to how Just Helicopters is, you tried your rubbish there and got trashed, you are bitter and twisted about something, don't take it out on us, this is the pilots forum............ if the bloody concept doesn't work my guess is that all of the people here at pprune would be dead............


You are a nasty piece of work when you use words like" if Ray Prouty disagrees with Nick you go tell him he is full of crap" some professional you are.

Lu, you are WRONG ACCEPT IT AND GET A LIFE

[ 12 August 2001: Message edited by: sling load ]

[ 12 August 2001: Message edited by: sling load ]

Round and round ... Now it's the "poor me" speech, geez, you are that sad.

That post made no sense to anyone but you of course, because it is meant as another distraction and diversion.

You made a point, and EVERYONE told you you were wrong, experts and novices alike (not "Two People").

You choose to go into whatever excuse you can dredge up at this point, and you are getting quite far reaching in those, but that seems to be better to you than actually admitting you are incorrect, and finally moving on.

You truly are hopeless, but that was known from the beginning.

By the way the real tower is Babel, but your mispelling is appropriate, for you have babbled your way to a new low.

Again:

It's not a difference of opinion.
It's not a difference in educational methods.
Not a difference in teaching.
You have no "Alternate theory", it is garbage.

Others have placed FACTS to your theory, and it is down in flames.

Deciding that the difference in statements between two EXPERTS telling you you are WRONG, will not change that FACT.

And no matter how many people want to give you differing reasons for it, the key point for YOU to consider is how they all come together to tell you you are wrong. It is no coinsidence, but at this point that's all you have left. Divert away, but I know by now with Sling's post that you don't have anything left in terms of:

credibility.
believabilility.
knowledge base.
professionalism.
sadly I add "Guru status, but to most you never were to begin with.

Realize it, accept it and move on, for all you do now is give more misdirection, insults to those who are the true professionals in the field, and excuses.

Obviously the "Learning" you set out to do is not going to happen, for learning is accepting when you are wrong, and since you cannot do that, then it is impossible for you to move forward. You would rather argue the point, for if not, then you have:

No arguement.
No theory.
No "Alternate" theory (crap excuse), and the fact that you use the FLAWED deductions you come to an apply them to other subjects is what has most here wanting you to shut up, the only danger here is a new person actually believing your crap, that could get them into trouble.
No differing of educational systems.
No more "Robbie is unsafe" rantings.
And a long list of people that you owe apologies to, starting with FR, the FAA, the NTSB investigators, NL, and all of us on this forum who fly and also fly Robbies.

If you read the posts above, you will realize that that would be a step upwards for the level you are at now.

I can truly understand the bind you are in, for if there were no more Robbie rantings and circle misdirections about offsets, you would have nothing else to say here. No direction in life, etc.

You don't have to respond, you are compelled to respond:

I also know that like a 6 year old in an arguement, even when proven wrong you will want to get the last word, you can't shake that either, so have it, but you only serve to ring true everything I have outlined about you, your flawed theories, and your behaviour throughout the period of discussion.

You are an unqualified wannabe who cannot accept that he has placed his foot in mouth too many times. You may feel you are gaining something as it continues, and you are not: your supporter list declines each time.

Well, go ahead with another 2-3 paragraphs that no one will really want to read, for it is full of I have to, I meant to, Ithe manual isn't .. excuses, misdirection, etc.

It will be another diatribe to circumvent previous postings, renew other directions in any attempt to throw the reader fromt he plain facts:

You proposed the same sad theory again here, it was shot down by ... aw heck >Insert anyone's name here< and you run to another excuse, redirection, resupposition, anything you think will cause a failed theory to rise up and smite FACTS you CANNOT UNDERSTAND. Previous examples of this include:

Didn't like the american answer so you run to the UK.
They tell you your'e full of it, and now it's a "Difference in teaching"
THEN you go to america vs Ft. Rucker, and the Rucker CFI's tell you your'e full of it,
Asking A known heli test pilot for the "Ultimate arbitration of this crap, and when he gave you the same answer (any suprise here? Anyone? ) you then go off to Ray Prouty.

Hope all you want, you will NOT change a flawed theory into FACT by repeated preaching and misdirection.

Just isn't going to happen.


So, in short, either discuss the points being made without any other ties to this failed, flawed theory of yours (everyone else seems to be able to discuss the points involved, you never do unless you have a way of bringing it back to ... etc. etc.) or just admit that you have no other agenda than trying once again to push something that has been proven on all populated continents to be crap.

[ 13 August 2001: Message edited by: RW-1 ]

Lu; You're going to love this.

Direct quote from 'Helicopter Flight Dynamics: The Theory and Application of Flying Qualities and Simulation Modeling', 1999, by Gareth D. Padfield, page 417.

"Pitch-roll and roll-pitch cross-couplings can be powerful and insidious. The natural source of both are the gyroscopic and aerodynamic moments developed by the main rotor and, in dynamic maneuvers with large amplitude excursions, the uncommanded and sometimes unpredictable off-axis motion can require continuous attention by the pilot."


Have a good day.

You poor ignorant sod.

You have the burden of proof here, not I.

Do you really think that everyone here hasn't figured out that you can dish out garbage, but can't be told anything? It's a reocurring pattern with you, and your asking lowly I for an explaination that you have refused from those with FAR GREATER KNOWLEDGE AND EXPERIENCE only serves 2 things:

Lowers you believability and credability again. (Yet ANOTHER LZ wind up excuse)
Insults those who are in the industry.

Everyone here has at some point proven your flawed theory for what it is. People I might add that have way more experience than I.
and SINCE THEY HAVE DONE SO, I have no reason to argue the aero, you cannot change FACTS, no matter how you want to preach.

By the way, they are not statements you make anymore, but either wind ups designed to illicit response; or excuses for you not to face what all on both sides of the pond have shown you, etc.

Therefore this quoted para above is just another excuse for you not to face the facts.

Now you are saying that everything everyone else has said means nothing unless I can explain it to you, well, sorry sparky, what makes you think that you would admit you are wrong to me all of a sudden, when you have insulted and refused everyone else on the planet?

That dog won't hunt either, but nice try ... It was one of the last excuses you had left for your arguement, you have used it, so lets not try that again.

Just about what I said previously in a prediction of your responses, thank you for validating my observations about you, you only serve to add reliability to my observations about your upcoming actions/statements. :D

To Lu Excuseman,

I havent "attacked" any other poster here because they show the capability of accepting when they are incorrect.

Refer back to above and previous posts so I don't have to retype all of it. :D

You don't get pissed, you are too ignorant to get pissed, your method of dealing with it is to just assume they have not the knowledge of the great LZ, so you ignore it. Too bad, so sad.

And I'm not pissed, for facts are facts.

Yet another posting by you that serves nothing but to delay the inevitable ...

You can say anything you want about me, I could care less, at least coming from you, that would be the LEAST of my worries, you poor sod.

Gee, another repeat, I covered this above. Others have covered it with you, I have no need to do so. And as for gaining respect of someone at your level, who has annoyed and ticked off most of the working professionals int he industry, geez, that's just another arrogant statement, you thinking I want or need your respect. Well Lu, you are not above ground on the totem pole, remember to take yourself off that pedestal you placed yourself. I have no need of your respect, nor want it. And taking the thread in that direction serves only what I have been saying all along, you just can't stay on topic, you are compelled to answer.

Make your next statement, prove to all here that you CANNOT stay on track, and discuss the topic. If you are not the 6 year old i have proposed, then you will have no issues at all in ignoring this and moving on, but you and I both KNOW you cannot.

Now, if for some miraculous reason you manage to keep on topic and not give the same sorry excuses you have been doing, then, and ONLY then shall I not make further observations.

You have a good day now, and remember to take your afternoon nappy, right after cookies and milk. I've some flying to do. :D

This about sums it up: http://www.dynamicflight.com/lz.gif

[ 14 August 2001: Message edited by: RW-1 ]

Got to be a bit cautious about getting caught in the crossfire between Lu and RW-1 here!

Lu - I put a post about aerodynamic flapping on one of the other threads.

What you're talking about in your last post, the disc flapping back with forward speed, is simply called 'flapback' in UK/Aust speak.

It's a pretty straightforward idea, which if you will indulge me I'll expound a bit about here, to clarify it. As I said on the other thread, if you already know about this, excuse me telling you how to suck eggs.

As you tilt the cyclic forward, the control orbit, ie the path that the rotating part of the swash plate follows also tilts forward. The disc quickly aligns itself with that plane (aerodynamically, I reckon, but obviously we may differ on that point!).

As the helicopter moves forward, the advancing blade has a greater airspeed and generates more lift, and this lift is at a maximum on your right (anticlockwise when viewed from above direction of rotation).

If the blades were rigidly attached, the helicopter would roll left. However, they are free to flap to a position of equilibrium between lift (pushing them up)and rotational forces (throwing them out and down towards the horizontal).

Now, the key to understanding aerodynamic flapping is that where the lift force is greatest, the blades will flap up at the maximum rate; therefore directly on our right, they are flapping up fastest.

However, at any point on the advancing side, there is more lift being generated than there was before, so when a steady state is reached, the blades will flap up (compared to their previous path) all the way round the advancing side, reaching a peak at the front, and will flap down all the way round the retreating side.

The net result is that the disc has now repositioned itself so that it has 'flapped back' with respect to the control orbit, and to keep the forward motion going as you wanted, you will have to put more forward cyclic in.

You can easily see the effect if you transition forward from the hover, get the aircraft accellerating forward, and then hold the cyclic steady in the fore-and-aft plane. The aircraft will pitch up due to flapback, and you will soon have to introduce more forward cyclic to hold the nose where you want it.

That's about it - not trying to convert you, just make the aerodynamic theory a bit clearer.

Well said Arm !

Oh and to that other person, your students wondering will cease when they get in the heli (something all here will note you still have not done for yourself ...) so stop hypothasizing aboutwhat they are thinking (it's what you are thinking) at any point in their training.

[ 15 August 2001: Message edited by: RW-1 ]

HH-65, Coast Guard detachment Gauntanamo Bay Flew with 'em on my weekends off.
And the Coasties in New Orleans.

Another wind up from the Queen.

Why not tell us all here of your hands on flying experience, not theory, not Walter Mitty LZ Dreams, not something you were involved in, or pondered from your cubicle, but FLEW, your hands on the sticks, for more than until you likely got banned from the cockpit for an offhand comment to the flight crew (that if on the CH-53E would reduce you to being given the relief tube to use as the intercom ....)

I (let alone any plain student!) certainly am not subject to your telling me what I should do, for you certainly have demonstrated far worse need of needing actual flight experience Mr. "lower the collective at the bottom of the autorotation" :D

Never in my life has there been a person more in need of an hour of dual actual flight instruction...

For you see while you can wonder away in your cube, pilots everyday are pushing cyclic, getting summed forces and the tip path tilts in the direction it was asked of it by us pilots. End of story, end of theory.

You should get your butt in a Robbie, unless of course you feel it is too much heli for you ...

Or are you over the 240 Lb seat crush limit ?

Now that excuse for not trying it is one I could buy without hesitation :D

Geez, this still not done? well, I've better things to do with my time ...

[ 15 August 2001: Message edited by: RW-1 ]

Lu,
Your facination with the swashplate is really something. Why do you always get into confusing discussions about the swashplate and horn angles? Do you have some more pet theories about how some designer made a mistake that happened when you went to the toilet during the design phase of the program?

The horn contribution to the swashplate phasing gets the reader all confused, as it confuses you, too. What would happen if I wrapped a pitch horn twice around the swashplate, so the horn angle was 720 degrees? Whould you then claim that the swashplate was 2 rebolutions ahead of the blade? How absurd can you be?

The horn angle and the swashplate angle are both summed when talking about the swashplate phase angle, which we call gamma. Why don't you stop all this confusing drivel, and get back to the basics?

The swashplate angle of virtually all helicopters is matched to the need of the blade to flap properly and give the pilot the tip path tilt that he demanded with his cyclic. I cringe when you start with the "Sikorsky has 45 degrees and shmidlap has 90 degrees" when it is all really the same!!

This whole string of threads started when you tried to yet again assert that the Robinson was off by 18 degrees, and that is why it is (in your eyes) such a poor helicopter.

Give it a rest, please.

To those who read Lu's seemingly curious questions and claimed facts:

He is mostly wrong in his facts, and very mostly wrong in his explanations. If you wish to learn something about helos, try to simply ignore his poor math and poorer explanations.

I have been the chief R&D test pilot of a major helicopter company, have written many technical papers on these subjects, hold a number of patents on helicopter controls, and I get the willies when I read yet another Lu Zuckerman explanation for some poor unsuspecting student pilot.

I get further steamed when he blows this hot air, then backtracks waffles and then finally blames those who he says taught him the stuff he spouts.

Sorry for the venting, but please take what I say to heart. I know Lu is only trying to help, but the only ray of light I can see is that Lu has not offered any advice on brain surgery, as this is a quicker way to get hurt than following his aviation advice.

What?! You mean there is no tooth fairy?!

Lu, as you said, the advancing blade is flapping down with respect to the horizontal when you're in forward flight.

However, as I said, flapback alters the path that the blades would otherwise follow, so the 'maximum rate of flapping up' mentioned above is with respect to the original, 'unflapped' tip path.

Regarding your comment about retreating blade stall; yes, the advancing blade will be producing high lift, but as the name implies, blade stall is all about stalling, and the subsequent loss of lift;

i.e. the retreating blade loses so much airspeed due to your high forward speed, and is already at a high angle of attack because of the power and blade pitch you have in to maintain that speed that it stalls like any other wing, loses a good degree of its lift, and there you have it.