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Certification of Robinson Helicopters (incl post by Frank Robinson)

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Certification of Robinson Helicopters (incl post by Frank Robinson)

Old 23rd Nov 2000, 08:39
  #141 (permalink)  
Lu Zuckerman
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To: Try_Cyclic

You are trying to fit the situation to the picture but it doesn't work that way. It is like taking one frame out of a movie film strip and saying this is what happens or, happened.

If the pilot pulled the stick back to position the swashplate as in the picture then an instant later, picture number two would look just like picture number one.

Regarding the underslinging of a rotor head, this is done not to minimize leading and laging, it is done to minimize spanwise bending of the blade. Under ideal conditions a rotor blade is designed so that the aerodynamic center and the chordwise CG are coincident with the pitch change axis.

That is why they have adjustable weights in the blade tip. The weights serve two purposes. One is to establish spanwise balance so that the spanwise CG or, center of blade mass is the same for all blades of a given type. The second purpose is to get the chordwise CG and the aerodynamic center as close as possible if not coincident with each other as well as to the pitch change axis.

Since the three points are not always coincident with each other there is some spanwise bending. This bending is caused by the tip of the blade moving relative to the root in order to get the points in alignment.

On older helicopters before they perfected the building and static and dynamic balancing of blades the design incorporated a drag link in the case of Bell to anchor the blade in a rigid position.

On Sikorsky blades they had internal stiffeners in the spar and the inboard pockets were attached to each other by a trailing edge strap. Even though the Sikorsky blades were free to lead and lag the tendency to bend spanwise was still there independent of the lead lag.

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The Cat
 
Old 23rd Nov 2000, 08:59
  #142 (permalink)  
lmlanphere
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if the r22 was suffering from a lead lag stress, then you would have to imagine that the same egg shape wear of the journals would appear at the coning hinges in addition to the teetering hinge (and since Lu didn't mention observing this I assume it was not the case).
as for retreating blade stall, Lu, as forward airspeed increases, the local airspeed experienced at the retreating blade decreases. examining the lift equation, to compensate, the angle of attack must increase to equalize lift on both halves of the disk. At some high forward airspeed, the flapping will cause the angle of attack to exceed the critical angle. I would hesitate to use the word "inflow" because this is most often a term relating to transverse flow, which is another subject. The actual speed at which retreating blade stall occurs depends on the helicopter and pitch setting. the r22 Vne of 102 kias at low density altitudes is probably in the vicinity of this speed. I've been told, however, that it was difficult to demonstrate the onset of retreating blade stall during the certification process of the r22, but I am not sure of the original source of that information.
 
Old 23rd Nov 2000, 19:04
  #143 (permalink)  
Lu Zuckerman
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To: Imlanphere

I am well aware of how retreating blade stall manifests itself. My question was, and maybe I was being a smart ass, in the description provided I asked at what time in the compensation for the inflow (pushing the cyclic forward) did the pilot encounter the onset of retreating blade stall?

The way the explanation was presented was that the pilot would compensate for the inflow by pushing the cyclic forward. This makes the helicopter fly faster and the velocity of the inflow increases proportionally. Does the pilot then push forward a bit more to compensate and it goes on and on until you approach retreating blade stall and possibly the restricted VNE.

Regarding the coning journals they had been removed. In checking the maintenance manual
I see that there were four modifications to the journal. Was it because of excessive wear and they changed the material to reduce wear. I don't know, I'm just asking.

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The Cat
 
Old 23rd Nov 2000, 19:28
  #144 (permalink)  
HeloTeacher
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Quot from Lu:

This is for Helo Teacher:

The certification requirements state that any new helicopter design demonstrate sideslipping by hitting the pedals to the stop while flying at .6 VNE. It must also demonstrate out of trim flight by +/- 10 degrees. If the Robinson helicopters are now restricted from flying this way because to do so will increase the flapping loads to the point of mast bumping then how did they demonstrate that capability during certification with out beating the helicopter to death. That is the main point of my report. I stated that if the helicopter were put up for certification now, and could not demonstrate these certification requirements, then the FAA would tell them to piss off.

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The Cat
*******************************************
Lu, you obviously didn't learn much about pilotage while you were in those helicopters long long ago, so I'll give a quick lesson.

Some basics:
ALL helicopters are designed to fly in trim.
An out of trim helicopter is less stable.
Inexperienced pilots react unpredictably.

I read the page in the manual, and I will try one more time to explain my point, try to listen this time. Out of trim flight is less stable, and the majority of R22 rotor-loss accidents are caused by overcontrolling. The tendency for low-time and inexperienced pilot who are sideslipping an R22 is to overcontrol in pitch. They quickly get into a condition of pilot-induced-oscillation (PIO) which can easily cause the mast bumping you are trying to pin on the design. They tend to do this alone because most instructors have a survival instinct. Telling the pilot that they SHOULD keep the aircraft in trim is common sense and keeps the inexperienced from killing themselves needlessly.

My point about the certification requirement, which went right past you, was that the act of demonstrating the capability to perform a maneuver doesn't necessarily make it normal. I've had students try many outrageous control inputs, and the R22/ Bell206, doesn't matter which, has so far always had the control authority to recover. That DOESN"T mean that I encourage them to try again. Now, how this relates to certification requirements:

For certification the manufacturer must demonstrate retreating blade tip stall, a condition which occurs above VNE. Does the more restrictive VNE invalidate the certification? NO! Is the VNE increased to this speed? NO! Does the demonstration of the capability, in the hands of a competent pilot, of the aircraft to fly out of trim make it a normal procedure? NO!

The recovery from low-G is not unique to R22's, its the same for any helo. I criticized your description about how to handle it because it made no sense. It is not flapping loads that cause mast contact in the low/0-g situation, it is the high flapping angles caused by a rotor disc not aligned with fuselage, usually induced by a scared pilot whose first instinct was wrong. And yes, hesitation is the wrong reaction.

I didn't want to get into this discussion but I'm getting tired of people maligning the aircraft because of misconceptions and prejudices. It is small and light. It is also responsive and tough. Too many people with too little experience will read what is here and believe it, so I gues Joe and I have to defend Frank's creation until gets off his duff and replies himself.

To helidvr: we have read that Frank will reply many times, no need to keep telling us until he does it. I have great respect for the man, but he is the king of CYA.

As an aside Lu, before you start attacking me as a brain-washed instructor who is defending the design on subconcious orders from Frank, let me say this. The R22 is a very economical helicopter and in the hands of an experienced pilot is a very effective tool. It found a place in the training schools because of low cost that allowed many pilot to get into helo flying. There are machines out there that are easier to teach in, and even preferable to teach in in some cases. Its touchy and unforgiving, and thats how people get into trouble.

With regard to the lawyers and their suits against Robinson, I have seen too many aviation lawsuits, especially from private pilots, that were so outrageous as to be laughable that have bankrupted very fine companies. Until the USA gains a little common sense in litigation, Frank is well advised to continue as he has to protect a company that is producing good machines at a reasonable price.
 
Old 23rd Nov 2000, 20:59
  #145 (permalink)  
Lu Zuckerman
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To: Helo Teacher

this is my quote taken from you post above.

"The certification requirements state that any new helicopter design demonstrate sideslipping by hitting the pedals to the stop while flying at .6 VNE. It must also demonstrate out of trim flight by +/- 10 degrees. If the Robinson helicopters are now restricted from flying this way because to do so will increase the flapping loads to the point of mast bumping then how did they demonstrate that capability during certification with out beating the helicopter to death. That is the main point of my report. I stated that if the helicopter were put up for certification now, and could not demonstrate these certification requirements, then the FAA would tell them to piss off."

My feelings are still the same. Regarding my saying that if you sideslip or fly out of trim you will introduce high flapping loads. These are not my words, they are in the 22 and 44 POHs and are most likely in FAA AD95-26-04 which is the document that precipitated the changes in the POHs restricting pilots from doing it.

It seems to me that this thread is digressing too much as many individuals making posts are trying to pick apart arguments of mine that were made in response to my answers to my posts that were made........

There is another point, several pilots stated that the cautions in the R22 and R44 POHs were not really binding because they were not mandatory. It seems that although the FAA generated the AD they obviously did not make it mandatory or, possibly Robinson engineering didn't want to indicate that it was mandatory as it would make their helicopters look bad. I don't know. The CAA in England however saw it in another light and made most of what was in the FAA AD mandatory.

The CAA indicated to me in a letter that this change would be in the next issue of GASIL. I don't know what GASIL is, and I can only assume it is their version of an AD. Maybe some of you Brits can tell me the definition of GASIL.

If you are interested in the letter log onto
http://205467.homestead.com/caa.html (please read it as it will help prove my point)

If you are interested in the diagrams log onto
http://205467.homestead.com/diagrams.html

The diagrams will help you to understand much of what I have said in my various postings.

Late info:

GASIL=General Aviation Safety Information Leaflet

The initial issue was GASIL No. 2 of 1995. That is when the AD was issued. In the letter the CAA indicated that the AD will be highlited in the next issue of the GASIL.

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The Cat

[This message has been edited by Lu Zuckerman (edited 23 November 2000).]
 
Old 23rd Nov 2000, 22:12
  #146 (permalink)  
RW-1
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Very interesting observations, however they are just that.

I'm a low time heli pilot in the 22, and just approaching CFR 61 req's for commercial.

I'm not going to get into the aerodynamics discussion, but the plain truth is that for what you are predicting to be a design flaw is not backed up by the evidence presented.

Reguardless of what you may think, I haven't yet when moving cyclic forward had to induce any lateral cyclic to correct my movement along track other than what is needed for dissymmetry of lift and transverse flow effects, (plus establishing a trim condition if I have a crosswind after reaching 50FT and beginning my climb).

I have to say I'm with JoePilot. It matters not to me if you actually fly or not, I did heli maintenance in the Navy on UH-1's and CH-53E's. But if the evidence doesn't support what you are putting forth, it is only a theory. Have you put any time in a Robbie at all to check if what you determine to be a problem is actually one?

The showcopter's accident was the result of the yoke cracking, an emergency AD is in effect due to that incident, and not from a mast failure.

For Mr. Robinson, your helicopter has brought me fun, joy, and a plethora of learning experiences that I hope to continue as I accumulate more hours, and progress to my Inst and CFI. Thank you!

Man, I'm tired from reading all that. will I stop flying the robbie? Nope, not at all. For all Mr. Zuckerman's fears of an improper low-G recovery, I've done several, and at the utmost i practice the most important thing of all, I try to not get into one in the first place.

Please do not feel the urge to reply to my post, I don't believe I'm even returning to it to read any more. It's been beaten to death, for the majority of people here I say let's move on. (Just a newbie's opinion)



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Marc
 
Old 23rd Nov 2000, 22:23
  #147 (permalink)  
Lu Zuckerman
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To: Helo Teacher

You say tomato and I say tomahto. You say flapping angles and I say flapping loads. It is the high flapping angles that induce the loads reflected at the rotor head so we are saying the same thing but using different words.

If you can't accept my theory that the design of the rotor head requires the input of a right bias beyond the rigged neutral setting of the cyclic then you can in no way understand what I am talking about when I state that in countering a zero G condition the pilot must be extremely careful in how he pulls the cyclic back and in which direction relative to the centerline of the aircraft.

My theory is that the pilot must offset the cyclic to the right in order not to fly to the left. In encountering a zero G situation he must move the stick back:

If he pulls back from the offset cyclic position he will not add to the right roll caused by the tail rotor.

If he pulls back and slightly to the left until he is on a line with the rigged neutral centerline he will add to the right roll and lose control

If he pulls back and passes over the centerline of the rigged neutral position he will not add to the right roll.

If he pulls back and further to the left he will generate high flapping loads (angles) and cause mast bumping.

This is all contained in the diagrams.

This is one scenario as visualized by myself
regarding mast bumping. Actually ther are two but one involves blowback as a result of retreating blade stall. I will address the first theory not the second.

When the pilot for whatever reason encounters high flapping angles and the resultant loads, the blade is flapping in an uncontrolled manner. Normally, when in flight the blades are coned so the spindle is separated from the down stop. When the high flapping angles are present there is a possibility that the balde will drop down to its' pure radial position and possibly beyond and in doing so the spindle contacts the stop.

If the contact force is strong enough it can act as the moving force on a first class lever and cause the rotorhead to pivot on the teeter bolt and make contact the mast stops with such force as to cause the mast to fail. What are your fellings about that (anyone)?



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The Cat
 
Old 24th Nov 2000, 02:52
  #148 (permalink)  
Lu Zuckerman
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To: RW-1 even though you might not be there.

You stated that the failure of the yoke assembly was the cause of the R22 crash in Watsonville, California.

"The showcopter's accident was the result of the yoke cracking, an emergency AD is in effect due to that incident, and not from a mast failure".

Where did you get this information all I have seen from the NTSB is that the helicopter lost its' rotor.

The AD you referenced, (AD 2000-20-51) was written, because some cracks had been detected on a yoke that was a part of a batch of yokes made from the incorrect material for the application and not as a result of an accident. Any yoke found to be cracked must be changed and all yokes made in that batch must be changed in the year 2001.

You also stated:

Regardless of what you may think, I haven't yet when moving cyclic forward had to induce any lateral cyclic to correct my movement along track other than what is needed for dissymmetry of lift and transverse flow effects, (plus establishing a trim condition if I have a crosswind after reaching 50FT and beginning my climb).

Is it possible that you are at the same time compensating for the offset I discused in my report. I would like to hear from some of you guys that have attended the Robinson school either for flight safety or as a mechanic and have you explain what they told you about the configuration of the Robinson swashplate as opposed to a Bell swashplate.

There is a pure Robinson website that is operated by a flight school in Connecticut. They have some excellent illustrations as well as some very technical text. On that website they showed a picture of a Robinson rotorhead and swashplate. In their explanation of gyroscopic precession they used a diagram of a Bell as opposed to a Robinson diagram. Why is that?

They were implying that the Robinson has a phase angle of 90 degrees but many of the posts have alluded to the Robinson having some magic dealing with pitch coupling resulting in a phase angle of 72 degrees. Why is that.

I am awaiting response from anyone that wishes to contribute even RW-1

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The Cat

[This message has been edited by Lu Zuckerman (edited 24 November 2000).]

[This message has been edited by Lu Zuckerman (edited 24 November 2000).]
 
Old 24th Nov 2000, 20:03
  #149 (permalink)  
HeloTeacher
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When pulling into the hover, left cyclic is required to overcome tail rotor thrust. You hover with a left of center cyclic, now you know why the travel is more on the left.

The tail rotor is coupled very short in the R22, hence the high TR thrust in relation to weight.

You intiate forward flight with forward cyclic. The flapback that occurs with increasing speed is countered with increased forward cyclic, the disc and fuselage attitude DO NOT change, the additional forward cyclic is overcoming the flapback that results from the (momentary) dissymetry of lift.

We keep telling you about the reaction of the disc on the ground because that is the simplest reaction. In flight there are many more factors. A 20 degree cyclic offset would be very noticeable. It isn't there.

If theory is not supported by fact, amend the theory. That is what we have tried to explain to you.

I made the distinction between flapping angle and flapping load because the reason the rotor so easily gets out of control in a zero-G condition is the LACK OF LOAD! there is no pull from the mast to force the disc into any particular state, so it can float freely.

I have to wonder, are the questions in your report actually questions you want answered? We have answered many of them here!

1. I explained it above
2. there is no RFM restriction, but if you jerk the controls around at any time you are dead, be smooth. pull back and you slow down unless you jerk on the cyclic
3. mast-bumping, for exactly the same reason as if he tried to induce left roll
4. never. none. he'd roll roll right. ditto
5. relevance??
6. same as dihedral

 
Old 24th Nov 2000, 21:26
  #150 (permalink)  
Lu Zuckerman
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To: Helo Teacher

Regarding left cyclic in a hover. I was under the impression that the mast was tilted to counter the propeller effect of the tail rotor.

I read the FAA Rotorcraft Flying Handbook and it agrees with your statement about inflow and cyclic stick position. Of course the same handbook addresses helicopter aerodynamics by describing the aerodynamics of an autogyro. However I will accept your explanation.

Regarding a 20 degree offset of the stick, that is not what I am saying. I stated that the pitch horn must travel an additional 18 degrees in rotation in order to achieve full pitch input. It is the displacement of the stick relative to the rigged neutral to compensate for the 18 degree difference.

That might equate to only several degrees of displacement from the rigged neutral setting of the cyclic. What with moving the cyclic to the left to compensate for propeller effect and then moving it to compensate for the inflow how do you actually know where the cyclic is when you are flying forward?

One pilot mentioned that with the cyclic grip in his hands he rests his arm on his lap and it is in that way he knows where the stick is. I have a question. which way and in what direction did he move the stick before achieving what he felt was the right place prior to resting his arm on his lap?

Regarding flapping angles and or loads I was not specifically addressing zero G. Although the rotor system is not controllable at that time, flapping angles and loads are still present. I was addressing any maneuver that would generate high enough angles as to transmit the associated loads into the rotorhead, via contact of the spindle with the internal down stops for the blades, resulting in mast bumping.

Now back to the questions in my post above.

How do you (or for that matter anyone) explain the statements made in the pro Robinson website which:

Provided an illustration of both a Bell and Robinson rotorhead and included a listing of all of the major parts thereof.

They then went into a discussion of gyroscopic precession and explained what it was.

To illustrate Gyroscopic precession relative to pitch input, still talking about the Robinson helicopter, they provided a diagram that applied to the Bell. Was it because they didn't want to address the 18 degree disparity of the two systems or, they assumed that they were the same.

For any given pitch input the swashplates on both helicopters move in the same manner. To fly forward or backward the swashplate tips forward or backwards. To fly left or right the swashplates tip left or right. On the Bell the pitch horn leads by 90 degrees and on the Robinson it leads by approximately 72 degrees.

If as the Robinson website says,the Robinson has a phase angle of 90 degrees just like a Bell please tell me how the Robinson compensates for the 18 degree difference and still has a precession angle of 90 degrees placing the tip path down over the nose.

Instead of commenting on what I said relative to stick position in my above post please log onto the websites provided and download the diagrams. All of the explanations are on the diagram. I would also suggest you ask for a report via my email address. I would be more than happy to send it.

I have one question of a personal nature. Where is Kenora? On the map I have I checked the X/Y locaters and it puts you in New York State just above Buffalo

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The Cat

[This message has been edited by Lu Zuckerman (edited 24 November 2000).]
 
Old 24th Nov 2000, 21:33
  #151 (permalink)  
Arkroyal
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fish

I hesitate to rejoin this increasingly technical and complex debate, but as HeloTeacher says 'If theory is not supported by fact, amend the theory'.

I remember from my training being told that the rotor acts in a similar way to a gyroscope, but it IS NOT one. How can a hinged system obey gyroscopic properties?

The similar but not identical properties are due to very complex aerodynamic effects, especially in the low speed regime, where you are combating flapback, inflow roll, tail rotor roll. Not difficult just instinctive.

I have great reservations about the safety of the Robbies (for reasons of rotor inertia mostly)but find it hard to agree with Lu's technical theories which simply don't show up in practice.

Pilots point the cyclic in whatever direction attains the required direction of travel. It varies with speed, but if it was habitually up to 20 degrees out, I think it would have been noticed by a pilot, rather than an engineer.

 
Old 24th Nov 2000, 21:36
  #152 (permalink)  
lmlanphere
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Lu- no right cyclic in the hover (mast tilt or cyclic rigging instead)- left cyclic in forward flight (to compensate for transverse flow effect).


[This message has been edited by lmlanphere (edited 28 November 2000).]
 
Old 24th Nov 2000, 21:41
  #153 (permalink)  
Arkroyal
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Last post crossed with LU.

Am I being too simple? But it seems to me that in the Bell, the swash plate rigging 0deg plus the pitch control lead of 90deg makes a total of 90deg

In the Robbie, the swash plate rigging 18dg plus the pitch control rod lead of 72 deg makes a total of 90deg

Same result surely, and same flying qualities.



[This message has been edited by Arkroyal (edited 24 November 2000).]
 
Old 24th Nov 2000, 21:49
  #154 (permalink)  
Lu Zuckerman
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To: Ark Royal Post one

The rotor system on a helicopter has the characteristics of a gyro. One, it has rigidity in space in that it will remain in the position it was placed in and will not move unless perturbed by an external force be it air flow over the disc or, input by the pilot via the swash plate.

The second characteristic is that it has a precession angle of 90 degrees +/- a wee bit. Like a gyro the rotor will move 90 degrees later in rotation from where the perturbing force was applied.

The gyroscopic phase angle will be present whether the helicopter is running up on the ground or, in the air flying in any given direction. Flapback as you call it is the result of the inflow but aside from that it has no effect on the phase angle.

It doesnt make any difference if you are dealing with a rotor system on a Bell which has a rigid teetering rotorhead or a CH-53 which has seven blades on a fully articulated rotor head. Although the blades are in effect independent of each other the disc will respond as if it were solid.

To: Ark Royal Post Two

The Bell pitch horn leads the blade by 90 degrees. Assume, that the blades can be frozen in the position of being over the lateral axis. At this point the advancing blade is at its' lowest point of pitch and the swashplate is tipped down over the longitudinal axis. 90 degrees later the disc will tip down over the nose and up over the tail.

Now we do the same thing with the Robinson. The swashplate is tipped down over the longitudinal axis. The blades are disposed over the lateral axis. Now, check the position of the rotating portion of the swashplate in relation to the stationary portion. In order to reach the maximum down pitch the blade must rotate an additional 18 degrees (approximately) which will cause it to tip down fully at some point to the left of the longitudinal axis. It may not be 18 degrees to the left but it will be far enough left that corrective input must be made to the cyclic.

On an articulated rotor head the pitch horn leads the blade by 45 degrees and the swashplate tips 45 degrees ahead of the point where the rotor would be tipped. This gives 90 degrees.


To: Imlanphere

According to the FAA Rotorcraft flying hand book Page 3-6 (Trasnsverse flow effect).

...the result of transverse flow effect is a tendency for the helicopter to roll to the right as it accelerates through approximately 20 knots. If that is true you would move your cyclic stick to the left. However, in your post you said that you would move the stick to the right to counter transverse flow effect. If the hand book is correct then what you are doing is compensating for the 18 degree off set and not transverse flow effect. Is this what they told you in Robinson flight school?

[This message has been edited by Lu Zuckerman (edited 24 November 2000).]

[This message has been edited by Lu Zuckerman (edited 24 November 2000).]

[This message has been edited by Lu Zuckerman (edited 24 November 2000).]
 
Old 26th Nov 2000, 05:38
  #155 (permalink)  
Kyrilian
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Lu,
First, you keep referring to the 'pro-Robinson' site as if it's official. It's not. I'm guessing that the people who put up that site don't really understand the dynamic effects of a delta hinge either (which as you recall I tried to explain some time ago). I opine that they don't understand how the Robinson head works, so they assume it's the same as a JetRanger and think of them interchangeably--it's not! Most texts written for heli pilots don't go into the complexities of rotor heads with a natural frequency of anything other than 1/rev. Because of this, virtually anyone you ask about how a rotor works will tell you how the head works on a 206. While many helicopters may function this way and such a rotor model may be considered the norm, it is NOT the rule! And as far as the delta hinge is concerned, it is there irrespective of collective position or speed. It just means that an upward flapping translation of a given blade will cause a more negative feathering angle on that blade. The magnitude of its effect will change with speed and collective position, but its fundamental effect will remain the same.

As far as an experienced pilot noticing an extra 18 of control input, I think it's not too unreasonable to expect someone to notice, even with all the other effects (transverse flow effect, translating tendency, etc). That's because all these effects are present in any conventional helicopter. I'm not extremely experienced (having flown 300Cs, R-22s and a few A109s briefly) so I can't really attest to this, but I'm guessing those who have flown many types would surely notice such an abnormal control system. And as Arkroyal has said, I think this would have been noticed by pilots long ago...
 
Old 26th Nov 2000, 08:35
  #156 (permalink)  
Lu Zuckerman
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To: Kyrilian

It's almost midnight so I can't be responsible for typos or technical errors.

Yes, I stated that the web site was pro Robinson and in searching my files I found a second identical web site. One is sponsored by a Robinson Dealer in Connecticut and the other is sponsored by a Robinson dealer in British Columbia. The web site was developed and is maintained by the Robinson Helicopter Association. Now, I don't think you can get any more pro Robinson than that. I would also assume that they get a great deal of technical support from the Robinson training departmen but that is only an assumption.

I recently read an FAA handbook on Rotor Craft Flying and that manual has the same errors that you will find in some of the major text book on helicopter aerodynamics.

If you had read one of my previous posts that addressed the teaching of helicopter aerodynamics it goes something like this.

First the discuss Bernouli. Then, they discuss Venturi. This is followed by fixed wing aerodynamics and when the students understand how a wing works they start talking about autogyros and how the advancing blade flaps up due to the relative wind and the retreating blade flaps down because its' attached (similar to a Bell).

The attach a great deal of importance to this action and once the students understand that, the go into helicopter aerodynamics but they are still talking about autogyros.

The error in teaching this way is analogous to taking a movie film and addressing the overall activity that is taking place based on one cell of that film strip. It is true that the blade wants to flap up due to the relative wind and assuming you have a Bell blade the opposite blade flaps down. Of course, they never talk about a fully articulated rotor because the blades are not attached and the argument falls apart.

Now, we get to the flapping up due to the relative wind on the advancing blade. At the time they tell you the blade is flapping up, it is actually flapping down over the nose as this is how you develop forward flight. If the blade does try to flap up and the pitch link/teeter / coning hinge are not coincident then you have a restoring force caused by pitch coupling. However,the aerodynamic effect is minimal as it can't react in the time it takes to go from the right side of the helicopter to over the nose. Now, what is really happening is that the aerodynamic forces cause a lift differential across the disc and the disc will be displaced slightly by gyroscopic precession unless corrected for by the pilot who moves his cyclic stick accordingly. The flapping you addressed is minimal at the most.

The action of the delta effect has no effect on the phase angle as it is fixed by the laws of physics. Here is something you can work out. Lets say that your theory is correct and the delta effect actually alters the phase angle. At some point in time the pitch horn/pitch link combination will be in a direct line with the cone hinge which means that there is no pitch coupling. Now, what happens to the phase angle?

Back to the 18 degree offset. You may have noticed that I defined the offset as the number of degrees the pitch horn must travel in relation to the blades which are disposed laterally and the swashplate is fully tipped down over the nose. The difference is approximately 18 degrees of rotation ahead of the longitudinal axis of the helicopter.

If what you said about pitch coupling altering the phase angle is true, it must occur in this 18 degree arc at a tip speed of 599 feet per second or, 408 MPH. Please explain how it happens in this distance and at that speed.

Relative to transverse flow this is discussed above in another post. Once you get above 20 knots this goes away.

Another point that has been brought up by several pilots is that theory doesn't always reflect reality. I have to agree as the text books that define helicopter aerodynamics always define it under specified conditions. That is why most designs have to be altered when the helicopter is first flown. The text books will in effect introduce the student to the engineering theories that will put him into the ballpark when he gets to design helicopters or any thing else for that mater.

Here is an example of an engineer that had limited knowledge of aerodynamic theory. When I was in tech rep training at Sikorsky I was assigned to the hydraulics tes lab.

One day, I saw one of the hydraulic engineers working on a mockup of a rudemetary collective control system. Attached to the collective stick was a hydraulic cylinder that would raise the collective stick until it was fully up and then the hydraulic cylinder which was spring loaded lowered the collective stick to the down position. I asked him what this was and he said that the hydraulic cylinder was actuated by the hydraulic system as the rotor was spinning up and the internal spring was being loaded. I asked him at what rotor speed the system was actuated up. He replied that it was really at what point the hydraulic system started to build up pressure which was 1200 rpm on the pump. He further stated that the system was designed so that if the engine lost oil pressure or shut down the cylinder would automaticly pull the collective down putting the helicopter into auto rotation taking the responsibility away from the pilot. I told him that it wouldn't work because at 1200 repm of pump speed the rotor blades were not fully aerodynamic and would flap up and stall contacting the tail cone. He had absolutely no idea about what I was talking about because he was a hydraulic engineer and not an aero engineer. He didn't even cordinate with the flight control or aero groups. The next day, the rig was gone and I think the engineer was also gone.

------------------
The Cat
 
Old 26th Nov 2000, 18:12
  #157 (permalink)  
HeloTeacher
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Unhappy

I'm in NorthWestern Ontario Lu, not so far from you ion the grand scheme of things.

Has the school in Montreal that had the roll-over operating again yet?

You can be assured that the next chance I get to closely inspect an R22 I will take it, curiosity is running rampant now. I notice you referring heavily to this FAA produced rotary aerodynamics book, have you consulted other publications or are you just pointing out the errors? Government publications have a nasty tendency toward error.

As an aside, one has to take a look at what the aircraft was being used for when assessing wear. A training machine with excessive wear on the rotor head would be expected in my experience. That machine would be doing a high number of autorotations under student control, resulting in regular rotor RPM excursions, rapid throttle recoveries at the bottom, inappropraite control inputs, and hard landings. Any sircraft used for training will take more abuse than one used for other purposes.
 
Old 26th Nov 2000, 19:59
  #158 (permalink)  
Lu Zuckerman
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To: Helo Teacher

I'll have to check my map for location. Evidently, even maps can be wrong.

The subject R22 that suffered the dynamic rollover was owned by Canadian Helicopters Ltd.-Eastern Division. I saw it at the local airport in Le Cedres about five miles from my home. I believe that the accident occured in the Eastern Provences and was trucked to the home base in Le Cedres. Although it really didn't suffer much damage from an an observers point of view it was stricken from the books and it was at that time owned by the insurance company.

Relative to the wear on the teeter journals these two heads came off of R22s that were owned by Geneva Aviation and to my knowledge were not used in training. In the hanger next to Geneva Aviation was a helicopter training school that was set up to train Japanese Students. They wouldn't let me near their maintenance shops as I wanted to check their rotorheads for the same problem.

I wanted to check the rotorhead on the dynamic rollover helicopter but it had been removed and packed up in a shipping crate.

Regarding my comments about the FAA Handbook I also indicated in an above post to Kyrilian that most textbooks get it wrong as well. Check above post for that comment.

Regarding your wanting to perform a test. I would appreciate it if you would perform two tests both of which require that you enter the hover with the cyclic stick in the rigged neutral position. You might have to have the assistance of a mechanic to help you establish that point.

When you lift off and start flying forward make sure that the cyclic is moved in a line parallel to the longitudinal centerline. Not to the left and not to the right. Pass through transverse flow without correcting (assuming this won't get you into trouble).

Check to see which way the helicopter is flying. Is it going straight ahead or is it going to the left? Now, perform the same check and make any necessary corrections. Is there any perceptible difference in stick position relative to where it was in the first test?

------------------
The Cat
 
Old 26th Nov 2000, 20:14
  #159 (permalink)  
430 driver
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I'm not a big robbie fan for the following reason. After leaving the military in 1992 I decided to obtain my helicopter CFI at a Pt 141 school in California. Admittedly, after flying 53s, 60s and 206s, the robbie seemed pretty 'rinky-dink' Still, I respected it's role as a trainer and believe it's an airframe that has served this role reasonably well. Several days prior to my CFI check, I was practicing a stuck left pedal - holding in full left pedal to simulate the manuever. Just prior to touchdown, the pedal snapped off at the weld. After our initial shock, my instructor safely landed the aircraft for me. A few days later I successfully completed my checkride in another aircraft - but the experience certainly reinforced my concerns about the aircraft. I did ask their lead mechanic to fill out a critical malfunction report as it seemed to meet the criteria for such a report. Whether he followed through - I have no idea.
 
Old 26th Nov 2000, 20:23
  #160 (permalink)  
Try_Cyclic
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Wink

This reminds me of the JFK conspiracies.
I suppose none of us can come up with anything that Lu won't distort to his own purpose.
The website he thinks is run by pro-Robinson agents is actually using the teaching diagrams and text created by Paul Cantrell. http://www.cybercom.net/~copters/helicopter.html
A lot of other sites are using his material.

Lu just tried to explain away the role of flapping in a helicopter.
He comes up with ideas that remind me of Zeno's paradox in school.
At one point he says:
"If what you said about pitch coupling altering the phase angle is true, it must occur in this 18 degree arc at a tip speed of 599 feet per second or, 408 MPH. Please explain how it happens in this distance and at that speed"

Lu, the blades do not flap in 18 degrees.
The blades in a Robinson and Bell flap in the same way. The flapping cycle is not phase shifted. The control inputs are phase shifted so that the blades wind up doing the same thing in Bell or Robinson.
Your grasp of these concepts seems to be horribly distorted. By spreading your misconceptions around to others , you are harming Robinson and scaring students off.
I have seen your attack papers passed around on other forums and people are believing your twaddle. No doubt you believe it yourself.




[This message has been edited by Try_Cyclic (edited 26 November 2000).]
 

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