More thoughts...

Accidentally switching off and on is not only ugly for transmission, it often results in an exhaust system like a peeled banana due to igniting unburned fuel in the muffler.

Idle check may be gone because rapid RPM changes upset the internals of the engine (crank twisting and upset balance).

Another odd one my CFI told me about... a recommendation to switch on governor at 82% RPM. This procedure avoids accidental flying without governor, but causes a slight overspeed (tried it this morning, under adult supervision).

------------------
More volts, Igor

Chips,

Glad you brought that up - The new startup requies the pilot to switch the governor on from 75% (of course it will not work and the throttle will have to be opened).

My concern is just as you say - Many a/c will overspeed due to the governor continuing to open the throttle until it gets the signal it wants, but the lag in engine RPM response will cause RPM to continue to overspeed (not huge) but this does mean that in the life of the a/c this can happen 3000 times, 2000 x average flights of 40 mins......

Interesting, I shall have to try it out too and see what it does for me.

Even thought the POH hadn't mentioned it prior, I had alwys finished up things in the cockpit, got my MP values, transponder to Alt, before coming back up to 100% Nr and engaging the governor. This so that while doing the previous I wouldn't inadvertantly move cyclic at 100% Nr.

I hadn't noticed an overspeed when bringing up the throttle to the 80's and engaging, but will go back and look closer.

blocked fuel tank breather pipes?

That is one of the ones I didn't write about yet!

The third involved a jacket sleeve...

I'll post it -


ARMED JACKET KILLS ENGINE......

An R22 pilot had flown out early to the hills. Sensibly dressed for the early morning chill and the bush terrain he was to land at, all seemed well planned. The doors were removed before flight began as the weather was forecast to become hot and hunting was the aim.

The first landing was on a ridge. The sun was up and insolation made the temperature rise in the bubble, even with the doors removed. The Pilot didn't want to shut down, but he did want to remove his jacket. A solution - Slip off the jacket and slide it down the seat, sit on it. No need to make the passenger get out to put it in the seatbox, no need to shut down.

All fine then?


NO....! Later, during an approach to a confined area one sleeve of the jacket became lose and flapped out of the door aperture. Why would this be a problem? It couldn't go anywhere because it was firmly attached to the jacket, sat upon by the Pilot.

But engine air intake is on the right hand side, behind the door aperture. The sleeve flapped over it and was held there by suction. The engine requires more air as power demand (as in the late stages of a confined area approach) increases. As the Pilot added power to arrest ROD the sleeve was sucked harder and harder onto the intake until it blocked it completely.

The engine was starved of air.

It stopped.

Thankfully this happened at a height of 2ft. The Helicopter settled onto the level area the Pilot had selected for landing.No damage or injury was sustained and the sleeve (intake suction now gone as the engine breathed no more) innocently slid off and hung downwards.

Lucky, just so LUCKY!


The Pilot's summary of the occurence?


"I won't do THAT again......!"

( I'll bet he won't !! )

talkturn :

To my knowledge on the R22, there's no breather pipes because the tanks caps are vented. The fuel is gravity fed as well, so that's out. The only thing I've heard of is a problem with the connecting tube from the aux tank which was a factor in a fuel starvation incident some time ago, but that's about it.

Otherwise the only fuel starvation incidents are plain old none left in the tanks, or ( as I once heard ) a passenger who used the fuel cock as a convenient place to hang his coat, which turned it off !!

Nr,

Sorry to clash, there are indeed breather pipes on the R22 and it has no vent holes in the caps to my knowledge.

The fuel tank vent pipes are hidden behind the mast cowling and jointed in at least one place by soft tubing (plastic material).

In at least one case in the UK the soft tubing had 'kinked', causing a lack of venting to the tank. The result was an engine stoppage due to fuel starvation.

A directive was issued and some aircraft had these pipe assemblies changed for a type that
had the fault designed out.

The problem has not recurred in the last 3 or 4 yrs (to the best of my knowledge).

BEWARE if the dual fuel gauges do not decrease at a similar rate during flight (from equalised contents) because this can indicate that one tank's vent is blocked.

The second occurence (that I have not 'written up yet')happened in California, the inside of the air intake tubing delaminated and blocked off induction. The engine stopped in the hover.A friend of mine was the pilot. He landed it with a slight yaw but held it upright and no damage was sustained, no injury either, thankfully. He made a really good job of a 'REAL' EOL in the hover!

The air intake tubing has been changed under directive, favouring a type and construction that cannot allow delamination.

SPS

My knowledge is increased. Thanks for that, SPS.

So is mine..... :)


Anyway, as you mentioned the coat/fuel cock
issue I thought I'd post this picture of the NZ solution to this problem.

At risk of being boring the whole article is on my site, through 'NZ flying' -'Deerhunting'and any that care to visit will see why it is relevant to that subject.

And the solution? Well, the simplest ideas are often the best!

http://www.helicopterpilotsguide.com/Fuel_valve

NR / SPS

I am a expert on the fuel venting systems on the r22 having owned one of the machines which suffered engine stoppage in the UK.

The aircraft G-OSEE a beta with approximateley 1550 hours total time had just been fitted with a new main rotor gearbox. Whilst completing the works i was offered a new replacement kit to replace the fuel vent pipes due to reports that following inspection of some aircraft the rubber sleeves had started to close and shrink after prolonged time submersed in the fuel tanks.

Although there were no reports of engine stoppage at the time i thought a bargain at £85.00 sterling.

I was not flying the aircraft at the time but the pilot concerned explained he had flown approximately 1 hour when the engine coughed several times next thing he new the aircraft yawed violently and down he went.

At five hundred AGL with wires ahead he dumped the lever and made for a grass field he flared the aircraft a little to high perhaps and raised the lever a little to early. I estimated at about six AGL the RPM decayed the aircraft landed hard and the slowing rotor see sawed and cut clean off the tail cone just before the strobe.

He did extremely well for a pilot with 200 hours who had not flown a helicopter for five months !!!!

Back to the point the fuel caps are not vented. There are two completely seperate aluminium vent pipes one to each tank which are attached to the mast assembly. The fuel tanks are connected via a seperate vent pipe. My retro kit had been installed wrong i believe and when the aux fuel tank ran dry it created a vancum between the tanks straving the engine of fuel.

An expensive days flying with a £5000 excess on the insurance and £8500 just paid for the new gearbox but thankfully nobody was hurt.

The pilot did very well, glad to hear no injuries were sustained.

It does not matter that we may not get many replies to this thread, the main thing is that a lot of knowledge is here for anyone to read.

Any more info out there?

I flew G-OSEE for 14.7hours at the end of 1999 when hour building with Burmans. Sort of makes you think when you hear about things like the above.
My personal checklist is going to be getting longer I think.

I flew G-OSEE today !!

ROBINSON TAIL ROTORS
 

Anybody no why the R22 and R44 tail rotors rotate in different directions

No

But somebody might KNOW why!!!

Don't really know, but here's a stab.

I remember someone telling me that the Bell 212 tail rotor went the other way to previous models (eg 205) because it was more effective aerodynamically to have the tail rotor blades 'chopping' up into the rotor wash rather than rotating back and away from it.
It seems to make sense that if the advancing blade was the one at the top of the disc, it would maybe get faster relative airflow in forward flight.

Could be just crap, but it sounded convincing to me at the time!

[This message has been edited by Arm out the window (edited 23 March 2001).]

AOTW
I agree with your T/R efficiency theory - inboard blade rising in to M/R downwash as in the R44.
Question is why the R22s T/R turns in the opposite direction (Frank Robinson being a T/R designer (Bell I think) before Roninson Helicopters)

talkturn :

I thought FR worked for Hughes before he did his own thing.

As for the T/R on the 22 turning advancing blade down, rather than up into the main rotor downwash, my understanding is that it was purely a weight and cost thing. With the main rotor turning anticlockwise, the easiest and lightest thing to do is a normal bevel gear on the main rotor shaft. This would make the T/R shaft turn anticlock when viewed from the rear. Another simple bevel gear in the T/R gearbox means the tail rotor turns in the direction we all know and love on the R22.

Solutions and possible disadvantages ? Extend the T/R drive shaft past the 90 degree final drive shaft, and a simple bevel gear would now make the T/R advancing blade go up into the T/R downwash at the expense of making the T/R gearbox longer and heavier. Similarly putting the T/R on the opposite side of the boom would obstruct the airflow in precisely the direction you want to push it, so you'd have to have larger T/R blades and so on and so on.

Even with the T/R as installed, at 80% NR in an IGE hover at a reasonable density altitude there's plenty of T/R authority to turn against torque, or even to arrest a slow turn with torque ( but not recommended !! ).

As a final comment, I believe FR was working at Hughes on the T/R design for the OH-6, as it suffered from LTE problems in its early life.

noise caused by the TR interacting with MR vortices mas also be a consideration - the faster the contacting blade, the more neighbor annoying noise

Buying an R22
 

I recently posted a message re Rotorway Execs v R22's. I would like to own and operate a helicopter from home, and not being rich, am considering the two most financially viable aircraft. The RW 162F is interesting, but I trained on a Robby & most people consider them much safer & more robust. Can anyone point me in the right direction to find a Robby with say 300ish hours left but at least 5 years to TBO as that would seem to be a financially viable alternative to the 162F.

Heli Air at Wellesbourne or Denham is usually a good bet, they always seem to have a good range of R22's with varying times and fits.

Worth a go. Check out there web site. www.heliair.co.uk

What does a decent R22 cost??
I have noticed at our flying club where engineering buys the shell of a R22 and completely rebuilds it with new engine,interior etc.
I have not got round to asking engineering/management what these reconditioned helicopters cost but when I asked another club member he reckoned about £50k.Sounds pretty good to me.I will investigate and post accurate costings later.

Good Evening NPT, In your rotoway thread you said you didnt want to here things like this , but if you want to run something which a lot of other have, then really you have to go for the R22 or 44, lots of people in the UK run them and lots of people service them,( as opposed to the Rotorway) just recently a 18mnt old R22 with 475 hours(from new) was sold for about £65/70k, it had all the bells and whistles incl perspex doors, but there seems to be trouble brewing for piston a/c for I have been told that 100LL fuel is being withdrawn, without a current certified replacement, I know nothing else about this perhaps some other ppruners will know the full tale! anyway good luck with whatever you pick.

I have been told that a Robby with around 300 hours left on it can be bought for about £35K, does this sound about right?
Also does anyone know of any good finance companies that do finance for aircraft?

I think that they are about £110k new and £30k with no hours left, the rebuild is say £60k making a just rebuilt one £90k. Those are the rough figures I have been told, and you should be able to draw a straight line depreciation graph to work out the price for one in the middle.

If you find one and you are in the Midlands, I might be interested in sharing it with you.

Helidata is a very good place to find R22's with those sort of times remaining.

You can get to their site through mine
(address is in my bio).

Heli Air is found at www.heliair.co.uk

Alternatively, Helidata can be found here.

[This message has been edited by The Nr Fairy (edited 03 May 2001).]

Thanks guys! Great site by the way SPS (is SPS to do with helos or are you also a Ducati nut?)

A Question for Lu ? re R22's.
 

Good Morning Lu, I hope you will be kind enough to expand a little, I saw your comments on the thread re the 22 break up in Canada, but thought it better to start afresh thread,please correct me if I am wrong but you said "when you people start asking questions about the design",
Like a great many others I was trained in the R22, I admit to being a total junkie on flying, but I also take the safety of my skin, and other's very seriously, I am now onto B206's, but occasionally I still do fly the R22, I have asked questions of the people who I SFH from and they say, "As far as safety is concerned with the R22, they can only be guided by the CAA here in the UK" yet I know they have a shed full of people queing up to train in their R22's. Fortunatly here in the UK we seem only to have had a few incidents with R22's that have produced fatalities,and you are right, these all seem to be put to PILOT ERROR, but if we had a lot of the same sort of problems I am sure that the CAA would start to get a little concerned, Given that a lot of interest has been shown in your past thread answers about the R22's, how do we, the single pilots, ask who , about what! for we can only be guided by these professional training schools and organisations, who seem more than happy to carry on using the Robinson products, in some areas of the UK you have Robinson, or nothing! Most of the Pilot Associations are related to FW, so the RW pilots seem to be out on a limb,waiting for the CAA or FTO's to get things sorted. Is any one organisation going to listen to the likes of me,or indeed any other pilot, when you, who are a man of immense knowledge and expertise cannot get through to the rule makers either ?
My Regards

To: Vfrpilotpb

So many questions. So little time. This might get a bit complicated and you will have to accept my answers as being my interpretation of the fact also realizing that I am a bit biased.

Regarding the actions of the CAA regarding the safety of R22s and R44s they are taking a more active approach than the FAA. Several years ago after experiencing several (31) in-flight breakups of R22s and 44s the FAA started to take interest. They commissioned Georgia Tech Aeronautical department to assess the crashes and make a determination of the causes. Although the report was never completed, the FAA issued direction to Robinson to incorporate into the respective POHs cautions that in many cases were interpreted as suggestions that out of trim and sideslip be avoided. It was determined that this would increase the flapping loads and amplitude to the point that mast bumping or fuselage strike would be incurred. They also warned about Zero G and how to recover from it.

I contacted the CAA and in a return letter they indicated that these same cautions as interpreted by the FAA would become mandatory when the next service letter was to be Issued. This was several months ago and hopefully the CAA followed through.

It is true that the Robinson R22s are the most prolific helicopter trainer and Robinson Helicopters knowingly sells them to organizations that use them in a training environment. Yet when a crash occurs Frank Robinson will state that he didn’t design the helicopter for training.

Here is another point. When a crash occurs the NTSB will allow Frank Robinson to participate in the investigation. His function is supposedly restricted to advising on only the technical aspects of the investigation but it has been indicated that he steers the investigation so that the only conclusion that can be reached is pilot error. I will include a newspaper article at the end of this post.

Understand that the FAA has a vested interest in the Robinson design. They certificated it and now they have imposed restrictions on the flight profile suggesting that the pilots avoid sideslip and out of trim flight. If the Robinson helicopters were put up for certification today and Frank Robinson told the FAA that his helicopters could not sideslip nor, could they fly out of trim the FAA would tell him to go back to the drawing board. If these restrictions were mandated as being warnings then they would have to admit they were in error in granting certification. Hopefully if the CAA follows through then UK pilots of Robinson helicopters will have to take a hard look at their training program.

The certification authorities and the Investigating agencies are like mules. The only way to get their attention is to hit them between the eyes with a baseball/cricket bat.

Here is the newspaper article.

Conflict of interest alleged in FAA crash investigations
By MARINA MALIKOFF
Sentinel staff writer
Of the dozens of R-22 accident investigations involving main rotor loss reviewed by the Sentinel, the National Transportation Safety Board frequently listed the probable cause as "undetermined" or pilot error — findings that do not surprise Palo Alto lawyer Michael Danko.
Because pilots and victims’ families are excluded from the investigation process, fault often is placed with the pilot, he said.
"Unfortunately, when there is a crash such as this and the NTSB wants to examine whether the aircraft is defective ... they call on all the manufacturers," said Danko, who is also a pilot. "They’ll ask Robinson if it is defective. To me, that is like asking the fox to find out what happened to the chickens."
Danko, whose firm is investigating a fatal August 1999 R-22 crash in Ireland nearly identical to the Watsonville crash in August, said the NTSB will "essentially staple their report to the technical report from Robinson, which will always point to pilot error."
NTSB accident investigations are conducted by what is known as the "party system," a process where the NTSB allows interested stakeholders, such as aircraft manufacturers and the Federal Aviation Administration, to join their crash probes. Anyone in a litigation position is excluded from the investigation.
The NTSB party system was the target of a 1999 study by the RAND Corp., a nonprofit public policy think tank. A RAND panel found significant potential for conflicts of interest when manufacturers are asked to police themselves.
The study, which was commissioned by the NTSB, recommended independent analytical and engineering resources assist in investigations "if (the NTSB) is to ensure its future independence and integrity," according to a statement issued by RAND when its report was released in December 1999.
The report was recently forwarded to the NTSB, where it is under management review, said NTSB spokeswoman Lauren Peduzzi. Recommendations and changes to the system will be considered, she said.
"The board’s mission is to investigate accidents, determine relevant safety issues and issue recommendations for improvements in order to prevent similar accidents from happening again," Peduzzi said. "Although the party process allows us to tap the manufacturer’s expertise with their equipment, the board’s investigators act as impartial leaders. ... It is their job to ensure that a fair and thorough investigation is conducted and that the probable cause accurately reflects the safety issues in the case."
Benjamin F. Venti, the father of a pilot who, along with two passengers, was killed in a Robinson R-44 crash in July 1993, was so troubled by the investigation into his son’s death, he appealed to his Los Angeles County congressman, Matthew Martinez.
Martinez contacted NTSB chairman Jim Hall, who appointed Venti an official member of the investigation team, contrary to NTSB policy.
Frank Robinson, president of Robinson Helicopter Co., said he and three others from his company had been on the team.
Evidence presented by Venti led the NTSB to revise its findings to show probable cause of the crash was a fatigue failure of the control stick assembly.
The report also found that lack of FAA oversight during the R-44 certification process may have contributed to the fatal crash.
The NTSB’s initial investigation had been hampered by a post-crash fire, which obscured evidence.
The RAND study also found that the 400-member NTSB staff simply doesn’t have the resources to thoroughly investigate each accident.
Jerry Sterns, whose Oakland-based firm specializes in aviation cases, agrees.
"The board does not have the budget nor the experts to do its job properly, so it is forced to rely heavily on outside people, who of course are supplied by the very companies being investigated," he said. "The companies many times drive the investigation, and the board has consistently refused to allow any representatives of the victims to participate and treats their lawyers as subversives."
However, Robinson, founder of the helicopter company, stressed that the NTSB investigator has full control over the crash probe, and that it would be impossible to conduct a thorough investigation without the manufacturer’s expertise.
"The manufacturer is not a theorist and is not allowed to touch anything at the site unless under the direction of the (NTSB) investigator," Robinson said. "He is there to identify the parts and has absolutely no input on probable cause."
In 1994, though, the NTSB learned that Robinson was serving as the quality assurance liaison to the FAA, raising concern of a conflict of interest during safety reviews.
Robinson confirmed he had served in that capacity — called the designated engineering representative — at various times over the years, and said it was "standard practice" in the industry for company officers to do so.
Robinson said he voluntarily resigned from that role four or five years ago. He now has three employees assigned to the job, one of whom is a company officer.
But accident investigations are still tainted by the cozy relationships that develop between FAA representatives and the manufacturers, according to several aviation law attorneys, who note that juries frequently reach conclusions about accident causes that are different than what the official investigators determine.
"In more than 50 percent of our cases, we have a cause that is different than the NTSB," said Richard Schaden, an attorney and aeronautical engineer. "The NTSB’s probable cause is heavily loaded on the pilot-error side."
When it comes to Robinson helicopters, that’s an appropriate finding, Robinson said.
"The fact remains that the vast majority of accidents do result from pilot error," Robinson said. "When they are used in training and by low (flying) time private pilots, it’s very high."
Those statistics don’t comfort families who have lost loved ones in Robinson crashes, said Danko, who maintains that a design flaw in the sensitive R-22 controls prevents flight instructors from responding quickly enough to prevent the crashes.
"History has shown the R-22 is not safe, and the fact is you have many high time pilots who have suffered the same scenario," Danko said. "You can’t blame all these accidents on pilots."
Aptos pilot Kent Reinhard and his student Gary Sefton died Aug. 18 when the rotor blades tore through the cockpit of Reinhard’s copter in midair during an instructional flight near Watsonville.
Reinhard, 57, had flown airplanes and helicopters for decades. He earned his first pilot’s license in 1961, and had logged thousands of flight hours — including 1,000 hours in the R-22 — at the time of his death.
In May 1996, Reinhard completed the Robinson Helicopter safety course and received an "average" rating — the most common rating, according to Robinson, who considers Reinhard a "high time" pilot.
Reinhard, a corporate pilot for Dole Food Co., operated a flight school out of the Watsonville Airport and was an R-22 stunt pilot with Showcopters, a Salinas-based air show team.
Sefton, 46, of Hollister, was studying for his airplane pilot’s license when he changed his focus to helicopters a year ago. The fatal flight with Reinhard was his first lesson.
Investigators from the NTSB, FAA and Robinson Helicopter Co. were at the crash scene the following day, along with local Sheriff’s Office inspectors.
The cause of the accident is still under investigation. The preliminary findings indicate loss of main rotor control is a factor, along with mast bumping, which is typically caused by abrupt input into the controls.
Reinhard’s sister, Jean Grace of Carmel, said Robinson’s position that pilot error likely caused the crash is predictable, but added that she is reserving judgment until the NTSB finalizes its report.
"From a liability standpoint, what else can (Robinson) say," Grace said. "At this point, we consider this a tragic accident."
Contact Marina Malikoff at [email protected].

To see how the safety record of Robinson helicopters is viewed from the Robinson perspective log onto the following:

http://www.hfi.ca/mech/r22_accident_analysis.html

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The Cat

[This message has been edited by Lu Zuckerman (edited 18 May 2001).]

perhaps you two should form a company, Lu the chief engineer and VFR the chief executive. The mind boggles!

------------------
Thermal runaway.

Hi TC,
Good idea that TC, but I'm afraid only one job that I feel would be right for you!
anyway weekend approaches, watch out for those speeding bikers, prep your Vascar, lite up your laser, get the Blue mist pills ready!

Lu, thanks for the answer, I am going thru the site suggested,
My Regards
have a good weekend, Peter R-B

Vfrpilotb -

I would like to join your Company as Flight Safety Officer. I will design flight paths that guarantee no danger to any person on the ground anywhere in the country at all times. And if this is not possible, I will ground all the helicopters until I have found a way.

Cheers!

A couple of questions and a thought.

1. Other then the Robinson R-22 and R-44, does any other helicopter have a rotor hub that has both a teetering hinge and a pair of flapping/coning hinges?

2. What was Robinson's intent by providing flapping/coning hinges in the rotor hub?
____________

A 'conventional' teetering rotor hub has a precone of approximately 3-degrees. The Robinson's rotor disk, when stationary, appears to have 0-degrees of precone. The Robinson R-22's has a rotor disk radius of 12'-7", therefor when not rotating, its blade tips are approximately 8" lower then what they would be with a 'conventional' 3-degree precone.

This would appear to mean that when the Robinson's blades flap downward, their tips are 8" lower then those of a 'conventional' rotor before the structural properties of the blade start resisting this downward flapping. Could this be a possible reason for blade incursions into the body of the craft?


------------------
Project: UniCopter.com

Lu,
I'm not intending to get into an argument about the R22, but I just wanted to point out one thing about your argument. You have often pointed out that restriction from sideslip would make the aircraft uncertifiable today, as a helicopter has to demonstrate the ability to fly in such a manner. The simplest counter argument I have is a parallel with airplanes.

Normal/utility airplanes are often restricted from spins, but as you can see below, they have to show the ability to be flown out of a spin.

Sec. 23.221 Spinning.

(a) Normal category airplanes. A single-engine, normal category airplane must be able to recover from a one-turn spin or a hree-second spin, whichever takes longer, in not more than one additional turn after initiation of the first control action for recovery, or demonstrate compliance with the optional spin resistant requirements of this section.

However, even with the operational restriction from spins, they have been shown to the FAA to be able to fly this way. Similarly, the R22 could still today prove that such flight is feasible, even if not recommended for normal flight ops.

On a slightly different note, consider this: What if the R22 was restricted to pilots with 1000+ hours (like it seems pilots of Jetrangers are restricted to by virtue of insurance minimums). Conversely, what if 50 hour private pilots jumped right into Jetrangers or Hueys (and lets not turn this into a military parallel, as they have different training methods). Would the number of rotor incursion incidents be reversed between these aircraft? I don't know, but I'd think the number of incidents would be linked with low-timers and training (even if a high-time instructor is present) than the type of aircraft.

I agree that it may be best to put low timers into something a bit more robust, like a 300C/CB, but that's not the topic. It's up to training operators to use whatever aircraft they want to use--and in this case it seems cost is a major driving force. I guess the best is to make all aware of the issues at hand, and let them decide. I still don't think there's something fundamentally wrong with the R22 requiring recertification, but I do agree that it is less forgiving than the other available training machines... but hey, it's got some advantages too (and not only the price)

;-)

To: Dave Jackson

Here are the answers to questions 1 and 2 (as I see them)

1) No other helicopter uses this type of rotorhead
2) The cone hinges were incorporated in order to minimize the bending loads on the blades.
3) Because there are cone hinges the rotorhead uses pitch horns that have a lead angle of 72-degrees as opposed to 90-degrees which you would find on any other teetering rotorhead but this is an old argument that very few participants on this forum want to get into.

While the blades are being rotated with no collective or cyclic pitch being introduced the blades are in the radial position with no coning. That means that the downward droop stops are engaged. When collective pitch is introduced the blades rise up at the tip and drop at the root end causing the droop stops to disengage. With normal cyclic application the blades are free to flap about the cone hinge and not engage the droop stops. If the helicopter enters into a maneuver that would result in excessive flapping of the blades there is a possibility of the droop stops making contact. If this is the case, the energy in the blade resulting from the flapping loads will cause the lock up of the droop stop forcing the rotorhead to teeter about its’ axis and bring the blades into close proximity to the fuselage or tail cone. Two such maneuvers according to the FAA report are flying out of trim and sideslipping the aircraft.

To: Kyrillian

Your analogy to spin restrictions on a fixed wing is well taken. However in the certification they don’t demonstrate spinning as a design requirement unless, the manufacturer states that his design is spin-proof. In the case of the helicopter certification the design must be shown to demonstrate a maximum sideslip to 90-degrees at .6 VNE and also demonstrate out–of-trim to I believe 10-degrees. I have to assume that the R22 was certified to those requirements but I find it difficult to understand why it wasn’t noted that the flapping loads were excessive when now the FAA restricts the helicopter from those same maneuvers because of excessive flapping loads.






------------------
The Cat

To Lu: Thanks for the reply.

Expanding on this thought and excluding any consideration of Delta-3 or the droop stops.

Assuming that there are two identical helicopters; except that helicopter [R] (Robinson) has an unrestricted flapping hinge and helicopter [X] has a fixed precone of 3-degrees. Assuming also that both helicopters operate with a 3-degree coning angle under normal loading.

It is also assumed that both helicopters will require the same amount of teetering movement.

If the rotors in both helicopters are unloaded during flight then the coning angles of both rotors will attempt to go to 0-degrees. , Helicopter [R] has nothing resisting this downward flapping and the tip will drop about 8". The downward flapping in helicopter [X] will be resisted by the 3-degree precone and the stiffness of the blades. In addition, the pivot point will be about halfway out the blade, not the 3" offset from the mast as in helicopter [R]. This means that the blade tips in helicopter [X] will not drop as much as the blade tips in helicopter [R].

Added to this downward flapping will be any teetering. To me, this implies that in an unusual, situation the blade tips in helicopter [R] will drop lower then the blade tips in helicopter [X] and bring these blades in closer proximity to the body of the helicopter.

Your thoughts on this possible cause of blade strikes will be of interest.

Dave J.

I want to apply for the position of Quality Manager!!! What a laugh that would be!

Lu, Hyperthetical question for you:

Could the FAA revoke the Robinson certification? If so what would have to happen for them to do that?

To: HeliEng

The FAA has the power to revoke the certification of the Robinson Helicopters but to do so they would have to admit that they were in error in issuing the original certification. The NTSB on the other hand can force the FAA to revoke the certification. In fact a few years back they wanted to do just that. The FAA called for an investigation and that launched the Georgia Tech report and it also resulted in the issuance of the flight safety directive that required special training for Robinson pilots.

I had a conversation with a NTSB investigator in 1996 and he said that since the safety program was initiated and the restrictions placed in the POH no further rotor incursion accidents were reported. He followed by saying that if just one occurred, the NTSB would jam it down the throat of the FAA and force decertification. Well, since that conversation there have been five rotor incursion accidents and four of them occurred last year and quite possibly the Abbotsford crash also involved a rotor incursion. So far, nothing has been jammed down the throat of the FAA and the NTSB is investigating those five crashes ably assisted by Frank Robinson.


------------------
The Cat

To: Dave Jackson

Hopefully I understand your question as well as the set-up. In stating that the rotor systems are unloaded in flight I am assuming that the helicopter is in a zero G situation. I assume that the R rotorhead in your scenario does not have a droop stop so the blades are totally unrestricted in the flapping mode.

If this is the case and both rotor systems are unloaded then the R rotor blades are no longer supporting the helicopter and therefore, the centrifugal loading will cause the blades to fly in the pure radial position so they are no longer in the 3-degree cone position. The X rotor system will try to go to the radial position but to do so there has to be sufficient energy to bend the rotor head to a flat position as opposed to the precone position and / or the blades must bend. I don’t believe that this will happen as the X rotor system is unloaded and therefore the blades will remain in the precone position. This would be the same as being on the ground with a centered cyclic and no collective.

In either case both systems are going to be unstable if this situation is not corrected by adjusting the cyclic to reload the rotor. Being unstable both rotor systems will teeter and strike the mast. The X system will most likely just have a mast bumping situation because the blades are acting in unison with one going up and the other going down. On the other hand the R blades, assuming no droop stops, will flap up and down and the centrifugal loading (blade interlock) will cause the system to teeter as well. In this case there could be mast bumping only or a combination of mast bumping and fuselage incursion.


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The Cat

[This message has been edited by Lu Zuckerman (edited 20 May 2001).]