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Robinson R44

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Robinson R44

Old 9th Oct 2005, 18:59
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the usual reason the R22 blades hit the tail boom is due to negative (or just a sufficient reduction in positive) G.
Don't forget low RRPM causing catastrophic 'blowback' of the rotor system after the carb ices up and the pilot doesn't get the pole down in time.

Not a problem for your new 44.

You have gone for an injected one, haven't you?
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Old 9th Oct 2005, 19:28
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I know a Pilot who took a Gannet thru the rotor of a MD520.Bit of a vibration as said Bird turned into mist.Landed no problem with blades and everything checked out at maint.Pretty big bird not to have caused a real problem...food for thought!!!
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Old 9th Oct 2005, 22:37
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Hairyplane,

most if not all tail strikes on a Robinson are induced by the pilot!

Wrong reaction to something:

# low-g
# imminent bird strike (mostly imagined)
# botched full touch down auto
# extrem overcontrol

Crab:
How many hours (or minutes?) do you have in Robinsons?

Your statement about low-g is only partial correct:

Though the helicopter will not react to control inputs when in zero or low g, the rotor is NOT free to do what it wants!
If you keep the cyclic centered it will stay parallel to the body just fine, the swashplate will keep the pitch where the pilot selects it and centrifugal force (or was it centripedal force?) keeps the blades in check with the mast.

Low g by itself is not the great killer either, it is actually (relatively) harmless, IF the pilot knows how to react when it is encountered.
The tail rotor induced roll is what makes non-aware pilots push to the left (in Robinsons and Bells), then, because of the low g nothing happens and they push, fast, hard to the limit - bang, mast bumping!
Roll to the right is just the start, it will also get the nose rather very low, of course now we are already scared ****less and smack the cyclic aft until it bends over the rear stop, just in time to have the rotor flex down enough to cut the tailboom!

Guess where they found out about it the first time:
Vientnam, with the all time favorite Huey!!
... when the Cobras came around they had allready figured out what the ***k is going on and how to avoid that part!!

So don't blame the R, just because you don't like it!
By the way there are a lot of Bell's getting trashed lately with LTE - speak " to weak a tail rotor on the bells!"
Also once you get Mast bumping on the Bell you don't worry about cutting your tail, you won't have a rotor to do that!
I'd rather take my chance in a Robinson!!

And yes I have time in R's (plenty!) and in Jet Rangers ( scant 60 hrs, but it was enough to show me its limits)

By the way the explanation of the low-g and teetering rotor movement didn't grow on my grey hair, but was shamelessly copied from THE man that teaches the Robinson Safety Course all over the world! (The man has around 16000 hours split between Bells, incl Hueys and Robinsons, he knows what he talks about!)

Hairyplane:

To the bird strike on the R-44.
We see them occasionally, mainly vultures and it is NO fun!
Never got one in the TR, lucky me!
Killed a couple of them with the MR though:

Worst case you have a shallow dent (no problem) somewhere on the blade. Generally the Robinson blade is VERY hard on the leading edge and takes the bird apart - tissue all over the helicopter, but that is it.

Vultures will take evasive action IF they feel/see you coming. Observe them and choose a course that will avoid impact, IF you can do so WITHOUT BIG INPUTS!!!
This will get you in big trouble, generally without even hitting the bird!!
IF you cannot avoid the bird, try to get the rotor between him and you, but again WITHOUT BIG INPUTS!!

The worst case is always if you don't see the birds and the strike comes through the bubble and hits you.
I saw this 2 times on the same helicopter (...most likely distracted pilot....), but he was lucky and he only got some vulture guts on his business suite and a new bubbles fixed the R-44.

Another guy in a Bell 206 was not that lucky 5 years ago, he got killed by the bird on impact and the 206 crashed, however most of the passengers survived with bruises and scratches.

Generally, just watch them, most birds never get close enough to do harm.
Most dangerous situations ( low g, extreme overcontrol) are caused by NOT necessary evasive manaeuvers!


You will be very happy with your 44!
Just do yourself a favor and afford a good high time instructor every now and then and have him do emergency training and advanced maneuvers with you!!

3top
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Old 10th Oct 2005, 13:40
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Thank you!

Hi Gaseous,

Yes it is injected.

Thank you all for useful and reassuring posts, especially HSH and 3T.

The R44 is a very impressive flying machine and I am indeed looking forward to flying my own machine very much.

I'm certainly not frightened to leave the house ( fixed wing pilot for 30 years etc.). However, life is full of risk. In the case of understanding and accepting the risks for ones innocent passengers I felt it prudent to study as hard as possible in order to make the best decisions.

In the case of the Robinson, so many accidents remain unexplained. This is the conclusion reached so many times by the NTSB for one.

Where else but on Forums such as these can I enjoy such a frank exchange with all that experience?!

Thanks a lot guys, it is appreciated. I hope more pilots will contribute too.

Hairyplane
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Old 10th Oct 2005, 19:45
  #645 (permalink)  

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so many accidents remain unexplained
But can you locate any 44 accidents in the UK that end up 'unexplained'?

The primary cause has been (since '94) pilot error and especially I-IMC (incl at night and poor weather).

"The man (or woman) who masters met, masters life"

h-r
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Old 10th Oct 2005, 20:15
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As a former full time flight instructor, I took a large interest in this publication, as the school I worked at was listed in two of the fatals. I had the opportunity to talk with the owner of the school about the incidents, as I was not employed at the time of the accidents. What was brought about in my talking has been shared very little and is obviously opinion, but does seem to make sense. I encourage any Robinson pilot to become familiar with this report and learn from it.

I hear a lot of discussion about the safety record of the Robinson and believe most accidents post '95 are more than likely due to pilot error, but the ones in this report are probably not, hence the need for the investigation. It has been argued that since the SFAR73 that the fatality rate has decreased significantly, which is true, but possibly misleading. At the same time it was found necessary by the FAA to issue AD 95-06-03. This may be the reason for the decrease in MR blade divergence. The info put out in the Safety course was not new by any stretch, and was being presented for years up to that point. Simply making it mandatory should not have the effect that most perpetuate. As any manufacturer would like you to believe, their product is not defective, and the problems associated must be with the operator, and residing in the US one could not accept blame and continue to do business what with all the lawyers around. As shown in the NTSB report, pilot error could not continue to be sited once there was audio recording that showed no obvious error in pilotage. It may be possible that the mast bolts being improperly installed could have caused an in-flight condition that would result in a negative pitch in the blades that would in turn, have the same result as a blade stall either coming through the cockpit or severing the tail boom. As a manufacturer it would not be prudent to point out a potential design flaw if you wanted to keep manufacturing helicopters or live in a house any longer.

Just my two cents.
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Old 10th Oct 2005, 21:01
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I read the report last night. you can't see all those incidents without it raising concerns!

The report with the tape recording doesn't eliminate the possibility of an abrupt control input, eg. student reacts to a bird, rotors can impact in less than 2 revolutions, instructor is helpless.

The report does still allows for the possibility of a number of different scenarios adding up - a few low RPM stall with reaction times not quite met, a few turbulence or low-G, a few abrupt inputs.

The improved safety awareness by RHC has improved the safety massively which, to me, indicates that some of the incidents must have been due to these causes.

However, a few of the incidents were high time pilots in good conditions. As a low time pilot, it makes sobering reading, and I find it hard to believe that all 31 incidents were down to the pilot's actions (or inactions), but thousands of hours of research by accident have failed to turn up any fundamental problem.

It has to be a possibility that there is a flaw there, but far brighter minds than mine haven't turned it up.

BW
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Old 11th Oct 2005, 16:11
  #648 (permalink)  
 
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Nr Fairy - no, not that old and I don't have a blanket dislike of teetering head helis - just the Robinson.

3Top - 13 hours and one rollover in R22. No the rotor can't do what it wants - I meant to imply that it would go where the pilot put it in an attempt to control the attitude and to highlight that the fuselage will not respond until normal G is resumed.

A few years ago the R22 claimed the life of a guy who I believe had 9000 hours on them so I figured if it could do for him then I would just leave them alone
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Old 11th Oct 2005, 19:30
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Crab,

I am sorry about your friend. Any hint which accident that was?
Causes?
In case it was in an "unknown" helicopter, remember there are still plenty of "cowboy-R22s" out there with who knows how many hours!

"I meant to imply that it would go where the pilot put it in an attempt to control the attitude and to highlight that the fuselage will not respond until normal G is resumed."

That's why you have to keep the rotor (cylic) centered - you keep it with the body until the body is positve again, so it can react....

I am sorry for your experience in the R-22, but 13 hrs is not enough in a R-22. It is problably the one helicopter where you don't get away with a 5 hrs check-out.

It took me about 25 hrs until I got the autos down well....

Why your roll-over?

3top
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Old 12th Oct 2005, 12:30
  #650 (permalink)  
 
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3top - I didn't know the guy who crashed but it was in Southern UK in the mid 90s operating out of Bournemouth if memory serves and it was an instructional sortie with a FW pilot who was converting to helis. Theirs was a tail boom strike (again if memory serves) and suspected to be negative G related.

Your suggested technique for centering the cyclic is a good one but I don't supoose there are many instructors willing to demonstrate it so few R22 students are likely to find out about it until it is too late.

As for the rollover, I re-learned a basic instructional lesson that it is always the best student that tries to kill you once you have relaxed - lowering the lever smartly when the Nr horn goes off is a good thing unless you are in a 5' hover over tussocky moorland which can trap a skid. Dynamic rollover here we come! It is the one occasion I have been thankful for a low-inertia rotor as the blades and engine stopped on impact.

I found the autos and EOLs straightforward using the same technique as on the Gazelle, just much quicker with a lower start height for the flare.
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Old 12th Oct 2005, 16:43
  #651 (permalink)  
 
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Robinson Tail Boom strikes

As an aside to the very worthwhile contributions above, I'd have to say that there are very few recorded mast separations/boom strikes on the other piston types.

Certainly not a single one on the Enstrom marque in thrity-five years. It seems the consensus of pprune opinion is poor Robinson piloting.

One might ask why all these sub standard pilots are only queuing up to fly the Robinson type.

The Bournemouth fatal involved a major south coast operator and a highly type experienced instructor and good friend of mine. most of us know.

The Robinson safety course does seem to have broken the back of the early problems, but sadly, they are still occurring.

Going back to the other types, it hasn't yet been necessary to offer a specific safety course to keep them flying safely.

Can Dick Sanford offer us some sage words please.

Dennis Kenyon.
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Old 12th Oct 2005, 18:04
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The suggestion to maintain centred cyclic position in a low-G condition is dangerous and could, due to the extremely quick fuselage roll that develops, have catastrophic consequences. See Robinson Safety Notice SN-11 (issued Oct 82, Rev: Nov 00) in the back of the pilot's operating handbook, or follow this link.

http://www.helicopteros.com.br/sn11box.htm
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Old 12th Oct 2005, 20:05
  #653 (permalink)  
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Low G

This got to be a classic.

The topic of low G especially in connection with R22 has been many times covered. From a scientific view point I posted several months ago the results of a very deep mathematical model that shows what happens if G comes below 0,5 on a R44-I.
My conclusion : Trust the safety notice : first load the disk by the collective to give it any 'inertial' authority on the body before attempting to do anything with the cyclic.
My suggestion : avoid any low G in theetering rotors. Simple if that means to avoid pilot introduced low-G. A bit more complicated to deal with down-draft induced low-G's.

d3
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Old 12th Oct 2005, 20:42
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Hopefully its just a typing error in the above:

first load the rotor disc using gentle aft cyclic (not collective), avoiding large cyclic movements.

the issue over low-G has been underlined to me since I started in R22 training, so any sensation of low G has immediate alarm bells ringing even if it's just a downdraft.

BW
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Old 12th Oct 2005, 20:50
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bladewashout

I guess I was a little careless.

Loading the disk can be done in many ways. In case of a push over gentle aft cyclic if perhaps the best move (also stated in Robinson notices).
In the case of down draft it depends on what happened before an how it is anticipated. If I sense a down-draft (alarm bells as you say) I will have flared gently before with collective lowered (in updraft) this gives extra possibility to take collective up in the subsequent downdraft. No aft cyclic is needed in that case because of the previous flaring.

Low G happens in a number of patterns and may require different actions.

d3

Last edited by delta3; 12th Oct 2005 at 21:03.
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Old 12th Oct 2005, 21:01
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My suggestion : avoid any low G in theetering rotors. Simple if that means to avoid pilot introduced low-G. A bit more complicated to deal with down-draft induced low-G's.
That's not very reassuring is it?

I don't do 'complicated', particularly when the consequences of getting it wrong are dire.

My Suggestion: Buy an articulated head with the rest of your aircraft.
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Old 12th Oct 2005, 21:09
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Gaseous

I agree and while we are at it, not one of those good weather IFR machines but one with two engines and rotor de-ice etc... But then again we may not have the budget.

I did not do the math, but by numbers I thought theetering heads are in the majority, so we would have to do away with a lot of machines.


d3
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Old 15th Oct 2005, 01:25
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Certainly it is correct to apply SLIGHT aft cyclic, according to the POH of the Robinson.
Problem is this STILL will not do anything until the Helo gets some G-loading again in some way.
So if you have the witts NOT to move the cyclic erraticly from one extrem to the other, you should be able to hold the cyclic, SLIGHTLY aft of center.
Once the right roll starts, the disc will also roll right.
Once you have some angle there your rotor will be able to pull some load in the resulting turn, THATS where the SLIGHT aft cyclic starts to work!
However if you kept pulling constantly this might also result in some impressively high RRPM, when recovering from the rather steep dive!
Remember that tail is still rising above you by inertia!

As mentioned before, best to avoid the whole thing, which implies that you know what you do in the first place!

You still can wring out the R brand (having fun, in other words), just know what you do.
I was lucky as THE man from the Safety Course had mercy with me and showed me a Low-g roll! Generally this was abandoned, as some low-time instructors ( being generally happy to stay in the air at all....) started to"demo" low-g on their first time out with a student after the Safety Course and didn't "do it right" - ending up mostly dead!
Actually no low-g is no big deal, once you know it!
Just like retreading blade stall, BUT you must know what you can expect when you approach these limits!
NEVER practise zero-g myself, nor do I show it to students. I do approachLOW-g though very carefully, but abort when I start to feel the G's disappearing!
Never let that nose go low!! BUT this serves to show how to avoid it by turning, thinking ahead, getting familiar with the feels when you approach the damn thing!

3top
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Old 15th Oct 2005, 01:43
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Mast bumping has been mentioned as almost generic to teetering rotors. I really don't think so. Look at the yoke on a Bell 47 for example. It is so large that there is no way it could possibly touch the mast. You simply don't hear of mast bumping in anything but the Robinson.
Regards,

Chopperpilot 47
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Old 16th Oct 2005, 05:57
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I think the point is that ALL teetering heads are susceptible to mast bumping, given the right conditions.

An AAIB report from 1997 (here ) which was inconclusive, but pointed to mast bumping, the head and blades having separated from the mast.
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