Robinson R22 Corner [Archive copy]
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206 autorotative characteristics
kissmysquirrel noted:
(Heyyyy, watch your goddam language, squirrel! My teenage daughter reads this board.)
Yes, the 206 is a great bird, no doubt. But many pilots are lulled into a false sense of security by the 206's seemingly benign autorotative characteristics during the practice autos they see during the checkout. This is especially true if the applicant comes from a ship with not-so-great autorotative characteristics (let's not mention any names).
The fuel control of the RR/Allison 250-C20 series engine in 206B has a decelleration schedule whereby it must take a minimum of two seconds to go from full-throttle to idle. Many C-20 engines take even longer, and there is no maximum figure specified. I've had them take as long as six or seven seconds.
So no matter how quick you are at twisting the throttle off during a practice auto, the power is only going to come down at the scheduled decelleration rate. What happens is, the power comes off "softly" compared to the snap you feel in a recip. In 206 (or any a/c powered by the 250-C20 series), this gives you an erroneous indication of what a "for real" engine failure will feel like.
Secondly, once the auto has stabilized, if the N2 needle is still married with the NR needle (and in a C-20 it will be), the engine is still providing power. It may not be much...only ten h.p. or so, but it is something. And that "something" will help lengthen your glide. It is the equivalent of being 100 pounds lighter or more, according to world renowned helicopter expert, Senator Dr. Raymond Xavier Prouty III, esq. Oh, and me.
Pilots who've had real engine failures in such a/c report that the power came off rather violently and with a lot of yaw-snap (compared to what they had been used to in practice) and that the glide was a LOT steeper than they expected. Fortunately, I haven't had that happen yet, although as I say that I am knocking on my head as you can imagine.
So be careful, all you new 206 pilots out there! Things may not be what you've been prepared for. Sure, when the inevitable happens it might seem like you'll have enough time to pull out the RFM and read up on the engine-out procedures. But I guarantee that it'll take you by surprise.
Forewarned is foreskinned.
I had throttle chop auts demo'd to me a while back. NOT NICE!!!!! Flare like f**k to regain rpm or die also whilst trying to peel yourself off right hand door!!!! this was of course in the r22. Twice I have now seen just over 75% rrpm and I don't particularly want to see it again.
Just completed the B206 rating today and have to say "engine failure?" "what engine failure?" Can someone please give me a 206 to fly full time please?
Just completed the B206 rating today and have to say "engine failure?" "what engine failure?" Can someone please give me a 206 to fly full time please?
Yes, the 206 is a great bird, no doubt. But many pilots are lulled into a false sense of security by the 206's seemingly benign autorotative characteristics during the practice autos they see during the checkout. This is especially true if the applicant comes from a ship with not-so-great autorotative characteristics (let's not mention any names).
The fuel control of the RR/Allison 250-C20 series engine in 206B has a decelleration schedule whereby it must take a minimum of two seconds to go from full-throttle to idle. Many C-20 engines take even longer, and there is no maximum figure specified. I've had them take as long as six or seven seconds.
So no matter how quick you are at twisting the throttle off during a practice auto, the power is only going to come down at the scheduled decelleration rate. What happens is, the power comes off "softly" compared to the snap you feel in a recip. In 206 (or any a/c powered by the 250-C20 series), this gives you an erroneous indication of what a "for real" engine failure will feel like.
Secondly, once the auto has stabilized, if the N2 needle is still married with the NR needle (and in a C-20 it will be), the engine is still providing power. It may not be much...only ten h.p. or so, but it is something. And that "something" will help lengthen your glide. It is the equivalent of being 100 pounds lighter or more, according to world renowned helicopter expert, Senator Dr. Raymond Xavier Prouty III, esq. Oh, and me.
Pilots who've had real engine failures in such a/c report that the power came off rather violently and with a lot of yaw-snap (compared to what they had been used to in practice) and that the glide was a LOT steeper than they expected. Fortunately, I haven't had that happen yet, although as I say that I am knocking on my head as you can imagine.
So be careful, all you new 206 pilots out there! Things may not be what you've been prepared for. Sure, when the inevitable happens it might seem like you'll have enough time to pull out the RFM and read up on the engine-out procedures. But I guarantee that it'll take you by surprise.
Forewarned is foreskinned.
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I'll endorse RotorHorn's comments on Dick Sandford's 1-day safety course. (I seem to remember it being a 2 day thing if you include some flying). Well worth the money! Dick even got me experiencing Rotor-Stall! Yes, we demo'd it, and it was quite sudden & dramatic, even in my '44. OK - don't panic, we were carefully placed in a nice steady 6-inch hover over grass!
...and as for the comments about dumping the lever the second you hear the horn, I'll go for that too.
However, I still remember when I did SFH in a '44 at Cranfield, and the darned thing had a RadAlt, with the threshhold set at 500 feet. So, every time I'm coming on finals, calling on the radio, looking for other a/c, final checks & really busy etc. off goes this horn thingy at 500 ft. Got me every time! Jumped out of my skin & had to override the instinctive desire to dump the lever!
Then again, I suppose I shouldn't complain. I got into this flying thing because it was exciting in the first place! ;-)
Holly_Copter
...and as for the comments about dumping the lever the second you hear the horn, I'll go for that too.
However, I still remember when I did SFH in a '44 at Cranfield, and the darned thing had a RadAlt, with the threshhold set at 500 feet. So, every time I'm coming on finals, calling on the radio, looking for other a/c, final checks & really busy etc. off goes this horn thingy at 500 ft. Got me every time! Jumped out of my skin & had to override the instinctive desire to dump the lever!
Then again, I suppose I shouldn't complain. I got into this flying thing because it was exciting in the first place! ;-)
Holly_Copter
I described the situation on the checkride AR, not to show that I'm a fool or a hero of the skys. One of the advantages of this board is to share experiences and opinions. Sometimes it's normally that we discuss some points from a different view and stand.
I described the checkride AR to show some problems you can encounter on an AR entry. Due to the high pitch climb we had a rapidly decreasing NR and IAS. I have made some hundreds of 206 AR's. There is so much difference between an AR entry on level flight (or on descent) with an IAS >> Vy and the described procedure. Rolling the engine to idle on level with good speed is on a 206 really unimpressive. You can count up to 10 and watch with interest the decreasing NR. Pitch down, a slight flare and everything is under control. NR is good, go for the best speed, control the the glide with speed and NR to reach the best landing site. With enough speed it's easy to recover NR. NR drop depends on flight conditions!!!
Skidbiter is right: "a low-inertia rotor is easier to recover" and this an advantage for the R22, compared to other helicopters. But you need speed to flare! And a low inertia rotor is allways tricky on the AR touch down.
Complete real power failure is definitivly other than on practise. Fuel system decelleration time, rest idle power (17hp c20) helps. Look on the h-v diagramm. Why is 300-500 ft with low speed dangerous? It's no problem on an established AR to glide with zero (or negative) speed to reach the best landing site if you have enough altitude to recover the speed for the touch down flare. (the flare decrease the descending rate and gives som extra MR rounds) Needs not so much time. But on this situation you have an established AR and full a/c control! On the AR entry transition with a decreasing NR and low speed it needs much more time. It takes some seconds to come into the AR airflow with additionally bad a/c control. With a very high descend rate on low speed and no effective flare it's not enough rotor inertia available for a smooth touch down.
OK back to R-22: Due to the very low inertia it's clear to get a big NR drop. But as said, relative easy to recover if enough speed is available. Immediately lower the pitch and flare for NR. If you have not enough speed or / and altitude to recover NR, good luck.
I described the checkride AR to show some problems you can encounter on an AR entry. Due to the high pitch climb we had a rapidly decreasing NR and IAS. I have made some hundreds of 206 AR's. There is so much difference between an AR entry on level flight (or on descent) with an IAS >> Vy and the described procedure. Rolling the engine to idle on level with good speed is on a 206 really unimpressive. You can count up to 10 and watch with interest the decreasing NR. Pitch down, a slight flare and everything is under control. NR is good, go for the best speed, control the the glide with speed and NR to reach the best landing site. With enough speed it's easy to recover NR. NR drop depends on flight conditions!!!
Skidbiter is right: "a low-inertia rotor is easier to recover" and this an advantage for the R22, compared to other helicopters. But you need speed to flare! And a low inertia rotor is allways tricky on the AR touch down.
Complete real power failure is definitivly other than on practise. Fuel system decelleration time, rest idle power (17hp c20) helps. Look on the h-v diagramm. Why is 300-500 ft with low speed dangerous? It's no problem on an established AR to glide with zero (or negative) speed to reach the best landing site if you have enough altitude to recover the speed for the touch down flare. (the flare decrease the descending rate and gives som extra MR rounds) Needs not so much time. But on this situation you have an established AR and full a/c control! On the AR entry transition with a decreasing NR and low speed it needs much more time. It takes some seconds to come into the AR airflow with additionally bad a/c control. With a very high descend rate on low speed and no effective flare it's not enough rotor inertia available for a smooth touch down.
OK back to R-22: Due to the very low inertia it's clear to get a big NR drop. But as said, relative easy to recover if enough speed is available. Immediately lower the pitch and flare for NR. If you have not enough speed or / and altitude to recover NR, good luck.
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All very nice to have that (relatively) big 206 blade whopping away with bags of inertia, but the R22's fatal accident rate in the UK between 1992 and 1999 (about one per 115,000 hours) was much better than the 206s (about one per 40,000 hours) and part of the reason was the fact that that big blade often comes whopping in the window in otherwise survivable crashes. (Figures relate to fatal accidents, not persons killed.)
And as yet I've had no replies to the question I asked in my first post on this thread. Does anyone know of an engine failure in an R22 that was not caused by fuel or oil starvation, or carb heat mismanagement? (With the exception of the pilot's coat incident mentioned above).
And as yet I've had no replies to the question I asked in my first post on this thread. Does anyone know of an engine failure in an R22 that was not caused by fuel or oil starvation, or carb heat mismanagement? (With the exception of the pilot's coat incident mentioned above).
Iconoclast
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Apples and Oranges
To: T'aint
When you compare the fatalities associated with different helicopter types you should zone in on a specific type of accident. It is suggested that you read the NTSB report contained in Dave Jacksons post above as it deals with loss of rotor control, mast bumping and/or rotor incursion.
Bell has suffered many mast bumping incidents and most of them occurred prior to the US Army discovering the cause. Bells have suffered probably no more than 60 rotor loss incidents since the introduction of the two-blade rotor system. I may be off a bit regarding the total incidents covered in the NTSB reports but I believe it is around 18 or more. Since the report was written and the introduction of AD 95-26-04 at least five more incidents have occurred and several of those were in the UK and Ireland.
Now compare the number of flight hours for both helicopters and divide those hours by the number of rotor loss incidents. The Robinson still comes off with the higher ratio.
Now for something that you may not have been aware of is what is acceptable.
When the Apache was designed the Army indicated that it was acceptable to have a single point failure or some defective procedure among other things that would result in the loss of an aircraft every 34,000 hours of collective flight hours.
If an aircraft is designed in accordance with FAA AC-25-1309-1A the frequency of suffering a catastrophic loss of an aircraft and crew is based on system or component reliability. The acceptable rate of system failure due to a single point failure or induced system failure is 1 10 9 or one time in a billion hours of collective fleet operation. There is no aircraft design at present that has ever met that design requirement and that includes 747s and R-22s.
When you compare the fatalities associated with different helicopter types you should zone in on a specific type of accident. It is suggested that you read the NTSB report contained in Dave Jacksons post above as it deals with loss of rotor control, mast bumping and/or rotor incursion.
Bell has suffered many mast bumping incidents and most of them occurred prior to the US Army discovering the cause. Bells have suffered probably no more than 60 rotor loss incidents since the introduction of the two-blade rotor system. I may be off a bit regarding the total incidents covered in the NTSB reports but I believe it is around 18 or more. Since the report was written and the introduction of AD 95-26-04 at least five more incidents have occurred and several of those were in the UK and Ireland.
Now compare the number of flight hours for both helicopters and divide those hours by the number of rotor loss incidents. The Robinson still comes off with the higher ratio.
Now for something that you may not have been aware of is what is acceptable.
When the Apache was designed the Army indicated that it was acceptable to have a single point failure or some defective procedure among other things that would result in the loss of an aircraft every 34,000 hours of collective flight hours.
If an aircraft is designed in accordance with FAA AC-25-1309-1A the frequency of suffering a catastrophic loss of an aircraft and crew is based on system or component reliability. The acceptable rate of system failure due to a single point failure or induced system failure is 1 10 9 or one time in a billion hours of collective fleet operation. There is no aircraft design at present that has ever met that design requirement and that includes 747s and R-22s.
I must disagree with the 'dump the lever when you hear the horn regardless' argument. Awareness of an engine failure should be from the change in noise of the engine/sudden yaw/Nr sound changing - with the final clue being the Nr horn.
Suppose you inadvertantly let the Nr decay in the hover and the horn goes off - if you are conditioned (as many are) to slam the lever down in a Pavlovian response to the noise then you are going to hit the ground hard and probably roll over. I know because this is exactly what an owner with 150 hours on type did to me - the aircraft went back to California in a box, fortunately we didn't.
Listen to the aircraft and get used to the noises it makes, it might just save your life one day.
Suppose you inadvertantly let the Nr decay in the hover and the horn goes off - if you are conditioned (as many are) to slam the lever down in a Pavlovian response to the noise then you are going to hit the ground hard and probably roll over. I know because this is exactly what an owner with 150 hours on type did to me - the aircraft went back to California in a box, fortunately we didn't.
Listen to the aircraft and get used to the noises it makes, it might just save your life one day.
I like that analogy Crab - the pilot (dog) responding to the horn (bell).
But isn't it important to have second-nature reactions to certain emergency situations? What I mean is that you would hear the horn and immediately react to instinctively lower the lever, BUT this reaction is mitigated by logic based upon the particular situation - i.e. engine failure in the hover, don't dump the lever.
But isn't it important to have second-nature reactions to certain emergency situations? What I mean is that you would hear the horn and immediately react to instinctively lower the lever, BUT this reaction is mitigated by logic based upon the particular situation - i.e. engine failure in the hover, don't dump the lever.
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Lu:
May I refer you to all my previous posts whenever you've jumped on your hobby horse and started playing your one-note tune. May I further suggest that you (a) get a pilot's licence and (b) design something that flies.
May I refer you to all my previous posts whenever you've jumped on your hobby horse and started playing your one-note tune. May I further suggest that you (a) get a pilot's licence and (b) design something that flies.
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I take Crab's point entirely. When I made my post I was thinking about all those 1500ft straight & level hours I've flown in Robbo's. Of course, in the hover the reaction should be somewhat different (pretty much the opposite, as far as the lever's concerned). Squiffy makes the "Consider the situation" point very well.
Did my R44 renewal this week, and the examiner was, co-incidently, the guy who taught me to fly & we've flown together many times around Europe since so we're very tuned in to each other. I think that's why several un-announced (Well, very late announced ;-) throttle-chops were included to sharpen my skills!
Feels different when it's your own aircraft too, I can tell you!
Holly_Copter
Did my R44 renewal this week, and the examiner was, co-incidently, the guy who taught me to fly & we've flown together many times around Europe since so we're very tuned in to each other. I think that's why several un-announced (Well, very late announced ;-) throttle-chops were included to sharpen my skills!
Feels different when it's your own aircraft too, I can tell you!
Holly_Copter
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Hello gang,
was rather busy, so here a late reply:
To Dave Jackson: Thanks for the Search string, I will try it as soon as I find time!(18 degree offset discussion....)
To the rest:
I just got a 1850 hr R-44 head through my fingers, except for cut lining by a bolt during a less than optimal procedure during blade install I could find absolutely nothing wrong. The bushings were changed according to manual and the head is like new!
The coning hinges have hardly any friction, however if the teeter hinge looses all friction and the coning hinge keeps some, a pronounced vibration at speed will result.
To Lu: As far as I understand the coning hinges will of course constantly work to adjust to different lift loads during their way around the disk, however the flapping action should be the same as with any underslung head, based on the teeterhinge. If not so, see above.
3top
was rather busy, so here a late reply:
To Dave Jackson: Thanks for the Search string, I will try it as soon as I find time!(18 degree offset discussion....)
To the rest:
I just got a 1850 hr R-44 head through my fingers, except for cut lining by a bolt during a less than optimal procedure during blade install I could find absolutely nothing wrong. The bushings were changed according to manual and the head is like new!
The coning hinges have hardly any friction, however if the teeter hinge looses all friction and the coning hinge keeps some, a pronounced vibration at speed will result.
To Lu: As far as I understand the coning hinges will of course constantly work to adjust to different lift loads during their way around the disk, however the flapping action should be the same as with any underslung head, based on the teeterhinge. If not so, see above.
3top
PPRuNe Enigma
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Interestingly, although the R22 has no explicit mention of a limit, the R44 does have a 100 kt limit in autorotation indicated by a red and white hatched line on the ASI.
Randy_G
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hi gang,
just called our chief flight instructor:
POH published power-off VNe is 100 kts for the R-44, same as doors off limit.
R-22 VNe general 102 kts ,no published power off VNe, so it is the same as power-on.
As metioned it is hard to press it a lot past 75Kts (R-22)
Vorticey: If you have to go down fast for any reason, like a cloud of birds (like a couple of thousand/cloud and then there are a couple of clouds on after the other...) - in eg a migratory area, the fastes way is at low or no power (speak - auto) and high forward speed. This is pretty safe as long as you keep rotor rpm in check.
The other way or a combination of both is a steep-turn(45-60 degree bank)-spiral, the faster, the bigger the radius, the easier the recovery (or should I say the less difficult...?). You have to be careful when you roll out and pull out of the dive - donīt over pull the cyclic - round it out nicely!! DONīT try either one the first time by yourself!!! Get the best CFI you can get hold off (the more hours the better!)!
You also can slow down and autorotate at 20-30 kts and recover early, but that means you have to wait some precious seconds to bleed off speed and enter an auto.
With the above you just lower the collective until Rrpm takes off and then roll off some throttle (donīt forget the carb heat...), so you can clearly control Rrpm and keep the collective at the lowest possible, meanwhile push the cyclic to accelerate to max speed possible before hitting VNe. You get a pretty good decent rate!
3top
just called our chief flight instructor:
POH published power-off VNe is 100 kts for the R-44, same as doors off limit.
R-22 VNe general 102 kts ,no published power off VNe, so it is the same as power-on.
As metioned it is hard to press it a lot past 75Kts (R-22)
Vorticey: If you have to go down fast for any reason, like a cloud of birds (like a couple of thousand/cloud and then there are a couple of clouds on after the other...) - in eg a migratory area, the fastes way is at low or no power (speak - auto) and high forward speed. This is pretty safe as long as you keep rotor rpm in check.
The other way or a combination of both is a steep-turn(45-60 degree bank)-spiral, the faster, the bigger the radius, the easier the recovery (or should I say the less difficult...?). You have to be careful when you roll out and pull out of the dive - donīt over pull the cyclic - round it out nicely!! DONīT try either one the first time by yourself!!! Get the best CFI you can get hold off (the more hours the better!)!
You also can slow down and autorotate at 20-30 kts and recover early, but that means you have to wait some precious seconds to bleed off speed and enter an auto.
With the above you just lower the collective until Rrpm takes off and then roll off some throttle (donīt forget the carb heat...), so you can clearly control Rrpm and keep the collective at the lowest possible, meanwhile push the cyclic to accelerate to max speed possible before hitting VNe. You get a pretty good decent rate!
3top