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Entering autos: discussion split from Glasgow crash thread

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Entering autos: discussion split from Glasgow crash thread

Old 16th Dec 2013, 20:00
  #221 (permalink)  
 
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GOULI - cock-all to do with rotor stall but lots to do with engine limits (usually T4/PTIT/T6 on a hot day) - the 'rolling takeoff' will likely have been a cushion creep transition to maximise power available in ground effect.
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Old 16th Dec 2013, 20:03
  #222 (permalink)  
 
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Gouli, by you living in Norfolk, it would have been a skidded police helicopter and they do very poor impersonations of rolling takeoffs, I would suggest.
Try again? What was it you actually saw and who told you he had DA issues?

Lonewolf: no please, please no more vietnam stories, please
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Old 16th Dec 2013, 20:09
  #223 (permalink)  
 
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TC, given where that flying took place, DA was a non trivial performance variable. Trying to provide helpful answer to our fixed wing friend, eh?
Thread drift from autorotations to max performance takeoff doesn't help the discussion intended, so objection sustained.
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Old 16th Dec 2013, 20:12
  #224 (permalink)  
 
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how do EC135's do rolling take offs then
smooth round pebbles on the tarmac and your take of is rock'n roll
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Old 16th Dec 2013, 20:12
  #225 (permalink)  
 
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Gouli,

I suggest that the hot-day density dependence reflects nothing more than the relatively marginal nature of helicopter flight. In exchange for those special capabilities, there is a compromise in the ability to carry great loads cheaply.

The power demands to haul vertically upwards are very significant, and when air density is down by about 10% at 30C, as compared with a freezing day, it gets tough. More rotor speed and angle of attack, and more power, wastefully beating up more intense tip vortices, and imparting rotation to the wake is required.

Then again, with fixed wings, the speed at which lift is adequate for flight also depends on the density, although the leeway between getting adequate lift and compressibility of the flow becoming an issue is likely greater.

While different outcomes might be achieved on different days, straying into territory where the outcome is that marginal is probably not a good idea. I would not encourage stalls to be considered as "chaotic". The airflow over the wing is chaotic post-stall, but when the flow breaks down for a certain set of temperature-pressure-humidity-turbulence conditions is very reproduceable. What about the Elmendorf C17 crash, where to paraphrase "the stall warning always sounds here"? It doesn't sound like a message you want to be giving.

Was that a "rolling take off" for a helicopter on wheels, or choosing/being required to accelerate in ground effect? I guess they're effectively the same thing.
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Old 16th Dec 2013, 20:14
  #226 (permalink)  
 
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Thanks all for the clarification of what I witnessed. It all happened years ago just outside London. Probably a Bell Jet Ranger. i haven't always lived in paradise

Lived in Australia during the Vietnam war. Watched the news reports every day. Never bothered me as a kid, it did when I was old enough to understand later.
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Old 16th Dec 2013, 20:16
  #227 (permalink)  
 
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Originally Posted by awblain View Post
Was that a "rolling take off" for a helicopter on wheels, or choosing/being required to accelerate in ground effect? I guess they're effectively the same thing.
Short answer is "yes" more or less the same thing.
As above, we used to call them "running takeoff" but I am not sure if that is only on this side of the pond. Likewise, at the bottom of an autorotation with forward GS maintained, we used to call that a "running autorotation" to differentiate it from an auto to a spot.
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Old 16th Dec 2013, 20:20
  #228 (permalink)  
 
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Originally Posted by awblain View Post
Gouli,

I suggest that the hot-day density dependence reflects nothing more than the relatively marginal nature of helicopter flight. In exchange for those special capabilities, there is a compromise in the ability to carry great loads cheaply.


In practical Terms you are probably right.
In theory it will make a small difference.
Higher DA means lower IAS of the blade. This corresponds aerodynamically already to a lower RPM. AoA at the same RPM will be higher. Stall will occur at somewhat higher RPM.
Since we don't know to an exactness of 10% what that RPM is it won't matter much, though.
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Old 16th Dec 2013, 20:24
  #229 (permalink)  
 
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Some of the comments and posts on this thread are beyond contempt, especially from supposed seasoned aviators. To insult and demean those who created the Flight Manuals in such a derogatory manner is beyond me.

On my part, this is neither hero worship as implied by HC, nor blind faith. These guys wrote the books that we rely upon to do our job; they come here to share their knowledge in an open discussion and get abused and denigrated.

DB, your post is just appalling: I hope that you are ashamed of yourself and realise that if we never see contributions from the likes of Nick and John ever again then you and HC should go, too.

This chest beating arse was responsible for the demise of the S92 in Newfoundland!
A simply shocking thing to say.
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Old 16th Dec 2013, 20:24
  #230 (permalink)  
 
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TC.
I'd like to see you install markerballs while staying out of the HV curve.
These aircraft were made to be hovered. The utility industry is proof of that. There is an increased risk when hovering in the curve, sure, but when looking at that risk along with all of the other risks we are exposed to its a drop in the bucket, hardly the difference between a mission that is overall safe, vs unsafe.

The statement in the RFM is little more than a disclaimer not "sound technical adivce". If you need to be there to work, you need need to be there. I dont know anyone who would spend more time there then is needed to do the job.

Before you say, re-evaluate the job, the aircraft, etc..... that is for a different thread....
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Old 16th Dec 2013, 20:37
  #231 (permalink)  
 
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Originally Posted by G0ULI View Post
Thomas Coupling
G0ULI (golf zero uniform lima india) happens to be my radio callsign, although I admit it might be deemed unfortunate in the context of this subject. I have fixed wing flying experience and attended the scene of a fatal light aircraft crash in a professional capacity many years ago, which prompted a lifelong interest in flight safety. I was mystified as to what set of circumstances could cause an apparently perfectly functional helicopter to fall out of the sky. It would seem from the answers in this forum and information elsewhere that something such as a vortex ring formation could in theory put a helicopter in such an attitude that the engines would stop from fuel starvation and in that event, the pilot would have very little time to recover the aircraft. I never knew that the main rotor rpm had to be constrained to within such tight limits or fully appreciated that a full main rotor stall would be unrecoverable irrespective of altitude. This thread has been most enlightening, irrespective of some of the irreverent comments. I have had several opportunities over the years to take a flight in a police helicopter, I never took up the offer, although friends thought I was mad not to. I will stick to fixed wing aircraft.
Funny, I don't trust airplanes. Anything that can't stop before landing just isn't safe!

The transfer from donk stop to moving the cyclic to its final position might appear (a) instant and (b) instinctive but I bet you, the pilot subconciously maintained attitude initially.
Thus (500) K.I.S.S. Keep it simple - lower lever, maintain attitude and then we haven't got to worry about Vy, 2 x Vtoss, half Vmin squared for each damn a/c
[SAS: Don't demean others by disassociating yourself from the 'maintain attitude' fraternity...its trite and unbecoming of you].
I had a friend have a non-catastrophic engine failure for want of a better term. He did what we all really do in the real world. As the RPM tried to drop he maintained it, looking for a spot. He used cyclic as req'd to maintain attitude and speed. When it was on the ground and the rotor stopped turning, he was certain it was an engine failure.

That's real life for many of us. No cut and dried directives, pearls of wisdom, or checklists of robotic control movements. Just pilotage.

Last edited by Senior Pilot; 16th Dec 2013 at 20:39. Reason: Glasgow Crash comments are for the Glasgow crash thread: not here
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Old 16th Dec 2013, 20:37
  #232 (permalink)  
 
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"Relatively Marginal Nature of Helicopter Flight"

I love that phrase! True or not, it represents the content of many of the posts in this thread, helicopters are apparently flying on the edge of the performance envelope quite frequently. If that is the case, then relatively small changes in density altitude, humidity and temperature could have quite large effects on the performance of helicopters and particularly so with relatively low powered, low rotor inertia helicopters.
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Old 16th Dec 2013, 20:47
  #233 (permalink)  
 
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500: I am not demeaning (thats a word that is getting used a lot lately) of your endeavours - far from it. In fact as I told 170' recently, I salute your bravery. And bravery is the word (not bravado) because you sure as hell need it to get your job done, when it is a known, well tested, well tried fact of life that hovering inside the H/V curve ends in tears.....as it did with your previous post statistics.
All I ask is (a) that operators like you recognise the work done by those test pilots who have laid out the danger zones for us mortals to fly around and (B) you don't try to mitigate your reasons for being there in the first place. Given the choice one would never do what you do ...but you have no choice it seems (as I dont know your industry).

PS: Describing the H/V curve as a "Disclaimer" is atleast disingenuous, at most ignorant.
Fly safely 500..................

Pilot and apprentice (you sure you arent rvdt as well?) IF he had done waht you suggested, the drop from his flare would not justify the impact crater size and depth. That is a very substantial deep crater: I'd say 30+ G?
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Old 16th Dec 2013, 21:03
  #234 (permalink)  
 
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Thank you TC,
We are not to far apart on this.
Every operator I know reccognizes and respects the performance envelope put out there by the test pilots and engineers. However, staying out of the avoid curve is just not a reality to our industry. Like you said, we do our best to limit the time there, limit weight to increase options in the event something goes wrong, and we all do far more than minimum required maintenance.

I called the avoid curve a disclaimer becuase that is exactly what it is. The manufacturer cannot assure a safe outcome if you are within it during an engine failure. If their objective was to keep you out of it they would have put it in the limitations section of the RFM. They know, as well as we do, that inside the avoid curve is where these machines (particularly utility machines) were ment to operate and they woiuldn't sell many if that were a limitation.

We are getting off topic
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Old 16th Dec 2013, 21:10
  #235 (permalink)  
 
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SAS: Don't demean others by disassociating yourself from the 'maintain attitude' fraternity...its trite and unbecoming of you].

If you are offended by that comment....perhaps some Self Reflection is in order.

Am I walking on your Corns or something?

I prefer to stick with Aviators and that leaves out anyone who embraces Cook Book Methods of Helicopter Flying.

Sadly, for some reason, we seem to be plagued with an over abundance of them lately.

As Cowboy Logic tells us.....lead a Horse to Water but you will have to wait for him to make up his own Mind to drink.
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Old 16th Dec 2013, 21:19
  #236 (permalink)  
 
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Pilot and apprentice (you sure you arent rvdt as well?
No he isn't.

Cant think of anyone on here that is a worthy match for you though TC.
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Old 16th Dec 2013, 21:35
  #237 (permalink)  
 
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Originally Posted by John Eacott View Post

On my part, this is neither hero worship as implied by HC, nor blind faith. These guys wrote the books that we rely upon to do our job; they come here to share their knowledge in an open discussion and get abused and denigrated.
I see absolutely no reason why a TP should be treated any differently from anyone else on here, though I am all in favour of courteous interaction rather than personal abuse of course. TPs have been trained and are just doing their job like the rest of us (well not me, I'm retired!). There are some good TPs and some incredibly useless and stupid ones. The good ones are not perfect, they have good ideas and attitudes, but also some bad ones at times. They are after all just human, and not gods, even if you would wish it were not so.

Last edited by HeliComparator; 17th Dec 2013 at 09:07. Reason: In the hope of an outbreak of peace.
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Old 16th Dec 2013, 22:02
  #238 (permalink)  
 
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After the AAIB Special Bulletin was released I stated that in order for the aircraft to meet the CAA's description of a high speed vertical impact with rotors stopped, it was likely that the aircraft suffered a complete loss of power and that, for whatever reason, pitch was maintained on the main rotor. (This being the only probable explanation for such an impact, albeit speculative).

From the examples provided in this thread, and from experience, we know that in single engine flying there is an attentiveness (or at least there is supposed to be) towards the potential for a loss of power. This attentiveness is geared towards rapid response in the event of an engine failure with the certain knowledge that it will be necessary to conserve and manage Nr. The lever is going to have to do down in nearly all cases (apart from a low hover etc.) meaning this action can be taken (along with the necessary cyclic inputs) without delay.

With twins there are additional considerations, principally the second engine, and specifically determining which one has failed. The multi-engine pilot response to a power failure is therefore slightly delayed (in principal) to that of a single engine pilot. This delay is compensated for to some extent by the relatively low risk of double engine failures in twins.

However, on those rare occasions that a double engine failure does happen, it is possible to see how a multi-engine pilot may not instantly take the required action in the same way as a single engine pilot would, and for the right reasons, because the multi-engine pilot must assess the nature of the power failure, even if it is to determine that both engines have failed. In a single, any sort of interruption to powered flight is not only obvious but it is equally obvious that there is no recourse. This is not the "normal" mindset of a multi-engine pilot who will be trained to recover from a power failure with partially powered flight from the remaining engine.

Now that Eurocopter have officially admitted that there is a problem with the EC135 (and related types) fuel indication system and that this problem includes the possibility of over reading, are we seriously looking at the potential of a double engine failure due to a shortage of fuel? A prospect which I had initially discounted as being improbable.

If the ill-fated G-SPAO suffered a double engine failure below 1000ft, at night, I am starting to see how it may have been possible with a low inertia rotor to maintain pitch for some moments after both engines failed - even though a part of me still struggles to accept this.

What I am still unable to envisage is how the rotors stopped so completely prior to impact in order to achieve the unscored and unmarked blades which were apparent at the crash site. We are talking about a few seconds from a loss of power to "blades still"!
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Old 16th Dec 2013, 22:12
  #239 (permalink)  
 
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SAS: That lure certainly worked - I'm out of your peanut gallery it seems....

500: Can you tell me how operators like yourselves get insurance cover? The company I mean not the pilot. Do the insurers know you live inside the H/V curve?

RVDT The reason I asked apprentice and pilot was because you said you were a pilot and engineer, just thought it was a close coincidence.

It getting close to Chrimbo, I finish work on Friday for 18 days - it's a tough life.
Let's see if we can get along in the run up - to set the scene over the festive season. Ooops I ve done it now...heh heh...
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Old 16th Dec 2013, 22:18
  #240 (permalink)  
 
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Originally Posted by [email protected] View Post

Lowering the lever first will NEVER be a bad thing (unless you are in a low hover - the exception to prove the rule) because it will prevent further Nr Decay.
Coming from a technical side I want to refrain from commenting anything from a piloting perspective.
However, from a pure technical perspective that is not entirely precise, it will not prevent NR decay but it will reduce it.
If done very violently at a very high forward speed you might even be able to achieve a rotor stall when keeping the cyclic forward.
That said no one would do that in reality.
However, maintaining RRPM Comes from the tilted back (read flared) rotor disc vs. the flight path during autorotation. However a tilted back rotor disc will slow down the Helicopter. This has to be balanced in order to maintain the necessary airspeed and thus airflow through the disc. Lowering collective will do that. The sequence in which you establish this stable condition won't matter unless it takes too much time.
In which case both ways if done to the extreme (Only flare without lowering collective as well as only lowering collective without relaxing cyclic) would render you equally dead.


The strange thing in this discussion is that when reading carefully everybody here seems to have the same actions in mind. It's just whereupon the emphasis is laid where the difference lies.
All the more unfortunate that such a harsh discussion has ensued. As (primarily) an interested Reader I hope the emotions calm down a bit and the interesting discussion can continue.
@John Dixson: Thanks for the explanation! I found the discussion about technical limits interesting and therefore thank you for your contribution but I also understand concerns that this might be taken by some out of context (which I hope really doesn't happen).
Any such values will only apply for a certain situation and numbers will vary significantly depending on Type (I would expect see a drastic difference between a lightly loaded S-70 and an R-22 close to MAUW), Weight and circumstances.
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