Autorotation?
 

Good evening Rotorheads,
If you are taught to fly rotory in the R22, it is drummed into your head ( or it should be) that if the Gerbil stops running you have about 1.5 seconds to re-act by pushing the collective down, the other important feature is a flare, to load the disc to ensure that RRPM dont fall down beyond the critcal, whilst undertaking this short but life saving task, roughly how much height would be lost, or is this an impossible answer to give, and at what height would stick down and flare be to late for any auto whatsoever,(apart from EOL from the hover), and last, is the speed of 1.5 sec's common in all helio types.
My Regards

My understanding is 1.5 seconds is the world's lowest reaction time !! It's due to the low rotor inertia, even with tip weights.

As to the height at which any collective down and flare would be too late, see the H-V curve, high speed / low altitude section.

The other questions I leave to people who know the answers.

[This message has been edited by The Nr Fairy (edited 24 April 2001).]

An instructor of mine many moons ago completed the robinson safety course and while up flying with one of those test pilots they chopped the throttle at 102kts and didnt dump the pole for 5/6 seconds
just did a very harsh flare , then dropped the collective.
as for 1.5 seconds , frank says 1.1 seconds but that all depends on power aplied, density alt etc.

Bigger helis , heavier blades and more time to react , however if you lose the rrpm in the robbie it is easy to get it back , in the bigger helis it is harder to lose the rrpm and likewise harder to get the rrpm back to the desired . Am i making any sense?

There is a Certification issue here. You must be able to delay action for a certain period of time before the situation becomes critical. This 'intervention' time is made up of the pilot's cognition factor and the time it takes him to react. Typically this is assessed, for certification purposes, at 2.5 seconds for the engine failure case. So less than this is cutting it fine. I have heard tell of delays longer than 1.5 seconds in the R22, though personally I wouldn't want to wait even that long. A word to the wise, PLEASE, don't even think of trying this for yourselves. Professional test pilots and flight test engineers have taken the risk on your behalf!
The best protection and cushion against catastrophic loss of RRPM is anticipation and having your hand on the collective whenever possible, but certainly if you are climbing. (Worst case: high blade pitch angle and longest delay in establishing rate of descent airflow.)
There are helicopters that have much more benign rotor decay; the B47,B206 and other machines with high rotor mass and thus high inertia.

During Height Velocity Chart development testing for Transport Canada or FAA certification (don't know about CAA or JAA), the pilot reation time delays depend on the area being explored. Typically, for regions which fall below the 'knee' of the chart, the delay is 0.5 seconds. Areas above the knee are subject to 1 second. I don't know if these were the criteria the Robinson was certified under, but it applies to most types being certified in Canada or the US today.

Right,
the R22 was originally designed without the governor so the blades were kept light to enable easy/quick control of RRPM using the throttle. As already said this does lead to rapid loss of RRPM on engine failure. I can't say much on the subject of 1.5 1.2 secs as this does depend on pitch angle due density and weight.
It also depends on Kinetic energy available to convert in to restoring RRPM. If you have 102kts of K energy very little flare is required compared to K of 60. In fact trying to convert IAS of 30kts or less is fairly inaffective in the R22.
As for height lost - if you were to flare enough to counteract the descent due to lever down, over that short period of time no height would be lost.
As you know you should have 65kts of K energy and RRPM 97-110% to covert before commencing the flare.
Does that answer your question?

In regard to when are you too low to be able to lower the collective/flare, I think the best way to think about it is to imagine a continuum from the hovering case (no collective lowering, no flare) up to the full -blown autorotation entry at height and with some decent forward speed (ie lower collective fully, flare to regain Nr and to get to best auto speed).

This is from AS350 experience, but it would be similar for most aircraft, in concept that is.

If you imagine transitioning from the hover into forward flight, it would go something like this:

hover - freeze collective, no flare.

taxi - as above

up the slope a bit - partial collective lowering, small flare (as much as you can for both without digging the tail into the ground)... and so on.

In the Squirrel, you can get a softish landing (albeit with some run-on speed) from anywhere up the slope from the hover to a 60kt/100 ft AGL gate (height figure may be wrong, it's been a while!).

The judgement part is getting the feel for how much flare and lever-lowering you can do before you have to give it away and adopt a skids-level (or maybe a tad nose up) for the run-on.

So (finally), in partial answer to your question I hope, you should be able to get a bit of lever down and flare effect anywhere from about 10 or 15 kts on takeoff.

Hope I haven't dribbled on about stuff you weren't looking for.

To all of you who have given answers, a big thank you, I have asked the Cfi where I SFH from to show me the actuall engine failure upon take of( ie just as 30/40 knts has been achieved) but they say to me they cannot show me for they are not allowed to practice that on their field, well ok, I can live with that, but their answer to several further Q's was, that its very similar to any Auto from height, only you have to more alert and quicker!, well you chaps have given me a lot, lot more, in your answers and suggestion, I see the problems with practising a low height( just airborne) possibly practising this particular thing would bend a lot of metalwork, so compared with actuall engine failures this is why the Cfi's won't allow it to be tried, could my assumption be right?
As a part of my monthly flying I practice EOL's and Auto's at least twice during every month,so I am pretty confident that I could cope, but have never done a very low alt one! hence that part of the question.

[This message has been edited by Vfrpilotpb (edited 28 April 2001).]

Hi there

Let me say at the start I've never flown a robbie, but I do understand you have to be pretty quick off the mark.

Ask your CFI as to whether you could flare and check at a greater height and treat the rest of the landing as an engine off from a high hover (i.e. dump the pole again). We find it's a good procedure in the 206 for people who don't fly a lot - the normal method needs a lot of practice to get it right every time.

Of course, it may not work as well with lighter blades, but it would be interesting to hear what the panel thinks

cheers

Phil

Going back to the certification issue, reference delays in lowering the collective, the JAR requirement for response to engine failures is given as 1 sec 'or normal pilot response time, whichever is the greater'. Hmmm, very useful if normal PRT is not defined! It isn't.
I have been canvassing opinion on the flight test forum regarding the JAR 'normal pilot reaction time'. I don't have a copy of BCAR here, but my extracts from AvP970, the UK Defence Standard for certification, gives an intervention time of 2 seconds for engine failures 'as a realistic reaction time for the average pilot to identify a total power loss under unfavourable conditions and then to lower the lever'; elsewhere 'active' response time for stability/flight control failures is given as 1 sec and 'attentive hands on' pilot response time is given at 1.5 secs.
Interestingly, my learned friend Genghis The Engineer points out that the fixed wing chaps are allowed a 2 second delay time after engine failure under JAR: we've been done down!
Since JAR are very close now to FAR, I suppose the FAR standard may be followed, but 1 second should be regarded as the maximum delay for the R22, where even a planned 1 sec delay in the climb at 60 KIAS is, to say the least, exciting.....

Last summer I had the chance to do some departure failures and low approach engine failures. Let me just say that they happen very quickly in a Robbie!

The approach failures were basically as has been described above--you just need to take them as you'd be doing them had the failure occured higher up. You'll probably be going much slower than in a regular auto (say, at <100 ft) but that just translates into waiting 'til you're a bit lower to flair.

However, on the departure failures, things happened VERY fast! Even when we counted down I'd be dropping the collective (fast!) as we started rolling off the throttle, and we still often got a low-RPM horn. Suffice it to say that you _don't_ have the 'leisurely' 1-2 seconds you do during cruise :) I'd recommend that you try it sometime so you realize the urgency during high power maneuvers, but be ready. Could you fly someplace else (another field) to do it, or is there a restriction against doing this in the heli you fly?

As to the altitude at which an EOL is not possible, I'd imagine you can do takeoffs and approaches that will always allow you to make it to the ground safely in an engine-out condition. I wouldn't suggest hovering over your house at 50 ft tho!