Wind Limits for Helicopters?

[Whirlybird]

Greetings. I've never even been on this forum before, but it was suggested to me that I post this question here rather than on Rotorheads.

I'm a helicopter instructor on R22s. Yesterday I did a couple of lessons in steadily increasing winds; by the time we finished it was 20 kts gusting 30, and forecast to increase (which it did). The school owner then cancelled the rest of the day, saying the wind was outside the R22's limits. At the time I thought, "what limits", but didn't say anything. I later looked through the POH, albeit somewhat quickly, and couldn't find any wind limits. I vaguely recall hearing of a crosswind start-up limit, which I suppose is possible, but all that would mean is that you should land and park into wind. And although far from being a rotary aerodynamics expert, I can't think of any reason for a wind limit....unless the wind was so abnormally strong that it would blow the helicopter apart or you'd get retreating blade stall in normal flight! I've flown the R22 in 40kt winds before; it's not fun, but it's OK.

I can think of a lot of good reasons for not teaching novices in strong gusty winds, but they all relate to helicopter handling, not the actual limits of the machine. There are also a lot of limits imposed by everyone from Frank Robinson to individual schools, designed to stop low hours pilots killing themselves. These occasionally get passed on in folklore as "the limits". So, am I missing something obvious that I ought to know? Or did the school owner get it wrong?

['India-Mike]

Might any wind limit be related to blade sailing on rotor start-up or shut-down, rather than being a flight or handling limit?

There's a cracking picture somewhere (Newman's book?) of a SeaKing blade sailing on the deck of a carrier....frightening looking stuff!

Found it! See http://www.afm.ses.soton.ac.uk/nav.cgi?s=node-rotor-res

[slowrotor]

An airworthiness directive was issued for the R22 that concerns operation in turbulence. May or may not be related to your question.

[Gadget freak]

I've never flown in an R22 and I don't know anything about them but I was really surprised when you said there were no wind limits. After a quick google I found FAA Special Airworthiness Information Bulletin, ASW-95-01 for the R22 which says.....

7. Do not fly if any of the following conditions exist: surface winds (including gusts) exceeding 25 knots, surface wind gusts exceeding 15 knots, wind shear forecast or observed, and/or turbulence forecast or observed to be moderate, severe or extreme. "Ride quality" in turbulence is a function of several factors, predominately gross weight. Relatively light gross weights make the R-22 and R-44 more susceptible to the effects of turbulence. Most notably, main rotor flapping and aircraft attitude are affected by turbulence and can lead to blade stall, abrupt control inputs in response to uncommanded attitude deviations and, ultimately, mast bumping. Two recent rotor/airframe contact accidents occurred with high surface winds, wind gusts and turbulence. At least seven rotor/airframe contact accidents were accompanied by such conditions.

This seems pretty clear so I wonder why there isn't similar advice in the POH?

[rotorfossil]

The CAA originally required a starting and stopping wind limit, and it was set at 26 kt, for no obvious reason as the Robinson rotor system is more resistant than most to blade sailing at low RPM, has large boom clearance and stiff blades. Usual precautions on gusty days, shut down with the wind from 2 o' clock so that the blades are rising as they cross the tailboom.
The Robinson homilies about flying in gusty winds relate to the possibility of attitude upset and mast bumping in the event of incorrect recovery action.
In reality, students don't get much use out of their flying due to the turbulence anyway when the wind is gusting up towards 30 kt.

[idle stop]

In the Limitations Section of the R22 Flight Manual (POH to our FAA brethren) is the following Limit, which I paraphrase as I don't have the Manual in front of me:
Surface Wind 25 Knots or more, or gusting 10 knots or more, aircraft may only flown by a pilot having 150 hrs helicopter time and 50 hours on type.
So, 25 knots or 15 gusting 25: do not fly unless you meet the criteria.
Whilst an FI may meet the experience requirement, the student is unlikley to, so training is not on. Unless the FI is going to hog the controls for the duration!
And what about controllability in crosswinds and tailwind? 'Demonstrated' at 17 Kts. Generally way beyond most PPL/SPL at 25 Kts anyway. And mine, even as a 9500+ hour graduate tp with 1000 hours or so on the R22!
Very good idea of CFI to put aircraft in hangar at 25 Kts!
I think Rotorfossil will agree that the organsiation we both worked for did operate above the (now) limit before that limit was introduced, and that generally one was limited (sic) in what work could be done with the aircraft in those conditions.
The Limit was imposed as part of the package of measures following th FAA /NTSB review of the spate of R22 accidents in the early 1990s involving possible low g, turbulence, loss of RRPM and mast bumping. I think the R44 has a similar Limitation.

[007helicopter]

Hi Whirly - I would be quite interested myself to see the response on Rotorheads, where I am sure there will be interesting response.

In fact I asked myself this very question yesterday, Sunday, which was 25knots plus at Rochester. I am rated on the R22, R44 and Hiller and personally would not have fancied it as I do not have much time in these conditions.

I actually would like to grab an instructor to see how it handles. One of the problems in doing the PPL is that you often do not fly in marginal conditions and gain this experience for when conditions deteriorate.

[Whirlybird]

Gadget freak,

I was looking at my own copy of the POH, and it's a few years old. I daresay that bulletin came out more recently, and I never got round to paying for the updates you can get from Robinson. As you say, it does seem pretty clear.

idle stop,

It does indeed say what you quote in the limitations section. However, the instructor is PIC, so whether the student has the required number of hours shouldn't matter...should it? As to whether they'll learn anything, IMHO it depends on the student, the precise conditions, and the exercise being taught, and is a whole other topic.

Anyway, people, thanks for the info. I'll read up-to-date info in future. I can't help thinking they've overdone things somewhat; I don't seem to find flying the R22 in 25 kt winds to be a problem. Or maybe I'm just getting overconfident.

[HillerBee]

As mentioned before it's really important to shut down with a crosswind so the blades won't be able to sail up and hit the tail. In flight you won't have many problems apart from the turbulence of course and the lower groundspeed. The R-22 has the limitations as stated earlier. Most other helicopters only have a demonstrated number which is not in the limitations part of the manual. The ability to always land upwind is one of the advantages of a helicopter of course.

[Shawn Coyle]

A very interesting question on wording in the flight manual.
Aside from the Bulletins on the R-22, most older flight manuals will have wording in the limitations section to the effect of 'the helicopter has been demonstrated in winds of 17 knots from all directions'.
Does this really sound like a limitation? What does it mean?
It means that the certification criteria, namely to be able to have adequate control margin to hover with winds of 17 knots from any direction, has been demonstrated at the weight and density altitude limitations for takeoff and landing shown in the flight manual. Nothing more.
You may be able to handle higher winds at lighter weights and lower density altitudes, but there's no guarantee.
A case of a something in the limitations section not really being a limit....

[Matthew Parsons]

Shawn,

You're implying that all information in the limitations section actually need to be absolutes, that flight above those limits would not be possible.

I understood that all aircraft manuals, but especially those for helicopters, were full of 'economic' limitations. I.e. the limitation is there only because the company but ultimately the customer doesn't want to pay for the testing, engineering, or maintenance required to expand them further.

I may be reading wrong, but it seems that you're suggesting that if flight is possible outside the envelope described in the limitations section then there would be no consequences at all. In fact, I know that for some types, performance and handling is extremely comfortable beyond the limitations, but fatigue of certain parts increases dramatically.

Am I way off on this?
Matthew.

[Genghis the Engineer]

I think that this will depend very much upon what the intent was, and how it was worded.

If something is stated as a limitation - then clearly going outside that is outside the CofA, and not to be done in normal operations. This might be for structural, fatigue, safety margin reasons...

Crosswinds, certainly in a fixed wing aircraft, are commonly defined as "maximum demonstrated", that's not a limitation: although may commonly be used to define local limitations.

Does anybody have the exact words to hand, as they apply to the R22, it would be interesting to read?

G

[The Nr Fairy]

From the "General" section of the R22 POH:

Hover control has been substantiated in 17 knot wind from any direction up to 9,800 feet density altitude. Refer to IGE hover performance data for allowable gross weight.

So it's not a limitation - I read it as stating that it complies with the relevant FAA standard. And - being pedantic/frivolous - surely we need more than a 17 knot limit anyway in normal cruise flight of 70 - 80 knots !

[Matthew Parsons]

My point is, if you don't reach an aerodynamic or structural limit, instead you just demonstrate it can reach a limit sufficient for certification, as far as the operator is concerned isn't that the same as all limits?

For the R22, apparently it's been demonstrated to 17kts. That might also be an aerodynamic limit (probably not, but according to flight test information we have right now it could be). Or you won't reach that until 18, 20, 30, or 80 knots. Who knows? When you only have what is demonstrated, that is all you know it is good for. That IS a limit.

[Shawn Coyle]

Matthew et al:
Aside from the side and rear wind issue, I can think of no other instance where numbers etc., in the limitations section are not absolute limits to be adhered to. In fact, exceeding them will invalidate your certificate of airworthiness (another subject).
Whether the limitations are 'economic' (as in being very conservative) is not the issue. The manufacturer is under no obligation to tell you why a limitation is a limitation - the reasons for limitations are legion.
I would never suggest that flying outside the limitations can be done without consequence (engineering, legal or otherwise). What I was saying was that, as worded, the side and rear wind phrase should not be considered as limiting, because it's not worded as a limitation.
The R-22 manual as an example - 'demonstrated up to 9,800... see performance for maximum weight'. This should be interpreted that at the maximum weight for that altitude for hovering (in ground effect or out of ground effect isn't clear from what was posted), that there will be sufficient yaw control up to those winds.
Now - how were the tests done? The tests for in ground effect would be done at the IGE hover height, in absolutely calm winds using a pace truck to generate 17 knots of side / rear wind.
So - out in the real world, in a mountain meadow, how would you know what the real wind speed is?
Assuming you did know the wind, when did you ever see a steady wind of 17 knots?
Would you hover at the flight manual IGE hover height in that much wind, or would you hover higher?
Now- what's the definition of 'sufficient' yaw control that the FAA needs to have demonstrated? It means that at that side wind condition, you can generate a yaw rate- how much of a yaw rate you consider to be sufficient is a judgement call. Would that much control margin be enough in gusty conditions? Don't know, as we don't specify a gust spread for this condition.

All this points to the reason why this statement isn't really shown as a limitation- it can't be a hard limit because of the impossibility of respecting it.

Hope that clears things up slightly.
Shawn

[Ascend Charlie]

The owner shut you down on the windy day for a good reason.

You won't always be able to shoot your approach into wind to your final parking position. You will probably have to hover-taxy some distance and turn around to get onto the pad. If the wind is too strong, you would have to taxy backwards around the airfield - not a good idea? Specially passing between other parked aircraft.

[Whirlybird]

All possibly true. But on that particular day, I had hover-taxied from the far end of the airfield, downwind, with no obvious problems....can't remember why at this point. But yes, that might not have been possible had it got even windier, and better safe than sorry.

[fdr]

wind limits

FAR 27.143 Controllability and maneuverability.
(a) The rotorcraft must be safely controllable and maneuverable—
(1) During steady flight; and
(2) During any maneuver appropriate to the type, including—
(i) Takeoff;
(ii) Climb;
(iii) Level flight;
(iv) Turning flight;
(v) Glide;
(vi) Landing (power on and power off); and
(vii) Recovery to power-on flight from a balked autorotative approach.
(b) The margin of cyclic control must allow satisfactory roll and pitch control at VNE with—
(1) Critical weight;
(2) Critical center of gravity;
(3) Critical rotor r.p.m.; and
(4) Power off (except for helicopters demonstrating compliance with paragraph (e) of this section) and power on.
(c) A wind velocity of not less than 17 knots must be established in which the rotorcraft can be operated without loss of control on or near the ground in any maneuver appropriate to the type (such as crosswind takeoffs, sideward flight, and rearward flight), with—
(1) Critical weight;
(2) Critical center of gravity;
(3) Critical rotor r.p.m.; and
(4) Altitude, from standard sea level conditions to the maximum altitude capability of the rotorcraft or 7,000 feet, whichever is less.
(d) The rotorcraft, after (1) failure of one engine in the case of multiengine rotorcraft that meet Transport Category A engine isolation requirements, or (2) complete engine failure in the case of other rotorcraft, must be controllable over the range of speeds and altitudes for which certification is requested when such power failure occurs with maximum continuous power and critical weight. No corrective action time delay for any condition following power failure may be less than—
(i) For the cruise condition, one second, or normal pilot reaction time (whichever is greater); and
(ii) For any other condition, normal pilot reaction time.
(e) For helicopters for which a VNE (power-off) is established under §27.1505(c), compliance must be demonstrated with the following requirements with critical weight, critical center of gravity, and critical rotor r.p.m.:
(1) The helicopter must be safely slowed to VNE (power-off), without exceptional pilot skill, after the last operating engine is made inoperative at power-on VNE.
(2) At a speed of 1.1 VNE (power-off), the margin of cyclic control must allow satisfactory roll and pitch control with power off.
according to the factory, the margin of cyclic (and pedal) used was 3/4" during testing. As Shaun rightly points out, the wind are demonstration values and not limits, however SFAR73 limitations are rational for the training environment. Better to be wishing to be flying than wishing to not be flying.
regards to the guys down the road at the pumpkin patch/mercy14

[oldbeefer]

Originally Posted by Whirlybird

I can't think of any reason for a wind limit....unless the wind was so abnormally strong that it would blow the helicopter apart or you'd get retreating blade stall in normal flight! I've flown the R22 in 40kt winds before; it's not fun, but it's OK.

Why on earth would the strength of the wind cause you to get retreating blade stall? Once airborne, the strength of the wind is irrelevant (apart from the turbulence it produces) as you are moving with the wind!

[FullTravelFree]

rebirth of an old thread....

....to ask this question:

A few years ago I've seen an old FAA circular or recommendation
on wind speed limitations for R44.

Now I can't find it back, does anyone know where to find this document?

Thanks in advance!

FTF