Operating in high winds??
 

Was shown a technique today to stop the Disc rapidly during high winds using the power pedal to slow things down.

Does anyone use this technique regularly and if so what reprocussions may it have on the airframe if any?

Does anyone have any other techniques,save for shutting down in a hangar?

Regards

Ralph:confused:

Using the pedal sets my tech's teeth on edge. He says it casues the TR to teeter and slam. Anyhow, at works less well as the rotor slows into rotor brake range.
I only do it when the rotor's autorotating after shutdown and won't slow into normal brake range.

My experience has mostly been on Bell Products without Rotor Brakes. And Most in the Military. Crew Chiefs used to say dont do it as its hard on Bearings etc., never did find the right answer.

This is definitely a Nick, Lou or Shawn Question.

B47 engineer (and the manual.....I think?) said that you could use one third of the pedal travel to slow the rotor. Worked nicely and made noticeable difference in slow down.

B206 Manual says nothing of the sort and the engineers don't like it at all.

Bell blames *all* the 407 tailboom problems on this. Of course, they have to blame them on something other than inadequate engineering. We keep a crew of sheetmetal repairmen busy repairing the cracks.

I don't like using it. That's what the rotor brake is for, and if you don't have one, then you should just wait for the blades to stop on their own. Of course, in some circumstances they will never stop. I've had the blades start turning on their own after being stopped by the old Bell system that had the rotor brake using the aircraft hydraulics system. After the transmission stopped, or even slowed considerably, there was no more brake, and no way to stop the blades on a small offshore platform. I can say that the t/r pedals won't help in this situation.

Thanks for the replies,
I understand that it is preferable to let the rotors stop themselves, but what do you guys do in strong winds.....ie 40kts without a rotor brake???

Ralph

Ralph - the technique is only effective at High NR and the whole point of stopping the rotor quickly is to avoid blade sail which occurs at low Nr. You are far better off using a normal shutdown technique trying to keep the disc as level as possible with cyclic.

Use the rotor brake a little more aggressively if you need to and shutdown with the wind in the 1 or 11 o'clock (depending on rotor direction of rotation) so any flapback puts the low point offset from the tailboom.

As for using the hanger, it trashes the inside of the hanger and the engineers will hate you for it so you had better have a really good reason to do it. Trying to hide behind a hanger in its lee can make things worse as the wind will gust and the turbulence can give you more bladesail problems than in the open.

In the end, your rotor starting and stopping limits are there for a good reason so going flying when you know it will be out of limits for the shutdown is not so smart.

As crab@ says, it's all to do with the blade sail at low Nr.

Windspeed limits are there for that reason, so if you get caught out there is little you can do.
Would you be prepared to lift up on the collective a little to slow the blades down? ....thought not.

If you have the fuel and the patience in that situation, one could always wait for the wind to die down, however as in this example in the Falklands, theres only a finite time you can stay at FI before you turn everything off, apply the rotor brake and close your eyes :ugh:

http://www.helicopterservice.com.au/...indy%20day.jpg

Blade strike caused by the blade sailing during shut down.

Aerodynamic braking
 

Aerodynamic braking should always be avoided.

As the rotor slows down the relative impact of wind and wind gusts becomes bigger (v gust stays, v tip decreases) : the perturbation to a rotor is greater because the disturbance forces remain while the rotor gets less stiff.

It should be clear to any one that tried it, that aerodynamic braking of the MR creates extra flapping. Exactly the same principles apply for the TR.

The greater the angle of attack the greater the disturbance, the greater the flapping, the greater the risk of a strike

An extra caution is that: as the system is slowing down the resonance characteristics change (the fase lags in the rotors) so points of max. flap need not be at the same angle as at nominal rotor speed.

Besides the risk of strike, the flapping also (over)loads the system.

The power the TR can give as a brake is further more quite limited as soon as RPM is below say 70%.

If left with no choice I would:

- use maximal rotor brake, even if I had to prepare a fire exstiguisher so to speak because of risk of overheated brakes. Dont start braking too soon because this is a waste of potential. And report this for inspection, it looks to me as the lesser evil.
- look for a good shelter : Vortices or gusts create an extra danger. Buildings can indeed be dangereous because they create strong vortices, natural protection such as trees (tree lines) can have less vortices (unless it storms and you have branches flying around..).

d3

Many thanks for all the posts........surely food for thought!

Adds a different spin on what I would usually just take for granted when being taught new techniques.

cheers

Ralph

This one has been weighing on my mind. Essentially, I come back to don't intentionally operate in "high winds" if you don't have a rotor brake.

There have been numerous instances of helicopters that were shut down and still the NR turned up in storm winds, disastrously. Adding in the times I've waited, seemingly forever, for the blades to slow to brake application speeds, and the times I've prayed that the uncontrollable, randomly flapping blades would stop before they hit something expensive- and I don't think it's a good idea. There's no way to control the blades once they're to slow for aerodynamics.
Yes, you could get lucky once- or perhaps several times- by keeping the disk absolutely edge on to the wind, but the first random bounce will put your job on the line- will it hit something this time? It will eventually.
never worked for anybody cheap- I mean, more economical, than PHI- and 100% of their birds had rotor brakes. We routinely operated in 40 knot winds and occasionally even higher winds, and mishaps were rare- 1 a year, GOM wide, seemed to be a typical. Blade flapping can be hazardous, no matter how you're equipped.

If operating the helo is important, even with significant winds (greater than 15 knots, my estimation)- the proposed operation justifies the expense of a rotor brake.

Flew in a R22 from EGNH when wind was 28knts from the west, Cfi who was with me showed me how to start up in high wind, and after about 45 mins of various ground manuveres I was shown to land as Crab has suggested at either 11 or 1 Oclock to the wind, shut down as normal and then apply brake as hard as I felt able, without breaking the thing, was a little hairy but gave me a lot of confidence.

Incidently on that day the strength of the wind allowed me to hover at about 35 ft with two people at 15/16" MP, quite impressive just how much help the wind gave to that little R22 when earlier it had been trying to stop me flying!

Vfr

Operating in a semi-windy environment (av15-35kts) where every landing is crosswind, I have found that using pedal to slow the rotor in a crosswind is not at all harmfull if you use the same pedal as the wind direction. ie, if the wind is from the right, put in right pedal and vice versa for left. This reduces the wind effect on the taill rotor and has no detrimental effect on bearings etc. as the tail rotor is completely unloaded. Into wind I guess you just have to let it slow down when it's ready. Don't know, forgotten how to do it

VFRPILOTPB. Sustained winds may allow you to get away with that stuff for a while. Get a gust coming across while doing it and maybe you can make the R22 shorter than necessary by a tailboom strike.
Its not nice to mess with Mother Nature............

Hovering an R22 at 35 feet - even in a high wind. Wouldn't want to be you if the donk stopped!!

About the tail rotor?
 

I ask this question because I want to know.

What damage could be caused by using left pedal to slow the rotor system? It's applying the same load to the transmission and bearings as it does in normal flight (unless there is something detrimental about having the MR ring driving the TR driveshaft).

I see that once the MR and TR have slowed to about 50% RPM, you want to reduce pitch on the TR to reduce flapping.

What am I missing?