Welcome Guest
HeliTorque
  
User Control Panel

Security Code: : Security Code
Type Security Code Here: :
 
Register Here
Lost Password?

Online Stats:
Visitors: 396
Members: 0
Total: 396

Membership:
New Today: 0
New Yesterday: 0
Registering: 0
Members: 6662
Latest: chrisw

Most Ever Online
Visitors: 546
Members: 0
Total: 546


Flying in the Wind

Story by Bill Reid, Photos by Ned Dawson

Page: 1/2

For those of you who didn't read the first installment, I began by discussing aircraft limitations and some general operating techniques, and offering tips for flying in strong wind conditions. In this part I will cover starting and stopping rotors in high winds, and securing the aircraft when gales are imminent.

Rotor Start

In researching this piece I couldn't find much helpful information in the rotorcraft flight manuals. It is almost as if were saying "go out and find out for yourself." That's not easy when I talked on the subject with different people. I've heard some wildly differing views. Obviously different types of helicopters require slightly different techniques, but I'd always been taught and was of the opinion that nose into wind was best. My friend Frank Gallagher, who has a lot of experience operating from ships, confirmed that this was standard operating procedure in the US Navy, where strong winds are the norm. One of the more radical views was from a senior flight instructor who advocates starting and stopping rotors with the helicopter parked downwind. He claims that using this method lessens the risk of blades flapping into the tailboom. I find this method difficult to comprehend, but several of his former students swear by it.

Pilots flying teetering rotor systems prefer to start in a crosswind, believing that the side wind lifts the advancing blade up over the tail, making it less likely to strike the tailboom. I can understand this to some degree, but surely with a fully articulated or semi-rigid rotor system, it would make the most sense to start rotor turn into wind with a little forward cyclic to help keep the helicopter on the ground. I have recently made a point of watching the blades during start up and shut down when facing into strong winds, and have found that at least on the AS350 and MD 500 the disc is actually at its highest over the tail, which is exactly where one would want it. There is actually more risk in front of the helicopter, from the blades flapping down and striking open doors, or some unsuspecting support person or passenger.

In a turbine helicopter, starting in more than 20 kts of wind, apart from any blade-flapping problem in a downwind start, you run the risk of a hot start caused by the wind blowing up your rear-facing exhaust pipe and causing back pressure. This problem was particularly bad in the Artouste engine of the Allouette IIIs and Lamas, but is a factor with most rear -facing exhausts. If you are forced to attempt a start in a downwind condition, it's good advice to get someone to hold a piece of cardboard, or preferably something not too flammable, a few inches away from the tail pipe, until the gas producer has passed through about 20 percent and ignition is achieved. Just make sure they hold on to it and not let it get blown up into the blades. When the downwind starting method was first mentioned to me I wondered whether these guys were talking about really windy conditions or slight wind conditions, because the thought of lifting off with a heavy load downwind, in a restricted area, in winds above 20-25kts frankly leaves me cold. If the passengers weren't already feeling sick from sucking in exhaust fumes they certainly wouldn't enjoy the shaky takeoff.

No matter which method you prefer, in blustery conditions it's best to have someone hang onto a blade tip for as long as permissible, even walking with it for a few paces to lift it over the tail so that you can get rapid blade acceleration. In some helicopter types it is permissible, even standard practice, to keep the rotor brake on for the start. Consult the flight manual or talk to your engineers as to how long you can hold the blades from turning without causing clutch, transmission or engine damage.

Shutting Down

Probably the greatest risk when operating in high winds is stopping your blades at the completion of your flight. Even aircraft fitted with rotor brakes run into problems in gusty conditions, as most have a relatively low maximum rotor revolutions-per-minute that the brake can be applied. Some brakes must also be released in the last revolution to prevent backlash. Smaller helicopters not fitted with brakes are particularly vulnerable to damage, and it is essential that the pilot continually monitors the disc until the blades are stopped. You should also make sure that the passengers or crew do not attempt to board or leave the helicopter at this crucial stage, as blades can easily flap below shoulder height.

The shutdown is more critical than the start, where the blades can be accelerated relatively quickly to a point where the disc has good rigidity. If it's blowing more than about 30 kts and your helicopter doesn't have a rotor brake, it can take several minutes to get the blades stopped after shutting down. You may have to reach up and slow the blades by hand, carefully putting a little pressure on the root of each blade as it goes past. Be extremely careful doing this, making sure you have no loose clothing that may be caught in pitch links, swashplates, etc.

When operating an MD500 when it's windy, I let the pedal-stop out as the blades slow through 300 rpm and allow the tail rotor to go to maximum pitch. This reduces the time to stop the blades by over a minute, and if you have a 4-bladed system the extra drag reduces the time even further. My engineer assures me that this does not stress the tail rotor in any way, even though the flight manual states you should hold the pedal in neutral until the blades have stopped. I guess that this practice would not be suitable on icy or slippery terrain, as you may run the risk of the helicopter yawing.




Next Page (2/2) Next Page


Sponsors


Billund Air Center

Visit HeliTorque!