Good afternoon to all PPRuNe Rotorhead readers and posters. I have more thoughts to add to this thread concerning the satisfactory entry to a real autorotation.
It is obvious that many pilots understand the real picture of what will happen if cyclic is not brought back almost instantly when a total-surprise engine or drive-line failure happens.
The problem is the definition of “instantly.” I put it this way: When something happens to your helicopter that you did not purposely initiate, do two things as quickly as you can. 1. Start the cyclic moving aft, and 2. Start the collective (or “lever” as I'm learning to say on this forum!) down towards the bottom. This must be a gut reaction, not a thought-out move on the pilot's part. DON'T take time to troubleshoot the situation before moving the flight controls.
One can take any procedure and find faults with it. Is Cyclic Back needed every time no matter what the mode of flight? Of course not. Hovering or making a low-power descent are two examples. But I'll put it this way: Whatever prompts you to quickly bottom the collective lever in an emergency, real or otherwise, must cause you to apply aft cyclic simultaneously when in forward flight, especially in a climb or cruise configuration.
Do you fly anything powered by the excellent PT-6 Twin-Pac? Take a flight in a sim and ask the operator to fail the one-and-only drive shaft by surprise during powered flight. Unless you apply aft cyclic “right now,” you will probably crash and burn. How do you prevent this? Cyclic Back!
A serious yaw? Big upset? Loud noise? Sounds you've never heard before in powered flight? Applying aft cyclic and lowering the lever will not cause you any problems. AFTER you've done this is the time to try and figure out what has happened. Have you lost the power plant? Do you still have yaw control? Check the panel. Is something wrong? Warning lights on? Horns blowing? SIC screaming? Or did you just dream this...
Dick Sanford, thank you for joining this thread and applying energy management to Cyclic Back. I am going to use your example of trading airframe velocity for rotor rpm. You are so right. For years we've been teaching the three sources of energy available to the pilot when energy from the engine is no longer available, trading energy back and forth as needed, but I've never included your simple explanation in what I've written and lectured about concerning Cyclic Back.
And Shawn Coyle, I thank you too for joining this thread. How often I dream that I could have the knowledge, skills and background that you and Dick have.
I extend my most sincere thanks to every poster who supports Cyclic Back or who is at least open to learning about it. To those readers who have the “My mind is made up; don't concern me with the facts...”, or “Secret? What secret? Everyone in the world of helicopters knows all about this, Pete, and you don't know what you are talking about...” Well, I hope you'll reconsider and come on board with this before you find yourself in a situation where you wish you'd brought the cyclic back more quickly.
Two more things: Probably more than half of my career has been spent flying well within the H/V curve. I've been lucky and never had a mechanical problem while doing this. But those of you who have practiced and demonstrated hover autos initiated from within the H/V curve, in turbine-powered helicopters, have not seen a situation involving REAL engine or drive-line failures.
Several posters have made this point. Try this: Hover at 250 feet agl and have your SIC flame out the engine while you are looking out the window. Now let's see what happens! Even chopping the throttle to idle is a lie. No matter how rapidly you or your SIC “chops” the throttle, the fuel control is in charge of how rapidly the engine heads towards flight idle. The best example is the very popular Allison/Rolls-Royce C20 series found in so many makes and models of helicopters. Wonderful engines. I've trusted them for years and never been disappointed.
Do a hover auto in a JetRanger or 500. Watch the dual tach. Notice something? The needles never split! The fuel control dials down N1 rpm at a rate that will not cause the engine to flame out or compressor-stall. YOU don't control this; the fuel control does.
Each make and model of turbine engine has its own rate of deceleration to idle when the throttle is chopped. The C28/C30 engines used in the 530FFs and LongRangers L-1 through L-4 drop much more quickly to idle, and a needle split usually occurs, but the idling engine power is over 40 horsepower to make the pitch pull look so easy... Same for AS350Bs/Squirrels.
And when you pull pitch...er,the lever...just before ground contact, you are benefiting from the 35 horsepower the C20 series will give you at that time! Do you doubt that? Check your Rolls-Royce technical publications. Look under “Horsepower available at idle.” See the number 35?
How about in the wonderful Huey? Same thing. Could you use over 80 horsepower to make you look so good when pulling pitch at the bottom? Sure you could. And the result makes you look like a super pilot...with a bit of credit given to the “high inertia” rotor system. And for you “Hook” drivers, each of your engines will put out about 300 horsepower at idle. See where I'm going with this?
No, if you want to see just how little time and rotor energy are available to you when the drive shaft fails or the engine(s) flame out, list me on your insurance and then find someone who will flame the engine(s) out OGE when your eyes and mind are elsewhere. This is the real world.
Every “contact” maneuver, whether a practice EOL (see? I'm catching on, guys!) at the end of a normal or hover auto benefits from the idling horsepower from the turbine. This is the same power that makes the rotor blades move at idle! It's always there, making the pilot and the rotor system look good when doing these training maneuvers.
By the way, several posters mentioned situations where the pilot does not have his left hand on the collective. This is true and getting truer as our cockpits demand more and more heads-down attention from the pilot. Lots of things to do with your left hand; frequencies to change, waypoints to insert, switches to switch, and on and on. It's beginning to look like a Space Shuttle cockpit. Except when on autopilot, most of us keep one hand or the other on or very near the cyclic. The collective requires very little attention unless power changes are being made. It is, after all, simply the thrust control, right? In a turboprop airplane it would be called the Beta control (prop pitch control). So it is very common to not have one's left hand on the collective at all times. Here we go; Cyclic Back, and THEN find and lower the lever...er, collective.
A few days ago I was thinking I'd made a big mistake in wanting to share Cyclic Back with my fellow professional pilots on PPRuNe. The snarky remarks were beginning to grind on me. But those of you who echo my thoughts or who have at least been willing to consider them have given me the confidence and support to stick with it. For this I thank all of you.
Pete Gillies