P51 Mustang wrote:
Quote:
OscarDuce: I wasn't there for the briefing, I can only assume some fixed wing guy gave it since I don't think they understood the danger.
Why do you think MODERN helicopters have turbine engines? They are at least 1 million times more reliable than piston engines.
Helicopters have a height/velocity diagram, in some it is on the panel or where the pilot can see it to remind him when he is doing something wrong. It set parameters of altitude and airspeed where you can accomplish a successful autorotation. Usually at ZERO airspeed, you need be lower than 10' or higher than 500'. If you are moving, you can only go at certain airspeeds and be able to recover. Example, 100Kts at 10' and an engine failure and you will be on the ground before you know it happened. 100Kts at 300 feet may be safe, or anything greater than 30 or so kts at that altitude.
You see fixed wing aircraft vs rotary wing aircraft, there is a difference. ITs the fact that fixed wing pilots don't need to keep their wings moving (rotating) to keep them as wings. When rotor RPM drops below a certain level, the rotor arc (which is your wing) stops functioning as a wing and you fall like a rock. At that point rotor RPM cannot be recovered by any little tricks you know.
That CH-34 was hovering at about 20' or so. If you hover at a safer (but still not safe) altitude of 10' you get even less time to get out of the way if the engine quits, but the chopper may survive, but the guys under it are toast sinc ethey are going to egt even less warning and who in the crowd wants to see a 6' tall guy winched into a chopper hovering 4' over his head.
An engine failure, might give you 1 second's warning and no more than 3 seconds later you are on the ground. They must have hovered 5 minutes or longer. So what do you do on the ground? It takes you like 1 or 2 seconds to realize that there was an engine failure and a 5 ton piece of the sky is falling 20' on to you. So do you screw up the show and RUN FOR YOUR LIFE (maybe it wasn't a failure and you'd look like a fool), or what? Which way do you run? And how fast can you get the 25' or so it takes to get out of the rotor arc (without considering that the chopper may have moved a few feet in the direction you are running). When it hits the ground the blades make a BIG MESS (watch assorted YOUTUBE videos on it) and pieces fly off that will kill you. COunt on at least 150' to 200' as a danger zone for flying parts
They are simulating a RESCUE which is done in an EMERGENCY. This isn't an emergency by a long shot. What if there is what we refer to as a "dope on a rope" (guy hanging off the helicopter) when it happens, what is he going to do? He is really dead meat.
Also helicopters do something called "vortex ring state" or "settling with power". Basically in a nutshell you get sucked into your own downwash and the blades start to stall. This happens when you are hovering or moving at slow speeds (in the air) and generally descending. Sometimes a windshift can make all the difference, even a few knots of wind, can blow the turbulent air back under you. (it makes a heck of difference in tailpipe temp when you start or shutdown a turbine based on the wind direction (ie wind "blowing" hot exhaust "back" into the engine, makes a warmer start))
The natural reaction is to add more power to climb, but it only makes the turbulance worse that is causing the blades to stall. The only recovery is to reduce power and fly forward (or anyother direction) out of the column of turbulent air (look for a youtube video of a Canadian Sea King Helicopter crashing at an airshow, straight down from a hover). To avoid that, you fly faster than ETL (effective translational lift) or about 15kts and don't do any fast desecents. (I've been in this one once and its scarrier than anything you can do in an airplane).
If we had settling with power happen, the guys on the ground would not have had the engine sound change as a warning to run. I didn't see how far they were away from the crowd where I was at, but I can say it was close enough that to recover he would ahve had to overfly the crowd at an altitude lower than the snowfence which would means he would have had another chopper problem (DYNAMIC ROLLOVER) along with probably hitting some people in the crowd.
THe big problem with settling with power is the pilot and I'm sure he's a good guy and very experienced. But if you feel you are settling, you need to react NOW, not wait a second to be sure thats whats going on so you don't screw up the show. The would probably be a tendency to delay a second or two to be sure that we had a settling problem. I would hope not.
Dynamic rollover is a something we have seen in the helicopter tows the boat video. The Idiot (er a PILOT) attached some thing to the side of the chopper that put an assymetic force on it. It works like this.
Static (blades not turning), you need to tilt a chopper 60 degrees to make it roll over just like a crowd of drunks tipping a car over. Once it is dynamic (blades spinning) it becomes like a toy gyroscope, a few degrees of movement means it KEEPS moving and tips over. Say 5 to 7 degrees, hence when you land, you ALWAYS land on something very level. So if you have a skid that sticks in mud or hot asphalt, and you pull power and take off, you are going over. That boat was tied to the side of the chopper, not the cargo hook on the centerline and the drag from the boat started it rolling and over it went.
If the CH-34 in recovering from settling with power caught a wheel on the snowfence in front of the crowd, it would go over like it was tripped, into the crowd.
Last, even if the pilot can make a successful autorotation from 20', he's going to hit hard enough that at a minimum the blades will flex down and hit the tail boom and come apart, and more than likely the inertia of the blades will cause it to rollover and then all kinds of parts are coming off.
So its not just an engine failure thats dangerous. An autorotation from the pattern is simple and pretty darn safe. One from 20' is pretty dangerous.
So I wasn't there. What was the briefing?
Was it? The CH-34 will hover and pick up 2 guy for 6 1/2 minutes maximum and then Snort will fly the P-51.
Or did they say? Guys on the ground if you hear the engine pitch change run like h311 or die, if you happen to be on the winch when it happens you are toast. If if settles with power (explain it) you are also dead without much warning. Crash crews if it settles and they try to recover, it might hit the fence and go into the crowd ..............
It would have been just as nice to see it fly around for a few minutes and do some of the kinds of things that only helicopters can do.
But they did it and it worked and they are probably going to keep on doing it until someday it doesn't work.
Fly safe
Mark H
What exactly was the point of this? Do you really think that anyone who has ever flown a helicopter is unaware of these basic elements of helicopter aerodynamics? Maybe not the best idea in the world, but far from the apocalyptic scenario you have painted in the post. We could write the same type horrible possible outcomes for many of the elements of every airshow performance, but what positive impact would that have?
Sorry, but the whole thing struck me as very condesending. I think the whole point could have been made in a much more polite/effective manner.
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He was happier on his 2nd tour flying CH-46s!
