The Scariest Helicopter Ever
on youtube
,Single pilot
, cruise 180 mph,,,,
Scariest
Some may refer to it as a Zeppelin, but the Piasecki Helistsat looked scary to me from the outset. One day the phone rang in the SA pilots office and the pilot who had hired on to fly it wanted to talk to anyone. He got connected to the pilot in our office who was our strongest in the area of structures/ dynamics ( a former USMC aviator with an Engr MS in that area who came to us from SA Engr Dept. ). The caller was given a whole list of things to look into. Later events seemed to say that some basics were missed. I say that based on the published info which said the landing gear wheels started to shimmy, which then kicked off a mechanical stability ( ground resonance ) situation. With all of the military history of that subject, on that machine, the V-leg gear vs the Straight-legged gear etc, one would have thought that the importance of the landing gear would naturally have been a primary design issue.
HelistatGear
That was my point, Hillberg. Instead of the normal landing gear, which incorporates a damper, the Helistat was hard mounted on wheels. The S-58 landing gear is a part of the mechanical instability attenuating system, along with the main rotor dampers. Sometimes the onset of that sort of instability is exceedingly rapid, so that just retarding the throttles and applying a rotor break simply takes too long, leaving the alternative of grabbing a handful of collective and applying it NOW is the only salvation. My recollection of the accident footage showed a fairly slow attempt to lift to hover, but structural failure had already commenced.
I wonder how it would have worked if they had used old H-25 Airframes instead of the H-34's? I have never heard any discussion about the H-25's having a ground resonance problem.
That video does make one wonder about the level and quality of engineering that went into the design.
That video does make one wonder about the level and quality of engineering that went into the design.
HUP vs S-58
Main reason for using S-58 vs HUP would be power: 1525 vs 550. I believe the HUP head was articulated, so the 2/3P inherent in the rotor was there. I don't know anyone to ask! Took a look at the video clip and one can see that the rotors are wobbling at a fairly low frequency but at " scary " ( sorry, couldn't resist ) amplitudes. Nobody around to report on whether they did a shake test on the frame to look for natural frequencies, and the other thing that comes to mind is that the 2/3P is a wobble, i.e., a combined pitch/roll excursion, which would transmit accompanying high oscillatory loads into the frame structure that it may/may not have been designed to take. The rotor is at high thrust in the clip, so the thrust is high, thus the oscillatory loads were high.
Last edited by JohnDixson; 10th Dec 2012 at 15:38. Reason: typos
You are a Test Pilot Brother Dixson.....would you have flown that thing? Did each H-34 have a Pilot....and if so....how would you coordinate control of the machine?
An interesting link.....
Piasecki "Heli-Stat" helicopter - development history, photos, technical data
An interesting link.....
Piasecki "Heli-Stat" helicopter - development history, photos, technical data
Last edited by SASless; 10th Dec 2012 at 19:02.
Helistat
SAS, the answer is no, with the information I had at the time, which was only that passed along by the Helistat pilot in the conversation reported in the earlier post.
You asked another question which pointed to discussion we had internally after that phone call. Specifically, it was our understanding that one pilot would fly the machine, thru interconnected controls. After the accident, it was reported that the four vehicles were manned. Perhaps those personnel were there to operate the engine and other basic S-58 systems? In any case the control runs were very long, and control slop and hysteresis, effects of frame structure deflection, statically and dynamically and a raft of related questions seemed to be open, again just our conclusion based on the phone call.
You may recall the CH-54 Twin Lift project, wherein the lifting power of two CH-54B's would be gained by utilizing a balance beam structure, the ends of which each of the two Cranes would pick up with their cargo hooks, after reeling out 50 ft or so of cable. While we did that manually, using the back seat controls, the plan was to link the two AFCS systems and couple up the control systems. We did one real flight with a load of 35,000 lbs, but it never went anywhere, as I believe that everyone realized that it was just too tricky to do on a regular basis in a tactical environment. I know that following that program, from time to time someone would ask me what I knew about twin lift, and I would plead absolute ingorance.
You asked another question which pointed to discussion we had internally after that phone call. Specifically, it was our understanding that one pilot would fly the machine, thru interconnected controls. After the accident, it was reported that the four vehicles were manned. Perhaps those personnel were there to operate the engine and other basic S-58 systems? In any case the control runs were very long, and control slop and hysteresis, effects of frame structure deflection, statically and dynamically and a raft of related questions seemed to be open, again just our conclusion based on the phone call.
You may recall the CH-54 Twin Lift project, wherein the lifting power of two CH-54B's would be gained by utilizing a balance beam structure, the ends of which each of the two Cranes would pick up with their cargo hooks, after reeling out 50 ft or so of cable. While we did that manually, using the back seat controls, the plan was to link the two AFCS systems and couple up the control systems. We did one real flight with a load of 35,000 lbs, but it never went anywhere, as I believe that everyone realized that it was just too tricky to do on a regular basis in a tactical environment. I know that following that program, from time to time someone would ask me what I knew about twin lift, and I would plead absolute ingorance.
from time to time someone would ask me what I knew about twin lift, and I would plead absolute ingorance.
As one Inspector Callahan once said....."A Man must know his own Limitations!".
Dangerous Helicopters
Avoid imitations
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At the opposite end of the scale to the R22 and still scary....
Wider than a 747. Too big for its own good.
Wider than a 747. Too big for its own good.
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As a fixed wing boy with only 2 hours on helicopters I think if had engines that were doing that i would jump out and run away to get the fire brigade and not get anywhere near it ever again
My scariest helo: Wasp. Balsa wood tail rotor blades, bicycle chain used to alter the pitch rod. Engine with a power output of a lawn mower.
Undercarriage wheels canted outwards to act as brakes on landing. [And we all pracitced EOL's to running landings].
Undercarriage wheels canted outwards to act as brakes on landing. [And we all pracitced EOL's to running landings].
Last edited by Thomas coupling; 28th Jan 2013 at 08:42.