complete hydraulic failure
Guest
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Lu,
You are certainly correct for some helicopters, possibly all Sikorsky ones. I flew the Whirlwind in full manual once and can confirm what you say about the feedback forces.
However, I believe some Aerospatiale designs are as I describe, depending on the configuration of the main servos and flying controls.
We are splitting hairs here as the outcome would be the same.
[This message has been edited by ShyTorque (edited 09 January 2001).]
You are certainly correct for some helicopters, possibly all Sikorsky ones. I flew the Whirlwind in full manual once and can confirm what you say about the feedback forces.
However, I believe some Aerospatiale designs are as I describe, depending on the configuration of the main servos and flying controls.
We are splitting hairs here as the outcome would be the same.
[This message has been edited by ShyTorque (edited 09 January 2001).]
Guest
Posts: n/a
To: Shy Torque
If what you say is true, then you would not be able to move the flight controls while on the ground unless the hydraulics were powered. On the newer Aerospatial helicopters as well as other helicopters that use elastomeric bearings moving the unpowered controls is difficult. But not incorporating bypass valves in the servos is like condemning the pilot and passengers to death if hydraulics fail. I don’t think the helicopters could be certified if that were true. Perchance your opinions stem from trying to move the controls with no hydraulics. What you interpret as the system being locked is the resistance of the elastomeric bearings.
I don't know for sure but it would seem that helicopters with elastomeric bearings should have dual hydraulics because of the stiffness problems. A helicopter with these bearings and with a single hydraulic system woud be extremely difficult if not impossible to control in the event of a total hydraulic failure.
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The Cat
[This message has been edited by Lu Zuckerman (edited 09 January 2001).]
If what you say is true, then you would not be able to move the flight controls while on the ground unless the hydraulics were powered. On the newer Aerospatial helicopters as well as other helicopters that use elastomeric bearings moving the unpowered controls is difficult. But not incorporating bypass valves in the servos is like condemning the pilot and passengers to death if hydraulics fail. I don’t think the helicopters could be certified if that were true. Perchance your opinions stem from trying to move the controls with no hydraulics. What you interpret as the system being locked is the resistance of the elastomeric bearings.
I don't know for sure but it would seem that helicopters with elastomeric bearings should have dual hydraulics because of the stiffness problems. A helicopter with these bearings and with a single hydraulic system woud be extremely difficult if not impossible to control in the event of a total hydraulic failure.
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The Cat
[This message has been edited by Lu Zuckerman (edited 09 January 2001).]
Guest
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Lu,
Yes, I have flown an aircraft where the controls could not be moved until the rotor rpm increased enough to power up the hydraulics. The military AS-330J is like this; it has a fully articulated head and no elastomerics.
This aircraft was originally designed and supplied with a disconnect in the No. 1 engine input, to allow the engine to run the No. 1 hydraulic system and No. 1 AC generator for ground servicing (these were / are primarily AC aircraft with the generators running off the main gearbox accessories). However, the "disconnect" facility was modded out of our fleet as they could slip in flight. I seem to remember if this happened the No.1 hydraulics and the No. 1 AC generator would go off line, but more importantly, the (only) MGB oil pump would stop as well, which took the shine off your day.
On these aircraft, if a single hydraulic failure occurred, the aircraft would be put down asap for obvious reasons. I spent a few occasions in fields waiting for hydraulic repairs during my time operating them.
However, it is academic only whether the cyclic becomes rigid or thrashes round the cockpit following a complete hydraulic failure. You cannot control the aircraft in either case. A joke we used to make was that in the unfortunate event of a total hydraulic failure the pilot's immediate actions would be to unstrap, drop trousers, sit on the cyclic. Just to give the BOI something to think about!
Another nasty problem with these aircraft was that if one of the two separate tail rotor servo control "pull" cables snapped, the servo would run to full travel the opposite way. This would result in either full positive or full negative T/R pitch, which rendered the aircraft uncontrollable in yaw. I know for sure that the RAF fleet flew like this for over twenty years but I understand they now have been modded with a centering device for the servo valve which gives some level of control, like later Sikorsky designs.
And then there was the engine response (Turmo 3C4) which was appalling from flight idle, due to the lack of a collective anticipator in the FCU design...
You are correct about the lack of certification for civilian use. There were many mods and additions to the civil version.
Edit: If we are going to continue discussing this we perhaps ought to start a new thread on Rotorheads as I feel we have diverted from Purplehaze's original line of discussion. Sorry, PH!
[This message has been edited by ShyTorque (edited 09 January 2001).]
Yes, I have flown an aircraft where the controls could not be moved until the rotor rpm increased enough to power up the hydraulics. The military AS-330J is like this; it has a fully articulated head and no elastomerics.
This aircraft was originally designed and supplied with a disconnect in the No. 1 engine input, to allow the engine to run the No. 1 hydraulic system and No. 1 AC generator for ground servicing (these were / are primarily AC aircraft with the generators running off the main gearbox accessories). However, the "disconnect" facility was modded out of our fleet as they could slip in flight. I seem to remember if this happened the No.1 hydraulics and the No. 1 AC generator would go off line, but more importantly, the (only) MGB oil pump would stop as well, which took the shine off your day.
On these aircraft, if a single hydraulic failure occurred, the aircraft would be put down asap for obvious reasons. I spent a few occasions in fields waiting for hydraulic repairs during my time operating them.
However, it is academic only whether the cyclic becomes rigid or thrashes round the cockpit following a complete hydraulic failure. You cannot control the aircraft in either case. A joke we used to make was that in the unfortunate event of a total hydraulic failure the pilot's immediate actions would be to unstrap, drop trousers, sit on the cyclic. Just to give the BOI something to think about!
Another nasty problem with these aircraft was that if one of the two separate tail rotor servo control "pull" cables snapped, the servo would run to full travel the opposite way. This would result in either full positive or full negative T/R pitch, which rendered the aircraft uncontrollable in yaw. I know for sure that the RAF fleet flew like this for over twenty years but I understand they now have been modded with a centering device for the servo valve which gives some level of control, like later Sikorsky designs.
And then there was the engine response (Turmo 3C4) which was appalling from flight idle, due to the lack of a collective anticipator in the FCU design...
You are correct about the lack of certification for civilian use. There were many mods and additions to the civil version.
Edit: If we are going to continue discussing this we perhaps ought to start a new thread on Rotorheads as I feel we have diverted from Purplehaze's original line of discussion. Sorry, PH!
[This message has been edited by ShyTorque (edited 09 January 2001).]
Guest
Posts: n/a
Speaking from limited experience(compared to some of you here) the UH1H flew just fine with out hydraulics. You just had to learn to relax a bit and not to turn on the hydraulics back (close to the ground)or in the case of a actual failure, turn them off as a precaution against getting them restored close to the ground without input from the pilot. The UH1 has one system. The civilian varient the B205 has 2 systems. The UH1N and BH212/412 both has 2 systems but would fly fime without any, with practice of course. The MD500/530 did fine without hydraulics. The BO105 had a rigid rotor so you needed one to fly ALL THE TIME but it had two, very reliable and safe.The AS350 uses a starflex rotor head(composite) and accumulators incase of hydraulic failure. The UH60 Blackhawk had 3 systems. Two mains driven off of the transmission and one electric(all 3 identical pumps) Would fly just fine with just one. But you had to have one, or else. You could fly with the pilot assist(boost off but you needed to practice, like all things.
hope this helps
j
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Here's to cheating, stealing, fighting, and drinking.
If you cheat, may you cheat death.
If you steal, may you steal a woman's heart.
If you fight, may you fight for a brother.
And if you drink, may you drink with me.
[This message has been edited by before landing check list (edited 10 January 2001).]
hope this helps
j
------------------
Here's to cheating, stealing, fighting, and drinking.
If you cheat, may you cheat death.
If you steal, may you steal a woman's heart.
If you fight, may you fight for a brother.
And if you drink, may you drink with me.
[This message has been edited by before landing check list (edited 10 January 2001).]
