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Elec generators


Oldfox
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Isn't that what the emergency hydraulic accumulator is for? I thought flight controls were mechanically linked to the rotor blades with hydraulic augmentation. Flight controls should respond. From all I have read, normal flight characteristics are expected during autorotation, except of course the yaw to the left and the fact that you have no torque. Rotor RPM needs to be maintained by diving. Sinkrate is minimized by maintaining aerodynamic trim.
Hydraulic or power failure is not mentioned anywhere near the dual engine failure in the TM. In fact it says that hydraulic pressure is enough to allow for 6 minutes of flight with no control inputs or 30 seconds with ridiculous inputs (cycling flight controls to full deflection left and right every second), which should be avoided.
That's why I was so irritated by the current implementation. Glad to hear it's WIP.
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I just found this section

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Failure of both primary and secondary drives to the accessory gearbox would result in the complete loss of all AC power and the failure of both the Primary Hydraulic System and the Utility Hydraulic System. All electrical systems, sights, communications,and lighting equipment not powered by the emergency bus would be lost. The crew must activate the Emergency Hydraulics and land without delay.

and

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Immediate emergency action must follow failure of both hydraulic systems.
Any hesitation could result in loss of helicopter control.

 


Edited by FalcoGer
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On 3/30/2022 at 5:24 AM, FalcoGer said:

Isn't that what the emergency hydraulic accumulator is for? I thought flight controls were mechanically linked to the rotor blades with hydraulic augmentation. Flight controls should respond. From all I have read, normal flight characteristics are expected during autorotation, except of course the yaw to the left and the fact that you have no torque. Rotor RPM needs to be maintained by diving. Sinkrate is minimized by maintaining aerodynamic trim.

Hydraulic or power failure is not mentioned anywhere near the dual engine failure in the TM. In fact it says that hydraulic pressure is enough to allow for 6 minutes of flight with no control inputs or 30 seconds with ridiculous inputs (cycling flight controls to full deflection left and right every second), which should be avoided.

No, the accumulator is there in the event of a loss of all hydraulic power in the helicopter. It has nothing to do with autorotations, the reason being that so long as you have NR, the generators and hydraulic pumps are running. That system was never intended to be use outside of a dual hydraulics failure, and it only provides you with a few tens of seconds worth of controllability before it locks up anyway. In general if you’ve reached the point where the generators cut out in an auto, you’re essentially dead. Unless you get very lucky the likelihood of you recovering the rotor is next to none. 


Edited by bradmick
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@FalcoGer remember the talk we had? Where you assuming how things worked without asking doesn’t necessarily workout. 

 

@Crysinator no, the accumulator will not save you in the event of an auto. It also doesn’t automatically engage. The only thing that will save you is by managing your nr appropriately in the auto. If you lose so much of your rotor that hydraulics drop you probably will never get your rotor back just due to how the air is working on the blades. There’s a point of no return and you’ve hit well below it. 


Edited by kgillers3
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2 hours ago, TheCrysinator said:

That's why I was so irritated by the current implementation. Glad to hear it's WIP.

Based on what bradmick's said it's likely excessive rotor drag that's the only thing wrong. So while the speed at which rotor RPM drops may reduce, the result of you letting it drop will not. Therefore you shouldn't concern yourself about losing power/hydraulics - it's a red herring.

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Based on what bradmick's said it's likely excessive rotor drag that's the only thing wrong. So while the speed at which rotor RPM drops may reduce, the result of you letting it drop will not. Therefore you shouldn't concern yourself about losing power/hydraulics - it's a red herring.
I manage to "catch" it at around 86% RPM consistently with a realistic reaction time. As bradmick confirmed you should be able to recover RPM and that's currently not the case. My problem was that low RPM with no feasible way of recovering some leaves you with no headroom at all.
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8 minutes ago, TheCrysinator said:

I manage to "catch" it at around 86% RPM consistently with a realistic reaction time. As bradmick confirmed you should be able to recover RPM and that's currently not the case. My problem was that low RPM with no feasible way of recovering some leaves you with no headroom at all.

It is possible to recover if you load the rotor by pulling back on the cyclic. Not easy though (especially if you're trimmed forward) I'll give you that.

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I was looking for electrical generator disconnect conditions. The only one I could find was a >1s while in the flight condition below a certain RPM. Depending which part of the system the generator is on (probably rotor side) that would tie the fate of the generator power to rotor RPM. Hydraulics I don't know if they are on engine or rotor side but traditionally hydraulic pumps are quite non-linear (lose 10% RPM lose half power type behavior).

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  • ED Team
6 hours ago, Frederf said:

I was looking for electrical generator disconnect conditions. The only one I could find was a >1s while in the flight condition below a certain RPM. Depending which part of the system the generator is on (probably rotor side) that would tie the fate of the generator power to rotor RPM. Hydraulics I don't know if they are on engine or rotor side but traditionally hydraulic pumps are quite non-linear (lose 10% RPM lose half power type behavior).

The generators and hydraulic pumps are all mounted to the accessory gearbox of the transmission. The only two things that can power the accessory gearbox on the AH-64 is the main transmission or the APU shaft.

Using transmission rotation for hydraulics and generators is a common thing in helicopters so that you don't lose such functions due to engine malfunctions. Imagine trying to do an autorotation without either.

Afterburners are for wussies...hang around the battlefield and dodge tracers like a man.
DCS Rotor-Head

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Assuming the generator produces 400Hz naturally and disconnects under 306 Hz that's 76.5%. I'm a little confused that it says under freq protection doesn't work in flight but then describes the flight under frequency protection limits. The other is <100Vac (normal 115) but that doesn't function if under freq protection is which it wouldn't be (unless it is). If potential vs speed is linear (looks like other generators are about so) that would be 87% which is roughly what the ground under freq ratio is.

I don't see any particular requirement for electrical power to operate the flight controls. Aerodynamic and hydraulic RPM relationships would be my primary and secondary concerns.

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12 hours ago, Frederf said:

... traditionally hydraulic pumps are quite non-linear (lose 10% RPM lose half power type behavior).

Not in power hydraulic systems they're not - they're always (at least I'm yet to encounter an exception) positive displacement. Aircraft usually use piston pumps too, which vary volume to provide constant pressure, meaning pump output can compensate for changes in RPM (within reason).

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