XMSN coupled generators
Thread Starter
Joined: Jun 2004
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From: Europe
XMSN driven generators
I've been going through the JAR TR syllabus and stumbled across "generators and generator drives" in the transmission system chapter. I googled it and found that chinook has a transmission coupled generator.
Any other helicopters out there with that kind of generator drive?
Where is the catch of transmission driven generators? I always imagined a combined starter/generator unit. I've only flown light turbine helicopters up to 412 and this is a big "WTF-mate?" for my knowledge.
Any other helicopters out there with that kind of generator drive?
Where is the catch of transmission driven generators? I always imagined a combined starter/generator unit. I've only flown light turbine helicopters up to 412 and this is a big "WTF-mate?" for my knowledge.
Last edited by Phoinix; 29th August 2011 at 21:28.
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From: Inside the Industry
Many aircraft have DC starter generators on the engine or engine driven DC generators if they have a separate starter.
Most AC generators are Transmission driven, S-61, S-92, AS332 series and EC225. Not sure about the Chinook as I have never flown it.
Most AC generators are Transmission driven, S-61, S-92, AS332 series and EC225. Not sure about the Chinook as I have never flown it.
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From: Lost again...
in my experience you tend to find that DC power is derived from the normal Starter / Genny engine driven configuration. However, types that also have AC power may have AC generators driven by the main transmission.
I'm sure that others will provide input.
OH
I'm sure that others will provide input.
OH
Thread Starter
Joined: Jun 2004
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From: Europe
Thanks for the input guys. I was convinced it's more efficient to use inverters to transform DC to AC. So, to sum it up, the big ships than have a seperate AC generator, usually transmission driven.
Is it than more efficient to use a AC generator than a big inverter (that needs even additional power supplied by the engine driven DC generator)?
Is it than more efficient to use a AC generator than a big inverter (that needs even additional power supplied by the engine driven DC generator)?
Joined: Jun 2006
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From: In the air with luck
Inverter efficiency varies with load.
Normally it will be highest at about two-thirds of inverter’s capacity. (peak efficiency)
The inverter requires power just to run itself, so efficiency of a large inverter will be low when running smaller loads.
Normally it will be highest at about two-thirds of inverter’s capacity. (peak efficiency)
The inverter requires power just to run itself, so efficiency of a large inverter will be low when running smaller loads.
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From: Den Haag
The Black Hawk also has 2 x transmission driven generators. Doens't work so well if you droop the rotor.
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From: Lost again...
Also - and i'm prepared to be corrected if i'm wrong here, but, if you have anything that requires three phase AC then i think you need an AC genny as i don't think you can get three phase from an inverter.
Joined: Mar 2007
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From: Hobe Sound, Florida
AC Generator Underfrequency Protection
212,
You are correct re the S-70 model line having AC Gen underfrequency protection. If I recall, that will keep the main AC Gens online down to something like 67% Nr ( assuming one is airborne and the WOW switch is functional )*. On the ground, the underfreq will drop the Main AC Gens at 94-96% Nr ).
The discussion needs to recognize that many aircraft have an APU and a third AC Generator these days, in addition to some sort of DC battery. Typically this third generator is not driven off the main gearbox.
* On reconsideration, I believe that what triggers the drop off is the under/over voltage protection circuit within the GCU ( Generator Control Unit ). Sorry.
Thanks,
John Dixson
You are correct re the S-70 model line having AC Gen underfrequency protection. If I recall, that will keep the main AC Gens online down to something like 67% Nr ( assuming one is airborne and the WOW switch is functional )*. On the ground, the underfreq will drop the Main AC Gens at 94-96% Nr ).
The discussion needs to recognize that many aircraft have an APU and a third AC Generator these days, in addition to some sort of DC battery. Typically this third generator is not driven off the main gearbox.
* On reconsideration, I believe that what triggers the drop off is the under/over voltage protection circuit within the GCU ( Generator Control Unit ). Sorry.
Thanks,
John Dixson
Last edited by JohnDixson; 25th August 2011 at 11:40. Reason: Further consideration
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From: Somewhere Cold
The Westland Sea King normally has two AC generators installed on the accessory part of the main gearbox. It is possible that some mark numbers has three generators as it is room for it.
Because of an actuated free wheeling unit on engine no 1 it is possible to drive only the accessory part of the MGB without turning the rotor. This will give you hydraulic power and AC power.
All DC power is provided by two TRU (transformer and rectifier unit) or the battery.
There is also a ground inverter, converting 28 VDC to 28 VAC for some instruments.
You will have under frequency protection on the ground only (around 94%).
This how it is on our Sea Kings, but i dont think there is going to be a big difference to other mark numbers.
Because of an actuated free wheeling unit on engine no 1 it is possible to drive only the accessory part of the MGB without turning the rotor. This will give you hydraulic power and AC power.
All DC power is provided by two TRU (transformer and rectifier unit) or the battery.
There is also a ground inverter, converting 28 VDC to 28 VAC for some instruments.
You will have under frequency protection on the ground only (around 94%).
This how it is on our Sea Kings, but i dont think there is going to be a big difference to other mark numbers.
Joined: Nov 2006
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From: Pensacola, Florida
I'll do you one better: I know they're antiques but there are still a few of them running around, including the ones I'm flying now - the S-55 *only* has a transmission-mounted generator, nothing on the engine at all! (And it would have to be a separate unit, as the radial engine was not able to have a starter/generator unit.) When I questioned it, I was told that not having a generator on the engine facilitated faster engine changes in the field when operated by the military back in the day. Which it does, I guess.
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From: On the big blue planet
The Westland Sea King normally has two AC generators installed on the accessory part of the main gearbox. It is possible that some mark numbers has three generators as it is room for it.
Because of an actuated free wheeling unit on engine no 1 it is possible to drive only the accessory part of the MGB without turning the rotor. This will give you hydraulic power and AC power.
All DC power is provided by two TRU (transformer and rectifier unit) or the battery.
There is also a ground inverter, converting 28 VDC to 28 VAC for some instruments.
You will have under frequency protection on the ground only (around 94%).
This how it is on our Sea Kings, but i dont think there is going to be a big difference to other mark numbers.
Because of an actuated free wheeling unit on engine no 1 it is possible to drive only the accessory part of the MGB without turning the rotor. This will give you hydraulic power and AC power.
All DC power is provided by two TRU (transformer and rectifier unit) or the battery.
There is also a ground inverter, converting 28 VDC to 28 VAC for some instruments.
You will have under frequency protection on the ground only (around 94%).
This how it is on our Sea Kings, but i dont think there is going to be a big difference to other mark numbers.
skadi
Joined: Sep 2007
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From: USA
Phoinix,
If the generator/alternator is driven from the MRGB, as opposed to an EMAD, the generator may likely be an Integrated Drive Generator (IDG). IDG's have an integrated variable speed transmission so that they can produce constant frequency AC power from a varying input shaft speed. While IDG's are efficient and reliable, they are also large and heavy. So mounting them on the MRGB, with a lower speed PTO, makes things easier.
Turboshaft engines also have high speed Permanent Magnet Alternators (PMA's) sometimes mounted on the engine accessory gearbox (EMAD). The PMA produces variable frequency AC power, which must be converted to a constant frequency. The advantage of the PMA is that it is very lightweight and can operate at high speeds.
With multi-engine rotorcraft, the main advantage to driving the generators from the MRGB is due to the fact that the generators will continue to be driven as long as the rotor is turning, even after the loss of engine(s) operation. However, the drawback to this particular MRGB accessory drive arrangement is that the generators also cannot be utilized as starter motors, due to the unavoidable presence of an overrun clutch between the MRGB input and engine.
Finally, large rotorcraft may also employ a separate Auxiliary Power Unit (APU). The APU is typically a small turboshaft engine that provides bleed air pressure, hydraulic pressure, electrical power, etc. while the aircraft is on the ground. The APU bleed air and/or electrical power can be used for engine starting, among other things.
Regards,
riff_raff
If the generator/alternator is driven from the MRGB, as opposed to an EMAD, the generator may likely be an Integrated Drive Generator (IDG). IDG's have an integrated variable speed transmission so that they can produce constant frequency AC power from a varying input shaft speed. While IDG's are efficient and reliable, they are also large and heavy. So mounting them on the MRGB, with a lower speed PTO, makes things easier.
Turboshaft engines also have high speed Permanent Magnet Alternators (PMA's) sometimes mounted on the engine accessory gearbox (EMAD). The PMA produces variable frequency AC power, which must be converted to a constant frequency. The advantage of the PMA is that it is very lightweight and can operate at high speeds.
With multi-engine rotorcraft, the main advantage to driving the generators from the MRGB is due to the fact that the generators will continue to be driven as long as the rotor is turning, even after the loss of engine(s) operation. However, the drawback to this particular MRGB accessory drive arrangement is that the generators also cannot be utilized as starter motors, due to the unavoidable presence of an overrun clutch between the MRGB input and engine.
Finally, large rotorcraft may also employ a separate Auxiliary Power Unit (APU). The APU is typically a small turboshaft engine that provides bleed air pressure, hydraulic pressure, electrical power, etc. while the aircraft is on the ground. The APU bleed air and/or electrical power can be used for engine starting, among other things.
Regards,
riff_raff
Joined: Nov 2007
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From: 55 degrees north ish.
As well as everything mentioned above, some aircraft have alternators, belt driven from the transmission. 
Basically any medium/large aircraft that has the potential to require large AC loads (winch, aircon, lots of IFE toys, etc) has the ability to be fitted with an AC generator, the Dauphin has it as an optional extra for example.
The British AH-1 has air driven starter motors, and as such all AC/DC power is developed by the transmission mounted generators. (then rectified, distributed etc)
Basically any medium/large aircraft that has the potential to require large AC loads (winch, aircon, lots of IFE toys, etc) has the ability to be fitted with an AC generator, the Dauphin has it as an optional extra for example.
The British AH-1 has air driven starter motors, and as such all AC/DC power is developed by the transmission mounted generators. (then rectified, distributed etc)
Joined: Dec 2001
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From: Philadelphia PA
British AH-1??? Pictures please!!!
The Polish W-3A has two transmission-driven generators - one AC and one DC. The AC is mainly for the blade de-ice. The engines have an electrical starter, not a starter generator.
The Polish W-3A has two transmission-driven generators - one AC and one DC. The AC is mainly for the blade de-ice. The engines have an electrical starter, not a starter generator.
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From: Fife
Most multi engined heavy helicopters i.e. Puma : Super puma L / L1 / L2 / 225 primary power supply is 3 phase 115v 400 hertz from two alternators driven from the main gearbox. Constant frequency is assured by the fact that main rotor rpm is constant. Both machines supply seperate bus bars that are not coupled due to the fact that synchronisation of the machines is not possible. DC power is obtained from two transformer rectifier units (TRU) and a 28v battery. No inverter is installed due to the fact that if one alternator fails the remaining machine is capable of supplying all ac loads including the TRU,s
The S61N has a similar system but is older and not so refined, DC being provided by a TRU and a motor generator also driven by the MGB.
The S61N has a similar system but is older and not so refined, DC being provided by a TRU and a motor generator also driven by the MGB.