Matt72033
Topic Author
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Joined: Sat May 14, 2005 10:03 pm

AC And DC Motors Used On Aircraft

Sat May 14, 2005 10:14 pm

Hi all
This is my first post on this site, but I have been watching from afar for quite a while now. I've learnt lots of new things in the last few months, and have come to realize that you guys have a hell of a lot of experience between you.

I'm currently an apprentice studying to become an aircraft engineer with an airline here in the UK. Last week I was given an assignment to do a powerpoint presentation on the use of AC and DC motors, to include :

1. Types of motors
2. Theory of operation
3. Uses on aircraft
4. Maintenance and servicing Considerations

Now I know general uses for motors (starting, older aircraft and APU's, Hydraulic pumps, as back ups to EDP's and so on) but I was wondering which type of motors are used for particular operations. and especially on the maintenance and servicing considerations!

I do have access to AMM's at work for a couple of aircraft but I'm not very good on them yet....can never seem to find what I need lol

Any help and information would be greatly appreciated

Thanking you all in advance
Matt

[Edited 2005-05-14 15:34:16]
 
cancidas
Posts: 3985
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RE: AC And DC Motors Used On Aircraft

Sun May 15, 2005 12:45 am

well, you use AC and DC depending on the a/c that you are going to hook it up to. at my airline, we use DC GPUs for everything but our CRJ-200s, including DHC-8-100/200s, EMB-145s, B-1900C/Ds and Saab-340s. The mainline a/c all use AC power. everything is dependant on the electrical system in the a/c, as decided by the manufacturer. i don't think that there is one a/c out there that will accept both AC and DC power.

now, that takes care of the usages. when it comes to engines, i'm not really the best person to ask on that. for that you should ask either an A&P or GSE mechanic.
"...cannot the kingdom of salvation take me home."
 
Matt72033
Topic Author
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RE: AC And DC Motors Used On Aircraft

Sun May 15, 2005 1:03 am

I'M asking about Motors, not what type of power is used on aircraft!
i.e. I know that both AC and DC motors are used on aircraft but what job in particular would a DC Shunt Motor be used for or a DC Series motor! That kinda thing.

Would I be correct in thinking that as a DC series Motor has a high torque it may be used for starting an APU?

Also are Auto pilot servo motors still used? Do/did they actuate the control surface directly or would they feed an input into a hydraulic control valve?

Once again....any info would be appreciated
Matt
 
Woodreau
Posts: 1243
Joined: Mon Sep 24, 2001 6:44 am

RE: AC And DC Motors Used On Aircraft

Sun May 15, 2005 2:06 am

Snapping back at someone who is trying to give you an answer is probably counterproductive and won't get you any more answers to this thread. You could have probably answered, "Thank you but that's not what I was looking for." and it would have gotten the same message across.

I'm not really an expert on electric things as I'm a pilot not a engineer.

I would assume the AC motors in aircraft are induction motors. Now, whether they are squirrel cage induction motors or wound-rotor induction motors I have no idea. On a CRJ-200 the flap power drive unit, hydraulic pump, horizontal stablizer trim actuator, galley and lavatory water pumps, and toilet pump are driven by an AC motor.

Some different types of DC motors are: shunt, series, compound, and stabilized shunt motors - judging from your question in post 3 you already know the different types of DC motors.

The fuel pumps are driven by DC motors and the APU start motor and the autopilot servo motors are DC motors. The autopilot servo motors drive a system of cables and pulleys to operate a hydraulic power control unit which moves the flight control surfaces - that's just for a CRJ, other types of aircraft are probably different.

I wouldn't know if an A&P mechanic would know whether a DC series motor is used or if a DC shunt motor is used. Well, pilots don't care too much what kind of DC motor is used... just does it work?

Sorry this isn't probably what you were looking for, but good luck on your studies.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
Matt72033
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RE: AC And DC Motors Used On Aircraft

Sun May 15, 2005 2:15 am

Sorry......i Didn't mean it to sound as if I was snapping back......i was just trying to clarify exactly what I meant!

Quoting Woodreau (Reply 3):
On a CRJ-200 the flap power drive unit, hydraulic pump, horizontal stabilizer trim actuator, galley and lavatory water pumps, and toilet pump are driven by an AC motor



Quoting Woodreau (Reply 3):
The fuel pumps are driven by DC motors and the APU start motor and the autopilot servo motors are DC motors. The autopilot servo motors drive a system of cables and pulleys to operate a hydraulic power control unit which moves the flight control surfaces

that's Great.....thanks very much

once again....sorry
Matt
 
troubleshooter
Posts: 420
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RE: AC And DC Motors Used On Aircraft

Sun May 29, 2005 6:42 pm

Quoting Cancidas (Reply 1):
i don't think that there is one a/c out there that will accept both AC and DC power.

The BAe146/RJ has an additional external DC receptacle. It is not used to supply power to the entire aircraft. But you can use it as an alternate power source for engine starting.
This job sucks!!! I love this job!!!
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: AC And DC Motors Used On Aircraft

Sun May 29, 2005 7:18 pm

Generally speaking, on large heavy jet transport aircraft, AC motors are used exclusively, simply because they are lighter in weight.
 
DC8FriendShip
Posts: 235
Joined: Fri Apr 29, 2005 7:35 pm

RE: AC And DC Motors Used On Aircraft

Sun May 29, 2005 7:28 pm

Quoting Troubleshooter (Reply 5):
The BAe146/RJ has an additional external DC receptacle.

As does the CRJ200 mentioned by Cancidas. It is located under the #2 engine, and is used for APU starting if 400 Hz. is not available( and the batteries are dead).
Come fly the Friendly Skies of United
 
Buzz
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RE: AC And DC Motors Used On Aircraft

Mon May 30, 2005 11:28 pm

Hi Matt72033, Buzz here. It's been a long time since A+P school , haven't given much thought to the different kinds of winding inside the motor. Out on the line we're thinking: is it AC powered or DC powered?
AC power can deliver more energy for the same weight in wire... or the aircraft designer can try to go lightweight and save a few pounds - they work with a weight budget.

On the Boeing airplanes, the main fuel boost pumps are AC powered. The 757 also has a DC fuel pump... it's a long way back to the APU and they want a positive fuel pressure to start that little screamer. The A320 has a DC fuel boost pump for APU starting also.

And i've seen little autopilot servos on the popular kit airplanes, the Van's RV-6 comes to mind. That's a DC powered airplane, the factory for the kits is not far from here at Aurora Oregon (KUAO). The autopilot is generally a wing-leveler so you can sip a cup of coffee and look at a map as you fly.

One consideration: a battery doesn't make AC power. Yes, you can make an inverter produce AC power. If the aircraft generators were to quit, what kind of things would you want to be "Battery Powered" for an emergency landing?

How about engine fuel valves so the engines can be shut off in case of fire, crossfeed valves so one fuel tank can be shared by 2 engines, landing gear selector (if it's not cable operated) would be a good thing. Bleed air valves / air conditioning would be worthwhile so that cabin pressure is controllable while you're coming down. The 757 has a DC powered over ride pump that unlocks the MLG doors (NLG doors too) and releases the uplock hooks so the landing gear can free fall - for energency use. We operate it on the ground when we need to get into the wheel well.

And most of the radios take DC power and invert it to AC power inside the box, it's reliable.

Does that give you some ideas?
g'day from Portland Oregon
 
DC8FriendShip
Posts: 235
Joined: Fri Apr 29, 2005 7:35 pm

RE: AC And DC Motors Used On Aircraft

Tue May 31, 2005 10:15 pm

Quoting Buzz (Reply 8):
The 757 has a DC powered over ride pump that unlocks the MLG doors

Does the RAT provide enough power to run hydraulics? and are there provisions to lower the gear incase of a total electrical failure? I know the 757 has multiple redunduncies, but how far do they go?.

Thanks, chris
Come fly the Friendly Skies of United
 
willo
Posts: 1331
Joined: Fri Dec 12, 2003 10:21 pm

RE: AC And DC Motors Used On Aircraft

Wed Jun 01, 2005 11:38 pm

I am not an Engineer but do work for a company that manufactures both AC and DC motors for Aerospace applications. You could have a look at our website where there are examples of the product:

http://www.airscrew.co.uk/

Additionally, our American parent company Ametek Rotron has similar product. You can get to that site via a Google search.

Andrew
 
kaddyuk
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Joined: Thu Nov 08, 2001 1:04 am

RE: AC And DC Motors Used On Aircraft

Wed Jun 01, 2005 11:46 pm

Quoting DC8FriendShip (Reply 9):
Does the RAT provide enough power to run hydraulics?

The RAT is a hydraulic pump... It does not power an electrical source, but a hydraulical one. If you search the forums there are plenty of replies which explain what a RAT does and where it is found etc etc
Whoever said "laughter is the best medicine" never had Gonorrhea
 
Matt72033
Topic Author
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RE: AC And DC Motors Used On Aircraft

Thu Jun 02, 2005 2:47 am

Quoting DC8FriendShip (Reply 9):
Does the RAT provide enough power to run hydraulics? and are there provisions to lower the gear incase of a total electrical failure? I know the 757 has multiple redunduncies, but how far do they go?.

am i right in thinking there is emergency gear release handles that release the gear using a freefall, with a restrictor in the up line to dampen the action?

Quoting Kaddyuk (Reply 11):
It does not power an electrical source, but a hydraulical one. If you search the forums there are plenty of replies which explain what a RAT does and where it is found etc etc

yeah this has been discussed, and it was said that on certain aircraft the RAT is used to supply electrical power and hydraulic power, through the use of an HMG on the 767 and other aircraft just have a generator and hydraulic pump driven by the RAT! and you posted on it?!?!?! lol
 
DC8FriendShip
Posts: 235
Joined: Fri Apr 29, 2005 7:35 pm

RE: AC And DC Motors Used On Aircraft

Thu Jun 02, 2005 9:47 am

Quoting Kaddyuk (Reply 11):
If you search the forums there are plenty of replies which explain what a RAT does and where it is found etc etc

But remember every manufacturer is different, and I specifically wanted info on the 757's RAT. So, even though it is a hydraulic source, it may only turn a generator, or it may turn a generator and pump. Also as the RAT is a redundant power source, does it then alleviate the need for a free fall system (I don't think so).

Thanks, Chris  Smile
Come fly the Friendly Skies of United
 
Matt72033
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RE: AC And DC Motors Used On Aircraft

Thu Jun 02, 2005 3:29 pm

i know on the ETOPS 757 an HMG is in place on the centre system which will use hydraulic pressure from the RAT to turn a 5Kva generator, only in emergencies though!
 
jeb94
Posts: 587
Joined: Mon Oct 04, 2004 9:19 pm

RE: AC And DC Motors Used On Aircraft

Tue Jun 07, 2005 3:39 am

Lets see if I can help a little. I'm going to use the DC-9 family as an example because that's what I know. The fuel boost pumps are all three phase 115volt AC motors except for the start pump. The start pump is a single phase 28 volt DC motor. The heat exchangers for the airconditioning use a pair of 3 phase AC motors for ground cooling, 1 per side. The auxilary hydraulic pump is a 3 phase AC motor. The radio rack cooling fan is a 3 phase AC motor. The primary horizontal trim motor is a 3 phase AC motor attached by a gearbox to the infamous jack screw. The alternate horizontal trim/autopilot horizontal trim motor is a DC motor. The instrument cooling fans are AC motors. The airstairs are extended and retracted by a pair of DC motors. APU starter is a DC motor not unlike a car starter. Autopilot servos are DC motors if I recall correctly. I'm not as familiar with the autopilot servos as I probably should be. Fuel refuelling valves are DC motors. Engine anti-ice and fuel de-ice valves are DC motors. I think that about covers that for DC9s and MD80s.
 
Matt72033
Topic Author
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RE: AC And DC Motors Used On Aircraft

Tue Jun 07, 2005 3:51 am

Thanx Jeb94 thats Great stuff  Smile

Quoting Jeb94 (Reply 15):
The fuel boost pumps are all three phase 115volt AC motors except for the start pump. The start pump is a single phase 28 volt DC motor

Why is the start pump DC and the others AC? would it be for starting the APU? with only baterry power?

Quoting Jeb94 (Reply 15):
primary horizontal trim motor is a 3 phase AC motor attached by a gearbox to the infamous jack screw.

Was it this jack screw that failed on the SAS aircraft that crashed into the sea?
 
jeb94
Posts: 587
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RE: AC And DC Motors Used On Aircraft

Tue Jun 07, 2005 4:02 am

The start pump is DC to provide that little boost to the APU fuel pump to help it start on battery alone, yup. As for the jack screw, yes, its what failed on the Alaska Airlines MD80 that then did a very wild and terrifying plunge into the Pacific. If you don't think maintenance is important and the pilots can get out of anything, try that in an MD80 sim. I can tell you right now there was absolutely nothing they could do once that horizontal broke loose.
 
Matt72033
Topic Author
Posts: 1589
Joined: Sat May 14, 2005 10:03 pm

RE: AC And DC Motors Used On Aircraft

Tue Jun 07, 2005 4:10 am

ahhh it was alaska!

yeah we have a tv series over here called air crash investigation and they featured that crash in one of there programmes! I completely admired the pilots of that aircraft! At absolutely no point through that emergency did they stop trying, they were flying inverted in a steep nose dive at one point an they still battled with the controls to try and save the aircraft, even trying to fly the aircraft upside down because they thought it was more controllable like that!

I think we could all take some ispiration from these guys! i bow down to them!

Matt
 
jeb94
Posts: 587
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RE: AC And DC Motors Used On Aircraft

Tue Jun 07, 2005 4:40 am

That is also a perfect example of why all aircraft maintenance people need to take their jobs very seriously. Their are men that will be spending the rest of their lives in prison with that on their hands.
 
Matt72033
Topic Author
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RE: AC And DC Motors Used On Aircraft

Fri Jun 10, 2005 2:24 am

still having problems finding info on mx and servicing considerations!
any help will be greatly appreciated, thanks for all the info already provided , i am very grateful!
 
jeb94
Posts: 587
Joined: Mon Oct 04, 2004 9:19 pm

RE: AC And DC Motors Used On Aircraft

Fri Jun 10, 2005 4:21 pm

Depending on the application the operational considerations all concern heating. Not a problem in fuel pumps run in tanks with fuel in them as the fuel cools the pump. The auxiliary hydraulic pump is cooled by hydraulic fluid. Fans are set up to be cooled by airflow and valves don't build up a lot of heat as the motors only run open or closed rather than constantly. The longitudinal trim motor (Horizontal Stabilizer) does have a time limit. The DC9 is pretty short, something like 5 or 10 seconds on the ground, while the MD80 max is 90 seconds. I'm not sure what is done at component shops to repair them, maybe rewind the motors or discard the motors altogether? The components are all serialized and repairable provided they haven't been damaged significantly. From the operational side with the DC9s and MD80s we replace them when they fail and other than that they are maintenance free.

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