Topic Author
Posts: 57
Joined: Sat Dec 27, 2003 4:14 am

Stupid question

Thu Feb 18, 1999 12:17 pm

Maybe this could sound stupid but when you want to turn on the engines of an airplane how do you turn them on? with a key as a car ?
A380 fever!!!

RE: Stupid question

Thu Feb 18, 1999 12:28 pm

i'm not a pilot or anything, but i think that first the apu bleed air is fed into the engine to get the fan and turbines spinning, via a gearbox and shaft attached to the fan. This must happen first to get the airflow going rearwords. Otherwise when fuel is ignited there will be nothing to keep the explosion from going forward out the engine. When the blades are spinning at 17% or more, the fuel is fed into the combustion chamber where the ignitor plugs ingnite it fuel air mixture. The hot air then blows out the rear through the compressor and turbines. There are engine start switches though, i think they take care of everything after the apu bleed air has done its job
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

My confusing explaination

Thu Feb 18, 1999 1:06 pm

Depends on the aircraft. In the small airplane it does work with a key. In the old days you had to get somebody to spin the propeller (Just like in all those old WWI flying movies). On the Piper PA-32 you have to turn the magnetos on (unground them via a switch) and then there is a rocker switch that engages the starter on each engine. Just push it until the engine catchs

DC-10 does do a pretty good of explaining how most jets are started today. I do want to add a couple of things.

Some smaller jet engines use and electric starter that is about the same as your car. Most large engines have a compressed air starter. In this type of starter there is a impeller in the starter that air is forced through to cause it to spin and in turn it spins the engine. The compressed air either comes from the APU(auxillary power unit), any running engine or a air start cart. I have started a lot of airplanes useing the airstart carts. The theory of starting the airplane is about the same in any case. Get the moter spinning fast enough and have the ignightors heat the engine hot enough so that if fuel is introduced it starts to burn and the engine is running.

There are two other ways that can be used to start an airplane. On the F-16 there is a fuel burn system where a seperate burners burns fuel producing expanding gasses that are passed through the starter much like the air start method. This doesn't require external connections. Also you can generate the pressurized gasses to turn the starter by firing a special cartridge that looks like an overgrown 12 gauge shell into the system. This isn't as popular now but was used on both piston and jet engines. If you want to see this system in action rent the movie 'Flight of the Phoenix'. It is a classic with James Stewart, Richard Attenbrough, George Kennedy and I can't think of his name, had the helicopter company off the TV show Airwolf. Sat in the back and ran the chopper.

Anyway it is a good classic movie. It was the one that Paul Mantz was killed during filming of it. I hope this explains how to do it and I didn't confuse you.
I have one more story to tell.

One day one of our electras landed and shut down. Our Electra's weren't equipted with APU's so you had to airstart them every time when they landed. Found out after it shut down that out Airstart was out of service and we had no other way of starting the airplane. About a half hour later one of our 727's landed. We went ahead and switched the loads on the two planes which was the original plane. They crew and passengers boarded. We started the 727 first since it had it's APU working and then the pilot of the 727 turned so his jet blast was blowing right over the Electras wing. The pilot of the Electra then edjusted the pitch of the prop blades on his aircraft so they started to spin in the blast on the 727. Once he got the prop spinning fast enough he started the engine and one he had that one started he used the bleed air off that engine to spin the other three. Schoolyard tactics, but just another day on the job.
Posts: 305
Joined: Sat May 22, 1999 12:31 am

RE: L-188.

Thu Feb 18, 1999 2:33 pm

First DC-10 and your post was first class in explaining how to start a A/C engine. But one question for L-188....Have you ever done a manual start on a large engine like a CF6, or JT whatever..?? Now that is a bit of scary fun to talk about oneday...
All the best..
See yah..
Topic Author
Posts: 57
Joined: Sat Dec 27, 2003 4:14 am

RE: Stupid question

Fri Feb 19, 1999 7:49 am

Thank you guys for your answers.
A380 fever!!!
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Joined: Wed Jul 07, 1999 11:27 am

Answer for Will.

Fri Feb 19, 1999 11:10 am

No I havn't. We didn't get much or if all widebody trafic through Cold Bay. The closest I got to the big engines where the RB-211 that where powering a Northwest 757 that Boeing had leased to take on tour in China. I didn't think much where they put the airstart connections. The door is on the fuselage right next to the right-hand engine. But other then being a more intimidating engine it didn't look any worse then where the airstart unit is on a 737. As long as they start the outboard engine first no problem.

The airstart port looks intimidating on a 727 also. It is on the rear fuselage just under the right hand engine also but that is a piece of cake when you realize that they start either the top or the left hand engine first.

The aircraft I considered the spookiest to start where the small buisness jets specificly the lears and the G-IV. The GIV is on the middle of the rear fuselage right between the engines. You stand about three feet away from that one when it starts. The Lear dosn't use air starters it has electric starters but the GPU connection is right below the left hand engine. Usually when a Lear needed ground power it ment somebody had left the lights on and since it is electric starting system usually the pilot will want to have both turning before you disconnect.

I am actually glad I didn't have to do this since I was running the office that day. We had a C-47 that had dead batteries on the field. A fueler freind of mine went down to start the airplane. If you ever see pictures of DC-3 hooked up to a power cart usually the cart is off to the side and a very long cable is run behind the main tires to the port on the airplane which is located on the fuselage, forward of the wing but aft of the propellors. Our 24VDC cable wasn't long enough to reach that far so he had to park infront of the airplane. He had to stand by the cable while the pilot started both engines, then pull the cable and walk out straight between the props right under the fuselage. It looked pretty spooky from my seat in the office. He said it was really spooky from where he was standing!

RE: My confusing explaination

Sat Feb 20, 1999 12:50 am



Gentlemen, there is a big confusion here!!!
APU is being used as a Electric power generator and sometimes- heating system assistant (it has more hot air than the politician!)

APU generates the energy, that turns the first stage turbine- N1 and N1 is that what creates the flow of air!

it usually being turned until N1 reaches 27% and then the flow of fuel starts.

APU does not supply any air to engines!
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

AC-65-12A explains how it works

Sat Feb 20, 1999 3:19 am

You need to get a hold of FAA Advisory Circular 65-12A This is the Airframe and Powerplant Mechanics Powerplant Handbook. Chapter Five page 263 explains the different types of starting systems found on aircraft.

The air turbine starter is used on most larger engines because of it's lighter weight. To quote from the book," The air to operate an air turbine starter is suplied from either a ground-operated compressor or the bleed air from another engine." This is on page 277. The APU acts just like another engine in this case and as you noted the APU provided at lot of hot compressed air. This air is feed into the starter which has a fan that the air makes spin that connects to a grear and in turn spins the engine fan. As you note APU bleed air is not sent into the engine itself just the starter.

I hope this clears things up.

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