LH423
Topic Author
Posts: 5868
Joined: Sun Jul 11, 1999 6:27 am

Cold Starts!

Sat Jan 15, 2000 2:08 pm

At this moment 00.03 on Sat. 15.Jan, it is 8°F (-13°C) in Boston, so I was thinking about all the places that are very cold during the winter i.e. Anchorage, Stockholm, Moscow, etc. You know how on a cold day your car won't start, well if it is that cold, how do aeroplane engines start? This maybe a stupid question, but I guess my mind is freezing, due to the cold.

Stay warm, from a VERY cold Boston.

LH423
« On ne voit bien qu'avec le cœur. L'essentiel est invisible pour les yeux » Antoine de Saint-Exupéry
 
twa747100
Posts: 549
Joined: Thu May 20, 1999 7:16 am

RE: Cold Starts!

Sat Jan 15, 2000 2:33 pm

.............Anti freeze?
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Cold Starts!

Sat Jan 15, 2000 2:33 pm

The engines ae started the same way as in a hot location.

The engine is fitted with a starter motor attached to the gearbox which in turn drives the HP compressor. When compressor speed reaches a set figure (depending on eng type, roughly 20%) fuel and igntion is introduced, the fuel ignites and the eng accelerates under its own power assisted by the starter motor. At 50% the starter motor Sw is released cancelling the motor & ignition. The engine will then continue to accelerate to an idleing speed of about 62% N2, 24% N1.

The starter motor is a turbine that is fed with compressed air from the APU.

The JT9 has a fuel enrichment selection to assist with eng starts when the EGT reads below 0 Degs with the eng stationary.

The RB211 has an automatic enrichment for engine start.

Early engines like the RR Spey in the BAC 1-11 had a 3 posn start lever for introducing fuel to the engine.

1. Off

2. Idle

3. Start - this was a fuel enrichment position which was selected for the start, then when the EGT reached 400 Degs the lever was dropped back into the Idle posn.
 
L-188
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

RE: Cold Starts!

Sun Jan 16, 2000 3:28 am

8 degrees......That is warm!!!

I have been dealing with with -15 degree tempertures up here in Anchorage......And worked with aircraft all my life up here....So here is the scoop.

We try to keep our aircraft inside our hanger.....because we don't have room for all of our aircraft we try to get our medivac aircraft inside first and then the morning flights.....The piston engined aircraft if at all possible......

If the aircraft has to stay outside in that weather the problem with starting comes with the oil in the engine or gearbox, in the case of a turbo-prop. Just like in your car it turns to a really thick sludge.....Basicly the same things that happen to your car engine happen to an aircraft piston engine.....One way to delay the oil from gelling is to switch to a lighter weight oil....going from 100 to 65 weight aeroshell in the winter for example......Some older radial engines had an injection system that would shoot fuel into the oil to dilute it.....The fuel would evaporate out when the engine warmed up........Other then that the only way to start a piston is too keep it warm......engine blankets, preheating are all going to be nessesary.....If these aren't available the pilot/mechanic will have to go out and fire the engines up periodicly to keep them warm.....

Turbo props run the risk of overtemping the engines......This is because the gearbox is turning very resitant due to the thickness of the oil in it....If you take a turboprop and try to spin the prop when it is cold, bring it inside to warm it up and then try to spin the prop after it has been warmed you will noticed the difference in the force needed to make the blade move........Because of all of the resitance in the blade you run the risk of overtemping the engine which will the require an overhaul.....The only way to run them in the winter with these aircraft are to again, keep them warm......

Aggrivating these problems is that the batteries also degrade in the cold and probably are not putting out their full rated power, Also the cabin has to be warmed because the fluids that are in the instuments and the compass will also gel and freeze......If you have a water system or lav system that can also freeze....One problem with the Beech 1900 is that the door will sometimes freeze shut....what happens is the locks on the door are these sort of key and hole arrangement...They fit into a slot and then rotate so the lock and slot aren't lined up......If the aircraft is warm mosture can get into the locks and then frost and freeze in that slot when the aircraft cools down......The frost and the ice wedge those door lock preventing them from rotating and you can't open the door until you heat it up and that frost melts.......You can still get into the airplane by going though one of the emergency exits....but it is still interesting watching them unload paying passengers that way.

AnywayI got a long winded but I hope this answered your question....Oh....The rule of thumb up here is that you don't even bother flying a piston aircraft when it is -30 or colder.......-40-50 for turboprops.........All of these tempertures are in fairenheit........The lear 35 will go down to -54C in the book......but the limit isn't because of the engines......below that temperture you will start to blow seals in the landing gear...
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.