Starting engines

[cherrylock]

We were on the multi story car park at manchester yesterday and we were watching a monarch airbus start its engines,we noticed how long it seems to take before the engine catches, the disc on the front was whzizing around for ages before it started, is this normal?

l would have thought that as soon as the pilot presses the start button it would start like a car does, thanks

[HEATHROW DIRECTOR]

How do you know when the pilot actually "pushed the button"? Aircraft engines are so well balanced that they often windmill in a slight breeze, which gives the appearance that an attempt has been made to start them.

[Whispering Giant]

It could also be that the engine need's to cool down to it's starting parameter's before fuel is put in to effect a light up.
On the aircraft that I fly, the ITT (Intermediate Turbine Tempreture) must be below 120 degree's C before the fuel is injected into the combustion chamber, Therefore if we do a quick turnaround and shut down. On the next start the starter will spin the engine and draw cool air through it untill the reaches 120 degrees before putting the fuel in and lighting up.

brgds
W.G

[spannersatcx]

Have a look at the VS when that starts (assuming no windmilling) the fan (the disc bit on the front) barely rotates when the engine lights off.

[GAZIN]

Cherrylock
All the above is correct. Most, but not all, jet engines require more than one action to start them. Very simply, first you engage the starter motor & then when the engine reaches a specified speed you switch on the fuel & ignition (fuel & ignition only require one action). The starter motor will disengage automatically at another specified speed & the engine will continue accelerate to idle speed.
The starter motor is not usually directly connected to the front fan which is why you may hear the engine start before the fan rotates, if you are close enough you may even see the fan rotating back-wards at the beginning if there's a tail wind.

[Dr Esteban]

Some of Monarch's Airbusses are fitted with IAE engines. IAE engines (as
opposed to CFM engines) will perform a 30 second dry-crank as part of their
automatic start sequence after which igniters are activated and fuel is
introduced into the combustion chambers.

This whole start sequence might take as much as 1-2 minutes per engine.

[kevlarcarl]

"The disc on the front whizzing round.. pilot pressing the start button".....dont ya just love spotter speak :ugh::ugh::ugh:

[leewan]

Modern jet engines actually start similiar to a car engine except the process is drawn out and more complicated with various parameters monitored. First of all, when the start switch and eng master switch is put in the on position, all packs are switched off to optimise the bleed available for engine start and the starter is engaged. Starters are usually linked to N2 or N3 and as such, it would be some time before the fan blades(N1) or "disc on the front" start spinning. The fan blades or N2 need to reach a certain speed before the ignition and fuel is introduced, signalling a light off when you can actually see the fan blades picking up speed at a rapid pace and heat exhaust coming from the turbine nozzle. For some a/c, the spinning cycle would be prolonged as either the ITT or EGT temperature needs to be cooled down as W.G mentioned.

Then once the N2 reaches a self sustaining speed( usually 50%) the starter cuts off and the engine is started. This process, depending on the engines and condition may take from 3 to 5 minutes. Hope that helps :)

[CEJM]

Dr. Esteban is right. If you were looking at the engine start of an A321 then it takes at least 30 seconds before any fuel goes into the engine. Start up times of the IAE engines seem a bit long.

So yes, it is normal for the IAE engine to do this.

[thetimesreader84]

I'll try and put it in laymans terms for the OP, and hopefully explain whats going on a bit. Not that the previous posters are incorrect in any way, i'm just a little concerned they might be pitching at a level above the original poster. Sorry if it is a little too "noddy level" for the OP.

First of all, a Jet and a Car Engine work in the same way. They have to take in air ("Suck"), compress it ("Squeeze") burn fuel in the compressed air ("Bang") and finally exhaust the used gas ("Blow"). Whereas in a car, all the above operations (suck, squeeze, bang, blow) take place inside a piston, in a Jet, they are split into separate parts of the engine. These parts are (from front to back) the Fan, or N1 section (Suck), the Compressor (Squeeze), the combustion chamber (Bang) and the turbine (Blow). The Turbine is split into (usually) two sections, which are connected by a driveshaft to the Fan and compressor sections, and use the exhause flow from the combustor to drive them.

So, what has all this got to do with the price of fish, or starting engines? well, in a car, you turn the key, which fires up the starter motor, turning the crankshaft, which turns the pistons, which suck, squeeze, bang, blow, quicker, and quicker, and eventually the engine reaches a speed which disconnects the starter motor, and the engine burbles away quite merrily.

A jet engine works in exactly the same way. The pilot will press a button (No keys to forget!) which will start the compressor section turning, using either a motor (like a big version of a starter motor) or high pressure air. At a particular speed, the pilot will move a lever, which will allow fuel into the combustion chamber. The igniters (like a car spark plug) will be switched on as well. This will cause the fuel to burn (not explode!), causing more high temperature, high speed gas to turn the turbine, causing the compressor to turn faster, and in time, the fan too (remember it was not connected to anything other than its part of the turbine?). When the engine reaches a certain speed, the starter will disconnect, and the engine will keep accelerating until it reaches a point where it hums merrily away. This is why the fan can appear to be standing still, turning the wrong way, or spinning for a while before the engine starts.

As has been previously explained, each part of the engine is very well balanced, and often quite light, in fact it is often possible to turn a fan blade by hand (although you wont be able to give it a push start!)

Hopefully that has answered your questions. As I said, all the other contributors have answered the question as well, but I just get a bit of an impression that the above might answer things a bit more fully. And pay no notice to Kevlarcarl, god knows I have difficulty enough telling engineers what is going on with my aeroplane, from outside the cockpit I can imagine some of the things that happen must at best be a bit baffling, at worst downright scary!

TTR

[Cymmon]

Further to engine starting, how fast do the fan blades rotate? I know that in older engines the distinctive "crackle" ie BAC 1-11 was air ejected at supersonic speed. If the fan blades close in on Mach 1 does that affect efficiency?

I also read that fan blades are tested for strength and distortion, maybe we could use Kevlarcarl to check on the strength of the Boeing 777 engine fan blades, see if he´s as much use to an engine as he is the spotters on this site, in a SPOTTERS area too!:}

[Old Fella]

Cymmon The Fan section is the slowest of the rotating members of an engine. For example, the Rolls Royce RB211-524 has three seperate rotating sections, all driven by their own turbines. They are N1 Fan (or Low Pressure Section), N2 Intermediate Pressure Section and the N3 High Pressure Section. The accesory gearbox is attached to the N3 section. At 100% RPM the speeds are as follows;

a. N1 3900 RPM
b. N2 7000 RPM, and
c. N3 10611 RPM.

Most of the thrust from the engine is produced by the "Cold Stream" airflow from the N1. In effect, the N1 is much like a ducted propeller, with a large proportion of the air from it being by-passed outside the "core" of the engine. And yes, the fan blades do have to withstand impact from FOD and are tested to measure how much they can handle.

[cherrylock]

Thankyou everyone for your replies people are so kind here (with one or two exceptions!) KC sorry my spotter speak annoyed you but unlike you im not a pilot /engineer which is why i asked

:ok::ok:

[Lafyar Cokov]

I think the real question here is - What was a Monarch Airbus doing trying to start its engines on top of the multi-storey car park at Manchester!

[Cymmon]

Hence the High Bypass turbofan nomencloture.....

So how fast are the blade tips travelling at full thrust? Even more if they have an APR like on the JT8D-17R´s on the later Boeing 727´s?


I have read many of the technical books regarding engines but never really remembered the tip velocities, only that the air departing the nozzle is supersonic on the older engines of the BAC 1-11, VC10, 707, DC8´s and Caravelles etc. But the slower air by-passing the central core air on turbofans would have muffled the noise somewhat? The original Turbojets would have been much noisier?

Not bad for a Spotter, I hope?:ouch:

Currently reading a book on an introduction to airline economics, looking at starting a service from Oxford, maybe to include Edinburgh and Newcastle, maybe even Cambridge?:O


I think the real question here is - What was a Monarch Airbus doing trying to start its engines on top of the multi-storey car park at Manchester!


Not sure, think my question would be, how did it land there? Was it used by Airbus to test the flaps from the DHC-7 dash-7 for a VSTOL A320? Going to, maybe, upgrade the engines, why not the wings?:}

[tom775257]

I hope I am not making this up, I seem to remember that when they first introduced the IAE V2500 it suffered from premature bearing wear, so they modified the start process to dry crank it; the idea being to get some oil pressure in the system before light-off.

Personally I don't like flying with the V2500. EPR pisses me off (We use the 'Engine Pressure Ratio' as the means of setting power in normal situations on the V2500, I find N1% speed 0-100ish much easier) and also it takes and age to start. Oh yeah and it smokes like a bastard after shutdown, making the walk around unpleasant.

Give me a CFM56 any day, sadly I almost always fly with the V2500s on the A321 these days.

Monarch have the V2500s on the A321s and the CFM56s on the A320s.

[forget]

KC sorry my spotter speak annoyed you but unlike you I'm not a pilot /engineer which is why i asked.

Don't think for one moment that the poisonous kevlarcarl is either. He ain't. Ignore him; everyone else does.

[Lamyna Flo]

KC sorry my spotter speak annoyed you but unlike you im not a pilot /engineer


cherrylock - if it makes you feel any better, neither is our sad little friend KC. If you check his profile, you'll see he's a Dispatcher, nothing more. Judging by the condescending tone (and poor grammar/syntax) of his posts, he's obviously a wannabe pilot who never made it. Rather unsurprisingly, with an attitude like his. Can't imagine a worse person to share the cockpit with, to be honest! ;)

[Northbeach]

Cherrylock,

Your “spotter speak” is perfect; I knew precisely what you were referring to. Further you placed your question in exactly the correct place. As for the individual(s) who criticized your word choice (and/or post), that was completely uncalled for. They have made precisely the same error a casual traveler makes when they post something completely inappropriate in the professional flight deck portion of PPrune. Give the criticism a rest guys; wrong place, wrong time and wrong population.

Cherrylock, your question was proper and your word choice refreshing. Keep them coming.


On the Boeing 737NG (Next Generation; models 700, 800) I fly the start sequence usually takes 38 seconds from the time I move the “start switch” to the “on” position and the time that the starter disengages following a successful start.

Respectfully,

Northbeach

[dixi188]

cherrylock.

I think TOM775257 is probably right for this aircraft.

However another reason for a long start cycle maybe an igniter failure.

On our A300s we alternate each Ignition system (A & B) for each start.
Sometimes one will fail so the start will be a bit like this:

Press button, starter motor turns HP shaft of engine.
At 15% N2 (about 10 secs.) Fuel lever On. Start timing.
If no EGT rise after 25 secs. (normally approx 12 secs.) Fuel lever Off.
Continue motoring engine for 30 secs. to clear unburnt fuel from engine.
Then select other Ignition system and Fuel lever On again. Start timing.
About 12 secs. EGT rise, and continue start.
Total time to stabilized idle will be about 2.5 mins.
We have a 5 min. limit on the use of the starter motor.

Hope this helps.

[Scarbagjack]

This thread is very interesting to me, as I would not even qualify as a spotter...just an enthusiast and a curious and interested flyer.
Thanks for the question Cherrylock, and thanks to all for the informative replies.
And to all you folk who take all those fantastic photos, keep 'em coming.
( especially B744's QANTAS style...one of my many weaknesses ):O

You are appreciated by many:D

Cheers, Scarbagjack

[dubh12000]

They found that the V2500 shaft flexed when the AC was turning in the holding pattern, and wearing out the honeycomb seals on the out board side in the compressor and turbine sections.

[yellowdog]

"The disc on the front whizzing round.. pilot pressing the start button".....dont ya just love spotter speak

Don't you just love idiot dispatchers.......:suspect: