N1 11%?? B737
 

I have come across a figure of 11% N1 when starting a jet engine on the above aircraft when starting. What is the relevance of this figure?

If forced to guess, i might say that is when fuel flow is started?

I await some responses with interest!

Many thanks,
BB

No idea about the 11% figure, fuel flow is typically started when N2 is 25% and not before there is an N1 indication, which will normally only be 2-3% and that stage.

It would help to see the figure. ;)
But during engine start the fuel flow starts when you put the start lever to idle (737CL at 25% N2).

Ingo

Values
 

At 11% N1 you are at the acceleration phase. You check your duct pressure, about 30 psi on Standart Sea Level. Then You start the engine and the N2 accelerates to 18% and you see the Oil pressure rising as well as N1.... by 25% N2 you raise the start lever and FF is rising and within 10 seconds EGT responds. You starter cuts out at 55% N2 and then you should see approxiamtly 20% N1, 400 C EGT and 60% N2. That is called a stabelized condition. If you are at a higher elevation, 5000 feet, then your N2 shows 25% about. I hope this helps for the CFM 56.

NG

You are not confusing this with 11% N2 are you?

11% N2 is the minimum N2 you need for an Inflight Engine Start on the 737NG. Page NNC.7.17 of the QRH refers.

Can't think of any relevance to 11%N1.

Hope this helps

Do you always wait to 25% N2? I thought in some conditions it can take 'forevever' to reach 25% N2.

Boeing asks for 25% N2 or 'max motoring' which is where it has virtually given up! Very common with old APU's for this to happen at as low as 22/23% sometimes.

For CFM56-3 Boeing procedure is as follow :
25%N2 or max motoring and a minimum of 20%N2.
Starter cuts out at 46%N2.
Standard day, sea level approximate idle indications :
N1 22%
EGT 475
N2 60%
F/F 325kg/hr

Dj.