Let's Talk Jet Performance

[HMR]

The following has turned into a friendly debate between our flight dept. and some others on the "proper" way to operate a turbojet. I'd like to hear thoughts from you FlightInfo'ers on how you do things and why.

To get us started:
How do you set T/O power?
Climb power?
Cruise?
For each segment do you primarily use ITT? N1? N2? Something else? Why?

 

[NoahWerka]

I normally use the method and settings recommended by the AFM.

 

[STL717]

The FMS, FADEC and autothrottles take care of setting power. EPR is used as the primary instrument to measure the amount of power.

 

[semperfido]

on my plane the autothrottles take care of this---but in their absence there are little thingys on the gauges that pop up to show you what to do (and they turn colors if you do too much!). The engine has a brain (FADEC). Many newer planes have these so it's a no-brainer for the pilot.

Many planes use different parameters for these settings. Some are common, but they do vary. So, there is no one right answer unless you talk about a specific Make and Model. I would think it is a result of the engine manufacturer's design.

But, as a general rule you can set the throttles anywhere up to a max temp and run them that way. Nobody buys a jet to go slow.

 

[atldc9]

You mean you have to touch the throttles? I thought they were there simply to use during sim rides.

Seriously, on the DC-9, for t/o we would advance the throttles to aboout half travel, or 'stand them up', then the non flying pilot would set the t/o power using EPR. For all other phases of flight, the PF would simply move the throttles to achieve the desired speed(barber pole, if your not clackin' your slackin', it is a goal not a limitation) within limits of the cruise limit EPR. The cruise limit EPR was displayed on a gauge in the cockpit that took temp and altitude into account.

 

[Gulfstream 200]

The following has turned into a friendly debate between our flight dept. and some others on the "proper" way to operate a turbojet. I'd like to hear thoughts from you FlightInfo'ers on how you do things and why.

To get us started:
How do you set T/O power?
Climb power?
Cruise?
For each segment do you primarily use ITT? N1? N2? Something else? Why?

Is the Astra TFE-731 powered?

My guess would be an AFM N1 setting for takeoff. If I recall (been a while) is that N1 is the # that you need to get your takeoff perf #'s for a given altitude and temp.

temp limited in climb and cruise...get what you can get..run it at max reccomended ITT.

anything else these days would be push it forward and let the autothrottles do their work.. (thats what IM talkin' about)

 

[Lead Sled]

But, as a general rule you can set the throttles anywhere up to a max temp and run them that way. Nobody buys a jet to go slow.

...get what you can get..run it at max reccomended ITT.

Where are you guys getting that advice from? Just wondering.
'Sled

 

[semperfido]

Where are you guys getting that advice from? Just wondering.
'Sled

seems to me that is what we have always done.....but i suppose the correct answer is to consult the AFM and do what they teach you @ FSI

...but he was asking some rather generic questions, so I tried to give a generic answer.

 

[Big Duke Six]

The best answer is to fly it per the AFM. But generally, the jets I've flown use EPR for takeoff. Sorry, no advice here for climb/cruise - it's been awhile since I've had to set my own power (my current airplane does it for me via the Flying FADEC Brothers), but I also know that in the smaller jets I've flown (T-37/T-38) we'd use fuel flow alot in the approach phase. It's handy because as your configuration/airspeed changes, fuel flow numbers are easy to remember and work fairly well in a wide range of conditions.


In turboprops we'd use temps almost exclusively.

 

[Lead Sled]

...as a general rule you can set the throttles anywhere up to a max temp and run them that way. Nobody buys a jet to go slow...seems to me that is what we have always done.....but i suppose the correct answer is to consult the AFM and do what they teach you @ FSI.

There may be some powerplants where that is OK, and FADEC and autothrottles are about the neatest thing since sliced bread but with regard to the EEC/DEEC equipped TFE-731s that a lot of us have, you won't find justification for it if you read the AFM. Fortunately the -731 is pretty tolerant. I've heard and seen a lot of different theories when it comes to -731 power management - for example, setting power according to some particular ITT, or N2, or N1, or my ever favorite: "fly it balls to the wall, the computers will keep you out of trouble." Actually the AFM is pretty specific when it comes to power management, the problem is most guys haven't really read the manual. [Note: Let the flames begin.]

'Sled