Rolling takeoff with a TFE-731

[svcta]

I've seen the paperwork right from the horses mouth: And I quote: "takeoff N1 is a MINIMUM value and must be achieved before brake release, on a runway limited or obstacle clearance takeoff, to obtain Aircraft Flight Manual performance."

It goes further and states that an overshoot by the EECs on the -3c of 1-2% N1 is normal. And that the DEECs on the -40 are programmed to overshoot by a number of around .5%.

And, of course, that the pilot should monitor the other parameters to make sure that no limitations are being exceeded.

 

[LJ45]

For the Learjet 45, per the AFM you add 300 feet for a rolling Take off

 

[gear_guy]

I have heard this restriction also. Next time you do a rolling takeoff, set T/O N1 and then look at it again about 80 knots. It will have reduced 1-2% from T/O N1. If I did a rolling T/O I would usually readjust the throttles at 60 knots back to T/O N1. Anyone else notice this?

 

[Lead Sled]

Avbug...
About 10 years ago we had an inhouse discussion on the proper operation of the TFE-731 engines that we had on four of our five corporate aircraft. I contacted Allied Signal with a series of quesions which they answered very directly in an e-mail. The gist of their reply is as follows:
1. N1 is the ONLY indication of thrust output in the TFE-731 engine.

2. N2 tells you the internal speed of the engine.

3. ITT or EGT essentially tells you the health of the engine - a "fresh" engine will be able to achieve its rated thrust at a lower ITT or EGT than an engine with some time on it. As an engine wears, the internal tolerances open up and it takes more heat energy (fuel flow) to generate the same amount of thrust. More fuel into the engine results in higher temperatures. A new engine will have a greater margin than older engines.

4. The takeoff N1 Power Charts give you a specific minimum N1 required to achieved the charted takeoff performance. Garrett/Allied Signal/Honeywell looks upon that number as a "minimum" number.

Takeoff is one area where if you get a little more that what the book says, you're fine - at least according to Garrett/Allied Signal/Honeywell. Although some manufactures state that takeoff N1 is a "maximum" value they didn't get that from the engine manufacturer and many aircraft AFMs, allow you to advance the power levers to the stops on takeoff regardless of whether the engines are EEC, DEEC, or FADEC, and allow the fuel computers to do their thing to keep the engine parameters in line. (There is also a time limit in this type of operation - 5 minutes.) I'm not advocating that you ignore the AFM, but it also doesn't make much sense to take your attention away from the takeoff to screw around adjusting power down to some specific setting that will guarantee that you will only have enough power to achieve a minimum level of performance.

5. After takeoff, you need to transition into the climb power charts. Climb (and max cruise) charts are based on specific N1 settings and should be used. The temperature limits mentioned in the charts are the maximum allowable for the specified N1.

LS

 

[LJ45]

I am glad we have a Learjet 45...Set TO detent, set MCT dentent, and set MCR dentent...Makes it really easy for us.

When we had the 31a, by the time we had the power set on a lite take off, it was Vr time...LOL

 

[gear_guy]

just use the auto throttles and forget about it

 

[SSDD]

scvta's quote makes more sense. Would you do a rolling takeoff on a runway limited, or obstacle clearance takeoff? On a short runway, I'm standing on the brakes until I see T/O N1.

 

[SoundBarViolatr]

In my humble opinion, stick to the book. As soon as you start using "techniques" to replace "SOPs", you are on your own. The performance numbers plotted by the manufacturers are based on the operational procedure performed at the time the performance was proven. Anytime you start drifting from it, you're a test pilot.

 

[Lead Sled]

In my humble opinion, stick to the book. As soon as you start using "techniques" to replace "SOPs", you are on your own. The performance numbers plotted by the manufacturers are based on the operational procedure performed at the time the performance was proven. Anytime you start drifting from it, you're a test pilot.

Well, not quite. If you made every takeoff according to the book you would sit at the end of the runway, set takeoff power and wait, for what? 45 seconds for the numbers to stabilize before releasing the brakes. Show me anyone who does that.

Like I said, I'm not advocating that you ignore book procedures. I'm the one who constantly harps that if you want to achieve book performance you have to fly the airplane by the book. What I am questioning is the wisdom of some pilots to dink around adjusting the power levers so as to set precisely a power setting that is guaranteed to provide nothing more than the minimum required takeoff performance - all while the airplane is accelerating like a raped ape and while all this is going on the guy in the right seat is missing the speed callouts. Tell me you've never had that happen. Set the power and don't mess around pulling it back to a precise N1 if you happen to go over a little bit. The engine folks aren't going to care; as far as they're concerned you can shove the power levers to the stops and leave them there for up to 5 minutes without exceeding any limitations - provided your computers are set up correctly.

LS

 

[gear_guy]

Good thread folks. We should have more discussions like these. It's wisdom sharing threads like these that make us all better informed pilots.