Rolling takeoff with a TFE-731

[Capt1124]

I have seen the Honeywell video in which the company adamantly states you must not do a rolling takeoff with this engine. The Westwind AFM doesn't say this. I would be willing to go along with this, however 1) static takeoffs are not always a good idea, such as on a slick runway, and 2) we have a regulator approved manual that says rolling takeoffs are permissible with extra runway.

My preference would be to let sleeping dogs lie, but since Honeywell is so insistent about this, what are the opinions of those who have flown 731 equipped airplanes?

 

[hawkerjet]

One of the effects of a static takeoff at heavier weights is hotter brakes. I usually pause through 65 % release the brakes and set power. On days when I do the full static then I leave the gear down for an extra second or two before retracting, for cooling. ( Westwind A/C)

 

[Canucit]

where can I see the video from honeywell, and is that for all 731"s or just on the westwind
thanks

 

[Capt1124]

A guy I used to do training with has the video. The airplane used in it is a Citation III so I beieve it applies to all aircraft with 731s. They say unless takeoff N1 is observed before brake release, you make not get full power until a few hundred feet off the ground.

 

[ultrarunner]

Better to have a carbon seal blow out earlier than later. I do no miss that engine.

 

[Seadogrun]

I'm interested in seeing this video also. What was the contex of the statement? Is it a CYA runway performance statement?

Some airplanes(may not be 731) you may not use static power under certain X-wind values.

 

[con-pilot]

I don't believe I have ever seen that restriction on any of the 731 powered aircraft I have flown, the Sabre 65, Falcon 50/900, JetStar 731 nor the Westwind I/II.

I'm not saying there is no restriction, but sure don't remember any about not doing a rolling takeoff. God knows I have done enough of them with no problems.

Could this be something fairly new?

 

[NW Flyer]

It was never mentioned to me during training for the Lear 45, and I do remember a blurb about adding a percentage to the takeoff roll if you perform a rolling takeoff.

I do know that if you wait to see takeoff N1 before brake release in the 45, especially a lightly loaded one, you will scare your pax and dump the catering on the floor. Not recommended.

 

[Lead Sled]

The only thing I ever remember hearing from Honeywell, ne Allied Signal, ne Garrett was that takeoff distances began from whatever point you were at when the takeoff N1 was achieved - regardless of your ground speed. They also specificed that takeoff N1 was a minimum number. I have documentation on the latter, but not on the former. It was years ago though at some NBAA shindig.

LS

 

[avbug]

I don't believe the N1 values are minimums; those should represent max values for takeoff, and are temperature and altitude based. I'm looking at a LR35 QRH right now and it states the %N1 numbers are maximum values.

I suspect that what's implied by the inference that they're minimum numbers is the meaning that these values are the gauranteed thrust producers. The only real limitation is the temperature and the upper RPM values. Likewise, published distances won't be valid unless the proceedures published with them are used. A rolling takeoff can't predict where and how fast power application will occur, and accordingly, puts the takeoff numbers out the window.

N1 is an easy to use value, but it also doesn't really describe thrust. It's just a speed, and the condition of the engine and fan, as well as the ambient conditions, really dictate what thrust is being produced. That may be the reason for the data being describe the way you have it; that fan speed is a number that may represent the minimum value to produce rated thrust...though the truth is that the engine may not really be putting that out, anyway.

If I'm setting a preplanned N1 value, I'm of course watching the temps, and may limit the engine before that value is reached, or be tweaking the power back to respect the temps during the roll. It's the engine temp that's limiting, assuming the fuel computer does it's job. If the mechanical goernor/fuel computer is working properly, especially with DEECs, then temp shouldn't be an issue either...but I never make that assumption.

If runway isn't a big issue, then I much prefer to let the airplane roll. I don't like to do rolling takeoffs from the taxiway; I've seen a number of pilots apply power from the first point they start to enter the runway, and that turning moment is very tough on gear. I saw a tire get peeled off the wheel assy on a C-130 that way. I prefer to line up, do a final check, then power up and let it roll. I'll usually hold the brakes for partial power; I prefer to establish a stable power setting and do a crosscheck through all engines, and I think it makes for a smoother power application. It eliminates any low end surges or hesitations if all engines are partially and equally spooled before brake release.

Someone else mentioned not wanting to do full power braked releases. I don't know that excess brake energy is imparted if the wheel isn't in motion, but the lurch as the aircaft comes out of brake release isn't smooth, and it's not good for passengers.

So far as there being problems with the TFE-731...it's one of the best corporate engines out there. I don't know why anyone would be glad to be rid of them.

 

[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.