Effects Of Takeoff Stabilizer Trim Setting

[AeroTech]

Hi,

Stabilizer trim setting varies with thrust rating. Derated thrust requires more nose up trim than max rated thrust.
I am assuming assumed takeoff thrust requires more nose up trim than max rated thrust (same as derated thrust).

If this statement is true, what are the effects of takeoff stabilizer trim setting on aircraft when using reduced thrust (assumed or derated) versus max takeoff thrust.

Feedback appreciated.

Regards

[AeroTech]

To clarify my question, I am asking for the effect(s) of takeoff stabilizer trim setting on aircraft performance when using reduced thrust (assumed or derated) versus max takeoff thrust.

Feedback appreciated.

[Intruder]

If you don't use the stab trim, you'll have to use more elevator. What else are you after?

Reduced thrust will decrease performance. I suspect the drag due to stab configuration is insignificant in comparison.

[dixi188]

Which aircraft type?

Our A300s don't have a change in stab trim for flex or max thrust.

[Sciolistes]

Derated thrust requires a separate performance data which may adjust the required trim when compared to full thrust or another derate.

Assumed temperature uses the same performance data as the selected thrust setting (full or derate) and so the same trim setting for that thrust setting.

So, for example, if using an assumed temp t/o with full thrust there is no change in the required trim setting.

[BOAC]

AT - NB I am not familiar with trim setting on ALL aircraft types and there may be a few where it is crucial, but in my experience as long as the trim is in the right 'area' there will be little problem with variations in thrust since elevator control is sufficient to compensate for minor differences, hence as Sc says, it does not change (737) for a reduced (assumed) temp - nor does it change for take-off speed incidentally. I never flew a 737 with a fixed derate so I cannot comment but it is possible that a very minor change is present in the published settings tables.

Where did your original quote come from?

[misd-agin]

AeroTech - performance charts don't give different stab trim settings for derated vs. max power.

With wing mounted engines, and the thrust line below the C.G. resulting is less nose up force by the engines, there's additional pitch force needed on rotation and retrimming after liftoff.

If there was a significant drag change I'd believe our performance charts would reflect that. Since I've never heard of it on DC-9's, A-300, or various Boeing models, I have to assume any difference that might exist is too small to worry about.

[Sciolistes]

AeroTech - performance charts don't give different stab trim settings for derated vs. max power.
I'm afraid they can. Looking at my 737 Perf Inflight. I have separate trim tables for 27K, 26K and 24K, each showing a different trim value for the same weight and MAC.

[AeroTech]

Thank you for your feedback.

I get my quote from smartcockpit.com (Boeing presentation by Performance Engineer: Reduced Thrust Operations, page/slide 51).

I thought there will be some changes in aircraft performance if more or less nose up trim is required. So far Sciolistes confirmed trim change (Thanks Sciolistes).

I am wondering if there will be significant change in aircraft performance if significant reduced thrust is used (for example assumed plus derated takeoff thrust) or even just assumed takeoff thrust.

Feedback appreciated.

[misd-agin]

Sciolistes - do they show different trim settings for 24K derate vs. max? 26K derate vs. max?

Different engines have different trim settings. I havn't seen different trim settings between derated vs max power.

The answer that I've been told is that the trim setting is for max power for a specific engine. It does not change if you're using derated power. Not sure it that's company SOP or manufacturers SOP but our trim does not change if we switch to/from derated power

[Denti]

Interesting question really, never actively checked if there's a difference. We always use FMC provided trim setting and i know it changes with flap setting but i haven't noticed that it changes with derate, it certainly does not change with assumed temperature.

Gonna check it out on my only sector tomorrow.

[misd-agin]

I'm using the term 'derated' in the same context of using 'assumed temperatures'. IE, less than max power for the selected engine.

[FE Hoppy]

De-rate is a fixed reduction with published data.

Reduced (flex) is a variable reduction based on corrections or adjustments to the published data.

On the Ejets the take-off stab trim setting is based on mass and CG position and is not adjusted for either De-rated or Reduced take-off thrust.

[Denti]

I believe it is the same on the 737, but i have to check tomorrow. If i remember correctly it is based on GW, CG% and flap setting.

And of course in boeing speak a derate means a fixed derate with a complete new set of performance data (VMCg/a for example). Derates on our 738s are 24 and 22k, 20 and 18k on our 700s. Base thrust setting is 26k and 22k.

[Sciolistes]

I am suprised at the confusion as the distinction between derate and assumed was clear from the first post.

Aerotech,
I am wondering if there will be significant change in aircraft performance if significant reduced thrust is used (for example assumed plus derated takeoff thrust) or even just assumed takeoff thrust.
Rather perversly, due to the lower VMCG/A derated thrust can increase the max takeoff weight on contaminated or slippery runways. I presume, for the same reason it may be possible to depart from a short runway that would be VMCG/A limited at full rated thrust too.

[Denti]

Well, from what i've seen today trim does indeed change with derate, but not necessarily with flap setting. Flaps 1 and 5 use the same trim as does flaps 10 through 25. Changes between thrust rating are pretty small, between the two different flap setting ranges much much bigger.