aerotech777
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Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 1:53 am

Hi,


Quote: "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
 
tdscanuck
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 4:34 am

Quoting aerotech777 (Thread starter):
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.

On aircraft with underslung engines, thrust creates a nose-up pitching moment. To get the same overall pitching moment with lower thrust, you need to get that pitching moment from somewhere else...nose-up trim.

Tom.
 
474218
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 5:35 am

The trimmable stabilizer is just like all other flight controls surfaces: The amount of surface movement required is dependent on speed. More speed less surface displacement required, less speed requires more surface displacement.

So for your de-rated takeoff (less speed) more stabilizer nose up trim is required.
 
aerotech777
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 6:03 am

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

Feedback appreciated.
 
tdscanuck
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 6:16 am

Quoting aerotech777 (Reply 3):
I am asking for the effects of takeoff stabilizer trim setting on aircraft performance when using reduced thrust (assumed or derated) versus max takeoff thrust.

More nose up trim means more drag on the tail, which means more runway required to reach the necessary speed. Not a huge impact but not zero either. The impact of having less thrust has a far larger impact on takeoff roll than the change in the stab setting.

Tom.
 
JETPILOT
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 6:22 am

Quoting aerotech777 (Thread starter):
"Stabilizer trim setting varies with thrust rating. Derated thrust requires more nose up trim than max rated thrust"

This is news to me. Show me a stab trim performance chart that factors in TO thrust please.
 
Tristarsteve
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 9:59 am

Quoting aerotech777 (Thread starter):
"Stabilizer trim setting varies with thrust rating. Derated thrust requires more nose up trim than max rated thrust"

So when the dispatcher gives you the loadsheet with the trim setting on it, how do you change this to correspond to whether you are doing a full-power or reduced-power take off?
 
aerotech777
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 4:37 pm

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.

Here a quote from another forum

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

A response from another member from the same forum: " 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"

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
 
tdscanuck
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RE: Effects Of Takeoff Stabilizer Trim Setting

Sun Nov 13, 2011 7:45 pm

Quoting aerotech777 (Reply 7):
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.

Yes, very significant. For equal weights, takeoff with derate, or ATM, or derate+ATM, will result in a longer takeoff roll and shallower initial climb-out.

Tom.
 
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ThrottleHold
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RE: Effects Of Takeoff Stabilizer Trim Setting

Mon Nov 14, 2011 1:28 am

Changing thrust setting for take off has no effect on stab trim setting.
 
474218
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RE: Effects Of Takeoff Stabilizer Trim Setting

Mon Nov 14, 2011 3:43 am

Quoting tdscanuck (Reply 8):
Changing thrust setting for take off has no effect on stab trim setting.

According to Boeing Flight Operations four (4) things effect the Trim Setting:

- Weight
- C.G.
- Flap Setting
- Engine Thrust Level
 
tdscanuck
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RE: Effects Of Takeoff Stabilizer Trim Setting

Mon Nov 14, 2011 4:12 am

Quoting 474218 (Reply 10):
Quoting tdscanuck (Reply 8):
Changing thrust setting for take off has no effect on stab trim setting.

According to Boeing Flight Operations four (4) things effect the Trim Setting:

Not my quotation...it was ThrottleHold from the post below.

Tom.
 
474218
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RE: Effects Of Takeoff Stabilizer Trim Setting

Mon Nov 14, 2011 4:23 am

Quoting tdscanuck (Reply 11):
Not my quotation...it was ThrottleHold from the post below.

Wow, how did that happen?
 
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ThrottleHold
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RE: Effects Of Takeoff Stabilizer Trim Setting

Mon Nov 14, 2011 4:11 pm

Quoting 474218 (Reply 10):

Those 4 factors will affect the trim setting inflight, but not the stab trim setting for take off.

A few days ago I departed BHX. Planned for a 15 departure with an assumed temp reduction. Load sheet received and stab trim set. On start up tower changed ops to 33. Take off performance was recalculated, with a change to TOGA power and the relevant V speeds. At no time was stab trim setting changed, nor is there any requirement to do so.
 
474218
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RE: Effects Of Takeoff Stabilizer Trim Setting

Mon Nov 14, 2011 8:11 pm

Quoting ThrottleHold (Reply 13):
Those 4 factors will affect the trim setting inflight, but not the stab trim setting for take off.

I don't make things up! I suggest you read the following:

http://www.captainpilot.com/files/B737?takeoff%20Performasnce.pdf

By clicking on Takeoff Performance you will end up at a Boeing Flight Operations pdf document.

On Page 70 of that Boeing pdf document you will find:

o A horizontal stabilizer trim setting is used during all takeoffs. These settings are designed to produce an in-trim condition at:

- The proper all engines operating climb-out speed of V2 +15 kts (V2 +10 to 20 for 3 and 4 engine airplanes)

- The proper one engine inoperative climb-out speeds v2.

- Reasonable column forces for the pilot.

o Trim setting is provided as a function of the airplane weight, C.G., flap setting and engine thrust level.
 
tdscanuck
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RE: Effects Of Takeoff Stabilizer Trim Setting

Tue Nov 15, 2011 5:40 am

Quoting ThrottleHold (Reply 13):
Those 4 factors will affect the trim setting inflight, but not the stab trim setting for take off.

In addition to 474218's link to the Boeing Flight Ops document, you can also look up the stab trim setting tables from assorted Performance Dispatch documents...they will give different trim values for different thrust settings.

Quoting ThrottleHold (Reply 13):
A few days ago I departed BHX. Planned for a 15 departure with an assumed temp reduction. Load sheet received and stab trim set. On start up tower changed ops to 33. Take off performance was recalculated, with a change to TOGA power and the relevant V speeds. At no time was stab trim setting changed, nor is there any requirement to do so.

If it was a Boeing (I'm assuming so because you used ATM) then you do have a requirement for the stab to be in the greenband. When you recalculated the performance for the new runway did you get a new stab value that was the same as the old one, or did you not get a value at all? Provided you were still in the green band you're correct that there was no requirement to change the stab setting but, if calculated from scratch, you could have gotten a different stab setting number (within the same greenband).

Tom.
 
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ThrottleHold
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RE: Effects Of Takeoff Stabilizer Trim Setting

Thu Nov 17, 2011 8:23 am

edited for spelling and grammar

[Edited 2011-11-17 00:36:31]

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