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Effects Of Takeoff Stabilizer Trim Setting  
User currently offlineaerotech777 From United States of America, joined Aug 2009, 68 posts, RR: 0
Posted (2 years 10 months 1 week 6 days 13 hours ago) and read 5246 times:

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

16 replies: All unread, jump to last
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 1, posted (2 years 10 months 1 week 6 days 11 hours ago) and read 5186 times:

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.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 2, posted (2 years 10 months 1 week 6 days 10 hours ago) and read 5172 times:

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.


User currently offlineaerotech777 From United States of America, joined Aug 2009, 68 posts, RR: 0
Reply 3, posted (2 years 10 months 1 week 6 days 9 hours ago) and read 5161 times:

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.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 4, posted (2 years 10 months 1 week 6 days 9 hours ago) and read 5156 times:

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.


User currently offlinejetpilot From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 5, posted (2 years 10 months 1 week 6 days 9 hours ago) and read 5153 times:

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.


User currently offlineTristarsteve From Sweden, joined Nov 2005, 4009 posts, RR: 33
Reply 6, posted (2 years 10 months 1 week 6 days 5 hours ago) and read 5116 times:

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?


User currently offlineaerotech777 From United States of America, joined Aug 2009, 68 posts, RR: 0
Reply 7, posted (2 years 10 months 1 week 5 days 22 hours ago) and read 5021 times:

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


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 8, posted (2 years 10 months 1 week 5 days 19 hours ago) and read 4961 times:

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.


User currently offlineThrottleHold From South Africa, joined Jul 2006, 657 posts, RR: 1
Reply 9, posted (2 years 10 months 1 week 5 days 14 hours ago) and read 4862 times:

Changing thrust setting for take off has no effect on stab trim setting.

User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 10, posted (2 years 10 months 1 week 5 days 11 hours ago) and read 4821 times:

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


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 11, posted (2 years 10 months 1 week 5 days 11 hours ago) and read 4816 times:

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.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 12, posted (2 years 10 months 1 week 5 days 11 hours ago) and read 4809 times:

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

Wow, how did that happen?


User currently offlineThrottleHold From South Africa, joined Jul 2006, 657 posts, RR: 1
Reply 13, posted (2 years 10 months 1 week 4 days 23 hours ago) and read 4697 times:

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.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 14, posted (2 years 10 months 1 week 4 days 19 hours ago) and read 4613 times:

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.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 15, posted (2 years 10 months 1 week 4 days 9 hours ago) and read 4548 times:

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.


User currently offlineThrottleHold From South Africa, joined Jul 2006, 657 posts, RR: 1
Reply 16, posted (2 years 10 months 1 week 2 days 7 hours ago) and read 4347 times:

edited for spelling and grammar

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

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