Question about trim

Hi,

I’m flying the 787 and I’ve always gone off the rule that if the purple/pink line goes away it means its the right trim, currently, I’m up to about 40%, I’m just wondering how I can better efficiently operate the aircraft and if this is the right way to do it?

Cheers

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G’Day mate. That is a very good question. I normally go 10 to 20% trim. But I think you are doing it right

Cheers

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For IF that’s normal, I too need significant trim when using the 787 family. Not sure if this properly simulates reality but yea…

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Does it add any benefit to the performance of the thing? I’ve got a long flight and I want to save every kilo of fuel I can

I’ve heard it does when researching it myself. Not sure how tho, bc trim resembles “calibrating” the elevators…like presetting them to pitch up/down orientations, which to me doesn’t help anything other than reduce the manual input required to pitch the nose up/down

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Makes sense, she seems to be using less thurst compared to when I was flying her without it. Thanks so much!

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Not on any IF aircraft AFAIK… Only the 772 even has trim aniamtion. Other aircraft show is as simply elevator input

@Louis
Trimming, ultimately, reduces drag (when talking about a commercial airliner at least). When you trim a light aircraft, you move a tab on the elevator surface in one way or another in order to neutralise the forces felt in the control stick/column. Although this makes the flying easier as you’re not constantly pushing/pulling on the stick or yoke (trust me, it’s gets very tiring very quickly), it also creates more drag.

Now, trimming works differently for a commercial aircraft with something called a Trimmable Horizontal Stabiliser (THS) - note that this is Boeing’s name for it, Airbus call it something else. The THS is essentially an elevator that hinges off another non-moving surface in front of it, all of which is then bolted to the aircraft fuselage. Pretty standard stuff, much like a lot of GA aircraft, and this can be observed on the vast majority of the aircraft in Infinite Flight.

The difference is in how the aircraft is trimmed. Instead of moving a tab on the trailing edge of the elevator surface, the entire unit is rotated relative to the fuselage on which it is mounted. This is the effect that @xsrvmy mentioned is only shown on the 772.

The whole point of moving the entire unit that, for a load of principles of flight reasons, it reduces drag relative to the other ways of trimming. The other reason is that by moving the whole front portion, full elevator authority is retained (i.e. you still have the full range of movement of the elevator, thus giving control over a greater range of speeds, weights, configurations etc).

This whole THS assembly moves about a nominated neutral point, which appears to be taken as ‘0%’ trim in Infinite Flight. The percentage shown is then how much the THS is deflected from said neutral position by. Therefore, 30-40% is perfectly normal and reasonable for cruise.

It’s worth noting that trim does not vary from person to person during the cruise, despite what some others may say. Is does, however, depend on personal preference when on final approach and landing - during this phase of flight, use what feels right.

I hope this explanation helps you understand how the trim system works and why it is represented how it is in Infinite Flight. I realise I’ve gone a bit overkill for Infinite Flight, but it’s interesting to know none the less.

Cheers

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Trim varies from person to person and on the aircraft weight. Usually I use +25-30 on B787.
It also depends upon you control sensitivity.

I usually trim until the magenta line disappears. The percentage varies amongst different aircraft. Trim on the CRJ family can be interesting for takeoff configurations, it’s common to be in the 40% range, even more so on the DC-10/MD-11 as well.