Trim (Boeing 787-10)

Trim doesn’t do anything while the AP is holding altitude. I’m assuming you guys aren’t hand flying for 17+ hours but it sounds like you’re seeing effects from trim. This shouldn’t be possible, can either of you explain this?

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While somewhat true, it actually does have a huge impact. And noticeable in overnight or long haul flights. Its noticeable in the fuel burn. What its doing is relieving the back pressure needed to hold the aircraft in level flight. By reducing this back pressure, you’re reducing drag which means your aircraft is more slippery in the air. Which in the end results in less power needed to get the aircraft moving at a constant rate

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I actually never knew that. That’s super cool. I’ll make sure to trim my aircraft in flight. Now we just need a “what is your favorite trim setting for aircraft” topic. 😂 I’m just kidding, you’ve seen way to many of those. Poor Deer Crusher

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This wasn’t the 787-10, but the 747-200. I was doing a 15 hour overnight flight in the 742, and it looked like I didn’t have enough fuel, even though I packed it full as that was what simBrief said to do. I didn’t know what trim was (this was a flight in my first two months of IF), so I left it alone. I crashed and got 6 vios. I was upset, but wasn’t on the IFC and didn’t know what the IFC was so I just waited a week to get back on TS1 (I was grad 2 then). Now (like right as I’m sending this message), I am trying an overnighter from KDTW to RKSI on a Northwest 747-200 and I have adjusted the trim to 66% which is the usual trim in a 747 of all variants, and so far my fuel is looking great!

It actually doesn’t, I highly encourage everyone to try it out for themselves. Once the aircraft re-stabilizes it will have the exact same fuel burn as before. I’ve tested this pretty thoroughly since I exclusively do ULH flights.

For example, the current flight I’m doing had 15:40 minutes of fuel remaining at 0% trim. I just went to -70 trim and it returned to 15:40

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Probably haven’t paid that much attention to the details then. 🙃

I’d like to hear what your reasoning is as to why my endurance improved when trimming the aircraft. Maybe I am wrong.

This is what not to do. Most if not all aircraft will require a positive trim of some sort. If you’re trimming in the negative direction, you likely did something wrong.

The only way to test it would be to go on solo and go to cruise, same weather and everything so the results aren’t skewed, then see if there is a change between the different trim settings. I notice a change in speed GS in group flights when I set my trim at cruise so I’d imagine what @DeerCrusher said is true to the sim.

You don’t trim just sake of it. Yesterday I flew A330 40000ft at mach. 85. (Recommend. 84) like butter with 0% trim. It was flying flat. There was big tail wind and trim was showing none needed. You check everything before you trim.

I can do anything with the trim since it has no steady state effect while the AP is engaged. I’m now at +100 with the same fuel burn as 0 and -70 (I also went to -100). Again, I highly encourage you all to test this for yourselves.

When you do these tests, wait a couple minutes for the aircraft to settle back down. No matter what trim setting you go to it’ll return to the same fuel burn as before.

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If you could private message me the details of the aircraft, weight, altitude and any other useful information that you are able use to come up with this conclusion. Perhaps there’s an issue with the sim because this is not suppose to be the case. Thanks for the help into looking into this.

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Honestly I do trim for the sake of it because it won’t effect my performance/range.

Sorry for being off-topic but what is the A380s optimal trim?

(I’m flying rn and I gotta know haha)

Thanks for all the help, fuel remaining/eta is out of the red/orange. So far have 9:11 remaining (flight time 8:26). Cruising FL 370 @ mach .86, and I am burning fuel at a rate of about 11,500 lbs/hr.

You do notice that in both the pictures, the condition isn’t the same right. (In your tutorial)

In the second picture, you have a decreased N1 and and -ve VS in comparison to your first picture.

I too agree with @s1b2p5 and the fuel consumption is nearly the same even after trim. Differs just by a small bit and not the margin showed by your pictures. But your explanation of how trim works is perfect; maybe IF slightly downplays the role of the trim.

@Ayush_Mathur I think the N1 went down because of the decrease in drag due to the trim. Everything else looks the same other than the trim and the N1.

You can checkfor yourself. There is a difference, But so extremely minor.

@Ryandyc

I’ll probably check that out later, I’m about 6 mins out of my TOD. Then I need a rest after flying for so long.

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There is no difference at all actually. Any change you’re seeing is probably from the aircraft re-stabilizing

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That was dead on: I ended up with 10% fuel when I landed. My flight time was 17 hrs 16 mints.

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