747-8 Flaps and Pitch

So I looked for topics relating to my problem, but they are about climbing. Mine is different.

So my weight is <25 %, and I deploy Flaps 10 at 230 KIAS. The aircraft pitches up to as high as 4000 fpm and just stays there. Doesn’t come back down.

Something wrong I’m doing? Not enough trim?

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My question is why would you have flaps at 230 kias

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It really didn’t make a difference…

Does it?

I mean having flaps at 230 kias when you’re not really heavy for the 748 doesn’t seem like something you should do.

l am not trying to attack you or anything so please don’t take it that way

Well, the flaps can cause excessive pitch when used at higher than needed speeds so yea it does make a difference.

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Okay that must be it…

Still, the MCAS system on all aircraft isn’t too good so the aircraft might pitch up a lot…

What was your trim?

I imagine not enough.

35%

Is that minus 35 or +35?

Now I’m not an expert so I don’t know technical names but I’m pretty sure positive trim raises the nose up, so 35% trim, with 230 KIAS which is quite fast at flaps 10 may raise the nose quite high

Well, at practically 20 KIAS under violation speed under 100FL with you deploying flaps, it’s like opening an umbrella while you’re speeding on a motorcycle ride… you’ll go up and up as well,

and you’re not gonna stay on that bike that’s for sure.

Hope the analogy clears it up, cheers! :)

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Don’t ask a question if you don’t want answers. 😬

Flaps help generate more lift. At a lower weight your flap speeds will also reduce. For a B747 below 25% weight I’d recommend getting below 200kts before selecting flaps 10°. It is common to get a slight bump in the nose when dropping flaps which you should combat with some nose down pressure.

Additionally, ensuring you’re at a proper speed for the different flap settings will significantly reduce that nose up tendency when selected.

If you want to see this in action, hop in the XCub and try putting in the first notch of flaps while above 70kts. Do the same when you’re around 60kts which is a more appropriate speed. You’ll see a big difference in aircraft characteristics purely by adjusting flaps at the correct speed.

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image

Alright then. Case closed,

Alrighty then. 😐

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