V/S Issue, plane likes to pitch up and down excessively

Device: iPad Mini 6
Operating system: iOS 15.4.1

Okay, so. When I takeoff and activate V/S mode, my plane tends to violently pitch up and down several times before stabilizing in a constant rate of climb.

For example, I could be planning on climbing out at 3000fpm. I would takeoff, and after I climb a few thousand feet activate V/S mode AS i’m actively climbing ~3000fpm while hand flying. The plane will pitch way down, sometimes to the point where I have a negative rate of climb, and then immediately pitch up to, let’s say, around 5000fpm, before stabilizing. Like I’m talking 20-25° pitch up. I don’t consistently fly every plane in IF, but as far as I know every plane has this issue for me.

I’ve tried a lot of things, waiting until I have a constant speed, activating V/S mode before I activate my ALT, I’ve even tried hand flying all the way to cruise altitude and then activating it, yet the problem persists.

I just wanted to know if anybody else has had this problem before, and if there’s a known way to fix it. Am I doing something wrong, or just missing something crucial? If anybody needs a screen recording of a replay file or something like that, I’m happy to provide it for you.

Thank y’all in advance, and anything helps! :)

2 Likes

you could try to keep the pitch neutral before activating the V/S, I think the IF should have the Autopilot transition smoother, because it really is kind of aggressive

I never experience this - what aircraft are you using when this happens?

You probably need to set trim.

Hey there,

It sounds like you may be retracting flaps a little too early, what aircraft are you in and what was the config? (weight, speeds, flap settings etc) and your clean speed (i.e your speed when all flaps were retracted)

Never experienced this. Make sure ur going fast enough to climb at 3000 fpm

I have this too. How I fix it is by increasing/decreasing my V/S slowly, just like how VNAV does.

Are you sure you are activating V/S rather than ALT, where ALT is below your current altitude? I have had similar to what you are describing when the ALT is below my current altitude and I activate it?

Hi! :)

I’ve actually considered this too. Like I mentioned in the original post, I’ve tried pretty much everything I can think of to prevent it from happening, but to no avail. Normally I don’t retract my flaps at all until I’m past 200kts at LEAST. And again, I have this issue with every aircraft I fly, irregardless of the weight, weather conditions, etc…

I never takeoff without first setting my ALT to my planned initial cruise altitude. For a while I thought this may have been the issue because it seemed worse whenever I forgot to set the ALT, but it happens regardless of if I set my ALT first or not.

So I was just now trying to reproduce what you described in some way.

(edit: What is puzzling is that hitting the V/S button by itself is one of the most stabilizing actions I can think of when flying. It pretty much always moslty holds what climb state you are in.)

The only way I could do it is (as mentioned before) if I hit the ALT button by “accident”, being next to the V/S button, and again, only if ALT setting is below my current altitude.

Even if my speed is at a “risky low” setting and even without flaps, if I just hit V/S alone, the pitch hold is still consistently very stable.

And if I hit the ALT button, as long as altitude setting is above my current altitude, again the pitch hold is very stable.

Sorry, I don’t think this adequately answers your issue. But I can’t think of anything else.

1 Like

Hey there,
I have had exactly the same problem for a long time now. I’m sure it’s not due to hitting the alt button by mistake, and i’ve just screen recorded two takeoffs where this happened moderately so you can see.
Whenever the V/S is engaged, the nose pitches down about 5°, thus destabilizing the flight parameters by raising the speed, then it reacts by pulling up too quickly and raising the V/S a few hundred feet more than initially set, and bleeding off airspeed.

Device: Iphone 11
IOS 15.5

The first video is of a pretty standard takeoff, 28°C, N1 90%, Pwr 83%, 15kt headwind, in a slightly heavy 737-8 (66.5 tons, 71% load)

Same conditions and weight for the second one but with higher thrust (N1 96%, Pwr 90%)

The nose down is more noticeable on the first video with lower thrust.
Maybe i’m being too nitpicky but it definitely isn’t what i would call “consistently very stable” :(.
For me, it consistently noses down every time i engage V/S, at a varying degree but always at least 3-4° and just enough to make the flight wobbly and go down to 0.8g.

Maybe I’m doing something wrong?
Looking forward to figuring this out together:)
J.

In both videos your trim isn’t set correctly as the pink bar is still visible on the trim bar. You need to adjust the trim so that there is no pink bar.

Try doing that and see if the issue persists.

This is almost exactly what happens to me, but just on a much larger scale. I’m gonna play around with it a little bit more later today and see if I can find out what the issue is. I’ll let you know if anything comes up :)

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