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Steep nose up on take-off, lots of trim needed


Lange_666

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Recently (don't know from when, bin a while since i've flown the F-5E) i notice that once the aircraft takes off it has the tendency to put his nose up quite heavily. It needs a lot of trim to get into level flight with minor stick input.
I can't remember such a heavy trim was needed. If i don't trim, the F-5 just stalls. Looked into controls, they are working just fine.
Did something change in the past few updates (stable and beta)?

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No, it always has been like this. Heavy nose up trim for take off, and then trim a lot nose down for level flight (depending on speed more or less trim needed) 

Yup, and I think they even mention why in the take-off training mission.

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5 minutes ago, MAXsenna said:

Yup, and I think they even mention why in the take-off training mission. emoji4.png

I'm gonna check that out.

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When I have gear up, I trim nose down and hold it, to the count of 8.

Edit: Just incase. Not sure if the speed of trim is tied in with frames per second, but Im in VR and fly with 45 fps.


Edited by Knock-Knock

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4 hours ago, Lange_666 said:

Recently (don't know from when, bin a while since i've flown the F-5E) i notice that once the aircraft takes off it has the tendency to put his nose up quite heavily. It needs a lot of trim to get into level flight with minor stick input.
I can't remember such a heavy trim was needed. If i don't trim, the F-5 just stalls. Looked into controls, they are working just fine.
Did something change in the past few updates (stable and beta)?

This is fairly common swept wing jet behavior. After rotation the nose will continue up and require forward stick to stop this motion. Aft stick to "unstick" the aircraft and then forward stick once airborne to stop the pitch up. I wouldn't use trim to fly the airplane. Use the stick to put the airplane where you want it and trim to relieve the stick force is the proper way to use trim.

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4 hours ago, =475FG= Dawger said:

Aft stick to "unstick" the aircraft and then forward stick once airborne to stop the pitch up. I wouldn't use trim to fly the airplane. Use the stick to put the airplane where you want it and trim to relieve the stick force is the proper way to use trim.

You're talking in riddles for me because:
- Aft stick to "unstick" and then push forward to stop the pitch up:  just tried it, it doesn't "unstick" and the behaviour of the airplane is exactly the same, unsticked or not.
- Use the trim to fly the airplane or use the stick and then trim to relieve the stick has exactly the same outcome in aircraft behaviour.

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1 hour ago, Lange_666 said:

You're talking in riddles for me because:
- Aft stick to "unstick" and then push forward to stop the pitch up:  just tried it, it doesn't "unstick" and the behaviour of the airplane is exactly the same, unsticked or not.
- Use the trim to fly the airplane or use the stick and then trim to relieve the stick has exactly the same outcome in aircraft behaviour.

"Unstick" is the term for when the aircraft lifts off the ground. This is something that it is necessary to force in aircraft with a negative angle of attack when on the ground such as the F-5. Aircraft certification requirements have a minimum unstick speed.

 

image.png

I was not describing how to prevent anything. What you are experiencing is the normal behavior of the aircraft. No matter what you do, the nose is going to continue to pitch up after you  'unstick' it. The proper technique is to apply forward stick to stop the nose at your desired acceleration attitude, hold that attitude with the stick and trim out the control force.

It is not proper technique to use trim to maneuver the aircraft. 


Edited by =475FG= Dawger

 

 

 

 

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50 minutes ago, =475FG= Dawger said:

The proper technique is to apply forward stick to stop the nose at your desired acceleration attitude, hold that attitude with the stick and trim out the control force.

That's how i did it in the first place. Just can't remember the pitch up was that hugh.

 

50 minutes ago, =475FG= Dawger said:

It is not proper technique to use trim to maneuver the aircraft.

I never did, guess you misinterpreted what i said in my first post (or i described it wrong, whatever you prefer).

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Thought so after reading your commend but that's not the case.
 

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  • 2 weeks later...

According to Spooky over at the BuddySpike Discord the difference comes from a cold start at an airport and a hot start on a road base.

From Spooky: Because they start hot started which includes the procedure of adding 5 degrees of nose up trim. You have to trim it back down after gear and flaps up.

 

So that's sorted.

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19 hours ago, Lange_666 said:

According to Spooky over at the BuddySpike Discord the difference comes from a cold start at an airport and a hot start on a road base.

From Spooky: Because they start hot started which includes the procedure of adding 5 degrees of nose up trim. You have to trim it back down after gear and flaps up.

 

So that's sorted.

Or trim it back down prior to takeoff to where all that mucking about after takeoff is unnecessary.

 

 

 

 

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  • 4 months later...

I trim nose down before takeoff. Yes, requires more aft stick to rotate, but it's more balanced once it gets airborne. I still need to trim, but not quite as much.

Also ensure you are rotating at the correct airspeed. If you're heavy, you'll be towards 200 kts before she'll fly.

Also check you have the correct flap setting for takeoff (it should say AUTO). Visually check the slats are extended and the flaps are in takeoff position.

At ~150 kts I pull aft stick and hold it until the nose starts to come up, then I ease the stick forward and just wait for it to fly off the runway. I hold the pitch attitude, let it accelerate, and clean up.

Don't forget also to extend the nose gear leg for takeoff (switch on the left sidewall). It raises the nose about 5 degrees.


Edited by Tiger-II

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  • 2 weeks later...
On 11/1/2021 at 4:05 PM, =475FG= Dawger said:

This is fairly common swept wing jet behavior. After rotation the nose will continue up and require forward stick to stop this motion.

The airplane is going to seek it's trim-speed. That has nothing to do with sweep-angle, but with excess-power. If the airplane can accelerate quickly enough to put you at a much higher than trimmed speed at lift-off, the nose will come up quite pronoucedly. This is where having good TOLDS-data would help, reather than eyeballing a rotation-speed and corresponding trim-settings.

So ein Feuerball, JUNGE!

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On 3/31/2022 at 6:27 AM, Bremspropeller said:

The airplane is going to seek it's trim-speed. That has nothing to do with sweep-angle, but with excess-power. If the airplane can accelerate quickly enough to put you at a much higher than trimmed speed at lift-off, the nose will come up quite pronoucedly. This is where having good TOLDS-data would help, reather than eyeballing a rotation-speed and corresponding trim-settings.

You are incorrect, sir.

 

 

 

 

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Swept wing causes a pitch up at the stall, but during takeoff you are above the stall and accelerating.

As the aircraft leaves ground effect, the center of pressure moves forward, causing a pitch-up moment. This, and the fact you're accelerating above trim speed, require that you trim nose down after lift-off.


Edited by Tiger-II
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Motorola 68000 | 1 Mb | Debug port

"When performing a forced landing, fly the aircraft as far into the crash as possible." - Bob Hoover.

The JF-17 is not better than the F-16; it's different. It's how you fly that counts.

"An average aircraft with a skilled pilot, will out-perform the superior aircraft with an average pilot."

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4 hours ago, Tiger-II said:

As the aircraft leaves ground effect, the center of pressure moves forward, causing a pitch-up moment. This, and the fact you're accelerating above trim speed, require that you trim nose down after lift-off.

Not sure we're talking about the same thing here. You normally don't trim for rotation, but for a safe (one engine out) climb-speed. Hence no trim-changes through the ground-effect should be required, as the trim-condition is for a speed outside ground-effect anyway.

As you're not blowing a motor on a normal take-off, you'll accelerate through this speed very quickly and hence the need for continuous nose-down-trim.

So ein Feuerball, JUNGE!

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21 minutes ago, Bremspropeller said:

Not sure we're talking about the same thing here. You normally don't trim for rotation, but for a safe (one engine out) climb-speed. Hence no trim-changes through the ground-effect should be required, as the trim-condition is for a speed outside ground-effect anyway.

As you're not blowing a motor on a normal take-off, you'll accelerate through this speed very quickly and hence the need for continuous nose-down-trim.

Regardless of where the trim is, the shift of the center of pressure will require you ease back-stick pressure through lift-off. I'm just pointing out that speed vs. trim isn't the only thing affecting the change of trim condition.

Motorola 68000 | 1 Mb | Debug port

"When performing a forced landing, fly the aircraft as far into the crash as possible." - Bob Hoover.

The JF-17 is not better than the F-16; it's different. It's how you fly that counts.

"An average aircraft with a skilled pilot, will out-perform the superior aircraft with an average pilot."

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