Trim Question

[pskomski]

I have a question...

When in level flight my aircraft always seem to fly nose up. I adjust the elevator trim down by pressing the assigned key on the keyboard. The nose will drop but as soon as I let go of the key the aircraft goes back nose up. How can I make the adjustment "stick"

Thank you!

[Speed of flight]

Hello there!
Trim works differently for different aircraft, and there are a couple different ways to trim. It's important to know what kind of aircraft you're flying.

[pskomski]

Thanks for getting back to me and sorry that I did not provide more info

In this case it is the Commercial Level DC-10. Speed is 250 knots at 13,000 feed. Autopilot is engaged. I pressed the Elevator Trim (Down) key until the nose started to drop. Then the nose would slowly rise back to where it was. All of my large commercial aircraft seem to do this (CLS 747 for example)

Any help is most appreciated

[Dieselpunk]

Hi,

the autopilot works by trimming the plane, so when the ap is engaged, it overwrites your manual input.

I hope i could Help

[Speed of flight]

Jets like that usually have a Stabalizer trim, and a trim tab. The stab trim usually is adjusted by the pilot on the yoke (2 thumb switches) and the trim tab control is usually on the center pedestal somewhere, usually next to the throttle quadrant.
Although either could be called a "pitch trim", they work differently, and are different control surfaces. The stab trim usually changes the pitch of the entire "flying tail" or stabilizer tailplane, and helps keep the yoke in a manageable comfort zone, and on some aircraft is completely necessary, due to limits in elevator travel. The trim tab is a small control surface on the trailing edge of the elevator. This one is typically used in manual flight for nose pitch adjustment, like what you're doing, but only works when the autopilot is off. If you adjust this in flight with AP on, the aircraft will cancel your tab adjustment with stab adjustment. The net result will be added drag.

Hope that helps!

[Speed of flight]

You know what, I just lied to you. If you have trim tab, then you have a fixed stab. If you have a full flying tail, then the tab is unnecessary. Sorry about that.

[Gringo6]

If your airliner is holding altitude with the A/P engaged and is flying nose high, then your airspeed is too low. Try increasing the airspeed and see if this doesn't correct the problem. Or, you could reduce the weight. Either solution should work. The reason it is flying nose up is that the angle of attack must increase for the wing to generate enough lift to support the weight at the currect airpeed.

[Speed of flight]

I use FSX really as an MD-11 simulator. The DC-10 is similar enough that this should apply:
You should be able to fully load that heavy max gross and keep to 250 kts until 10,000. Then, you can increase to 320 to cruise altitude. If at 13,000 and 250 kts your AOA is high, it should be. Increase airspeed to 310-320, or adjust your CG with cargo to compensate. Beware the 2nd, though, as burning fuel will change your AOA in flight over time. You can transfer fuel to maintain balance, but you're really managing the airane then.
Really, a MTOW loaded DC-10 shoul fly slightly nose up, but that's just how she flies. Especially at 250 kts. Speed up!

[Speed of flight]

I thought to myself, "Self, I hope that wasn't too harsh..."

There are airspace classifications assigned to certain altitudes in certain areas. Below 18,000 a pilot is pretty much free to do whatever. ATC doesn't care. However, at and above there are many more regulations to follow.
At 10,000 and below, there is a "speed limit" of 250 KTS. I believe it's 10,000. Above is whatever you're planning to cruise at. That's why I tell you that you can speed up. Also, the density of the atmosphere is significantly lower there, and I think that's why the allowed increase.

Another factoid: Half of the Earths atmosphere is below 18,000. The other half is from 18,000 to the end at the ionosphere.