Full forward trim

[ahmebane]

I'm finding that I need to pretty much trim my DA40-180 (50 gallon tanks with 20 gallons loaded) full forward to maintain straight & level flight at just 65% power. (All the way to the stop). Makes me a bit uncomfortable! By all calculations I have done I am well within the CG envelope. I weigh 170 pounds. Maybe 5-7 pounds of weight in the baggage area. Where do other people end up with their trim? I've had the plane for 3 years and hadn't really noticed needing this much forward trim. In fact, the trim started getting stuck & i just had some of the trim wheel components replaced. Before that, it was sticking to the point where I could not trim as forward as what was required. No maintenance has been done on the plane that would affect the elevator trim. Now I can run it all the way forward, but it doesn't seem right.

With a passenger, not as much forward trim required, as would be expected.

I don't think its a W&B issue, but perhaps a trim adjustment is required? (If that's even a thing).

Thoughts?

TIA.

[dmloftus]

I've wondered the same, although my case is not as extreme as yours. My trim wheel reference mark is significantly forward of takeoff position, about halfway between takeoff and its forward-most position when flying solo at 65% power, ie 23/22 at 6500'. Do you ever receive a trim fault from the autopilot? Seems if it was all the way at the forward stop, the AP would throw a trim fault as it tries unsuccessfully to trim the aircraft further forward, ie in a pocket of turbulence.
My trim wheel is never behind the halfway point in flight. Seems like a waste of trim authority without that nose-up portion ever being used. Possibly needed if I swapped my MT prop for a heavier Hartzell aluminum?

[ahmebane]

I got a trim fault from the AP once (on an ils approach in IMC). ATC had asked me to keep my speed up, and that incident is when I started dealing with the trim getting stuck. It would get stuck about 3/4 of the way forward. I had a passenger with me at the time, so it didn't need quite as much forward trim. I also have the mt prop. The trim is right at the takeoff position when set for 70 knots and full flaps, landing. That's about as far back as it ever gets. It all seems pretty normal until I'm at higher power, by myself.

[Chris]

My trim wheel reference mark is significantly forward of takeoff position, about halfway between takeoff and its forward-most position when flying solo

That sounds pretty typical to me.

I'm finding that I need to pretty much trim my DA40-180 (50 gallon tanks with 20 gallons loaded) full forward to maintain straight & level flight at just 65% power. (All the way to the stop).

That doesn't sound normal to me. I would have it checked. There's an elevator trim measurement and adjustment procedure in the AMM.

[Lou]

Having the wheel far forward in cruise is pretty normal in my experience. As I understand it, the tail generates downforce to compensate for the wing’s pitching moment. Pitching moment depends on angle of attack. When the aircraft is traveling faster, angle of attack deceases. You have to look at the polar curves for this airfoil (Wortmann FX-63-137/20-W4) at the Reynolds number for our size and speed to see the relationship for this airfoil. I looked at another Wortmann airfoil (FX60-100) and the pitching moment is at its weakest in the 0 to -5 degree AOA. Let’s say this the high end of the cruise range AOA, then you will need down trim to compensate for the weakened pitching moment. In your case you are quite light and have a light fuel load, the wing is at a relatively low AOA since it needs to generate less lift. So you need less downforce and more forward trim. At least according to my hobby level amateur analysis.

In other words, normal behavior.

[ahmebane]

Yeah, I get why it needs more forward trim at light load, higher speed. What seems abnormal is having the trim at the forward stop. Any lighter or faster and I can't keep the plane from climbing. Have to reduce power (hence airspeed).

[dmloftus]

... I can't keep the plane from climbing. Have to reduce power (hence airspeed).

Or keep constant forward pressure on the stick. You still have far more elevator authority available, I'm assuming. But I get it, if you want to be hands off.

[CFIDave]

Yeah, I get why it needs more forward trim at light load, higher speed. What seems abnormal is having the trim at the forward stop. Any lighter or faster and I can't keep the plane from climbing. Have to reduce power (hence airspeed).

That's abnormal. Please have a Diamond-knowledgeable service center take a look at your plane.

[Lance Murray]

Are the drain holes in your tail skid open? Could the tail skid be filled with water? Flying in rain lately or does it sit outside? Check to make sure ALL of your drain holes on the bottom side of the airplane are clear and open.

[Steve]

Just as a data point, when I was flying this morning:

6500', 14 deg C, 131 KTAS, 2150 GW:

Cruise flight trim index