Trim Takeoff Setting

[bobsk8]

I know this is a very old thread, and I have been away from the C 172 for quite awhile, flying the Cherokee and some floatplanes, but started flying the 172 again. The takeoff trim was really giving me a problem, since I have about 250 real flying hours in the 172 Skyhawk, and remember that you could set the trim at takeoff and it was pretty well trimmed for a nice docile climb rate. The A2A 172, will take off like a F18 if you don't get on the trim right away after rotating. I read some posts on this issue today and I too found out that setting the trim at the bottom of the K in takeoff, or around - 35% mousing the trim wheel, results in a nice climb rate with full fuel and the pilot, of around 700 fpm. I also notice that if the AP is engaged and set for a 700 fpm climb, the trim goes to that same setting of around -35% .

[Great Ozzie]

Hi Bob,

Yeah Scott mentioned that very thing here. From the bit of experience I had, I didn't think that was at all uncommon with just one or two up front. I'd imagine too it is going to has something somewhat to do with the model, and the airplane itself depending on its rigging.

-Rob

[DHenriques_]

I know this is a very old thread, and I have been away from the C 172 for quite awhile, flying the Cherokee and some floatplanes, but started flying the 172 again. The takeoff trim was really giving me a problem, since I have about 250 real flying hours in the 172 Skyhawk, and remember that you could set the trim at takeoff and it was pretty well trimmed for a nice docile climb rate. The A2A 172, will take off like a F18 if you don't get on the trim right away after rotating. I read some posts on this issue today and I too found out that setting the trim at the bottom of the K in takeoff, or around - 35% mousing the trim wheel, results in a nice climb rate with full fuel and the pilot, of around 700 fpm. I also notice that if the AP is engaged and set for a 700 fpm climb, the trim goes to that same setting of around -35% .

The use of trim is a highly misused topic in flight simulation. Sim pilots usually tend toward gross over complication on how trim should be used on takeoff.
In actuality, trim in the sim should be used exactly as it is in the real airplane, especially if using an A2A aircraft in the sim.
The correct way to visualize takeoff trim is that unless marked at a specific location on the trim index. (Some heavier and higher performance aircraft require different trim settings for different takeoff configurations but a 172 is more basic in this respect.
The NEUTRAL MARK on the trim index in a light GA type airplane can be considered as a SAFE POINT for takeoff.
This means in effect that loaded normally with the cg and gross weight in limits if you take off with the trim set at that neutral position flying the airplane with the yoke you will be within the limit of the yoke to handle the pitch changes without the trim having to be reset.
I will make a strong caveat here. Something I've noticed many CFI's omitting from the way they teach preflight inspection to be done and indeed being omitted from many many preflight checklists I've seen in use. That caveat postulates that when a pilot does a preflight inspection the trim should be set at the neutral index line before beginning the inspection then checked for proper alignment during the walk around.
Back now to takeoff and trim;
So all the above means is that you don't use trim or attempt flying the plane with trim during the takeoff or at any other time. You fly the aircraft making all pitch change using the yoke THEN retire to whatever the yoke is telling you by feel it wants to be neutral in your hand.
Dudley Henriques

[bobsk8]

I know this is a very old thread, and I have been away from the C 172 for quite awhile, flying the Cherokee and some floatplanes, but started flying the 172 again. The takeoff trim was really giving me a problem, since I have about 250 real flying hours in the 172 Skyhawk, and remember that you could set the trim at takeoff and it was pretty well trimmed for a nice docile climb rate. The A2A 172, will take off like a F18 if you don't get on the trim right away after rotating. I read some posts on this issue today and I too found out that setting the trim at the bottom of the K in takeoff, or around - 35% mousing the trim wheel, results in a nice climb rate with full fuel and the pilot, of around 700 fpm. I also notice that if the AP is engaged and set for a 700 fpm climb, the trim goes to that same setting of around -35% .

The use of trim is a highly misused topic in flight simulation. Sim pilots usually tend toward gross over complication on how trim should be used on takeoff.
In actuality, trim in the sim should be used exactly as it is in the real airplane, especially if using an A2A aircraft in the sim.
The correct way to visualize takeoff trim is that unless marked at a specific location on the trim index. (Some heavier and higher performance aircraft require different trim settings for different takeoff configurations but a 172 is more basic in this respect.
The NEUTRAL MARK on the trim index in a light GA type airplane can be considered as a SAFE POINT for takeoff.
This means in effect that loaded normally with the cg and gross weight in limits if you take off with the trim set at that neutral position flying the airplane with the yoke you will be within the limit of the yoke to handle the pitch changes without the trim having to be reset.
I will make a strong caveat here. Something I've noticed many CFI's omitting from the way they teach preflight inspection to be done and indeed being omitted from many many preflight checklists I've seen in use. That caveat postulates that when a pilot does a preflight inspection the trim should be set at the neutral index line before beginning the inspection then checked for proper alignment during the walk around.
Back now to takeoff and trim;
So all the above means is that you don't use trim or attempt flying the plane with trim during the takeoff or at any other time. You fly the aircraft making all pitch change using the yoke THEN retire to whatever the yoke is telling you by feel it wants to be neutral in your hand.
Dudley Henriques

I am very experienced in flying light aircraft, since the mid 70's. I use trim to relieve any elevator control pressure for the pitch attitude and airspeed that I want with a normal CG. If the trim is in the takeoff position, and I rotate, and the aircraft immediately pitches up with airspeed rapidly decaying, requiring a great deal of down elevator to maintain a speed that is safe, something is not right. I have never has a real aircraft do that when I was flying...

[DHenriques_]

I know this is a very old thread, and I have been away from the C 172 for quite awhile, flying the Cherokee and some floatplanes, but started flying the 172 again. The takeoff trim was really giving me a problem, since I have about 250 real flying hours in the 172 Skyhawk, and remember that you could set the trim at takeoff and it was pretty well trimmed for a nice docile climb rate. The A2A 172, will take off like a F18 if you don't get on the trim right away after rotating. I read some posts on this issue today and I too found out that setting the trim at the bottom of the K in takeoff, or around - 35% mousing the trim wheel, results in a nice climb rate with full fuel and the pilot, of around 700 fpm. I also notice that if the AP is engaged and set for a 700 fpm climb, the trim goes to that same setting of around -35% .

The use of trim is a highly misused topic in flight simulation. Sim pilots usually tend toward gross over complication on how trim should be used on takeoff.
In actuality, trim in the sim should be used exactly as it is in the real airplane, especially if using an A2A aircraft in the sim.
The correct way to visualize takeoff trim is that unless marked at a specific location on the trim index. (Some heavier and higher performance aircraft require different trim settings for different takeoff configurations but a 172 is more basic in this respect.
The NEUTRAL MARK on the trim index in a light GA type airplane can be considered as a SAFE POINT for takeoff.
This means in effect that loaded normally with the cg and gross weight in limits if you take off with the trim set at that neutral position flying the airplane with the yoke you will be within the limit of the yoke to handle the pitch changes without the trim having to be reset.
I will make a strong caveat here. Something I've noticed many CFI's omitting from the way they teach preflight inspection to be done and indeed being omitted from many many preflight checklists I've seen in use. That caveat postulates that when a pilot does a preflight inspection the trim should be set at the neutral index line before beginning the inspection then checked for proper alignment during the walk around.
Back now to takeoff and trim;
So all the above means is that you don't use trim or attempt flying the plane with trim during the takeoff or at any other time. You fly the aircraft making all pitch change using the yoke THEN retire to whatever the yoke is telling you by feel it wants to be neutral in your hand.
Dudley Henriques

I am very experienced in flying light aircraft, since the mid 70's. I use trim to relieve any elevator control pressure for the pitch attitude and airspeed that I want with a normal CG. If the trim is in the takeoff position, and I rotate, and the aircraft immediately pitches up with airspeed rapidly decaying, requiring a great deal of down elevator to maintain a speed that is safe, something is not right. I have never has a real aircraft do that when I was flying...

Well, my installation doesn't do that so I'll defer to someone else to try and figure out what's happening at your end.
DH

[Oracle427]

As usual, the first thing to ask is, "Have you run the updater?"

[bobsk8]

As usual, the first thing to ask is, "Have you run the updater?"

A week ago......BTW I adjusted the trim at -35, just now, and the takeoff was perfect.

[bobsk8]

Well, my installation doesn't do that so I'll defer to someone else to try and figure out what's happening at your end.
DH

If you set you AP on with a 700 fpm climb from sea level with just the pilot and 50% fuel, what does your elevator trim read?

[DHenriques_]

Well, my installation doesn't do that so I'll defer to someone else to try and figure out what's happening at your end.
DH

If you set you AP on with a 700 fpm climb from sea level with just the pilot and 50% fuel, what does your elevator trim read?

Have you tried going to outside view with the aircraft on a ramp and the trim set at neutral and looking at the tab close up to see exactly where it sits at neutral in relation to the known neutral setting in the cockpit?
DH

[bobsk8]

Well, my installation doesn't do that so I'll defer to someone else to try and figure out what's happening at your end.
DH

If you set you AP on with a 700 fpm climb from sea level with just the pilot and 50% fuel, what does your elevator trim read?

Have you tried going to outside view with the aircraft on a ramp and the trim set at neutral and looking at the tab close up to see exactly where it sits at neutral in relation to the known neutral setting in the cockpit?
DH

Doing the preflight with the trim set at neutral ( takeoff position), the trim tab is flush with the elevator vertically. I will check it again when I land, right now I am flying level at 8,000 on autopilot and the trim is at -30% nose down.

[DHenriques_]

Doing the preflight with the trim set at neutral ( takeoff position), the trim tab is flush with the elevator vertically. I will check it again when I land, right now I am flying level at 8,000 on autopilot and the trim is at -30% nose down.

I'm wondering if there's a conflict somehow between the AP and the trim. That can happen even in a real airplane if the AP climb profile is fed into the AP before takeoff. Have you tried taking off with the AP off by any chance?
DH

[bobsk8]

Doing the preflight with the trim set at neutral ( takeoff position), the trim tab is flush with the elevator vertically. I will check it again when I land, right now I am flying level at 8,000 on autopilot and the trim is at -30% nose down.

I'm wondering if there's a conflict somehow between the AP and the trim. That can happen even in a real airplane if the AP climb profile is fed into the AP before takeoff. Have you tried taking off with the AP off by any chance?
DH

I never take off with autopilot engaged. Only put it on after climb is stabilized.


Just landed at CYZT....( Pretty airport in Orbx NW) With the trim at neutral ( 0%) the trim tab and the elevator are exactly even.

[DHenriques_]

Doing the preflight with the trim set at neutral ( takeoff position), the trim tab is flush with the elevator vertically. I will check it again when I land, right now I am flying level at 8,000 on autopilot and the trim is at -30% nose down.

I'm wondering if there's a conflict somehow between the AP and the trim. That can happen even in a real airplane if the AP climb profile is fed into the AP before takeoff. Have you tried taking off with the AP off by any chance?
DH

I never take off with autopilot engaged. Only put it on after climb is stabilized.

I misunderstood your initial post concerning the AP.
Whatever it is I'm not getting it here so it's a mystery for me anyway. Hopefully somebody will be able to shed some light.
DH

[Nick - A2A]

The A2A 172, will take off like a F18 if you don't get on the trim right away after rotating. I read some posts on this issue today and I too found out that setting the trim at the bottom of the K in takeoff, or around - 35% mousing the trim wheel, results in a nice climb rate with full fuel and the pilot, of around 700 fpm. I also notice that if the AP is engaged and set for a 700 fpm climb, the trim goes to that same setting of around -35% .

Hello Bob,

I have to say, this doesn't reflect my experience of the A2A 172R, at least not for a normal take-off from sea level with flaps retracted. If I set the trim at 35% nose down, significant back pressure on the controls is required during the initial climb.

However, a take-off under the same conditions (single occupant and full tanks) with the trim neutral (i.e. 0% according to the tool tip) and no pitch control inputs whatsover will result in the aircraft lifting-off, accelerating, pitching up gradually to a max of around 18° I'd say, as the speed drops and the nose lowers accordingly. Certainly nothing F18-like! In fact, in the quick test I just did, it seemed to stabilise quite nicely at ~65 KIAS and about 10° of pitch up. In other words, the aircraft established itself in a stable climb with no control inputs required from the pilot to avoid a stall.

This seems to me like exactly the sort of behaviour you'd want to see from a take-off trim setting for a GA trainer. However, if for some reason we pitch for a 700 fpm climb initially rather than a target speed (VX or VY), the aircraft will accelerate pretty fast and quite a lot of nose down trim will be required to relieve control pressure.

Are you 100% sure the update was successfully applied Bob? If you've reinstalled at some stage using your original download from the store, you should probably try deleting this file...

C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X\A2A\Cessna172\Update_fsx\client.wyc

...then try running the updater again.

Cheers,
Nick

[Oliver Branaschky]

Or maybe it's as simple as a mis-calibrated joystick/yoke? I definitely cannot reproduce the behavior either, Bob.


Viele Grüße/Best regards
Oliver

Oliver Branaschky