c172 trainer takeoff trim

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jb44mag
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c172 trainer takeoff trim

Post by jb44mag »

FSX:

Using CH eclipse yoke, CH throttle Quadrant, CH rudder peddles, all properly calibrated. Settings as per A2A recommendation.

I have seen a couple of posts stating elevator trim is not working properly, but have not seen a helpful response. plane configured with full fuel and two pilots, and elevator trim set to "takeoff," hands off the yoke, the plane will quickly pitch up to a stall at about 45kts, and bank slightly to the left. I can use full yoke "down" and keep the plane from pitching up into a stall, but then have to rapidly trim nose down to keep control of the aircraft.

I saw one post that suggested the trim be set to "A" of "take off" on the trim indicator, and this does make for a controlable takeoff. but I don't think this operates like the real a/c. also once the plane is properly trimmed for its speed, the A/C will tend to bank slightly left, requiring constant correction to the right. is this real a/c performance.

All a2a updates have been applied.

While not a real pilot, I have hundred of hours in fsx simulator planes, (almost all, add ons not default planes. I have several accusim planes, including B-17, Texan, and Constellation. no trim issues with these planes. I have been operating FSX/Acceleration since day one.

Suggestions would be appreciated. setting trim to "A" does not count. :-).

Best regards,

-Jim

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DHenriques_
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Re: c172 trainer takeoff trim

Post by DHenriques_ »

jb44mag wrote:FSX:

Using CH eclipse yoke, CH throttle Quadrant, CH rudder peddles, all properly calibrated. Settings as per A2A recommendation.

I have seen a couple of posts stating elevator trim is not working properly, but have not seen a helpful response. plane configured with full fuel and two pilots, and elevator trim set to "takeoff," hands off the yoke, the plane will quickly pitch up to a stall at about 45kts, and bank slightly to the left. I can use full yoke "down" and keep the plane from pitching up into a stall, but then have to rapidly trim nose down to keep control of the aircraft.

I saw one post that suggested the trim be set to "A" of "take off" on the trim indicator, and this does make for a controlable takeoff. but I don't think this operates like the real a/c. also once the plane is properly trimmed for its speed, the A/C will tend to bank slightly left, requiring constant correction to the right. is this real a/c performance.

All a2a updates have been applied.

While not a real pilot, I have hundred of hours in fsx simulator planes, (almost all, add ons not default planes. I have several accusim planes, including B-17, Texan, and Constellation. no trim issues with these planes. I have been operating FSX/Acceleration since day one.

Suggestions would be appreciated. setting trim to "A" does not count. :-).

Best regards,

-Jim
In a 172, anything within a mark of the neutral point should be all right for takeoff. You should never be rotating with your hands off the yoke. It sounds like you might have a slightly nose high trim setting for your aircraft's GW at takeoff that under normal circumstances you would simply counter with yoke pressure then get rid of the excess by re- trimming during your climb but because your hands are off the yoke, the trim is taking over and allowing the positive pitch.
Just hold onto that yoke until you are stabilized in the climb at your climb attitude then re-trim if necessary. This should solve the issue.
Dudley Henriques

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Oracle427
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Re: c172 trainer takeoff trim

Post by Oracle427 »

It is realistic for at least one 172N I used to fly. If you didn't hold the yoke it would pitch very nose high and likely stall or at least pitch down from low airspeed and start to oscillate.

You had to push forward to make it fly at Vx or Vy. If you relaxed the forward pressure it would want to pitch up again. I don't know if it was rigging, but that was how that one flew.
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DHenriques_
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Re: c172 trainer takeoff trim

Post by DHenriques_ »

Oracle427 wrote:It is realistic for at least one 172N I used to fly. If you didn't hold the yoke it would pitch very nose high and likely stall or at least pitch down from low airspeed and start to oscillate.

You had to push forward to make it fly at Vx or Vy. If you relaxed the forward pressure it would want to pitch up again. I don't know if it was rigging, but that was how that one flew.
One of the great mistakes we correct immediately when starting takeoffs and landings is to get the student to recognize that relaxing on the yoke at rotation is the natural tendency for a new pilot. What's needed is a firm but relaxed hold on the yoke.That prevents the airplane controlling the takeoff.
Once the student learns that the hold on the yoke can be with the fingers and still maintain a positive control takeoffs can commence and the transition through rotation becomes much more positive.
Dudley Henriques

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Nick - A2A
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Re: c172 trainer takeoff trim

Post by Nick - A2A »

Jim,

Just to add to the advice above, it's also worth noting that the aircraft's pitch behaviour during take-off will depend on whether you have the factory stock 75" / 70° propeller fitted, or the optional 'S equivalent' 76" / 60° prop which gives an extra 20 hp. With the more powerful S equivalent prop, the 172 will tend to pitch up more readily on take-off, so an initial trim setting which is slightly nose down may be beneficial. This is where I find setting it at the 'K' may be appropriate depending on weight and balance.

However, with the stock prop, significant nose down pitch inputs shouldn't be needed after take-off if the trim is in the take-off position.

The prop can be swapped in the maintenance hangar (shift 8 ). Which do you currently have fitted?

Thanks,
Nick

jb44mag
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Re: c172 trainer takeoff trim

Post by jb44mag »

Thanks all. Your comments cleared things up.

Regards,
-Jim

wbrown
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Re: c172 trainer takeoff trim

Post by wbrown »

I am having the aforementioned problem. I purchased the C172 trainer for FSX. I now have Prepar3d v3. I ported the aircraft over to Prepar3d. I fly real C172 SPs. I never flew a C172 R.

In FSX the takeoff trim worked as my experience with real SPs. In Prepar3d the plane sometimes jumps off the runway prior to rotation speed, and always climbs quickly into a stall. I tried changing the prop back to the C172 R default. That helps only a little. If I add lots of nose down trim to correct the climb rate, then when I turn crosswind the plane pitches sharply down, and I have to put all the nose up trim back in.

Other than that, I love your sim, and it seems very close to the real world 172. The Microsoft C172, while not as nice, does not have this issue.

I have not applied any updates. If I need to purchase the Prepar3d version of the sim, I am happy to do that.

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Nick - A2A
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Re: c172 trainer takeoff trim

Post by Nick - A2A »

jb44mag wrote:Thanks all. Your comments cleared things up.
Glad to hear you're sorted Jim.

Hello wbrown and welcome. :)
wbrown wrote:I purchased the C172 trainer for FSX. I now have Prepar3d v3. I ported the aircraft over to Prepar3d. [...] If I need to purchase the Prepar3d version of the sim, I am happy to do that.
Yes, sounds like that's what you need to do (purchase the P3D version) then apply the latest Accu-Sim update. For what it's worth, I have the appropriate versions of the A2A 172 installed in both FSX-SE and P3D and the pitch behaviour on take-off is consistent across both platforms. Something else to check for would be defects to the elevator and trim tab in the maintenance hangar (shift 7).

Thanks,
Nick

wbrown
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Re: c172 trainer takeoff trim

Post by wbrown »

I figured out what the problem is. I just purchased P3d v4. I also purchased the latest A2A version of C172 for P3d.
Prior to that I ran the A2A update on my FSX copy. That caused the same trim problem in FSX, which had been working OK.
In P3d v4 the C172 still has the same crazy trim problem. So I looked at the aircraft.cfg file, and therein lies the problem.

A2A has the following wrong settings:
elevator_trim_effectiveness=0 (It should be 1.0, or maybe 2.0)
elevator_trim_limit =100 //19.50000 //Degrees (This should be set back to 19.5 which is commented out)

After I modified these to reasonable values, the excessive pitch-up problem disappeared. However now there is a strong roll to the left, and I can't figure out which setting fixes that.

A2A, please fix this.

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Oracle427
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Re: c172 trainer takeoff trim

Post by Oracle427 »

There are no issues with the 172 for A2A to fix. I fly a C172SP weekly and a C172N from time to time and fine that the simulated version is a very accurate replica of the real world aircraft behavior. I flew my 172SP just yesterday for a couple of hours.

Also, changing the aircraft.cfg file is not appropriate for A2A aircraft as their system operates outside of the standard FSX/P3D file and engine framework. The parameters you edit may have all sorts of unintended consequences.

The aircraft is not perfectly stable for hands off flight for extended periods of time and it is perfectly normal to have to apply small corrections frequently. There are a lot of variables that can affect handling such as having too much power for cruise flight, or while initially accelerating to cruise airspeed. Those will dramatically increase the left turning tendency.
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DHenriques_
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Re: c172 trainer takeoff trim

Post by DHenriques_ »

wbrown wrote:I figured out what the problem is. I just purchased P3d v4. I also purchased the latest A2A version of C172 for P3d.
Prior to that I ran the A2A update on my FSX copy. That caused the same trim problem in FSX, which had been working OK.
In P3d v4 the C172 still has the same crazy trim problem. So I looked at the aircraft.cfg file, and therein lies the problem.

A2A has the following wrong settings:
elevator_trim_effectiveness=0 (It should be 1.0, or maybe 2.0)
elevator_trim_limit =100 //19.50000 //Degrees (This should be set back to 19.5 which is commented out)

After I modified these to reasonable values, the excessive pitch-up problem disappeared. However now there is a strong roll to the left, and I can't figure out which setting fixes that.

A2A, please fix this.
The settings for the A2A 172 are an exact replication of the actual aircraft.
Not sure exactly what issue you were having but one thing I could mention is this.
I don't know your actual experience flying real airplanes but one of the most common problems we have with our airplanes is getting them used to the REAL way the airplane flies. This means that for the sim, if the flight model is correct as the A2A 172 is correct, you can expect to be constantly making corrections to maintain control of the aircraft.
This is real behavior. Many people, especially after flying other sim airplanes, come to expect that "positive on rails" behavior found in non-A2A airplanes.
Generally speaking, if you have to be watching your attitude and maintaining positive control all the time you are in the air with an A2A plane, it's working correctly for you.
Now just to be clear, you COULD be having a problem with a controller. That's a whole other ball game.
Whatever you do, don't go changing the cfg file to solve a problem. Just do what you are doing now and ask here. Somebody will help.
Dudley Henriques

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mallcott
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Re: c172 trainer takeoff trim

Post by mallcott »

wbrown wrote:I figured out what the problem is. I just purchased P3d v4. I also purchased the latest A2A version of C172 for P3d.
Prior to that I ran the A2A update on my FSX copy. That caused the same trim problem in FSX, which had been working OK.
In P3d v4 the C172 still has the same crazy trim problem. So I looked at the aircraft.cfg file, and therein lies the problem.

A2A has the following wrong settings:
elevator_trim_effectiveness=0 (It should be 1.0, or maybe 2.0)
elevator_trim_limit =100 //19.50000 //Degrees (This should be set back to 19.5 which is commented out)

After I modified these to reasonable values, the excessive pitch-up problem disappeared. However now there is a strong roll to the left, and I can't figure out which setting fixes that.

A2A, please fix this.
Sounds like you are still approaching this airplane like you the others you have hundreds of hours in with the simulator. Don't.

The FDE is mostly external to the standard .air and .cfg files and as Dudley says, all you will achieve by modifying settings in the aircraft. cfg is UNintended consequences.

That being said, it's your sim and your product and you can do with it whatever you like, but no-one here; not the developers, not the experienced real wold flyers, not the vastly experienced user base, will be able to help you if you choose to start flailing about with files you oughtn't be messing with.

Suggest posting a new topic about your crazy trim issue if you put those files back to standard, or leave the mods you have applied and go fly, with no support from the user base. Your choice.

If you do need support for you local issue, then do create a new topic with as much info as possible. But a simple piece of advice: DONT expect this aircraft to trim itself. 80%+ of issues with trim in this simulation are caused by the aircraft not being in-trim before the a/p is applied, leading to exaggerated pitch effects. As for the roll, a number of simmers reported this and they ALL fixed it with a reinstall, or by not flying in slow speed, high angle of attack, high power regime with a lazy foot.

JUST like the real one.
Last edited by mallcott on 12 Jun 2017, 09:59, edited 2 times in total.

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Lewis - A2A
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Re: c172 trainer takeoff trim

Post by Lewis - A2A »

I have to agree with the others, it sounds like you are comparing it to sim aircraft rather than real aircraft.

The C172 Trainer simulation you are using is a professional simulation, we license the same out to our professional clients who use it in certified and non-certified motion and non motion simulators for flight training practice and logging sim hours towards licenses and ratings.

We are one of the few if not only developers who have taken to test flying aircraft and developed a test flight programme that goes with our development, so rather than by the book or by what someone told us wherever possible we have hands on video recorded footage of the aircraft, the controls the gauges etc to enable us to create a very realistic simulation of a given aircraft variant, in this case a C172R model.

Whilst bugs etc can be a part of the software experience and we do our best to fix these up and go as far as to upgrade parts as we go via our updater system etc, the issue you mention hasn't been reported by anyone else since 2013 upon release and I think given your editing of the cfg files is more an issue with expectations of a sim aircraft against a professional sim and reality.

thanks,
Lewis
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wbrown
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Re: c172 trainer takeoff trim

Post by wbrown »

Thanks to all who replied so quickly. HOWEVER... I am not mistaken about this problem. I am a private pilot who flies C172s. I was out on Saturday, in fact, and I did six takeoffs and landings. The way this sim works on my system right now is absolutely nothing like a real C172 flies. I understand that others might be getting different results, but if a real airplane acted like this is would be an absolute death trap. With the original settings it pitches sharply up and needs immediate hard forward pressure in the yoke or lots of nose-down trim, just to not climb to a stall. It also rolls sharply left, like p factor X 20. so I have to use a ton of right aileron/rudder, just to not crash. Not at all realistic. Impossible to keep it going straight. If I fix the elevator setting in the .cfg file, which BTW is ridiculously wrong (angle of 100 degrees possible on the trim tab??), then I get rid of the elevator trim problem, but it still yaws/rolls sharply left, both on the runway, and in the air, far more than p factor would account for in real life.

I calibrated my flight controls, and they work perfectly with other sim planes. I Re-installed the C172 and it went back to the original config, with the same problems. I am a computer programmer and I can handle mods to the cfg, and I keep a backup of the original. There is possibly something going on with the sim that's beyond what's in the cfg settings.

Looking at the Microsoft C172 from FSX, the elevator trim limit is 19.0 degrees, the same number A2A commented out and replaced with 100. I would expect maybe a slight variation, but not that.

Again, I understand that this might be working right on other systems. A mysterious problem to be sure. I'm not the first one to have it, it appears.

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Re: c172 trainer takeoff trim

Post by Tomas Linnet »

Did you run the latest updater as suggested by Nick?
Kind Regards
Tomas

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