c172 trainer takeoff trim

[Oracle427]

wbrown,

You need to restore the original aircraft.cfg settings or all of the advice that we are giving you is pointless.

As we said, the .cfg files are not going to appear correct for to the behavior of the A2A aircraft. They have an external simulator engine and the entries in the .cfg file no longer behave the same way as they would with stock FSX aircraft. You can not expect your changes to work in ways that are expected.

What model 172 do you fly IRL? The 172N I fly that has a 180HP STC with the trim set in the center for takeoff will definitely pitch up very sharply in a slower than Vx airspeed if no action is taken with the yoke. I have never let it get to the point of a stall but it certaintly feels like it would stall unless I take positive action by applying forward pressure to maintain at least Vx. The 172SP I fly does not exhibit this tendency at all. The A2A sim models a 172R and I have no hours in those.

I you have not applied the updates, then you are trying to debug a very old version of the sim. First things first apply the update as suggested.

Then run through the preflight and ensured that the aircraft is fit to fly. Consider performing a "complete overhaul" to put the aircraft in factory new condition.

Are you using the A2A specific Shift-4 menu to load the fuel and passengers into the aircraft or the default weight and balance menu. The latter will cause handling issues.

Dave

[Lewis - A2A]

Hello,

the editing of the cfg is not recommended as it will interfere with our simulation engine, so if you know what you are doing or not this isn't a standard ESP platform aircraft so much of the SDK parts do not apply. They are set to work with our simulation engine.

The next time you fly trying recording your self flying, you will be very surprised about what you do as a pilot without thinking, as we ourselves found when we first did this and found that even minutes after shut down what we recall is often wrong compared to what actually took place. We also have a few pilots on the forums here who questioned some things at first based on what they where used to as a flight sim aircraft but when they recorded there own flights in the real world they realised it had been modelled correctly all along despite there memory telling them otherwise. From this we now use video recordings at all time to keep the data 100% on all our test flights.

thanks,
Lewis

[Oracle427]

I am among that group of pilots that Lewis speaks about that had serious doubts about the fidelity of the sim only to be proven wrong when I replicated several scenarios.

[mallcott]

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.

OK, so you appear to have decided to go with modifying what you have been told not to. I think we can take that as no longer needing our assistance. Either you are ignoring or not able to understand what the implications are for an external flight dynamics engine, despite being informed by the developers. Leave resolution to your superior programming skills.

Signing off.

[wbrown]

Here's the latest... I tried flying the sim again this morning and it was still trouble. I left my computer on all day, and after work I went back and tried again. Now, it's working more realistically, not jumping off the runway, climbing steeply, etc. Just a little right rudder keeps it in line, and the climb out is just right, without deviating from the takeoff trim marker. There might be something going on with my system. Since a recent Win 10 update P3d has had a bit of stutter, even ver 4 which is full 64 bit. I've been working through getting unnecessary stuff turned off, and other performance tweaks in and out of P3d. Yesterday the C172 sim developed a really bad stutter, worse than the other sims. I didn't even mention that. Today that's mostly better. I have a video card upgrade on order too.

But anyway, the C172 is mostly back to the sim I have enjoyed for years. I really like the detail, and the sounds and the (now) realistic flight characteristics.

[Oracle427]

Did you leave it in sim or just left the computer running and then launched the sim later in the day?

[Scott - A2A]

One thing we learned with the C172 is not all 172's fly the same. In fact, out of all the 172's we've flown, none of them had their trims calibrated the same. Some jump off the runway and even stall when hands off, and some are a bit more gentle.

So we tested three different C172S's doing exactly this, taking off full throttle with no back pressure on the yoke (listen to Dudley, this isn't the way to takeoff but we do this for testing). All three airplanes launch off the runway, pitch up, and go right to the edge of the stall, and pull left towards the end.

The thing is this. When you fly a 172S, this is what happens: You take off, the plane lifts off, then you add some NOSE DOWN trim after liftoff. This is what most pilots do with 172S's, but they are not really conscious of it. We, as pilots, do many things subconsciously (like trimming).

If you fly a real 172S that doesn't have this behavior, I can say it is different to the three we tested. I even spoke with Cessna about this behavior because I, like you, was surprised. But, you don't notice these things until you simulate a plane.

Interestingly, the 182 is exactly the opposite. It will stick to the runway like glue. I know because when I was doing my test flights, I was aware that the control tower must have thought I was an idiot barreling down the runway at 100 kts and still on the runway, because I was doing a "hands off" takeoff for Accu-Sim testing. And, our Accu-Sim 182 handles the same way, and the 172S handles like the ones we fly. Also, keep in mind, the earlier Cessna 172's (like the N model) don't exhibit this sharp nose-up behavior like the S.

Scott.

[Medtner]

Here's one of those tests that Scott mentioned. Glued to the pavement, indeed.

https://youtu.be/uQynZwcDZSE

[wbrown]

Just to follow up...
Oracle427 - I left the machine on all day but not the sim.

After a couple of days it's still working as it's supposed to. I believe there was something going on with my system, but I can't pinpoint it. I replaced the aircraft.cfg file back with the original and it still flies OK. So it wasn't that.

I recall that when I purchased the FSX version years ago I had the same problem, and that I also edited that .cfg file and it seemed to fix the climb problem right away. That sim had been working fine for years until I ran the A2A updater. Or maybe it was just my system that day.

So I'm totally confused as to the cause of this behavior. But now I can set the trim to the takeoff mark and with a slight pull of the yoke it takes off at 55-60. It climbs at Vy without touching the trim, just needs the usual amount of right rudder. Joy is back.

From some of the comments, I wonder if anyone has to do something dramatically different with their trim.

I'm sorry some people got pissed that I touched the cfg file. Not something I normally would do, but I was desperate to try something to get it working.

Anyway, thanks for everyone's input.

[DHenriques_]

Just to follow up...
Oracle427 - I left the machine on all day but not the sim.

After a couple of days it's still working as it's supposed to. I believe there was something going on with my system, but I can't pinpoint it. I replaced the aircraft.cfg file back with the original and it still flies OK. So it wasn't that.

I recall that when I purchased the FSX version years ago I had the same problem, and that I also edited that .cfg file and it seemed to fix the climb problem right away. That sim had been working fine for years until I ran the A2A updater. Or maybe it was just my system that day.

So I'm totally confused as to the cause of this behavior. But now I can set the trim to the takeoff mark and with a slight pull of the yoke it takes off at 55-60. It climbs at Vy without touching the trim, just needs the usual amount of right rudder. Joy is back.

From some of the comments, I wonder if anyone has to do something dramatically different with their trim.

I'm sorry some people got pissed that I touched the cfg file. Not something I normally would do, but I was desperate to try something to get it working.

Anyway, thanks for everyone's input.

There are two things to remember about takeoffs that are all important. First, as speed increases so also does lift on the wing. Second, lift can also be increased by increasing the angle of attack on the wing. Normally what happens on a regular takeoff assuming lots of runway, is that you establish some arbitrary angle of attack as the ground run progresses then allow the wing to develop lift to where the lift force equals the gross weight of the aircraft ON THAT TAKE OFF!
At that point the plane will fly. What YOU as the pilot should be doing when the plane rotates is to FLY the airplane using the yoke, PUTTING THE NOSE in a climb attitude. All things considered you will usually find the climb attitude that gives you the Vy for your airplane.
What happens with some pilots (and especially sim pilots is that instead of FLYING the airplane with the yoke they allow whatever trim they have set to take over. When you do that the trim will find whatever the trim speed is for the power setting you are using. NEVER allow the trim to fly the airplane! Use the yoke, find the climb attitude, THEN retrim the airplane as whatever trim setting you had selected will most likely NOT be the trim setting you actually need to trim off the yoke pressure.
Do it this way and you're well on your way to solving all your trim issues assuming those issues involve how the aircraft is being flown and not something else.
Dudley Henriques

[flapman]

I even spoke with Cessna about this behavior because I, like you, was surprised.

I'm curios, what was Cessna's response?

Thanks,

[wbrown]

DHenriquesA2A:

I've been busy for a while so I didn't get right back on this thread. All you say about using the yoke and trim is absolutely correct. And I do know all of that. I was just contrasting how the sim is currently behaving vs. the wildly unrealistic pitch action I was originally getting. I know that the amount of elevator and trim needed can vary due to load, altitude, atmospheric conditions, the individual plane, etc. Taking off from my home airport KMTN (Martin State, MD, 22ft. MSL), in fair weather, full load of fuel, two persons, the sim now holds a Vy climb with the trim on the takeoff mark. Yes, I have to pull on the yoke to get in the air, and then ease up and it settles in around 75 kias without touching the trim. That's not always the case in reality, but it's about ideal if it happens.

Again, I was pointing this out in contrast to how the sim was initially behaving for me, pitching up wildly, which is documented in my earlier messages, so I won't rehash. I take it that people don't believe I had that problem. I think it perhaps had something to do with my system, but I don't know for sure. I had the same problem for a while when I bought the FSX version years ago, but it too got resolved.

I'm past all that now and enjoying the C172 trainer. It's quite close to the real thing. I often use it to practice pattern work and other maneuvers, like Prepar3d is "supposed" be used. However if I want to go cross-country, I'll likely grab a faster plane - I don't have all day.

Other stuff I like to do: Take the F22 off from KMTN, head 060 and try to coax it to 80,000 ft. by the time I get over New York. The service ceiling is 65, but you can get it to 80 with some porpoising. Then I turn it around, pull out the power and glide it back to land at Martin - an exercise in energy management.
Or take off from the Grand Canyon airport in the 172, dive down to the bottom and follow the twists and turns of the Colorado River without hitting the rocks. When I get tired of that, I climb back out, which takes some patience and coaxing to regain altitude and clear the rim. I wish the terrain textures looked a little better down there, though.

[DHenriques_]

DHenriquesA2A:

I've been busy for a while so I didn't get right back on this thread. All you say about using the yoke and trim is absolutely correct. And I do know all of that. I was just contrasting how the sim is currently behaving vs. the wildly unrealistic pitch action I was originally getting. I know that the amount of elevator and trim needed can vary due to load, altitude, atmospheric conditions, the individual plane, etc. Taking off from my home airport KMTN (Martin State, MD, 22ft. MSL), in fair weather, full load of fuel, two persons, the sim now holds a Vy climb with the trim on the takeoff mark. Yes, I have to pull on the yoke to get in the air, and then ease up and it settles in around 75 kias without touching the trim. That's not always the case in reality, but it's about ideal if it happens.

Again, I was pointing this out in contrast to how the sim was initially behaving for me, pitching up wildly, which is documented in my earlier messages, so I won't rehash. I take it that people don't believe I had that problem. I think it perhaps had something to do with my system, but I don't know for sure. I had the same problem for a while when I bought the FSX version years ago, but it too got resolved.

I'm past all that now and enjoying the C172 trainer. It's quite close to the real thing. I often use it to practice pattern work and other maneuvers, like Prepar3d is "supposed" be used. However if I want to go cross-country, I'll likely grab a faster plane - I don't have all day.

Other stuff I like to do: Take the F22 off from KMTN, head 060 and try to coax it to 80,000 ft. by the time I get over New York. The service ceiling is 65, but you can get it to 80 with some porpoising. Then I turn it around, pull out the power and glide it back to land at Martin - an exercise in energy management.
Or take off from the Grand Canyon airport in the 172, dive down to the bottom and follow the twists and turns of the Colorado River without hitting the rocks. When I get tired of that, I climb back out, which takes some patience and coaxing to regain altitude and clear the rim. I wish the terrain textures looked a little better down there, though.

Sounds like you're all sorted out and having a good time. That's good.
I've been into Martin many times in the old days. Looked a lot different then.
Dudley Henriques

[iefbr14]

Thanks to all who replied so quickly. HOWEVER... I am not mistaken about this problem. I am a private pilot who flies C172s. ...

Same happens to me. I fully agree with wbrown! I've finished my 100hrs on RW this week, mostly on c172's and c152's. And I can confirm, none of them tends to turn to the left that way during t/o especially with light cross winds from the right. This happens with FSX, and P3D v1-to 4, with different yokes. I carefully monitored the forum over the years, and a lot of people reported these about (drag left) problems. But never I read a solution about. You have to leave the A2A c172 nose wheel on the ground until Vy to circumvent this problem. But this is a work around, and not a behavior of real world c172. A2A guys really make a very great jobs on their planes, I love every nut on these machines, but to tell certified pilots not to be able to take off a c172 when they report real existing drag problem's on 2 of their modelled planes, this is why I'm very disappointed about these discussions.

Sorry for some clear words.

Andreas

[mallcott]

Thanks to all who replied so quickly. HOWEVER... I am not mistaken about this problem. I am a private pilot who flies C172s. ...

Same happens to me. I fully agree with wbrown! I've finished my 100hrs on RW this week, mostly on c172's and c152's. And I can confirm, none of them tends to turn to the left that way during t/o especially with light cross winds from the right. This happens with FSX, and P3D v1-to 4, with different yokes. I carefully monitored the forum over the years, and a lot of people reported these about (drag left) problems. But never I read a solution about. You have to leave the A2A c172 nose wheel on the ground until Vy to circumvent this problem. But this is a work around, and not a behavior of real world c172. A2A guys really make a very great jobs on their planes, I love every nut on these machines, but to tell certified pilots not to be able to take off a c172 when they report real existing drag problem's on 2 of their modelled planes, this is why I'm very disappointed about these discussions.

Sorry for some clear words.

Andreas

Equally there are pilots with hundreds of hours on the particular 172 versions replicated here who seem to know a lot more about the aircraft and its performance than you. Maybe you fly well-rigged aircraft that are nearly-new with just a few hundred hours TT; equally you may fly terribly rigged aircraft that are tatty and falling apart having served the training environment for nearly fifty years, but one thing we can comment on is your defining of the criterion you are using to judge in such peremptory terms seems as sketchy as your knowledge of the sim you fly your virtual aircraft in.

Your disappointment in these discussions is duly noted. Perhaps you should just ignore them?