lift increase whan applying flaps

[Nick - A2A]

Flying a 182 on approach it's automatic that with every change in flap position your hand goes immediately to the trim.

Thanks Dudley - I should have clarified that the yoke movement in the GIF above is without any trim input; merely an attempt to try and depict/quantify the control inputs which I'm talking about in my installation.

Okay, it's not a huge movement of the yoke but I don't think I'd need to push the yoke by this much in any other 'normal' regime of flight (except perhaps at the top of a VX climb and even then it'd probably be a bit excessive). To put it another way, pushing the yoke forward this much in level cruise (over just 2-3 seconds mind) will place the aircraft into a 2000+ fpm dive and I can't imagine this is a manoeuvre that would be too common in the GA world, or at least one that would be popular with the passengers!

I then applied 10 degrees of flaps, and got a small amount of pitch up, which the AP easily handled [...]

Thanks Bob - that seems to fit with what I've seen (and what Oracle describes too) but remember the aircraft is pitching up and actually ballooning into a climb because the AP can't pitch the nose down quickly enough to remain stable on the glideslope. This doesn't qualify as "easily" handling it to me, even though it manages to get things back under control after a while. Again, compare to the "Cap.Alberto" vid.

Thanks,
Nick

[Caldemeyn]

After reading the topic, i checked the behavior of the flaps vs AP just now.

Straight and level flight at 87 KIAS, first stage of flaps deployed, the VSI got to 700 before the AP catched up

One person in the plane, full tanks and the S prop, some 2100 rpm without lowering it to help the AP, no thermals in sight

I believe im patched correctly.

Is it a correct behavior ? Im curious If it is then thats great.

[bobsk8]

I just did another flight with the C 172, standard prop and I think I may have found what is causing the problems with pitch up on autopilot for some. Many months ago, I saw a video on the very slow response for the trim wheel on some A2A aircraft, and that was the issue that I had from day one. The trim wheel barely crawled along if you used the standard trim settings in P3D and I am assuming it is the same in FSX. The speed of the trim adjustment, I felt , was unacceptable and totally unrealistic compared to the trim response in the real C 172. I watched a video on how to use FSUIPC and a key press to change the trim wheel response, by Froogle, and a link to the video was posted on this forum. Froogles solution was better, but there was still something wrong with it too. The trim wheel would start out slowly, and then after about 2 seconds would speed up to what I would call a normal speed. I didn't like this either, because in real life the trim wheel has a linear response on the pitch.

At this point, I read a post about using the A2A Input Configurator to set the trim function, rather than the default FSX-P3D or FSUIPC. Using the Input config, now, the trim wheel speed is quick, and it is linear.. Perfect, and that was the end of all my trim adjustment issues flying the 172, 182 and Cherokee.

Now to today's flight. I set up an approach to the ILS, with airspeed at 90 knots, in the 172 standard prop. Upon intercepting the GS, and starting descent at around 300 fpm , I applied 10 degrees of flaps and I watched the trim wheel carefully, and the trim wheel moved at the same fast rate that it has been moving at since I set the trim control with the A2A config. I saw an initial climb of around 200 feet, which was almost immediately reduced to the previous descent rate, and the autopilot had no problem at all in going back to the 300fpm descent. By the way, that is the way the auto pilot works, by trimming the aircraft. If the trim response is snail like, as it was prior to me reconfiguring the trim wheel speed, guess what, I don't believe the autopilot could reduce the pitch up from flap deployment in time, and the result would be a high climb rate that would last a long time.

My suggestion, to anyone that is having this climb with AP engaged when on the GS and lowering flaps, is to make sure you have the trim wheel set using the A2A Input config, and that the trim wheel moves at a good speed, and does it in a linear manner when manually adjusting your trim. Then get on the GS, got to around 90 knots, and apply one notch of flaps and see what happens.

[Nick - A2A]

Hey Bob,

Thanks for the post. If the autopilot was using just the trim to control pitch, I'd perhaps understand why it couldn't keep up with the pitching moment we're describing. However, the AP directly controls the elevator too (you should see the yoke move fore and aft as well as left and right.)

Also, I think you'll find the autopilot control of the aircraft is completely independent to anything we might set up in the A2A input configurator or FSUIPC to control pitch trim.

For manual control of pitch trim, I certainly agree that assignment via the input configurator is best though.

Cheers,
Nick

[bobsk8]

Hey Bob,

Thanks for the post. If the autopilot was using just the trim to control pitch, I'd perhaps understand why it couldn't keep up with the pitching moment we're describing. However, the AP directly controls the elevator too (you should see the yoke move fore and aft as well as left and right.)

Also, I think you'll find the autopilot control of the aircraft is completely independent to anything we might set up in the A2A input configurator or FSUIPC to control pitch trim.

For manual control of pitch trim, I certainly agree that assignment via the input configurator is best though.

Cheers,
Nick

The trim forces the elevator to move, that is how it works. If the trim tab goes down, it forces the elevator to move up, and the aircraft climbs. You can easily fly a 172 just using the trim wheel for pitch, although it lags a bit. When the elevator moves, of course the control column has to move too, because they are connected to each other by the elevator cables. That is why, when the autopilot is set for climb or descent, you see the trim wheel move. The AP on small aircraft is basically a trim controller. Much different in an airliner. Conversely, if you have the AP on, you won't be able to manually adjust elevator trim without disengaging the AP first.

[Nick - A2A]

No doubt there are GA autopilots that only control pitch trim Bob, but the two-axis version of the KAP 140 which A2A have simulated uses a pitch servomotor to directly control the elevator/yoke, as well as a pitch trim servo.

The AP on small aircraft is basically a trim controller.

The S-TEC System 30 in the A2A Pipers doesn't control pitch trim at all remember. It has just the elevator servo for altitude hold. (Well - the only way it controls trim is by beeping at us annoyingly until we do the job for it!)

Cheers,
Nick

[bobsk8]

No doubt there are GA autopilots that only control pitch trim Bob, but the two-axis version of the KAP 140 which A2A have simulated uses a pitch servomotor to directly control the elevator/yoke, as well as a pitch trim servo.

The AP on small aircraft is basically a trim controller.

The S-TEC System 30 in the A2A Pipers doesn't control pitch trim at all remember. It has just the elevator servo for altitude hold. (Well - the only way it controls trim is by beeping at us annoyingly until we do the job for it!)

Cheers,
Nick

Well I guess that ruins my theory....

[L.A.]

I'd say that almost every GA altitude AP, as well as servos for the roll function (heading), are directly connected to the elevators & ailerons (push rods, cables). Some APs will let you know when the aircraft is out of trim. More expensive units will adjust trim through servos also.

[AKar]

Yes, it is an 'FSXism' that the autopilot flies the pitch via trim. That's not the case in reality, and not all autopilots are equipped with trim servo at all. In KAP 140 (used in A2A Cessnas) it is an optional feature, and the only one I quickly remember having seen in reality (installed on a 172) did not have one if I recall correctly. When equipped with such, the 'auto-trim' essentially relieves the constant loads beyond a given threshold from the pitch servo instead of the system prompting the pilot to trim the plane.

Also, in FSX the trim doesn't 'fly the elevator': you can quickly test that out yourself by noting that the hands-free elevator position is not altered by trimming. This is another area where the FSX takes some artistic freedom from the reality, when it comes to the airplanes trimmed aerodynamically through the control surfaces.

-Esa

[bobsk8]

I decided to try something else this evening, I took the C 172 down to Ft Lauderdale airport where I soloed back in 1978, and eventually got my PPL. I have many, many hours in real life of doing touch and goes in both C 152 and C 172 at that airport. I did not want to use the autopilot to set up the initial descent, I wanted to do it like I used to in the real aircraft with no AP. Now I started flying the pattern in the A2A 172, not using the AP, but just hand flying the aircraft. Now I remembered why I stopped flying this A2a 172 many months ago, I just don't like the way it handles in pitch, and frankly, if I had a plane back in 1978 that handled like this aircraft, I probably would have never received my pilots license. The pitch stability in this plane is not realistic at all. Flying the pattern, I slow the aircraft down opposite the numbers, set RPM at 1700, and apply 10 degrees of flaps, and it balloons up, like 700 fpm. Now the AP is off so it is not correcting for this ballooning, so I have to apply a great deal of down elevator to force it out of this 700 FPM climb, nose up attitude, and back into an approach descent attitude. Now without touching the trim, it starts descending too fast requiring another elevator correction to stop it from diving and to bring the nose back up. So I finally get that sorted out, and now I am approaching the numbers and it is time to flare. and no matter how many microns I pull the yoke back, it balloons up, and floats and floats and floats. At this point any normal aircraft. if you just hold the correct pitch attitude, as the speed bleeds off, it should start to slowly descend, but the floating continues until it runs out of airspeed and then starts dropping like a rock. Of course if I add some power to slow this high sink rate that is developing, then we are back to more floating. Now before anyone says, "you need to calibrate your flight controls", they work perfectly in all the other aircraft I have including the Q400, the A2A Cherokee, the A2A Skylane, the Beaver, The Kodiak, Grumman Goose, the 737 NGX, etc. etc.

I flew a bunch of patterns today with it, and I can see right now, that this behavior of it's trim and elevator control, is just not going to work well, even if if I fly touch and goes for a year. And by the way, I have had a couple of instructors on the frequent check rides that I did when I was actively flying, tell me that I landed an aircraft as well as they did, so it's not anything I am doing wrong. I can set a 172 down in real life, with the airspeed right on the money, and you can barely identify when the wheels touch the runway. There is something not right with the handling of this aircraft. So back in the hangar it goes. And, this C 172 has all the updates and they have been run properly.

Your mileage, as always, may vary.

[Oracle427]

The weird thing is that I do not get the behavior at all. The aircraft flies very smoothly, is easy to manage and pitch and requires rather gentle forward pressure on the yoke to overcome to initial tendency to pitch up when flaps are initially added. I can also keep it right over the runway without working too hard without ballooning until I run out of back elevator and touch down.

I'm not sure why there is such a spread of behaviors among us...

[bobsk8]

The weird thing is that I do not get the behavior at all. The aircraft flies very smoothly, is easy to manage and pitch and requires rather gentle forward pressure on the yoke to overcome to initial tendency to pitch up when flaps are initially added. I can also keep it right over the runway without working too hard without ballooning until I run out of back elevator and touch down.

I'm not sure why there is such a spread of behaviors among us...

I tried something different this evening, since I am reading all the threads on this topic, and there seem to be many of them. The first thing I did was edit the cfg file and reduced the sensitivity to 1.5 from 2. I still have plenty of elevator authority, so I don't think reducing this will have any effect on normal controllability. Then I read another thread where it was suggested that the final approach speed should be much lower than one would do in a real Cessna. I can remember always seting my speed at 67 knots which always resulted in a very smooth landing in the real 172. It was suggested to try going as low as 45 knots when flying over the numbers. I did several landings tonight, and no float and no bouncing. I think I will try this for awhile and see how both those items work.

[Oracle427]

IRL and in the sim, 65 KIAS is a normal approach speed I use on final. Once I start the glidebreak I don't pay attention to the airspeed (unless I'm going around) so I couldn't tell you what it is. 45 KIAS is extremely slow and I certainly do not have to do that in the sim.

[L.A.]

IRL and in the sim, 65 KIAS is a normal approach speed I use on final. Once I start the glidebreak I don't pay attention to the airspeed (unless I'm going around) so I couldn't tell you what it is. 45 KIAS is extremely slow and I certainly do not have to do that in the sim.

A difference of airplanes. In that short wing 180 HP, constant speed RV of mine, I'd pay attention to the airspeed until the wheels touched the ground. Used the same airspeeds as a Piper, 90,80,70 & 65 over the fence. As the airspeed hit 60, I had to make sure I was only a few inches off the ground, because the plane would litterly fall through the flare at the point. The C/S prop was acting as a good speed brake, and the wings didn't really know what ground effect is suppose to be. Agree with the 45 KIAS as being too slow for a Cessna.

[Nick - A2A]

The topic's drifting a little bit off centreline, but I should add that I don't have any particular problem in terms of the general handling and flare behaviour in the 172. I think one potential explanation for the issue Bobsk8 describes is that the control input needed during the flare is less linear than with some other sim aircraft. In other words, rather gentle pressure is needed early in the flare with the need to pull harder on the yoke coming only as the speed bleeds away. This takes a bit of getting used-to, and I suspect it explains the difficulties some customers have had with landing, flaring and ballooning in particular.

I fly the A2A 182 much more than the 172 to be honest, and after a few Accu-Sim updates the behaviour in the flare seems fine. I've still got my suspicions about the flap pitching moment though, partly because what I've observed in the sim and tried to describe just doesn't seem consistent with the behaviour that Oracle described right at the beginning of this lengthy thread (albeit in a 'Q' model):

So I just happened to be flying a 182Q yesterday [...] When I added 10 degrees of flaps at idle power and 110KIAS I intentionally did not touch the yoke or trim. The nose pitched up probably by 5 degrees and I gained about 200 feet before the aircraft slowed to around 85KIAS.

I'm not surprised if this is just a bit of an FDE compromise to get the pitch attitude of the 182 where it needs to be for different configurations. The main issue (for the AP in particular) seems to be that the change in pitch is too rapid and isn't matched to the flap extension speed.

At any rate, the best 'solution' seem to be to to make sure that a power reduction accompanies selecting the first stage of flaps; partly because this'll obviously cause the nose to drop anyway, and partly because the prop wash modelled over the flaps seems to be a factor here.

Nick