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C172 severe wing-over on take-off

Postby macnab » Wed Aug 24, 2011 1:39 pm

Did the same in FG2 and now in FG2.4. Nothing is mentioned in the tutorial or the FG get started manual about the drastic measures I need to take during take-off.

I set Global Weather for no winds or turbulance at any level.

I get bad wing-over to the left as the plane takes off. To make sure it is not me, I have opened up the throttle and then left my hands off the joystick, so the plane lifts off by itself. The left wing immediately goes down, and within 5 seconds the wingtip touches the ground.

If I take control of the yoke, I need a lot of right-aileron to keep the wings level. Tried this method: Need a bit of right-rudder to stay running down the runway anyway, so when I pull back to take off I maintain right-rudder. This keeps the wings level for a bit, but it doesn't take long before any rudder causes the plane to yaw wildly. If I then leave the rudder alone, I once again need a lot of right-aileron to keep the wings level.

This doesn't seem right to me and doesn't ring any bells of being taken for flips with my father.

Any tips?
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Re: C172 severe wing-over on take-off

Postby curt » Wed Aug 24, 2011 2:12 pm

Could it be a joystick calibration issue? You should be able to activate the hud ("h" key) with most aircraft and look at the little control surface indicator when you move the joystick. It should of course be centered when the joystick is centered.

Another thing you could try is unplug your joystick and try flying with only keyboard/mouse. This very much sounds like it could be a joystick calibration issue ...
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Re: C172 severe wing-over on take-off

Postby macnab » Wed Aug 24, 2011 3:16 pm

Tried with joystick and with mouse (joystick unplugged.) HUD on. HUD shows wings level, elevator level, rudder moves to reflect staying on centre-line. At 55 Kts I release the mouse-button and pull back. HUD shows elevator up a bit, ailerons level, rudder centered. Aircraft starts to climb. HUD bank indicator matches panel turn-and-bank indicator - bank to left. It takes 3 seconds to reach "ideal bank". And keeps on banking more and more. If I had enough height it would do a barrel-roll.

Have un-installed and re-installed. (More than once.)

If I fly straight-and-level I can go hands-off on the yoke. So not aileron-trim setting in -set.xml file. (Which it shouldn't be.) Can't be a problem with the C172 file in the setup.exe, otherwise I wouldn't be the only one complaining. And I had the same problem in FG2.0.

How I am going to manage a take-off with a cross-wind from the right I don't know - won't have enough aileron to compensate!!!

EDIT: Tried it with the Citation - perfectly level take-off!?
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Re: C172 severe wing-over on take-off

Postby durk » Wed Aug 24, 2011 3:34 pm

Hi,

Are you sure that this is not related to the normal Torque and p-factor effects that one has to compensate for during takeoff?

Just a thought...

Cheers,
Durk
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Re: C172 severe wing-over on take-off

Postby macnab » Wed Aug 24, 2011 3:50 pm

Well, that is why I need a bit of right-rudder to go straight down the runway. But is it normal for a C172 to be 45 degrees 3 seconds after lift-off?
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Re: C172 severe wing-over on take-off

Postby durk » Wed Aug 24, 2011 4:21 pm

Hi,

I'm not sure; I just did a quick test. I can takeoff without touching the yoke, but I do need to step pretty hard on the right rudder to compensate (about halfway it's maximum range using a set of Saitek pedals). I hope that a real cessna pilot can tell whether that's normal or not. Anyways, just sharing my experiences. :-)

Cheers,
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Re: C172 severe wing-over on take-off

Postby ThorstenB » Wed Aug 24, 2011 8:48 pm

There was a longer discussion about the c172's behaviour in cross-wind and due to prop-wash. If the effects are too strong/unrealistic, you could add comments here:
http://code.google.com/p/flightgear-bug ... ail?id=250

Apparently, the effects are realistic - but maybe their strength/calibration needs to be revised?
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Re: C172 severe wing-over on take-off  

Postby macnab » Thu Aug 25, 2011 1:22 am

Thanks, everyone. It seems that the behaviour is expected, just not mentioned properly in the tutorials and documentation. I've never seen it written anywhere that "at the moment of lift-off apply strong right-rudder to maintain course and then reduce gradually as the necessary" ot what ever is needed.

Still, it's not just my setup, it is the way things are. I will consider the matter closed and go back to developing the correct technique.
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Re: C172 severe wing-over on take-off

Postby dany93 » Thu Aug 25, 2011 2:52 pm

Hi Macnab, Hi Durk,

I hope that a real cessna pilot can tell whether that's normal or not

MAKG is a Cessna 172N pilot IRL. Several times in his posts, he has insisted on the propeller effects, which can be very important (I confirm, and I even feel they are a bit weak on some FG single prop aircrafts). Try P51D JSBSim for strong effects.
I presume you have seen Understanding_Propeller_Torque_and_P-Factor.
Among MAKG's posts,
viewtopic.php?f=40&t=12190#p125883
viewtopic.php?f=25&t=12368&p=126594#p126594
I don't know for the magnitude you need on rudder and ailerons (in the air with full thrust, I need about 20 - 30% aileron alone, or 6 - 10% rudder alone to keep the FG C172P level-winged. In fact, both are needed at the same time), but the effect is real. If present, rudder and aileron trim can be appreciated...

Tried it with the Citation - perfectly level take-off!?

Cessna Citation-X is a jet... No such propeller wash and torque effects!

Cheers,

Dany
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Re: C172 severe wing-over on take-off

Postby macnab » Thu Aug 25, 2011 6:13 pm

I'm starting to get the hang of it. In fact I've almost got to the point where I am still aligned with the runway during my climb. Takes a bit of practice to be really gentle with the controls. I have an idea using a joystick (not yoke) with pedals for the rudder might be easier, you need some funny arm positions with a twist rudder.

Thanks for the help and guidance.
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Re: C172 severe wing-over on take-off

Postby MAKG » Fri Aug 26, 2011 12:03 am

It takes a lot of practice to get this right.

IRL, to take off with a crosswind, you lift off the downwind wheel first. In practice, the controls are set at the start of the takeoff roll. This effectively rolls the aircraft into the wind at liftoff. If you want the nose pointed down the runway (and it sure feels comfy that way) and to simultaneously stay over the runway, you can't possibly do it level with a crosswind. Pilots with more experience than me like to crab the aircraft -- point the nose upwind -- rather than rolling, to keep the ground track along the runway. The claim is that passengers are more comfortable that way. The only passenger I've had (my 6 year old son) couldn't care less. He just doesn't like turbulence on short final, and frankly neither do I (it's a fact of life with a bayside airport, though).

Make sure you turn off "auto-coordination." Takeoffs and landings are not coordinated, even with no wind. Trimming for takeoff is normally done IRL prior to clearance to the runway, with marks on the elevator trim wheel and notches on the rudder trim lever; this is hard in FG, as those aren't modeled. But IRL, trim varies very quickly during and right after takeoff, so I just try to get it right for a stabilized climb at best rate (75 KIAS for a 172), and don't bother otherwise. Rudder trim I set for neutral rudder during downwind (80 KIAS level) or cruise (100 KIAS level). I don't like to screw with that close to the ground becuase it involves reaching almost to the floor.

I wish I were flying today...but I'm stuck at KPMD. A bit too hot and windy (28 knot gusts, almost 40 deg C).

You are absolutely right about the rudder pedals vs. twist axis. I wonder if two joysticks (one for pitch and roll, the other for yaw) might work. Pedals are certainly more realistic, but they cost quite a bit more. I've only used a sim yoke once. It does feel slightly more realistic for a Cessna. They still don't have nearly correct feedback forces, and that's a bigger issue than yoke vs. joystick. And some aircraft really do have joysticks. Not Cessnas, though.
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Re: C172 severe wing-over on take-off

Postby macnab » Fri Aug 26, 2011 3:32 am

Thanks for your comments. IRL I have been in the right-hand-seat of a 172 landing in a cross-wind and it is a bit unnerving looking down the runway through the side window!!

Maybe a 2nd joystick just for rudder is a thought - I don't suppose hand-hand co-ordination is any different to hand-feet co-ordination, and rudder-pedals are expensive. Also means a couple of extra buttons which are easy to reach without having to use combinations to switch purpose. But so far the wrist movement combinations are manageable - I just occasionally forget to be gentle with the joystick. The rudder is very sensitive and it is easy to yaw all over the place. So what I do is take-off and climb to 500 feet, reset, take-off and climb to 500 feet, reset, etc. When I am happy with still pointing in the same direction as the runway at 500 frrt ( nearly there) then I'll start to practice turning to the required heading. Then progress to the transition to straight-and-level. Then my circuits and bumps - that seems easier to me than flying to a different location and finding and lining up with the runway.

I am not using auto-co-ordination. It might make things a bit easier when learning to turn to a heading, but then to do greater things, one needs it switched off, and the learning process starts from scratch. If you want to fly a sim easy-peasy then get FSX - their 172s don't suffer from p-effect and torque-effect.
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Re: C172 severe wing-over on take-off

Postby Dragonmaster Lou » Fri Aug 26, 2011 3:07 pm

Another option instead of a second joystick is something like the Thrustmaster T.Flight HOTAS X, which has a rocker switch on the throttle control that you can use as a rudder control in addition to/instead of the twist axis of the joystick. It's what I use, although I find myself usually using the twist axis more (although I may try the rocker switch to see if it helps on take-off).

My first new hardware purchase, though, will definitely be some rudder pedals.
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Re: C172 severe wing-over on take-off

Postby macnab » Fri Aug 26, 2011 3:50 pm

Using a toggle-swicth for the rudder could have the advantage that for a 2-minute turn you kinow it is 34 presses on the switch to give the exact rudder setting :)
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Re: C172 severe wing-over on take-off

Postby Dragonmaster Lou » Fri Aug 26, 2011 4:38 pm

Well, the HOTAS X is an analog, self-centering switch that shows up as another axis (in fact, if you press a mode button on the joystick it sends the signal along the same channel as the joystick twist axis).
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