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FG and The Amazing World of Taildraggers (which turn right)

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FG and The Amazing World of Taildraggers (which turn right)

Postby OE-LML » Fri Aug 30, 2019 2:55 pm

Hallo! :D

Recently I have tried out the Beaver, Mudry CAP 10C and Piper (Super) Cub, all from official FG hangar.
To my amazement these taildraggers have a tendency to turn right during take off run. I was curious and pulled out all my old issues of "fliegermagazin" (a German aviation magazine) and looked for articles about propeller effects and flying taildraggers. I found some, but I couldn't find any reason why a taildragger with clockwise turning propeller should turn right during take off. On the contrary, P-Factor (due to the diagonal propeller axis at the beginning) and gyroscopic effect (because of the to the front tilting propeller axis) should force the plane more to the left than a similar aircraft with nose wheel.

It would be great if a real life pilot could provide clarification.

Thx in advance.
CU.
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby Alant » Fri Aug 30, 2019 4:03 pm

The torque required to turn the prop is balanced by an equal an opposite torque on the engine mounts. This in turn generates the same torque between the two wheels The wheel with the highest loading will have more ground (rolling) friction than its opposite.
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby OE-LML » Fri Aug 30, 2019 10:39 pm

I know. But with clockwise turning propellers, the torque effect should be a force to the left and therefore pushing down the left wheel.
All 4 propeller effects force a taildragger to the left. Maybe not all at the same time, but during take off run they should appear all.
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby Alant » Fri Aug 30, 2019 11:08 pm

Are you viewing clockwise rotation from the front of the aircraft or the pilot ?

The big difference with tail dragers is that on the ground they are unstable in yaw. So any yaw motion will increase unless the pilot corrects, or better still, anticipates it.

This video shows clockwise from the pilot´s view https://www.youtube.com/watch?v=XP1VAEKCjUE

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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby OE-LML » Fri Aug 30, 2019 11:28 pm

Alant wrote in Fri Aug 30, 2019 11:08 pm:Are you viewing clockwise rotation from the front of the aircraft or the pilot ?

From pilot's view.

Alant wrote in Fri Aug 30, 2019 11:08 pm:So any yaw motion will increase unless the pilot corrects, or better still, anticipates it.

Yeah, I know. Because of the center of gravitiy behind the main gear.

Still very strange to me ...
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby Alant » Fri Aug 30, 2019 11:38 pm

Clockwise prop from the pilot´s POV means that the airframe will try to rotate counter clockwise. Therefore more load (and therefor friction) on the left wheel, and the aircraft will yaw left.
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby Alant » Sat Aug 31, 2019 12:16 am

I have just re-read your original post, agree with your remarks.. It is late here, so I will try to look into the J3Cub tomorrow.
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby Alant » Sat Aug 31, 2019 9:03 pm

I had a chance to look at it this evening. Opening the throttle makes the left wing go down slightly, but for some reason the undercarriage generates a positive yaw moment (nose to the right) which is not what I expect.
I have asked a question on the JSBSim list, as this code is all in JSBSim, not Flightgear.
Will keep you posted on developments.
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby dilbert » Sun Sep 01, 2019 12:51 pm

Flew it this morning and see what your referring to; which I can't 100% explain.

With everything in default and viewing from astern, plane wanders right going down runway. Tailwheel is straight, so that's not the problem.

One thing to note is that in default, the Beaver auto coordinates, irrespective of what is selected in the start menu.

Go to Beaver>Options>Auto Coordinate and uncheck the box. Then using rear view, observe as you start down runway (hands of the controls), aircraft will track straight, rather than wandering right. Maybe the assumption is that the tailwheel is holding it straight, simulating a "locked" tailwheel ?

Anyway, once the tail is up and you're airborne (still hands off); it will want to bank and turn to port (which is more like it should be), requiring right rudder during climb out.

Never flew the Beaver in real life; but think the FG version is a very nice model. 8)

Been 60 years, but my recollection is that the SNJ required 5 notches forward on the trim wheel (right rudder), and tailwheel locked to keep it straight down the runway during take-off.

Kind Regards
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby Alant » Sun Sep 01, 2019 1:37 pm

I´m deep into JSBSim C++ with this at the moment. ;(
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Re: FG and The Amazing World of Taildraggers (which turn rig

Postby OE-LML » Sun Sep 01, 2019 6:12 pm

Thank you for looking into it and for your effort.
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