J3 Cub won't Bounce

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robjahnke
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Joined: 29 Sep 2021, 20:39

J3 Cub won't Bounce

Post by robjahnke »

Either my settings are wrong, or the simulation does not take into account that the CG of the airplane is behind the wheels and that the landing gear will spring back from an impact with the ground.

If I "dive" the airplane into the runway by doing an approach at 60 mph with NO FLARE, the wheels spread, the tail goes to level, and it stays there until the speed bleeds off and then the tail settles to the ground. If I pull back on the stick as soon as the wheels hit the ground, I get a nice "balloon" but there is no bounce.

There are two things that cause a real J3 to bounce and/or balloon in that situation. First, the bungees on the landing gear will spring back and toss the airplane into the air. On the real J3, the bungees will absorb some energy but not a lot. The bungees on the A2A J3 seem to absorb ALL of the energy and provide no bounce from the spring back of landing gear.

But even in that situation, with the CG behind the wheels, the real cub will "bounce" or actually "balloon" with a tail high landing unless you really "grease it on". That is because the CG is behind the wheels, so if the airplane is descending when the wheels touch down, the tail will continue to descend when the wheels touch down and cause the angle of attack to increase and send you back into the air. The greater the vertical velocity on touchdown, the greater this balloon effect will be. If you "grease it on" or touch down with near zero vertical velocity, the tail will remain in position and there will be no "balloon".

Either the landing gear bounce and the downward momentum of the tail with the CG behind the wheels is not simulated in the A2A J3 Cub, .... OR... I have the wrong settings.

I am running the Steam edition of FSX 10.0.62615.0 (FSX.10150710-1055) on Windows 10. In Realism Settings, the General Slider is ALL THE WAY to the right. In the Mini Controls Panel, AccuSim is ON.

Any suggestions?

Thanks, Rob

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Scott - A2A
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Re: J3 Cub won't Bounce

Post by Scott - A2A »

Hi Rob,

Keep in mind FSX ground handling leaves much to be desired. I do have access to a J3 but do recall how it feels on touchdown and will have to give the sim a test flight again and report back to you. Thanks for the feedback.

Scott
A2A Simulations Inc.

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Oracle427
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Re: J3 Cub won't Bounce

Post by Oracle427 »

I would echo the feedback. I'm assuming that this is a simulation engine limitation with the way it handles the mass and inertia of the airframe, and moments around pivot points. I'm not sure that FSX does this at all.

Same for the compression and dampening effects of the landing gear. I have never seen this modeled, though it would be wonderful if it could be done.
Flight Simmer since 1983. PP ASEL IR Tailwheel
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robjahnke
Airman
Posts: 25
Joined: 29 Sep 2021, 20:39

Re: J3 Cub won't Bounce

Post by robjahnke »

Thanks Scott,

I had assumed that you had redone the physics model so you would have taken the moments around the CG into account. If you are just tweaking the FSX physics model, I completely understand the lack of realism in this scenario. As far as the spring back from the gear, again that would require a modified model, not just some parameter changes in the FSX model.

If you repeat my experiment, fly to touchdown at 60 mph and DO NOT FLARE.... Just hold the stick steady before and after touchdown, you will see the plane go to level with no bounce and no balloon at touchdown. It makes it easy to fly as a game, but it does little to demonstrate the practice it takes to land a real J3.

Rob
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