Wheels effect upon touchdown
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@airtex2019 Just try a crosswind landing with 25 kts perpendicular to the RWY and you’ll see it yourself. The sudden change of direction upon touch down should not be possible due to inertia.
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@Bowser Sure, I’ve done plenty, and as I say it “feels right” to me. But I’m not a fighter pilot. I’m more accustomed to landing a single-engine Cessna in crosswind. Much lower inertia.
We might be able to find some videos of crosswind landings, to roughly calibrate the yaw-acceleration, IRL vs BMS. Not sure how much it would vary, due to things not visible like fuel in wings… and engine rpm (rotational inertia).
This vid has a long stream of examples, and you may be right. Yaw transient appears barely noticeable as they touch down.
There was another recent thread about brake-channel and anti-skid behavior. I think I read there’s a difference in “touchdown anti-skid” (only channel 1) vs “wheelbrake anti-skid” (available on both channels)
Does F-16 landing gear have a mechanism to get the wheels rotating, with passing airflow, before touchdown? That would greatly reduce any transient upon touchdown.
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@Bowser - I don’t get you…even if you are countering a crosswind your mains should both be on deck before your nose, and NWS should not be engaged before the nose touches down - if it is, you could be touching down with your nose wheel cocked…which it likely would be if NWS is engaged and you are countering a crosswind with rudder.
What do you mean by “two point”?
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@Stevie Only main gear touching the RWY.
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The gear has no mechanism to get the wheels spinning prior to touchdown.
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@Bowser said in Wheels effect upon touchdown:
@Mav-jp Even without de-crabbing, the aircraft makes an abrupt change of direction upon touch down in crosswind conditions. E.g. when still in the air the center line is followed in a crab position. Then upon touchdown the aircraft instantly moves in the direction of the main wheels. This is physically impossible due to inertia and the fact that the wheels have close to zero grip upon touch down due to the airflow over the wings. There should be a slow transition in which the wheels first skid over the runway in landing direction (so center line) and then when speed decreases the aircraft will slowly start going in the direction of the main wheels if no rudder is applied.
Open your AFM file , reduce lateral friction of the gear 1 and 2 . Have fun
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@Bowser - ok. That’s what I was thinking.
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@Mav-jp said in Wheels effect upon touchdown:
Open your AFM file , reduce lateral friction of the gear 1 and 2 . Have fun
Out of interest, What’s the current default lateral friction for the main wheels?
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I don’t see where the danger is or why not de-crab with the BMS model. I did the crab landing, the sideslip, and the decrab, all of which was possible. It was a clean jet on weight, winds blowing 28kts westerly.
Edit: I guess what was mentioned above about Crab only is for the real thing.
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" no reason to ever use the rudders on the F16 is my recollection."
I was chatting with Keith Rosenkranz “Vipers in the Storm” last year and this was a direct quote.Mud
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just thought about this again and not quite sure if I have a good answer as to why it happens but it is all what I was able to do for now, here it goes. Why would the jet’s nose point in the direction of the wind? it’s because viewing it from the top the jet experiences a rotation since the wind force at the tail is larger than the nose. But why does the rotation stops at some finite angle? because the wind force is directly proportional to the tail area, and the rotation will reduce the tail area until the wind’s force equals component of the thrust opposite to the wind. So what happens at touch down? the friction from the wheels are in the same direction as the thrust (forward) causing the nose to rotate downwind which will immediately increase the tail area and thus the wind force.