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Landing x-wind reduction as rcr increases

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Landing x-wind reduction as rcr increases

Old 21st Feb 2024, 16:08
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Landing x-wind reduction as rcr increases

Good evening all, let me pick your brains if I may.
An old Boeing 4 jet has a x-wind limitation graph that, as you would expect, shows a greater x-wind max value as the rcr goes up. But then it hits a max value and any subsequent increase in rcr actually decreases the x-wind limitation. For a light aircraft, it loses up to 3 kts, for a max weight aircraft, up to 7 kts. I have racked my feeble brain, but cannot think why this would be. I've thought about tyre to surface contact, derived momentum as the aircraft tries to centralise from a crabbed approach etc etc, but can't come up with a good reason. In disgust I'm off for a large Lagavulin, but if the collective PPrune knowledge base can enlighten me, I'd be very, very grateful!!
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Old 22nd Feb 2024, 08:06
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In a crosswind all aircraft will experience a side force. In order to remain on the runway this force has to be countered.
The mechanism of balance will depend on the aircraft type.

Start here:
Cornering force
Effect of thrust reverse

https://skybrary.aero/sites/default/...kshelf/179.pdf

https://skybrary.aero/sites/default/...kshelf/871.pdf

https://skybrary.aero/articles/landi...inated-runways
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Old 22nd Feb 2024, 13:34
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Thank you safetypee,

I was aware of most of this, and the type in question was re-engined, so bank and pitch angle at T/D are limited. Are you referring to the greater braking force on a high RCR runway leading to reduced cornering force? Which, logically, would have a greater affect on a heavy mass A/C?

Thanks,

Isaneng
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Old 22nd Feb 2024, 18:02
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isa, your questions raise interesting aspects, which may have no simple answer.

First, consider if there are different standards, requirements, or terminology between 'old' aircraft and those which are used today.
Thus RCR (Runway Condition Report ?), is now described by category where the contributing factors in each reduce the braking effectiveness; e.g. 6 dry, 5 wet, Are we discussing the same issue ?

The assumption might be that wheel side-force is related to RCR, but the science is wide ranging - runway texture, drainage, tyre type or tread, Also, that the categorisations and certification are based on more recent science - not just the old wet vs dry runway.
Then there is the possibility of a complex mix of wheel/ runway forces and the aerodynamic contributions; rudder / reverse have greater effect at higher speeds.
Additionally, the methods of determining an acceptable 'demonstrated' value have changed / changing, particularly in considering crosswind gusts and flight test demonstrations; these and published demonstrated values vary between manufacturers and regulators, civil military - even if there appears harmony with the use of RCR.

Overall there does-not appear to be an instant answer, but at least interesting questions to keep on considering.


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Old 22nd Feb 2024, 18:39
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Fella, thank you v muchly for your thoughts. The consideration of legacy aircraft and current regulation isn't one I had considered.
Thank you for your time!!
😁
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