Originally Posted by Mach Stall
(Post 9451185)
The question is how much hotter. |
A Squared-
Good post. The only thing I would add is that the heat transfer mechanism to the strut is via compression work applied to the hydraulic fluid mass within the cylinder. Obviously, the hydraulic fluid mass absorbing the energy would get hotter than the strut body it is transferring heat to. |
I recall being told by a landing gear designer that the critical L/G loads were those induced by wheel spin-up on touchdown!
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which of course is only relevant if you have more than one axle per leg or more than two main landing gear legs. The Vulcan has 4 tires on 2 axle per leg.
Even the 4 tires on one axle design of the Trident prevents most of this type of load. This is how it looks if you turn an A380 around tight corners... |
The sole concern with A Squared's calculation is that it assumes thermal equilibrium is reached for the assumed gear strut mass (i.e., plenty of time for the thermal energy to diffuse through that mass) -- whereas in reality, we're talking about on the order of a half-second for strut compression. During this short time, the fluid friction would transfer heat to the comparatively tiny local mass of steel surfaces adjacent to the heat source. Bottom line, the uppermost piston and cylinder steel surfaces would see a drastically higher peak temperature rise than would the bulk mass of the strut.
As I said in my previous post (having run the same sort of back-of-the-envelope calc), I thought the temperature rise of the whole strut would be under 50 deg C, and I remain in agreement with A Squared on that front. And since pulse1 described the entire lower leg being blue, I still think there was probably some other cause at play in that large-scale thermal damage. But I'm leaving the door just a little cracked in my mind that during a violently hard landing, some small, localized surface (e.g., upper piston) could possibly get hot enough to blue steel (over 275 deg C). I just can't quite rule it out intuitively without seeing actual data or a dynamic thermal analysis. You generated an interesting sub-discussion, pulse1. |
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