PPRuNe Forums - View Single Post - Most demanding loads on aircraft landing gear
Old 25th Jul 2016, 10:16
  #13 (permalink)  
Mach Stall
Join Date: Aug 2014
Location: Miami, FL
Posts: 17
Pulse1, I can't support the 500 deg C temperature, but what some seem to be overlooking is that shock absorbers function precisely by generating heat. Kinetic energy is absorbed by internal fluid friction forces within the shock, resulting in heat, which heat is what dissipates the descent rate.

Basic physics -- unless the shocks are converting their work to electricity or powering some device or storing energy, then if they did not generate heat, they would necessarily function only as springs, and the airplane would go bouncing back up into the air. This is our friend, the First Law of Thermodynamics (aka conservation of energy) at play.

The fact that the descent of the massive tonnage of a large commercial aircraft is able to be arrested by dissipating all that energy (in the form of heat) with such a small device as a shock absorber, and in such a short time as it takes to compress the strut, does lend credibility to the idea that they could get noticeably hotter with a hard landing.

The question is how much hotter.

We all know the heat generated from the brakes is sufficient to cause a fire, so that would be one's first thought as to the cause when looking at heat damage on landing gear. And as someone pointed out, the brakes have a lot more kinetic energy to dissipate because the forward speed is so much faster than the vertical descent rate (about 2 orders of magnitude more energy).

The temperature limits of hydraulic fluid and seals tell us the shocks are not intended to get very hot (nothing remotely approaching 500 deg C). But there will be some temperature increase of the strut from the shock absorption during a very hard landing (though I would guess less than a 50 deg C increase, rather than 500 deg C). If someone has actual data, it would be fascinating to find out.

Last edited by Mach Stall; 25th Jul 2016 at 14:23.
Mach Stall is offline