Minor point: the Airbus that landed with a 90 degree cocked nosegear last week had magnesium wheels. When the wheels finally got to the tarmac after the rubber was scrubbed off, that was the white fire we saw.

IMO, the little extra O2 in the air filled tires would not be the reason to use N2. At -70F at cruise altitude, any moisture in the airplane tire would freeze into a chunk of ice which would probably unbalance the tire something fierce. Well, not if it were an SR-71...but we retired those, didn't we?

If brake fires were a big problem, perhaps mag wheels wouldn't be used so much.

I suggest dry N2 is used to eliminate moisture in the tires. Whadayathink, ASRoff?

 

Yes, Magnesium corrodes very quickly (intergranular corrosion is severe). Ithink you'd be supprised on how many aircraft use aluminum wheels. the no oxygen is a minor point. but anything to prevent fire in an aircraft the better.

Case in point the hydraulic fluid used in aircraft is phosphate based and nasty stuff. it eats the paint on aircraft which reduces the corrosion control. and if left on the skin it burns like crazy. But, unlike petrolum based hydraulic fluids that Skydrol (brand name) replaced. It doesent catch fire. The hydraulic dident attack paint, It dident cause chemical burns but it was flamable.

My notes from the last time I taught Landing gear systems says 1. corrosion control 2. fire protection and 3. Because an inert gas is more stable.

 

Good points. Inert gas has lots of advantages.

Keeping the hydraulic fluid mostly in the system helps keep the paint looking good.

FWIW, what kind of tire pressures are used in commercial airliners? Some military aircraft main gear tires, especially those landing on carriers use pressures most of us wouldn't believe. 300+ psi comes to mind.

 

Everything that can be filled with nitrogen is filled with nitrogen in the apache.. Struts, tires, fuel tanks, all of it.

They even have a nitrogen capturing membrane that pulls nitrogen out of the atomosphere to pump the fuel cells up. The fuel cells are even placed in places to protect other things from small arms.

keeping things as inert as possible is the name of the game.

 

Yup. One of my latest projects was mounting one of those systems (pretty big one) to the 747 to "inert" the fuel tanks (thanks to the TWA Flight 800 thing....). It'll now come on all new 747's and the kits will be retrofitted to all existing ones. More models to follow, but the '47 was the first.

 

I 'think' that commercial airplanes use something around 120psi of nitrogen. Generally 'low wing' commercial aircraft rely some part on ground effect for cushion when they land. The normal passenger would also appreciate a soft landing.

Carrier landings require a controlled crash of sorts and is not a soft landing. I think about 50K+ lbs. of F-14 coming home with fuel and unused armament....or better yet, a zero-zero night carrier landing. I'd say that the two relatively small main(rear) tires/wheels take A LOT of stress.....as well as other components.

I wouldn't think commercial plane tires endure as much stress. They weigh a hell of a lot more but land much lighter. They use more wheel/tires as well. Maybe they can afford it where as a fighter can't afford more weight?

 

Helium does not catch fire.

 

Of course not. Wrong column of the periodic table.

Personally I like to use the inert gas Ununoctium (Uuo) in my garden tractor tires when I can get it. It gives off a nice glow when mowing at night.

The in the original post was used because I couldn't find one with "tongue-in-cheek". I was attempting mild sarcasm. I'm not a nice person.

 

100psi to 150psi depending on the aircraft. As far as carrier A/C are concerned (It's been a while but as I remember it) we had two pressure settings one for Carrier landings and one for land base.


one other thing, helo rotor blades are filled with nitrogen.

By the way OldSStroker thanks for the math quote, I used it the other day when I was teaching some new students how to calculate IHP, BHP, BMEP ect. (they were intimidated by the formulas)

 

to get a better picture of the forces on the landing gear when touching down on a carrier, just look at some of the early jets that the navy had. Landing gear looked like it was 4-5 ft tall...the plane actually looked like it was on stilts. I dont recall what aircraft it is...i saw it on the military channel while flipping through.

I got a question for some of you chem guys...ive been through chem I in college, but ive never understood how at my work (a testing lab) we have bottles of nitrogen gas for a customer at ~4000 PSI and yet when we got a dewer of LN2 (liquid nitrogen) it was in some dinky stainless steel container where the walls could not have been more than 1/8 inch thick?? I think the liquid was held at 30 psi or so. How can the liquid be at such low pressure but the gas be at such high pressure, wouldnt the gas turn to liquid at some point?
Rich

 

That might have been the A4 Skyhawk. Yes, there was quite a bit of strut travel, but the high attitude was mainly to be able to carry "stores" like bombs and fuel tanks under the wings and fuselage. Higher wing birds like the A7 Corsair were a lot closer to the ground and had wider track mains which made them easier to handle during cross-wind landings on shore bases

Not a chem guy, but here's a quote I cribbed:

"Liquid Nitrogen, often abbreviated as LN2 is used extensively in all fields of research and industry. The important things to remember is that as a liquid its boiling point is around -195°C (-320°F) at normal pressure which means that unless its temperature is kept below that temperature, it will boil and turn into Nitrogen Gas. Increasing the pressure under which it is stored increases the boiling point. At -147°C (-232.6°F) it reaches the critical temperature above this temperature, the gas cannot be liquefied by pressure alone."

Here's the link:
http://www.finemech.com/tech_resourc...nitrogen.shtml

 

Chitty Chitty Bang Bang?

 

heh now i get where i went wrong. I didnt know the dewer was assembled like a thermos. Thanks man for the link, its another one of life's mysteries that is solved!!
Rich