Some landing gear questions
Ive heard they tyres are inflated with nitrogen as it expands less than air if brake heat gets to the wheels when gear is retracted, there were exploding tyres when air was used
is there a blow out plug in the wheel in case things still get to hot to save tyre from exploding?
also Ive seen 747s climbing with gear down, apparently to cool brakes from passing air
is there a blow out plug in the wheel in case things still get to hot to save tyre from exploding?
also Ive seen 747s climbing with gear down, apparently to cool brakes from passing air
Yes, on all larger aeroplanes there is a plug made from the metal lead in the wheel, and it's made to melt at a certain temperature to let excessive pressure out.
And it's pretty rare to see a 747 climb-out with the gear still down as you would normally not takeoff until the brakes are cool enough, though I guess if you were doing short multiple sectors (I've done four in one day) or circuits then to help cooling you may elect to leave the wheels out for a minute or so.
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Nitrogen also used due to inert properties in the event of wheel fire & lack of moisture which can cause internal corrosion of wheel hubs. The wheels on a 747 are left out on T/O if a brake has been deactivated. There are two methods of brake deactivation (747 classic) one uses a lock out tool which maintains inflight braking (approx 400ps) so gear can be retracted normally, the other method is for the hydraulics to be toatally blanked of removing inflight braking & the mel gives a figure for gear to remain down to allow the wheel to stop rotating before entering the gear bay (think its about 2 mins). If this method is used climb out is affected so there can be weight penalities incurred. No T/O should be attempted until the brakes are in the correct temperature range.
Exup
On the C-5, there were "spin down" sensors, so until spindown occurred, the gear would not begin retraction. Is that true on the 747?
GF
On the C-5, there were "spin down" sensors, so until spindown occurred, the gear would not begin retraction. Is that true on the 747?
GF
No, no such device fitted.
They have a system that applies a touch of brake pressure to the main gear and the nose gear has a rubbing strip when the strut is in the retracted position.
They have a system that applies a touch of brake pressure to the main gear and the nose gear has a rubbing strip when the strut is in the retracted position.
We had a braking system that applied 150 psi to the brakes but if it failed, retraction waited for spindown signals. 2 minutes was the time for spindown, if operating with anti-skid inop.
GF
GF
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Originally Posted by MarkerInbound
Ok, bad choice of words. How about, after the main landing gear touch down and with all four hydraulic systems powered and the Speedbrakes ARMED, all twelve spoiler panels will be driven to their full travel position.
The spoilers do not compensate for crosswinds in the ground spoiler mode, that is left to the flight crew with aerilons and rudder.
The spoilers do not compensate for crosswinds in the ground spoiler mode, that is left to the flight crew with aerilons and rudder.
From the Boeing 747-400 Maintenance Manual (27-61-00 Item F (7))
"Do the test of the spoiler control system with the speed brake control lever in the UP position:
(a) Put the speed brake lever in the UP position
1) Make sure that the spoilers No.1 thru 12 are in the fully up position (45 degrees)
(b) Turn the aileron control wheel fully clockwise
1) Make sure that the spoilers No. 1 thru 5 are in the fully down position
2) Make sure that spoilers No.6 thru 12 are in the fully up position (45 degrees)...."
Spoilers 6 & 7 are not used for lateral control at any time, hence they are included in the up group of spoilers.
Rgds.
NSEU
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Originally Posted by Mustafagander
Boeing like to have gear hydraulics depressurised in flight hence the "OFF" position for the gear selector. This removes pressure from the gear system and allows the gears on most Boeing jets to hang on the up locks provided for the purpose. It makes sense to remove 3000psi whenever possible. If it's not pressurised, it can't leak.
I guess, rather than train their maintenance personnel properly, they chose to modify the operational procedures (The expensive of maintaining hydraulic systems under constant pressure is apparently less than repairing damaged doors?)
Rgds.
NSEU
Another reason for nitrogen inflation of wheels is that the fine rubber dust inside the tyre is very flammable and has, in fact, been blamed for a few serious wheel explosions.
