Post by LOU on Jun 19th, 2011 at 3:05am
Not too much holding now unless something weird happens. The time with the long hold was a long time ago. Started holding at high altitude so fuel burn was not too bad. It was just thunderstorms with some shifting winds that required constant runway changes. Every time they turned the airport around it took a while to get the flow back in line. Took all the fuel I could and still be legal for landing. The 757 was good at that.
How about a look at the gear and anti-skid system?
The gear on the 727 and to some degree the 707 was fairly simple. After takeoff, with a positive rate of climb, you would reach over and select gear up with handle with the little plastic wheel. As you pulled the handle out of the down detent and moved it up a bunch of things happen. First you operate a cable and pulley system that opens a sequencing valve. The gear doors swing open and when they reach the full open position the next sequence is to open the valve to operate the landing gear. As the gear begins to move a shot of in-flight brakes stops the wheels from turning. Then as the gear reaches the wheel well, it hits a stop and the gear up-locks engage. As soon as the up-lock is satisfied, the next sequence is to close the gear doors. In the original 727 design, the nose wheels had brakes. Later mods took the brakes off the nose wheel and wheel stoppers, like the 707 were installed. The big difference was the loud noise of the wheels hitting the stoppers and the smell of burning rubber. As soon as the gear was retracted and locked up, the gear handle was placed to the middle or off position to remove hydraulic pressure.
To extend the gear, just reverse the above procedure, except you left the gear handle in the down detent. All pretty straight forward. The gear was moved by A system pressure in the 727 and utility system in the 707. When the gear was extended and locked down the anti-skid panel would show 5 REL lights in the 727. This showed the anti-skid system was OK, and locked wheel protection was armed. At touchdown the spin up of the wheel would activate the anti-skid system. A small generator in each wheel would generate voltage as the wheel spun. This voltage information was sent to an anti-skid computer to process. The 727 had a more advanced system than the 707. The 707 had cycling anti-skid which was more like your car. The break pressure was cycled on and off to the wheel that was showing a skid. The 727 used modulating anti-skid which is what all the modern planes now use. As you applied the brakes, the system would compare the voltage from each wheel and "modulate" or reduce the pressure to the wheel that was decelerating too fast. If the wheel stops during braking, the coefficient of friction drops to zero and you loose that wheel for braking. The modulating system would apply just enough pressure to approach a skid and then back off just enough to keep the wheel at maximum braking.
Now lets have a look at manual gear extension.
To extend the gear without hydraulic power was a chore in either the 707 or the 727. In either plane you needed to plan when you would put the gear down since once extended, it stayed down. So if you were short on fuel that could be a factor. The main gear, when unlocked, would free fall. In order to get the door out of the way a large spoon or arm would be hit by the gear falling and push the door open. The nose wheel had a cable system which controlled the door.
MANUAL GEAR EXTENSION
1. Gear lever off................................................OFF
2. Crank each gear down....................................DOWN
[each gear has a separate guide for which direction to turn the crank, it's a two step process, crank one way to unlock the gear, crank the other way to lock it.]
3. When gear down gear handle down..................DOWN
4. Visual check of gear.......................................CHECK
A crank handle is stowed on the lower, aft P6 panel. The gear extend area is just aft of the F/E seat.
In this screen capture you can see the three small doors - one for each gear - next to the F/E's chair.
In each plane you had to go back in the cabin to look through the viewing ports to see the lock indicators.
In the 727 and 707 the main gear viewing ports were just aft of the rear window exit about where the edge of the isle met the seat track. Some of the ports were pretty dirty and at night you hoped the light in the wheel well worked. The nose wheel port in the 727 was just outside the cockpit in the middle of the isle. In either case you had to rip up the carpet.
In the 707 the nose wheel down lock indicator was in the lower 41 area under the cockpit. There was a small tunnel you had to slither down through to check the lock indicator.
This is what you hoped to see through the viewing port in the cabin floor.
It could take 15 minutes to go through the whole checklist, so that is where the planing for the landing came in.
Lou
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How about a look at the gear and anti-skid system?
The gear on the 727 and to some degree the 707 was fairly simple. After takeoff, with a positive rate of climb, you would reach over and select gear up with handle with the little plastic wheel. As you pulled the handle out of the down detent and moved it up a bunch of things happen. First you operate a cable and pulley system that opens a sequencing valve. The gear doors swing open and when they reach the full open position the next sequence is to open the valve to operate the landing gear. As the gear begins to move a shot of in-flight brakes stops the wheels from turning. Then as the gear reaches the wheel well, it hits a stop and the gear up-locks engage. As soon as the up-lock is satisfied, the next sequence is to close the gear doors. In the original 727 design, the nose wheels had brakes. Later mods took the brakes off the nose wheel and wheel stoppers, like the 707 were installed. The big difference was the loud noise of the wheels hitting the stoppers and the smell of burning rubber. As soon as the gear was retracted and locked up, the gear handle was placed to the middle or off position to remove hydraulic pressure.
To extend the gear, just reverse the above procedure, except you left the gear handle in the down detent. All pretty straight forward. The gear was moved by A system pressure in the 727 and utility system in the 707. When the gear was extended and locked down the anti-skid panel would show 5 REL lights in the 727. This showed the anti-skid system was OK, and locked wheel protection was armed. At touchdown the spin up of the wheel would activate the anti-skid system. A small generator in each wheel would generate voltage as the wheel spun. This voltage information was sent to an anti-skid computer to process. The 727 had a more advanced system than the 707. The 707 had cycling anti-skid which was more like your car. The break pressure was cycled on and off to the wheel that was showing a skid. The 727 used modulating anti-skid which is what all the modern planes now use. As you applied the brakes, the system would compare the voltage from each wheel and "modulate" or reduce the pressure to the wheel that was decelerating too fast. If the wheel stops during braking, the coefficient of friction drops to zero and you loose that wheel for braking. The modulating system would apply just enough pressure to approach a skid and then back off just enough to keep the wheel at maximum braking.
Now lets have a look at manual gear extension.
To extend the gear without hydraulic power was a chore in either the 707 or the 727. In either plane you needed to plan when you would put the gear down since once extended, it stayed down. So if you were short on fuel that could be a factor. The main gear, when unlocked, would free fall. In order to get the door out of the way a large spoon or arm would be hit by the gear falling and push the door open. The nose wheel had a cable system which controlled the door.
MANUAL GEAR EXTENSION
1. Gear lever off................................................OFF
2. Crank each gear down....................................DOWN
[each gear has a separate guide for which direction to turn the crank, it's a two step process, crank one way to unlock the gear, crank the other way to lock it.]
3. When gear down gear handle down..................DOWN
4. Visual check of gear.......................................CHECK
A crank handle is stowed on the lower, aft P6 panel. The gear extend area is just aft of the F/E seat.
In this screen capture you can see the three small doors - one for each gear - next to the F/E's chair.
In each plane you had to go back in the cabin to look through the viewing ports to see the lock indicators.
In the 727 and 707 the main gear viewing ports were just aft of the rear window exit about where the edge of the isle met the seat track. Some of the ports were pretty dirty and at night you hoped the light in the wheel well worked. The nose wheel port in the 727 was just outside the cockpit in the middle of the isle. In either case you had to rip up the carpet.
In the 707 the nose wheel down lock indicator was in the lower 41 area under the cockpit. There was a small tunnel you had to slither down through to check the lock indicator.
This is what you hoped to see through the viewing port in the cabin floor.
It could take 15 minutes to go through the whole checklist, so that is where the planing for the landing came in.
Lou
Uploaded with ImageShack.us