USAFHummer From United States of America, joined May 2000, 10685 posts, RR: 53 Posted (11 years 1 month 2 weeks 2 days 21 hours ago) and read 4524 times:
My question is...when the main gear bogies of aircraft with 4 or more wheels extend, they are obviously tilted as such in this picture...Im assuming that the reason for this is so that the gear bogie can fit in the main gear bay
Cdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 28 Reply 2, posted (11 years 1 month 2 weeks 2 days 15 hours ago) and read 4431 times:
I'll explain the B757 for you. There is a truck positioner actuator located on the aft part of the gear. When weight is off the wheels, hydraulic pressure positions the actuator to extend and drive the aft wheels down. Now the purpose as the Aircraft manual states is to permit clearance between the gear and aircraft structure during gear retraction and extension. But I remember an instructor once telling me that they testes a B767-200 some time ago to see if it would clear the structure if not tilted. He said it did. (The B767 has the actuator on the front part of the bogie and the forward wheels go down.).
I also remember another incident at my airline a couple of years ago. And aircraft had to do an air return due to the landing gear lever lock solenoid not releasing after the aircraft transitioned to air mode. Now, I believe the crew pushed the lever lock override button and raised the gear. I mention this because when the aircraft was troubleshot, it was found that there was a hydraulic leak upstream of the truck positioner actuator and the wheels were sort of dangling, meaning that you could tilt them with your hands up and down. There was no hydraulic pressure to position the gear. Maybe the gear just happened to be in the correct position when they retracted the gear that time, because there were no problems.
So the gears are tilted to allow for clearance into the gear (official reason), and a secondary function is to provide air/gnd mode logic, since sensors depend of gear angle and wows (This applies to the B757/B767/B777).
As for you other question as to when this happens. On the B757/B67, the gears are tilted whenever weight is off the wheels. The gears are always tilted. The B777 is different. The rear wheels are tilted downward for ldg (unless there is a high approach angle. At that point the gear will actually adjust to help compensate for a steep ladg angle) and the rear wheels are tilted up during retraction. The can only fit into the wheelwell this way.
Hope this helps, I need water now!
PS...Maybe someone can shed some light on Airbus. I'm going to ASS-U-ME it works in a similar manner on the A300/10/30/40. But u know what happens when you ASS-U-ME
Rydawg82 From United States of America, joined Sep 2001, 838 posts, RR: 8 Reply 4, posted (11 years 1 month 1 week 5 days 7 hours ago) and read 4250 times:
Quick correction, and thanks for the great info so far. The 777 truck actually tilts back at takeoff and landing. When the truck is positioned for retraction, the truck tilts forward, and remains in this position until it has been lowered again. It's a rather interesting process to observe....Ryan
You can take the pup out of Alaska, but you can't take the Alaska out of the pup.
Cdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 28 Reply 5, posted (11 years 1 month 1 week 5 days 3 hours ago) and read 4239 times:
The rear wheels are tilted downward for ldg (unless there is a high approach angle. At that point the gear will actually adjust to help compensate for a steep ladg angle) and the rear wheels are tilted up during retraction.
That's what I said. Just said it a little differently
USAFHummer From United States of America, joined May 2000, 10685 posts, RR: 53 Reply 6, posted (11 years 1 month 1 week 4 days 20 hours ago) and read 4211 times:
Just to check also, at takeoff then on aircrafts qith 4-6 wheel bogies, the front wheels will lift off first before the aft wheels? The aircraft won't pivot on the gear so that all 4 wheels get off at the same time?
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