Dear friends and followers, welcome back to my channel and to a video I have been really looking forward to edit for you guys.
Why are some landing gears tilted and others are not
And what have high heels got to do with tilted landing gears?
By the way, these belong to "Dutch Pilot Girl",
she forgot them after great night out the last time she was here. (smirk)
Gear down, three green and let's get started!
So let's look at the different types of landing gears.
Now the most common one out there is the single axle landing gear
with one tire fitted on each side, mounted on a large strut,
mostly used on passenger jets such as the A320 or the Boeing 737.
But with increasing weight you need more surface
so more tires to evenly distribute the weight of the aircraft.
So, if we look at the main landing gear of a Boeing 757 you have the main landing gear strut
which is by the way filled with nitrogen acting as a spring force and hydraulic fluids for dampening.
Then you have the truck or the boogie and four tires in tandem pairs
But more importantly for today's topic you see the little hydraulic actuator right here,
the so-called truck positioning actuator, or a.k.a the gear tilt actuator.
Now this little actuator is attached aft of the main gear strut and pushes their rear wheels downwards
Forcing the forward wheels to move upwards as the truck is actually mounted on the main strut
So as the plane comes in for landing, the rear wheels touch down first
the actuator holds up against a pushing force otherwise the rear tires could bounce up,
slamming the forward tires into the ground.
Now once the weight of the plane presses the tires onto the ground,
a pressure relief valve opens up and the actuator collapses, letting both tire axles touch down
Now this all happens obviously in split of a second,
but once the little actuator is fully compressed so weight on wheels,
it triggers the air/ground sensing unit from air (or flight) to ground,
even before the nosewheel has touched down automatically extending the speed brakes
or the ground spoilers on Airbus models
and engaging the auto brake system, allowing the thrust reverser deployment,
and depressurising the aircraft and many many more other things
but the Air/Ground sensing unit activation can differ from plane to plane.
Now, you might have the impression it's pretty obvious why the engineers have built it that way
as the plane is landing in that direction,
and the landing gear is comparable to your foot. So if you walk (not run)
your heels touch down first
Then your body weight presses downwards and then you roll out with your toes, right?
Unless you do a moonwalk, but that's a whole another story (chuckles)
Well, not really - because if you look at the landing gear of a Boeing 767 or a new Airbus model/s like the A350
The heel to toe example is meaningless as their main landing gear is tilted in the opposite direction
It's the same kind of actuator. It's just now mounted at the front of the strut pushing the forward wheels
Downwards now to make you completely rethink your whole landing gear tilt knowledge
Look at the landing gear of a Boeing 747 now the outer
Landing gear or the wing gear as it's mounted under the wings are
Tilted to the max upon touchdown and the body gear which is mounted under the fuselage isn't tilted at all
So how can it be that some of the landing gears are tilted forward?
Some of them are off and some of them are not tilted at all. The answer is so simple. You think I am joking?
the number one reason for the gear being tilted is...
wheel bay space.
The landing gear needs to be tilted to fit into the wheel bay.
Now the best example to show this is with the Boeing 747:
So after liftoff the wing gear needs to be tilted by the gear till actuator so it can pass
the body gear and be retracted into its housing, the wheel bay.
And if you look closely you can see that the body gear can retract upwards and slightly
rearward to make more space for the wing gear
So the question arises - "Why not just place the gear further down the wing,
and have it retract into the wing instead of the belly?"
The answer again is space
So the wings hold tons of fuel and so does the belly;
so the less the gear uses up space, the bigger the fuel tanks can be fitted, which increases the range,
and is again a key selling point for airplane manufacturers.
Now we've primarily spoken about the tilted gear during landing
But at the beginning I mentioned the high heels and that obviously relates to planes
There is a plane which relies on a tilted gear for takeoff and you've all seen her before: the Boeing 777
But here's a difference between the 200 and the 300. If we take a closer look at both landing gears upon liftoff
You might notice a difference the wheels on the 200 lift off simultaneously
And the ones on the 300 lift off pair by pair
why is that so the 777 300 has this big diagonal thing fitted at the front of the landing gear the
So-called "semi levered gear strut" , which acts as same as a truck positioner
So while airborne the semi leaveit gear does the same job as a truck positioner,
tilting the landing gear truck beam in the correct angle for landing and for storage,
but now the only difference is when on ground the semi levered gear locks into position.
This fixes the forward section of the truck beam and
creates this walking on heels effect adding a bit of height to the aircraft on rotation over the gear and
reducing the tail strike risk. And the tail strike risk is significantly
higher on the 300 as she is 10 metres longer than the 200.
I've spoken to 777 pilots and they said that the high heels add a little kick during rotation and gives it more
controllability with the last axle still on ground.
So the next time you see a 777 300 at liftoff check out if you can see her High heels
and if you still don't believe me - "It's just because of the wheelbase space"
check out the landing gear of a c5 galaxy
It extends and then rotates into the correct position as it otherwise wouldn't fit into its belly
It's not even a tilt, it's an extension, lock and turn.
Hats off to the pilots and mechanics trusting and maintaining this landing gear.
That's it for today
Sorry for not going into the non normal such as the gear tilt checklist
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See you next week all the best your captain Joe