In a post on 1st December 2004 I asked three questions:
(a) how far behind the outer bogies are the inner bogies on a 747-244?
Answer is 10 feet 1 inch.
(b) how high is the berm?
Answer estimated to be 11 feet 6 inches (3.49 meters).
(c) and hence what must that minimum nose-up angle have been for the outer bogies to have cleared the berm?
Answer is that no angle allows this.
TyroPicard 2nd December 2004 18:37
Even if you point a 747 vertically upwards the wing gear is nowhere near 4 metres above the body gear. From the side, on the ground, each pair of bogies looks like this: OOOO no overlap but not much of a fore/aft gap.
You are absolutely right. The front gear is 3.07 meters from the rear gear. The spacing between the wheels on a bogie is about 12 inches, and between bogies as seen from the side is about 17 inches.
broadreach 2nd December 2004 21:46
Perhaps you're right, Picky. But, just perhaps, there's a little window of AOA where the outboard gear is dangling but still a foot or so above the inboard gear which itself, along with the tail, is only a foot or so off.
..
I afraid that the numbers do not seem to indicate that an AOA window could be possible.
TyroPicard 2nd December 2004 21:43
Why not make the theory fit the evidence? The ruts were not made by a 747, but by something else. The berm is covered with traces of similar ruts!!!!!
broad reach December 2004 12:49
. I am going to stick my neck out a bit further and make a guess as to what happens when the centre gear of a fully loaded 747 suddenly encounters a steep gradient which I'm estimating at 4-5m high and very solid. The gear assembly fully compresses and then punches up into the aircraft up just aft of centre, breaking its back.
broadreach 3rd December 2004 18:18
.......... The only other thought that occurs is that the outboard gear is designed to compress more easily; it's the first to touch the ground on landing and the last to leave the runway. Could it be that the outboard gear actually did ride up the berm but, more easily compressed, without leaving marks discernible in that low-resolution photo? ........
Maybe the change in the theory should be that either the outer bogies ran up the slope without leaving a detectable track or that they punched up through the wing but the rear ones did not collapse (the grass between the tracks seems to be undisturbed). The outer legs are twice as long as the inner ones, and supported by the wing structure which may be less robust than the fuselage structure.
I estimate that the front wheel of the front bogies at their dangle angle would at near the level of the top of the berm if the rear bogies and the tail were in contact with the ground.
I see shadows of the antenna masts on the berm, but no similar ruts.
The answers given at the start of this post came via page 188 of a pdf document on the
www.boeing.com site, 747 Airplane Characteristics, Airport Planning, May 1984.
Page 188 shows a drawing with a front/rear bogie spacing for 747-200 aircraft of 10 feet 1 inch.
From the same diagram the spacing between the outer wheels of the rear bogies calculates to be 16 feet 3 inches.
The photo of the tracks on the berm show this distance (always assuming that these tracks were made by these bogies) is about equal to the slope height of the berm, i.e. the outer tracks and the top and bottom edges of the berm form a square. If the slope angle is 45 degrees, then the vertical height of the berm is 11 feet 6 inches.
By the way, the wheel spacings which I earlier estimated from photos and posted on Dec. 1st as being in the ratio of 1:3.3:3.5:3.3 are actually (from the Boeing document) 44:141:151:141 inches, a ratio of 1:3.20:3.43:3.20. Near enough.
Cheers,
