SheikhDjibouti wrote:patrickjp93 wrote:Not. Good. Enough.scbriml wrote:That gear doesn't raise the height of the 737-10 by a single mm. It only helps at rotation. Next idea?
It DOES raise the MAX 10 off the ground an additional 4 inches during rotation to avoid tail strike.
It can be pilot controlled and have a failsafe activation in the case where the flight control computer can no longer communicate with the gear.Revelation wrote:Rev; I first got a handle on this several months ago, but your description of the system takes it further, and leaves me with some questions....so it allows for a longer tail, but not a bigger engine. The extension at rotation happens because gravity pulls the gear down once the aircraft weight is removed which in turn fills a cylinder with air which allows the gear be supported once it is elongated, it is not a powered lift mechanism.
(Hopefully answering them will assist Patrick too.)
What happens to this "air suspension" following take-off (when there is even less weight on the undercarriage)? I'm guessing that whilst still on the runway, as ground speed increases, the wings generate lift and take some of the load, allowing the gear to extend naturally via it's own spring mechanism. But it surely needs to be "locked" at that height, else at rotation when the weight firstly comes off the nosewheel, there will be a momentary transfer to the main u/c causing it to collapse again. I'm a bit fuzzy on this part, so pretend you are explaining it to a complete idiot.
Apart from that, my understanding is....
The gear extension at rotation is purely to (help) avoid a tail strike.
It can only happen at rotation because at all other times the gear must NOT raise the height of any 737, otherwise it would invalidate the (grandfathered) overwing emergency exits.
Finally, it must exhibit a failsafe default whereby when all other systems fail (electric, hydraulic, whatever) the gear allows the aircraft to sit low enough that pax can use the overwing emergency exits. This is just about do-able for the MAX10.
But if you are relying on this extending undercarriage to re-position the LEAP engines underneath the wing, it simply cannot be there for you, and you will find that even whilst taxying towards the runway, anything more than a crisp packet on the pavement, will bring the MAX to a halt.
(At this point I have an absurd mental image of a re-engined 737 MAXv2 stranded somewhere on a taxiway, balanced on a combination of it's nosewheel and the undersides of the two engine nacelles, whilst the main undercarriage itself is "airborne". Kinda like a wheels up landing, but in a more gentle way)
Summary; designing an extending undercarriage that is both totally failsafe, and yet also fits within the existing wheel wells is only part of the answer. You need to factor in new emergency exits, with new doors that are easier to open than the existing 1967 design. And suddenly grandfathering becomes impossible. Add several more $$$billion to the cost.
Have I missed anything?
And basically everything you just said proves to me the regulations are too rigid for their own good. It's a perfectly safe, valid solution to the problem, usually a mark of excellent engineering. And no, no new emergency exits.