The video gets it mostly correct.
The flattened nacelle with the flat-bottomed inlet lip was done on the 737-300/400/500 (AKA "Classic" now). The nose gear was actually lengthened but the main gear was unchanged save for beefing up (the Classics being heavier than the original -100/-200 family and most versions longer).
With the Next Generation 737s (-600, -700, -700C, -800, -900/-900ER, P-8) the nacelle was redone so that the inlet lip is round though the nacelle itself is was still flattened on the bottom for the same reasons - to make room for the IDG (integrated drive generator - the electrical generator), and the EDP (the engine driven hydraulic pump) while maintaining ground clearance. The fuel pumps are not on the engines as the video stated - they are in the wings. The gear lengths were not changed going from Classic to Next Generation but the main gear was actually all new as the wing itself was new and larger.
On the MAX the nose gear was lengthened again (which made repackaging a bunch of stuff that is in the lower nose of the airplane in order to make room "fun") and the even larger diameter engine was pushed even more forward and up to allow enough ground clearance and they were able to get the engine-driven accessories on in such a way that the nacelle did go back to being nice and round as was shown in the inset picture of one of the flight test MAX airplanes.
There's a design criteria typically used for wing engine nacelles where the bottom of the nacelle should be (from memory) at least one nacelle diameter above the runway, to minimize ingesting FOD. For the 737 with the higher bypass ratio engines, this would have involved lengthening the landing gear, so they went with the bent bottom cowl. There was a lot of CFD involved to make sure flow quality requirements into the engine were met.
There's the other requirement that with two flat tires on one side you don't drag the engine nacelle, but the ingesting FOD requirement was the driver. Even with bent bottom cowl, the bottom of the engine proper is still closer to the runway.
Charles E. "Chuck" Rogers
Methinks you're a Boeing guy. The -700C was my first program as a shiny new Boeing engineer back in '97. Later was a Lead Engineer on Section 46 of -900ER and Lead on Section 44 for Max 8 and 9. Never did work 737 propulsion, but dabbled in Struts for 777 and 747 briefly.
As what you Boeing guys call a "meat servo" i can say the -10 is going to be VERY interesting.
With the 900 now tail clearance is a big issue, the trailing link gear of the -10 will be interesting.
I still haven't seen how they will retract, the gearwell does not have much room as it is now.
Until the split scimitar winglets were put on we had to worry about dragging an engine nacelle
in certain wind conditions, now we worry about the lower winglet. With the trailing link main gear
the engine out characteristics in a cross wind should be interesting.
I'm guessing the -10 won't have anymore thrust because the vertical stab is the same size as the
other MAX's?
Yup the -10 is going to be interesting to fly...
As what you Boeing guys call a "meat servo" i can say the -10 is going to be VERY interesting.
Ha! Just a loose nut behind the yoke! (I'm a mechanic):grin:
"meat servo"
Even flattened, those don't even have a 1/2 diameter clearance from the ground. Besides a generic caliber type distance criteria, is there any CFD to show FOD suction? For example in fuselage and wing structures we have criteria loads for tool drops that are a weight x height energy...is there something analogous for suction forces?
Yes, I figured it was for ground clearance, but I wondered why design the aircraft to be so low to the ground that that was necessary while others weren't doing that. The video made the reason clear.Because they all landed hard and hit the engine cowling on the runway. They just left the dent, as it didn't interfere with continued operation.
Just kidding. It is for ground clearance. With two blown tires and a deflated strut, they don't want the engine hitting the ground
Yep, and that was the answer to my wondering about why the plane was designed to be such a low-rider that the flat portion was necessary on the intakes. Also, I should have realised, but didn't, that the low model number (737) might mean that the design was so old that it was designed for turbojet engines and any upgrade to the much larger OD turbofan engines would present ground clearance problems.As the fellow in the video noted, two objectives of the initial 737 design were ease of loading and ease of servicing. Another is the ability to use over wing escape hatches for emergency egress without having to have off-wing escape slides. This saves space and weight.
I don't know, but it is plausible. At the time there was a Cray-1 at the Bellevue data center as well as some big IBM and CDC hardware, so there were the best resources on the market at the time (early 1980s) available for CFD.
It has certainly been used to help refine the nacelle shapes on subsequent generations - the Next Gens and now the MAX.
Ah....that certainly is plausible. I was absorbed in 757 and then B-2 systems work during the time the 737-300 was being done so was unaware of major aero changes like that. I only got involved on 737 at the beginning of the Next Generation after I made it back to Renton following a stint on 777.
I will revise my mental "history of the 737 configuration". Thanks.
Added later: I remember seeing pictures of the -300 (in model form) with flutter booms on the wingtips but I figured that was due to the rather major effect of the larger, heavier and differently attached engines. I didn’t realize that the wing had been relofted as well. But they figured out how to do without that form of flutter ballast before the airplanes actually flew.
This makes me wish I still had access to the configuration document for the -300 as I’d want to read about this wing change. But of course that’s now not possible since I don’t work there anymore.....
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