Thursday, September 5, 2019

Douglas XB-42/43 Main Landing Gear



Sometimes the question is so interesting that I can't stop myself from trying to answer it. In this case it was the configuration and operation of the Douglas XB-42/43 main landing gear. For background on the program, see https://oldmachinepress.com/2017/08/05/douglas-xb-42-mixmaster-attack-bomber/

The interesting question was how the fuselage-mounted landing gear went from being extended with the wheel outboard of the strut (see picture above) to retracted with the wheel inboard of the strut, which was covered by a bulge along the underside of the wing when retracted. My guess is that the retracted arrangement was desired to minimize the internal space required for a wheel well. Note that this picture is of the propeller-driven XB-42, which had a slightly different gear door arrangement than the jet-propelled XB-43's.

I mocked up the strut and wheel using a rotating-head toothbrush, a paper clip, and a toothpick for the angle of rotation.
The answer was that it could be done with a single axis of rotation, angled at about 45 degrees to the strut (the axis of rotation might also be angled a bit laterally but determining that exactly would have been a even bigger time-waster).

The landing gear door arrangement was about as convoluted as I have ever seen, even after it was probably simplified for the B-43.
When retracted, the wheel is covered by three separate doors, the middle one being hinged to the upper one rather than the fuselage. The bigger door that covers the strut is hinged so it drops well down to be out of the way when the gear is retracting. Then there is a small door under the wing that appears to allow the forward side of the upper end of the strut to swing aft and a larger one forward that covers the drag link/retraction actuator after gear retraction.

Ian Shillingford created a 3D video model of the retraction:


One thing he noticed was the vertical fork on the strut: "it is now
obvious that that fork attaches to the rear wing spar when the
undercarriage is extended to transfer the weight away from the strut
hinge and onto the spar".


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2 comments:

  1. Pat DonahueSeptember 5, 2019 at 3:40 PM

    I think LeRoy Grumman would have liked your methodology as to figuring out how all this worked! Great post.

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  2. AnonymousOctober 9, 2019 at 6:42 AM

    But it must have worked pretty well, because this is pretty much the same main gear Douglas used on the A-3 Skywarrior and look how long that thing flew off carriers with minimum fuss and bother. Douglas engineers apparently learned their lesson, however, and reduced the number of main gear doors on the Whale from half a dozen to just one per side.

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