As a former maintainer of that airframe, in its now-retired "G" model, testing that feature required placing the airframe on "greaseplates", which were much like their name. Two large, (~1yd/1m on a side) square steel plates, with a handful - literally - of grease sandwiched between, were placed under each of the four main gear trucks. Nosewheel (actually the two forward trucks) steering was separate from the crab feature, but used the same component on the gear. All four trucks were effectively identical, with some small detail differences, based on the individual locations. Each truck location carried a different safety switch set.
To test the alignment and proper functioning of the steering and crabbing features, the friction of the tires on the runway/taxiway surface had to be reduced. Brakes could not be locked, nor chocks installed. At Loring, this operation was usually only done in our big Arch hanger, where the plane was shielded from wind, and the floor was reeeeally level. Ya don't want the thing to start rolling around...
Watching your airplane taxi in slightly askew, after a flight, was always a bit strange. The flight crew would get roundly called out, if they forgot to straighten out the gear, before engine shutdown. Towing the big bird around, with the gear crabbed, was unsafe, and generally not allowed. To square the gear back up needed either an engine running, or a ground mule, to get enough hydraulic pressure and flow, to do the job. Plus, the plane had to be on the greaseplates...
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