This picture shows the dial of the torque dynamometer in the rear cockpit of the Vought VE-7 setup. An electric starter was used to start the engine. The starter which can be seen just in front of the fuselage (the large gear with the chain) was "secured to the entrance cone.... A hollow shaft with a pin meshing with a dog on the propeller shaft is driven by means of a chain from an electric motor. The whole unit is arranged to swing down clear of the air stream during a test." (NACA TR No. 300, p. 438) Initially, the propellers had to be cranked by hand; an engineer precariously perched on a ladder would do the honors.
