The Steering Sled: Runners That Bend Sideways and Spring Back

"My invention consists of an improved sled embodying certain novel features of construction, the details of which are hereinafter fully described, and wherein the steering is accomplished by the lateral bending of the runners." "B B are the runners of my improved sled, constructed of any desired elastic material and made in such a form as to be capable of being bent sidewise, and preferably capable also of instantly regaining their normal position when the bending pressure is removed. I prefer to construct the runners each in one piece of steel rolled in the shape shown in the drawings, preferably T-shaped in cross-section." "The peculiar form of runner herein shown is particularly adapted for carrying out the principle of steering by bending the runners laterally, since from their shape they are exceedingly stiff vertically, but may be readily bent horizontally to accomplish the desired purpose." "When, however, the pressure on the foot or handle bar R is removed, the runners will immediately spring back into their straight normal position".

Clamp an aluminium flat bar in a vise so 30 cm sticks out, standing on its edge. Hang a weight from the tip and measure how far it drops with a steel rule. Turn the bar to lie flat and repeat with the same weight and length. Work out the ratio of the two drops and compare it with the ratio of the two second moments, (width/thickness) squared. That ratio is why Allen's T runner carries a rider without sagging yet bends sideways under a foot. On a real sled, check the runners spring back straight after a turn, and steer only on slopes with a clear run-out.

**Samuel L. Allen** of Cinnaminson, New Jersey, filed US 408,681 on 14 February 1889; it is dated 13 August 1889. Its first claim is simply "a sled having laterally-bending runners". **Honest limits.** The patent gives no runner dimensions. The T-section sizes, runner length and forces in the notebook are examples.