Originally Posted by
washoutt
What a fascinating instruction movie. It shows that necessity is the mother of inventions!
What I do not understand however, is how the shock of the sudden load due to the build up of zero speed to 130 miles on the glider is gradually applied, so that the airframe is not pulled apart by the increase of impulsl. Is it all in the elasticity of the nylon rope?
I remember that when needing to tow a car to the garage in the sixties (when cars still could stall and stop driving), we used a tow rope on the tug car, a pair of old bycycle tires tied to the other end, and then a rope attached to the stalled car tied to the other end of the bycle tyre. The resulting ovalisation of the tyres was the needed elastics to put a gradual speed built-up on the towed car and dampen the shocks of pulling.
So how was this achieved in the case of glider towing? Can any body shed light on this?
Extract from ...
https://ps.ci.lubbock.tx.us/docs/sil...rsn=191cd8c6_2
The use of tow ropes made of nylon fiber developed by the E. I. DuPont Company greatly enhanced glider "snatch pickups." This fiber, when woven into a rope, was elastic. It would stretch 25% to 30% of its length and thus absorb much of the shock as the glider became airbome. The rope would then retum to its original length. Because of this characteristic, the average acceleration for pickup was only 7/10 of one G, which according to AAF Manual No. 5- 17, lasted about 6%2 seconds. This is significant if you consider that pilots catapulted from an aircraft carrier experience 2% G's. The glider would usually become airbome in no more than 200 feet. Twin-engined Douglas C-47 transports were the primary aircraft used to test the Model 80C pickup system. Several were retrofitted with the device for the tests. The M-80C Glider Pick-up Mechanism, as it was officially designated by the AAF, consisted of a controllable, motor-driven, energy absorbing drum containing 10003 feet of flexible 5/8"steel cable, twin pulleys, torque tube, hydraulic cylinder and explosive cable cutter controls. The mechanism was bolted to the floor on the left side of the cabin about six feet from the front bulkhead of the aircraft. The reel was equipped with friction clutch that could be adjusted for different glider weights and speeds. The amount of cable played out was directly proportional to the weight of the glider and the nature of the acceleration of the glider after the pickup. Under most circumstances the cable pay-out was usually less than 600 feet. The maximum designed load of the pick-up unit was 8,000 pounds.
In addition to the normal crew of a pilot, copilot, crew chief and radio operator, the retrieval aircraft required a winch operator. The aircraft crew chief and radio operator assisted the winch operator if necessary. The winch opera- tor's function was to properly set the pickup drum clutch snubbing adjustment, which was based on the glider's weight and the aircraft's proposed speed at the instant of the cable hook/ glider rope loop engagement. The drum manufacturer (General Aviation) provided a chart with recommended snubber settings for various glider weights/aircraft contact speeds, etc. The shock of the initial contact with the nylon rope was the critical moment that placed the greatest stress on the flexible steel cable. At the very instant of "snatch" the winch operator's judgment received its most critical test. A misjudgment could result in a broken cable and possible severe injury to the operator or damage to the aircraft, or both.