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• December 9, 2016 Create Date
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National Advisory Committee for Aeronautics, Technical Notes - Spin Tunnel Investigation to Determine the Effect on Spin Recoveries of Reducing the Opening Shock Load of Spin Recovery Parachutes

An investigation has been conducted in the Langley 20efoot free—
spinning tunnel to determine whether the effectiveness of a spinerecovery
parachute would be influenced by a reduction, through the use of a shock
absorber, of the opening shock load. In addition, the effects on the
parachute opening shock load of varying the fabric porosity of the para—
chute canopy and the towline length were investigated.

The results of the investigation indicated that a given spine
recovery parachute was equally effective with or without a rubber shock
absorber installed in the parachute towline. Increasing the fabric
porosity decreased the parachute opening shock load, whereas increasing
the towline length increased the parachute opening shock load.

Prior to the acceptance of some types of airplanes by the Armed
Services, the contractor is required to demonstrate that the airplane
will exhibit satisfactory spin—recovery characteristics, and the air—
plane is usually equipped with a tail parachute for use as an emergency
spin—recovery device during the spin demonstration flights. When it
has been necessary to use parachutes to recover from spins, or when the
parachute has been opened in level flight to check the operation of the
opening mechanism, towlinexand parachute failures due to the opening
shock load have been reported. ‘In addition, the force on the airplane
structure due to parachute opening is approaching a critical value
because of the high rate of descent in the spin of many present—day
airplanes. Accordingly, an investigation was undertaken to determine
the effectiveness of spin—recovery parachutes when the parachute opening
shock load was diminished by means of a shock absorber. Models of a
contemporary fighter and a torpedo bomber were used in the investigation
made in the Langley 20—foot free—spinning tunnel, and each model was
tested with and without a rubber shock absorber installed in the para—
chute towline. The models were tested with tail parachutes only. In
addition to the spin tests, tests were also conducted to determine the
effects on the opening shock load of varying the fabric porosity of the
canopy and the towline length.