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D297-26 · Miscellaneous
c.1960
Object Overview
This Barometric Parachute Release is a Soviet/Russian mechanical parachute safety device of approximately 1960, made by the Second Moscow Instrument-Making Plant. It can fire either on elapsed time or at a barometric altitude, and it can actuate not only the opening of the parachute pack but also other units of parachute rescue systems and of certain ejection installations. The official designation of this group of instruments — (PPK-U, , "parachute semi-automatic device, combined, unified") — corresponds to what is known in the West as an automatic activation device (AAD). The instrument considered here, however, is the predecessor of that group, while sharing an identical design layout. It is designated (KAP, , "combined parachute automatic device") — an aneroid semi-automatic release for opening the parachute at altitudes from 500 to 4000 m. It was produced from 1950 to 1970 and was superseded in 1971 by the ППК-У.
NB54188
self-elastic capsule movement
aluminium, brass, copper bronze, glass, plastic, steel
The purpose of the instrument is to duplicate the actions of the man: it fires when the parachutist is for any reason unable to open the parachute himself by means of the manual ripcord assembly. In that case the barometric parachute actuator opens the twin-cone lock or the pack after a preset interval, or at a preset altitude. It was therefore used not only on main airborne systems, but also on reserve, special-purpose, sporting, rescue and cargo systems. On different parachutes the underlying principle is one and the same; only the points of attachment differ.
The instrument consists of a housing containing the clockwork and barometric mechanism, an extractor unit, and a flexible pin. To bring the instrument into its working condition it is cocked, the flexible pin having first been inserted into the shutter. The steel cable is drawn out with force until the springs are compressed and caught by the sear of the spring mechanism.
The instrument combines two independent blocks: a clockwork (lever-escapement) time-delay mechanism and an aneroid (barometric) device. The aneroid blocks the going of the clockwork until the set altitude is reached, whereupon the clockwork completes its remaining 0.8–1.2 s and the power springs, expanding (with a force of not less than 28 kgf), draw out the cable that opens the pack.
External arrangement
Externally the barometric parachute release is a compact metal housing finished in hammered enamel, with two round windows, an extractor unit and a flexible hose protecting the cable.
The housing and the cover are of aluminium alloy; the housing is a metal box closed at the top by a cover on six screws with a gasket. Two windows are cut in the cover: the larger for observing the hand of the clockwork (the "СЕКУНДЫ" — SECONDS — scale), the smaller for checking the aneroid pin and the working of the blocking lever. On the side wall there is a separate round window with a Plexiglas pane and an index mark, showing the altitude scale, calibrated in metres over the range 500–4000 m. The altitude scale is set through an aperture in the rear wall of the housing by means of a special key-screwdriver from the accessory set (a key of square section).
The housing accommodates the aneroid-and-clockwork mechanism and the power part of the extractor unit and protects them against contamination and moisture. The instrument is resistant to hoar frost and dew. The cover is secured by screws, one of which is sealed; the bottom of the housing carries the seatings for the mechanism and an aperture for the altitude setting screw. Screwed separately into the housing is the shutter, which closes the aperture of the housing automatically once the flexible pin has been withdrawn.
Internal arrangement
The internal arrangement is conveniently divided into several functional parts: the clockwork, the extractor unit, the barometric block and the blocking system.
Clockwork (lever) mechanism. The mechanism is built on the pattern of a clock with a constrained lever escapement, that is, one in which the pallet fork remains in contact with the escape wheel during almost the whole of the oscillation. Its parts are mounted between two plates. It is driven by a toothed sector, which through a train of wheels and pinions turns the escape wheel; at each oscillation of the balance the escape wheel advances by one tooth, giving a uniform count. The period of oscillation (the rate) is not adjustable, being determined by selection of the moment of inertia of the balance. It is this mechanism that counts out the delay set on the dial (2–5 s). A most important feature: it has no mainspring of its own, but is driven by the energy of the power springs of the extractor mechanism, transmitted through the piston roller, the pawl and the sector. The "clock" here is thus not self-contained — it restrains and meters the energy of the power part.
Extractor unit with power springs. Within the guide tube are two power springs, one inside the other, compressed in the cocked state with a force of not less than 28 kgf. The springs bear against a piston to which the cable is attached. The piston is held by a pawl connected to the clockwork through a roller. When the clockwork has run off the set time (the hand reaching zero), the roller comes out of engagement with the pawl, and the piston, under the pressure of the springs, travels along the tube, drawing out the cable with its connecting fitting — which in turn withdraws the pins from the cones of the pack (or opens the twin-cone lock).
The barometric (aneroid) block consists of a setting pinion, a setting wheel, a threaded sleeve, and the aneroid capsule itself with its pin and altitude scale. The aneroid capsule is a corrugated metal sensing element which changes its volume as the atmospheric pressure changes. Turning the setting screw with the key does not merely rotate the scale: acting through the pinion and the setting wheel, it simultaneously displaces the aneroid capsule along its thread, bringing the required graduation to the index mark and altering the position of the pin relative to the upper plate. The scale is graduated from 500 m to 4000 m and calibrated against the standard atmosphere. The aneroid works on the barometric method of altitude measurement — the relation between atmospheric pressure and the elastic deformation of the aneroid capsule's diaphragm. As altitude is gained the pressure falls and the aneroid capsule expands; as altitude is lost the pressure rises and the capsule contracts.
The blocking system is the assembly linking the aneroid to the clockwork. It comprises the driving lever, the blocking lever, the vertical driver and the guide plate. So long as the instrument is working on time alone and the altitude is certainly above that set, the blocking lever passes freely over the initial part of its travel; but in prolonged stabilised descent, in the "altitude" mode, it comes up against the projecting aneroid pin and arrests the further running of the clockwork until the pressure corresponds to the altitude set. The pin then descends, the lever is released, and the instrument completes its last 0.8–1.2 s before firing.
The mechanics of the interaction:
The altitude scale is calibrated against the standard atmosphere with an excess of 100 m — this compensating for the height lost between the firing of the extractor mechanism and the filling of the canopy. The graduation "500 m", accordingly, corresponds to an actual opening altitude of about 600 m. The accuracy in altitude is governed by tables of permissible deviations.
The logic of the two modes
With the flexible pin inserted, the instrument cannot fire from shaking, from blows or from vibration; nor does it hinder manual opening of the parachute.
Setting and use
The instrument has no in-flight starting button: it is not switched on by a button, but is prepared beforehand as a matter of routine, and in the jump it is started by the drawing out of the flexible pin. The normal sequence is: insert the flexible pin, cock the instrument, compressing the power springs, set the required values of time and altitude, and then safety-tie the pin. The instructional descriptions state plainly that, to prepare the instrument for action, the pin must be inserted into the shutter, the stirrup hooked over the loop of the extractor unit, and the springs compressed by drawing the cable out as far as it will go; the hand is then set to the required time graduation and the altitude scale to the required altitude.
Before the jump the parachutist carries out:
An important rule of use: irrespective of the altitude of flight, withdrawing the flexible pin from the instrument while in the aircraft is categorically forbidden. In the standard arrangements the pin is drawn out after separation — by the activation cord, by a tape, by the drogue link, or by another standard device of the particular parachute system.
Installation on the parachute. The instrument is secured in a special pocket of the pack by tie-tapes; the hose is firmly tied to the pack; the loop of the cable is joined through a shackle either to the twin-cone lock or to the pins of the pack. The lanyard of the flexible pin is attached to the pin by a lark's-head loop, and by its other end to the static line of the parachute or to a snap hook.
Starting in the jump. The snap hook of the stabilising system is attached to the static-line cable in the aircraft. On separation of the parachutist, the link of the stabilising system is drawn out to its full length and withdraws the flexible pin from the instrument — the clockwork begins its count. Stabilised descent proceeds on the drogue, the pack of the main canopy remaining closed. Once the set time has been run off (and, if the altitude was great, after release by the aneroid at the set altitude), the instrument draws out the cable and opens the twin-cone lock, and the drogue draws out the deployment bag with the main canopy. Withdrawing the pin while in the aircraft is categorically forbidden, irrespective of the altitude of flight.
Kinematics of the instrument
The last photo (N 14) shows the kinematic diagram of this automatic activation device with a detailed key, against which the following description of the kinematics may be followed.
On withdrawal of the flexible pin 12, which locks the balance 11, the clockwork — driven by the springs 27 — begins to work. The piston 28 with its roller 23 presses on the pawl 29, which is pivotally connected to the sector 18. The sector 18, turning on its axis, sets in motion the gear train and the lever escapement.
As the clockwork runs, the arbor of the pinion 15 turns clockwise (the direction of rotation of the wheels of the train and of the levers is shown by solid arrows); the ratchet wheel 8, rigidly connected to the arbor of the pinion 15, engages one of its teeth against a tooth of the click 7 and carries with it the intermediate wheel 6, which is connected to the pinion 14 of the escape wheel 9.
As the escape wheel 9 turns, each of its teeth delivers impulses in turn to the entry and exit pallets of the fork 10, giving a definite period of oscillation of the balance 11. At each oscillation of the balance the escape wheel advances by one tooth, its rotation proceeding, as it were, in steps made at equal intervals of time. Such rotation is conventionally regarded as uniform.
As the sector turns, the extended arbor of the pawl presses on the adjusting screw of the driving lever and turns the lever about its own axis. The lever , by means of the vertical driver , turns the blocking lever . The opposite end of the lever , on reaching the stop of the aneroid , arrests the whole clockwork if the altitude of flight is greater than the altitude set on the scale, since the face of the stop then lies above the upper surface of the plate . On reaching the set altitude, the face of the stop descends as the aneroid contracts and, at the moment of coinciding with the upper surface of the plate , releases the blocking lever , whereupon the clockwork completes its remaining 0.8–1.2 s.
The altitude scale is linked to the aneroid , and the setting of its graduations against the index mark is effected by the screw , which, turning the setting pinion and setting wheel , produces the reciprocating displacement of the sleeve with the aneroid . The greater the altitude set on the scale, the lower the aneroid , and with it the stop , descends relative to the upper plate . In jumps from an altitude below that set on the scale, the blocking lever passes freely over the aneroid stop and the clockwork runs off the time set on the dial . As soon as the clockwork has run off the set time (the hand reaching zero on the scale), the roller comes out of engagement with the pawl and the piston with the cable , under the pressure of the springs , travels along the tube . As a result, the cable with its connecting fitting (or other attachment) withdraws the pins of the extractor cable from the cones of the parachute pack, or actuates some other device.
The balance 11, having stopped, locks with one of the pallets of the fork 10 the escape wheel 9 and, through the pinion 14, the intermediate wheel 6 connected with it. The springs 21 and 22 return the remainder of the train and the levers to their initial positions. The ratchet wheel 8 thereby turns anticlockwise, its teeth slipping over the teeth of the clicks 7 (the return travel of the train and levers is shown by broken arrows).
To make the instrument ready for action once more, the balance 11 must be locked by the flexible pin 12 and the instrument cocked. The roller 23 of the piston 28, pressing on the pawl 29, turns it about its axis and allows the piston to pass freely. As soon as the roller of the piston has travelled beyond the edge of the pawl, the latter returns to its initial position under the action of the spring 22 and holds the springs 27 in the compressed state.
The history of automatic safety devices
Prehistory. The impulse to the creation of a Soviet device was given by the deaths of the parachutists Lyubov Berlin and Tamara Ivanova in delayed jumps; in 1936 an All-Union competition for an automatic parachute-opening device was announced. More than 300 entries were submitted.
The Doronin brothers. The students — later engineers — Nikolai (1903–1980), Vladimir and Anatoly Doronin created the ППД-1 (PPD-1, parashyutny poluavtomat Doroninykh, "Doronins' parachute semi-automatic device", first model) with a clockwork based on that of an alarm clock, introduced by the end of the 1930s; the results were published in Vestnik Vozdushnogo Flota (Herald of the Air Fleet) in 1939. The demonstration before the state commission has become legendary: the device was thrown against a wall, whirled about on a lanyard and used to drive a nail — and fired exactly on time. Anatoly Doronin was killed in 1957 on his 1442nd jump, while testing a new parachute.
Savichev's aneroid. In 1940 the engineer L. Savichev created the aneroid device ПАС-1 (PAS-1, pribor aneroidny Savicheva, "Savichev aneroid instrument") for opening at a set altitude.
The combination. Uniting the Doronins' clockwork with the aneroid gave, in 1948, the КАП (the prototype of the ППК-У), and then the КАП-3 / КАП-3П (the suffix П denoting the dust-protected variant): a combined aneroid semi-automatic device for altitudes of 500–4000 m, in series production from 1950 to 1970. In parallel there was produced the time-only device АД-3УД (used, among other applications, on ejection seats).
ППК-У. In 1971, for the sake of unification, a single five-second combined instrument, the ППК-У (altitudes 0.3–8 km), was brought out, replacing the КАП-3П, ППК-2П and ППК-4грП (the last of these a cargo variant, гр for грузовой). The maker is the Second Moscow Instrument-Making Plant (2-й МПЗ). All the instruments of the family (ППД-1 → КАП-3 → ППК-У → АД-3УД) share a common design layout — clockwork plus power extractor unit, and, in the aneroid instruments, an aneroid as well — differing in the graduation of their scales. For the creation of the parachute instruments the Doronin brothers were awarded the Stalin Prize (the decree published in Pravda on 27 June 1946); they were twice laureates. In all, the brothers created more than thirty varieties of parachute and airborne instrument; the design of the twin-cone lock is likewise theirs.
Conclusion
The barometric parachute release is not simply an alarm clock strapped to a parachute, but a mechanical barometric-and-horological executive automaton highly characteristic of the Soviet engineering school: simple in idea, yet distinctly cunning in its kinematics, and existing in a great number of variants of one and the same basic mechanism. It is for this reason that it has lasted so long — on military round systems, on reserves, on cargo platforms, and even alongside later electronic instruments. These devices are still produced by the 2nd MPZ and are fitted as standard to the parachutes of the Russian Airborne Troops (ВДВ), as well as being used in the flying clubs of DOSAAF and in the air-mobile forces of the CIS countries.