Hot Gas Initiator (HGI) | PacSci EMC
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Hot Gas Initiator (HGI).

PacSci EMC / Products / Hot Gas Initiator (HGI)


A Hot Gas Iinitiator provides a method of converting one signal transmission method into another. Typical conversion types as part of an Emergency Escape System include:

Hot gas (i.e. from an Ejection Seat System) to a detonating signal (i.e.: to an attached SMDC,

  • Detonating signal to hot gas
  • Hot gas to a deflagrating signal (i.e. HGI to attached RDCTL)

Some of the different types of HGIs designed and manufactured by PacSci EMC are shown below.





The advantage of a hot gas initiator is the ability to mix different signal types in one system without severe design or reliability penalties.  The HGI function either at the beginning of the canopy removal sequence or after the canopy system has functioned and the seat is ready to ejection.  In the case of SMDC to Gas this is usually the later situation as the canopy removal is associated with a jettison system rather than CFS / TRS.  HGIs are manufactured to contain all the by-products of combustion regardless of type.  Design can be both inert and explosive loaded.  They can be designed with single or dual input.

Function of these initiators is described below with legacy explosive loaded technology then the inert device.

This initiator receives Ballistic Hot Gas from an ejection seat applying it at the inlet end of the housing. A shear pin securing the piston type-firing pin is severed, releasing the firing pin and impacts a percussion primer.  The output of the percussion primers is funneled to a transfer charge containing a load of primary and secondary explosives.  The percussion primer output ignites the primary explosive material.  The high energy output of the primary initiates secondary explosive material providing a detonating output.  The output of this transfer charge initiates the attached ETL allowing it to transfer either a detonating or deflagrating signal along its length.

This initiator receives a detonation signal from an ETL HE end tip.  The HE output drives an annular firing pin into two percussion primers.  The output from the primers initiates an ignition charge.  This charge in turn ignites a propellant gas generating explosive material.  The gas pressure is routed through a braided hose to the ejection seat gas system so the remaining ejection events can occur.

This initiator is inert, no internal explosives. The initiator receives hot gas pressure from the ejection seat. Gas pressure is applied at the inlet end of the housing. A shear pin securing the piston type-firing pin is severed, releasing the firing pin and impacts a percussion primer. The percussion primer is part of the end tip fitting of the RDCTL. The RDCTL is ignited and the deflagrating explosive signal transmitted to the remainder of the system. This inert component is a derivative of an explosive component used on the TA-7C. The only difference in the units is that the explosive material have been taken out of the initiator and placed on to the RDCTL end tip.

Operating Temperature
–65°F to +200°F

Leak Rate
1×10-5 cc / sec. Air at 1.0 + 1 Atmosphere

5-2,000 Hz sinusoidal vibrations at 10 g’s maximum amplitude per MIL-STD-810, Method 514.1, Procedure I

10 shocks of 15 g’s maximum acceleration in 8 milliseconds maximum, exceeding 8 g’s for 11 milliseconds maximum, per MIL-D-23615

Drop 6 feet onto a steel plate at least 2 inches thick, over concrete per MIL-D-21625; 40 feet onto a steel plate over reinforced concrete per MIL-D-21625

Temperature/Humidity Cycling in two and three week segments from –80oF to +160oF at 90% RH per MIL-D-21625

High Temperature
+200°F +/- 5°F for 1 hour per MIL-D-21625

Low Temperature
-65°F +/- 5°F for 1 hour per MIL-D-21625

.3 +/- .2 gm./ft. 3 dust concentration, with a maximum air velocity of 1,750 +/- 250 fpm and +145°F maximum per MIL-STD-810, Method 510

Salt Fog
48 hours at +95°F +/- 2.5°F per MIL-STD-810,Method 509

-65°F to +100°F +/- 5°F at 90% RH, then returned to -65°F and functioned, per MIL-D-23615

Platform Use & Heritage
F-15, F/A-18, B-1B, Scorpion, Improved CFS w/Inerts

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