GENERAL
1. The primary purpose of door guns on the CH 146 is to provide self-defence during flight and on the ground, for the helicopter, its crew and its passengers. They supply a suppressive fire capability that, along with other protective techniques such as evasive manoeuvres and ASE, allows the helicopter to carry out missions in a hostile tactical situation. Door guns will normally be part of the mission equipment for any operations where there is a risk of the helicopter being fired upon by hostile forces.
DESCRIPTION
2. The C6 LEP installation is composed of three separate assemblies, the Machine gun External Pintle Connection (MEPC), the Light External Pintle Connection (LEPC) and the Light Pintle Head (LPH). An optional intercom foot switch is also available.
3. The normal self-defence configuration for a CH 146 is a C6 mounted on each side of the helicopter. Each installation consists of one General Purpose Machine Gun (GPMG), 7.62 mm, C6, with spade grips and trigger housing, fitted on a LPH, mounted on the LEPC (Figure 4-1). A right hand installation requires the GPMG LH/RH conversion kit (Figure 4-2). The LPH
incorporates an elastic cradle assembly with approximately one centimetre of available travel designed to absorb vibration caused by weapon firing and prevent transmission of this vibration through the mount to the airframe. The assembly is installed on the hard points located at FS 129 and 155 and permits flight with doors closed. The left and right pintle heads and guns are different and not interchangeable.
4. In addition to the vibration absorption mechanism, the LPH is composed of the C6 attachment mount, an articulated fork that allows azimuth and elevation movement, the
ammunition box bracket and catch bag. The LEP gun mount was designed to cover an arc of fire of approximately 130 o and is limited by physical stops. The user can adjust the specific arc of fire with respect to the helicopter during installation of the mount. The total arc of fire, however, cannot be changed. A 60o forward and 70 o aft (measured perpendicular to the helicopter
centreline) arc of fire was determined to provide the best overall compromise and ensure
adequate clearance from compatible mission kits. Elevation coverage is approximately 50 o; +5 o up and -45 o down, measured with respect to the helicopter floor. Total travel is again defined by physical stops.
5. In order to minimize the risk of FOD to the helicopter, a canvas bag is fitted under the LPH to collect empty casings and links. The capacity of the bag is limited to approximately 450 casings and links, the equivalent expenditure of two full belts of ammunition. Shortly after the expenditure of two complete belts, the casings and links will fill the bag to the point where they will interfere with the machine gun’s mechanism, causing a stoppage. Few engagements in a combat situation would allow the firing of even this much, but if a prolonged firing of more than
two belts is required, the bag should be opened. Such a situation implies that damage to the helicopter is more likely from enemy action than from FOD.
6. The characteristics of the machine gun, as well as the handling drills, are described in B- GL-385-004/PT-001 General Purpose Machine Gun, 7.62 mm, C6, and will not be repeated, in detail, in this publication. The handling drills will be carried out as detailed in that publication, the only required deviation for the door gun application being the inversion of left and right where necessary for the right hand feed gun. Also, barrel changes in flight are not advisable, and are normally not even required due to the short engagements and additional cooling by the relative airflow. Barrels are matched to specific machine guns and serialized; they must not be interchanged. In an emergency, such as being downed in hostile territory, the guns may be removed from the mounts and, with the bipod re-installed, used to provide local defensive fire.
Figure 4-1: Right Hand Installation LIMITATIONS
7. The airspeed with the guns secured and the doors closed is 140 KIAS or the calculated VNE With the doors open to operate the guns, the cargo door open VNE applies.
8. The door guns are compatible with the following external mission kits: Thermal Imaging System, Nite Sun, Skis, HF Antenna and Aircraft Survivability Equipment. The C6 LEP
installation is not compatible with the following internal mission kits: auxiliary fuel tank (same side), longitudinal litter kit (same side), lateral litter kit and spotter windows (same side). When the rescue hoist is installed, the right hand machine gun and mount must be removed before the hoist can be operated.
9. While in flight, 100% Rotor RPM is maintained for all normal operations. 10. The C6 GPMG will be operated at low rate of fire (650 rounds per minute) only. AIRCRAFT CONFIGURATION
11. As noted above, the normal defensive configuration consists of GPMGs mounted on both sides of the helicopter. Two guns will provide an adequate defense for the helicopter by
providing nearly all round fire, mutual support, and depth, particularly in formations. Any resort to the use of a single gun must only be made after a complete estimate of the tactical situation and thorough risk assessment that considers the inadequacy of such a configuration. The use of the rescue hoist will not allow for installation of the right hand door gun; missions requiring the use of the hoist in a hostile situation will likely require the addition of a second helicopter for the mission to provide the necessary covering firepower.
12. The right hand door gun will be manned by the Flight Engineer (FE), who will be seated on the right hand transmission seats. While still able to provide clearing calls from that side, he must remain at that station, and will be unable to move through the cabin in order to carry out such functions as “two full” checks, or to assist the pilots in any other cockpit drills.
13. An appropriately trained door gunner, who will be seated on the left hand transmission seats, will man the left hand gun. Although the responsibility to clear the left side remain with the left hand pilot, the left hand gunner is also required to voice appropriate clearing calls for the left side of the helicopter when necessary, but like the FE, must remain at his station, and is normally unavailable for other duties in the cabin.
14. Each door gun requires a locally produced bag for carrying a spare barrel, cleaning/tool kit, and the bipod for the gun. This bag may be carried in the baggage compartment. A locally produced strap, with six snap hooks, is tied to the floor rings and is used to secure the
ammunition boxes.
15. The positioning of the two gunners precludes the normal eight-passenger capability for the CH 146. Retaining the five forward facing seats may allow the stanchion posts to interfere with the gunners’ ability to traverse the gun easily through its allowable arc of fire. Use of the four man, rear facing seat to provide additional capacity should only be considered if the
passengers are not wearing fighting order. To carry more than five soldiers in fighting order, the forward facing seats may be removed and seat belts installed on the floor tie down rings in a suitable, mission specific arrangement.
16. Each door gunner will wear a FE restraint harness, with the tail attached to the
transmission bulkhead lashing rings. Flight gloves are adequate for handling the gun, including barrel changes, but arctic mitts with trigger fingers may be necessary during cold weather operations. Door gunners will also wear flight helmets with visor down to communicate and to protect head, eyes and hearing. Due to the increased sound pressure, it is recommended that the gunners should also wear earplugs during firing.
Figure 4-2: C6 GPMGs with Left and Right Hand Feeds MACHINE GUN THEORY OF FIRE FOR DOOR GUNS
17. During firing of machine guns from ground or air, an understanding of the factors affecting MG fire, and methods of compensating that may be available, will allow the door gunner to effectively engage targets.
18. Ballistics is the science of the motion of projectiles and the conditions that influence that motion. The four types of ballistics influencing helicopter-fired weapons are interior, exterior, aerial and terminal. Each type produces dispersion, which is the degree that projectiles vary in range and deflection about a target.