Birds with a Bigger Bite
Written by Adam Baddeley
SOTECH 2009 Volume: 7 Issue: 9 (November/December)
The Demands for Suppressive Fire
Call Upon Different Combinations
of Range, Caliber and Rate of Fire.
Rotary wing aviation, designed to lift troops into and out of position, needs protection, an obvious but multi-faceted capability and one that increasingly requires pintle-mounted machine guns and cannon, fired by crewmen from doors and ramps. Gunships they are not, nor do they aspire to be. Furthermore, a dedicated fire support platform cannot always be available. Instead, aircraft also may need their own, on-board means of suppressing enemy troops and engaging light-armored vehicles. The demands for suppressive fire call upon different combinations of range, caliber and rate of fire, with different mission types requiring different solutions.
FN
In the air, FN Herstal has developed an optimized solution for airborne applications in 12.7 mm caliber with the M3 machine gun, a development of the venerable M2, which comes in two variants: the M3P for fixed, podded implementations and the pintle-mounted M3M operated from ramps and doors, which has also been integrated on ground platforms. With the M3P, the firing is done by the pilot using the helicopter’s sighting system, whereas the M3M is fired by the gunner.
In the U.S., FN supplies pintle-mounted solutions of the 7.62 mm M240 and the 12.7 mm M3M— known as the GAU-21 and the M3P, now becoming the favored choice among a growing number of users.
The substantive differences between the M2 and the M3 are barrel weight and firepower—the latter capable of 1,100 rounds per minute (rpm)—twice that of the M2’s 550 rpm. Christophe Heron, head of marketing at FN’s Systems Division, explained, “The M3 is an FN machine gun design, with a high firing rate, and thanks to its low weight, it is particularly well-suited for airborne applications.”
Heron said, “Generally speaking, our customers are looking to have range and firepower, so the .50-caliber offers a range of 2,500 meters while the M240 is limited to 600–800 meters maximum. The 7.62 mm MAG/M240 is purely an anti-personnel weapon, while the GAU-21 is also an anti-vehicle weapon—at 1,000 meters it can penetrate 10 mm of armor plate.”
In the pintle-mounted domain, explained Mark Cherpes, vice president, military operations at FNH USA, a major customer has been the Marine Corps, which selected FNH USA to supply the GAU-21 on the ramps of helicopters like the CH-53D and E with close to 300 systems having been delivered.
In addition to the ramp, the other key locations on a helicopter are the right and left doors. The Marines are now contracting to add the GAU-21 at these points. Cherpes said, “We are working on additional weapon stations on the left and right doors and windows. We will also equip the CH-46 aircraft doors left and right and ramp, and then we will also equip the four-bladed UH-1Y Huey. Both sides will be equipped for, but not necessarily with, the GAU-21—as the mission might require, for example, a minigun to be used on one side.”
The GAU-21 is designated the Common Defensive Weapon System. Cherpes said, “It is common across all the services—not just the Marine Corps—and across all platforms that need to use a .50-caliber weapon. The Navy is also putting it on the MH-60 Sierra and Romeo variants, and we have also had some interest from the Army on their CH-47s and the UH-60s. We are hoping that it will go defensewide in the U.S. in the next few years.”
FNH supplies the GAU-21 with a soft cradle mount with recoil mitigation, aircraft interface hardware and ammunition storage, although Cherpes notes that there can be some other, third-party interface to the aircraft.
FNH’s work with SOCOM currently has focused on the M240 as the standard medium machine gun. In those instances where the M240 is being used, U.S. users are transitioning from the M240D to the newer H model.
Looking to the future, the services led by communities such as combat search and rescue (CSAR) are currently reviewing how they provide suppressive fire from door and ramp mounts on rotary wing aviation and looking at how to overcome threat gaps. Self-evident range limitations however don’t exclude 7.62 mm weapons in the future. Cherpes said, “In an urban mission the 7.62 mm is a better option because it limits collateral damage. In the non-urban environment however users want the range and stopping power of the GAU-21.”
The logical extension of this is to develop a mount that could host both the M240H and GAU-21, depending on the mission. Right now, however, the situation is such that users can’t move down to a 7.62 mm weapon on a 12.7 mm mount.
Cherpes outlined what DoD is seeking to do to resolve this: “DoD is looking at a modular aircraft interface that will allow a drop-in soft cradle pintle mount. What they would do is to have a mounting structure—even having ammo cans that are multi-role—that will be standardized. Then from the pintle connection up you put on the 50-cal pintle connection or the 7.62 mm pintle connection.”
In addition to pintle mounted systems, FN Herstal’s M3P was selected for operation on the Army’s OH-58D Kiowa Warrior fleet. Heron said, “We were selected earlier this year to equip 340 helicopters. This is the first U.S. platform that has an actual fixed for forward machine guns from FN.” The conversion will take place in the United States.
There are already 120 helicopters deployed with the M3P, the weapons having been taken from the Army’s existing Avenger program inventory.
NEXTER
Nexter’s latest offering in this area is a little bigger: the 20 mm SH20 retractable door mounting for helicopters. This door mounting is designed to provide multi-mission helicopters (for CSAR and other roles) with air-to-ground fire support capability. Nexter is under negotiation with France’s DGA for the qualification of the SH20 door mounting on the Eurocopter Cougar and Caracal and serial production.
The start point for the SH20 was to achieve an improvement on the existing 19A, Nexter’s legacy door-mounted cannon system.
The main advantages over the 19A are reduced weight (360 kg with 480 rounds of ammunition) and susceptibility to detection prior to deployment. The 19A003, an electrically driven swivel mount, weighs 716 kg, albeit with ammunition stowage of 960 rounds.
The SH20 is not visible in flight while the door is closed; the 19A however is a fixed door mounting, mounted in an open door while in the air. In contrast the SH20 is bolted to the floor on a swivelling arm. When needed the doors are opened and the cannon is then rapidly swung into position manually.
Christophe Rousseau, sales manager at Nexter’s Weapons and Turrets department, said, “[You] can go with the open doors closed, and 10 seconds later you can fire.”
The SH20 uses the Nexter 20 M 621 20 mm cannon, the same weapon used on the 19A, and which uses NATO standard 20 x 102 mm ammunition and has an effective range of 2 km at 750 rpm with an average recoil force of 250 daN. This same cannon has also been fitted on a lightweight variant of the 19A for use on the Dauphin tactical helicopter, which is in USCG service as the HH-65.
DILLON AERO
In terms of volume firepower, nothing compares to the minigun. Now delivered to over 20 customers worldwide, Dillon Aero’s M134D and, most recently, the new M134D-T variant are employed on a variety of rotary wing platforms including the UH-60, MH-47, MD 530F, with two of the latest customers being the government of Afghanistan and Iraq via U.S. contracts announced earlier this year.
Somewhat counter-intuitively, the minigun poses few recoil challenges, which can be acutely felt in airborne platforms. Mike Dillon, president of the company, explained why: “Whereas a single barrelled gun like the M240 rolls and bounces back and forth, there is none of that with minigun. When you pull the trigger it takes the slight step aft and stays there. The gun doesn’t torque left or right or up or down, and you can literally put one hand on it and shoot it like a pistol. You don’t have to fight recoil or force the gun back on target because it never goes anyplace you don’t move it.”
While the rate of fire is a positive boon both for suppression of the enemy and recoil, the same can’t be said for the feed system. The feed systems on the original General Electric GAU-2 were such that if the belt tangled in the box, the belt would snap in half or jam the gun. To solve this, Dillon Aero patented several changes to the design to ensure it is considerably more reliable and easier to fix, illustrated by the training package the company provides to military customers for this unique weapon.
Dillon explained, “An important part of the training is to teach them to clear stoppages. To do that we have each student clear five stoppages in the classroom. Then we go into the field and let them fire the gun from the helicopter. We then deliberately induce a stoppage and have them clear it in flight with live ammunition. We expect them to do that in 45–60 seconds as against the old GAU-2 system, which took more like 25–30 minutes. We subject the feed systems to up to 50 stoppages in training sessions without damaging any part of the system. We have probably fired more than 5 million rounds doing trial and error development to ensure everything works smoothly.”
The M134DT, available since early 2008, is the latest minigun variant. The T stands for titanium, which has been substituted for steel in most of the feeder/delinker, suppressor rotor, the yoke and most of the mount. There is a cumulative loss of 13.6 pounds in weight versus the steel M134D. Dillon said, “Not everybody buys it because it is a little more expensive. It’s mostly the groups where weight is critical that are using it.”
Another innovation is a key improvement to the drive motors. At start, the M134 pulls roughly 400 Amps (100 ms)—a substantial portion of a platform’s on-board power. To meet SOCOM’s needs, Dillon Aero redesigned the drive motor to reduce this to roughly 130 Amps and is now taking back all the motors for weapons supplied over the past three years for modification. ♦