A Warning Sensor for the Chinook

Episode A-011

Sponsored by SDB Partners

The terrible tragedy in Afghanistan early on Saturday morning August 6th has electrified the nation.  It was the greatest single loss in Afghanistan and it took some of our finest fighting men.  It is a national tragedy.

The Defense Department has launched an investigation.  Not too many details are known.  The best we can say is that a Chinook was dispatched with crack Seal Team forces to carry out a rescue mission.  Either while landing or taking off (the details vary), the Chinook was hit by a rocket propelled grenade, crashed, and all on board were lost.

The RPG-7 as it is known is a simple weapon that terrorists have used effectively against American forces.  Originally from Russia, RPG’s are made around the world, from China, to Iran, to Syria.  The RPG is relatively simple but lethal: it consists of a primary charge that launches a rocket and a warhead/grenade from a tube that is made up of metal and wood, or metal and cheap composite material.  Once out of the tube the rocket ignites and propels the grenade.  The device is aimed manually and the rocket travels in more or less the same direction as it was launched (subject to wind conditions where it has a tendency to turn toward the prevailing wind).  There are different type fuse arrangements, but the simplest is to detonate on contact.  Recently, RPG’s have been equipped with a passive infra-red site so that targets can be identified at night.  It is not known with any certainty if the RPG that struck the Chinook was aimed with such a night vision device, but some suspect that is what happened.

Currently helicopters flying such missions have limited warning systems to help them against RPG’s.  The best is a RWR or radar warning receiver, but it was designed against heat seeking missiles and is reportedly not too good at identifying RPG’s.  Also it cannot get a read on a missile until it is pretty far along on its trajectory, which limits the utility of an RWR against a short range RPG fired from the ground, often in a highly radar-cluttered environment.

Safety Dynamics, a sensor company in Tucson Arizona, may have a solution to help pilots react quickly to an RPG threat, or even the threat of a high powered sniper rifle or anti-aircraft gun.

Safety Dynamics designs and builds acoustic sensors based on neural network technology. The company is headed by Sally Fernandez and is privately held.  Her technology has had Army and Navy sponsorship and most recently was featured on National Geographic.

The sensor works inside the range envelope of the RPG and can react to an RPG launch in less than a second. Since the travel time of an RPG can be a mere 5 seconds, an alarm in the cockpit alerts the pilot to take a drastic evasive action.

Because the RPG does not have a sensor and must follow its launch course to completion, a rapid, severe and immediate reaction in the cockpit may be enough to avert an RPG hit.

A key element of the technology is its virtual immunity to other sounds, such as rotor whop, jet engine whining, and wind and vibration noises.  Helicopters are very noisy machines, so being able to immediately hear an RPG launch is non-trivial, but in the case of the Safety Dynamics technology, workable.

No one can replace what was lost in the Chinook crash.  Tactics need to be changed.  But there is technology to help solve the problem -in short, there is a warning sensor for the Chinook.

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4 thoughts on “A Warning Sensor for the Chinook

  1. Nighthawk13 says:

    Surely you jest. Any RWR (Radar Warning Receiver) is passive. It receives and analyzes EM (Electro Magnetic) emissions from an active seeker. IR (Infrared) seekers are passive, no active emissions. An RPG (Rocket Propelled Grenade) is a dumb (point and shoot) weapon, again no active emissions. A RWR won’t work against this uncomplicated threat.
    An acoustic sensor on a Chinook, or any helicopter, ignores the high noise environment. Sound levels outside a large helicopter can exceed 120 decibels. While it may not be impossible to tune out some of this noise it would probably be difficult, slow, expensive and unreliable.
    Also, consider that if an RPG hits a helicopter it probably is fired from close range (100 meters or less). If an air crew received warning of an RPG launch, they would have less than 2 seconds before warhead impact. Just enough time to voice half of your favorite expletive. Not enough time for any evasive action.
    The only obvious solution is active suppression. Imaging systems combined with effective IFF (Identify Friend from Foe) systems linked to high firing rate antipersonnel guns would be more effective in suppressing the would be RPG launcher before the RPG is launched.

    • In response, I did not mean a stand alone RWR but something like the AN/APR-31 suite which includes RWR, a laser warning system, a missile warning system, and CIRCM for infra red threats. The CIRCM may be capable of detecting the rocket motor of the RPG and I have been told informally that sometimes it gives an alert. I don’t know how reliable they are.
      I think your range for the RPG is too little –RPG’s can be fired at targets from 300 to 500 meters, and be effective. If the enemy is 100 meters away and firing at you, you better not be there.
      Timing is an issue. My estimates are between 3 to 5 seconds to detect and respond. Luckily the boom sound of the RPG happens at launch, so there is a very limited time for a radical and urgent evasive action. This is far from ideal, but because the RPG is aimed and fired and has no sensor to correct, it can be evaded.
      As for detecting the sound in a very loud environment. loudness is not the issue; the issue is the profile of the sound. Safety Dynamics has tested successfully in very loud environments, but not as loud as a helicopter. But they believe it will work. It needs testing.
      Of course active suppression is the best if you know where the enemy is, or can keep him pinned down sufficiently. The problem in built up areas is this is very difficult to do without a lot of collateral damage, and it still may not prevent a bad guy from popping up and shooting.
      Finally there is an argument about not using such big helicopters in highly dangerous environments. I gather the experience in Iraq was that the smaller machines, like the Kiowa Warrior, survived better in high threat environments because of their small profile and agility.
      Thank you for your comments.

  2. mike m says:

    having operated in kashmir for about 7 years including the most turbulent period in the 90s, and having experienced the tactical acumen of mercenaries especially from Afghanistan, i am sure the sad loss of finest fighting forces is a direct outcome of intelligence failure. as you have correctly identified that RPG is very potent against aerial platforms operating closer ground, i.e, helos,the fact that the footprint of deployment is limited , proves that its fairly easy to sanitise the area rather than looking for purely a tech solution. my recommendation is that a mix of an RWR apparatus coupled with the thorough area sanitisation will yield positive results.

  3. Acoustic vector sensors have been proven to not only to detect the launch of an RPG but also been able to point at the launch position.
    Background noise from the helicopter itself can be eliminated.
    Not sure if the response time with any sort of detection sensor will be long enough to change the flightpath of the heli.
    But in case of a miss, as the position of the attacker has been identified, immediate response is possible, and this might disencourage many.

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