The Delta K Avalanche Control Programme

In 1999 Delta K conducted a series of research studies with the support of The Center for Snow Science at Alta (CSSA) in Utah, USA and the Avalanche Artillery Users of North America Committee (AAUNAC). Following a successful demonstration of the use of a specialised reactive shaped charge design for stimulating artificial avalanche release, plans were made to fund a broader programme of study to review and assess the current use of explosives for avalanche control and identify areas of application of advanced explosives technologies. This led to a contract for a three year programme jointly funded by the AAUNAC members, the CSSA and three US Departments of Transportation.

Avalanche control programmes are intended to mitigate the threat of damage caused by avalanche run-outs through: management of natural stabilisation features; introduction of permanent stabilizing structures; construction of physical barriers to protect key assets and continuous artificial stimulation of controlled releases by blast, shock and vibration primarily generated by energetic materials.  

Delta K’s contribution to these mitigation programmes is associated with the optimisation of explosive effects intended to stimulate artificial avalanche release.   Whilst the methods and techniques adopted in avalanche control programmes vary considerably depending on geographic location, accessibility, local topography, and prevailing weather conditions, the need to conduct active control work is based on local experience underpinned by a continuous interactive process of regional and local weather monitoring conducted throughout the avalanche season. The methods and techniques employed in these control activities can be grouped under the following generic headings.

Typically, artillery operations include the use of 105mm Pack Howitzers, 75mm and 106mm Recoilless Rifles and other military gun systems. These provide long range capability but the disadvantage is maintenance cost, specialist training, risk of overshoot and the fragmentation hazard associated with HE rounds. The 106mm recoilless rifle, at Alta in Utah, shown to the left has a lower range and maintenance requirement, but ammunition is both old and scarce.  Shorter range requirements (less than 2km) are met with compressed gas launchers (Avalaunchers), and other fixed remotely operated mortar type launcher systems such as the Avalanche Guard. High performance gas launchers, such as the LoCAT and AVCONS systems with range capabilities up to 5km also exist.  Delta K has designed and developed commercial ammunition for the Avalauncher and LoCAT launcher systems.

Work on the DeltaLancer ammunition for the high performance launchers has paved the way for long range (5km) ammunition together with the more complex considerations for 105mm and 106mm replacement ammunition. The underlying problem with heavily cased military ammunition is that the Bare Charge Equivalent (BCE) of a 15kg shell carrying 2.5kg is actually less than 1kg of HE and this probably detonates after partial penetration of the base scree. Delta K studies have, therefore, concentrated on determining if advanced gas launchers could be a more cost effective overall solution to Artillery ammunition.

In remote areas charges can be pre-positioned at the start of the season and fired remotely, however the charges are susceptible to damage by slides and/or incremental snow pack weight, the charges also need to be many kilos and are difficult to manage from a security perspective. Relatively low pressure wide area pulses can be generated by fixed installations that ignite and direct explosive gas mixtures.  Gaz-Ex (shown left) is an established commercial example in which a Propane/Oxygen mixture is injected into the combustion chamber and ignited by remote control. The pipe guides the pressure pulse that exits and propagates across the start zone triggering any prevalent instabilities. This installation shown left is located at Teton Pass in the USA.

The broad objective of this development programme was to exploit the inherent modularity of Delta K’s DeltaLancer carrier vehicle technology to produce a common blast or shaped charge assisted explosive payload to which appropriate safe arming and fuzing options could be fitted to meet the broad requirements of Hand Charge, Gas Gun and Aerial avalanche control operations.

The photograph shows an example of the DeltaLancer Hand Charge (HC) charge configuration.  The common Forebody moulding (Red) can be loaded with a cast explosive, deformable commercial gel, plastic explosive or liquid explosive in a sealed insert - with or without the shaped charge liner.  In this particular case a canister containing spooled shock tube is shown located coaxially over the Fin body (with the fin vanes removed).  The two loops can be hooked into a carabina whilst the operator is casting the charge.  This provides a means of tethering and controlling the charge position before firing and also provides a means of recovering the charge in the event of a dud or vetoed shot.  The Shock Tube can be initiated with an electronic firing pack or 209 shot shell primer initiator. 

Note the Forebody assembly is common to all three variants.

The maximum range achievable with the DeltaLancer ammunition is governed by a complex interaction between projectile strength of design, projectile aerodynamics and the launcher’s design and performance parameters.  For compressed gas launchers, the optimum range achievable with mortar type “fin stabilised” projectiles, is constrained by aerodynamic drag considerations, primarily because aerodynamic drag increases rapidly above and around Mach 0.85 (280m/s @ MSL).

Given this 280m/s constraint and a typical drag coefficient of 0.15 at Mach 0.85, for DeltaLancer, mass becomes the key parameter affecting the maximum range potential, provided the launcher can achieve a 280m/s muzzle velocity.  By way of example: for a launch velocity of 280m/s (MSL) and quadrant elevation of 41 degrees, the “modelled” range for a 1, 2, 3, and 4kg projectile would be, 2.4km, 3.6km, 4.3km, and 4.8km respectively.   This, however, assumes the launcher is indeed capable of driving the mass, in each case, to 280m/s - and the projectile stays in one piece.

Considering the DeltaLancer projectile, with a 1kg payload, the maximum practicable range for a muzzle velocity of 280m/s would be 2.9km.  This, however, is of academic interest with respect to current Avalauncher designs as the maximum firing pressure for the latest variants is probably around 600psi.  For the Nitro Xpress launcher the “modelled” muzzle velocity, for a 1.29kg DeltaLancer round, would be about 250m/s, so the maximum range potential for DeltaLancer could be about 2.6km.  This is realistic as the DeltaLancer GG ammunition has already been fired at 600psi, albeit from Delta K’s launcher with a smaller pressure chamber and shorter barrel.

Ongoing development work on a replacement round for the LoCAT and AVCONS launcher system is studying a ruggedised DeltaLancer based ammunition with a standard mortar fuze interface.