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Issue No 53, 8 January 2023
By: Anthony O. Ives
Search and rescue operations is something helicopters are very good at, you could say they were nearly invented to do search and rescue operations if you consider Igor Sikorsky's quote “If you are in trouble anywhere in the world, an airplane can fly over and drop flowers, but a helicopter can land and save your life.”. However, even fixed wing aircraft in co-operation with a ground units greatly improve the chance of a search and rescue operation being successfully. Before the helicopters were a practical search and rescue asset, a typical airborne search and rescue operation would involve searching for survivors from the air, and then when survivors are located parachuting rescue personnel into that location. The rescue personnel would then provide medical treatment if necessary and arrange extraction usually by ground. We will review how rescue operations have advanced from parachute operations to helicopter operations and look at how tiltrotor aircraft could possibly improve search and rescue operations in the future.
While aircraft improved search and rescue operations they also made them more necessary as aircraft can crash in remote areas obviously search and rescue operations can be needed for all sort reasons but will usually be necessary when someone becomes lost and/or injured in a remote area. In the early days of airborne search and rescue, fixed wing aircraft did the search part and then when they found those needing rescued they parachuted the rescuers too them. The US Air Force's pararescue service [1] where formed for that specific purpose as land forces such as army or navy could use existing units to do rescue operations. The US Air Force (USAF) being a completely airborne service required them to create the specialised pararescue service to rescue their personnel who had ended up injured and/or lost on the ground. The USAF pararescue service has built up a reputation as being one most elite search and rescue units in the world as they have being doing it for a long time and then have to sometimes do it under combat conditions known as Combat Search and Rescue (CSAR) which just makes an already difficult operation even more difficult.
USAF pararescue service intially started of doing their rescue missions as described above by parachuting into the locations where rescue is needed, pararescue servicemen are still trained as precision parachutist today. Generally there are two ways to parachute:
Static Line: This method uses a device which deploys the parachute straight after the parachutist has left the aircraft, this method is used for low altitude parachute jumps
Freefall: This method requires the parachutist to decide (usually with the aid of a altimeter) when to deploy the parachute this method has to be done at higher altitude in order to be safe
There is also two types of parachutes:
Circular Parachute: This parachute relies on drag [2] to reduce the rate of descent of the parachutist, it typically has a drag coefficient of 1.3 to 1.75, it is circular in shape and generaly has a hole at the top to allow airflow to escape and keep it stable, this parachute is typically used for static line parachute jumps and as a reserve parachute
Rectrianglar Parachute (or Parafoil): This parachute mainly uses lift [3] to reduce the rate of descent of the parachutist and has an opening at the front to let air in and inflate the enclosed section which is airfoil shaped hence the parachute requires some forward speed to function which requires the parachute jump to be at a higher altitude or from an aircraft travelling at a higher speed, both static line and freefall jumps can be conducted using this type of parachute
The rectrianglar parachute or parafoil is more commonly used especially for freefall operations but also for static line operations if the aircraft airspeed and altitude is high enough. Parafoil type parachutes also give the parachutist more control, it can also look very similar to a paraglider [4] however the biggest difference is a paraglider is not designed for opening shock and would shred if it was used as a freefall parachute. The circular parachute is really only used as a reserve parachute or for static line operations at a lower altitude or speed. A diagram of the two types of parachute is given below:
Parachute operations are still used by the USAF Pararescue Jumpers (PJ) particular in cases where it is not possible to deploy using a helicopter, but extraction of survivors or those being rescued would nearly always been done by helicopters. Where it not possible to land the helicopter such as dense jungle, over water or for time reasons then the helicopter hoist would be used to lower the PJ down and bring them back up. The PJ or rescue personnel usually use something similar to climbing harness that would be typically used for mountaineering to attach to the hoist hook in addition to carabiners, etc to connect the climb harness to the hoist hook [1]. There is also a wide range of equipment you can use with the hoist hook to help with the extraction of survivors such as forest penetrators, medvac litters, etc [1]. A tagline technique can also be used to control the hoist hook as it is lowered and brought up again.
Fast rope is sometimes used by PJs and other military personnel to deploy from a helicopter quickly, it uses a fairly thick rope and personnel slide down it much like firemen down a fireman's pole. The advantage of this method is it needs the minimum of equipment just really a pair specific designed thick gloves. The rope can also be used as tagline [1] once all the required personnel are on the ground. Fast rope can also be used when personnel are deploying into high seas where a freefall swimmer deployment is not possible due to the waves crests not allowing the helicopter to descent to the recommended freefall swimmer deployment height [1].
Rappelling or abseiling is another method PJs can use to deploy from a helicopter it is similar to fast rope however, this method requires more equipment such as a climbing harness, a carabiner and a friction device. The friction device is usually a figure eight but rescue personnel typically use rescue eight which is a slightly modified verison of the figure eight friction device. A rescue eight prevents someone using it to rappel getting stranded due a lark's head knot and also makes it possible to tie in part way down a descent, which allows rescuers to descend to survivor trapped on mountain hence its name rescue eight. See picture below of the rappelling or abseiling setup using a rescue eight:
The USAF view that tiltrotor aircraft will provide further advantages in search and rescue missions due to their extended range, some versions of the tiltrotor also have pressured cabins which gives certain advantages when it comes to onboard medical treatment. Tiltrotor aircraft are essentially a fixed wing aircraft with a hover capability in which both engines and rotors are located at the wing tips. The engines and rotor can swivel to point forward as in a conventional fixed wing aircraft or vertical as required for hovering and vertical flight. In some versions of the tiltrotor the engine and rotor turn, however this cause problems if the exhaust is near the aircraft hoist door as the hot exhaust can prohibit its use. So therefore some versions only the rotor swivels which reduces the problem of the hot exhaust prohibiting the use of certain aircraft doors for hoisting ,etc. See diagram for different versions of tiltrotor design:
Apart from the swiveling engine and rotor, tiltrotors function very similar to the UAV eVTOLs [5] I described in an earlier article. While tiltrotors have their advantages there has also been a number concerns raised about their safety and reliably [6], so only time will tell if they are widely adapted. I have also mentioned the tiltrotor mission in another earlier article I did [7].
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References:
[1] Pararescue Operations, Techniques, and Procedures, US Air force, 2005, University Press of the Pacific, http://afpubs.hq.af.mil.
[2] http://www.eiteog.com/EiteogBLOG/No2EiteogBlogDragCD.html
[3] http://www.eiteog.com/EiteogBLOG/No1EiteogBlogLiftCL.html
[4] The Art of Paragliding, Denis Pagen, 2001, Sport Aviation Publications
[5] http://www.eiteog.com/EiteogBLOG/No36EiteogBlogUAV.html
[6] 'Why the V22 Osprey is Unsafe', 2003, Carlton Meyer, https://www.g2mil.com/V-22safety.htm
[7] http://www.eiteog.com/EiteogBLOG/No17EiteogBlogMissions.html
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