As we approach the RAF’s 100 year anniversary year it is interesting to note the absence of information about airborne towing, a discipline that has been proven to be effective over many years and one which continues to be used by all major air forces today.
During early combat air operations, low payloads and fuel loads meant the utility of air power was compromised.
A solution was needed that allowed operators to escape the constraints of existing engine technology and aerodynamic knowledge, and so airborne aircraft towing was born.
These initial efforts required operators to connect towing line whilst still in flight, synchronising airspeed and altitude being the major technical and flying skill challenge to overcome, as can be seen, it was a very hazardous activity
Attempts to mechanise the process were introduced but it did not remove the need to attach the towline whilst in mid-air.
Airborne towing was used extensively in the interwar period by the RAF, especially in Iraq and wider Middle East. It was also adopted by some civilian aircraft operators in order to extend the distance mail flights could go without delays caused by refuelling stops.
The ‘Express Mail’ route between London and Sydney was one such example and in 1932, set the world record for fastest letter delivery, smashing the previous record by 47 hours and 56 minutes.
By the late thirties, however, airborne towing had reduced in popularity due to improvements in engine technology but in the Pacific Theatre, the huge distances meant that the technique had somewhat of a revival.
The image below shows a US Boeing B-29 bomber being towed towards Tokyo on a bombing raid in 1944.
As can be seen from the image above, US engineers had replaced the traditional flexible tow rope with a new design, a fixed bar. This fixed bar was better able to cope with the increased stresses placed on it by virtue of greater towing thrust.
As WWII closed, airborne towing was finding use in a number of air forces, the RAF for example.
Although the RAF chose to stay with the tried and tested flexible tow rope, the construction of this rope benefitted considerably from work done on flexible pipelines used for the D-Day PLUTO fuel transfer system, especially the helical reinforcement technique.
As the Cold War progressed, variations on the basic theme included formation towing, asymmetrical towing and in some cases, unequal towing where smaller aircraft were used to tow larger aircraft.
During the 1982 Falklands Conflict, the RAF made extensive use of Airborne Towing and many commenters have since said that without airborne towing, the conflict may have been very different.
Attempts by Argentine forces to use their Chinook helicopters in the airborne towing role were not a success, likely due to their poor understanding of the overall concept and lack of suitable tow ropes.
The design of the tow rope has also changed considerably, instead of rubber hose to provide flexibility and natural fibres to provide strength, modern tow ropes make extensive use of composites and experiments are now being carried out with carbon nanotubes and graphene.
The most experienced airborne helicopter towing operators are the US Marine Corps.
The image below shows a towing operation underway. The underslung load adds considerably to drag, without the Hercules, those CH-53 would struggle to achieve any kind of operational range.
What does the future hold for airborne towing?
There will certainly be some use of the technique for unmanned aircraft and a number of research activities are underway for the robotic attachment of the tow hitch, an area that continues to cause problems and requires a great deal of training for what is a very perishable skill.
I will finish with an image of a towing test rig, a reminder that however glamorous airborne aircraft towing is, engineers still need to take care of the little things, without them, airborne aircraft towing would be impossible.