Vickers Valiant medium bombers in service with the R.A.F. since 1955 will shortly have their?
Vickers Valiant medium bombers in service with the R.A.F. since 1955 will shortly have their striking capability greatly increased through the use of in-flight refuelling.
The British "probe and drogue" technique for increasing the range of fighter and bomber aircraft has been applied to the Valiant by Vickers-Armstrongs (Aircraft) Ltd., working to Ministry of Supply contract in conjunction with Flight Refuelling Ltd., the originators and manufacturers of the equipment.
Valiants as Tankers and Receivers
All Valiants in service with the Royal Air Force can be modified to supply or receive fuel in flight. A large number of production Valiants were in fact completed with the basic fittings for the tanker or receiver roles and may be converted to tankers on the Squadrons in a matter of hours. The receiver conversion, involving only the fitting of a probe. is completed within minutes.
The principal operations involved in converting a Valiant to the tanker role are as follows:-
the installation of bomb bay fuel tank complete with turbine pump and piping; figment of turbine pumps in the fuselage tank cells;
installation in the bomb bay of the hose drum unit, piping and fuel pump; figment of a bomb bay fairing, wing stalks and underwing tanks; and the installation of the fuel transfer control panel in the cockpit.
The use of Valiant jet tankers significantly improves the scope of flight refuelling as contacts may be made at high altitudes and speeds. In the past, with piston engined tankers, the jet receiver aircraft was compelled to reduce operating height and speed to establish contact. Fuel flow transfer rate is high, the tanker's equipment being designed to meet the normal pressure refuelling requirements for military aircraft.
At the start of the operation the tanker Valiant trails the refuelling hose to its full length of some 90 feet. To resist the air loads on the drogue an electric motor is geared to the hose drum via a fluid coupling and tends to wind the hose back on to the drum. The drogue, however, gives a set load for a given airspeed. This load is in [text missing] "wind in" load of the hose unit, and [text missing] its full length. If the drag is reduced, the motor winds in the hose on the drum and any slack is taken up.
The receiver Valiant flies the probe into the drogue at a relative speed of three to four knots and proceeds to close on the tanker. The surplus hose is then being wound back on to the hose drum. When the receiver is in the refuelling position, which will be indicated on the tanker control panel, the tanker operator switches on the fuel valve. Provision is made for de-icing the probe before contact and for earthing the difference of electrical potential between the two aircraft on initial contact.
After completion of refuelling the receiver aircraft falls back to the limit stop at full hose extension. At this point the load on three spring loaded toggle arms, which closed on to the refuelling probe on contact, will be increased until the break away load is reached. The refuelling cycle is then complete.
Development with the Valiant
In spite of the large amount of experience gained with other types of tanker and receiver, many particular problems had to be resolved with the Valiant installation before the system could be considered proven up to the operational standard required. These problems have been solved by Vickers-Armstrongs (Aircraft) Ltd., in conjunction with Flight Refuelling Ltd.
For fuel booster pumping, air turbines were chosen, using air tapped from the engine compression. Tappings from each engine had already been provided into a common feed to cater for pressurisation, de-icing, and now extended to fuel transfer. The rate of flow provided by the booster pumps is suited to the individual fuel capacity of the tanks to be used for transfer to ensure reasonably simultaneous emptying.
The technique for hose trailing took some time to perfect. Initially it was decided to open the bomb doors on the tanker and trail the hose. This proved unsuccessful at first due to buffeting and vibration of the hose drum unit. This trouble was cured and a trials receiver aircraft was brought in close to the trailed hose. Turbulence over the receiver aircraft from the open bomb bay of the tanker was severe, and a bomb bay fairings as now fitted to tanker aircraft was evolved.
A great deal of development was required before the length of probe and type of drogue was finalised, since turbulent air behind the drogue was causing vibration problems on the receiver and difficulty in making contact at the required air-speeds was encountered. Several main drogue types were investigated. Solid and perforated cones of various angles were tried. Some models were tunnel-tested, using fuel as the medium, to study flow patterns through and around the drogue. The final drogue configuration is a generously slotted cone.
The Background of Experience
The success of in-flight refuelling of Valiants to-day is due in large measure to the far-sightedness of Sir Alan Cobham in founding Flight Refuelling Ltd., in 1934. The "looped hose" system of air refuelling was developed by how company and much exploratory work was carried out before the war with the aim of enabling commercial aircraft to cross the Atlantic. After the war the [text missing] tanker B-29s
It was not until the advent of the turbo-jet engine with its high fuel consumption, and the requirement to refuel single seat fighter aircraft, that the probe and drogue method was devised by Flight Refuelling Ltd. First trials were carried out with a Meteor refuelling from a converted Lancaster tanker in 1949.
With the advent of the Korean war the U.S.A.F. adopted the Flight Refuelling Ltd., probe and drogue system to increase the range and endurance of their Japan based fighter aircraft. The United States Navy are currently using the British-designed equipment to increase the range of their strike aircraft.
The equipment used on the Valiant stems back to work carried out from 1951 onwards with Lincolns and Canberras as tankers, and Meteors and Canberras as receivers.