Past Talks : JuLY 2023

“Flying the Hunter and other things”, by Sqn Ldr (Rtd) Rod Dean

What a splendid evening talk by Rod Dean on the Hawker Hunter. He has a lot of hours on Hunters in his log book, but as ever, there was not one line-shoot “There I was at 40,000ft ….”, but instead a very different slant on the aircraft itself, how it came about and how the inevitable snags were solved.

In total 1,972 Hunters were built and a great many of these were rebuilt and then re-sold to yet another customer. In November 1964, Rod flew his first Hunter and roughly 40 years later, in March 2003, he made his last Hunter flight, with 2,810 Hunter hours in between.

Where did it all begin? Unsurprisingly WW2 gave first notice of impending problems that needed to be resolved in terms of coping with increased aircraft speeds. Higher speeds resulted in the extremely disruptive effects of compressibility plus risk to the integrity of the aircraft itself. Solutions began to be developed, one of which was to make wings thinner to offer less resistance. In 1947, the USA adopted very thin straight wings for the first planned supersonic flight of the Bell X-1 (ultimately as little as 3½” at the root). That was one approach, but it meant that almost nothing could contained within the wing, there just was not enough space. Meanwhile, studies of the novel WW2 German Me 262 jet fighter continued, to identify why it was 100mph faster than the powerful P51 Mustang. The Me 262 had a 19º sweep back of its wings and so were the Me 163 wings heavily swept.

In October 1947, the very sleek, swept wing North American F86 Sabre appeared, followed two months later in December 1947 by the Mig 15 (powered by a copy of the RR Nene engine). In the same month, the B47 Stratojet 6-engine bomber with a 35º swept wing took to the air in the USA.

In Britain, we were well behind the creative curve, with front line aircraft such as the straight winged Meteor, Vampire, Venom and Attacker (with a tail wheel). The start of the Korean war in 1950 gave a much needed impetus for Britain modernise its fighter capability, when RAAF Meteors were truly outclassed by Migs. This led to design forays into swept wing aircraft with the experimental Supermarine 510, followed by the Swift entering a short-lived service in 1952. Meanwhile, Hawker offered the swept winged P1052, based on the delightful Sea Hawk, followed by the P1081 with all swept surfaces throughout. Close behind it came the Hawker Hunter prototype, which first flew in July 1951.

The Hunter prototype, serial WT555, looked promising, but at the early development stage it revealed a number of features that were to be troublesome:

• No airbrake, but very robust flaps instead, intended to serve the function – unsuccessfully.
• Ammunition link ejectors were flush with the fuselage, causing links to impact the fuselage and risk ingestion to the engine.
• Cartridge case ejectors were flush with the fuselage, similar to the link problem.
• Gun ports were flush with the fuselage, causing the engine to surge when the guns were fired and the aircraft nose pitching downwards at altitude.
• A straight leading edge to the wing, resulting in the wing tips stalling before the rest of the wing, causing the aircraft nose to pitch upwards.

The first aircraft flew with an early RR Avon 103 series engine, giving around 6,500lb of thrust and using the well-established cartridge starting method, which was fine, but once all three cartridges had been fired it was an unpleasant and tedious process to replace them. The second prototype was fitted with an uprated Avon 107 engine giving 7,550lb thrust. Finally, the third prototype was altered to take the 8,000lb thrust Armstrong Siddeley Sapphire engine, with its electric starter, in case problems were encountered with the Avon installation. In the event uprated versions of both the Avon and the Sapphire engines continued throughout the Hunter’s service life.

The development snags listed above were all overcome in due course:

• Air brake, several variations were tested, concluding with the successful installation on the underside of the fuselage towards the tail. The original robust flaps were retained.
• Ammunition link and cartridge case ejections were resolved by projecting the chute tubes beyond the fuselage and by installing ‘Sabrina-collector’ blisters to catch the cartridge cases (Sabrina being a notably well developed actress at the time).
• The gun ports were modified so that the gases created when firing took place, were deflected from the engine air intake.
• The wing stalling problems were not unique to the Hunter. The Mig 15, Mig 17 and the Mig 19 each used rather large fences on the wing, while the F86 Sabre tried automatic slats which caused problems of their own, before reverting to fences, as did the Swift. Hawker adopted a much more attractive and innovative approach by creating a dog-tooth leading edge, so that a vortex formed to give a better airflow, which delayed the stall. Pitching was transformed and Rod enthused greatly about how effective a solution it was. Both the Swift and the Lightning followed suit with the idea.

The fuel capacity and subsequent aircraft ranges were typically British and utterly inadequate. Fuel tanks were installed in various locations and fed from the furthermost point, forwards towards the engine – starting with fuselage tanks installed around the very hot rear jet pipes – honestly. Initially the Hunter F1 fuel tanks could give around 400 miles range. By the time the Hunter Mk 6 emerged this was increased to around 1,450 miles at 40,000ft altitude with the introduction of drop tanks, typically 2 x 230 gallon, plus 2 x 100 gallon tanks. All this was achieved after extensive drop tank trials to ascertain the best size of tank, its positioning under the wing and emergency release to avoid tail strikes, etc..

The standard armament fit was 4 x 30mm Aden cannon mounted in a pack beneath the cockpit. The pack contained 150 rounds of ammunition per gun and could be changed in 7 minutes. This was simplified by installing the four gun barrels within the aircraft, so that they remained in place and accurately aligned, while the pack itself was replaced. Under wing pylons enabled additional weapons to be carried including, in the early days, the original WW2, 3” 60lb unguided rockets, which were devastating if they hit the target. Alternatively Hunters often carried instead the French SNEB rockets, which although smaller, were more accurate.

Flying controls were hydraulic throughout, except for the rudder. Manual reversion was built in although the controls were very heavy, as you might expect. The instrument panel generally remained largely the same throughout, with the familiar 6-pack primary flight instruments immediately in front of the pilot.

Several Hunter Marks from FR 1 to Mk12 (and yet more I expect) emerged to fulfil different roles, plus to meet the needs of the 20+ foreign operators. It was interesting to note that the F9 and FR10 aircraft were all previously Hunter F6 models returned to the factory, refurbished and upgraded, leaving the factory gleaming like new aircraft.

In 1953 one of the prototype aircraft, a F3 was specially prepared for an attempt on the world speed record, which it successfully achieved in the hands of Hawker Chief Test Pilot Neville Duke, at a speed of 727.63mph. Subsequently, a standard operational Hunter F6 could achieve 620 knots (about 713mph) at sea level. The F6, F9, FR10 and Mk12 were all fitted with the very good “bullet-proof” (according to Rod Dean) Avon 203 engine capable of 10,000lb thrust.

The Mk12 series was the two-seat version with the pilots sitting side by side. The concept was significantly aided by the modular construction of the Hunter. The complete single-seat nose section was replaced by the wider, two seat cockpit which was designed in such a way that absolutely minimal alterations needed to be made to accommodate it. Getting the airflow correct around the new canopy required some original thinking, but ultimately it proved very successful and as a bonus added a laminar flow effect that under certain circumstances made it faster than a single-seat Hunter.

Several Hunters are still flying now in civilian identities and Rod indicated that to his knowledge a fatigue life for them has not been defined.

As really interesting talks go, this talk was elbowing its way to the front for me. Thank you Rod Dean for a very professional, well illustrated presentation. Plus thank you to all the invisible SOFFAAM backroom people who made it all happen in the auditorium and on Zoom.

Wherever you are in the world, do join us on Zoom. At £4 each talk, believe me it is worth it and so easy to do.

Summarised by Robert Heath