Flight Test: B-24J Liberator
A rare opportunity to fly the only example of the USAAF’s ‘other’ WWII heavy bomber currently airworthy - a capable machine that is not at all easy to fly
Mentally exhausted I slump back in my seat, while out on the big bomber’s wing four huge radials grumble contentedly. “Good work Dave,” says our captain, Jim Harley. “Now, d’you reckon you can get this thing out to the runway...?” Taking a deep breath, I sit up straighter in my seat, slide my feet up the rudder pedals, release the parking brake and ? with no small sense of occasion ? grasp the four throttles. These are the reins of 4,800 horses, waiting to be set loose.
In a series of ugly, uncoordinated lurches the big machine makes its unsteady way along the taxiway. Witchcraft is currently the only airworthy B-24 Liberator in the world, and as its nose wanders drunkenly from side to side I feel the first rivulet of sweat run down my back. Out of the corner of my eye, I see Jim struggling to suppress a grin. As I continue to wrestle with this unwieldy beast, I am sure of one thing: this is going to be one of the most memorable and demanding flights of my life.
Of course, you don’t just jump in a ship (and it is a ship) like the Liberator. My introduction to Witchcraft had started the day before, when Jim had given me a thorough ground school session on the B-24. Jim is the Collings Foundation’s Chief Pilot, and his ready grin and relaxed demeanour hide the fact that he is one of the most experienced warbird pilots in the world. For example, although he mostly flew the Foundation’s B-17, B-24 and B-25 in 2012, he still managed to log around 300 hours on the P-51. Jim has a great job! After four hours of ground school, he left me with a forty-question exam paper and said he’d see me at 0830 this morning.
Shortly after that time, we conducted the pre-flight walk-round, Jim pointing out some of Witchcraft’s salient features. It’s a B-24J, which was the most widely produced version of the Liberator ? of which 18,482 were built ? and also the only model to be manufactured in all five of the factories involved. It’s also really quite big: the wingspan is an impressive 33.5m, and it stands 5.5m tall.
One of the Liberator’s many claims to fame is that it was the first heavy bomber to enter production fitted with a tricycle undercarriage. Close-coupled though it is, the nosewheel is not steerable and only castors. Jim confirmed that taxying is a bit tricky, as is landing. It is imperative that you do not land on the nosewheel, while care must also be taken to avoid hitting the tail bumper. The mainwheels retract outwards into the wing, and as this is mounted high on the fuselage, the legs are long and reinforced with a side brace and forward drag strut. Stopping and steering is done by hydraulically-actuated expander brakes, two on each wheel. According to Jim the brake pucks are made from ‘Unobtanium’ and must be used sparingly and with care.
The high aspect ratio ‘Davis wing’ (so-called after its designer, David Davis) features a much more advanced aerofoil section than had been fitted to combat aircraft previously. This wing played a large part in the Liberator’s phenomenal range, reducing drag by a claimed twenty per cent. However, it was also the aircraft’s Achilles Heel, being very susceptible to failiure after even relatively light combat damage. Metal-skinned Fowler flaps cover approximately sixty percent of the trailing edge, while the ailerons and all the other control surfaces are fabric covered.
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The Liberator is powered by four Pratt & Whitney R-1830 Twin Wasps. Produced in greater numbers than any other big aero engine, this air-cooled fourteen-cylinder two-row radial was fitted to not only the B-24 (which itself was built in bigger numbers than any other US military aircraft) but also the DC-3/C-47 and many other types. Witchcraft’s R-1830s are the ‘dash 65’ variant, and produce 1,200hp each at 48in manifold pressure (MP) and 2,700rpm. They’re quite unusual engines, as they feature single-stage, engine-driven superchargers working in series with exhaust-driven turbochargers.
Witchcraft’s engines are also unlike any radials I’ve ever flown behind in that there was no evidence of oil leakage. As Chief Pilot, Jim is very proud of his team, and he grins and says, “that’s down to Crew Chief Whitney Coyle ? keeper of the driest radials on the circuit!”
As the turbocharger ‘buckets’ can suffer no less than eight different types of defect, Jim studied each one very carefully before moving onto the three-blade Hamilton Standard Hydromatic propellers. The Liberator was the first aircraft to use these new props, which had the advantage of being quick-feathering.
Having paused briefly to inspect the tail bumper, unique roll-up bomb bay doors and waist gun positions, we examined the large tailplane and oval-shaped vertical surfaces. As the twin rudders sit squarely in the avalanche of air blasted backwards by the giant props I could see that they would work well as soon as the engines hit takeoff power.
We then climbed in through the open bomb bay, up to the cockpit and sat down. As you’d expect, it’s a very busy cockpit that is dominated by a large console between the two seats. This carries a veritable forest of levers, although my immediate impression was of just how many toggle switches there were ? literally dozens of them. Jim patiently led me all around the controls and instruments, and then left me to familiarise myself with them while he slipped off to talk to the crew. To say that it was initially rather bewildering is an understatement, but I slowly began to make some sense of it all.
The primary power gauges (RPM and MP) are mounted top centre in the panel and clearly delineated by a white line, while the fuel and oil pressure instruments, and oil and cylinder head temperature gauges are in front of the co-pilot, on the right. The pilot has the flight and navigation instruments, although all the gauges can be seen ? and most of the controls reached ? from either seat.
The centre console carries three sets of four levers. These control, from left to right, the turbochargers, throttles and mixtures ? and although the turbocharger and throttle levers work normally, the mixtures are forward for idle cut-off and back for rich. Immediately aft of these levers is a long row of toggle switches that operate the propellers, intercoolers, cowl flaps, pitot heat and emergency hydraulic pump. The prop and cowl flap switches have gang-bars which are used only when running up, and not in flight. Behind the throttle quadrant is a large box that houses the three trim wheels and more toggle switches, while another box set slightly lower and further back carries various handles and levers that operate the undercarriage, flaps, park brake, control lock and bomb jettison (not needed today!).
Returning to the cockpit, Jim quizzed me on some of the other systems. Having spent several hours the previous evening reading the notes he’d provided, I answered confidently that we could carry up to 1,300 US gallons of fuel, that we must land with at least 400 remaining and that there is no facility for transferring fuel across the wing. I even remembered that the hydraulic system’s total capacity is 18usg, and that the accumulator’s pre-charge should be at least 600psi.
We were now ready to start the engines, and ran through the ‘challenge and response’ checklist. Starting the massive Twin Wasps was a real flight back in time, and here’s an interesting factoid: each one of Witchcraft’s cylinders has almost 1.6 times the swept volume of an entire Rotax 912 ? and it has 56 of them!
Having checked that the prop arc of number three was clear (this engine is always started first as it also powers the hydraulic pump) and that crew chief Whitney was standing by with an extinguisher, I placed my right hand on the correct rotary mag switch (in a row by my right thigh) and turned my attention to the large block of toggle switches by my left knee. These operate the fuel boost and pre-oil pumps, energise and mesh the starters, and activate the primers. As each ‘Accel’, ‘Mesh’ and ‘Primer’ toggle switch is for two engines, it is imperative that you know what you’re doing! Furthermore, under or over-priming, backfires and a host of other mishandling-related transgressions are treated as beer-buying offences ? and Witchcraft’s crew looked thirsty. Having finished pre-oiling the engine I lifted the appropriate Accel and Mesh toggle switches, waited until six blades had marched past my window, then lifted the primer switch, counted three more blades and turned number three’s mags to both.
Deep within the bowels of its plump cowling, the engine slowly awoke, smoke streamed back from its exhausts and the prop began to blur as I moved my hand quickly to the mixture lever and drew it back gently into auto rich. With the engine rumbling happily and the oil pressure steady, I began the process of starting number four. Eventually all the engines were running smoothly but there was no time to waste, as the B-24 burns around 80us gph at tick-over.
LURCHING DOWM THE TAXIWAY
Taxying was just as challenging as I’d imagined and we set off along the taxiway in a series of lateral lurches?the brakes are quite ‘grabby’ and as the nosewheel castors, it’s not easy to keep straight. The trick was not to apply any rudder (so that the pedals remain central) keeping the feet up on the top of the pedals and only braking lightly and occasionally. God knows what it’s like taxying across wind…
I was acutely aware of the 33.5m wingspan, and very grateful that Whitney was keeping watch from the hatch immediately in front of the top turret, as the pilot’s field of view is surprisingly poor. Having successfully made it out to the run-up area we commenced the run-up checks. These are numerous and included cycling the electric props from fine through coarse and back while checking that the ‘pitch stop’ lights illuminate, testing the feathering buttons, magnetos, turbos, cowl flaps and many other items. While using the gang-bar to cycle the electric props it was interesting to note the difference in rate of change, and I was not surprised when Jim reiterated that in flight the props must be adjusted individually. Checking and testing the myriad systems took time, and I was slightly embarrassed when the accompanying Mustang’s pilot (who was behind us) grumbled good-naturedly about the delay, as his engine was becoming uncomfortably warm.
Eventually everything was set, and we lurched out onto the runway. Having rolled forwards a couple of metres to ensure that the nosewheel was straight and straddling the centreline, I stood on the brakes and eased the throttles forward until the MP gauges showed thirty inches, then released the brakes and opened the throttles to about forty. Leaving Jim to fine-tune the power to 42in and 2,700rpm, I concentrated on keeping straight as the airspeed began to build.
The rudders came alive immediately, and as the ASI’s needle swung through 75mph, I eased the yoke back just enough to lift the nosewheel off the runway. The speed continued to build and at 120, I increased the back pressure slightly, the urgent drumming of the wheels stopped and the big bomber slid into the sky.
“Positive rate,” said Jim. “Undercarriage up please,” I replied, dabbing the brakes to stop the still-spinning wheels. The speed kept increasing and as we passed through 500ft I eased the power back to my best approximation of maximum continuous, while Jim raised the flaps from a third down to up. Just as he’d warned me, the Liberator sagged and then sank momentarily as the flaps retracted.
At 2,000ft and 150mph I levelled out and re-trimmed while Jim delicately adjusted the power from ‘climb’ (35in/2,300rpm/auto rich) to ‘cruise’ (30in/2,000rpm/auto lean). Jim controlled the manifold pressure primarily with the turbochargers, using the throttles to reduce power to a couple of inches below that required and then gently adding the extra boost with the turbochargers. Even at these parsimonious power settings the four mighty engines were still guzzling around 160us gph (600 lit/hr, in new money!)
With the fuel and hydraulic boost pumps off, cowl flaps set, intercoolers open and all the other details attended to, I settled back and tried to get a feel for the Liberator’s handling. During the briefing Jim had emphasised that although you need to be this machine’s master and not its servant, you definitely can’t bully it ? it’s just too big. He’d also explained that it is mostly flown with the elevator trim wheel, and as our excited passengers insisted on walking around inside the cavernous fuselage I soon saw what he meant ? I was constantly re-trimming. In fact, the Liberator is very sensitive longitudinally and it is extremely important during taxi, takeoff and landing that everyone remains seated and no one is aft of the waist guns or forward of the cockpit.
IMPORTANT TO LEAD WITH RUDDER
Nor is the Liberator very speed-stable: if the nose is allowed to drop even slightly below the horizon the aircraft accelerates rapidly, and if pitched above the horizon it decelerates just as quickly. I tried some gentle turns and quickly realised it is important to lead with the rudder and that the controls are quite heavy and also not very powerful. This may be because they’re all fabric covered. The indifferent controls, poor longitudinal stability and below-average field of view must’ve made a heavily-laden Liberator a right pig to fly in formation at high altitude.
But that was in the 1940s. Today, the P-51 slid into formation, and as it did so I realised just how privileged I was. I was flying a Liberator ? the only one currently airworthy ? with a Mustang escort. What a thrill! One of our passengers was a ninety-year old Liberator crewman, and to see the ‘little friend’ sitting just off our starboard wing must have been a very emotional moment for him.
On the way to our destination of Zephyr Hills we made a small diversion to fly over Kermit Weeks’ famous Fantasy of Flight museum, Jim suggesting I fly a couple of reasonably tight turns overhead to “wake Kermit up”. I was grateful for the opportunity as ? needless to say ? this particular flight could not follow the format of a typical Pilot flight test, and I knew there certainly wouldn’t be the opportunity to examine the slow-speed or asymmetric characteristics. As Witchcraft is the only airworthy B-24 it’s far too precious for these kinds of tricks.
Zephyr Hills appeared much too soon for me, and having completed the pre-landing checklist with the props at 2,000rpm and between 25-27in MP, I concentrated extremely hard on keeping the speed and altitude nailed as we turned downwind. Jim is an excellent instructor, and just gave me gentle prompts such as “here’s about right for the first stage of flap” and “I usually drop the gear about now” or “try about 24 inches and 2,000rpm ? you want 130mph on base”.
I gave myself a generous downwind leg and a wide base, and as the Liberator settled onto final I was immensely gratified to see that (thanks to Jim’s excellent coaching) the speed and glideslope were bang on. The rest of the flap went down and I juggled the throttles gently to keep the speed steady at 120mph as we flashed over the fence.
Easing back on the yoke I drew the power off and tried to maintain the right attitude. Although I needed to avoid touching the tail bumper (another beer-buying offence) it’s imperative to land on the mainwheels and hold off the nosewheel.
The wheels touched fractionally sooner than I’d planned, but the touchdown was reasonably smooth and, remembering those Unobtanium brake pucks, I held the nose up for aerodynamic braking. The runway is about 1,500m long and I knew that Jim expected me to use it all, as long as the last 150m was at a slow speed. As they say; the runway is free, but brakes and tyres are expensive.
As the speed diminished I lowered the nosewheel and just thought about braking. The brakes are powerful, and if applied firmly they’ll certainly stop the wheels ? although the tyres may continue to revolve. Never mind a beer, this probably constitutes a brewery-buying offence.
Once clear of the runway we raised the flaps, pushed the mixtures back into Auto Lean, then opened the cowl flaps and bomb bay doors. “Great job Dave” grinned Jim, before adding “you can start breathing again now!”
Words: Dave Unwin Photography: Dave Unwin & The Collings Foundation