A CLASSIC EXPERIENCE
On a recent visit to Springfield, Illinois I had the chance to fly one of the great bomber classics of World War Two - the North American B-25. At the Air Combat Museum (Springfield airport) there is a collection of immaculately presented aircraft that are all owned by a father-son team. Michael George (son) runs the collection and the museum with Don George (father) providing support in the background. The B-25 is actually owned by Don, who also owns a T34 Mentor. Mike on the other hand owns a beautifully 'stock' P51 Mustang, a superb Corsair, a Taylorcraft L2-M and a Soko Galeb jet.
The initial aim of the visit to Springfield was to get some exciting air-to-air pictures of the collection for John Dibbs' 'Flying Legends' calendar. However, it was decided that to get that picture with a difference the B-25 was needed as the photography aircraft - Mike said that he was sure that his dad would not mind me getting a short 'checkout' to allow me to fly the bomber for the photo's - of course I thought it would be impolite to argue with such a suggestion!
It was decided that I would get one dedicated sortie to learn the handling of the aircraft and the emergency procedures. Then to continue my conversion an experienced B-25 pilot would sit in the other seat to offer advice and help during the photography sorties. This approach worked very well and I was lucky enough to have two excellent B-25 pilots to learn from. Greg Vallero started my training and a veteran B-25 pilot, Doug Rozendaal, finished it off on the later sorties.
EARLY B-25 HISTORY (back to top)
The origins of the B-25 can be traced back to 1938 when the USAAC (USA Air Corps) asked the American industry for a new twin-engined attack bomber. The North American company took up the challenge and developed the NA-40 prototype.
The First Prototype (back to top)
The NA-40 prototype was radically different from any of North American's previous designs and featured the 'new' style nose-wheel undercarriage as well as a shoulder mounted wing, large transparencies covering the cockpit and the nose position for gunner/bomb aimer. The tail design incorporated twin fins and a rudder. The team in charge of the development was led by JL Atwood and RH Rice.
The NA-40 was powered by two Pratt and Whitney R-1830-S6C3-G, 1,100 horse power, engines. It was designed for a crew of three and had a gross weight of 19,500 pounds (8,864 kg), carrying a maximum bomb load of 1,200 pounds (546 kg). It made its first flight in January 1939, piloted by Paul Belfour. The aircraft was then fitted with 1,300 horse power Wright Cyclone GR-2600-A71 engines, becoming the NA-40B. Some two months after its first flight it was sent to Wright Field, Ohio, for operational testing. At this stage it was in competition with the Douglas A-20 to meet the attack bomber requirement of the USAAC. Unfortunately, two weeks after arriving at Wright Field it crashed, as a result of pilot error (the crew thankfully escaped unhurt), and the Douglas was chosen.
Time To Rethink (back to top)
All was not lost and North American were asked to develop the aircraft to meet the Air Corps' requirement for a medium bomber aircraft. During 1939 many improvements were made and incorporated into the newly designated NA-62 design. In September 1939 this was ordered straight into production 'off the drawing board' with a contract for 184 aircraft worth 11.7 million dollars. The first of these aircraft flew on 19 August 1940 and it was at this stage that the aircraft was named the 'Mitchell' after General 'Billy' Mitchell.
The NA-62 had a wider fuselage than its predecessor to allow side-by-side pilot seating, carried a crew of five and could lift twice the bomb-load of the NA-40. The Wright Cyclone R-2600-9, (1,700 horse power) engines were added and the wing was lowered from its shoulder mounting to a mid position with some up-slope (dihedral). The first aircraft was tested with two different rudder and fin designs before the final design was evolved. Flight testing had highlighted some directional control problems and after nine aircraft had been delivered the wing was again changed to the gull-wing design that has become the trade mark of the B-25.
Basic Design (back to top)
The construction of the B-25 was typical for the period with an all-metal, stressed-skin construction throughout apart from the ailerons, twin rudders and elevator, which were fabric covered. The wing had a single enormous spar with extruded booms at the top and bottom. The ribs were light-alloy sheet, with light spanwise stringers added before attaching the skin panels with flush rivets. The fuel was contained in wing tanks, which from the B-25A onwards were 'self-sealing'. The large main wheels had single oleo legs and retracted backwards, hydraulically, in to the engine nacelles. The nose wheel similarly retracted backwards, under hydraulic pressure, in to the fuselage. Steering was accomplished by the use of differential main-wheel braking, which caused the nose wheel to castor in the desired direction. The flaps were of a 'slotted' design and were hydraulically operated.
A Distinguished Combat History (back to top)
The Mitchell had an extremely distinguished career during the war serving on all fronts with virtually all the Allied forces. It first became operational as the B-25A with the 17th Bombardment Group, based at McChord Field, Washington. However, perhaps the most remarkable raid was flown on 18 April 1942, when 16 B-25Bs, manned by volunteer crews from the 17th B Group and the 89th Reconnaissance Squadron (led by Lt Col James H Doolittle), flew off the deck of the USS Hornet (CV-8) to make an attack on Tokyo and other Japanese cities. This daring raid showed more than any other the Mitchell's capability to operate very successfully even under the most arduous battle conditions. During the war 9,889 aircraft were built with various type designations. The changes in type designation were mainly concerned with changes to the armament or the powerplant installations. The final production variant was the B-25J, which reintroduced the glazed nose. Deliveries to the USAAF totalled 4,318 (all built between 1943 and 1945!), with another 72 built but scrapped at the end of the war. The US Navy received a further 255 as PBJ-1Js and the RAF received 314 as Mitchell llls. Brazil received 29 B-25Js on a lend-lease scheme and a number went to Russia. The B-25J was the most prolific variant of the Mitchell and was still serving in Brazil and Venezuela in 1971. Even as late as 1978 the Bolivian Air Force still had a few serving Mitchells flying.
GETTING TO GRIPS WITH THE AIRCRAFT (back to top)
To fly the B25 was an exciting prospect, but getting the chance to obtain some excellent tuition on how to 'really' fly the machine was a dream come true. Mike George introduced me to Greg Vallero, who was the usual pilot for Don's B-25J (N898BW - painted in a British colour scheme representing a Mitchell lll). Greg's 'day job' was an airline pilot so he was used to flying the bigger aircraft and more importantly used to passing on such knowledge. He started off by giving me the 'books' to read (both the Flight Manual and a 'how to fly the B-25' book, which I believe had been produced by the Confederate Air Force). He also gave me an overview of flying the aircraft, stating that it really was a gently machine to fly with good handling characteristics. However, it did have one problem area: after lift-off the aircraft had to be accelerated to its 'safety' speed of 145 mph before the climb was initiated. This safety speed was the minimum speed at which you could suffer an engine failure and still continue to fly safely, without losing directional control. The main limiting factor with respect to this speed is the capability to keep the aircraft straight and level with just one engine running at full power.
Back at the hotel I got stuck in to the books. These showed the aircraft to be relatively conventional with the systems being straight forward in both design and operation. The checklist items seemed logical and the emergency procedures were again straight forward and essentially the same as any modern twin engine aircraft. The main 'warning' areas were the need to get to safety speed as quickly as possible and the need for care while taxying because the nose wheel was not very tolerant of side-loads. They also stated that the biggest problem during an engine failure was containing the roll rather than the yaw. This was the reason that the wing design was changed to the gull-wing shape. (The design tends to reduce the secondary rolling motion due to sideslip after the engine has failed.) Another area I always pay particular attention to is engine starting. On some types this can be quite tricky and can cause engine damage if not performed correctly.
Using the books I prepared a 'how to fly the B-25' knee-board to help me remember the key facts about operating the aircraft. It also listed all the operating limitations to ensure that I did not do anything embarrassing while flying the aircraft.
The First Flight (back to top)
The next day, armed with my new knee-board, I arrived at the Museum, I thought bright and early; however, Greg was already there preparing the aircraft and waiting to give me a flight briefing! Greg gave me a thorough briefing on what we were going to do and the best ways to do it. The main areas that he covered included take-off and landing techniques, general flying and emergency procedures (engine failure after 145 mph, single engine approach and go-around as well as a single engine landing). We then went to the aircraft for a cockpit briefing, which entailed a spot of mountain climbing getting in to the aircraft! The hatch to the cockpit area had a built in ladder that lowered when it was opened, giving access to the first level behind the pilots' seats. Once in the aircraft there was a second ladder that went up to the main cockpit area. The cockpit itself was big and comfortable. Sitting in either seat it was possible to reach all the primary controls. The layout was conventional for the class of aircraft with a centre pedestal containing the main engine controls (throttles, propeller controls and mixture controls). In between the seats at the back of the centre pedestal there were two unusual levers that operated the emergency brakes. These could be either used separately to give differential-brake nose wheel steering or together to give normal braking. The flight instruments were conventional as were the rest of the cockpit switches - the main difference between them and modern cockpits being size and an older fashion design. The initial checks were performed from the checklist as in a modern multi-engine aircraft.
Starting (back to top)
Starting these bigger engines is relatively simple but it does require finger dexterity and is much easier if you have seen the process before! The magneto system in the B-25 has a master switch as well as individual engine magneto switches. This master is switched on before start along with the 'emergency' booster pump for the engine being started. Then the starter switch and the primer switch are selected together for the appropriate engine (usually the right first). After the propeller has rotated through 'six' blades the magneto is selected on. Once the engine fires you keep the primer selected until the engine is running smoothly, but you release the starter switch. At the appropriate time the mixture lever is put to 'Full Rich' and the primer released. At the same time the engine instruments are scanned to check for oil temperature and pressure. The throttle is set at 1,200 rpm, the booster pump switched off and the hydraulics checked. The process is then repeated for the second engine.
After start checks are similar to any other multi-engine aircraft and include checking the emergency brakes, propeller functioning and feathering checks. Taxying took some getting used to because there was a delay between pressing the toe brakes and the braking action. This meant that when trying to turn using differential braking you had to 'guess' the appropriate amount of pedal to apply, wait for the brakes to 'bite' then decide if it was enough or not. The initial tendency was to press the pedal, think that nothing was happening and then press a little bit more; then when the brakes did come on you turned too quickly or too much! Not ideal when getting out of a tight space! However, the 'right' amount of brake pedal to use quickly became intuitive, and by the second flight the problem was not noticeable.
Getting Airborne (back to top)
Again, all the before take-off checks were performed from the checklist and 20 degrees of flap was the normal take-off setting (30 degrees could be used if obstacle clearance was a problem). Greg discussed what to do if we had a problem on the take-off: "before 145 mph if we have an engine failure close the throttles and land straight ahead, above 145 mph get the gear up and fly away, reducing power slightly if directional control becomes a problem". The take-off technique was to increase power on the brakes to get the engines accelerating evenly, then to release the brakes and to keep straight using the differential application of power. Brakes could be used early in the take-off roll but this extended the take-off run and caused unwanted side loads on the nose wheel. Rotation was started at 80 mph with a heavy pull; once the nose wheel was off the ground the control column was checked forward to prevent the aircraft getting airborne too quickly. Lift-off occurred at about 115 mph. The undercarriage was then raised and almost the same height maintained until the aircraft had reached the magical 145 mph. At this speed you gave a sigh of relief and started the climb. Engine parameters during the take-off were 2600 rpm and 44 inches of boost. During the initial acceleration, the normal technique was to reduce power to 2400 rpm and 40 inches boost at 145 mph followed by a further reduction to 2200 rpm and 30 inches boost at 160 mph. This was the normal climb speed and power setting. Throughout the take-off trimming was very important because the control forces were quite heavy. At a safe height, the flaps were retracted and the after take-off checks completed.
General Flying Qualities (back to top)
Once established in the cruise the power was again reduced this time to 1800 rpm and 28 inches of boost. At this power setting you could hear again! The cockpit is very noisy at high power because the propellers are almost inline with you head - active noise reducing headsets would be a 'god-send' during the take-off!
Up-and-away the control forces were quite heavy, particularly in roll. Elevator forces were not so heavy but continual trimming was required to keep them manageable, particularly over any large speed changes. Turning was impressive with the large wing producing a very tight turning capability (if you could manage the large aileron forces). Fuel consumption in the cruise was about 110 US gallons per hour at a speed of about 180 mph.
Formation Flying (back to top)
During the photographic sorties I had the chance to have a good look at the formation flying characteristics of the aircraft - not easy. Formation flying in the B-25 was characterized by heavy control forces and delays between moving the controls and the aircraft actually moving. This latter problem was the most difficult to master during the high-workload formation flying. In close formation short quick control movements are required continually to stop any large positional errors from developing. This meant one hand on the control column and one on the throttles, preventing the use of both hands during larger control movements. This was particularly tiring if continued for any length of time. As described above the aileron forces were the heaviest, which, coupled with the delay between moving the control column and the aircraft's movement, made 'in and out' positioning very difficult. As experience developed I found myself using the rudder to start the roll movement going (the secondary effect of yaw is roll) and then using the ailerons to finish the manuvre. Using this technique the formation task became much easier and the aileron control forces needed were much reduced. The formation flying was hard work but great fun.
Back In The Circuit (back to top)
Coming back to the airfield gave the opportunity to relax a little and recover feeling in the hands and arms after the formation flying! General flying in the circuit was easy, but to fly accurate patterns, using the 'numbers' was the best advice. Downwind was flown at 160 mph with a power of 2100 rpm and approximately 22 inches of boost. At this stage gear and one quarter flap was lowered and the speed reduced to 150 mph by the end of downwind. Round finals 150 mph was maintained for safety reasons until rolling out on runway heading when the speed was trickled back towards the landing speed.
To get a good landing was more tricky until the correct technique had been explained to you. Then it was a 'by numbers' task: on finals the speed is reduced to 120 mph and you 'aim' 500 feet short of where you want to touchdown; then at about 200-100 feet you 'flatten' the approach to land on your required spot, while reducing the speed to 105 mph. The important thing here is to keep trimming otherwise the control forces are too heavy to flare correctly. When over the runway the power is slowly reduced aiming to touchdown at 85 mph on the 'backs' of the main wheels. Once the main wheels touch the ground the aircraft tries to de-rotate rapidly, which would 'slam' the nose wheel on to the ground if not caught in time. Use of trim during the flare helps to reduce the control column forces during the de-rotation, making it much easier to hold the nose wheel of the ground until a lower speed. As mentioned, the nose wheel is a weak area and needs looking after. After landing at 85 mph and lowering the nose at about 65 mph the aircraft does not take much stopping.
Single Engine Flying (back to top)
To complete my training I had the chance to practise a simulated engine failure at 145 mph followed by a single engine go-around and a single engine landing. The engine failure itself was not too difficult to control, but it had been given to me at safety speed. However, you could feel that delicate flying was required to stop the aircraft 'getting away from you'. The climb rate was not very good on one engine but the curvature of the earth did help! The best technique was to level as soon as possible (allowing for obstacles), ensure the gear was up and the engine feathered and then wait for 155-160 mph. When at this speed a climb could be slowly started. When safely away from the ground the flaps were retracted to help the acceleration. The single engine go-around flying technique was similar, with the main difference being that you had to go-around early enough to give sufficient height to continue descending while retracting the gear and obtaining 145 mph. Once 145 mph had been obtained then the climb could be commenced. For the single engine approach to landing the power had to be gradually reduced and the rudder trimmed accordingly. Ideally, 145 mph (safety speed) was maintained until landing was assured. At this point the speed could be further reduced towards the normal landing speed. When there was no chance of going around, and you were close to the flare, the flaps were lowered to full. At this stage you were committed to landing and could not go around.
The single engine flying qualities of the aircraft were similar to those of the more modern 'twins': survivable as long as the rules were followed and the aircraft flown accurately.
TIME TO GIVE THE TOY BACK (back to top)
By the end of the visit I had managed some six and a half flying hours' on the aircraft, and had been lucky enough to experience some of the delights that have made it so popular with pilots over the past 60 years. I am not sure that I would have liked to take it to war but as a peacetime mount it was a great thrill. Unfortunately, however, the time had come to give it back. It just wasn't the same sitting on the Boeing 747 on the way back to England!
I would like to thank Mike and Don George for giving me the opportunity to fly such a wonderful piece of history, and Greg Vallero and Doug Rozendaal for sharing their knowledge (and stories) with me.
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