Battle of the biplanes
Distinguised by very different design and manufacturing qualities once so typical of their parent nations, these classic aircraft simply ooze character
By Dave UnwinThere’s something very special about flying open-cockpit biplanes. With the pulse of the engine throbbing through the throttle and the wind rushing like a river past the cockpit, it’s a truly physical experience. On a warm summer’s evening there are few finer flying machines in which to take to the air. Soaring and wheeling around the clouds, you can smell the engine, feel the wings pressing down on the air and sense the very soul of the aeroplane. They really do feel like living creatures – at least to me.
As you swing down from the sky in a continuous, sweeping curve to settle softly back to earth, the sensation of subtle and sublime transference of weight from wing to wheel is even more profoundly gratifying when landing a vintage biplane on grass. Taxi (slowly!) back in and shut down. Snap the switches off and listen to the sound of the engine cooling and the gyro unwinding into silence. Then, reluctantly, undo the straps and leads and slowly climb out. That’s what flying is all about.
This trio of biplanes is not only worthy of the much overused appellation ‘classic’, but they are products of three of the greatest names in aircraft manufacture: de Havilland, Focke-Wulf and Boeing. And if a Tiger Moth, Stieglitz and Stearman were standing together in a row, most pilots could make a pretty good guess at the country of origin of each. The Focke-Wulf looks typically Teutonic, while the big Boeing looks brash and American. And as for the Tiger...well the elegant curve of the rudder gives it away instantly as a de Havilland design. So let’s take a closer look and a flight in each to see how they stack up. Compromised de Havilland
Of the three, the DH.82a – better known as the Tiger Moth – is the oldest, smallest and least powerful. Derived from a 1920s design, the DH.60 Gipsy Moth, the prototype first flew in 1931 and it entered service in 1932.It is powered by a Gipsy Major I, an air cooled, inverted inline four that produces 130hp, and is fed from an 86-litre tank in the centre section. Of all the primaries I’ve flown, the Tiger definitely has the worst handling. This is particularly curious because the Gipsy Moth (which is from the previous decade) is actually quite nice to fly. The answer as to why is that the Government got involved.
Basically, the DH.60 had a few design features that needed changing before the RAF would consider it as a trainer. One of the military test pilots’ complaints was the difficulty the instructor in the front cockpit would have in abandoning the aircraft in an emergency, due to being directly under the centre section fuel tank and surrounded by various struts and wires. De Havilland’s solution was to move the entire centre section forward, leaving the instructor an easier exit route. This of course played havoc with the Centre of Pressure and Centre of Gravity, so the designers then swept the wings aft to move both back to where they belonged. (Interestingly, the Tiger thus became the RAF’s first swept-wing aeroplane.) Unfortunately, this didn’t quite fix things, so the upper wings were swept back slightly more. It was then realised that the ailerons, which are mounted on the lower wings only, were rather too close to the ground, and to rectify this the lower wing’s dihedral was increased. The net result of all this tinkering was to significantly degrade the handling qualities, as the combination of swept-back wings and increased dihedral caused a strong coupling of roll to yaw. (I would say that the Government made a similar hash of procuring the Tucano some 55 years later). It is also interesting to note that the Tiger’s illustrious ancestor, the straight-winged DH.60, responds much more conventionally to control inputs. Another noteworthy feature is that the upper wings carry leading edge slats, which deploy automatically at low airspeed. These must be unlocked just before takeoff and locked after landing and before spinning or aerobatics.
Access to either cockpit is adequate, there being drop-down doors on both sides, however, the cockpit is quite snug and the seats do not adjust (although the rear rudder bar does). No matter what I do, I never seem to be able to get really comfortable in a Tiger. Taxying out reveals forward visibility that’s not bad for an aircraft of this vintage, although you are very conscious of the absence of brakes.Slow and steady is the only way to go, and don’t be embarrassed to ask for someone to walk the wing. You’ll be a lot more embarrassed if you taxi into something!
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Full power produces reasonable acceleration, and coarse rudder keeps everything pointing the right way, although of course all aircraft of this type are sensitive to crosswinds. The climb rate is around 500fpm, which is acceptable. Less so is the handling: although the Tiger has differential ailerons you’d never know it in the air – the adverse yaw is tremendous. The Pilot’s Notes recommends cruising at 1,950rpm, which should give between 65-70kt for a fuel flow of around 30 lph.
Slow flight is easy because the stall characteristics are essentially the same for all three aircraft we are looking at here – benign. Those big biplane wings retain a tenacious grip on the air, helped by the leading edge slats. Recovery is also easy and immediate, simply release the back pressure.Landing is fairly straightforward, as long as the wind is relatively calm. In more boisterous conditions the rather ineffective ailerons can make things a little ‘knife-edge’ but the solution is surprisingly simple – don’t fly Tigers in boisterous conditions. Despite the lack of wheel brakes, the skid – once it has dug into the ground – really does slow you down. It also helps keep you straight because the braking force is being applied behind the C of G. Despite – or possibly because of – the rather poor handling, the Tiger is a popular aircraft, for although docile and relatively easy to fly, it is difficult to fly well. Indeed, to perform a well executed roll requires more skill than I possess! On most aircraft you time the roll rate with a stopwatch, but with a Tiger a calendar works equally well.Nevertheless, the DH.82 served with air forces all over the world, and remained in service well into the 1950s. Around 8,600 were built, mostly in the UK, although approximately 2,000were built in Australia, Canada and New Zealand. One final point well worth mentioning is that de Havilland also built the engine.Fine Focke-Wulf
Next up in terms of age, weight and power is the Focke-Wulf Fw44J Stieglitz (German for Goldfinch). Originally designed as a two-seat civilian biplane for pilot training and sport flying — or at least that’s what they told people at the time — the prototype first flew in 1932. It is powered by a Siemens Bramo SH14A-A4 seven-cylinder air-cooled radial that produces up to 160hp at 2,200 rpm and turns a wooden two blade fixed pitch prop. It is fed by a pair of fuselage-mounted tanks with a combined capacity of 135 litres.
Focke-Wulf’s new chief designer, Dipl-Ing Kurt Tank undertook many of the flight trials. He would eventually prove to be one of the most talented aeronautical engineers of the 20th Century.
The Stieglitz was an immediate success, and was not only operated in Germany but also many other countries, including Brazil, Bulgaria, Chile, China, Czechoslovakia, Finland, Romania, and Turkey. It was also built under licence in Argentina and Sweden. It is a single-bay biplane and both sets of wings have identical span and feature a very subtle sweepback, with just a slight stagger. Both the top and bottom planes also have a small amount of dihedral, but of far more interest is that there are ailerons on both the upper and lower wings. These grant the Stieglitz a fine roll-rate.
Being a Focke-Wulf it was designed with traditional German thoroughness: there are literally dozens of well-sited access panels for inspection and maintenance. The various servicing hatches for the fuel and oil are colour coded, and this is carried over into the cockpit. Not only are the ASI and engine instruments picked out in different colours, but so are some of the controls. For example, the knob on the fuel selector lever is yellow while the oil shut-off valve is brown. Although common today, this was innovative stuff in the 1930s and in fact it was the Germans who invented the system.
Any primary spends a lot of time doing circuits and bumps and the Stieglitz’s undercarriage is better than a Tiger’s – it has hydraulically actuated drum brakes – but inferior to a Stearman’s with stock aircraft having a skid rather than the American aeroplane’s tailwheel. The Stieglitz I flew (Peter Holloway’s G-STIG) has been retro fitted with a castoring tailwheel, which has not improved the ground handling.
Access to either cockpit is good. There are doors on both sides, and well-located grab handles. The seat adjusting mechanism is very neat – you simply twist the top of the lever to unlock it, and then raise or lower it to suit you. All the controls are well located, with the only ergonomic aberration being the pitch trim wheel, which is on the right-hand side. This, of course means you have to change hands on the stick when trimming. Interestingly, the engine primer has its own separate reservoir inside the cockpit which must be filled before trying to start the engine.
Taxiing out reveals forward visibility that’s quite good for a biplane of this vintage, although I was not very impressed by the brakes. They aren’t very progressive, and the geometry of the pedals is such that you really have to point your toes to operate the things. Full power produces adequate acceleration and there’s no difficulty in keeping straight with coarse rudder, while the elevator becomes effective almost immediately. The climb rate is around 600fpm.
My initial impression was that the directional stability is somewhat ‘soft’, although in fact this was actually my fault because the powerful rudder is remarkably light and sensitive and it took me awhile to master it. Apart from this, the handling is very good, with an authoritative elevator, responsive rudder and amazing ailerons. Slow flight is very predictable, as is the stall.
The recommended cruise power setting is 1,950rpm which produces about 90kt and a fuel burn of around 40lph. Landing is fairly straightforward: indeed of our three classics the Stieglitz is certainly the easiest to handle in lively conditions and crosswinds. It’s only at the end of the rollout (where the rudder becomes ineffective) that things can get interesting.
The problem with the one I flew is that the castoring tailwheel bestows a nasty propensity for trying to swap ends during the ground roll. There’s no doubt in my mind that the Stieglitz would be a lot easier with a tailskid, which is of course how Kurt Tank intended it. That said, it would still be only too easy to f... er, Focke things up. As they say, if in doubt there is no doubt – leave it in the shed for another day.
Big, beautiful Boeing
Last but by no means least is the Boeing Stearman, correctly known as the PT-17, N2S or Kaydet. Just like the de Havilland and Focke-Wulf machines, Boeing’s big beautiful biplane is one of the great trainers. This might explain why more than 1,000 of the 8,585 that were produced are still flying.
Based on a design by Lloyd Stearman, the prototype first flew in 1934. The example I flew is powered by an air-cooled radial but, somewhat surprisingly, not a Jacobs, Wright or Pratt &Whitney: it’s a Lycoming R-680, which was that company’s first successful aero-engine. The R-680 produces 220hp and is fed from a single fuel tank with a capacity of 174 litres, mounted in the centre section.
As you approach a Stearman you can’t help but feel that it must have looked rather intimidating to an 18-year-old US Army Air Corps cadet, with precisely zero hours in his logbook. It towers over its European contemporaries and is easily the largest and most powerful of the WWII primary trainers.
The design is typical of an inter-war single-bay biplane, the wings being staggered and of unequal span. One item worthy of discussion is the trim system. Although all three machines were designed for the same mission – and are broadly similar in many respects – they all have different pitch trim systems. The Tiger uses springs attached to the base of the control stick, while the Stieglitz has an adjustable tailplane and the Stearman has trim tabs in both elevators.
It’s easy to see why the Stearman has a reputation for being a bit tricky on the ground. The wheel-track is rather narrow, while the centre of gravity is relatively high – you do, after all have 125kg of fuel and 234kg of engine mounted a fairway above the undercarriage. On the plus side, it’s blessed with two very useful features that you certainly wouldn’t find in its European contemporaries: a steerable tailwheel and good hydraulic toe brakes.
In fact, the tailwheel is one of the few subtle differences between a PT-17 and an N2S-2. Because the pilots of US Army Air Corps aircraft were land based, the tailwheel of a PT-17 steers through the rudder pedals. Should it swivel through an angle greater than full rudder deflection (35�) it automatically disconnects and becomes fully-castoring. However, many US Navy aeroplanes, including the N2S-2, have lockable tailwheels that are not steerable. On most Stearmans the original hydraulic drum brakes have been replaced with modern disc units. Of our three trainers, the Stearman is easily the most ruggedly constructed. Compared to the dainty Moth, or even the tough little Stieglitz, the Stearman is massively over-engineered.Access to either cockpit is quite good, and the cockpit is spacious.Then as now the average American was larger than the typical European, and the cockpit is sized to accommodate the ‘fuller gentleman’. Both seat and pedals adjust – the seat has no less than eleven settings!
The impression of the Stearman being of robust construction is carried over into the cockpit. The exposed steel tubes look sturdy, and if the fixtures and fittings aren’t castings they’re forgings, with the notable exception of the polished Mahogany control column. Everything is totally functional and there are no frills. You’d really have to apply yourself to break something, which isn’t true of the European trainers.
The tall control column (actually, stick is probably more apposite, it being a long, straight piece of wood) is well placed, as is the chunky throttle quadrant on the left.While taxying out, I made a point of ensuring that I was slow and careful. In fact, the ground handling was not too demanding – courtesy of the steerable tailwheel and hydraulic toe brakes. Nevertheless, the big, round engine means that the forward visibility is distinctly limited, making S-turning essential.
It also seems to rock laterally on its undercarriage slightly. This is that high C of G reminding you not to take any liberties. Acceleration is good but not great, although any tendency to swing is easily contained by the rudder. As for the handling, the controls feel quite heavy and, with ailerons on the lower wing only, the roll rate is not exactly sparkling. There is also a significant amount of adverse yaw that requires prompt and accurate rudder to keep the ball in the centre. Slow flight is very straightforward, and at the stall it merely drops its nose in a very leisurely fashion.
The Stearman flies very much like a southern gentleman drives – conservatively! As we’ve come to expect of American machines, it is the thirstiest of our trio. A typical cruise speed of 90kt is achieved with the power set to ‘19 squared’ (1,900rpm and 19 inches of manifold pressure) with the engine drinking around 55 lph. Just like American cars and motorbikes, it is thirsty, slow and noisy. And just like American cars and motorbikes, it absolutely oozes charisma.
The Stearman is quite easy to land, although keeping straight during the rollout requires deft and accurate application of rudder and brakes. In its defence, though, I should admit that I’ve only ever landed a Stearman on tarmac, while I’ve never landed a Tiger or Stieglitz on anything but grass. I much prefer operating vintagetailwheel types off of grass because it makes landing so much easier. In his wonderful book Flying the Old Planes the great Frank Tallman wrote that ‘you can physically remove 50 percent of your landing problems by flying from grass or dirt strips’ – and he wasn’t wrong! The Boeing Stearman is a wonderful thing, the aerial equivalent of a ‘good ole boy’.
AND THE WINNER IS...
Flying any or – if you’re really lucky – all of these classic aircraft is an experience that is both hard to describe and difficult to resist! “So Ace,” I hear you say, “money’s no object, which one do you want?” Well, if money’s no object I’ll have one of each. However, if I could only have one it’d probably be the Stieglitz. Mind you, I do love the Stearman… and then again, the Tiger is such great fun…