1915 Airco DH2 Flight Test
PUBLISHED: 16:53 10 November 2011 | UPDATED: 14:10 10 October 2012
The WWI ‘pusher’ is a piloting challenge, even without the vagaries of a period rotary engine — but flying and displaying it is hugely rewarding
By Stewart Smith (DH2 pilot) & Phil Mobbs (Hawker Memorial Project)
Sat in the open cockpit of a replica 1915 DH2, goggles pushed up over my flying helmet, I am looking out over the magazine drum and open sights of a Lewis gun at an airfield and surrounding farmland ‘somewhere in Lincolnshire’. The chattering sound of the radial engine behind me is now stilled; relaxed and happy after flying a short display and the thirty-minute flight
home, I am still slightly bemused at the serendipity of it all.
“Never mind all that claptrap,” cry the pilots amongst you, “What’s it really like to fly the thing?”
The reality, of course, is that every flight in the DH2 follows a relatively lengthy preparation period on the ground. This
is a simple airframe made complex by myriad bracing wires, turnbuckles, control cables and flying surfaces.
In service, the original DH2 was fitted with either the nine-cylinder 100hp Gnôme Monosoupape (single-valve) rotary engine, or the comparable 110hp Le Rhône 9J. Wickenby’s replica, built in
the late 1970s, has a 125hp five-cylinder Kinner radial – a more ‘modern’ engine, albeit one of 1930s vintage.
If left standing for a period of time, radials can be prone to hydraulic locking due to the accumulation of lubricating oil in the lower cylinders. This is drained by removal of a spark plug from the Kinner’s cylinders three and four. A plug spanner and large drip tray are essential tools for the daily ‘A’ Check routine.
The sole aid to taxying is a marginally steerable, steel-shod wooden tailskid, which also provides the only braking force. This is totally ineffective in either respect on paved surfaces. So, in Tiger Moth fashion, the aircraft must be handled to its grassy point of departure, chocked, and prepared for start. Ground manoeuvring, however, requires a team of chaps. Not least, two stout ones to lift the rear fuselage in order to remove the temporary tailskid castor wheel, and one brave enough to enter the triangular cage formed by the mainplane trailing edges, rear fuselage booms, control cables and bracing wires, to prime and start the engine by swinging the eight-foot diameter wooden ‘pusher’ prop.
Pre-flight preparations complete, it’s now time to contemplate the best manner of gaining access to the cockpit. This sits seven feet above the ground, on the wrong side of a wire fence made up of external elevator control cables and forward bracing wires. By way of steps, you have a two-foot diameter mainwheel and forward of that, at chest level and in line with the pilot’s seat, there is a foothold set in the fabric fuselage side, bearing on the fuselage lower longeron.
So, right foot on the wheel and reach up with your right hand to grab the cabane strut whilst insinuating your upper torso into the narrow gap between the lower two cables and fuselage side. Raise your left foot into the foothold and reach out with your left hand for the spade-grip on the Lewis gun. The right hand is now needed to free your bum from snagged wires before grabbing the shoulder harness straps. Lean slightly backwards, raise your right foot over the cockpit coaming and plant it on the seat. Transfer grip of the Lewis gun to the right hand and use the other to help the remaining foot over the coaming. Slide down into the seat, being careful to place your feet only on the cross bracing struts of the cockpit floor. Have you got all that?
At this point, you, as pilot, become somehow other-worldly. Lord of all you survey, dependent on others to do your wishes and retrieve any dropped or forgotten items. However, you’d better treat your ground crew well.
The initial actions are the familar ones: check the mags are off, throttle closed and fuel on. Strap in, check the controls, ready helmet and goggles, turn on the radio.
Call to ground crew “mags off, throttle closed, priming”. (The Kinner engine has priming lines to the upper three cylinders only – hydraulic lock, remember.) “Primer closed and locked. Ready to suck in”.
Hopefully the ground crew replies with confirmation that he is now ‘sucking in’, i.e. pulling the prop through at least five blades to induce fuel vapour into all cylinders. Now it starts to become comedic. The prop-swinger (who is at risk and therefore has command of the performance until the engine is running) calls “chocks in, throttle set, contact”. You oblige with throttle and mag switches and confirm with a thumbs-up.
The engine goes ‘phutt’ on one cylinder, coughs more encouragingly on a second, and then bursts into irregular life. You are deprived of the sight of the carnival being enacted behind you as the brave and devoted ground crew, galvanised by the second cough, drops to the floor and rolls quickly under one of the rear fuselage lower booms to escape the increasingly lethal prop arc and rapidly billowing cloud of whitish-blue exhaust fumes.
Oil pressure rises immediately, and, after a short throat-clearing period for the spark plugs (more puffs of white smoke), the engine note settles to the point at which you dare risk a dead-mag check. Warm-up time is two to four minutes, depending on the heat of the day and any inclination you may have to delay the now inevitable commitment to launch.
Engine handling is very simple – no mixture control, no carb heat, fixed-pitch prop, etc. However, throttle movements in flight must be made with sensitivity, as abrupt changes may induce a second or two’s total silence from the beast behind. The mag checks are made at 1,600rpm, you check the idle, then set 800rpm and take a few moments to arrange the helmet and goggles, check the radio, altimeter and oil pressure. Then it’s back to idle, before waving away the chocks. At rest, the Lewis gun’s foresight sits on the distant horizon. This is the picture you will need for a good three-point landing – something that may come in useful later. After a last look around for any other traffic, line up, apply full throttle, get the stick forward and catch the swing – which may initially require full left rudder. You are airborne in ground effect after 150 metres, at less than 50 knots.
From now you have airspeed indication, altimeter, engine rpm, and a piece of string on the Lewis gun foresight serving as a slip indicator to help you. (Actually, providing that your cheeks are exposed and not already numbed with cold, the gyrations
of the piece of string are interesting, but superfluous: healthy blasts of air on
either cheek are waiting to announce any sideslip tendency.)
Maintain quite a heavy pressure on the left rudder bar during climb and you are rewarded with a reassuring 600 to 800fpm rate of ascent at around 60 knots. Settle
into cruise at 1,850rpm/70 knots, straight and level.
Rudder is actually the primary control in turns, and forces can be quite heavy. I’ll say that again: rudder is the primary control. In the DH2, you think ‘turn’, apply rudder and tidy it up with aileron. Left rudder pressure is to be maintained in the climb and can be tiring. Right rudder pressure is required if power is much reduced on the approach to land. The ailerons are quite effective at cruise and approach speeds, but suffer the typical adverse yaw of their era and are moderately heavy. Effectiveness is very much reduced below fifty knots. The elevator is light and powerful. There is no pilot-operated trimmer, but the aircraft is set up for the comfortable climb and approach speed of 60 knots. Cruise at 70 knots requires a 5lb forward stick force to maintain straight and level. A temporary bungee chord has been tried for transit flights and the aircraft can be trimmed quite nicely. The power-off glide characteristics encourage a healthy interest in the fields immediately below. Fear not, in the event of engine failure, any clear run in excess of 200 metres or so is more than adequate – but do be aware of wind direction. The approach to land will focus your attention in no small way. Flaps are replaced by airframe drag, ‘power off’ – and a moderate sideslip feels like freefall. Brakes are applied automatically when you get the tailskid down. It’ll be a three-point landing then…
Pick your approach into wind, reduce power to give a steady descent at 60 knots, anticipate a wind-shear induced airspeed reduction as you near the ground. Start to ease the rate of descent at 30ft. Reduce, but don’t cut the power. Rotate to almost level at 15ft, keep it flying, keep it flying, keep it flying… and somewhere south of 40 knots there’s a bump (without the Tiger Moth bounce from a softly sprung undercarriage) and you’re down but not yet finished. All you have to survive now is around 100 metres of ground roll. Keep it straight and be ready with full rudder and a burst of power to arrest any tendency to swing.
You probably now feel like completing a virtuoso performance by taxying with panache back to the start point. The first challenge then is to turn round through 180º to face downwind. You will need confidence, a goodly grassed area free of obstructions ahead and to the side, the stick forward, full rudder, large bursts of power and… patience. The DH2 will begin to turn and, once started, you have to keep the tendency alive with judicious bursts of power.
So, you are now taxying happily back down the field. This is the time to do a ‘dead mag’ check. You also have reason and time to think about mass balancing of control surfaces − or lack of it − as, energised by every small bump in the ground, the control column becomes a frenzied thrashing beast requiring two-handed restraint.
Overall, the DH2 is a flyer’s machine. Once you’re accustomed to the exposed cockpit, then the 70 knot buffet and the clatter of the Kinner will fade into the background and your senses will start to open to all that is happening around you. But you’re not necessarily in sole command – more a kind of accepted contributor to the process, who is allowed influence over progression through the ether. You’ve formed a partnership and, with time, the aeroplane will join willingly in your ever more spirited investigation of her abilities.