The Collections Deperdussin is unique even amongst the Collections aircraft in that it is the only machine without any cockpit instrumentation whatsoever. If that were not enough, the pilot also has to contend with lateral control by wing-warping, a method of control that was aptly described by a recent Chief Pilot with the words: "It’ll never replace the aileron". But lets’ leave the handling qualities for later and look now at the history of the machine.
Although not a significant increase in power, when the 24 HP Fan Anzani in the Bleriot was developed into a three cylinder radial of 35 HP, it led to aircraft that could achieve much more than the Bleriot’s ground effect flight. The 1910 Deperdussin was one such machine. It also had a thin, streamlined, covered fuselage which further added to the performance by reducing drag; the result was an aircraft that performed rather than hopped. However, with due respect being given to the age and uniqueness the machine, at the time of writing flight demonstration of the Collection’s example is limited to hops only. Nevertheless, following confirmation of the engine’s integrity, a short circuit may be attempted when air and ground conditions permit.
It may be worth noting that a hop is defined by the Collection as a take off followed by a few seconds straight flight and landing on the same runway. It allows the Shuttleworth Collection philosophy of demonstrating the sight and sound of genuine historic aircraft and engines in their natural element to be followed without prejudicing their safety.
The Collections example is a school or ‘popular’ version of the machine constructed in 1910 and is thought to be the 43rd to have been built. It was initially used at Hendon, then offered for sale in a damaged state in 1914. Following purchase, A E Grimmer used it for some years with his Bleriot then both machines were sold to Richard Shuttleworth in 1935. It was restored to flight worthy condition and flew again in 1937. Apart from storage during World War II, during satisfactory weather conditions it has been a regular performer at Old Warden.
The machine is of wood and fabric construction, having conventional elevator and rudder for pitch and directional control and wing-warping for roll. The cockpit area is essentially a wooden bathtub for the pilot to sit in which gives minimal frontal area to minimise drag. The engine is lubricated by total loss castor oil and the tanks for that and the fuel are fixed to the longerons between the pilot’s seat and the engine. Sight gauges on the sides of the tanks give an indication of the relevant tanks contents.
Engine controls consist of an advance and retard lever located near to a single ignition switch under the cockpit coaming. Further in the depths of the cockpit, under the coaming, can be found fuel and oil cocks fitted in the fuel and oil lines. A rudimentary throttle, similar to that fitted to modern lawnmowers, is located on the roll and pitch control bracket and an ignition blip switch has been fixed to the control wheel.
Flight control is by conventional rudder bar for direction and control wheel for pitch and roll. The wheel is mounted on a bracket that is hinged to move for and aft for pitch and the wheel is allowed to rotate for roll. The system is simple in concept but gives several characteristics, all of which are in roll, that must be fully understood before the embryo Dep pilot takes to the air.
In order to prevent flutter in flight, wings must be torsionally stiff. However, for adequate roll control via wing warp, the wing must be readily twistable. For safety, the former of the two requirements must win, which leads to rather heavy roll control. Further, the neutral position is ill defined and in flight, little aerodynamic feedback serves only to make matters worse. So, if only to find the neutral position, the pilot must be ready for energetic warping as soon as the wing starts to work during the take off roll.
Let’s go flying. The first problem after walk round is mounting the cockpit. The help of a ladder is essential and great care must be taken as a liberal coat of caster oil, waiting to catch the unwary, will be found on most surfaces of the machine. The pilot’s position can only be described as exposed, but looking on the bright side, the resultant field of view from the cockpit is excellent. With no instruments, the cockpits checks are minimal, but time must be taken to identify the neutral position of the wing warp. Both planes are compared and when the pilot is satisfied that the wing is at zero twist, the relative position of the ‘blip’ switch on the control wheel is noted. The wing can now be easily set to neutral in flight should control difficulty be encountered. Engine priming and lubrication rate are set by ground engineers before flight so for starting, all the pilot has to do is set the fuel, oil and ignition on, set the timing to full retard and crack the throttle slightly. The latter is in good reach of the pilot, but the former controls are buried in the cockpit at the limits of the pilot’s reach and are not practically accessible in flight.
The propeller is swung and as the engine bursts into life the pilot juggles the throttle and timing to achieve smooth running. At low settings and when cold, only one of the three cylinders will fire, at higher settings, the engine tends to falter and may stop. There are no instruments so the engine rpm can only be checked by ear but in practice this is sufficient. As the engine warms, higher powers may be achieved. An engine run at full power with ground crew holding the tail down is carried out and the position of the levers are noted – normally full advance and three quarters throttle. Idle, however, is unpredictable and at its lowest setting with full retard and throttle closed, at worst, the engine is unstable and often stops, at best it provides too much thrust to stop ground movement. It proves better to set a fast idle and use the blip button to control power for taxy and thus accept the shock load that this method gives to the engine rather than risk the engine stopping just before a display flight.
The chocks are waved away and the aircraft taxied, with help, to the take off point. A final check is made by the pilot of his harness and the aircraft flight controls, and we are now ready for flight. Meanwhile, two groundcrew will have moved to the rear of the machine to take position holding the tailskid. A thumbs up confirms the crew are ready and the traditional rotating finger signals the intention to set full power. The levers are set and full power is checked by ear. A glance at the crew, who nod in agreement, signals that all is well and they are signalled to release the machine by the pilot raising then sharply lowering his right arm. We’re off!
The aircraft accelerates slowly but progressively for about ten or so yards. There is no feel to the controls yet and there is surprisingly little swing. With no flight instruments, control must be by feel and as the slow acceleration reduces, the control wheel is eased forward to raise the tail. It’s barely perceptible, but the acceleration rate improves. It is now vitally important that the pilot be ready for energetic control input in case of any upsets.
I’m going to take time out now to describe a fundamental characteristic of wing warp control that could be the undoing of the potential Edwardian aviator. Consider first a right wing drop. The instant reaction of the pilot will be to introduce left roll control. Edwardian aircraft fly at low speed with high angle of attack on heavily cambered wings. Putting in left warp increases the angle of attack on the starboard wing and reduces it on the port. One or both of two things happen. Either the right wing stalls, serving only to exacerbate the wing drop, and/or the increased drag on the right wing causes substantial right yaw. Although not too significant on the Dep, dihedral effect will lead to right roll and again, we have the opposite effect to that intended. The message here is use only the rudder to control any wing-drop, the wing warp should be used only to balance the aircraft. So, back to the take off.
If the wing drops, or the aircraft turns, only the rudder should be used to right the upset. If rudder control is insufficient, roll control may be used with extreme care, but it may have the reversed effect.
When the aircraft has reached its velocity limit, after a further 20 yards, say, the control wheel may be eased back to attempt flight. Again, aggressive use of the controls may be necessary to stabilise the machine. In the air, she is responsive in all directions and as speed increases and wing incidence reduces, the roll control will operate in the correct sense. However, as the machine is unstable in both roll and yaw, careful control input is required to prevent side-slipped flight. Sideslip will increase drag and thus reduce performance; in the limit it may cause an unintended premature return to terra firma.
Another characteristic of the roll system may now be noted. At times, more than 180 degrees of rotation will be required on the control wheel. To avoid crossed arms, the pilot then has to revert to the ten-to-two motor car driving technique much recommended by driving instructors. Two problems result. First, the neutral position is lost and even greater care must be exercised to prevent flight in sideslip. Second, as the advance and retard control is out of reach and the throttle is singularly ineffective on its own, the only way to reduce power for the descent and landing is to use the ‘blip’ button, the position of which has now most inconveniently moved relative to the pilot’s hand. The only course of action open to the pilot is to look into the cockpit to discover its position, which is not a desired manoeuvre as full concentration on the outside world is required at all times to safely control the machine.
We are now running out of runway available and the flight must be curtailed. The ‘blip’ button is pressed, power and thrust abruptly fall to zero and the nose must be lowered to prevent a stall. The manoeuvre is surprisingly easy, compared to the co-ordination required to fly the aircraft, and we sinks slowly to earth. There is no round out as such: the aircraft is flown until she runs aground. The throttle and ignition lever are reduced and the ‘blip’ button used to bring the speed under control. Hopefully, two groundcrew will appear at the extremities of the machine ready to arrest it and prevent an over run at the end of the field. They help turn the machine for taxy back or a repeat flight in the opposite direction if the wind speed allows.
After the display, the machine is eased back to its parking slot by groundcrew and the engine run at low power for a few minutes to temperature stabilise the engine. It is cut by switching off the ignition from a stabilised idle and the throttle is opened fully to clear the engine as it dies – frustratingly, the idle at this stage is nicely stable and the engine shows no desire to cut on its own. The cockpit is vacated carefully by ladder as entry.
Strangely, the lack of cockpit instrumentation is neither noted nor missed in flight. One could proffer the argument that most of the pilot’s concentration is in use in keeping the machine in flight and there is little left to assimilate extraneous information. Personally I believe that the machine is well designed and gives good feedback to the pilot making cockpit instrumentation an unnecessary and un-required extra.
When conditions permit – normally defined as the tops of the trees not moving – all the Collection’s Edwardian aircraft are demonstrated during the Collection’s open days. Although, apart from the annual pageant in September, only up to three of the five are demonstrated during any one show. So given an average season Edwardian flight should be witnessed about every third show. Life is never average and in 1998, the Edwardians flew on only one of the thirteen shows yet in 1999, they flew on all but one. However, even if the weather is not perfect, they are at least pushed out for public static display on any display day when rain is not forecast.
The five Edwardians are: Bleriot XI, 1910 Deperdussin, Blackburn 1912, Avro Triplane and Bristol Boxkite.
If you would like to see the machines in flight, the Collection holds a Display on the first Sunday of the month from May to October and during the evening of the middle Saturday of May, June and July.
If you would like to support the Collection more proactively, join the Shuttleworth Veteran Aeroplane Society (SVAS). The Society was set up to help the Collection both in kind and financially. Membership costs just £20.00 per annum and includes a quarterly magazine and concessions at the Collection. Details may be obtained from: The Membership Secretary, SVAS, PO Box 42, Old Warden Aerodrome, Biggleswade, SG18 9UZ.
© A J Sephton