I’m strapped in and ready, parked at the end of the duty runway. The sky around Old Warden is clear, the airfield closed to all other traffic. I’ve checked the cockpit, the switches are off. The blocktube and fine adjustment had full and free movement and are now closed, the fuel is wire locked on, and the Jones air pressure valve was free to move. The condition of the instruments was fine and the altimeter bezel was rotated so that the needle now points to zero. The fuel tank air pressure was pumped to 2.5 psi and is holding with no significant leaks. The flight controls have full, free and correct movement.
I call to the ground crew: “Switches off, ready to prime”. They turn the propeller slowly to expose each cylinder in turn and using an antiquated brass syringe, squirt a measured amount of fuel into each by depressing the exhaust valve.
They continue: “Switches off?” I confirm: “Switches Off”. They spin the propeller a few times to distribute the mixture. I check clear all round and confirm I have a man holding down the tail.
They shout “Set”. I open the blocktube about 35%, ensure the fine adjustment is closed and confirm: “Set”.
The groundcrew call: ”Contact”. I set the switches on, hold the control column hard back and reply: “Contact”.
They turn the propeller as sharply as they can, it turns slowly, there’s a cough, followed by another. The propeller accelerates, there’s a cloud of smoke, whipped over the cockpit as the engine bursts into life, a brief smell of burnt castor oil, then the engine’s winding down….. I slowly advance the fine adjustment to introduce pressurised fuel to the engine. If done too quickly, there’s a bang and silence (too rich). If too slow, the initial silence remains (too lean). Just right and the engine bursts back into life.
I shuffle the blocktube and fine adjustment levers to stabilise the engine at about 7 – 800 rpm. Each adjustment is made slowly and its effect noted before another movement made. The mixture of air and a certain amount of fuel from the blocktube must be matched to the fuel introduced by the fine adjustment. Too much or too little fuel will lead to a rich or lean cut – either way the engine stops. In practice, about 35 to 40% on the blocktube and about 30 to 35% on the fine adjustment gives smooth running at the required engine speed.
A minute after engine start she’s now warm and ready for a run up. The engine cylinder walls are thin for lightness and heat up easily. The oil is total loss, impossible to pre-warm.
I open the blocktube slowly to about 75%, the engine coughs and falters, before she loses momentum and stops, I slowly open the fine adjustment by about 5%, the engine picks up. I run her at about 1050 rpm for about 30 seconds, any more and she’ll overheat. Rotary’s can be run for about 2.5 minutes in the summer and about 3 minutes in the winter before overheating, but that’s all I need to check all is well. I check the rich and weak end of the running range with small movements of the fine adjustment – about 35 to 40% on the fine adjustment lever. I note the positions of both control levers for best power and bring her back to ‘idle’.
Time is now running out, I have about a minute left to get her off the ground before the engine overheats. I wave the chocks away. The engine is now ‘idling’ at about 800 rpm. It’s a very fast idle and gives about 60% thrust, far too much for taxi, or even a descent when in the air. I depress the ‘blip button’ on the control column, which instantly cuts the ignition. The engine noise dies, she continues to rotate, slowing all the time. Before she stops, I release the ‘blip button’, she bursts into life again, accelerating to her fast idle. I repeat the process and the groundcrew pull the chocks. Before we move off, I note the position of the far horizon with respect to the nose of the aircraft – I’ll need that later to judge the three-point attitude for landing.
The Pup edges forward, I release the ‘blip button’ and advance the blocktube, the engine falters. I advance the fine adjustment, the engine comes back, the aircraft swings, hard, to the left. Full right rudder brings her back, I centralise the rudder, she’s now off to the right, left rudder, centralise, control the swing…. We accelerate and the rudder has more effect. A small pressure on the control column lifts the tail. She’s off to the left again, but this time with more purpose – gyroscopic precession from the rotating engine initially wins over the small rudder, but as airspeed increases, she comes back onto the straight and narrow.
I ease back the fine adjustment slightly as the Pup accelerates – as airspeed increases, the propeller unloads, the engine accelerates and centrifugal force enriches the engine. I can’t support a rich cut on take off, so the mixture is leaned during the take off run.
The controls now have feel and presence, the aircraft is coming alive. She bounces over the grass, she’s talking to the pilot, the sign of a thoroughbred, she’s eager to fly. Slight backpressure on the control column raises the nose, slight right pressure on the rudder kills the precession and we’re in the air again…….
It’s been a long time coming. The Pup was on the ground for a year or so, undergoing major servicing which included a recover and repaint as a rocket equipped balloon fighter. Initial flight tests have been made without the rockets, as to fly them requires aircraft modification and CAA approval. The timeframe we gave ourselves didn’t allow for the flight testing of the rockets as there were other more important things to do with the Collection engineering time. But here’s hoping that we can get them into the air one day!
The Shuttleworth Pup came off the production line as a Sopwith Dove, the two seat variant of the Pup. She was initially constructed as a Pup, but was changed into a Dove during production. Older aviation lists will show her registered as a Dove from 1925. Richard Shuttleworth acquired her in the 1930’s and converted her back to single seat status. She has remained with the Shuttleworth Collection ever since. Now registered as a Pup, she retains her original registration of G-EBKY.
On the day, a final check of the paperwork was made, all was found in order. The loadsheet was checked again and the aircraft fuelled to the required weight.
As time goes on, aircraft, as with humans, gain weight. Further, as time goes on, the average weight of a human increases. In the days of the Sopwith Pup, the average pilot weighed around 10 stones, we (Collection pilot’s that is) now approach 15! The cleared all-up-weight of the aircraft was based on a pilot of the day, so it can be easily seen that we have a continual weight issue with the aircraft. We don’t have to carry ammunition any more, which helps, and we can wear less clothing as we don’t need to go to high altitude, but the problem remains. We manage it by reducing the fuel and oil carried, and by ballasting for the various weights of the pilots we use.
To reduce taxi time, the aircraft is moved to the end of the duty runway before flight. The pilot makes his walk Around check prior to strapping in and completes all checks prior to take off before engine start. Thus, once the engine is running, all is ready for flight. Any delay would lead to engine overheat, so the machine would have to be shutdown and a cooling period taken.
Now, lets get back to the flight…….
She’s climbing steadily at about 60 mph indicated, Shuttleworth airfield falls away beneath the wheels. The Pup is an absolute delight in the air. The feel of the controls is light and positive. Small pressures on the control column suggest to the machine where she should go and she follows without delay. Larger movements of the control column are answered with enthusiasm by the airframe, a large grin appears on my face. Alright, I admit that I’m looking at all of this with some rose-colour in my spectacles, and she is a little bit loose in yaw, but the machine is truly a delight in the air and nobody can take that away.
After take off, I make a gentle turn back over the airfield, always minded of engine failure in the early stages of the flight. The speed at lift off was about 45 to 50 mph and I can use that as a last-look over-the-hedge speed should the worst occur. We continue climbing, circling over the field, listening to the engine for any sign of distress and to the airframe for any weakness. Fuel tank air pressure is holding at 2.5 psi, although the needle is vibrating somewhat. Luckily, the Rotherham propeller pump is working well for if not, fuel air pressure would have to be maintained by the handpump – not a happy duty for the pilot. As the aircraft climbs, I ease back the fine adjustment to reduce the fuel flow to the engine to match the lowering outside air pressure. As with the acceleration on take off, if nothing was done during the climb, the engine would eventually run rich, then stop.
I stop the climb at about 2500 feet above Old Warden and let the Pup accelerate to cruise speed – the engine setting remains at full power. She settles at about 85 mph. Gentle control inputs and sideslips confirm that nothing is untoward with her reconstruction. The load factor is increased towards about 2 G, still nothing unusual is noted. In fact, the airframe is remarkably ‘tight’ – the boys have done an excellent job!
Now for some engine-off work. Remember, the fast ‘idle’ of about 800 rpm provides too much power for a descent at normal airspeeds so she must be shutdown to go down. Good practice is to shut her down by cutting the fuel rather than ‘blipping’. The latter shock loads the engine every time it’s applied, whereas cutting and re-introducing the fuel will give a more measured acceleration and deceleration and reduce engine loads.
I gingerly move the fine adjustment back, the engine falls silent, I return the lever, slowly to it’s original position and the engine comes back to life. I try it again and again, increasing the time with the engine off to ensure that engine handling is acceptable. Old Warden airfield is still underneath, I may need to return quickly if the engine decides not to re-start.
The engine’s fine, I leave her off for a few seconds longer and reduce the airspeed until the wings stall. The nose is high, wind noise reduces to an eerie silence, there’s a light buffeting increasing through the airframe, then, with a slight shudder, the nose gently drops, she’s had enough, the wings have stalled. Slight forward pressure on the control column further lowers the nose and un-stalls the wings, the noise increases as does the airspeed. I re-introduce fuel to the engine, she fires back into life. The air speed indicator at stall read 35mph, just as she has always done.
I now know that a good approach speed will be 50 to 55 mph, so I confirm that the airframe will accept full rudder sideslips in both directions with the engine off. Progressive left rudder needs progressive right aileron and the force on the controls increases with the deflection. It’s a similar story side-slipping the other way – just as it should be.
There’s just one more thing to try before a return to Old Warden, a simulated go-around. I cut the engine and leave her in a glide for about 500 feet. I bring the engine back on line and she picks up without faltering. I now know that if I need to go around on approach to land, the engine will not let me down.
I fly over the airfield and check the windsock. Whilst being a delight to fly, the Pup is very unforgiving in some areas; the landing being the most critical. It must be into wind and it must be on three-points. The engine is shutdown for landing, so there is little airflow over the rudder to control a swing should one develop. If she’s not into wind at the start of the landing run, then she will be at the end! Further, if she’s wheeled on, she’ll swing markedly to the right as the tail is lowered due to the gyroscopic precession of the still rotating engine. The precessional swing is now more powerful than the rudder and she’ll certainly ground loop.
Looking down, I find a path into wind on the ground in the middle of the airfield. I only need about 50 yards once I’m down, so I can afford to aim well into the field. I fly abeam the planned landing line, about ½ mile displaced and in the opposite direction to that of the planned landing. We’re about 800 feet above the ground. I’ve checked my harness is tight and fuel air pressure is holding – both are good.
Abeam the touchdown point (the middle of the airfield), I cut the engine by retarding the fine adjustment lever. Engine noise stops, wind noise remains. I look at the touchdown point and start a spiral towards it. I check the aspect of the ground. If it steepens, I ease out of the turn to lower it. If it lowers, I turn into the airfield to steepen it. Eventually, I find a happy medium when the touchdown point aspect remains the same. I continue the gentle turn down into the field. As I approach the airfield boundary and I’m sure of getting in, I steepen my approach with sideslip and bring the touchdown point nearer the boundary fence. At about 50 feet to go, I slowly move the fine adjustment forward to bring the engine back on line, engine noise increases, as does power – I kill it with the ‘blip switch’ before it takes effect. I now have useable engine that I can bring on line by releasing the ‘blip switch’, should I need it to control a swing.
I bring her out of sideslip and align her with the direction of flight. I hold her off. The nose comes back, slowly, slowly, the picture out of the front of the aircraft is as noted before take off. I feel a rumble as the wheels touch the Old Warden turf. There’s no time for self congratulation, she’s off to the right, or is it the left, no it’s the right, now left….I dance on the rudders, release the ‘blip switch’, the engine fires, she backs off to the left, I retard the fuel, now to the right, I bring the blocktube back to fast idle, right again, replace the fuel, then ‘blip’ as the aircraft slows. We come to rest in a final flurry of rudder input and “blip switch”. The engine’s now brupp-brupping, oblivious of the frenzied activity of a few moments ago, but the airframe’s still pointing in the direction we started – a success! I let the engine temperature stabilise for a minute at slow idle, then I cut the fuel. The ensuing silence is broken by the sound of the approaching ‘Fergy’, the boys (and girls) have arrived to tow me back in. I can’t stop grinning, but neither can the groundcrew – the successful flight was as much theirs as mine.
I forgot to tell you about the oil. It’s important to the engine that oil flows throughout the time that the engine is running. An oil pulsator is located on the instrument panel to check this fact. The pilot should note the slow raise and fall of the meniscus in the pulsator as the flight progresses. I have to say, I have yet to notice any change in the level at any time. Notwithstanding, as the oil system is total loss and a copious amount is thrown out of the engine during operation, the pilot is never in any doubt that oil is flowing. And that is a fact that I shall confirm when I get up tomorrow morning………….
© Andy Sephton