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Aviation History
1956
1956 - 1510.PDF
666 FLIGHT HANDLING THE E.P.9 Edgar PercivaVs Agricultural and Bush-flying Aircraft By C. M. LAMBERT LAST week I went to the Edgar Perdval Aircraft, Ltd.,factory at Stapleford Tawney Airfield, Essex, talked with' Mr. Edgar Percival, looked at E.P.9 production and flew the first prototype G-AOFU. The E.P.9, which still has no name, is being built in batches often, and the first batch is now in recognizable form in the works. Material is on hand for some 50 machines and most of the fabri-cated components for the second ten are ready. The first com- pleted production machine has been packed and dispatched toNew Zealand. It is remarkable that production aircraft differ hardly at all fromthe prototype. Main innovations are that toe brakes are substi- tuted for a ratchet hand lever; the cockpit instruments are slightlyrearranged; and engine cowling panels and rear-loading door have been redesigned so that most panels have only single asopposed to double curvature. The latter change brings obvious savings in production and repair. As foreshadowed some timeago, the tailwheel suspension has been changed from rubber in tension to rubber in compression, improving efficiency andsimplicity. The E.P.9 is offered not only for agricultural work, but also forsupply dropping, ambulance, passenger and freight duties, com- munications, photography and geophysical survey. It can operatefrom short strips, has a freight cabin volume of 185 cu ft, and can carry six people and baggage, including pilot. It has a cruisingspeed of 128 m.p.h. and can lift a maximum useful load of 2,190 lb. Access to the rear cabin is by a door to port orthrough the clam-shell door under the tail. Standard 44 gal petrol drums can be rolled straight in at the back. The wing is metal covered3 as are flaps and ailerons. Steeltubing and fabric covering have been used for the fuselage. Main and tail undercarriage legs have rubber disc shock absorbers withFerodo snubbers for damping. The hydraulic disc brakes at the main wheels take care of steering, the tailwheel having only alight centering spring. The engine is a Lycoming GO-480-B1B geared, unsupercharged unit driving a Hartzell metal, two-bladed, constant speed propeller. Take-off power is 270 h.p. The two-place cockpit is located very high up, ahead of thewing leading edge and almost clear of the top of the engine. The windscreen is therefore extremely large and affords superbvisibility. Two extra small windows above the wing root give very good visibility over the wing during turns in either direction.Neither seat nor rudder pedals are adjustable in the prototype, but the position and cushioning is comfortable. Only lap strapsare provided. Flying controls are fully duplicated and the instru- mentation, including basic blind-flying instruments, is clearlyvisible from both sides. Flap, brake, fuel hand-pump, primer and engine control levers are between the pilots. Two metal tanksin the wing roots hold a total of 56 Imp. gal. Battery and genera- tor, with electric starter, are standard equipment. Flaps andailerons are slotted, the former being mechanically actuated by a three-position lever, and the ailerons droop automatically to15 deg when flaps reach 30 deg deflection. I flew first with Mr. Percival. The turn-and-bank indicatorhad been removed, but he nevertheless carried out some perfect cloud-flying without instruments, while trying unsuccessfullyto get above the lowish cloud then prevailing. After ten minutes we landed again and I took over, flying from the right-hand seatbecause I like a left-hand throttle. Visibility was then some- thing over a mile and cloud-base was down to 700ft. I had a one-third fuel load and 3£ cwt of gravel in the back. The e.g. was at the 27 per cent mid-setting. The engine was very smooth indeed and noise level was notexcessive. Throttle and propeller-pitch control response were admirably precise. Taxying, using bursts of throttle to initiate turns and brake to straighten up, was simple. Some difficultyI experienced in turning on very wet grass was traced to a sticky tailwheel swivel. This part is different in production aircraft.Ample braking power was available and the ride on the ground was smooth. Undercarriage track is no less than 10ft lOin. I found the handling characteristics of the E.P.9 in the air verygood indeed. Visibility, as stated before, was superb, with a relatively small blind area directly astern. The engine is mountedon the fore-and-aft axis, being tilted neither downwards nor to one side, and the wing, of 12 per cent thickness/cord ratio, isquite thin; overall drag appears to be low. Trim changes caused by variation in power setting were negligible. Controlforces remained remarkably constant over the whole speed range which I tried (40 m.p.h. to 125 m.p.h.) and never became exces-sive. The three controls were well harmonized, with the excep- tion that the ailerons became heavy at large deflections. This hasbeen cured in production aircraft by re-arranging the aileron gearing. Take-off was simple. Rudder became effective soon after open-ing die throtde and the E.P.9 got airborne cleanly without particu- larly wanting to have its tail raised. Unstick speed was verylow, acceleration quick and the ensuing climb most satisfyingly steep. For take-off I used the recommended setting of 30 degflap (ailerons drooped) and set the trim lever in the roof two-thirds forward. The trim lever had, I found, its own friction nut. Though30 deg of flap are normal for take-off, die best climb is achieved with the 10 deg setting, and this can be selected after take-off withno noticeable sink. The trim change is firmly, but not heavily, nose down. Maximum engine r.p.m. are 3,400, a normal climbsetting being 3,000 r.p.m. and -2^ lb intake pressure. I tried the aircraft first at 95 m.p.h. widi 2,900 r.p.m. and —7 lb.It appeared to be somewhat more stable laterally than directionally so that, with hands off, rudder application caused plenty of yawwithout very much bank. With feet off, successive reversal of bank resulted in some yawing away from the direction of changeof bank. This was not pronounced, however, and Mr. Percival told me it is possible to initiate a co-ordinated turn with aileronalone. From a trimmed condition at 95 m.p.h. I pulled the nose about 15 deg up and let go of the stick. Very slowly the nosedropped again after the speed had fallen off about 10 m.p.h. For a while the aircraft continued in a very gentle dive, and then,after gaining about 15 m.p.h., it made a positive recovery to the The Percival E.P.9 has an ample freight hold, as can be seen from these two views. Above, the clam-shell door is open to show the freight floor reaching forward to the engine bulkhead. A man may stand up- right in the cabin. "Flight" photographs
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