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The first Rollason built D.31 Turbulent G-APBZ

G-APBZ1The construction of G-APBZ was started in June 1957 at Croydon and its first flight was on the morning of 1st January 1958, at the controls was the owner of the Tiger Club, Norman Jones. In spite of a gusting wind and light rain, the smart blue machine gave an impressive show on a number of circuits and low runs across the field. It was the first of a batch of five in the initial production run. The Rollason built aircraft were different from the original French design, they included some changes to the Druine Ardem 4CO2 engine, which itself was a conversion of the four cylinder air-cooled 1192cc capacity Volkswagen car engine. Rollason’s actual conversion work involved the installation of dual ignition and a carburetor heater, this work was done at the Croydon engine shop. The major differences in the airframe were the smaller wheels, the tailskid and the top cowling "bump" which covers the carburetor air heater.

Rollason’s announcement at that time was that they were planning to market complete aircraft for about UKL1000 and also complete kits or components for amateur assembly would also be available. The engine which produced 30 b.h.p. would be available at UKL272 per unit. Rollason went on to produce 35 complete aircraft between 1958 and 1966 and sold many plans.

The first Turbulent seen in England was a French built one that toured the country in 1956 being flown by Harold Best-Devereux and over 80 sets of plans had been sold by 1958 by the Popular Flying Association. The PFA chose the Turbulent as the first imported type for amateur construction in the U.K.

A full flight test program was carried out on this aircraft between 12th January and 11th April by Lt. Cdr. J.R.S. (Jack) Overbury RN, who was the test pilot at Saunders Roe Ltd. He wrote up a full test report on this aircraft and some extracts are reproduced here to give a flavour of what it was like.

Brief Handling & Performance Trials of Druine Turbulent D.31 - G-APBZ dated 15th May 1958.

Condition of Aircraft

The aircraft was the first prototype Turbulent built in the U.K. by Rollason Aircraft and differed from the standard French model in having a non-standard instrument panel and smaller diameter wheels with tail skid. The Ardem 4CO2 modified Volkswagen engine was used in conjunction with a Merville Type 880, 4 ft 8 ins x 4 ft pitch propeller giving a reputed 30.7 b.h.p. at 3,000 r.p.m.

Loading of the Aircraft
The aircraft was flown at a take off weight of between 606lbs and 577lbs, and at an estimated c. of g. position at take off of between 16.7 inches and 17.6 inches aft of datum.

Number of Flights
A total of 17 flights were carried out with a total flying time of 10hrs, 10mins. A few of these flights were cross country and demonstration flights. The weather conditions varied from zero wind and smooth air to strong winds of 20 gusting 25kts with moderate to strong turbulence.

Handling at Take off
The aircraft was lined up into wind, on grass, and the throttle opened smoothly to the full throttle position. With the r.p.m. showing 2850 and the oil pressure 47 p.s.i., the aircraft moved forward and the rudder became effective immediately. A slight swing to starboard was corrected easily and immediately with a 2 inch movement of the port rudder and only light foot loads. The stick was held approximately 1 inch forward of its neutral position and the tail rose at 18 - 20 m.p.h. I.A.S. The stick was centralised and there was no tendency to swing further. The ailerons became effective between 26-27 m.p.h. I.A.S. A rearward movement of the stick to about 1 inch aft of neutral lowers the tail of the aircraft to its flying attitude and the aircraft left the ground at about 30-32m.p.h. I.A.S. with a rather indeterminate unstick. All controls were very light and responsive and a little care was required not to touch the tailskid again. The propeller clearance was such that there was little danger of it striking the ground during take off, even with an exaggerated tail-up attitude. The view, once the tail is up, is very good. There was no evidence of crabbing, pitching or trim change at, or after, take-off.

Take offs. Performance.
In this test, made at Ford Royal Navy Air Station, the aircraft was lined up at a pre-set point on the grass in front of the control tower facing into wind and a series of eight take offs were made. An observer in the control tower marked, on a gridded photographic chart of the airfield, the point where the aircraft cleared the ground. The average distance was 150yds.

Approach and Landing
Some simple tests were made to determine minimum flying speed and it was found that the aircraft could be flown straight and level at 35 m.p.h. at about 2400 r.p.m. and medium turns could be carried out.

Due, however, to a rapid decrease of speed with increase of incidence and to line up with the final selected climbing speed (of 50 m.p.h.) an approach speed of 50 m.p.h. I.A.S. was chosen and in practice gave an adequate margin over the stall speed for manoeuvring without causing any marked float on landing.

With the aircraft lined up with the runway, and the engine throttled back (r.p.m. 1500), an approach was made at 50 m.p.h. I.A.S. the stick being held about one inch back from the neutral position with very light load. Speed stability is reasonable under normal conditions and the speed was immediately responsive to power or incidence changes. The speed was reduced to 45 m.p.h. "over the hedge" and with a movement of the stick rearwards to about two inches off of neutral position, the aircraft was rounded out. The float was not unduly prolonged and the aircraft touched down on three points at 26 m.p.h. I.A.S. No swing was evident after touch down and the aircraft came to rest in a commendably short distance on grass.

No crabbing or pitching was evident on the approach and the view was very good. Average landing run was 120yds.

At a height of 1800 feet, engine throttled and 1100 r.p.m. indicated, the speed was reduced at about 1 m.p.h. per sec. or 1.0g indicated. The controls did not lighten perceptibly and there was absolutely no aerodynamic stall warning prior to the stall proper at 26 m.p.h. I.A.S. At the stall, the stick was about 2 inches aft of the neutral position and the force required at the controls was negligible. The aircraft showed no tendency to pitch up at the stall. When the stall occurred the nose pitched down firmly to about 20-30° below the horizon at a moderately fast rate. There was no tendency for the aircraft to drop a wing or yaw and no tendency to enter an incipient spin. All the controls remained responsive to the stall though the ailerons and rudder became much less effective just prior to the stall, the elevator retaining its effectiveness. Normal recovery action of stick forward and power on was immediately effective and height lost was approximately 50 feet.

To summarise; this aircraft is a small reasonably inexpensive attempt to produce a "sports plane" within the ultra light category. To achieve economy of running costs a low powered, long life, engine is employed. The aircraft itself has handling qualities reminiscent of the best in fighter aircraft design - crisp light responsive controls are allied to immediate aircraft response and combine to produce true sports plane handling. Lack of stall warning is a drawback that may be inseparable from good design but fixed wing-tip slots produce a stall of such safe characteristics as to somewhat compensate for the lack of warning.

G-APBZ had only a short life. It ended its days when it was destroyed in a forced landing after take off from Berck-sur-Mer, France on 15th April 1963.

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Essex RM14 2TN

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