Flight, December 1937

THE PERCIVAL "TWINS"
The Q4 and Q6 Monoplanes: Choice of Engine and Undercarriage Installations Cruising at 185 m.ph. with Two Gipsy Six IIs

   THE elegance which has always been associated with the Percival monoplanes is well preserved, and even enhanced, in two recently announced additions to the range. But whereas our ears have hitherto been regaled with delightful names of ornithological derivation, the newcomers will be known as the Q4 and Q6, depending on whether the engines are Gipsy Major IIs or Gipsy Six IIs. Captain Percival considers that he has very good reasons for adopting this system of nomenclature.
   The two new Percival models belong to a class of aircraft in the construction of which Great Britain has always excelled: they are low-powered twin-engined machines calculated to appeal to the well-to-do private owner and to the air-line operator for feeder or charter work. Quite apart from these qualifications they have obvious applications in a military air service, notably for training.
   A large number of parts are interchangeable between the two models, and the dimensions of the cabin and luggage compartment are the same in each case. The span of the Q6 is, however, 2ft. 8in. greater than that of the smaller machine.
   In principle the wing construction follows standard Percival practice. There are two closely spaced box spars with plywood webs, spruce flanges and stiffeners of spruce placed quite close together and connected by a system of rigid bracing members (taking torsional and drag loads) in the planes of the top and bottom flanges, attachment being by plywood gusset plates. The cross-bracing members are parallel, whereas in previous Percival machines the upper and lower members in each bay were arranged in lattice formation. The rib structure, with diaphragms, is seen to advantage in the accompanying sketch. Except for one small section inboard of each aileron the wing is plywood covered, for the greater part, with 3 mm. ply, although that over the nose section is 2 mm. Suitable stiffening is provided for the leading edge on the inner bays. The internal structure is carefully protected against deterioration before covering. The ailerons are of high aspect ratio and are of similar construction to those of the Vega Gull.
   As the wing is built in three separate sections (centre section, with spars running through the fuselage, and two outer panels) it is a comparatively simple matter to arrange for the wings to fold, although the standard versions of the Q4 and Q6 are not so equipped. The wing fittings are of stainless steel.
   The split trailing edge flaps are in four sections, and are vacuum-operated by the Theed system from a switch in the cockpit.
   Four fuel tanks - all of approximately 20 gallons capacity - are housed in the wing, two being in the centre section and the other pair in the outer panels. If required, additional tankage for 10-15 gallons could be housed outboard. The oil tanks are behind the engines.
   Installed in a machine like the "Q," the inverted air-cooled de Havilland engines are particularly happy. The thrust line falls conveniently in relation to the wing, and the tail fairing behind the inverted cylinders is ideally suited for housing the retractable undercarriage, if specified.
   As already intimated, the engines are normally 140 h.p. Gipsy Major IIs (Q4) or 205 h.p. Gipsy Six IIs (Q6) driving "1,000" size de Havilland two-position variable-pitch airscrews.
   The basic "Q" design is stressed for engines of up to 300 h.p., which gives quite a choice of alternative power plants if such should really be necessary.
   The first “Q” machine will be demonstrated with the fixed undercarriage, which has trouser-type fairings merging smoothly into the engine cowling. The fixed version is essentially similar to the retractable gear, although the jointed radius rods which characterise the latter are, of course, deleted. Each unit incorporates two long-travel compression legs with steel springs taking compression and hydraulic recoil dampers. Wheels and tyres are Dunlops and the brakes are Bendix.
   Basically, the shapely fuselage is a plywood box with stringers and formers carrying the fabric fairing. The nose section, forward of the front spar, has plywood covering over an arrangement of formers and stringers. The grain of the nose sheeting is set at 45 degrees to prevent buckling. There is cross-bracing in the rear section of the fuselage, though the cabin itself is unrestricted except for the spars which cross the floor but are very little hindrance. Detachable panels under the nose facilitate inspection. The nose, incidentally, houses the air intake.
   Of typical Percival design, the tail has a cantilever fin and tailplane, and rudder and elevator incorporating trimming tabs.
   The pilots' compartment ends at the front spar and will accommodate two side by side. A quite exceptionally neat windscreen of Plastilume-moulded Rhodoid is fitted and, apart from being aerodynamically efficient, conveniently sheds rain.
   Swing-over controls are used in conjunction with two sets of rudder pedals. The prototype has the majority of the instruments grouped on the port side, the opposite panel bearing the air temperature and fuel gauges. On the extreme port side are grouped duplicated A.S.I.s, tachometers and boost gauges (the latter are necessary to measure the ''depression'' in the induction systems of the D.H. engines), and then come the Sperry panel, starter buttons, pitch controls, air intake controls and flap switch. The comfort of the pilot has been well considered, and there is no lack of such items as map pockets. View, as will be gathered from the G.A. drawings, is well up to standard for this type of aircraft.
   The cabin has been treated by Rumbold; that is sufficient indication of the standard of finish and comfort. There are four chairs and, at the rear end on the starboard side, a fine luggage locker, measuring 20in. by 39m. by 26in., and holding 200 lb. Access is through a door on the port side at the rear of the cabin. Dimensions of the cabin are: width, 4ft. 4in., average height 5ft. 2in., length 9ft. 2in. A bulkhead or heavy curtain between the cabin and the cockpit is optional.
   Provisional prices are: Q4, with fixed undercarriage, ?3,975; Q6, with fixed undercarriage, ?,4,350. The following are included as standard: Landing light, navigation lights and instrument lights, bonding for radio, electric starters, electric generator, artificial horizon, direction gyro and normal engine and flying instruments. Wings and tail surfaces will normally be finished in silver, with the fuselage any one colour.
   Orders have already been received for a number of "Qs," and delivery has been promised for January. Work has started on a batch of ten ; when those have been despatched another, dozen will be put down. The prototype has done about 20 hours' flying and will soon be off to Martlesham.
   According to Captain Percival, the "Q" reproduces many of the familiar and popular Percival characteristics. The approach is quite steep, and the take-off run of the Q6 with full load in no wind is, on an average, 200 yd. The machine will fly, with the help of the trimming tabs, hands and feet off with one engine out of action.
   The cabin gives a delightful sense of roominess, and the decibel reading must be very low.

PERCIVAL Q4 and Q6
Light Twin-Engined Cabin Monoplanes
   Q4 Q6
   Engines Gipsy Major II Gipsy Six II
DIMENSIONS
   Span 44ft. 46ft. 8in.
   Length 32ft. 3in. 32ft. 3in.
   Height 9ft. 9in. 9ft. 9in.
   Wing area 260 sq. ft. 278 sq. ft.
WEIGHTS
   Tare weight 2,740 lb. 3,200 lb.
   Gross weight 4,525 lb. 5,100 lb.
PERFORMANCE
   Top speed (sea level) 170 m.p.h. 195 m.p.h.
   Cruising speed (7,000ft.) 165 m.p.h. 186 m.p.h.
   Landing speed (with flaps) 44 m.p.h. 50 m.p.h.
   Service ceiling 20,000ft. 21,000ft.
   Ceiling on one engine 5,000ft. 6,500ft.
   Range at cruising speed 660 miles 750 miles

Flight, October 1938

British Commercial Aircraft

PERCIVAL

   ALTHOUGH the Percival Q.6. has only been in existence for a comparatively short time, quite a number of them are in use, and, more recently, two have been sold for internal air­line work in Lithuania. There are actually two versions of the Q type; one, the Q.6., is fitted with Series II Gipsy Six engines and v.p. or constant-speed airscrews, and the other, the Q.4., is fitted with two Gipsy Majors. The latter is not perhaps so well known, and the more important figures for loading and speed are as follows: All-up weight, 4,750 lb.; weight empty, 3,000 lb.; maximum speed, 173 m.p.h.; cruising speed (with fixed undercarriage), 155 m.p.h.; and standard range 700 miles.
   With two Gipsy Sixes the Q.6. may be described as a six-seven-seater de­signed for the fast yet economical work either on airlines or for special charter and general military or civil duties, though one or two private owners are already using them. As in the case of the smaller Percival types the structure is of wood with a new type of torsionally rigid spar and ply-covering for the three-section cantilever wing, and plywood box construction with fabric covering (carried on stringers and formers) for the fuselage. The tail unit is fully cantilever. In standard form the undercarriage is fixed and is faired in deep trousers, but the retractable type of undercarriage can be fitted if the purchaser so desires.
   In the ordinary way the cabin is arranged without a bulkhead between the pilots’ section and that used by the passengers. Dual control is provided, with the throttle, mixture, airscrew, flap, brake, and trimming controls centrally disposed between the two pilots. The standard equipment includes Sperry free gyro instruments, landing and navigation lights, and engine starters. Heating and ventilation are controllable.
   Percival Q.6. data: Span, 46ft. 8in.; length, 32ft. 3in.; all-up weight, 5,500 lb.; weight empty, 3,500 lb.; wing-loading, 19.8 lb./sq. ft.; power-loading, 13.4 Ib./h.p.; maximum speed, 195 m.p.h.; cruising speed at 7,000ft. (fixed undercarriage). 172 m.p.h.; landing speed (with flaps), 58 m.p.h.; service ceiling, 21,000ft.; ceiling on one engine, 6,500ft.; rate of climb, 150ft./min.; and cruising range with standard tankage, 700 miles.
   Makers: Percival Aircraft, Ltd., The Airport, Luton, Beds (Luton 2960), and 20, Grosvenor Place, London, S.W. 1 (Sloane 3274).

Flight, September 1939

To-day's Light Aeroplanes

PERCIVAL

   The Percival Q.6 is a twin-engined low-wing monoplane designed for fast feeder work, charter services or private ownership. It has two Gipsy Six Series II engines with v.p. airscrews, and is normally equipped as a 6-7-seater, though for training or ownership, of course, smaller accommodation would be arranged. The standard equipment includes a free-gyro panel, navigation lighting and electric starters, while the machine is bonded for radio. In fact, it is exceptionally well equipped in normal form. Several Q.6s have been used by private owners and others, of course, for airline and charter work. These figures are for the type with a fixed undercarriage.
  
Span 46in. 8in.
Length 32ft. 3in.
Weight empty 3,600 lb.
All-up weight 5,600 lb.
Max. speed 195 m.p.h.
Cruising speed 172 m.p.h.
Landing speed (flaps down) 58 m.p.h.
Initial rate of climb 1,150 ft./min.
Range 700 miles.

Flight, November 1939

Britain's Civil Aircraft

PERCIVAL

   THE largest of the Percival series is the Q6, a six/seven-seater cabin monoplane with two D.H. Gipsy Six Series II engines. A fixed or retractable undercarriage can be fitted, data for the version with the retractable gear being: Top speed at sea-level, 195 m.p.h.; cruising speed at 7 000ft., 181 m.p.h.; take-off run, 200 yards, and range, 700 miles.

Percival Aircraft, Ltd.. Luton Airport, Beds.