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de Havilland Chipmunk N1114V Modifications


ENGINE CONVERSION: Fitment of a six cylinder inline Ranger 6-440C-5 engine of 200 hp and strengthening of the bulkhead area to cope with greater engine torque – with this engine the standard Chipmunk cowlings were retained with just small vents or humps for clearance being added. The nose cowling cooling inlet for the original Gipsy Major engine on the port side was faired over and converted to the starboard side. As the Ranger engine had no electrical starter unit a hand cranking facility was incorporated on the port side immediately aft of the cowling and a Kopper Aeromatic variable pitch propeller converted the power.

WING CONVERSION: The wings were shortened by two bays (twenty inches) and the ailerons modified to suit although, unlike N13Y, on N1114V the flaps were retained – eighteen inch stall buffet strips were fitted to the wing leading edge approximately three feet in from the wingtip in order to help stall the outer wing for improved snap rolls. All fabric sections on the wing were replaced by aviation spec aluminum but the fabric covered control surfaces of ailerons, elevators and flaps were retained - triangular reinforcing plates (5 x 6 inches) were also added to the inboard section of the top of the wing where the skins overlapped. Cessna fiberglass wing tips completed the wing conversion.

OTHER MODIFICATIONS: Strengthening of the horizontal and vertical stabilizer (fin) attachments to the rear fuselage in order to prevent cracking due to stress loads during the ‘Lomcevak’ maneuver. The fitment of a 25% enlarged rudder to the design of Maurice Hunter ‘Pappy’ Spinks with a modified upper hinge to allow more throw to counter the effects of increased engine torque and slipstream effect. Better directional control during slow-speed aerobatic maneuvers such as the slow roll could also be achieved and strengthening through metal instead of fabric covering. To accommodate the modified rudder the fin height was reduced by about eight inches and that amount added to the rudder to act as a counterbalance.

ADDITIONAL MODIFICATIONS: The installation of a flat-opposed 6 cylinder Lycoming G0-435-C2 of 260 hp.@ 3400 rpm. with a new engine mount giving1 downthrust and with 0 offset and a completely redesigned one piece cowling which fitted over the nose and required the removal of the prop to service the engine. The standard Chipmunk with Gipsy Major 145hp engine was never fitted with an inverted fuel system so a flop tube was installed in the starboard rubber bag tank of twelve gallon capacity, a Bendix PS-5BD ‘all attitudes’ pressure carburetor and an inverted Christen oil system completed this part of the conversion. Once again an Aeromatic air controlled wooden bladed propeller was used with an overall diameter of 150” with modified pitch settings. With the closely cowled engine there was no room to fit an oil cooler and this was installed in the fuselage behind the rear seat and cooling ducts fitted in the fuselage. The centre section of the fuselage also received attention with beefed-up spars (7075-T6 material and specification 4130 steel plates) and a modified (flatter) dihedral angle in order to help with inverted flight - the centre section control box area in the cockpit which had proven liable to cracking with harsh aerobatic use was also beefed-up with additional plates.

The original seat pan was retained as it also housed the parachute but some strengthening of the lower edge was required to accommodate an additional seat belt making a five-point harness. Weight and balance, always critical on the Chipmunk, was closely monitored with 9 pounds being added to the tail wheel strut. Even the undercarriage legs received fairings, the standard wheel covers were retained and the braking system was converted to a Cleveland system.

A smoke system on the front cockpit floor comprised a tank, regulator and switch system introducing diesel fuel into the exhaust and thus allowing the crowd to follow the performance.

Total costs for modifications at the start of the 1970 season are reported to be $35,000 and the weight of the aircraft had increased by some 57 lbs to 1495.5 lbs. - air show performance with the larger capacity engine used at 80% power was quoted as 1200 feet per minute and speeds of 140-150 mph. Such was the wear and tear on the airframe that further strengthening work on the tailplane and lower rear fuselage was required and the wing root fittings required new bushings in February 1971 the aircraft having flown some 279 hours during that aerobatic season. At the time of the annual inspection in Feb 1972 the airframe hours are shown as 3763.9.

PAINT SCHEME: Pennzoil sponsorship was advertised on the rear fuselage instead of the Aqua-Craft titles and the change in engine cowling resulted in a revision of the color scheme ahead of the front cockpit to blue anti glare panel and a white line separating from the red upper cowling. In this form it was also known as ‘the Pennzoil Special DR Chipmunk’. The paint specifications are as follows: DuPont Dulux Enamel: Bluetone white 93-21667, Red 93-94124-N, Blue 3430.

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