Riddle C-46R Commando

1957 civilian conversion.

Unknown number of C-46A, C-46D, C-46E and C-46F converted.

By the mid-1950's, Riddle Airlines had become the world's largest Commando operator, with around 30 units in its fleet. The sheer size of its Commando fleet made it meaningful for them to develop their own Commando conversion, featuring improvement similar to those included in the CW-20T conversion already on offer from L. B. Smith Aircraft Corporation. On 12 March 1957, supplemental type certification was awarded by the CAA to Riddle's C-46R conversion.

Riddle started upgrading its own fleet of Commandos, and by 1958 all 35 units in its fleet had been upgraded to C-46R standard. The performance improvement was such, that on the New York, NY to Miami, FL route - Riddle's most important one - flight time was reduced from 5 h 50 to 4 h 50, and payload increased from 11,500 to 13,500 lbs. Operating costs were reduced from 11 to 9 cents per ton-mile.

Three C-46R variants were on offer, with varying degrees of enhancements: C-46R-1, C-46R-5 & C-46R-10. The conversion encompassed many modifications to the original Commando, including:

• The replacement of the old B-series R-2800-51 or -75 engines by the enhanced C-series R-2800-34, featuring several major design improvements including a longer TBO. Horsepower was ramped up from 2,000 to 2,100 per side. An ingnition analyzer system simplifies fault finding. Fuel flow indicators and carburetors with manual leaning-off control improve the fuel consumption. BMEP gauges are installed to indicate power output. Engine cooling is enhanced by micro-positioning cooling gills mounted on top of the engine cowlings.
• A new stainless steel firewall, completely separating the power and accessory section of each engine.
• An improved engine fire protection system, featuring an Edison continuous-wire fire detection system, a Kidde CF3BR fire extinguisher system and fire-proofing of all emergency wiring, fuel lines and oil lines in the fire zones.
• Extra fuel and hydraulic pumps, including an electrical auxiliary hydraulic pump able to pressurize all components of the aircraft without the need for an external hydraulic cart on the ground.
• New wheels and BF Goodrich brakes.
• Larger accessory access compartment doors to make maintenance easier.
• Improved freight equipments, including reinforced flooring covered with plywood, able to sustain 903 kg/m², and the ability to attach the plywood under the cargo door to minimize damage from ground equipment. Freight lashing points were provided in the cabin walls and floor. Two belly luggage holds were created, each with a 1.04 x 0.97-meter door and a capacity of 5.58 m³ / 3,450 lbs (forward) and 6.65 m³ / 1,750 lbs (aft).
• A new instrument panel featuring red night lighting and improved radio navigation equipment.
• New Janitrol heaters providing 100,000 BTU for the cockpit and 200,000 BTU for the cabin.

The resulting performance increases and operational improvements were as follows:

• Maximum takeoff weight increased from 45,000 to 50,000 lbs.
• Passenger capacity increased from 40 (or 44) to 62 seats.
• Cruising speed of 195 knots at 10,000 ft.
• Maximum range of 1,390 NM with 400 USGal of fuel.
• Service ceiling of 22,000 ft.
• Sea-level MTOW climb rate of 1,140 fpm on all engines, and 315 fpm on one engine.
• Takeoff distance required of 938 meters, or 1,670 meters with an engine failure at 100 knots.
• Landing distance required of 1,055 meters.

Soon thereafter, Riddle started licensing out the C-46R conversion to other workshops: American Airmotive Corporation of Miami, FL and Officine Aeronavali of Venice, Italy. Customers included:

• Westair Transport of Seattle, WA (4 airframes converted).
• L & J Trading Company (3 airframes converted).
• RANSA of Venezuela (13 airframes converted).
• Delta Air Lines of Atlanta, GA (5 airframes converted) which used the type for cargo only and dubbed it the Super D-46.
• Fred Olsen of Norway (at least 3 airframes converted).

Converted by American Airmotive Corporation:

• Curtiss C-45A-45-CU Commando: N7772B

Converted by L & J Trading Company:

• Curtiss C-46A-55-CK Commando: N7848B (demonstrator)

Converted by Miami Airlines:

• Curtiss C-46A-35-CU Commando: N10435

Converted by Officine Aeronavali:

• Curtiss C-46A-40-CU Commando: N9887F
• Curtiss C-46A-45-CU Commando: N9889F, N9888F

Converted at unknown locations:

• Curtiss C-46D-10-CU Commando: N9883F, N9884F, N9885F