10848A – Air Tractor OEM Meggitt Oil Cooler Assembly
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The Air Tractor 10848A is a high-performance, flight-critical oil-to-air heat exchanger manufactured by Meggitt (formerly Stewart Warner/Dunlop) for the Air Tractor series of agricultural and firefighting aircraft. This OEM assembly is a vital component of the engine’s lubrication system, specifically designed to handle the massive thermal loads generated by high-shaft-horsepower turboprop engines, such as the Pratt & Whitney PT6A-67 series. In the demanding "low and slow" flight profiles of aerial application—characterized by high torque and reduced ram air—the 10848A ensures that oil temperatures remain within the strict green-arc parameters required to maintain viscosity and protect critical engine bearings.
Utilizing a sophisticated vacuum-brazed aluminum plate-and-fin architecture, the 10848A is engineered for maximum thermal rejection with a minimal weight penalty. The unit is designed to withstand high internal pressure transients, particularly during cold-start cycles when high-viscosity oil can create significant pressure spikes. Its ruggedized construction is specifically tailored to the Air Tractor airframe, providing the durability needed to resist the corrosive effects of fertilizers, pesticides, and fire retardants common in the field.
Key Features
Vacuum-Brazed Aluminum Core: Manufactured using advanced furnace-brazing techniques to ensure monolithic structural integrity and superior heat transfer between the oil passages and cooling fins.
High-Efficiency Turbulators: Features internal mechanical flow-disturbers within the oil channels to prevent laminar flow and maximize the Nusselt number, significantly increasing the rate of heat exchange.
Agricultural-Grade Corrosion Protection: Treated with specialized surface coatings to prevent intergranular corrosion caused by exposure to aggressive agricultural chemicals and saline environments.
Vibration-Resistant Mounting: Features reinforced mounting flanges designed to interface with the Air Tractor’s forward cowling, engineered to isolate the core from the high-frequency vibrations of the propeller and engine.
Optimized Air-Side Fin Pitch: The fin density is calibrated to provide maximum surface area while resisting clogging from dust, debris, and chemical residue typical of dirt-strip operations.
Technical Specifications
Part Number: 10848A
Manufacturer: Meggitt (Dunlop/Stewart Warner)
Component Type: Oil-to-Air Heat Exchanger
Material: High-Strength 6061 Aluminum Alloy
Application: Air Tractor Turboprop Aircraft
Operating Pressure: Designed for 100+ PSI continuous operation
Max Surge Pressure: Tested for cold-start transients exceeding 250 PSI
Core Style: Plate and Fin
Fluid Compatibility: MIL-L-23699 and MIL-L-7808 Turbine Oils
Aircraft Compatibility
Air Tractor AT-802 / 802A: Primary application for PT6A-67AG and -67F powered airframes.
Air Tractor AT-602: High-capacity cooling for heavy-load operations.
Air Tractor AT-502B: (Check specific engine modification and IPC for compatibility).
Note: The Air Tractor Illustrated Parts Catalog (IPC) is the final authority for part number verification based on aircraft serial number and engine dash-number.
Applications
The 10848A is utilized for Engine Thermal Regulation. It is typically mounted in the lower engine cowling or a dedicated cooling duct, where it intercepts the high-velocity slipstream. It serves as the primary heat sink for the engine's lubrication and reduction gearbox oil, ensuring the thermal stability of the powerplant during high-ambient-temperature "hot-day" takeoffs.
Why Choose 10848A?
The use of a genuine Meggitt 10848A oil cooler is essential for protecting the time-on-wing of expensive turboprop engines. Non-OEM "equivalent" coolers often fail to match the internal turbulator design, leading to localized oil "coking" and higher steady-state temperatures that reduce the life of turbine bearings. Furthermore, the 10848A’s structural design accounts for the unique cyclic loading of Air Tractor missions, where frequent power changes create constant thermal expansion and contraction stresses that would cause inferior coolers to leak.
The 10848A functions as a cross-flow heat exchanger where the heat transfer is governed by the principles of convective heat transfer. The internal turbulators are critical; they increase the Reynolds number of the oil flow, forcing it into a turbulent state even at lower temperatures. This disrupts the insulating boundary layer of stagnant oil against the cooler walls, allowing for a much higher convective heat transfer coefficient. The vacuum-brazing process creates a metallurgical bond between the cooling fins and the oil plates, minimizing thermal contact resistance. This ensures that the thermal energy from the $180^\circ \text{F}$ to $200^\circ \text{F}$ oil is efficiently conducted to the aluminum fins and subsequently dissipated by the ambient airflow, maintaining the engine's thermodynamic equilibrium.
Note: This is a flight-critical component. Prior to installation, the oil system must be flushed, particularly if the previous cooler was removed due to engine metal contamination. Use only approved MS-standard fittings and O-rings. Installation must be performed by a certified A&P/IA mechanic in accordance with the Air Tractor Maintenance Manual. Proper ducting alignment is essential to prevent localized hot spots on the core.