Aircraft environmental control: An ordinary passenger aircraft typically requires an air-conditioning (cooling) capacity closest to which tonnage?

Introduction / Context:
Aircraft environmental control systems (ECS) provide ventilation, pressurization, and cooling. For sizing and academic problems, a representative cooling tonnage is often cited for “ordinary” passenger aircraft.

Given Data / Assumptions:

• “Ordinary passenger aircraft” refers to small-to-medium capacity passenger airplanes in textbook contexts.
• Cooling tonnage is the refrigeration rate; 1 TR = 3.517 kW of cooling.
• Loads include people, equipment, solar and skin heating, and ventilation air cooling.

Concept / Approach:
Rule-of-thumb classroom values place ECS cooling capacity for such aircraft on the order of several tons of refrigeration. Among the offered choices, 10 TR aligns with widely used illustrative estimates and permits handling peak cabin and avionics loads with margin.

Step-by-Step Solution:

Verification / Alternative check:
Typical ECS pack capabilities for small commuter jets or turboprops fall in the tens of kW, supporting the 10 TR order-of-magnitude figure for instructional problems.

Why Other Options Are Wrong:
2–8 TR can undersize peak latent/sensible loads; 20 TR may be more suitable for larger platforms or special operating conditions.

Common Pitfalls:
Confusing TR with electrical input power; or comparing aircraft ECS (air-cycle) directly to building vapour-compression systems without considering different COPs and operating envelopes.

Final Answer:
10 TR