Purpose of Aerospace Test Cell

An aerospace test cell is a specialized facility used to validate the design and performance of gas turbine engines. Commercial Test cells are used to demonstrate compliance to 14 CFR Part 33 regulations to obtain type certificates and verify performance post maintenance activities per 14 CFR part 43. A DER or ODA unit member will review data and submit to the FAA to show the engine meets original design spec or revised spec via STC. Test cells are designed to test various types of engines and the facility layout will vary depending on if the engine is a turbofan, turboprop, or turboshaft. We will touch on two key engine parameters and how they are measured in test cells. The focus will be on thrust/shaft horsepower and fuel flow. The topics will be high level as test cells are complex systems used to validate even more complex engines.

Thrust and Shaft Horsepower(SHP) :

We will break this up into two sections based on engine type, thrust followed by shaft horsepower.

Thrust is the resultant force of the airflow leaving the turbofan nozzle and it is measured in Pounds or Kgs, it is the force that moves an aircraft through the air. How do we measure that? We measure thrust in a test cell using calibrated load cells attached to the thrust bed. The resultant force is applied to the installed load cells which measures the force and relays the information to the Data Acquisition Systems (DAS).

Shaft Horsepower applies to turboprop and turboshaft engines. It is the measurement of the rotational force applied on a gearbox by the engine. Inside a test cell, that torque is measured by a calibrated dynamometer. Similar to the turbofan, the dynamometer output is relayed and recorded on a DAS.

Fuel Flow:

The beauty of test cells is they have unlimited fuel supply that allows for extended engine testing, unlike aircraft which are limited to what they can hold in their fuel tanks. Each engine model has a minimum specification level and that needs to be accurately measured to ensure the engine confirms to the Type Certificate. Fuel flow is generally quantified by a volumetric turbine flow meter, an alternative that is increasing in popularity is the Emerson Coriolis flow meter. Correct fuel flow and thrust/SHP combined to give specific fuel consumption, how much fuel is burned at a given engine power level.

Getting these measurements right matters because the data has to hold up. Whether the engine is being tested for initial Part 33 certification or being verified after maintenance under Part 43, the numbers coming off the cell are the basis for the FAA determination. That's why test cell correlation — proving that your facility's data is traceable to a known-good baseline — is such a critical piece of operating a test cell. The measurements are only as trustworthy as the facility producing them.

As test cells are complex systems, there are many factors to consider beyond thrust and fuel flow such as inlets, exhausts, pressures, temperatures, engine speeds, and more measurement systems. It takes understanding all the contributing systems when trying to characterize a facility and understand the facility and engine performance. At Prime Propulsion we have years of experience working test cells, testing engines, and performing test cell correlations (more on this next month).

Where Prime Propulsion Fits

Test cells are where the engineering meets the real numbers — and getting those numbers right depends on understanding the facility, the measurement systems, and the engine as a whole. That's what our team does.

Our in-house DER has years of experience working test cells, testing engines, and performing test cell correlations — including APU correlations, where the parameters and setup differ from engine cells. Whether you need help understanding your facility's performance, correlating your cell, or interpreting test data for an FAA submission, contact us — we're happy to help. You can also learn more about our test cell correlation services.

Prime Propulsion delivers expert FAA certification solutions for small to medium-sized aerospace firms. Our DER-led team specializes in PMA, STC, Test Cell Correlations, and Repair Specification support.