Sonex Research, Inc. - Sonex Combustion System | Annapolis, MD

Combustion specialists

Engine Testing Services

• Evaluate and trouble-shoot engines powering UAVs

• Combustion analysis and emissions tests

• Federal Aviation Regulation 33 (FAR 33) endurance testing

• Conduct static and dynamic propeller load desert and arctic tests

• Portable propeller-load test stand

Engine Design and Testing Current and Former Customers

• The Boeing Company:

Defense, Space and Security Systems, St. Louis, Missouri:  Development of a small, two-stroke, SCS HFE for use in an experimental UAV, including development of an electronic fuel injection (EFI) system, integrated starter-generator and remote start capability. Engine performance testing, including at high altitude using Sonex designed portable propeller-load test stand.

• Insitu, Inc., Bingen, Washington:

Now a subsidiary of The Boeing Company: Development and design of SCS cylinder head and Cold Starting System for HFE used in ScanEagle UAV. Engine performance testing, including FAR 33 endurance testing.

• QinetiQ North America, Inc., Waltham, Massachusetts:

A subsidiary of QinetiQ of the United Kingdom:  Development of heavy fuel capability for 1 kW portable generator set for military applications. Included engine endurance testing.

• U.S. Department of the Navy’s Office of Naval Research (ONR):

On behalf of the United States Marine Corps design and develop auto start and multi-fuel capability for 1 kW portable generator set for military applications.

• U.S. Defense Advanced Research Projects Agency (DARPA):

For the development of a multi-cylinder, four-stroke, HFE combustion process for potential Department of Defense applications. Sonex successfully demonstrated to DARPA the Sonex Controlled Auto Ignition (SCAITM) lean-burn, piston-based combustion process, in a laboratory engine operating on JP-8 heavy fuel at power levels up to 250 hp with significant reductions in fuel consumption when compared to a gasoline engine.

Evaluate and trouble-shoot engines powering UAVs

Troubleshooting ignition systems, EFI, intake & exhausts


Substantial equipment is dedicated to the development and testing of small engines for unmanned aerial vehicles (UAVs) and other applications.

  • Dynamometers

  • Static propeller thrust and torque test stands

  • Air intake/exhaust system to support running engines

engine test engine test

Combustion analysis and emissions tests

The Company's approximately 6,000 square foot facility is equipped with emissions test equipment, advanced combustion analyzers and several engine dynamometers rated from 5 hp to 500 hp. Laboratory data acquisition/combustion analysis is handled by a High-Techniques PC based system.

engine test engine test

Federal Aviation Regulation (FAR 33) Endurance Testing

The FAR 33.49 (Federal Aviation Regulation Section 49, Endurance Test) is a 150 hour endurance test that is a requirement for aircraft piston engine airworthiness approval. Conducted by Sonex on [equipment]. The test consists of 150 hours of various loading conditions on the engine ranging from wide open throttle to 50% power. During 50 hours of the test the engine is operated at the maximum limiting temperature. Sonex operates the engine for approximately 6 hours per day until the test is completed, resulting in approximately 30 starts and stops. A post-test inspection normally reveals wear concerns with the design.

Conduct static and dynamic propeller load desert and arctic tests

The Sonex Environmental Chamber (EC), located adjacent to the main facility, is an 8 foot wide, 16 foot long and 10 foot high walk-in freezer that Sonex has adapted to conduct hot and cold temperature engine testing of a running engine with propeller on a test stand which can be set up for testing at temperatures from -20 deg. C to 55 deg. C and with simulated air velocities of up to 50 knots.  

engine test engine test engine test

A control room is attached to the EC to permit the test operator to view the inside of the EC through a window cut into the outside wall of the EC. The safety glass window also has a heating feature to allow frost free cold temperature operation. The control room is equipped with interfaces to the EC and engine instrumentation to enable data recording and real-time adjustments.


Sonex can also cold soak an engine with propeller to temperatures as low as -60°F to determine starting ability in low temperature extremes.

Portable propeller-load test stand

Sonex has designed and built a lightweight, portable propeller-load test stand which incorporates a low influence structure to minimize the impact the stand itself may have on the engine performance characteristics. The stand is capable of measuring the rotational torque as well as linear thrust produced from the engine. The stand utilizes an aerodynamic single 48” high mast structure mated to a 32” x 32” base for stability. All wiring for communication and instrumentation is routed within the mast to maintain a streamlined profile. An engine can be operated as it would during a “vehicle installed” configuration.

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