B29i AXS UAV EFI Engine System

System Overview

  • Low-noise exhaust design
  • Stall-resistant throttle response
  • Significantly expanded throttle-RPM envelope vs Carburetor
  • Full EFI suite including automotive-quality ECU processor, self-priming fuel pump, ignition, sensors, injector and custom intake, all with over 40,000 hours on UAS platforms.
  • Seamless CAN-bus autopilot integration, compatible with Piccolo.
  • Passed FAR-33 150 Hour Endurance Profile

Summary Specifications

Engine Type: Air-cooled 2-stroke single
Displacement: 28.5 cc
Weight: 1.98kg (4.4lb) excluding power supply
Fuel Delivery: up to 48g/min at 3 bar
Power Output: 1.8 kW (2.4 HP) at 9000 RPM
Fuel Consumption: 500 g/kW-hr (0.82 lb/HP-hr) at cruise
Generator output: 250W (500W intermittent duty cycle)

Data sheet:

Endurance Report:

EFI Engine with Integrated Generator

The B29i UAV Engine System is a 29cc single cylinder engine having a high power density and minimal maintenance requirements. The engine features an advanced function ECU, a positive displacement high-pressure fuel pump, a fuel pressure accumulator, a super-atomizing fuel injector, capacitive discharge ignition, and MAT and CHT sensors. The engine incorporates an integrated generator and generator drive system. A custom muffler is fitted as standard.

Engine Technology

The B29i UAV engine is an advanced version of the 3W-28, with a principal improvement being the use of fully machined crankcases manufactured by Currawong Engineering that overcome porosity issues, provide a more precise path for internal fuel/air circulation and incorporate an integrated generator and generator drive system. Other improvements include a new propeller hub design, incorporating a more accurate crank angle sensing system. The ignition system is based on a Desert Aircraft CDI unit with modifications to facilitate control by the ECU.

B29i<br /><br /><br /><br /><br /> UAV Engine System

B29i AXS UAV EFI Engine

B29i UAV Engine System

The B29i EFI Engine has an Integrated Generator



B29i AXS (Corvid-29) Engine Performance

B29i AXS UAV Engine Tabular Performance

Maxon Generator

The B29i UAV engine is equipped with a 3-phase Maxon brushless motor used as a generator. The generator is driven by a toothed belt from the engine output shaft and produces 250 watts of continuous (500 watts of intermittent) electrical power.

Exhaust System

The exhaust system used on the B29i UAV engine system is designed and manufactured by Cobra Aero, a division of Cobra Moto. Cobra Moto is a producer of mini-motocross motorcycles that have a worldwide reputation for reliability and performance. Cobra Moto design and manufacture their own engines and their bikes are more than competitive against the products of much larger producers such as KTM and Honda. The exhaust system used on the B29i both maximizes performance and substantially reduces acoustic signature.

Electronic Fuel Injection

The B29i UAV Engine System has the latest version of Currawong’s EFI system. CE has developed EFI systems for a number of engines for use in UAVs. CE’s conversions include the 3W-56 two-stroke engine used on the Honeywell T-Hawk MAV, with over 700 systems delivered to date. The Raytheon Silver Fox UAS, using a Robins/Fuji 34cc four-stroke engine, was refitted with CE EFI systems, with over 85 systems delivered to date.

Note: In the fourteen months following the Silver Fox refit there were no major engine faults during in-theater operations. We have been informed that in excess of 20,000 operating hours have been logged with this aircraft and its propulsion unit.

The Currawong EFI system is the most mature and reliable of any system currently available for small engine use in UAS.

Key features

  • An ECU that is fully featured for aeronautical use and which has the ability to communicate with various avionic systems. When used with Cloud Cap Technology’s Piccolo Autopilot the connection is plug-and-play. The ECU has a proven record of reliability in extreme conditions of temperature and at a wide range of altitude. The ECU incorporates sensors for manifold air pressure and fuel pressure. External sensors are used for manifold air temperature and engine cylinder head temperature.
  • A high pressure positive displacement fuel pump, incorporating a fuel pressure accumulator in the lower flow applications, with extraordinary self priming capability and unchallenged ability to maintain pressure, even in the event of aeration of the fuel.
  • A robust fuel injector that uses an automotive injector body with proprietary interior modifications that provide the very fine atomization that is essential for use on small engines.
  • A CE designed throttle body that is lightweight and accurately machined.
  • Wiring harnesses that are dedicated to the EFI system but which can be customised for individual applications.


Typical ECU Interface diagram

UAV Engine System Engine Control Unit Diagram