The UH-IH upgrade, described in detail in this report, features: 

• Complete engine overhaul and fully modernized upgrade to the enhanced
  Honeywell T53-L-703 configuration. The upgrade from the T53-L-13B engine alone provides approximately 30% more power at high/hot conditions along with greatly reduced operating and support (0&S) costs. 
•  Low cost airframe modifications to enhance directional control power by over 40% at high/hot conditions, necessary to match the more powerful T53-L-703.
   

The Joint Venture team of Airwork Limited leads the HUEY703 project and Global Helicopter Technology, Inc. as the prime contractor. Airwork will be serving as the system integrator while providing overall program management for the upgrade effort.  (click on the picture at left for a full sized photo of the Huey703 conversion)

Airwork will also provide long term warranty and aftermarket support for the airframe modification hardware. Global will provide directional control enhancements, long term configuration control, and overall technical oversight. 

Other key team members include the following subcontractors:

• Honeywell (formerly AlliedSignal Aerospace) will supply the T53-703 engine upgrade and provide warranty and aftermarket support for the new OEM engine parts.
• Helipro will conduct the airframe and engine upgrade installation, inspection, and repair. Helipro will also be the US FAA authority to approve airworthiness for each upgraded helicopter through its subsidiary, Helipro Completions. 
• Boundary Layer Research will supply the NASA-patented tailboom strakes for improving helicopter directional control power.

UPGRADE FEATURES & BENEFITS

The HUEY 703 Program provides significantly greater useful load and improved directional control. The HUEY703 Program will provide 1500 to 2500 pounds more payload from 3000 to 10,000 feet altitude on an ISA + 30°C day. Figure 2 illustrates the increase in operating envelope for the HUEY703.  This is accomplished by a combination of the following engine and airframe modifications.

The existing T53-L-13B turbine engine is modified by the installation of a kit supplied by Honeywell that increases engine performance by 400 shaft horsepower while enhancing component life/durability.  Installation of this kit along with complete engine overhaul re-identifies the engine as a T53-L-703. Only minor engine-specific changes are required such as basic instrument markings, start fuel switch, and electric engine oil cooler blower for increased cooling efficiency.  

The improved design of the T53-L-703 will lower operating cost via extended Time Between Overhaul (TBO) to 5000 hours and by use of Original Equipment Manufacturer (OEM) parts during the overhaul and upgrade process. Of course, if the upgrade is conducted during a regular scheduled overhaul, the incremental cost of the -703 upgrade is significantly lowered. The basic HUEY703 Upgrade price includes the engine overhaul and upgrade kit installation conducted by Honeywell or an Authorized Service Center.  This results in a 30% increase in shaft horsepower of the T53-L-703 compared to the current T53-L-13B model for a range of operating altitudes.

To fully and safely utilize this increased power and also supply FAA-required tail rotor controllability, the HUEY703 incorporates a directional control power improvement system. This low risk, low cost combination of proven enhancements dramatically extends the UH-IH high/hot takeoff and landing operations when combined with the higher engine power of the T53-L-703. These enhancements consist of the following four approaches:

• Installation of strakes on the tailboom 
• Conversion to a tractor tail rotor configuration 
• Control of increased tail rotor blade pitch limit by an electro-mechanical Density Altitude Compensator (DAC) 

Brief highlights of these enhancements are identified in the figure above and are discussed below:

• Tailboom Strakes:  NASA data and subsequent BLR FAA STC testing show that incorporation of tailboom strakes will decrease the requirement for tail rotor anti-torque by about 10% in those flight regimes where tail rotor anti-torque is critical, such as right sideward flight or hover flight with winds from the right.  The tailboom strake acts as a spoiler of downwash flow over the left side (U.S. main rotor rotation) of the tailboom, reducing the pedal input required for hover flight, aiding the tail rotor in critical right sideward flight.
• Conversion to Tractor Tail Rotor This modification, illustrated in Figure 5, is the most labor intensive of the enhancements. It requires significant changes to the tailboom configuration, utilizing the existing tail rotor gearbox  from 205A-l's, UH-IH's or AH-IG's. The modification provides approximately 20% increase in tail rotor control power, according to Bell Helicopter and Army data, and verified by the recent Huey703 performance tests, while requiring no additional drive train power.