Overall GXT Engine Package Creation Process

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Here is a simplified bullet point type description of the GXT creation process.

For the first few conversions, we will be supplying completed motor assemblies.  This is done to control quality and to fully vet the build up process so that others can reproduce the effort with great quality.  The assembly is based on a motor that was run on the pylon, comes with a Honeywell E-Engine data log of the power assurance run and all appropriate log book entries inclusive of gearbox pressure measurements during the power assurance run.  Nothing is ever guaranteed when purchasing a used engine but we do our best to properly vet candidates before purchasing.  Prior to evaluation, we do an AD compliance analysis and a cycle life limited component (mostly disks) analysis to make sure the motor is airworthy and has sufficient disk cycles remaining to be of value.  Our current Approved Inspection Programs (for the two already issued) allow for hot section on condition but we must still comply with certified limits on cycles and Core Zone Inspection - CZI (better known as compressor overhaul).

The motor assembly is complete from carbon composite inlet to 731-3 motor to carbon composite fan duct to exhaust exit tube to exhaust exit cone.  All flow path cross sections from type certified installations have been faithfully retained insuring proper engine performance and efficiency.  The assembly includes front and rear motor mounts installed along with throttle bell crank and fuel control link.  Turbo Cooler plumbing is provided in addition to the adapter to permit mounting the customer supplied AI-25's bleed air valve to the Turbo Cooler's air cleaner.  The DEEC and Honeywell produced DEEC to engine harness is supplied with related schematic documentation.

The above engine assembly will literally roll on the existing unmodified L39 engine rails right into place using the original front and rear motor mount facilities with only one modification.  The TFE731-3 motor has a larger fan than the AI-25.  We accommodate this by producing a tapered inlet which expands the L39s "Y" ducting out to the 731-3's inlet diameter.  This cone is larger in diameter where it passes though the engine firewall than the AI-25 inlet tube and thus the AI-25 inlet tube support flange on the engine to RAT bay fire wall must be removed.   The inward facing lip which has the nut plates (used by the before mentioned tube support flange) must be trimmed off and a silicone rubber u-channel protector placed over the sheet metal edge.  The forward facing portion of the firewall pass though remains thus its strength stays intact.  The tail is then rolled on and appropriate adjustments to rear motor height are made so that the exit cone is centered in the tail exit.  The ACM (Turbo Cooler) bleed air valve (AI-25 part supplied by the customer) is installed on the air cleaner using the supplied mount then the supplied engine to bleed air valve tubing is installed to complete the AC and cabin pressurization circuit.

Starter/Generator and engine instruments are the responsibility of the installer.  Reference schematics for the Starter/Generator are supplied using standard business jet components (main contactor, start contactor, reverse current relay, feeder protection and Generator Control Unit or GCU).  Installs to date have used the Garmin G3X package for engine instrumentation.  The engine interface module can connect directly with most of the original TFE731-3 sensors like Oil Temperature, Fuel Pressure Switch, Oil Pressure Switch, turbine interstage temperature (TIT K thermocouple) and the like.  Where original engine sensors are not compatible with modern experimental avionics, custom or bespoke sensors or signal conditioning is provided.  These include Oil Pressure, Fuel Flow and signal conditioning for the N1 and N2 monopoles so as to provide conditioned and reduced frequency waveforms which the G3X (and other) systems will accept.  HP/LB bleed air temperature and pressure sensors are provided.  The fire detection loop on the type certified installation is retained and schematic documentation is provided for generating proper cockpit test/indication.

The TFE731-3 package described above provides about 25% of the performance increase that is the GXT.  This is my estimate only and not based on any hard facts.  The remaining 75% comes from weight reduction which can only be realistically achieved with the TFE731-3 engine conversion.  This is not an exhaustive list but here are some of the changes that must be made to achieve maximum weight reduction.  Remove all remnants of the AI-25, engine/rat bay harnesses, sapphire and supporting elements, RAT, all cockpit wiring paring down those harnesses that contain support for the ACM, flaps, gear and trim systems. Replace ejection seats with carbon/composite seats.  Remove all O2 and Nitrogen components.  Canopy seals and hydraulic reservoir can be pressurized by a regulator off the HP/LP ACM supply line.  O2 for cross country and racing is by a pilot carried aboard pulse demand system.  Wing tip tanks are removed along with all their associated wing plumbing.  We produced very small profiled wing end caps with or without integral Aero LEDs NSP lighting that weight but a few pounds each but many other wing tip designs are available from other vendors (but they are HEAVY).  The effort involved here is significant but the end result is stellar.

The package described above comes with reference schematic documentation from our first GXT which includes an electro-hydraulic pump pack.  We also provide our Inspection Program which has been accepted by the FAA on two previous occasions and supporting engineering documentation covering analysis of the front and rear motor mounts and other major modifications required to generate a GXT.  These documents are provided in an engineering report assigned to each aircraft serial number and bearing a PE stamp. In addition to being used for issuing an Experimental Airworthiness, these documents have been submitted, along with relevant flight test data, to authorities for inclusion at the Reno Air Races.

Included below are some pictures of our first customer delivery motor assembly.  Our normal engine stand was modified with new uprights to accommodate the L39 front motor rollers and stays were added at the rear to support the motor's rear mounts.  Custom aluminum fabrications are given a coat of Boeing's green epoxy primer.  The throttle bellcrank shown connects directly to a customer lengthened standard L39 longitudinal throttle rod.

Looking at the completed assembly on the stand, here are most (I'll add more when I think of them) of the changes made and parts supplied working from the front to the back.

Custom inlet cone to expand the L39's "Y" duct out to the 731-3's fan inlet - front motor "velocity stack" carbon ring which acts to guide the inlet cone to the front of the motor when the motor is rolled into the airframe - Re-positioned starter/generator with shortened air inlet (screen added) - Ti or Stainless front motor mounts using customer supplied front L39 rollers (we will likely start producing these ourselves) - Oil pressure adapter and standard oil pressure sensor (any acceptable 1/8" male NPT sender can be used) - custom fuel Rf fuel flow pick up fitted to the original Hawker/WestWind fuel flow turbine - jet core support hanger - custom composite fan duct with integral throttle bellcrank mount tower - customer supplied L39 rear motor mounts (we may begin producing a custom mount if original equipment items become scarce) - throttle bellcrank and mating push/pull rod to the fuel control - custom fuel control actuation arm - patched green sheets to fill in the unused HP bleed exit - modified HP bleed pipe exiting the combustion chamber - exhaust exit tube - exhaust exit nozzle.   Separate from the engine is the N1/N2 signal conditioning box that generates waveforms acceptable to experimental EFIS' like the Garmin G3X and Dynon Skyview.  An N1 DEEC and associated harness are supplied as well.