L39GTX Bleed Air System

UltimateL39 Bleed Air System

The UltimateL39 bleed air system is a combination of design concepts from the L139, components from the AI-25 and bespoke elements to simplify the system and provide for a high quality, low production run repeatable solution for our customers.

Overall, the bleed air system starts by mixing High Pressure (HP) and Low Pressure (LP) bleed air from the TFE731 motor in such a way as to not exceed the energy in the bleed air provided by the original AI-25. This is accomplished on the TFE731 engine using a bespoke HP pressure dependent shut off valve connected to a LP port mounted mixing manifold. The mixing manifold as a commercially available one way "flapper" valve to prevent HP air from entering the LP port on the motor when the airframe systems are consuming HP air. This approach is similar to that employed on the L139. It allows for good air conditioner performance at idle using HP bleed air then a transition to LP bleed air slightly above idle. Bleed air energy is controlled and the minimum parasitic loss is applied to the motor saving that energy (thrust) for the pilot.

The L39 uses several flow limiting valves that are matched to the energy in the one (and only) bleed air source (final compressor stage) of the AI-25. If you use the existing flow limiter/regulators but dramatically exceed the bleed air energy of the AI-25, bad things can happen like blowing up the Air Cycle Machine (ACM) or Turbo Cooler as it is known in the L39. Ask me how I know :) The mixed air described above is piped via 1 1/2" thin wall stainless tubing covered in fiberglass heat wrap (header wrap) and high temperature shielding tape to one of the original AI-25 bleed air shut off valves (part number LUN 567 7.22-8) which is mounted to the original L39 air cleaner by an adapter supplied with the installation kit. ****Note: The original L39 air cleaner bracket (the one that touches the air cleaner) must be de-riveted and moved OUTBOARD by one rivet hole. This is necessary to provide clearance between the air cleaner and the TFE731-3 oil tank which sits on the front side of the motor right next to the air cleaner.**** This completes the path from the engine to the ACM/Pressurization system. There is a pressure sensor and a thermocouple installed BEFORE the bleed air shut off valve (the one mounted on the air cleaner using our adapter). A 1 1/2" tube is "Y"ed off the ACM bleed air line going forward to supply inlet and windscreen de-ice air. This pipe attaches to another customer supplied stock AI-25 bleed air valve mounted to the engine/RAT bay firewall. The Engine to ACM Bleed Air Shut Off Valve and De-Ice Shut Off Valve tubing is supplied as part of the installation kit. The AI-25 bleed air shut off valves are provided by the customer/installer. In addition, the installer must fabricate tubing and install the original L39 de-ice flow limiting valve (part number LUN567 7.02-8) originally mounted on the side of the AI-25 to limit de-ice bleed air flow to the original L39 design volume. So, to summarize, we supply the tubing and adapters in the engine bay. The installer does the RAT bay plumbing. The customer/installer provides the stock L39 bleed air valves and the stock de-ice flow regulating valve.

We have begun bench testing the first HP bleed air shut off valves. Here is a quick look. I've added a picture below of the dry graphite treated piston with PTFE seal ring.