L39 GXT

Ultimate L39 New Look

Email Questions or Comments Last Updated 02/02/20

The Ultimate L39 or CarbonL39 project has moved beyond the initial creation phase so I am taking some time to clean up this page to focus it more on what is happening now and less of the history of the project. The original work can be found here.

We are currently working on several paths simultaneously. These are our own CarbonL39-3 in house demo plane, the CarbonL39-5 development plane and the UltimateL39-62. These are covered in the following paragraphs.

The L39GXT-62 uses our UltimateL39 engine conversion combined with significant weight savings with an aspirational target weight of 6200 lbs empty. Like our ultra light weight builds, the 62 series will have all the modern avionics and associated wiring. However, it will not have the relocated hydraulic reservoir, accumulators and pump pack nor will it have the Challenger 600 series pitot/static and static components. These two sets of tasks literally double the labor to convert a stock L39C but yield only a 400 lb estimated weight reduction. We currently have two 62 series builds in progress, Ivy and Toledo. These planes are not currently committed to a customer and are being built in sequence. Build time is estimated at six months.

The engine conversion element of our projects has turned out way better than we could have hoped for. The engine mounting techniques we have employed have been rigorously flight tested and have been accepted for the Reno Air Races in 2019. Loading and fatigue life of the primary motor mounts have been subjected to Finite Element Analysis by a Professional Engineer and stresses have been shown to be less than 20% of the ultimate yield with an infinite fatigue life. A serialized copy of the engineering report (stamped) is provided with each engine conversion parts set to aid in airworthiness issuance and is tied to the aircraft serial number being converted. The inlet and exit designs combined with superior mounting stability have allowed us to out perform other TFE731-3 conversions on the market. I knew it in my bones but up until the summer of 2019 I really did not feel comfortable making the claim. We have now had an experienced warbird pilot in an UltimateL39 powered L39 (Grey, our development mule). This pilot has owned an L39 along with other jet warbirds and has flown the leading competitor's current 731 conversion.

When the pilot landed, he was literally giddy. It reminded me of my first few flights in the plane. The feedback he provided confirmed that engine response and performance is exceptional. On the way to lunch, the pilot said there was no comparison between our conversion and that of the leading competitor. He asked me how much of that difference was due to the engine modification and how much was weight reduction. I had no way to answer as I've not flown another conversion but I asked him how our engine responded to power changes. He said much faster and smoother like a piston engine. I pressed for a quantitative assessment and he said its like ours responded a second faster and responded more aggressively. I then asked how much airspeed they had initiating a loop and how much energy they had over the top. He said they started the loop straight and level and had 120 KIAS at the top; he paused and said L39s do not have that kind of energy at the top of a loop. We he said there were no throttle changes for the maneuver, I told him that was attributable to the weight reduction. It was clear that the overall balanced performance of Grey was due to both a superior engine installation and the significant reduction in weight. He ended up answering his own question, perhaps half and half.

Although our plate is full right now and lead times are long, we are considering making the conversion available in the form of an Engine Build Kit to one or more vendors currently active in the L39 community. As the name implies, these are the components necessary to build up a motor so that it will roll into the back of a standard L39 with but one modification. A completely built up motor assembly looks like this and this ready to roll into the back of a L39. To be clear, the motor would not be included. Here is a list of the components so far but this work is nowhere near complete. We have found from many conversations with interested parties that the solution needs to be more complete and include elements like bleed air plumbing and a battery box / starter generator support solution. There is simply not enough time right now for us to generate customer versions of these items; we are still perfecting them in house. A complete installation solution is not available today.

The UltimateL39-3 project is called Mallard. The plane rolled in as Ugly Duckling and is undergoing transformation. I try to keep progress updated here. This will be our in house demo plane so that friends can come visit, fly the plane and judge for themselves. One of our friends has joined our L39 family and is a 50% owner in Mallard. Being a demonstrator, we've tried to show the very best of what we think can be done from the avionics to the complete bespoke Tefzel wiring harnesses to the custom components like flap control, relay/diode functions and Generator Control Units (GCU). We also implement all our weight savings like very low profile wing tips and carbon reclined seating. Mallard incorporates our electro-hydraulic pump pack allowing us to move significant weight forward (reducing the need to carry extra ballast), remove the engine drag and fire fuel source of an engine mounted hydraulic pump (with 5606 fluid in the engine bay) and allowing the hydraulic system to be serviced anywhere without need for a special hydraulic mule. I appreciate the little things having tested the brakes, flaps, air brakes and knowing I have full emergency and standard accumulators before firing up on the ramp. The upgraded pump assembly has dramatically increased the gear swing speed from that of our development mule as well. It will also be the very lightest L39 we know how to build coming in hundreds of pounds less than the previous conversion (which weighed in at 6000 lbs empty). Come fly it and see just how good an L39 can be.

The CarbonL39-5BR (Mojave) is our pushing the envelope development project. This project requires all new molds for the carbon composite inlet and exit ducting along with all new fixtures for exhaust gas exit tubing and nozzle. So, unlike Mallard, Mojave will receive only the weight reduction work and not the aesthetic treatment. It is pure performance we are looking for. You can check in on Mojave's progress here.

Our development mule continues to go through its paces. The Fort Lauderdale Airshow is an example.

Our version 2 Electro-Hydraulic Pump Pack seems to be addressing the slow gear retraction issue. Here is the original pump pack and here is the up-rated version two. The current draw graph and tabular data between the two pump packs says it all.

Here is a quick pass at a cost analysis for do it yourself conversion. And here is an ongoing cost/hours/weight assessment for stripping an L39 (Mojave Strip) along with forward progress.

Thoughts on quality, reproducibility and cost control.

Available Motors