UltimateL39 Performance

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This page will be ever evolving as I add more data.  The UltimateL39is faster, lighter, turns better and lands much slower than a stock L-39C.  Hopefully the following data will convince you of this.

A L39MS owner was kind enough to share some data from his Garmin G3X system.  The MS has the DV2 motor with 1000 lbs more thrust than the AI-25 normally installed in the L39.  This is a time to climb comparison between the L39MS with DV2 motor and the UltimateL39 with TFE731-3 motor.  The gaps in the curves are sections where each plane leveled out on the way to altitude.

Stall performance is greatly improved over the stock L-39C.

We can add Scott Farnsworth's dirty stall of 67.2 kts wtih 2 plates and 1/2 moon of lead in the nose.  This was accomplished with partial power approaching stall speeds in slow flight (versus mine with idle power nose up trying to maintain altitude).  L39 simply do not stall under 70 kts!

Scott Fansworth with Race 38 was kind enough to let me fly his bird shortly before first flights with the UltimateL39.  His race plane is lighter than a stock L-39C and stalled at roughly 83 kts landing and 88 kts clean.  The UltimateL39 represents a significant reduction from these numbers.  The raw data for the above stall numbers can be found here Flight 1, 2, 3, 4, 5.  It was interesting how the stall speed went up as CoG went aft.  It took me a bit to get accustomed to stalling the UltimateL39 but even with the inconsistent holding altitude for the first few flights, the stall numbers are mighty consistent.

Scott has now taken delivery of Grey and had a chance to fly her.  It was nice to get a vastly more experienced L39 pilot in the plane.  He summed his first flight up nicely when he said I'm not sure what plane it is but its definitely not an L39 anymore.  I guess this when the name UltimateL39 was "born".  Things like the acceleration when you release the brakes and the dramatically slower landing speeds really stand out but the most striking thing about the package is how well it is all integrated.  It is a hundred little things that just work together.  The plane is quiet on the inside and the outside.  All control responses are just better in every way.  It feels like a completely different plane.  I'm really looking forward to Phase 2 and getting other L39 owners in the bird.  Given it was Scott's first flight he repeated the stall sequences with similar yet better results to mine.  Here is the plot and data for a dirty stall half tanks.  He got the plane to stall under 70 knots using "Airline" technique which is apparently to slow the plane under power as you would on approach slowly bleeding off energy until it stalls. A L39 STALLING at less than 70 knots.  Wow!!!!    He was still flying the L39 downwind to final turn speeds but had to lower landing speeds significantly to get the plane to settle.  First attempt floated to mid-field :)

The TFE731 offers fantastic throttle response with very little spool up time.  The stock L-39 requires the pilot to dirty up the plane and drag it to the runway with the engine spooled up above 80%.  The training mantra is "125 - stay alive" telling you to stay above 125 kts. With the CoG well within the stock L-39 envelope I found the plane perfectly controllable turning base to final at 100 kts and 22 degrees of bank.  I would not choose this all the time but, if needed to control energy into a short field, it is perfectly do-able if the pilot is comfortable and competent in slow flight.  My normal landing pattern has me downwind to final at 110 kts dropping to 100 kts when coming out to final, 90 kts over the fence and 80 kts over the numbers.  This is with the preferred CoG of 30% MAC.

Top speed seems to be a fascination with people.  I'm a bit boring in that I can not imagine burning that much fuel as I'm more interested in going somewhere then burning a ton of fuel going fast.  It does seem as though top speed does not disappoint with the GTX.  Here is a quick speed run at 16,500 ft (Baro Alt).  Here is a plot of another top speed run along with supporting data.  The first was 328/428 IAS/TAS at 202 g/hr while the second was 339/433 IAS/TAS at 208 g/hr.  ALL of the flights so far have been with ITT at top of the green arc or maximum continuous cruise of 885 DegC (or there abouts).  Maximum take off power for five minutes is achieved at 908 DegC and Automatic Performance Reserve (APR) for five minutes is 928 DegC.  There is a limit of something like 14 APR events between hot sections on the TFE731-3 along with cycle penalties for each APR event.  Pilots who fly the Hawker and other aircraft with -3 motors tell me max take off is good for about 300 lbs more thrust while APR is good for another 250 lbs.  GreyBird would do well at Reno with such thrust.

Climb performance  This is where taking a bunch of weight off a bird really makes it shine.  I've done a few VFR cross country simulations.  Here is one of the climb outs.  One of my buds that flies Hawkers told me you can get an idea of fuel flow in the Flight Levels by extrapolating the climb and fuel flow curves out on a straight line to the desired altitude.  If this is correct, we have the potential for true airspeeds in the high 300s/low 400s on just over 100 g/hr.  This sounds way to good to be true but is somewhat consistent with Hawker numbers of 1400 lbs/hr in climb around FL28.  I can not wait to test this one once Phase 1 testing is complete.  If you are just going out for a joy flight, the climb numbers are still entertaining.  This plot and supporting data was linked on the main UltimateL39 page but is included here for completeness.  Release brakes to-  lift off off was 13 seconds, 2000 ft in 53 seconds, 4000 ft in 85 seconds and 6000 ft in 115 seconds with a 15 kt wind coming down the runway.  It was over 4000 ft by mid field downwind.  When it comes to cross country flight, I've tested two climb speeds.  My first was around 225 kts (with poor speed control) which resulted in about 5 1/2 minutes to 16.5 feet.  The second was 250 kts resulting in just over 7 minutes to 16.5 and a full 10 NM further down the road.  VFR cross country simulations to 17.5 have resulted in mid fifty gallons used from start to shut down not inclusive of any cruise segments.

Cruise performance, this table lists some initial values from one of the cross country simulations.  More data is needed to better define this important area.  Of most importance to me is performance in the flight levels.  If top of the green arc power levels can be extrapolated to cruise in the flight levels, there is a chance the UltimateL39 will be a very strong cross country performer.

Although not of Grey, there are some pictures of the cockpit (from UglyDuckling) showing exactly what I mean when I say everything was removed to reduce weight and increase performance.  All the original avionics and almost all of the wiring was replaced by two pieces of Garmin G3X 10" glass, a 650 IFR navigator and remote com, txp and audio panel.  Both front and rear cockpits have access to almost all functions.  The only concession to creature comfort was the inclusion of pitch and roll autopilot servos.

So here is some gentle aerobatic work as Scott practiced for his low altitude waiver.

Here are some plots from our maximum performance work. First Take Off, Second Take Off, Second Landing, Third Take Off, Third Landing, Forth Take Off, Forth Landing.

GreyBird at Reno before she went on a diet