Distributed Electric Propulsion
Electric airplanes are coming. In the near future, they will fill many missions: urban taxi, personal air vehicle, regional commuting, and others, still evolving. It is too soon to know what these vehicles will look like and, more importantly, what technologies they will include. Some believe they will take the form of multi-copters or Vertical Take-Off and Landing (VTOL) aircraft, but these need very high power, are inefficient, and will most likely be noisy.
While much current effort is going to VTOL development, there are other technologies that may offer better solutions for some missions. eSTOL (electric Short Take Off and Landing) is made possible by providing propulsion with many small electric motors, distributed electric propulsion. This allows the propulsion to affect the airflow over the wing in ways not possible in the past, with one or a few large propulsors. This is often referred to as Upper Surface Blowing and is a form of Propulsion Airframe Integration (PAI). PAI is, for the most part, not a new concept, its roots are in the 1940s. That said, research on upper surface blowing with distributed electric propulsion is new, and its potential is only beginning to be appreciated.
Ullman has been instrumental in two distributed electric projects, The JabirWatt (2019) and ELAS, with CubCrafters (2020 -present). He holds multiple patents for this technology.​​
The JabirWatt
The JabirWatt was a stock Jabiru J230-D complete with its original Jabiru 3300 IC engine and with four Electric Ducted Fans (EDFs) mounted inboard on the wings. The Jabiru was purchased as a wrecked, stripped hulk in 2016 and rebuilt over the next eighteen months. The Jabiru airframe was ideal for experiments as it was originally designed as a four-place airplane and decommissioned to two-place to meet LSA requirements. Thus, it has space behind the front seats for over 300 lbs ( 136kg) of batteries while staying with the weight and balance limits.
The EDFs used were 120mm off-the-shelf model airplane units powered by a custom LiPoFe 120wh/kg battery pack. The four EDFs were not designed to sustain flight, but sufficient to collect data to compare with wind-tunnel and theoretical results.
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The JabirWatt was first flown in 2018 as a stock aircraft to gather baseline data. JabirWatt experiments were begun in July 2019. It was decommissioned back to a stock airplane in 2020.
The project was dubbed IDEAL (Integrated Distributed Electric-Augmentation Lift). A report detailing the results of the experiments is available.
Key results included:
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With just 12% coverage, the EDFs lowered the stall speed 3 kts.
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Significant lift augmentation in all features of the lift curve, the zero intercept (Cl0) the lift curve slope (Clα), and the maximum lift coefficient (Clmax).
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Significant decrease in takeoff distance potential.
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Improved cruise potential.
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Minimal additional drag when EDFs are unpowered.
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Good agreement between the wind tunnel and in-flight results .
Successful results of the JabirWatt program led to Ullman teaming with CubCrafters Inc. and jointly mounting NASA-funded flight tests in 2023.
A CubCrafters NX was modified by the addition of EDFs integrated into leading edge slats, with the configuration specifically designed to enhance takeoff and landing.
The configuration shown has twelve 90mm EDFs mounted in six ELAS modules (Electric Lift Augmenting Slats).
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Results of 2023 inflight testing include:
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Bolt on system.
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Reduced Vs (stall speed) significantly in all flap conditions.
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Shortened takeoff distance to easily depart from a football field.
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Had a minor effect on cruise velocity.
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Had a minimal effect on handling qualities, even in failure modes.
ELAS