{"id":12400,"date":"2020-04-30T20:49:39","date_gmt":"2020-05-01T03:49:39","guid":{"rendered":"http:\/\/cafe.foundation\/blog\/?p=12400"},"modified":"2020-06-10T20:49:00","modified_gmt":"2020-06-11T03:49:00","slug":"jabirwatt-pai-and-dep-with-david-ullman","status":"publish","type":"post","link":"http:\/\/cafe.foundation\/blog\/jabirwatt-pai-and-dep-with-david-ullman\/","title":{"rendered":"JabirWatt: PAI and DEP with David Ullman"},"content":{"rendered":"

Electric aircraft, especially in their early state of development, will require aerodynamically capable forms or extremely light structures, or both. That may account for the early adoption of sailplanes as test beds. These are graceful and high performance units, but not all that practical for hauling loads or for daily commuting. Other first attempts adapted ultralight, but not necessarily aerodynamically efficient structures to make electric flight possible. David Ullman makes use of two dynamic technologies, PAI\u00a0 and DEP, to achieve performance with the potential for great practicality.<\/p>\n

PAI and DEP<\/h4>\n

David, a professor emeritus in mechanical engineering, is also an enthusiastic pilot and inventor. His texts on the design process and decision making are best sellers. Recently, he’s been exploring the potential of Propulsion Airframe Interaction (PAI) and Distributed Electric Propulsion (DEP) by augmenting the power and lift of a conventional aircraft with Electric Ducted Fans (EDF).<\/p>\n

A Creative Airport Community<\/h4>\n

If you are fortunate enough to visit the Independence, Oregon airport, you can see myriad examples of creativity and craftsmanship. On the road leading into the airport, Experimental Aircraft Association’s Chapter 292’s hangar houses a reverse engineered cop of Barnaby Wainfan’s FMX-4 “Facetmobile” and a replica DH-2 “Gunbus,” one of several built (the rest were sold to New Zealand).<\/p>\n

Across that road, Vince Homer’s hangar is filled with an astounding array of experiments and beautifully-crafted models. Vince is David Ullman’s partner in developing and testing JabirWatt, a very serious attempt at improving short takeoff and landing (STOL) performance, but also in preventing dangerous departures from controlled flight.<\/p>\n

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JabirWatt’swing with two EDFs. Performance, even with only four total EDFs, is enhanced<\/p><\/div>\n

David has a large wind tunnel in his hangar on which he’s tested all facets of design he and Vince adapted from a once-wrecked Jabiru. Having seen the airplane in its mangled and restored states, your editor is a bit incredulous. The workmanship is beautiful – not surprising considering David’s craftsmanship on a Velocity a few years ago. That airplane included cooling vents that improved performance and engine longevity.<\/p>\n

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All four EDFs. Consider the performance possible with fan arrayed across the full span<\/p><\/div>\n

By the Numbers<\/h4>\n

Of all the inventive things in David’s hangar, the most prominent is a large wind tunnel, well-instrumented and calibrated enough that others can use it to obtain reliable data for their projects. Recent flights of his Jabirwatt show excellent agreement between wind tunnel and flight data.<\/p>\n

What (Watt) Kind of Beast is a JabirWatt?<\/h4>\n

Dave explains, “The JabirWatt is 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 is ideal for IDEAL 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.<\/p>\n

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Close agreement between wind tunnel tests and actual flighy data<\/p><\/div>\n

“The EDFs are 120mm (4.72 inch) off-the-shelf model airplane units powered by a custom LiPoFe 120wh\/kg battery pack. The four EDFs are not enough to sustain flight, but sufficient to collect data to compare with wind-tunnel and theoretical results.”
\nAn interim report issued on December 1, 2019 highlights six major results of the detailed testing:<\/p>\n

“1. Significant decrease in the stall speed.
\n“2. Significant increase in all features of the lift curve, the zero intercept (Cl0) the lift curve slope (Cl\u03b1), and the maximum lift coefficient (Clmax).
\n“3. Significant decrease in takeoff distance potential
\n“4. Improved cruise potential
\n“5. Minimal additional drag when EDFs are unpowered
\n“6. Good agreement between the wind tunnel and in-flight results”<\/p>\n

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Results with conventional airfoil.\u00a0 Yet to be tested – airfoils optimized for PAI<\/p><\/div>\n

Testing Time<\/h4>\n

“David reported, “The JabirWatt was first flown in 2018 as a stock aircraft to gather baseline data. JabirWatt experiments were begun in July 2019.”<\/p>\n

An interim report can be found on David’s IDEAL web site<\/a>. .<\/p>\n

David’s web site includes a broader description of the aircraft, the theories behind it, and the results from testing<\/a> – which are exciting.<\/p>\n

Battery Constraints<\/h4>\n

Asked about the batteries on board, David responded, “I used a safer, less energy dense battery chemistry. Lillium and Alice have made claims to investors that they now have to live up to. I don\u2019t have any investors and don\u2019t want a cockpit fire. I am eager to see what you know about the fires. My electric car buddies were not surprised.”<\/p>\n

Jabirwocky\/JabirWatt<\/h4>\n

To finish with a literary flourish, Lewis Carroll was a professor of mathematics. Possibly writing Alice in Wonderland<\/em> as a satirical protest against new math theories arising in the late Victorian era, he included a bizarre poem that used a bizarre vocabulary.<\/p>\n

\u2019Twas brillig, and the slithy toves
\nDid gyre and gimble in the wabe:
\nAll mimsy were the borogoves,
\nAnd the mome raths outgrabe.
\n\u201cBeware the Jabberwock, my son!
\nThe jaws that bite, the claws that catch!”
\nLewis Carroll<\/p>\n

Portmanteau (port-man-toe) words, two words squeezed into one: “lithe and “slimy” becoming “slithy,” abound in the poem.\u00a0 According to Google, “”Portmanteau words” is now a standard name for such word blends. Among the portmanteaus Carroll invented for Jabberwocky were “galumphing” and “chortled”: the former from “gallop” and “triumphant,” the latter from “chuckle” and “snort.” Both have entered the English language.”<\/p>\n

JabirWatt may well be classified as a portmanteau airplane, folding a conventional craft together with advanced technologies.<\/p>\n

Extreme Model Example<\/h4>\n

One modeler took things to an extreme demonstration of what channel wings can do.<\/p>\n