Order From Chaos
The amazing story of the CAFE Foundation’s flight test innovations, and why CAFE is the ideal organization to manage and conduct Personal Air Vehicle Challenges.
Introduction
“Excellence is a habit” — Aristotle
Innovation is a fundamental tendency of volunteerism. Beyond the obvious necessity to innovate when resources are scarce, it is the volunteer’s clear sense of personal responsibility and freedom from fear that propel this tendency. The history of the CAFE Foundation’s volunteers is vivid example.
Volunteers are free from corporate conservatism, bureaucratic stagnation and the ruts those entail. This makes them eager to try other paths and thus overcome challenges. Volunteers can better afford to be decisive, to commit themselves, to experiment and thus, to learn. The surest mechanism for such learning is that of the academy, wherein each volunteer does not experiment in a vacuum, but rather is both abetted and held accountable by their peers. CAFE has always been just such a ‘think tank’ and its members courteously hold one another to high standards while operating on the principle of “Prove it”.
The academy approach has made CAFE volunteers “savor the surprises”, i.e., drill down and learn more from each new insight. As CAFE Board member Jack Norris’ 2nd Law states, “If you thought it was simple, you simply didn't understand.” Jack convinced the CAFE team that “It’s all out there if you just keep digging”.
The following Story of the CAFE Foundation’s Flight Test Innovations shows how much can be accomplished by dedicated volunteerism.
The Birth of the CAFE 400
Saving fuel was a popular topic in the mid-70’s, when Americans were experiencing fuel rationing and long lines at gas pumps. At that time, outlandish advertising claims were being made about the high MPG of high speed kit aircraft. In 1977, Roy LoPresti introduced a new standard-setter in aircraft efficiency, the sensational 200 mph Mooney 201, a plane capable of over 20 MPG. The Experimental Aircraft Association’s Oshkosh Airshow became the focus of an annual aircraft race that emphasized fuel efficiency - the winner had to complete the 500 mile triangular race course while consuming no more than an allotted amount of fuel. Many felt that the fuel allotment was too arbitrary and constrained entries in the event. The race’s minimum qualifying speed also limited participation.
Brien Seeley, an eye surgeon who had built his own electric-powered car as an intern, turned his interest in saving fuel to the task of designing a new kind of flight efficiency competition. He set out to find a simple yet mathematically correct formula for aircraft efficiency around which to organize the competition. After much consideration, Seeley concluded that the aerodynamically valid, universal formula was rather simple: multiply the aircraft’s average velocity on the race course times its MPG times the cabin payload (W) in pounds. The formula, V x MPG x W was later found to be essentially the same as that derived by Nobel Physicist Teodor von Karman in the 1950s.
V x MPG x W became the CAFE Formula and led to the birth of the CAFE 400 race, as well as the volunteer CAFE Foundation which was founded to host the event. From 1981 to 1990, each summer’s CAFE race attracted the premier aircraft designers in the US to bring their sleekest aircraft to compete. The event became a kind of aeronautical academy for designers to test their innovations. It was no surprise that the best ones were adopted by rival competitors in the following year. The CAFE 400 popularized such innovations as high intensity ignition systems, lean of peak mixture settings, laminar flow surfaces made of high tech composite materials, leakage drag reduction, flush antennae, special propeller designs, cowl flap design improvements and many others.
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The CAFE Scales |
The CAFE 400 was made possible by funding from the Experimental Aircraft Association and the hard work and dedicated talents of volunteer members of EAA Chapter 124. These volunteers helped develop a special set of high-tech electronic scales that allowed each aircraft’s fuel consumption to be measured accurately by weighing before and after the race. The CAFE Scales became a key capability in allowing CAFE to later create other innovations.
Though its prize purse was a mere $2000, the CAFE 400 stimulated the design and building of several advanced experimental aircraft, including the Rutan Catbird, Niebauer’s Lancair, Jones’ White Lightning, Hamilton’s Glasair RG, Griswold’s Questair Venture and Sheehan’s Q200. In 1983, EAA awarded Brien Seeley its prestigious President’s Award in recognition of his work in founding the CAFE 400. In retrospect, the CAFE 400 spurred a renaissance of innovation in light aircraft that has yet to be duplicated. And it was all accomplished by volunteers.
The CAFE Triaviathon
In 1986, CAFE Board member Steve Williams, a brilliant engineer at Hewlett Packard, volunteered to design and build a highly accurate Barograph for the Voyager World Flight. This instrument could measure and record airspeed, altitude and temperature with great accuracy on a second by second basis. In what would become another of their many innovations, the CAFE team devised a way to externally mount this “CAFE Barograph” to the wingtip of any aircraft so that it could collect flight data throughout the flight. The flight data was obtained via a CAFE-designed-and-built, free swiveling pitot-static pressure probe that effectively eliminated sampling errors by self correcting for the aircraft’s angle of attack. After tests showed it worked flawlessly, a new flight competition was announced - the “CAFE Triaviathon”, which was to be held concomitantly with the CAFE 400 each year.
The Triaviathon was modeled after the popular athletic events called triathalons, in which contestants had to simultaneously excel in 3 separate tasks. The CAFE Triaviathon used the Barograph to measure each aircraft’s top speed, stall speed and rate of climb, three key parameters complementary to those measured in the CAFE 400 (cruise speed, fuel consumption and range). From the start there was great interest in the Triaviathon, and designers again set about winning by improving thrust, increasing lift and decreasing drag by a variety of innovations.
A New Direction—CAFE Aircraft Performance Reports
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APRs in Sport Aviation |
After 10 years of racing, and a great deal of evolution in small aircraft design, people concluded that the $2000 prize purse for the CAFE 400 was insufficient to stimulate the sizeable expenditures necessary to produce an aircraft that could surpass the current reigning champions. In 1992, EAA President Tom Poberezny proposed that CAFE should turn its talents toward performing comprehensive flight tests of the most popular experimental kit aircraft. CAFE agreed, provided that the work could be done with high quality equipment making objective measurements and with complete freedom from reporting bias. To enable this, EAA funded the building of a CAFE Flight Test Center at CAFE’s home field, Sonoma County Airport. The Flight Test Center was completed in Spring of 1993.
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APRs Feature Detailed Graphs
(click to view PDF) |
The first of many Aircraft Performance Reports (APRs) for publication in EAA’s Sport Aviation magazine was produced that summer. These were the most comprehensive reports available on small aircraft, and included measurement of the aircraft’s flying qualities as well as a thorough set of performance parameters. The accuracy and completeness of the reports led to them becoming recognized as the final word on an aircraft’s performance. All of these were produced entirely by volunteers.
One of the features of the APRs was their innovative graphical depiction of the entire cruise performance characteristics of the aircraft. CAFE found a way to show true airspeed, miles per gallon, exhaust gas temperature, cylinder head temperature and CAFE Challenge score all as a fuel flow:
A Wonderful New CAFE Barograph
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The CAFE Barograph |
The key to these APRs was a third-generation CAFE Barograph whose pressure sensors were coddled in a special heated compartment that kept them at a constant 100°F. The new Barograph was tested and calibrated in the NASA Ames Research Center’s wind tunnel and was found to be able to detect increments of 0.1 mph and just 6-8 inches of altitude. The FAA officially designated the CAFE Barograph as the reference standard for small aircraft certification . After being simply strapped on to an aircraft’s wing it could independently measure its speed, altitude and temperature with extreme accuracy, second by second throughout its flight. This enabled instantaneous computation of true airspeed and density altitude, which, in turn allowed many other CAFE flight test innovations.
For example, when combined with a manifold pressure sensor, the Barograph became a tool for the very accurate determination of an aircraft’s stall speed and stall characteristics. The altitude lost during a stall was automatically recorded by the Barograph, and the range of stall speeds obtained when using high or low deceleration rates, alternative power settings and various flight paths of entry could be explored. By this technique, CAFE routinely found that aircraft’s book stall speeds were optimistically low and their estimates of maximum lift coefficient too high as a consequence.
By some very innovative programming by Steve Williams, it became possible to use Barograph recordings to re-register the altitude window through which an aircraft had performed a rate of climb test so that the sampled window was a true standard atmosphere in terms of density and geometric height. The computation of standard geometric altitude was essential to assuring fairness to all contestants when rate of climb tests were conducted on different days with different air masses. The same computation could be applied to power-off glide data in which the sink rate of the aircraft was the indicator of its drag.
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The CAFE Manometer |
CAFE also used the Barograph to search for a test aircraft’s key performance numbers, such as speed (power off) for minimum sink rate and speed for maximum glide. Both an instantaneous sink rate and glide ratio were calculated and displayed real-time on the flight deck of CAFE test aircraft for this purpose. Because of its extreme accuracy in altitude, the Barograph could detect the exact time that an aircraft lifts off or touches down on the runway and the calibrated airspeed at that moment. These figures helped define the runway requirements of each aircraft tested, and eliminated the effects of wind on such measurements.
CAFE spent many years investigating the cooling drag of aircraft using a multi-channel water manometer. The prime importance of relative cowling exit air velocity to overall cooling drag led CAFE to routinely place exit pitot tubes on the cowl, along with inlet plenum piccolo tubes, in order to study the cooling drag of each aircraft. With the Barograph, it became possible to accurately reference the cooling system air pressures to those of the free-stream and derive typical cooling system performance standards for air cooled engine cowlings. All of this research was conducted by volunteers.
A Major Innovation: Zero Thrust Glide Testing
The APRs included measurements made by “zero thrust glide testing”, an innovative technique developed by CAFE Board member Jack Norris. Drawing upon prior work by August Raspet, Jack discovered that an aircraft’s propeller could effectively be made ‘invisible’ (i.e., produce neither thrust nor drag) if it were set spinning at a particular RPM relative to the aircraft’s forward speed. At such an RPM and airspeed, an aircraft became a pure glider whose weight and sink rate could be measured and used to calculate the aircraft’s drag.
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ZTG Graph
(click to view PDF) |
Finding the particular RPM for zero thrust proved difficult until CAFE applied its Barograph and a highly accurate capacitive proximity sensor to the aircraft’s crankshaft. This sensor allowed the range and sensitivity of the zero thrust technique to be delineated. It also led CAFE to build yet another innovation - a real-time flight deck digital display of “Revs per mile”, the key guide number for finding true zero thrust. It turns out that, equipped with a fixed pitch propeller, every aircraft has its own characteristic value for “Revs per mile” at which true zero thrust is occurring, and this value remains constant at all airspeeds. The Revs per mile display enabled CAFE to quickly compile accurate and extensive data on an aircraft’s drag characteristics. The classic drag polar of each aircraft, i.e., its signature performance curve, was the result. From the drag polar, one can accurately calculate best lift to drag ratio, flat plate drag area, parasite and induced drag, power required and many other key parameters. The insights from zero thrust drag testing led CAFE to many other flight test innovations: Total Energy: “It’s The Atmosphere, Stupid”
When the zero thrust drag polars did not agree with other drag calculations, Jack Norris was determined to lead CAFE to find out why. This involved towing a propless Cessna 152 to 12,000 feet and releasing it as a pure glider and then comparing the glide data from those glides with that measured by the zero thrust RPM technique on the same aircraft. CAFE’s talented volunteer test pilot, C.J. Stephens, did a very professional job of smoothly performing the ‘deadstick’ landing of the propless Cessna after each glide.
The results of the propless glides finally proved that measuring drag by the zero thrust glide technique was indeed valid, but showed that such glides had to be conducted in smooth air, where no atmospheric lift or sink was occurring. The magnitude of error that could be caused by rising or sinking air was alarming, and led CAFE to search for a way to prevent such air mass disturbances from affecting other flight test measurements such as cruise speed or rate of climb. The solution was yet another CAFE flight test innovation - a technique called the “Total Energy Computation” or TEC.
The remarkable electronic CAFE Scales can detect 0.05 pound increments. Thanks to pre- and postflight weighings and careful calibrations of a fuel flow sensor with totalizer, a software program was created that computed continuous real-time values of aircraft weight during a flight. By knowing the instantaneous aircraft weight as well as its accurate velocity and altitude from the Barograph, a second by second computation of both its kinetic and potential energy could be made and summed to create the TEC. In level cruise flight at any fixed engine power setting, the TEC should remain constant. If the TEC is rising or falling, it proportionately indicates the effect of a rising or sinking air mass movement. When the TEC is unstable, the flight engineer makes sure that the aircraft simply continues its cruise flight until it enters an air mass that yields a stable TEC and thus allows valid cruise performance data to be obtained. The TEC is able to distinguish between air mass effects versus change in airspeed or altitude instead brought about by the pilot moving the aircraft’s controls.
Barograph-derived TECs allowed CAFE to solve yet another mystery in flight test lore. For years, pilot’s had argued about the speed gained by applying a fresh coat of wax to their aircraft. The CAFE Barograph finally nailed an accurate study of this question. In an article entitled “Wax Job”, it was found by carefully controlled cruise flight data analysis that a fresh coat of wax applied to an otherwise clean Mooney aircraft yielded a speed gain of 2.6 mph. The Barograph also allowed CAFE to study the difference in gliding sink rate that occurred with a dead engine in either throttle open or throttle closed position as well as the cruise speed performance changes due to altered center of gravity.
Carson Speed: “The Least Wasteful Way of Wasting”
Professor Bud H. Carson of the U.S. Naval Academy, independent of the CAFE Foundation’s derivation of the CAFE Formula, developed the mathematical description for a new characteristic airspeed that he called “the least wasteful way of wasting” (time or fuel). In honor of Dr. Carson’s work, CAFE dubbed this new airspeed as Carson Speed, and its importance was that it defined the speed at which the CAFE Formula optimized for any aircraft. Quite interestingly, Steve Williams proved that Carson Speed could be found using Jack Norris’ zero thrust glide test and its resulting drag polar graph (a plot of airspeed versus drag). By drawing a line from the origin on such a graph (0,0) to a point tangent to the underside of the “J” shaped drag polar curve, it was always the case that the tangent point represented Carson Speed.
Stick Force Standards
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Stick Force Graph
(click to view PDF) |
The APR program included measuring the flying qualities of small experimental aircraft and presenting them in a graphical way that all pilot’s could readily understand. The goal was to gain understanding of the range of performances that existed and what characteristic findings made for the best flying qualities. For this, CAFE combined its Barograph readings and accelerometer readings with those from a mechanical stick force gauge, to develop standardized graphs whose slope indicated the degree of an aircraft’s “twitchiness”, “steering effort”, and stability hands off. Just as with comparing sports cars, finding out about an aircraft’s handling qualities is, from the pilot’s viewpoint, a key determinant of whether that aircraft is deemed appealing or treacherous. CAFE pioneered such measurements and the innovation of presenting them objectively in their APRs was again made possible by the Barograph.
When an aircraft’s handling qualities are less than ideal, the aerodynamic ‘fixes’ that can be applied need to be measured objectively to see how well they succeed. The CAFE graphical method of recording flying qualities is a valuable tool in making those assessments.
Education on the World Wide Web
A visit to www.cafefoundation.org opens access to nearly all of CAFE’s useful flight research reports in the form of downloadable pdf files. Among the many talents of CAFE Treasurer Scott Nevin is that of volunteer webmaster. Scott has built a quick-loading home page that students and aircraft designers can easily navigate through the many areas of aeronautical insight that CAFE has explored. The material available includes many detailed graphs as well as the stunning photos taken by trend-setting aviation photographer and CAFE Vice President Larry Ford.
This website is intended to fulfill CAFE’s charter purpose of conducting and sharing accurate and detailed flight research and other information about personal aircraft and the many components and technologies that apply to such aircraft. In the future, it will hopefully domicile a great deal more of the cutting edge information about aerodynamics and air vehicles.
The Gorgeous CAFE Perpetual Trophies
In 1993, CAFE also launched its replacement event for the CAFE 400 – The CAFE Challenge. Using the CAFE Formula, the Challenge improved upon the previous event by using the then-new technology of GPS tracking to create a 500 mile race course for the contestant (250 miles out and 250 mile return trip). Though no prize money was offered, CAFE’s volunteers designed and built two gorgeous new perpetual trophies to commemorate the winners of both the Challenge and Triaviathon. Their inspired designs were built of diamond polished machined aluminum with pyramind bases made of 500 year old, clear heart redwood. These trophies now reside in the main lobby of EAA’s AirVenture Museum in Oshkosh Wisconsin.
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The CAFE Challenge and Triaviation Trophies |
Voyager pilot Dick Rutan was the first to capture the CAFE Challenge Trophy, flying the Rutan Catbird designed by his brother, famed aircraft designer Burt Rutan. His score was later eclipsed by Gary Hertzler flying a Rutan Varieze. The CAFE Triaviathon Trophy was first won by John Harmon in his Harmon Rocket. His score was later surpassed by Dave Anders in a highly modified RV-4 designed by Dick VanGrunsven. The performances of the reigning champion aircraft in these two events represent outstanding achievements in aircraft design and are show below:
Hertzler Varieze: CAFE Challenge Champion:
Velocity: 169.3 mph
MPG: 48.0
Payload (W): 400 lb
Dave Anders RV-4: CAFE Triaviathon Champion:
Vmax: 250.7 mph
Rate of Climb: 3308.4 fpm
Stall Speed: 44.8 mph
Experienced and Ready For NASA’s PAV Challenge
Intuit’s leaders employ what they call the ‘follow me home’ concept to learn what their customers really care about and can use. For 25 years, CAFE has enjoyed the unique opportunity to do exactly that – and thereby gained first hand insight from its visiting aircraft builders as to why they built that particular plane, how they use it, and what they would need to extend its usefulness. The diversity of interests among CAFE’s team members magnified their ability to dissect the ‘anthropology’ of what people want, need and use in aircraft. From that perspective, and from its wealth of objective data about small aircraft performance, CAFE was able to help NASA define the goals for the PAV Challenge.
- By consensus, the clearest mandates for future PAVs are:
GPS based synthetic vision with Wi-Fi uplinked weather (to fly in nearly any weather)
- Ease of use (ala Honda Accord)
- Short runway capability and safety (including air bags, automatic vehicle parachutes and autopilots with computer-aided ‘horse-sense”)
The good news is that the technologies necessary to bring forth all of these mandates already exist. And, by meeting these key objectives through the incentive of NASA’s PAV Challenge, the attractiveness of PAVs will naturally raise their production numbers to the tipping point of making them affordable.
The 2011 Green Flight Challenge Sponsored by Google
The 2011 Green Flight Challenge sponsored by Google marks an historic achievement in aviation—the first demonstration of practical, cross-country emission-free flight. The NASA provided purse of $1.6 Million was the largest in aviation history.
Team Pipistrel-USA.com’s winning 4 seat, electric-powered aircraft, the Taurus G4, flew nearly 200 miles non-stop while achieving 403.5 passenger MPG! (Click Here for Flight Data). Its astounding efficiency was more than twice that of the piston-powered aircraft in the competition.
Equally promising: Team e-Genius won the Lindbergh Prize for Quietest Aircraft, with a peak take off noise of just 59.5 dBA at a 250 foot sideline. This achievement heralds the real transformative potential unique to electric powered aircraft—the capability to be quiet enough to land very near dwellings and businesses.
Two Essential Tools That Need Engineering Funding
Although all of the flight test work for the PAV Challenge will be performed by CAFE volunteers, they will need the specialized tools to conduct the testing. These tools demand the dedication of full time work by professional engineers who are attuned to the flight test domain at CAFE. These engineers must be paid and this comprises a significant part of the budget needed for the PAV Challenge.
A key element in the PAV Challenge will be a careful and accurate determination of each aircraft’s landing distance. CAFE and NASA agreed that such cannot be safely or fairly done in actual landings on pavement. Fortunately, CAFE’s Barograph along with modern sensor technology and GPS will allow the use of a Runway In The Sky (RITS) to measure landing distances in a fair and accurate way. And the RITS will have value far beyond the PAV Challenge as a flight training tool that enhances safety as well as the understanding of high lift devices and controllability at low airspeeds. Designing and building the RITS flight test equipment is the major hurdle in being able to conduct NASA’s PAV Prize, but CAFE has already found ways to do it at a minimal cost and in a way that its benefits will be shared publicly. What is needed is adequate funding.
The other key element in the PAV Challenge will be designing and building an objective flying qualities assessment tool that uses a portable digital stick force gauge (DSFG). CAFE already has much of what is needed for this, but the design and building of the DSFG will also need funding.
Experienced and Ready For Aviation's Next Challenge
Intuit’s leaders employ what they call the ‘follow me home’ concept to learn what their customers really care about and can use. For 28 years, CAFE has enjoyed the unique opportunity to do exactly that – and thereby gained first hand insight from its visiting aircraft builders as to why they built that particular plane, how they use it, and what they would need to extend its usefulness. The diversity of interests among CAFE’s team members magnified their ability to dissect the ‘anthropology’ of what people want, need and use in aircraft. CAFE's team members continually track the diverse technologies necessary to advance personal aircraft. From those perspectives, and from its wealth of objective data about small aircraft performance, CAFE is able to help NASA define the goals for its Centennial Challenges for Aviation. CAFE expects by this effort to evolve highly useful and consumer-attractive personal aircraft whose production numbers rise to the tipping point of making them very affordable.
Conclusion: CAFE Needs Your Help
CAFE is the ideal organization to manage and conduct aviation's technology prize competitions. It has the requisite experience and the passionate commitment of a uniquely talented team. The funding that you contribute to make possible CAFE's good work is tax-deductible. Please donate generously!!
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Electric Aircraft 