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Details of Johnson Flight Test.
In 2003, when I began flight testing Dr. Sinha's deturbulator drag reduction device,
we anticipated that public acceptance of this new technology would be hard to achieve.
A key element in our plan was to obtain independent verification at the earliest possible date.
Since Dick Johnson has perhaps more experience testing sailplanes
(gliders) than anyone in the world and
is known around the world for his uncompromising flight test evaluations, we asked him to do
the job. He agreed.
Two years later, we finally got my glider (Standard Cirrus, #60, 1970, N2866, QZ) to him.
On 12/13/2006, at Caddo Mills, Texas, Dick and Jeff Baird logged four high altitude
test flights in QZ with modified wings using the 2nd prototype of
Dr. Sinha's deturbulator tape which had been installed nearly a year earlier. The next day,
they flew two more flights. At that point, Dick felt that he had enough data for
a clear measurement of performance. The wings were then cleaned to
restore them to standard condition. Then on 12/23/2006 they flew three additional flights to
measure the unmodified (baseline) performance. Additional flights also were taken to calibrate
the airspeed system.
I had logged our best two flights
on 9/27/2006 and 10/21/2006 that yielded optimistic results indicating more than 20% improvement at best L/D
speed. These flights encouraged us to take QZ to Dick Johnson immediately rather than
delay another year. As reported earlier, we have not yet implemented solutions to our performance
consistency (stability) issue, so this was a risky decision. Our purpose, however, was
not to present a product to the market, but merely to demonstrate the potential of Dr. Sinha's invention.
The results in a nutshell
Evaluating this deturbulator prototype by time honored means applied to rigid wings yields a respectable
5% improvement. However, at 50 kts (IAS) the data in this test series, as well as prior test flights,
are will established at a point far beyond the reach of the traditional 4th order polynomial fit
to glide ratio points. These data indicate a best glide ratio improvement in the range 13% to 18%.
A 4th order curve fit is not appropriate because the glide ratio curve contains airspeed
dependencies that are not found on normal, rigid wings. The deturbulators tested were only the
second to be installed on an aircraft and contained some design deficiencies that were not yet corrected.
The result was performance variations that cannot be followed by a 4th order curve fit.
Furthermore, variations in performance with changing atmospheric conditions, have been documented
for the early prototypes. Consequently, data that are averaged indiscriminately, without regard
to flight conditions, reduce performance information as well as scatter and bias in the data.
When only data from equivalent atmospheric conditions are averaged (not done in
this test series), then larger performance improvements emerge. This has been demonstrated
repeatedly in prior tests. A full analysis of this test series and prior data,
taking this into account, can be found in the report
Analysis of Independent Flight Test Data.
Following is a summary of that analysis.
The orange curves in Figs. 8 and 9 are an average of the two best flights (9/27/2006 and 10/21/2006)
prior the Caddo Mills tests.
(Note: These points are sparse, so the connecting line should not be taken as strictly meaningful since
structure between the data points could be missed. It should also be said that some points
were dropped from the data because they deviated exceedingly from a curve fit to the data. The dropped points
were 2, 2, 2 and 1 from flights 2, 3, 4 and 5 respectively. No points were dropped from flights 1 and 6.
A 4th order fit to the data indicates 15% improved maximum glide ratio.
That is a considerable improvement, more than adequate to verify the effectiveness of Sinha deturbulators.
However, the 50 kt point (41:1 glide ratio) falls almost directly over the same point from two
or flights (orange).
(Click the image for a better look.) Notice that the red line (4th order fit)
is hardly influenced by this high point which is well established in the Caddo Mills data
by four flights and by two additional prior flights. Six points are normally enough to smooth data
even under poor conditions. A huge residual error would be needed push this point so far above the
traditional curve fit.
So, this point should be accepted as real and the faired glide ratio should run through it!
The improvement indicated by these six data points is then 20%.
Figure 8. Six Flights Glide Ratio
Figure 9. Six Flights Percent Change
Perhaps it is enough simply to walk away with an image of Fig. 25 burned in your memory. The green and
blue curves show the glide ratios measured on day 1 (four flights) and day 2 (two flights) respectively.
The orange is our best two, nearly identical, flights taken in ideal conditions in September and October
before the Caddo Mills tests.
Do the Caddo Mills measurements corroborate the our measurements? Considering that the deturbulator design
is not yet stable over changes of temperature, humidity and rapid altitude changes, we did not expect the results
to match ours. Five features stand out in fig. 25:
The first four features offer convincing evidence that the Caddo Mills data, in piecemeal fashion,
confirm our measurements over all airspeeds except the lowest. That is, when conditions were
(nearly) right at Caddo Mills the deturbulators were found to perform (nearly) the same as in our tests.
All of the differences can be explained in terms of the deficient vent design of the present
deturbulator prototype, as Dick Johnson suggested in his report with respect to high speed performance.
- All eight flights converge around 42:1 at 50 kts (ISA).
- Day 2 at Caddo Mills follows our data very closely from 50 kts to 65 kts.
- Day 1 at Caddo Mills follows the baseline from 60 to 70 kts, corresponding to the dip in our measurements.
- Day 1 at Caddo Mills follows beneath our high speed points.
- There is a major point of disagreement at the low speed end.
Figure 25. Days 1 and 2 and Best Ever Glide Ratio
Our thanks to Dick Johnson for conducting these tests, Jeff Baird for sharing the piloting duties,
tow pilots David Cheek and Howard Hughes, Paula Lara and her staff at
Southwest Soaring, Inc. and
the Dallas Glider Association (DGA) for funding these flight tests.
Oxford Aero Equipment