F li g h t Te s t in g Te c hn i q u e s
Sawtooth Climbs VX
Determination
Determing best climb angle
By Ed Kolano
Last month we took the raw data from the sawtooth climb
test flights and created a plot of best climb rate airspeeds
(VY) versus density altitude. This handy plot can be used
for flight planning as well as in-flight reference. We also
spent a few words on data reduction engineering judgment to assess the quality of the data, illustrating when
it's appropriate to exclude and include suspect data. This
time, we'll use the same flight test data to determine the
airplane's best climb angle speed (VX). Oh, and a little more
of that judgment.
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Vol.2 No.9 / Sep tember 2013
Figure 1 is the same data reduction worksheet we used
last time for the 3,800-foot density altitude test, but we've
added two columns—"True Airspeed" and "Flight Path
Angle." These values appear in blue on the worksheet,
along with all the other post-flight calculated values. We'll
need the true airspeed for our VX calculations. We'll talk
about why we included the climb angles a little later.
First, the airspeed conversions; we recorded the
observed airspeeds during the flight tests. Using our