The fin is not the only location for good compensation.
A total energy probe works best when the flow p***** by it at nearly the
same angle and at nearly freestream static pressure for the range of
speeds of interest.
Mounting in front of the fin puts the probe in a location that is close
to the freestream static pressure. The flow angularity may vary some
amount, but the combination of glider angle of attack and the downwash
field of the wing will tend to reduce the overall variation in flow
angle. Changing flap position will induce a step change in flow angle,
but again this is not too large.
Mounting the probe on the top of the fuselage a little aft of the wing
again puts the probe in a region that is close to freestream static
pressure and the straightening effect of the wing and fuselage produce
only a very small change in the flow angle at the probe.
Now, what about the forward fuselage? For a Ka6, the static buttons are
on the side of the fuselage at the bulkhead ahead of the instrument
panel, where they register near the freestream static value for the
thermaling and cruise conditions. On the top of the forward fuselage,
the canopy will slow the flow at its base, producing higher than
freestream static pressure, and then rapidly accelerate the flow as it
moves up and over the curved ****tion of the canopy, thus producing a
lower than freestream pressure. By placing the probe at the bulkhead
ahead of the panel, it is enough ahead of the canopy disturbance to have
a pressure value that is close to freestream, but possibly with more
variability than for the other two locations mentioned above. The pitch
flow angularity is pretty constant though. For the Ka6 with the speeds
mostly between 40 to 70 knots, the forward position is reasonable.
...... Neal
unclhank@[EMAIL PROTECTED]
wrote:
>>
>>- Show quoted text -
>
>
> If objective is just simple installation, do what JJ says and put it
> on the nose.
> Putting it anywhere close to the flow field of the wing- that is
> anywhere near the top, means that the local pressure
> changes every time you change angle of attack. This is the reason why
> it is on the fin on essentially all modern gliders.
> UH
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