On Mon, 10 Mar 2014 06:49:19 -0700, Steve Leonard wrote:

On Friday, March 7, 2014 6:30:41 PM UTC-6, Martin Gregorie wrote:
IOW, if the IAS in flight shown by a freshly calibrated ASI is not the
same
as independently measured TAS then the error is due to the placement
of the static vent and/or the pitot.

This is true only at sea level, standard day conditions in the airspeed
range we are interested in. At 5000 feet, IAS and TAS are NOT the same.

Yeah. Treat that as a rather bad short-hand. A fully qualified
explanation would be quite long by the time you factor in the different
IAS errors on a different type of glider flying with the one that's
trying to check his ASI. Most people don't own the same sort of trailing
bomb device that Dick Johnson used.

For example, its well known that pressure under the wing is above bulk
atmospheric pressure, so a static vent anywhere near the underside of
the wing will make the ASI read low.

Disagree with this. Look at the airspeed corrections on a Schempp-Hirth
sailplane using the underwing statics. The Ventus A that Dick Johnson
tested is a good example. Goes from reading 4 knots too slow at low
speed to 10 knots to fast at high speed.

The general effect of the wing is like I said, but it can obviously be
affected by factors specific to some airframes such as turbulence round
the root or kicked off by the nose shape. Most gliders have, at best,
quite rudimentary root fairings. I imagine Will Schueman would be quite
unimpressed if he saw them.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |