Why is total energy difficult using delta pitot pressure?

On 7/27/2012 1:35 AM, Jim White wrote:
At 23:17 23 July 2012, Eric Greenwell wrote:
On 7/23/2012 1:18 PM, Steve Koerner wrote:

The triple probe is usually in the prop wash of a self-launcher,
rendering it almost worthless under power. Using the fuselage
pitot/static avoids that problem. That's why I do it, but I'm not sure
the original poster had in mind.

--
Why do you need total energy when running your engine?

The TE response isn't really needed because I'm flying at a fairly
steady airspeed; instead, the problem is the prop wash makes the
pressure at the probe very unsteady, and that makes the vario needle and
audio very unsteady, making the vario almost useless for finding and
centering a thermal.

Some pilots work around the problem with a panel-mounted pneumatic
switch to connect the vario TE input to cockpit static, and I'm told
that works well enough.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz