REFLECTOR: Altimeter v. Airspeed

[Chuck Jensen]

Tom,

It's understood that cabin pressure can be affected by opening vents, changing aircraft configuration, such as putting down the gear or opening the alt-air valve in the cabin.  But if at cruise, the altimeter is reading correct, is that not an indication that the pressure in the cabin is near ambient and thus the IAS will also be correct.

Al, my pitot is on the pointy nose so its outside of the influence of a pressure wave from either the canard or wing (unlike my static port, which is the reason I'm doing this test), so the starting assumptions is the IAS is accurate if the static system pressure is correct.  But you're right, the final word is to do the triangulation flight and input the data into any of the several spreadsheets out there on the web---which to be really accurate, are a bit more complex than one would think at first.

Chuck Jensen


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Tom
Sent: Sunday, January 06, 2008 6:23 AM
To: reflector at tvbf.org
Subject: REFLECTOR: Altimeter v. Airspeed


You can also have variations in pressure when static is ported to cabin. 
Flew a neighbors MustangII last week and I had his trutrak a/p on which 
is vented to cabin. I opened the air vents and the a/p read the sudden 
pressure increase in cabin as a quick descent and shot to the sky.
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