|
|
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
<< Lancair Builders' Mail List >>
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
>>
<<Greg Nelson likes GPS GS..>>
Greg:
There is a quick and dirty method to check your IAS by using the GPS. As you
know, IAS is the sum of Pitot (total) minus Static (total) or Pt - St = V, or
put another way, IAS =1/2 V roe X V2.
To test your Static system for having the correct port location on the
fuselage, just fly two legs at low altitude, holding exactly the same IAS,
both directions. Note the GS from the GPS each leg. Total the 2 GS readings
and divide by 2, this will give you your exact TAS. Then compute your TAS
from your IAS using altitude and temperature. Remember how to do this? The
TAS you receive should match the TAS you derived from the average of the two
GPS ground speed readings. If your computed TAS is "higher" than the GPS
derived TAS, then your error *high*. Your IAS will then have to be corrected
for critical speeds, mentally. I.E. when doing slow flight, or at Vx or Vy.
There is another test you can do to confirm your Static port position error:
Select a quiet airport that will allow you to make low passes at different
speeds. Set your altimeter to read the airport elevation. Then takeoff and
make a low pass at slow speed, and note the altimeter reading when you are at
50' above the runway. Do this at several speeds, finally at your highest
speed, noting the altimeter reading at 50' above the runway. If the altimeter
shows "higher" that 50,' then you have an error in the location of the Static
port.
You can then plot a curve on a chart and see the error at all speeds. This
error is related to "Q", or dynamic pressure. The error should confirm what
you found on your GPS GS readings for TAS. This static error at "Q" will
effect everything in your airplane that uses static inputs, even an air data
computer.
Both test are fun, and informative. If the error is 6 knots or less in your
plane, forget it. If higher, maybe you should try another port location.
Regards,
Tony Durizzi
DAR(F)636157NM
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
|
|