Pitot pressure
Todd Pattist
differential between pitot and static at a speed of ... say 80 knots?
I'm not looking for exact information, just an answer that's not off
by more than a factor of 2.
---------------------
Todd Pattist
pat...@ix.netcom.com
Ventus C - N210WH
Todd Pattist
>> differential between pitot and static at a speed of ... say 80 knots?
>> I'm not looking for exact information, just an answer that's not off
>> by more than a factor of 2.
>Well, erm, delta p = 1/2 rho v^2
>v = 80 knots = 40 m/s (for all practical purposes)
>rho = 1.225 kg/m^3 (if I recall)
>so delta p = 1/2 * 1.225 * 40^2 = 1000 Pa (pretty nearly)
> = 10 mB (aren't there 10^5 Pa in a bar)
Amazing what you forget when you don't use it much. Thanks
So 10 mb ought to be about enough to hold up a 10 cm column of water.
If I put some water in a U formed in some clear tubing, then hook one
end up to my total energy system at the T.E. tube, and set up a 10
cm. water column height difference, I should be able to monitor the
T.E. system for leaks by ensuring that the water level diffference
remains unchanged over time.
Jeffry Stetson
>
>Can anyone tell me the approximate magnitude of the pressure
>differential between pitot and static at a speed of ... say 80 knots?
>I'm not looking for exact information, just an answer that's not off
>by more than a factor of 2.
>
--
Jeffry Stetson ... Comm ASEL, Pvt SES & Glider, Instrument Airplane
EAA, SSA, AOPA, IAC, MAPA
Mooney M20E "Superduper 21"
Salto H-101 "Shiva - The Cosmic Dancer"
Jeffry Stetson
>
>Can anyone tell me the approximate magnitude of the pressure
>differential between pitot and static at a speed of ... say 80 knots?
>I'm not looking for exact information, just an answer that's not off
>by more than a factor of 2.
>
pressure(cm of water) = 1.744x10e-3 [v (kts)]^^2
kts cm of water
10 .17
20 .70
30 1.57
40 2.79
50 4.36
60 6.28
70 8.55
80 11.16
90 14.13
100 17.44
110 21.10
120 25.11
130 29.47
140 34.18
150 39.24
160 44.65
170 50.40
Erwin Bejsta
>Can anyone tell me the approximate magnitude of the pressure
>differential between pitot and static at a speed of ... say 80 knots?
>I'm not looking for exact information, just an answer that's not off
>by more than a factor of 2.
>
60 kts = 0.1727 inches of mercury (Hg3)
80 kts = 0.3075 Hg3
100 kts = 0.4814 Hg3
120 kts = 0.6950 Hg3
Conversion: Hg3 * 0.4912 = PSI is 0.4912
this information is from a databook on solid state pressure
sensors by the brandname of SenSym
if you need any more data, let me know via email.
Good Soaring
Erwin
John Giddy
>
> Can anyone tell me the approximate magnitude of the pressure
> differential between pitot and static at a speed of ... say 80 knots?
> I'm not looking for exact information, just an answer that's not off
> by more than a factor of 2.
>
> ---------------------
> Todd Pattist
> pat...@ix.netcom.com
> Ventus C - N210WH
>
The answer for 80 knots at SEA LEVEL and "standard" barometric
pressure is about 1030 Newtons/sq.metre (= approx. 0.15 lb/sq.in)
The pressure difference is the "dynamic pressure" due to the movement
of the aircraft (or anything else) through the air. This dynamic
pressure is given by the formula:
dynamic pressure = 0.5 x (air density) x (airspeed squared)
(can't do maths formulas in ASCII text :-( )
A good reference is "MECHANICS OF FLIGHT" 9th edition, by A.C.Kermode
published by Longman Scientific and Technical, pp 58 - 64, and table
of values on page 438.
Notice that the dynamic pressure depends on the air density, which
decreases with height, thus the INDICATED airspeed is not the same
as the true speed except at sea level, where very few of us fly !
Also from Kermode's book, true speed is about double indicated speed
at an altitude of about 12,200 metres ( 40,000 ft), so watch it in
those super wave flights ! Vne is given for a standard atmosphere,
and although the aerodynamic forces are also proportional to the
dynamic pressure, flutter and other nasties are not. Don't fly at
INDICATED Vne at high altitudes !!
Best regards, and great soaring, John