19.09.2019 Views

fluid_mechanics

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

3.5 Static, Stagnation, Dynamic, and Total Pressure 107<br />

(3)<br />

(4)<br />

V<br />

(1)<br />

p<br />

(2)<br />

F I G U R E 3.6<br />

The Pitot-static tube.<br />

where p and V are the pressure and velocity of the <strong>fluid</strong> upstream of point 122. The outer tube is<br />

made with several small holes at an appropriate distance from the tip so that they measure the static<br />

pressure. If the effect of the elevation difference between 112 and 142 is negligible, then<br />

p 4 p 1 p<br />

Pitot-static tubes<br />

measure <strong>fluid</strong> velocity<br />

by converting<br />

velocity into pressure.<br />

By combining these two equations we see that<br />

which can be rearranged to give<br />

p 3 p 4 1 2rV 2<br />

V 221 p 3 p 4 2r<br />

(3.16)<br />

The actual shape and size of Pitot-static tubes vary considerably. A typical Pitot-static probe used<br />

to determine aircraft airspeed is shown in Fig. 3.7. (See Fig. E3.6a also.)<br />

Four static pressure ports<br />

Heated outer case<br />

Stagnation<br />

pressure port<br />

Mounting flange<br />

Stagnation pressure fitting<br />

Heater leads<br />

(a)<br />

Static pressure fitting<br />

V3.8 Airspeed<br />

indicator<br />

(b)<br />

F I G U R E 3.7 Airplane<br />

Pitot-static probe. (a) Schematic, (b) Photograph,<br />

(Photograph courtesy of SpaceAge<br />

Control, Inc.)

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!