Tuesday, August 6, 2013

DIY Pitot fixation flange


Until now the fixation of the 8 mm pitot tube was left to the user concern. Now it's time to face the music. The main issue here is that sometimes the pressure line brass tube break away, it's not possible to bend it too much around. Another important aspect is the needed installation space, since the pressure lines are aligned with the pitot principal axis  some layout problem can arise.  I've began to search for a more comfortable and hassle free pressure line connections set up and pitot fixing.
Common fixation masts seems too heavy and unfortunately installation dependent ; flanges designs 
as per figure P8.1 are not so easy to implement nor adapt to our model sized pitots. In our DIY applications pitots are mainly positioned in thre different locations , the nosecone, underneath the wing or on the wing leading edge.
Neglecting accuracy related considerations the most critical, with heavier space restrictions, is the leading edge installation. Mounting the pitot into the wing leading edfe require minimun thickness for the fixation flange


Figure 8.1 Pitot suitable for flange fixation

Given that I've set the main requirements to be
-Reduced weight, less than 20 grams
-Reduced dimension, Around 20x20x40 mm
-Easy connection of pressure sensor by means of Tygon or similar standard tube
-Easy fixation to airframe, suitable also for marine and automotive use.
-When operating in air the condensate flow to sensor should be minimized, flange should act as a syphon and the assembly should be drainable.
-The assembly can be disposable, it's not primary to allow disassembly.
Recalling consideration on dynamic response of pitot pneumatic lines the possibility of local mount for the sensor is a plus.
After some requirement blend I get the arrangement depicted on figure P8.2
Figure 8.2a Preliminary pitot flange arrangement

Figure 8.2b Preliminary pitot flange arrangement detail
Right now I'm experimenting with this flange layout that allow pressure line connection by mean of two barbed ports on the top side of the flange, mechanical fixation is assured by four M3 hex cap socket screws. Final material and required work machines are not defined at the moment.
Two different physical prototypes are under testing, one in nylon material the other in alluminium alloy.


JLJ
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