swisseagle

swisseagle

Well Known Member
Static and pitot tube diameter .. does it have influence?

Hello builders

A question that poped up during the decision of which tube should I use to route the static and pitot line into the panel section:

Does the inner diameter of these tubes has an influence in the readout/displaying of the airspeed or altitude? I mean, does a smaller tube "damping" the change of the singal or does this has no effect because it is such a small pressure difference when you go faster or slower/ higher or lower?

The AOA as a example, has very thin tubes 3.2mm outside 1.8 inside.

Maybe a small amount of damping is desired for an easy to read display.

Any thoughts are welcome.

Dominik
RV-7A
 
Last edited by a moderator:
Hi Dominik...

... It doesn't affect the accuracy of your instruments since there is no flow of air but simply a steady pressure at any given airspeed. A good example is a water hose...its diameter will affect the amount of gallons per minute but if it has a nozzle on it, only pressure would be felt...similar to your pitot-static system.

Regards,
 
Dominic

Pierre is correct but I have to add a caveat.

Assuming the pitot and static openings remain constant, as the diameter of the tubing increases, so does the volume between the inlets and the instruments and this would certainly cause a lag in instrument response as the pressure of the volume would change slower than the pressure at the pitot.

This same thing happens as tubing length is extended.

I assume that you're not going to be using any tubing that is so large it could possibly be a problem and the whole conversation is moot as the lag would be so small that it wouldn't matter much to airspeed or altitude readings.

However, I too noticed that the tubing provided for angle of attack is quite small. I won't be changing that just because I have no idea what was in the engineer's mind when the system was designed. The almost instant pressure changes in the system that would result from a very small diameter tube may be necessary for proper operation. I just don't know. I'd call their engineers before changing that.

I would think that the smaller tubing would clog easier though.
 
My Pitot line

I used a heated pitot and the run goes through a bulkhead fitting and the new tube in the fuselage is the same size. The fitting on the pitot head determined the size for me. Flying for several years now and airspeed instrumentation has not been a problem. With the standard bent tube Van calls out I would stick with that size.

Bob Asxom
 
Here was the question.........

Quote:
Originally Posted by dmaib View Post
You just push the small ring on the fitting in and pull the tube out. I did my airplane from the beginning with these fittings (some from Safeair1 and some from Stein) and they have been bulletproof so far. I have disconnected and reconnected a few times for various reasons, and they work great!

GASMAN..
Truck air brake systems have been using a system like this for years. Their fittings appear to be smaller in bulk.

What is the minimum I.D. tubing size for use on pitot/static systems? Lines used on truck air systems are very lite and compact and can be purchased at any NAPA auto parts store.
 
Thanks for your answers!

I dont want to change the "general" system, just like to take tubes and fittings like the on from Stein or others, but a brand that I can get here in europe, with metric mesurements. There are different tube materials and so on small difference int the inner diameter. Lets say, outside 6mm, inside 4.0mm or 4.4mm

The standart Nyloseal is 6.35mm outside (1/4") and 4.3mm inside.

So I'm not far away with mine and will go on.

Regards,

Dominik
 
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