Pitot/Static ?

[Chappyd]

As I've been building my -7, I've been a little guilty of a lack of forward planning for wire routing and all the associated plumbing. My plane was always meant to be a fairly simple VFR bird. I'm now starting to get into the wiring and plumbing for the systems I have. My question concerning the Pitot/Static system is how many instruments can I run from 1 pitot and 1 static line? I have a Trutrak EFIS, an ASI and Altimeter, and I also bought an AOA sport. The AOA and the TT both need the static and pitot, while the instruments alson need to tap into one each. Can I run 3 things off each line and still maintain a high degree of accuracy?

Thanks

[SkywayCaptain]

Yep, should be no problem.

[flyeyes]

Originally Posted by Chappyd

(snip) Can I run 3 things off each line and still maintain a high degree of accuracy?

Thanks

Accuracy, yes. Redundancy, no.

This is typical RV practice, but be aware that a pitot problem (ice, bug, whatever) takes out all of your airspeed/AOA instruments. Same with a static problem.

At least one Cirrus accident in IMC is suspected to be due to water in the static system

I think I'm the only one, but I used a separate pitot/static source for my AOA sport.

Bernie Kerr tapped the back of his cylinder cooling plenum for an ice-resistant backup pitot source on his first RV. He found it accurate to within a couple of percent through the entire IAS and power range of his aircraft (which surprised me)

[Chappyd]

Thanks!

I'm really not too worried about redundancy in a VFR plane. My pitot /static set up isn't really any different then what was in my Mooney. The big difference is that the pitot line only did one thing.

Bringing the Mooney home after an annual in the winter I did experience an icing condition in the pitot line. They had washed the plane inside, and shortly after rotation the airspeed stopped functioning correctly. It didn't get over 80 mph until I had been in criuse for a while, then it gradually came up. When I went into the pattern it was way high. I was really glad I had plenty of time in the plane and was somewhat comfortable flying it by feel, rather than relying on the ASI. When I turned off at the taxiway I was still doing 80 mph!

Now thinking about it, the stall indicator/buzzer would still have worked normally because it was an independent system. In that plane there was also a knob I could pull for alternate static.

Food for thought. I could do dual pitot's, and then an alternate static as well.

[pierre smith]

....is all there is, Dave, not any flow per se. My buddy has a backup airspeed for the Dynon 180 and also static hook up. You will also need static to the encoder,

Regards,

[CESSNADON]

Originally Posted by Chappyd

As I've been building my -7, I've been a little guilty of a lack of forward planning for wire routing and all the associated plumbing. My plane was always meant to be a fairly simple VFR bird. I'm now starting to get into the wiring and plumbing for the systems I have. My question concerning the Pitot/Static system is how many instruments can I run from 1 pitot and 1 static line? I have a Trutrak EFIS, an ASI and Altimeter, and I also bought an AOA sport. The AOA and the TT both need the static and pitot, while the instruments alson need to tap into one each. Can I run 3 things off each line and still maintain a high degree of accuracy?

Thanks

The pitot and static systems are dead headed in the instruments, thus there is no flow in the tubing and no pressure drop. You can connect as many devices as you like to the system with no change in the accuracy of the devices. The exception is the ROC which has a small calibrated leak but it is relatively insignificant. Leak free connections and instrument cases are the most important issue in building a good pitot/static system.
You might take a page from Cessna's book on the alternate static source. They install a three way valve in the panel which allows the alternate static to come from within the cockpit. There may be a slight change in calibration because of a difference in atmosperic pressure outside vs inside the cockpit.