pitot static port system

[dan carley]

i have a rv-4 flying, i did not build it. going to install a dynon 10a and got confused about pitot- static lines. are they 2 seperate systems or is the pitot the begining and static port the end. are there any drawings on this system?

thanks
danny
rv-4
N2275S

[mgomez]

The pitot system and the static system are separate.

With all due respect, your question suggests you have a ways to go before you are qualified to safely make modifications to this very important part of your airplane. Please take a few hours to read a couple of books on the subject.

We don't want to lose a fellow aviator and member of this community (or the privilege of maintaining and building our own airplanes.)

Regards,
Martin

[dan carley]

martin,

i did find a web site on the system but it's a little unclear on the actual install.
before i start a project i always do the research. that's why i asked the question and help on this system.or where i can find reading info. like i said i did not build the plane.


danny
rv-4
N2275S

[Ironflight]

Dan,

It may be just that I'm an engineer, but I find that Tony Bingellis's books (Sportplane Construction Techniques in particular) is not just a great reference (it has a section - with drawings - on Pitot/Static systems), but just out and out a good read! For someone that has inherited an already finished Experimental, it would be a great book to have on the shelf for exactly the kind of questions you're asking.

Paul

[mgomez]

All of Tony Bingelis' books are very useful, and are easy to read. They won't tell you how the builder of your RV-4 installed anything, of course, but chances are he read those books too!

The other thing to do is have another builder take a look at your airplane. They're pretty simple systems, and having someone point out what does what will be very helpful.

By the way, what are the legalities involved in repairing a homebuilt one didn't build? The Repairman's Certificate doesn't transfer to the new owner, does it?

[dan carley]

paul

thank you for the information on tony's books. i'll order it today.

danny

[Steve Sampson]

Originally Posted by dan carley

i have a rv-4 flying, i did not build it. going to install a dynon 10a and got confused about pitot- static lines. are they 2 seperate systems or is the pitot the begining and static port the end. are there any drawings on this system?

thanks
danny
rv-4
N2275S

Danny - I can see the logic of your question. In a sense they are the two ends of the same system though there should be no flow between them. But if you consider an ASI, what it measures is the differential pressure between the static and the pitot. In that sense they ARE two ends of one system.

However, they are systems in their own right. For instance the altimeter measures the absolute pressure of the static air pressure in an absolute sense.

Worth reading up. I think Wikkipedia or the NASA web site might clarify.

Good luck!

[flyeyes]

Originally Posted by dan carley

i have a rv-4 flying, i did not build it. going to install a dynon 10a and got confused about pitot- static lines. are they 2 seperate systems or is the pitot the begining and static port the end. are there any drawings on this system?

thanks
danny
rv-4
N2275S

The other advice you've gotten is dead on, especially (and minimally) to have someone with a deeper understanding to look over your shoulder.

Disclaimer aside, the pitot and static are separate, and each has a line which attaches somehow to the back of the Dynon.

The pitot gives ram-air pressure to the instrument. It is nothing more than a tube fished through the wing and fuselage from the pitot tube, which, if your airplane is built to plans, is nothing more than a 1/4" aluminum tube under the left wing which is bent to face directly into the airstream.

The static system feeds local ambient pressure to the airspeed indicator and altimeter and VSI (+/- the Dynon which combines all these instruments). Theoretically, this pressure is not affected by airspeed, but in practice it's hard to find a perfect position.

If your airplane is built to plans, the static ports are on the aft fuselage. They are simple pop rivet heads with the center mandrel pushed out and tubing attached to the inside stem. There should be one on each side, abd they are connected together to average out effects of the airplane slipping to one side or the other.

The materials for the tubing can be almost anything, but typically they are the white translucent plastic stuff sold at the hardware store to plumb icemakers in refrigerators.

Occasionally, people leave the static inputs open to the cabin (i.e. no tubing to static ports) and this kind of works, but will lead to significant instrument errors.

In your RV-4, you can take off the aluminum skin in front of the instrument panel by removing the zillion screws holding it on. Put some blue painter's masking tape at the edge (on the panels you don't remove) so that you don't inadvertantly scratch the paint as you pull it off.

With access to the back of the instrument panel, you will see the pitot tubing attached to the back of the airspeed indicator. The static tubing will be attached at a different port, but will also be attached to the altimeter. The ports will be labeled, but you can tell which is which by how they are hooked up. Take digital pictures before you take anything apart.

Hook the dynon up just like the airspeed indicator. Depending on what you are or aren't removing, you make need to change some plumbing. If you get confused which is which with everything disconnected, have someone blow into the pitot tube under the left wing to positively identify the pitot line (this may also be an opportunity to take embarrassing photos of your helper which may be handy later). All connections need to be airtight.

When you reassemble, some of the screws from the access panel will be usable, but many will not. Do yourself a favor and don't use boogered up screws. They are cheap, so just get a couple hundred extras from wick's or somewhere. Put a speck of anitseize or fuel lube on the end of each screw before installing it and you will be happy next time it comes off. Don't use the electric screwdriver to put the screws in, and don't overtighten them.

Hope this helps.

James Freeman

[dan carley]

jim,

thanks for the walk through, i have a better understanding of the system now. i just wanted to bone up a little before i started working on this. i have a good friend who is a a&i that will be looking over the work.

thanks
danny
rv-4
N2275s

[Mel]

This is a prime example of why Technical Counselors were invented.
Please contact one. You can find one near you by going to the EAA webpage.

BTW, as far as repairing or modifying an amateur-built aircraft, anyone can do it. The repairman certificate is only required to sign off the annual condition inspection. I don't particularly agree with the way this rule is written, but it is the way it is. In other words, It may be legal, but not prudent.