dan carley said:
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