Combined Pitot / Static Probes?

[James]

Hi Guys,

there's a couple of pitot threads out there, but they're all pretty old, so I'm gonna relaunch this one with a new question -

What's the consensus on combined pitot/static probes?

My wing's got a raven boom-type probe installed already: will this do the job for simple day VFR, fair-weather flying?

1) Will this setup give me accurate static, or do I need to put in 2x static ports on the aft fuselage?
2) How do these probes perform in the real world? How do these probes handle crosswind, high AOAs or sideslipping?

3) I'm tossing around some other options: Battson's got me sold on the Dynon AOA system, which will use a separate probe (and needs separate static ports).
I'm thinking about connecting the existing PS probe in the left wing to an old steam-gauge airspeed indicator, and then having a separate Dynon AOA in the right wing, connected to the EFIS.
I know running 4x nylon lines is extra weight, but the dial ASI gives all the redundancy I'll ever need, so I won't bother with batteries, dual screens, etc etc with the EFIS.

Suggestions?
I have to think about this now, because I'm hopefully closing up my wings soon.

Thanks in advance, this forum is a great resource :-)

James
Nowra, Australia

[Bcone1381]

Combined Pitot Static Tube.....I have no experience with one except for the Piper aircraft I flew once upon a time. I installed one on my Patrol's wing, and trust it will work when that time arrives. The placement of static ports on the fuselage is very sensitive and can introduce error in airspeed and altitude, plus the installation of the combined unit seem easier. But I see most builder go with fuselage mounted static ports.

[James]

Yeah, that's the feeling I get as well - everyone's going for separate static ports, but lots of people seem to struggle with the placement.
Maybe this is a problem I can avoid with a combined P/S probe?

Thanks Bcone - James

[zkelley2]

The dynon and garmin AoA probes also have pitot, so you don't have to install 2 separate booms. It doesn't have static on it so, yes you then have to run a static line from somewhere(s).

The combined pitot/static bend tube things work fine except with large slips, but separate static ports don't either unless you install 2.

[James]

Yeah, I understand how I'm doubling up on pitot tubes, but the combined pitot/static probe is already installed in the wing.
I can use the static line from the existing probe to reference back to the dynon probe, if the static works as well or better than installing twin static ports on the aft fuselage.

Thanks for the insight zkelley :-)

[Mark Goldberg]

For what its worth - I used an AN5814 combo pitot/static tube when I first flew. The static port never worked like that. I had airspeed readings 20 mph too high and other bad readings as well in altimeter and vert climb. After trying a bunch of different places for the static port I ran plastic tube aft under the floor and put static lines on either side of my fuselage like I had done on my RV8. Problem solved. Of course your mileage may vary. Mark

[Bcone1381]

I did not install an AN5418, rather a bayonet looking tube from Steen Aero Labs. It is a straight 20.5" tube that mounts to the main spar, and penetrate forward about 9 inches beyond the leading edge. The pitot/static tube is actually a tube inside of a tube. The inner tube carries the ram air pressure to the base, and the area between the outer and inner tube is used to carry the static pressure to the base.

There are simple ways to adjust static pressure. I've read an o-ring ahead, or behind will change things in one direction, or the other. But I hope this design has both the pitot and Static port far enough ahead of the leading edge and outboard of the prop to give good data. We'll see how it works. It seems stout to me. Either Bob's Patrol Book or Eric Newton documented a pitot tube design made of AL tubing. Maybe the Steen design is an improvement on that...we'll see.

https://secure.steenaero.com/Store/site/product.cfm?id=B6853D82-102E-BB20-1868CF89D388401B

The Steen description has an error, the base uses 1/8 NPT fittings, not 3/8"
Screen Shot 2019-04-09 at 2.13.38 PM.png

[James]

Hi Mark and Brooks,

thanks for the replies!

Mark - I see the AN5814 is an older L-shaped PS tube - as Brooks says, maybe the more modern boom-type design has addressed some of these accuracy problems?

Brooks - Thanks for the lead. Going by the product picture in the Steen Aero store, this probe looks exactly like the Raven item I already have... maybe rebranded? I'll print off the drawing, and go over it with a set of verniers.

In any case, the existing probe will get me into the air, and if it doesn't perform up to expectations, well I can remove it during a future "mid-life upgrade". Running a separate static line back to the fuselage after-the-fact isn't too hard - many builders have done it (some multiple times! :-)

Thanks again guys,

James

[Battson]

For what it's worth, the two static ports on the aft fuselage sides works great - first time, every time as far as I know. It sounds like the combined option is hit and miss.

You can pop rivet on brackets to the stringers, then rivet or screw the port in. Running the tube is a snap, a few cable ties or clamps and you're away. Then you have two static supplies which you join together and get stable static readings at all times (including slips).

It's not much extra work to retrofit either, over top of the fabric if the fuselage is done - no messy glue or anything like that.