EFWD Build

[jiott]

I have ADS-B both in and out. The traffic info I get on my screen shows other aircraft altitude relative to my altitude with 100' accuracy. So I recommend if you are planning eventually to have ADS-B that your altitude reporting is accurate to at least 100' rather than 200'. As you can see, if my altitude was off by 200' and the other guy coming at me was off by 200', the total error on my readout could be as much as 400'; kind of ruins the usefulness of the whole thing. I say be as accurate as you can; its not that hard when you are in the building phase.

[jiott]

I could be wrong here, but I believe ADS-B out requires a WAAS GPS that is referenced to a calibrated/tested (every 2 years) altitude source. This tells me that it is not relying exclusively on GPS altitude. If this is not correct, I am open to being educated.

[jiott]

My thinking is based on this quote from the FAA website:

"In fact, ADS-B reports two kinds of altitudes: barometric and geometric. Barometric or pressure altitude is the one pilots know best – this is the altitude that is displayed on the altimeter in the aircraft. Geometric altitude is calculated by GPS (Global Positioning Satellites) as the height of the aircraft above the earth ellipsoid. These two altitudes are not the same, but having both allows for applications that require one or the other as an altitude source and provides a means of verifying correct pressure altitude reporting from aircraft."

[efwd]

Well this has turned into an interesting discussion IMHO.
If I recall, someone here informed us that one technique of verifying accuracy of the altitude reporting of the WAAS GPS is doing it with ATC and their Radar.
So, bench testing a system, to my understanding thus far, is done with a vacuum test device. Apparently under these conditions there is no taking into account for fluid dynamics of how the air stream moves across the pitot static ports. I may just research how it comes out with the pitot static behind the panel. Here is just one benefit from using Oratex fabric. Build phase or not, all I have to do is punch a hole, Iron on the doily, install the ports and attach hoses.
Eddie

[rv9ralph]

If I remember correctly, ATC gets your altitude on their display from your transponder/encoder, which uses pressure altitude. It is not connected to your altimeter but uses standard pressure, adjusted in their computer for local barometer settings.
As of last Wednesday, 11/29, we had a pilot/controller meeting here at Livermore (LVK) and they do not see ADSB information on their displays yet.

Ralph

[PapuaPilot]

Anybody that has a digital panel will have an AHRS which provides the data for altitude. The altitude displayed on the screen is the one sent to the transponder and used for your ADSB altitude. I don't know if it uses pressure or corrected altitude. Personally I want to provide the most accurate altitude and know it for the traffic around me.

[efwd]

Beleive me, Im all about safety, aka accuracy. Im just wondering if accuracy means plumbing a static port. Our airframe is pretty much an open vessel when you consider the lack of seals throught the cockpit. If its not accurate I will definetly put static ports in.

[jrevens]

The fact that it has so many potential openings could work for, or against you. It's closed up just enough that at any particular time with air flowing past, or in, any particular opening, those air leaks could cause either a vacuum or pressurization effect. I don't mean to denigrate nor dispute the experience of those who have done it that way. If it works, it works. That's the bottom line. I think that the possibility of having a variable pressure situation in the cockpit is likely, but that's just an educated guess.

[David47]

I'm doing exactly what Phil did; ie static port in each side, below the rear handhold. Incidentally, this is similar to the location of each static port in the Super Decathlon I'm currently flying, which is where I got the original idea from. On the Kitfox though, it may be slightly better because the fuselage is wasted down quite a bit toward the lower backend so influences of dynamic pressure should (hopefully) be minimised. A bit of experimentation will be done to check it out.

[efwd]

Yeh John, I thought of that. Wondering, Steve, Do you notice a change in your altimeter when you open your doors in flight?