Pinpoint GADAHRS Install
Completed 5/31/2006 - Updated 8/17/2006One of the hottest issues for the Chelton-buying RV-10 builders in the past year has been the issues surrounding the Crossbow AHRS. For background, the Crossbow 425EX, which was supposedly better performing and more feature-filled than the A500 AHRS, also came with a few flaws. There were 3 items that were identified as potiential issues. One of them was unlikely to affect most metal plane builders, but the other 2 could cause a few different problems. Some units upon startup would not display attitude, and some units would would have other in-flight issues. The lucky people like me, would just have problems on startup and a power-cycle or two would take care of the system for that flight. Other users weren't so lucky and experienced innacurate and unsafe attitude information in-flight. From what I understand, Direct2Avionics, the Chelton Sport distributor, had tried to get Crossbow to fix the issues, and after a lengthy period they did eventually come up with a fix for the 2 most critical of issues....the 2nd being discovered only after fixing the first. The Chelton system itself performed fine, but the AHRS was having issues, so the fix needed to come from the manufacturer. After the lenthy wait for a fix, the politics started to heat up as customers were hopping mad at D2AV for informing them that they shouldn't fly IFR until the issues were resolved. D2AV tried to work various returns to Crossbow, or even falling back to having to accept the 500 AHRS, but Crossbow didn't want to deal with refunds, only with repairs...but unfortunately it was taking a long time to figure out the problems. Eventually, the D2AV guys lost faith that the units would indeed be "fixed" properly and promptly, so they called on another manufacturer to adopt some technologies used in carrier-class planes, and build them a rock-solid AHRS, also equipped with WAAS GPS, and a built-in Air Data computer, and build it to even more stringent specs and then take it to a 3rd party for independent testing to ensure that it met the high standards. At some point, they need to then drum up some planes to test for themselves, to ensure that the system performed well in a variety of actual installations. That's where I came in and decided to be a guinea pig, hoping that by participation I could finally move the process along so I could fly IFR again.
So below are some photos from before, during, and after my pinpoint installation. It's a retrofit, so I had the pain of having to look over the new wiring diagram and identify which wires I could keep, and which ones were now going to be wired differently. I had some extra wires in the conduit from front to rear, but I needed some 3-conductor shielded in order to follow the wiring diagram, so with the pull of a couple of wires, I was ready to go. Since the unit also contains a built in Air Data Computer, I had to also Tee my Pitot and Static lines and run those to the GADAHRS. (GPS, Air Data, Attitude and Heading Reference System....I think) One other thing that is actually a benefit over the old 425EX is that the magnetometer isn't inegrated into the AHRS body anymore. This is nice because the goal is to mount the AHRS box close to the CG, but to mount the magnetometer (think compass) in some remote area that will be unaffected by ferrous objects. This may actually work to some builders benefit and allow a better installation. In my case, I used this benefit to mount the AHRS itself towards the forward area of the section behind the baggage compartment wall, but mounted the Magnetometer a few feet further aft to prevent interference by the battery contactor, the battery cables, and the autopilot pitch servo. It also is very handy for tapping into the static system, and is not a very long run to bring a pitot line back to the rear from where the line enters the fuselage.
Both the Crossbow and the Pinpoint use an SMA connector for the GPS antenna, and the other end of the Pinpoint terminates at a Comant GPS antenna that uses TNC connectors. The Pinpoint uses a nice round, twist/ratcheting type connector that is very solid. Even the OAT probe (yes, you need to mount another OAT probe for it's Air Data Unit) comes with a very nice solid connector, and nifty OAT probe. All of the items feel like they're made of very good quality and are of precision build. I put the 2nd OAT probe very near the other one, just outboard of my first under-wing inspection panel. The GADAHRS box serves as the central hub for the MSU and OAT probe to wire to, and then the other wires run from the GADAHRS to the Chelton system.
The pinpoint has a couple of features that differentiate it as well. One is that it can be used with the Cheltons to provide redundant AHRS systems, and they cross check eachother. Another is that when they get thrown out of whack for any reason, they will throw an error bit to the Chelton so it knows it is receiving an unreliable signal component. This should prevent some of the possible inadvertent failures from causing the pilot to continue relying on bad data, as was evidenced by one pilot on his way home from OSH 2006. Additionally, there is upgraded software in the Chelton system used for performing the leveling, compass swing, and compass alignment procedure for the pinpoint, so it is much easier to perform for the builder. Another cool benefit is that with the alignment procedure, the builder can now mount the AHRS in any orientation with the connector facing forward, aft, left, or right. The Alignment procedure takes care of it all for you. From what I've heard, the system is also much more sensitive with it's air data measurements than other systems. It was built to live up to RVSM (Reduced Vertical Separation Minimums) standards, which is another plus.
Here's some additional information that builders may find helpful:
* Note: These were only current as of 8/8/2006
GADAHRS Drawing
Wiring Diagram with Digiflight Info
MSU Diagram
OAT Diagram
Install Help Guide
So on to the photos...
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More AHRS Install Photos
I just took some additional photos now that I installed the production unit in the plane. The production unit is performing flawlessly for me. You Chelton guys stuck with the 425 Crossbow are going to be really happy once you get this one installed.
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