P

petersb

Well Known Member
A local builder placed his on the bottom skin under the seat. Makes wire runs and maintenance easy, however Rainer of MGL wrote that one aircraft ( type unknown) did have issues when airflow caused drumming of the lower skin and thus bad AHARS performance.

Any experience out there with this location in an RV7 ?
 
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Hi Peter,
Rainier may have been referring to my installation. I had the AHRS mounted about 12 to 15 inches back from the spar, on the bottom skin, under the passenger seat pan (one rib outboard of the centerline). The sensor was mounted right in the middle of the skin, so it had about 3 inches (I'm guessing) on each side from a rib.

For the most part, it worked very well, but when I would stay in a cruise-climb for more than a few minutes, the horizon would start to tilt. It only happened at certain RPM's, too. I believe it was the perfect harmonic of the prop/engine/exhaust pulses that caused the problem.

I ended up moving the AHRS about 6 inches back from the spar, and as close to the rib as I could get. Problem solved. Glad I used velcro to mount it, so it was easy to relocate.
 
I used tank sealant to adhere an "L" shaped bracket (basically a piece of aluminum with a 90 degree bend) to the right side of the fuselage, just behind the baggage compartment. Again, the sensor was mounted with velcro.

So, let me tell you why this isn't the best place to mount it...it is harder to align your sensor in that location than, say, somewhere on the centerline of the aircraft. After 2 years of flying, I finally got tired of my heading being incorrect and built a small jig to go over the top of the sensor. The jig had a "real" compass mounted to the top of it and using a mirror, I could align the compass to the exact same heading that the airplane was pointed.

It is within 1 degree now, if that. Also, make sure that both SP2 and SP4 are on the same horizontal plane.
 
I put my SP2 in the left wingtip. Easy access when necessary, but long wiring run. Never had any issues with accuracy, heading always matched my electric Ritchie compass.

7-24-09-006w.jpg


SP4 was mounted behind the baggage bulkhead-

5-11-09-008w.jpg
 
Sonny, that sounds very close to the servo. I understood that it should be as far as possible from magnetic sources. I was thinking the next bay back from the pitch servo. Obviously it's not causing you any problems.

Peter
 
Hey Chad, is that a couple of stainless bolts on your wingtip mounting plate? :D

Peter, no, it's actually about 3 linear feet away from the servo. It's mounted above the longeron, just behind the baggage compartment bulkhead. I have 2 ferrous metal items in that area, but after checking with a handheld compass, they're not a factor. One is the canopy frame. The other is the passenger step.

The canopy WILL cause the compass to swing about 30 degrees off when it's 2/3rd's open. It's funny to watch the EFIS compass go back into alignment right when you start to close the canopy. Fortunately, when it's closed the compass is accurate.
 
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