The International Cessna 170 Association

Folks,

I purchased a kit from the fine folks at Approach Fast Stack in Minnesota and I'm hoping to get some time this spring to work the install with my local A&P/IA. The full kit includes a G5 HSI, a GNC 355 navigator and comm radio, as well as the supporting equipment to include a GMU-11 (magnetometer) GAD-29B (AIR Inc data bus module) and GAD-13 (OAT interface unit) as well as the wiring harnesses custom built to interface with my existing items which include a G5 ADI, the GTX-335 transponder and my comm panel.

Reading through the G5 HSI installation manual a key consideration is the location of the GMU-11. In general, this sensitive digital magnetic field sensor, gets placed in deep in the tail or out on a wingtip. I recall from reading that at least a few of our members have a Dual G5 set up that would likely have required placing the GMU-11.

Where have others had success in locating the GMU-11? I understand there is a set of diagnostic tests to ensure that interference thresholds are not exceeded but I'd like to start testing with the most likely solution first. Thanks!

Here's a shot of my as is panel now. The venturi driven DG and second ADI will be removed and the HSI will go where the DG is now. In addition the existing GNC250 XL will come out of the radio stack. (Not sure why the photo is inverted ... that's not how I fly 94D ... but if you click the photo you will see it properly)

I instruct in a fleet of 172s with G5s. They all have the GMU-11 in the left wingtip. It works great, and I suspect the aircraft are similar enough that it would be good in the 170 as well.

Check out this thread.

If you install an inspection cover/plate to accommodate this installation…do not make the mistake of using steel PK screws and Tinnermans which are ferrous (magnetic)….use SS, but check them with a magnet. (We operated a former employers Gulfstream-I for several years in which we could never get the co-pilots’ compass and Captains RMI to operate correctly even after spending thou$and$ on the flux-valve at the avionics shop. Then one day the catering truck ran into the right wing and damaged it. During the repair which required skin-replacement…we found a magnetic screwdriver which had been left Inside that bay of the wing, apparently ever since original manufacture at Grumman….as it had “Grumman” engraved on the handle.)

No problem after it was removed.

(This may also explain why A&P’s almost never engrave their names on their tools (as opposed to the common practice of sticky-fingered automotive mechanics. It’s better to lose a tool permanently than to suffer through the interview with the Chief as to how your tool was found inside the airplane or engine.)

I have fitted twin G5,s in my 170a ,and fitted the GMU-11 just outboard the left hand fuel tank. The kit contains SS screws. Getting the GMU-11 aligned correctly was the hardest part. I thought aligning it with the rib in the wing would be correct.”wrong” The rib wasn’t aligned exactly for and aft with the spar [90 degs] . It makes the whisky compass obsolete . I found aligning the G5 readout very time consuming and a pain in your known what. It took me about 4 hours by myself. I read the instructions a dozen times and thought this was easy,”what could go wrong”?

Folks,

Thanks for the feedback. I will plan for the left wingtip.

Cheers.

Mine is in the right wingtip along with a WAT Orion 650 nav/strobe light. Works great.