Thorp Air Command - T18.net

I see. Bill, I ding worry too much about what the actual temp is as much as the dynon calculates the true air speed based on that sensor.

Thanks;
I have a D-10a also. The 'in unit' compass doesn't work well for me either. I have a remote compass, so I'll start looking for a good place in the baggage compartment too.
I have Crow cam lock seat belts, so I wonder if the steel anchor pieces on the turtle deck, or anything else would make the top center back of the baggage compartment, a problem?

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Scott Emery
EAA Chapter 326
T-18 N18TE

It’s a shame the installation manual doesn’t give a distance from ferris metal recommendation. Harness hardware along with canopy hardware (rollers/bolts) could potentially cause problems. Control cables and bellcrank hardware (my cockpit vent contol) could also interfere. You have to get fairly close to a whiskey compass with screwdriver to notice a change. Could the Dynon unit be mocked up to check sensitivity to the various metals in the area? Another option could be to swap some hardware for stainless. Some stainless is ferris so it would have to be checked with a magnet before installing.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I assume we are not talking about a lot of weight compared to the old remote compass that would break your foot if it fell on it . If I were me and I am , I would mount it on a shelf far back towards the tail . It would be away from 99% of that pesky metal that drives it crazy ( including any metal objects carried in the baggage compartment ) and above the rudder cables .

RB
CAPTAIN ELECTRON

I would as well. You also need to be aware that electronics will affect the compass. If I simply plug my iPad into the cigarette lighter, it swings the compass about 7 degrees. That's even when the Ipad is already on.
Cubes

Ah, so maybe I'll put it further back. I think off to the side of the fuselage behind the rear baggage bulkhead would be away from the cables and electric trim motor. It would be serviceable in that area as well.

The other option would be pulling the vertical stabilizer and putting it down in there if it's easy to get the tail off. I haven't had it off yet.

I've been under the vertical stab when the trim motor driveshaft failed. That area has the electric trim motor (with it's permanent magnets) a steel driveshaft and steel jackscrew + nut for the trim. I think the elevator counterweight has steel in it as well. That's a bunch of steel that moves. Stationary steel is bad enough (tailwheel spring). Moving forward, the Com antenna is on the fuselage top in front of the vertical stabilizer, the rudder cable run the full length along the floor. 'Feisty' used to have the battery and external power plug behind the baggage compartment, so I presume many T-18s do also. Then consider potential magnetic junk in the baggage, or the pockets of the occupants.
The T-18 is a compact aircraft! Seeking a spot that is magnetically clean, I'm considering the left outer wing panel. Could put the remote compass near the leading edge, away from the aileron bellcrank & counterweight or in the fiberglass wingtip away from the nav light? The right outer wing panel has the landing light.
Also, the outside air temperature is taken thru that module, and the wingtip air won't be heated by the exhaust...
The question is getting the wires from the cockpit out to the wingtip?

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Scott Emery
EAA Chapter 326
T-18 N18TE

If you have a conduit running out to the wingtip ( for them there lite wires ) you could use a nylon ( very small dia. ) fish tape . They sell them on ebay in shorter lengths other than the standard 50-100 ft. I have not used one , but I certainly would try one for the $10.00 asking price . You could also try using some shielding on the position lite in the wing tip ?

RB

Hi Scott,

You could use a simple piece of bailing wire as a fish tape... it’s a pretty short distance to the center gap from either direction. If it’s really tight in your conduit already, you probably don’t even have to put a loop on the end to pull the wire - just lay about 2 or 3 inches of wire & “fish tape wire” together and wrap tightly with some stretchy electrical tape. You probably know all that already, but just thought I’d mention it.

As far as the rear fuselage area, if you have stainless rudder cables they may be a non-issue... depends on the alloy. It could be that the trim motor (permanent magnets) also might not be an issue - the steel case is usually a pretty good shield. You have to check it with a compass. As I recall, there is no steel in the stabilator counterweight, other than the fastening hardware. Just some random thoughts. The wing tip area sounds like your best shot, and the most easily accessable.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

I used a telescoping crappie fishing pole...thats a fishing pole with only one eyelet on the very tip. I broke that off and taped my wire to my pole. I did have to drop the outer wing for this work, but I couldnt come up with another way to get it from the fuse to the end of the center wing section. I went from the outer wing towards the fuse. If I tried through the fuse, it would put a bind on my pole to where it wouldnt go any further.

I guess I got lucky with my setup in the baggage area. My compass stays dead on and I get good reading.

Several years ago when Bob and I built the RV7 we installed the remote compass on a shelf on the back side of the luggage bulkhead. Worked as advertized