The International Cessna^® 170 Association

I've read through the various post on the stall warning system and don't see where anyone has mentioned the Safe Flight model number for the lift detector. Does anyone know the specific model number that goes in a 170B?

My recently purchased '54 B has a Safe Flight model 150 lift detector in the left wing. The detector works fine on ground test but won't alarm in the air even though I've adjusted it as high up toward the stagnation point as it will go. It also feels slightly heavier than other 170B units I've lifted. I know from the posts the microswitch should be in the 5 gram range.

It seems the model 150 detector is often associated with Bonanzas while Cessna 150-182s seem to have Safe Flight model 146 or 148 variants. Any help identifying which Safe Flught model has the 5 gram micro switch and is appropriate for the 170B would be appreciated.

Thanks,
Jeff

Edit: for those who may be interested I found out that Cessna part #0511062-4 (for the 170B) equates to Safe Flight part number 148. Among others, I'm sure, this is the same part number used in C-182Gs. Cessna part 0511062-6 equates to a Safe Flight P/N 146 and is used in variants of C-310s and 401s. Safe Flight P/N 150 is used in C-210 variants. What the difference is and whether or not they are interchangeable in terms of the actual microswitch and tab, I don't know. I just know that my Safe Flight P/N 150 (which looks untampered with) can't be made to actuate in the air regardless of adjustment position even though it checks 4.0 on the ground.

Jeff, my own airplane had the same problem.
When I acquired it the stall warning lift-detector worked/tested fine on the ground... but would never activate in flight.
I eventually discovered that someone, somewhere, had apparently substituted the original microswitch with an identical-appearing computer-store microswitch.

I bought a used unit from a salvage yard and it worked fine for many years.

When I talked to Safe-Flight technical help, they are the people who gave me the specification of 5 grams. I ended up buying a unit from an individual which included the stall horn/light assy, the lift detector all in the original box, and the ORIGINAL LIFETIME WARRANTY PAPERWORK which Safe-Flight provided back in the day.

(NO! No one is getting it from me. I installed it when I removed my in-service-units and gave them to another Member whose IA correctly would not sign off on his annual until he had a serviceable Stall Warning in the airplane.)

You're on the right track. I'll bet your microswitch has been swapped with an incorrect one. Shop around at the salvage yards . (I looked high/low for a 5-gram microswitch and gave up.)

PS: I hope you haven't told your IA that it doesn't work in the air. (He'll be none the wiser if you don't tell him.)
This is not to say you shouldn't fix it, however. As silly as the attitude of the airplane can look, and as ridiculous as I once thought it would be for anyone to inadvertently stall this airplane.... I was once saved by an operating stall warning in C206 on a dark-night takeoff with a failed airspeed input tube that indicated I was building up speed... when in fact I was approaching a stall in the mountains with no horizon.
Get yours fixed.

Thanks, George. I absolutely plan to get it working. If for no other reason I just like the the things I own to work properly. But as you say, it can't hurt and it may one day truly help.

I also was able to talk with Safe Flight Tech Support yesterday and the person (Chris) I spoke with was very helpful. While he couldn't find an exact part number for the 170B, he did some research and called back to let me know that SF P/Ns 146, 148 and 150 all have the same specs for the microswitch and vane, so they all should (in theory) work identically in the 170B. Apparently the differences between those part numbers/models are in the heating unit (whether or not it has one, voltage, heating element temperature, etc.) and the shape of the mount for the leading edge.

Jeff

The heated lift detectors are merely a cylindrical capsule about the size of a AAA battery which clips onto the detector inside the wing. It is a resistance heater. Voltage of all units are not critical (unless the heating element is utilized) since all the lift detector does is complete an electrical circuit to airframe ground.
I have a heated unit but did not wire it into the circuit because I recognize that C-170 aircraft are not approved for flight in icing conditions.