1966 M20E Alternate Static Air Source

[Cessna738]

The placard on my pilot side panel refers to the alternate static source behind the VSI. I found it. But, not sure it would be useful as it is. There is no knob to pull while in flight. Is there suppose to be some kind of knob? Open pull down, close push up is the operation according to the placard. Appears to be closed at this point.

[bhtitle]

My 67F did not have a knob or anything, and I never found a valve behind the panel.  So I had my mechanic install an alternate static switch on the panel, similar to this one:

https://www.aircraftspruce.com/catalog/elpages/togglevalve11-12168.php?clickkey=35326

Tried alternate static in cruising flight- I’d say it causes a 1 needle width bump in the VSI, which returns immediately to zero.  No noticeable effect on the other instruments.

[Cessna738]

Thanks.

[Shadrach]

My 67 F came with a static valve similar to the one pictured below. The were also common on the Pipers and Cessnas of the era. Mine is mounted in the upper right hand side of the pilot’s footwell, next to the ram air cable. It is well labeled and easily accessible. I will try to get pictures when I am next at the hangar.

[Cessna738]

Mine doesn't look like that. Will contort, and get a picture.

[DCarlton]

Anyone know if ALTs are required.  I’ve never found mine.  Perhaps it was removed.  Need to add to to-do list.  

[Shadrach]

23 minutes ago, DCarlton said:

Anyone know if ALTs are required.  I’ve never found mine.  Perhaps it was removed.  Need to add to to-do list.  

I cannot find any regulatory requirement under 91.205. File under nice to have but not needed. I wonder how many pilots on this board have ever needed an alternate static source.

[RescueMunchkin]

Mine is between the throttle and mixture knobs. Early 68 F

 

[Shadrach]

7 hours ago, RescueMunchkin said:

Mine is between the throttle and mixture knobs. Early 68 F

 

Judging from the font differences, I’d bet that was added the end of the production line as an option or at a later date after delivery.

[RescueMunchkin]

2 hours ago, Shadrach said:

Judging from the font differences, I’d bet that was added the end of the production line as an option or at a later date after delivery.

You're right, the font looks the same as the placard for WOT before turning the turbo on, so maybe it was part of the Rajay turbo work.

[RescueMunchkin]

21 hours ago, Shadrach said:

I cannot find any regulatory requirement under 91.205. File under nice to have but not needed. I wonder how many pilots on this board have ever needed an alternate static source.

It's not required in the regs, if people need it, they can break the glass of the VSI gauge.

[Shadrach]

14 minutes ago, RescueMunchkin said:

It's not required in the regs, if people need it, they can break the glass of the VSI gauge.

Yea, that's pretty common knowledge. I was just wondering how many static system blockages occur in the real world. The only failure I've had was during taxi back to my hangar after an IFR cert where the tech left both fuselage static ports covered. ASI did not come off the peg during taxi.

[Cessna738]

On 2/20/2024 at 1:59 AM, Cessna738 said:

Mine doesn't look like that. Will contort, and get a picture.

Here is a picture of the alt switch (below VSI under panel). Also, I have this "pull on" button. I do not think it is for alt air. I think it is for the vacuum pressure for the old autopilot - which I have yet to use. This lines look like they move up the panel, not toward the VSI.