Airspeed Indicator broken?

[Paul B]

I have an airspeed indicator in my hand, not connected to anything. I can blow into the AI's pitot port and quickly bring the indicated airspeed up to any value I want. When I quit blowing into the AI, the needle very slowly goes back to 0. It takes 60 seconds for the needle to go from 120mph indicated to 0 with both pitot and static ports open. Is this normal or does the AI likely need repair?

 

[flyinga]

There is a small needle-type valve in the AS pitot input that can be adjusted to change the rate at which airspeed can change. Usually can be done with a small screwdriver. In too much and the airspeed changes too slowly (like yours); out too much and the airspeed will "bounce" around in unstable conditions.

 

[Mel]

And for anyone else reading this thread; NEVER blow into an ASI.
If you want to operate it by mouth, apply suction to the static port.

 

[Sam Buchanan]

I have an airspeed indicator in my hand, not connected to anything. I can blow into the AI's pitot port and quickly bring the indicated airspeed up to any value I want. When I quit blowing into the AI, the needle very slowly goes back to 0. It takes 60 seconds for the needle to go from 120mph indicated to 0 with both pitot and static ports open. Is this normal or does the AI likely need repair?

And for anyone else reading this thread; NEVER blow into an ASI.
If you want to operate it by mouth, apply suction to the static port.

It probably needs repair now......

 

[krw5927]

And for anyone else reading this thread; NEVER blow into an ASI.
If you want to operate it by mouth, apply suction to the static port.

I haven't ever done this but can you tell us more about why blowing into the ASI is a bad thing? My first thoughts are this is exactly what the pitot tube does.

Is it the speed and force with which one could possibly peg the needle if they were not used to how much pressure it takes?

Thanks Mel, always learn something from you.

 

[Mel]

The ASI is very sensitive to force and speed of the "blowing" and the moisture of breath.

 

[Paul B]

Thanks for responding!

I am always grateful for the collective wisdom at this site and the eagerness to share it. It sounds like I may have damaged the airspeed indicator by blowing into it (I only did this about 100 times), if it wasn't already broken. Can anyone recommend a place I could send this instrument to get checked out and possibly repaired?

 

[pierre smith]

A rubber squeeze bulb and a length of hose attached, can be used more gently while you're watching the needle move.

Best,

 

[gasman]

A large syringe works well and has good control when testing for leaks or to compare markings on gauge with a manometer.