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It's been a long time since I flew a C172.. and even longer since I've practiced stalls

You

[quote]You CAN get zero ground-speed (even negative ground-speed), doing slow flight into a good headwind.. Been there, done that

crank your winds aloft in the weather control panel up to about 40 knots...

then try slow flight into the wind, you should be able to get nearly zero ground speed.

the higher you set the wind speed the slower your ground speed will be during slow flight (assuming you fly into the wind) as brett said... you could even go backwards.

I asked my instructor if it was possible to get 0 knts on ASI in slow flight, he said you can. What will happen in very slow flight is the area of low pressure under the wing begins to move forward and above the wing, and the low pressure flowing forward and above the wing will stuck air out of the pitot tube instead of the ram air going in. He said it is the same principal the stall warning horn works on.

[quote]It's been a long time since I flew a C172.. and even longer since I've practiced stalls

I asked my instructor if it was possible to get 0 knts on ASI in slow flight, he said you can. What will happen in very slow flight is the area of low pressure under the wing begins to move forward and above the wing, and the low pressure flowing forward and above the wing will stuck air out of the pitot tube instead of the ram air going in. He said it is the same principal the stall warning horn works on.

I like these discussions, but I'm gonna circumvent the hair-splitting. I've taken a C172 in and out of slow flight enough to know that by the time the condition you've described happens (I've yet to see it)... you've long-since stalled.

[quote]It is possibly to zero the ASI in slow flight, the air entering the pitot tube is no longer directly entering the tube.

**also.. (per your original post).. older ASIs simply stop responding accurately below 40 knots.. so your experince is possible ... it's a shortcoming in the equipment (why I suggested an inspection), not because of the AoA.

I think you hit it on the head with the older ASI stuff. The aircraft is a 1981 model Skyhawk so it probably still has the original ASI. But common sense will tell you, 0 knts in controllable flight is not possible in a Skyhawk.

I may have fudged up my instructors definition of how it happens, because his nerdy definition involved a lot of math problems, aerospace engineering terms, graphs, charts, and what looked like nuclear launch codes to me....

So he was talking about airflow dynamics over an airfoil and pressure dynamics, or a tuna sandwich...

I'm a very visual person, I can show you what I'm talking about, but I can't describe it worth a dang. If you show me I'll get it, if you write it, well, I'll think your talking about sandwiches. Sorry about all the hair you've pulled out during this thread...

Oh lordy.. no hair pulled (honest).. I love these discussions.. I could sit around a hangar and talk this stuff all day. It's how we learn.

I found a couple images.. and modified them to show the pitot tube location.



The pitot tube sees pretty much what the wing sees. Extreme pressure displacements reaching the pitot tube, just don't happen (exept for abruptly entered stalls). C172s and Warriors don't have enough HP to stay airborne at AoAs that would cause that. And even jets don't.... all they can really do, is make it all happen at higher airspeeds. But they can put wings into AoAs where wing-mounted pitot tubes are not a good idea.. that (among other reasons), is why you'll see most high performance aircraft with fusealage mounted pitot tubes.

Cover that airspeed and fly the same maneuvers.

[quote][quote]It is possibly to zero the ASI in slow flight, the air entering the pitot tube is no longer directly entering the tube.

A Cherokee 140, that no good flat spinning piece of s##t.