25 knot IAS - Slow flight in a Cessna 172 - Video

Comments most appreciated on this video especially on ASI reliability at these slow speeds.

[youtube]http://youtu.be/yPG05Dz8P6c[/youtube]

I revisited slow flight in the practice area today

I will let the viewership be the judge and jury on actual read of the ASI since there are no speed indicators below 40 knots. Not videod, but GPS GS had me at 32 knots. Based on earlier flight experiences, I don't think there was any winds aloft (calm)

At 1800 lbs in and airplane with a 2550 MGW (one SOB and minimal fuel) the power off stall speed comes to around 33 Kt assuming a MGW stall at 40 KCAS. With power on the stall speed is likely knot or two less so 32 sounds plausible under the right circumstances but 25 is clearly some combination of instrument, pitot, and static error.

Thanks Lance,

Not on video, I was able to maintain level flight and zero IAS for short periods of time however buffeting of the controls precluded me videoing (I had to man the shop). My AOA was higher to maintain that ASI indication.

I guess a secondary question would be that as I remember, for the 411. 413 check, ASI accuracy is not checked? Or is it behind the scenes and I am not aware of it.

The results only show altimeter reads, not ASI accuracy testing? It would be plausible the ASI accuracy would degrade with time like any other instrument?

If not checked, I am surprised at this considering the critical element that gauge plays in our day to day flying.

Your recollection is correct, there's no mandatory check of the ASI accuracy at any speed during a "Pitot/Static Check", at least on non-heavy GA airplanes. The potential for such checking is present on most Pitot/Static test sets in that they have a calibrated ASI plumbed into the same pressures as are delivered to the airplane and a cross check of that with the ASI in the panel would reveal any discrepancies in the instrument itself. Unfortunately, any such error is at least as likely to be due to anomalies in the pitot and/or static ports. I've seen tests which show that a 0.10" ridge ahead of and near a static port can cause a several knot error. Just another justification for having AoA in the cockpit IMO.

Of course, when an ASI is overhauled by a repair station they are required to make it conform to it's TSO which I'm sure includes some accuracy specifications.

This is the entire flight from yesterday's slow flight exercise..

[youtube]http://youtu.be/5HSO6wwqKaY[/youtube]

Pattern work at KJAN and KMBO Sloppy approach seen on second landing at KJAN. Oh well, thus the reason I still keep working at this :-)

Always amazes me how ATC squeezes me in between airliners.

I may be wrong... But i understood Cessna engineered theri airspeed indicators for the 60-70 range.

Below 50... you are getting down into the Error range of the indicating systems.

If you want to fly slow consistienly .. get the AOA indicator systems installed.