Airspeed Indicator Accuracy Tolerance

Bob Gardner wrote:

If there is no means of adjustment, the question answers itself. Keep in
mind that the blue line is not sacrosanct...actual Vyse will vary with
weight and density altitude. The vertical speed indicator is a much more
accurate means of determining best rate of climb.

Well, not really. My question is whether their is a good way to measure
the absolute accuracy of a ASI. And my concern is that 6 nts is too far
off when it could make a significant difference in performance in
critical situations, like single engine operation.


Bob Gardner

"O. Sami Saydjari" wrote in message
...

In my Cessna 421C, the pilot-side airspeed indicator reads 6 nts below the
co-pilot-side airspeed indicator. When I pointed this out to a mechanic,
he said that it was "within toleraance." He said it was possible that one
was 3 nts high and the other 3 nts low and so both could be within
tolerance. He added that there is no real internal adjustment, so there
is not much he could do about it anyway.

Seems to me that when you are talking about a possible 6nt difference and
given the need for accurately maintain blue-line speed in case of a
single-engine failure, it is important to know that one's airpseed
indicator is accurate. Isn't there a way to judge true accuracy of speed
indicators (just as there is for altimeters)? Should I be satisfied with
my mechanic's answer and move on?

-Sami
N5554G, Cessna 421C

And my point is that absolute accuracy is not important.

Bob

"O. Sami Saydjari" wrote in message
...
Bob Gardner wrote:

If there is no means of adjustment, the question answers itself. Keep in
mind that the blue line is not sacrosanct...actual Vyse will vary with
weight and density altitude. The vertical speed indicator is a much more
accurate means of determining best rate of climb.

Well, not really. My question is whether their is a good way to measure
the absolute accuracy of a ASI. And my concern is that 6 nts is too far
off when it could make a significant difference in performance in critical
situations, like single engine operation.


Bob Gardner

"O. Sami Saydjari" wrote in message
...

In my Cessna 421C, the pilot-side airspeed indicator reads 6 nts below
the co-pilot-side airspeed indicator. When I pointed this out to a
mechanic, he said that it was "within toleraance." He said it was
possible that one was 3 nts high and the other 3 nts low and so both
could be within tolerance. He added that there is no real internal
adjustment, so there is not much he could do about it anyway.

Seems to me that when you are talking about a possible 6nt difference and
given the need for accurately maintain blue-line speed in case of a
single-engine failure, it is important to know that one's airpseed
indicator is accurate. Isn't there a way to judge true accuracy of speed
indicators (just as there is for altimeters)? Should I be satisfied with
my mechanic's answer and move on?

-Sami
N5554G, Cessna 421C

Compare the reading son the airspeed, altimeter and VS while
pressurized and with the cabin vented at ambient. You could
have a static leak inside the pressure cabin that is letting
pressurized cabin air into the pilot's static line.


--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Bob Gardner" wrote in message
...
| And my point is that absolute accuracy is not important.
|
| Bob
|
| "O. Sami Saydjari" wrote
in message
| ...
| Bob Gardner wrote:
|
| If there is no means of adjustment, the question
answers itself. Keep in
| mind that the blue line is not sacrosanct...actual Vyse
will vary with
| weight and density altitude. The vertical speed
indicator is a much more
| accurate means of determining best rate of climb.
|
| Well, not really. My question is whether their is a
good way to measure
| the absolute accuracy of a ASI. And my concern is that
6 nts is too far
| off when it could make a significant difference in
performance in critical
| situations, like single engine operation.
|
|
| Bob Gardner
|
| "O. Sami Saydjari"
wrote in message
| ...
|
| In my Cessna 421C, the pilot-side airspeed indicator
reads 6 nts below
| the co-pilot-side airspeed indicator. When I pointed
this out to a
| mechanic, he said that it was "within toleraance." He
said it was
| possible that one was 3 nts high and the other 3 nts
low and so both
| could be within tolerance. He added that there is no
real internal
| adjustment, so there is not much he could do about it
anyway.
|
| Seems to me that when you are talking about a possible
6nt difference and
| given the need for accurately maintain blue-line speed
in case of a
| single-engine failure, it is important to know that
one's airpseed
| indicator is accurate. Isn't there a way to judge true
accuracy of speed
| indicators (just as there is for altimeters)? Should I
be satisfied with
| my mechanic's answer and move on?
|
| -Sami
| N5554G, Cessna 421C
|
|
|

I wrote an article in Kitplanes magazine 15 years ago or so about using
plastic tubing, a yardstick, and tinted water to make a water manometer for
testing airspeed indicators.



"O. Sami Saydjari" wrote in message
...
Bob Gardner wrote:

Well, not really. My question is whether their is a good way to measure
the absolute accuracy of a ASI. And my concern is that 6 nts is too far
off when it could make a significant difference in performance in critical
situations, like single engine operation.