Replacing an airspeed indicator

Seriously, none of the Winter ASIs come with 0 to 120 knot scales. In fact this is one of few ASIs that does. It seems very easy to read and the price is good. Does anyone have any comments on the brand (Skysports)?

http://www.aircraftspruce.com/catalo...p-10-05384.php

On Friday, March 7, 2014 10:43:14 AM UTC-8, Soartech wrote:
Seriously, none of the Winter ASIs come with 0 to 120 knot scales. In fact this is one of few ASIs that does. It seems very easy to read and the price is good. Does anyone have any comments on the brand (Skysports)?



http://www.aircraftspruce.com/catalo...p-10-05384.php

The Winter ASW-27 ASI goes to about 160 kts. the arcs are of course calibrated for the ASW-27. for my homebuilt, I've tested it for a VnE of 135kts, so the arcs need to be changed accordingly. who knows, this glider may go to 160kts, but do I really need to go that fast?

Brad

who knows, this glider may go to 160kts, but do I really need to go that fast?

YES!

On Friday, March 7, 2014 12:19:16 PM UTC-7, Luke Szczepaniak wrote:
who knows, this glider may go to 160kts, but do I really need to go that fast?



YES!

What he said!!!!

Altitude is safety, speed is life!

Kirk
66
(VNE does not mean "do not approach", it means "do not exceed")

On Friday, March 7, 2014 12:43:14 PM UTC-6, Soartech wrote:
Seriously, none of the Winter ASIs come with 0 to 120 knot scales. In fact this is one of few ASIs that does. It seems very easy to read and the price is good. Does anyone have any comments on the brand (Skysports)? http://www.aircraftspruce.com/catalo...p-10-05384.php

Just a bit of advice. Do NOT get an airspeed indicator that has its max range limit at your plane's redline. Why? Do you really know if you are at redline or maybe 20 knots past it if your indicator hits a stop (either visible or not) at your indicated redline?

http://www.ntsb.gov/aviationquery/br...30X01573&key=1

Willing to gamble your life on a couple of hundred dollars?

As UH says, FWIW.

Steve

On 3/7/2014 12:17 PM, Steve Leonard wrote:
Snip...
Just a bit of advice. Do NOT get an airspeed indicator that has its max
range limit at your plane's redline. Why? Do you really know if you are
at redline or maybe 20 knots past it if your indicator hits a stop (either
visible or not) at your indicated redline?

http://www.ntsb.gov/aviationquery/br...30X01573&key=1

Willing to gamble your life on a couple of hundred dollars?

As UH says, FWIW.

Steve


Dsve Lawrence (PIC in the aforenoted NTSB report) wrote up the accident for
AW&ST (Aviation Week & Space Technology) and Soaring magazine (online archive
available). I know and have soared with Dave (former Libelle/ASW-20 owner),
and shared more than one post-camp-flight B.S. session with him. Good
pilot/person/guy. He has an extensive background in (manned and unmanned)
flight test, flown military aircraft, and IMO is very much a 'switched on'
pilot, with no obvious "I am God-personified" in his pilot attitude that I
ever sensed. Yet he was fortunate to not lose his life in this 'he screwed up'
accident. Human perfection isn't an option...

Also, "What Steve L. said."

Also also, FWIW...

Bob W.

Is there any reason to suspect that an ASI (especially a non-TSO'ed one) might be more accurate in the middle of it's range?

Also, to anyone with a combo vario/secondary ASI like LXNAV V7, does the AS indicated on the V7 agree with your primary ASI and if not, which one do you trust? A sanity check on the primary ASI with a secondary instrument seems like such a good idea to me. I mean... when my ASI eventually goes broken, I want to know right away. The redundancy is nice in the meantime, especially if they agree on speed.

On Friday, March 7, 2014 2:45:53 PM UTC-7, son_of_flubber wrote:

Also, to anyone with a combo vario/secondary ASI like LXNAV V7, does the AS indicated on the V7 agree with your primary ASI and if not, which one do you trust? .......
Son,
You have to remember that your ASI shows IAS and the V7 shows TAS. Typically these are always different (With a larger difference at higher altitudes and hotter than standard atmosphere). I trust either one but of course you use IAS for things like flap speeds and approach speeds.

On Fri, 07 Mar 2014 13:45:53 -0800, son_of_flubber wrote:

Is there any reason to suspect that an ASI (especially a non-TSO'ed one)
might be more accurate in the middle of it's range?

On this side of the pond the rules say that ASI calibration must be
checked as part of the Annual Inspection and must be within 2kts
throughout its range.

The calibration check applies a known pressure to the pitot inlet and and
records the ASI reading. This is done at 10 kt intervals from the ASI's
highest indicated speed down to 20 kts.

An ASI is a sensitive pressure gauge that happens to be calibrated in kts.
The calibration is independent of the airframe. IOW, if the IAS in flight
shown by a freshly calibrated ASI is not the same as independently
measured TAS then the error is due to the placement of the static vent
and/or the pitot. For example, its well known that pressure under the
wing is above bulk atmospheric pressure, so a static vent anywhere near
the underside of the wing will make the ASI read low. Similarly, a static
vent placed on a convex bulge in the fuselage away from the wing will see
a lower pressure and so will make the ASI read high. That's why the
static vent is commonly halfway along the boom: at that point the boom is
a straight taper and so has minimal curvature in relation to the
slipstream while the vent is placed well away from the flying surfaces.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Thank you Martin. Pointing out how the pieces fit together is very helpful..

An annual test of the ASI over the entire range suggests that they have in the past found a few ASI that were not accurate over the entire range and that ASIs might go bad gradually over time. I wonder what those tests find in the field.

(My question may sound like FUD, but I have a habit... people paid me to find defects in their technology.)

Do I have it right that at a given point in time and altitude, the difference between TAS and IAS is constant over the entire range? I'm still figuring out how to use my LXNav V7 to check the calibration of my 15 year old Made in China ASI (and vice-versa, if I find a problem, either one of the devices could be the culprit.)



On Friday, March 7, 2014 7:30:41 PM UTC-5, Martin Gregorie wrote:
On Fri, 07 Mar 2014 13:45:53 -0800, son_of_flubber wrote:



Is there any reason to suspect that an ASI (especially a non-TSO'ed one)

might be more accurate in the middle of it's range?



On this side of the pond the rules say that ASI calibration must be

checked as part of the Annual Inspection and must be within 2kts

throughout its range.



The calibration check applies a known pressure to the pitot inlet and and

records the ASI reading. This is done at 10 kt intervals from the ASI's

highest indicated speed down to 20 kts.



An ASI is a sensitive pressure gauge that happens to be calibrated in kts..

The calibration is independent of the airframe. IOW, if the IAS in flight

shown by a freshly calibrated ASI is not the same as independently

measured TAS then the error is due to the placement of the static vent

and/or the pitot. For example, its well known that pressure under the

wing is above bulk atmospheric pressure, so a static vent anywhere near

the underside of the wing will make the ASI read low. Similarly, a static

vent placed on a convex bulge in the fuselage away from the wing will see

a lower pressure and so will make the ASI read high. That's why the

static vent is commonly halfway along the boom: at that point the boom is

a straight taper and so has minimal curvature in relation to the

slipstream while the vent is placed well away from the flying surfaces.





--

martin@ | Martin Gregorie

gregorie. | Essex, UK

org |