Replacing an airspeed indicator

[Soartech]

For some reason my glider came with an indicator with a ridiculously high maximum reading. I would like to replace it with something that has much more space in the most often used regions of the dial. Can you just install a new instrument or does it need to be somehow calibrated or tuned to an individual Pitot tube installation?
Thanks for your experience.

[K]

On Wednesday, March 5, 2014 11:15:35 AM UTC-7, Soartech wrote:
> For some reason my glider came with an indicator with a ridiculously high maximum reading. I would like to replace it with something that has much more space in the most often used regions of the dial. Can you just install a new instrument or does it need to be somehow calibrated or tuned to an individual Pitot tube installation?
>
> Thanks for your experience.

The ridiculously high reading should be a good excuse to fly faster (Kidding!). Check your maintenance manual and possibly the TDCS and there should be a list of approved instruments. You also have to make sure the A/S has the proper markings. Granted, If your ship is experimental you could possibly do anything you want as long as your mechanic signs off but I would not use a mechanic who would sign a condition inspection without properly marked instruments. Calibration is a good idea but it is complicated.

[Soartech]

I forgot to say this glider is experimental. So you are saying that any new airspeed indicator (factory fresh) should be accurate to some reasonable extent with a standard Pitot tube installation? Is calibration normally done on new installations or not? As far as markings on the dial, they are easy to duplicate so no problem there.
>
>
>
> The ridiculously high reading should be a good excuse to fly faster (Kidding!). Check your maintenance manual and possibly the TDCS and there should be a list of approved instruments. You also have to make sure the A/S has the proper markings. Granted, If your ship is experimental you could possibly do anything you want as long as your mechanic signs off but I would not use a mechanic who would sign a condition inspection without properly marked instruments. Calibration is a good idea but it is complicated.

[K]

On Thursday, March 6, 2014 10:43:09 AM UTC-7, Soartech wrote:
> I forgot to say this glider is experimental. So you are saying that any new airspeed indicator (factory fresh) should be accurate to some reasonable extent with a standard Pitot tube installation? Is calibration normally done on new installations or not? As far as markings on the dial, they are easy to duplicate so no problem there.
>
> >
>
> >
>
> >
>
> > The ridiculously high reading should be a good excuse to fly faster (Kidding!). Check your maintenance manual and possibly the TDCS and there should be a list of approved instruments. You also have to make sure the A/S has the proper markings. Granted, If your ship is experimental you could possibly do anything you want as long as your mechanic signs off but I would not use a mechanic who would sign a condition inspection without properly marked instruments. Calibration is a good idea but it is complicated.

Check out this page on W&W http://www.wingsandwheels.com/altimeter_united_wultrad_winter.htm
Should explain most everything and if you have further questions give Sean a call.

[Soartech]

K, none of those Winters, in either size, are 0 to 120 knots which is what I need.
I was looking at this one as best available. Low price, easy to read.
Does anyone have any comments on this brand, other than the fact that there is no such measurement as KPH?
http://www.aircraftspruce.com/catalog/inpages/ssp-10-05383.php

[Brad[_2_]]

On Wednesday, March 5, 2014 10:15:35 AM UTC-8, Soartech wrote:
> For some reason my glider came with an indicator with a ridiculously high maximum reading. I would like to replace it with something that has much more space in the most often used regions of the dial. Can you just install a new instrument or does it need to be somehow calibrated or tuned to an individual Pitot tube installation?
>
> Thanks for your experience.

I bought a used ASW-27 altimeter from someone on RAS. I now have a glider that flies as fast as the ASW-27 for substantially less money.

Brad

[Soartech]

On Friday, March 7, 2014 1:24:43 PM UTC-5, Brad wrote:
> On Wednesday, March 5, 2014 10:15:35 AM UTC-8, Soartech wrote:
>
> > For some reason my glider came with an indicator with a ridiculously high maximum reading. I would like to replace it with something that has much more space in the most often used regions of the dial. Can you just install a new instrument or does it need to be somehow calibrated or tuned to an individual Pitot tube installation?
>
> >
>
> > Thanks for your experience.
>
>
>
> I bought a used ASW-27 altimeter from someone on RAS. I now have a glider that flies as fast as the ASW-27 for substantially less money.
>
>
>
> Brad

Cool. So that really worked for you, eh?
But how does the altimeter change your speed? Something to do with
mirror-image photon physics?

[Brad[_2_]]

dunno, not smart enough to know all them fancy wurds

Brad

[Soartech]

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/catalog/inpages/ssp-10-05384.php

[Brad[_2_]]

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/catalog/inpages/ssp-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

[Gary Ittner[_3_]]

"Soartech" > wrote in message
...
> K, none of those Winters, in either size, are 0 to 120 knots which is what
> I need.
> I was looking at this one as best available. Low price, easy to read.
> Does anyone have any comments on this brand, other than the fact that
> there is no such measurement as KPH?
> http://www.aircraftspruce.com/catalog/inpages/ssp-10-05383.php


KPH is kilometers per hour. 120 KPH equals 65 Knots, unsuitable for your
use. Try this one instead:

http://www.aircraftspruce.com/catalog/inpages/falconasi120n-3.php

[Steve Leonard[_2_]]

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/catalog/inpages/ssp-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/brief.aspx?ev_id=20061030X01573&key=1

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

As UH says, FWIW.

Steve

[Luke Szczepaniak]

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

YES! :)

[mike]

On Friday, March 7, 2014 11:41:38 AM UTC-7, Brad wrote:
> dunno, not smart enough to know all them fancy wurds
>
>
>
> Brad

LOL!

[Brad[_2_]]

On Friday, March 7, 2014 11:33:00 AM UTC-8, mike wrote:
> On Friday, March 7, 2014 11:41:38 AM UTC-7, Brad wrote:
>
> > dunno, not smart enough to know all them fancy wurds
>
> >
>
> >
>
> >
>
> > Brad
>
>
>
> LOL!

agreed!

last year we towed the Tetra15 out to a mountain airstrip to do some late fall flying. On the way back my buddy flying the Colt towplane had it firewalled and I caught up and passed him. The air was smooth a silk and I was going as fast as I had ever gone in the ship............it was a great opportunity to expand the speed envelope. We have all the control surfaces mass balanced and the ship is incredibly torsionally stiff.........bet it would go faster....game on!

[Bob Whelan[_3_]]

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/brief.aspx?ev_id=20061030X01573&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.

[Matt G.]

K, none of those Winters, in either size, are 0 to 120 knots which is what I need.
I was looking at this one as best available. Low price, easy to read.
Does anyone have any comments on this brand, other than the fact that there is no such measurement as KPH?
http://www.aircraftspruce.com/catalog/inpages/ssp-10-05383.php

Um, kilometers per hour?

[son_of_flubber]

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.

[Soartech]

On Friday, March 7, 2014 2:17:45 PM UTC-5, Steve Leonard wrote:
> 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/catalog/inpages/ssp-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/brief.aspx?ev_id=20061030X01573&key=1
>
>
>
> Willing to gamble your life on a couple of hundred dollars?
>
>
>
> As UH says, FWIW.
>
>
>
> Steve

Are you kidding me? I think anyone can tell when going 100 knots or 20 knots.
Slow down! Who wants to go over 100 knots? Not me.
I have no idea what FWIW means, nor do I care. YIMMV

[K]

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.

[Martin Gregorie[_5_]]

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 |

[kirk.stant]

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")

[son_of_flubber]

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 |

[[email protected]]

On Monday, March 10, 2014 9:11:34 AM UTC-4, son_of_flubber wrote:
> 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 |

Use of a simply made manometer should clarify the delemna of comparing 2 instruments, both of which have unlnown accuarcy.
UH

[Steve Leonard[_2_]]

On Friday, March 7, 2014 6:30:41 PM UTC-6, Martin Gregorie wrote:
> 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.

This is true only at sea level, standard day conditions in the airspeed range we are interested in. At 5000 feet, IAS and TAS are NOT the same.

> 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.

Disagree with this. Look at the airspeed corrections on a Schempp-Hirth sailplane using the underwing statics. The Ventus A that Dick Johnson tested is a good example. Goes from reading 4 knots too slow at low speed to 10 knots to fast at high speed.

If you are curioius about the calibration of your indicator, the following should be of interest to you:

http://www.rst-engr.com/rst/articles/KP89JUL.pdf

Steve Leonard

[Soartech]

>An ASI is a sensitive pressure gauge that happens to be calibrated in kts.
>The calibration is independent of the airframe.

Thank you Martin for this answer.
That is what I needed to know.

[Martin Gregorie[_5_]]

On Mon, 10 Mar 2014 06:26:26 -0700, unclhank wrote:

> Use of a simply made manometer should clarify the delemna of comparing 2
> instruments, both of which have unlnown accuarcy.
> UH

Yep, my club uses a water-filled manometer with the vertical tube being
cut from a roll of soft plastic tube - most likely its the same tubing
you'd use to connect the ASI to static and pitot.


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

[Martin Gregorie[_5_]]

On Mon, 10 Mar 2014 06:49:19 -0700, Steve Leonard wrote:

> On Friday, March 7, 2014 6:30:41 PM UTC-6, Martin Gregorie wrote:
>> 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.
>
> This is true only at sea level, standard day conditions in the airspeed
> range we are interested in. At 5000 feet, IAS and TAS are NOT the same.
>
Yeah. Treat that as a rather bad short-hand. A fully qualified
explanation would be quite long by the time you factor in the different
IAS errors on a different type of glider flying with the one that's
trying to check his ASI. Most people don't own the same sort of trailing
bomb device that Dick Johnson used.

>> 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.
>
> Disagree with this. Look at the airspeed corrections on a Schempp-Hirth
> sailplane using the underwing statics. The Ventus A that Dick Johnson
> tested is a good example. Goes from reading 4 knots too slow at low
> speed to 10 knots to fast at high speed.
>
The general effect of the wing is like I said, but it can obviously be
affected by factors specific to some airframes such as turbulence round
the root or kicked off by the nose shape. Most gliders have, at best,
quite rudimentary root fairings. I imagine Will Schueman would be quite
unimpressed if he saw them.


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