Air speed indicator

[Silvaire]

I would just tape a bubble level to it and fly the plane at cruise speed, level it to that, and call it good, it's not really all that bloody critical.

I think tying the yarn to it would be better, you want it aligned with the relative wind and if you are flying at a constant altitude that will be the same as a spirit level would indicate.

 

[N801BH]

Did you really read the first post?

 

[Fearless Tower]

You can bend the tube, and throw the airspeed off. the pitot tube does not come out of the wing sticking directly into the wind. It actually comes out below the leading edge and is bent. there is no template for aligning it to the wind.

you must eye ball it, how do you know if you got it right?

Tom, I believe Bruce Fenstermacher has a template. IIRC, it is actually for an early 172, but it used the same curved tube design. I got it from him when the paint shop bent mine up toward the sky. I can't remember if he sent it to me, or posted on the 170 board. If you'd like it, I'll see if I can dig it up.

 

[Tom-D]

Tom, I believe Bruce Fenstermacher has a template. IIRC, it is actually for an early 172, but it used the same curved tube design. I got it from him when the paint shop bent mine up toward the sky. I can't remember if he sent it to me, or posted on the 170 board. If you'd like it, I'll see if I can dig it up.

I made a template, it's close I have access to a 49. we will see how well it works soon.

 

[timwinters]

Did you really read the first post?

I'm sure he did, as did I and, I'm sure, many others did too...and I'm confident that no one knew what you were asking. You didn't properly articulate the question until posts number eleven and twelve.

I made a template, it's close I have access to a 49. we will see how well it works soon.

Am I understanding correctly that you sketched up a template based on an existing pitot tube installation on a 1949 model? If so, how can you possibly have any confidence that it hasn't been bent back and forth a couple hundred times over the last 65 years?

I only owned my 172 ('57 model) for three years but remember bending the pitot at least twice...and probably did more times that I no longer remember. I would just bend it back to a shape that looked about right and I never noticed any adverse effects.

 

[kontiki]

http://www.casa.gov.au/rules/1998casr/021/021c40.pdf

This is more than I wanted to know. It's like Pi to 700 decimal places.
This is what made us invent GPS and AOA indicators.

I haven't got time to dig in this AM, but this link is to an Australian regulatory body. In any case, when you want to know what factors are involved, specs can give you an idea what the design goal is.

I think with GA, instrument is calibrated on bench. You could fly a series of flights in various directions and try to calculate accuracy of airspeed using a GPS in post flight analysis.

I believe someone shared that recipe with me in an earlier thread (couple years ago). I still plan to try it just for the fun of it.

 

[Tom-D]

I'm sure he did, as did I and, I'm sure, many others did too...and I'm confident that no one knew what you were asking. You didn't properly articulate the question until posts number eleven and twelve.

How to calibrate ?

I have a completely new system, How can I verify it is correct prior to flying it?

I know how to calibrate the gauge.

If you can't read this and understand the message it's got to be my fault, isn't every thing I do wrong with you


Am I understanding correctly that you sketched up a template based on an existing pitot tube installation on a 1949 model? If so, how can you possibly have any confidence that it hasn't been bent back and forth a couple hundred times over the last 65 years?

Because I know that the 49 reads correctly. I've cared for this aircraft since 1990.

I only owned my 172 ('57 model) for three years but remember bending the pitot at least twice...and probably did more times that I no longer remember. I would just bend it back to a shape that looked about right and I never noticed any adverse effects.

If your tube was bent, how do you know it reads correctly. or is that typical of how you maintain your aircraft?

 

[Tom-D]

I haven't got time to dig in this AM, but this link is to an Australian regulatory body. In any case, when you want to know what factors are involved, specs can give you an idea what the design goal is.

I think with GA, instrument is calibrated on bench. You could fly a series of flights in various directions and try to calculate accuracy of airspeed using a GPS in post flight analysis.

I believe someone shared that recipe with me in an earlier thread (couple years ago). I still plan to try it just for the fun of it.

It's a whole lot easier to simply follow the directions given in the AC 43,13-1A page 913 para 914(b)

Leak Testing of the system is easy, accuracy of the gauge is easy, getting the right position of the pitot isn't.

 

[Silvaire]

The absolute bottom line is that IT AIN'T THAT BIG A DEAL Luscombes have the exact same type of pitot tube, my Champ has a little tube right at the jury strut that sticks down below the main strut and gets caught on your shirt and subsequently bent on a regular basis. These airplanes have been flying for about seventy years now and there is not one single NTSB report of one going down because the darn pitot tube was bent out of alignment a little.

We're not talking about jetliners here...

 

[timwinters]

If your tube was bent, how do you know it reads correctly. or is that typical of how you maintain your aircraft?

Because I had the template. It was either in the Owner's Manual or I pulled it out of CPAs documents or...???? I don't recall exactly how I came across it but I had it. Also, I had a good friend who was an A&P IA for FedEx, within 100' from my hangar, who used to help and/or inspect and sign off on everything.

Love how you immediately turn to personal insults with anyone who simply asks for clarification and/or (gasp) actually disagrees with you.

And you wonder why the "credibility of the blue board" is suspect?

 

[Tom-D]

Love how you immediately turn to personal insults with anyone who simply asks for clarification and/or (gasp) actually disagrees with you.

And you wonder why the "credibility of the blue board" is suspect?

Did you post this?

I guess I didn't realize Tom and Brien were such liberals. Each one has, numerous times in this thread, "changed the subject or gone off on a tangent."

Thanks for pointing that out.
...

And wonder why you get a hostile answer.

 

[timwinters]

Did you post this?

I guess I didn't realize Tom and Brien were such liberals. Each one has, numerous times in this thread, "changed the subject or gone off on a tangent."

Thanks for pointing that out.
...

And wonder why you get a hostile answer.

Simple and accurate observations are far from personal attacks.

 

[Tom-D]

Simple and accurate observations are far from personal attacks.

Yeah right, knowing what you have said of me in the past, why should ever expect a civil answer?

 

[weirdjim]

Nauga,
the tower flyby guy

Nauga? You mean Nauga HYDE? Good God, man I haven't seen you in YEARS.

Jim

 

[weirdjim]

Tom is working on a CERTIFIED plane....

United Stated Mail can be CERTIFIED; aircraft and pilots cannot. Besides, both Experimentals and Standard Category both are CERTIFICATED under different sections of the same rule and both have airworthiness CERTIFICATES.

Jim

 

[N801BH]

United Stated Mail can be CERTIFIED; aircraft and pilots cannot. Besides, both Experimentals and Standard Category both are CERTIFICATED under different sections of the same rule and both have airworthiness CERTIFICATES.

Jim

Good point... I stand corrected..

 

[kontiki]

FWIW I did get back to this and look in the 43-13B it says

12-53. PITOT/STATIC TUBES AND LINES. The pitot tube (see figure 12-6) is installed at the leading edge of the wing of a single-engine aircraft, outside the propeller slipstream or on the fuselage of a multiengine aircraft with the axis parallel to the longitudinal axis of the aircraft, unless otherwise specified by the manufacturer.

 

[N801BH]

FWIW I did get back to this and look in the 43-13B it says

12-53. PITOT/STATIC TUBES AND LINES. The pitot tube (see figure 12-6) is installed at the leading edge of the wing of a single-engine aircraft, outside the propeller slipstream or on the fuselage of a multiengine aircraft with the axis parallel to the longitudinal axis of the aircraft, unless otherwise specified by the manufacturer.

I would agree with that concept as a baseline..... Especially for an experimental... It is the last sentence that will haunt the certified aircraft owners /mechanics..

 

[WBI Flyer]

At what speed? and why level flight? You mean it's not going to be accurate in a climb or descent?

it will have a greater margin of error in a high aoa... ie. mushing. other than that... relative wind... relative wind. correct?

 

[Silvaire]

... It is the last sentence that will haunt the certified aircraft owners /mechanics..

"Haunt"? Why would it haunt us? I've been doing this for a long, long time and I have yet to have a nightmare over a pitot tube.

 

[Silvaire]

...other than that... relative wind... relative wind. correct?

Well in regards to it's relation with the wing/airframe to which the pitot tube is affixed the relative wind is different for every speed.

 

[nauga]

Well in regards to it's relation with the wing/airframe to which the pitot tube is affixed the relative wind is different for every speed.

And pitot tubes are relatively insensitive to misalignment with the relative wind, up to as much as +/- 20 deg off-axis (posted with cite way back in the thread). Most of the installation errors in a pitot-static system are due to static source position, and the resulting airspeed errors tend to be larger at high AOA.

Hey Jim. Yeah, it's me again.

Nauga,
and his echo

 

[N801BH]

"Haunt"? Why would it haunt us? I've been doing this for a long, long time and I have yet to have a nightmare over a pitot tube.

Interesting..... I guess all certified planes maintenance manuals will just say " bend it so it looks close" under the chapter on pitot tube alignment... ..................

 

[Silvaire]

Interesting..... I guess all certified planes maintenance manuals will just say " bend it so it looks close" under the chapter on pitot tube alignment... ..................

On pretty much any certificated GA airplane designed later than maybe about 1950, your typical Piper or Cessna, there is nothing to bend and there are no adjustments to be made. On airplanes from the 30's and 40's with pitot tubes of the type such as being discussed here, when you say "maintenance manual" what are you talking about? You may have gotten a glorified Owners Handbook but not much beyond that. Furthermore, as has been pointed out multiple times already by myself and others - it ain't that big of a deal, nobody is losing sleep at night over this