Dual airspeed instruments questions

Does anyone know how one would install two separate airspeed indicators? I
suspect one would need a separate pitot tube systems. Is this correct?
Also, how does one go about correcting an error (either too fast or slow) in
the indicator. I'm 2/3 done with the fuselage of my Zenith Zodiac 601XL and
was just thinking ahead.
Thanks in advance,

Louis G.

"Louis Gallego" wrote in message
news:kdMKb.80815$xX.581325@attbi_s02...
Does anyone know how one would install two separate airspeed indicators?
I
suspect one would need a separate pitot tube systems. Is this correct?
Also, how does one go about correcting an error (either too fast or slow)
in
the indicator. I'm 2/3 done with the fuselage of my Zenith Zodiac 601XL
and
was just thinking ahead.

Use a tee fitting just as you would for a static source; you only need one
pitot system to supply two ASIs.

Too fast or too slow airspeeds are usually the result of static error.
I think Ron just posted an article on how to remedy this with airdams just
before or just after the static port (depending on whether the ASI is
reading too high or too low).

Eric

"Eric Miller" wrote in message
et...

Use a tee fitting just as you would for a static source; you only need one
pitot system to supply two ASIs.


A problem (bug, dirt, ice) in the pitot would influence both ASI's. Two
pitots makes sense if you install dual ASI for redundancy.

Rob

On Wed, 07 Jan 2004 04:49:20 +0000, Louis Gallego wrote:

Does anyone know how one would install two separate airspeed indicators?
I suspect one would need a separate pitot tube systems. Is this correct?
Also, how does one go about correcting an error (either too fast or slow)
in the indicator. I'm 2/3 done with the fuselage of my Zenith Zodiac
601XL and was just thinking ahead.
Thanks in advance,

Louis G.

You could feed as many ASIs from one pitot and static source as you want.
But the more ASIs you have, the more chances you have for a leak, and the
more lag you will have in the indication due to the increased volume of
the system. But two ASIs from one pitot tube shouldn't be a problem.

Errors in indicated airspeed can have many sources:

instrument error,
leaks in pitot or static systems,
position error in static system (present on every aircraft to some degree),
position error in pitot system (negligible unless you have chosen a very
poor location for the pitot tube).

I've got a web page that explains how to check ASI instrument error with a
water manometer and how to do flight testing to determine the airspeed
error and translate that into static source position error and thus know
the error in the altimeter that results.

http://go.phpwebhosting.com/~khorton...out.php?&ID=31

My Flight Test Links section has a bunch of stuff that might be useful to
you. The Pitot/Static section is at:

http://go.phpwebhosting.com/~khorton...ex.php?&PID=47


--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

"Rob Turk" wrote in message ll.nl...
"Eric Miller" wrote in message
et...

Use a tee fitting just as you would for a static source; you only need one
pitot system to supply two ASIs.


A problem (bug, dirt, ice) in the pitot would influence both ASI's. Two
pitots makes sense if you install dual ASI for redundancy.

And two statics wouldn't be a bad idea either. On larger aircraft the pilot and
copilot have independent static sources as well.

I've had two static system failures and one pitot failure over 25 years of flying.
All were the result of some foreign object lodged in the tubing (2 mud daubers
and a gooey piece of something which we weren't quite sure what it was).

I've also come out and found the static ports taped over after maintenance.

"karel adams" wrote in message ...
In the "Instruments" chapter of my PPL ground school,
I was taught that many planes have two static ports
and a three-way valve to select between
"static" and "alternate static"

In the one plane I had the static problem, there was an alternate static (that
just opened into the cabin).

In my own plane, I was amused in that I do have two static ports (they are
teed together from opposite side of the plane). The mud dauber managed
to climb in past the tee to plug the thing up totally.

Curious why you would do that in the first place? Couldn't you get
away with GPS speed (average of 2 runs in opposite direction to pull
our windage) to check your differential air pressure based airspeed
instrument.

Also, if you put 2 instruments on the same ports, one of the biggest
sources of error (port placement) will be applied equally to both
instruments.

I'm leaning towards the idea of an all electronic panel (GPS centric)
with minimum no-electric emergency cluster.

Regards

"Louis Gallego" wrote in message news:kdMKb.80815$xX.581325@attbi_s02...
Does anyone know how one would install two separate airspeed indicators? I
suspect one would need a separate pitot tube systems. Is this correct?
Also, how does one go about correcting an error (either too fast or slow) in
the indicator. I'm 2/3 done with the fuselage of my Zenith Zodiac 601XL and
was just thinking ahead.
Thanks in advance,

Louis G.

"Louis Gallego" wrote in message
news:kdMKb.80815$xX.581325@attbi_s02...
Does anyone know how one would install two separate airspeed indicators?
I
suspect one would need a separate pitot tube systems. Is this correct?
Also, how does one go about correcting an error (either too fast or
slow) in
the indicator. I'm 2/3 done with the fuselage of my Zenith Zodiac 601XL
and
was just thinking ahead.
Thanks in advance,

Louis G.

I don't know if you are kit or scratch building the 601XL but if you are kit
building and haven't bought or opened the wing kit yet you should know that
the Pitot Tube that ships with the kit is a combined Pitot/Static unit.

I installed mine this weekend.

Gig Giacona
www.peoamerica.net/N601WR

"Ron Natalie" wrote in message
m...

In my own plane, I was amused in that I do have two static ports (they are
teed together from opposite side of the plane). The mud dauber managed
to climb in past the tee to plug the thing up totally.

You gotta respect a bug that goes to *that* much trouble to ruin your day!

Eric

On Wed, 07 Jan 2004 10:13:19 -0800, Jay wrote:

Curious why you would do that in the first place? Couldn't you get away
with GPS speed (average of 2 runs in opposite direction to pull our
windage) to check your differential air pressure based airspeed
instrument.


Averaging the ground speed from two runs in opposite directions only
provides the right answer if the runs are aligned exactly with the wind.
But you have no way of being sure exactly what the wind direction is, so
your average speed will be off by some amount.

Example 1, if the TAS is 100 kt, you have a wind of 270 deg at 20 kt,
and the runs are done on headings of 360 and 180. The ground speed on each
run is 102 kt, so have an error of 2 kt in the test technique.

Example 2, use the same TAS and wind, but do the runs on headings of 300
and 120. The ground speeds are 83.3 and 117.7 for an average of 100.5.

But, small errors in the heading on one run can make a big difference -
how accurate is your compass swing, and how closely can you fly a heading
while doing this test? E.g. same TAS and wind, but the actual headings
flown are 305 and 120 (5 deg error on one run). The ground speeds are now
84.4 and 177.7 for an average of 101.

Yes, the error can be small if the wind speed is low, and you are somewhat
aligned with the wind, but why not use a technique that gives the exact
answer, rather than an approximation?

For an accurate method, see:
http://members.rogers.com/khorton/rv...y/TAS_FNL4.pdf

Spreadsheet to do the calculations for the above method, and lots more
info on calculating TAS using GPS data at:

http://go.phpwebhosting.com/~khorton...ex.php?&PID=49

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com