Hercules Engines

From: "Jim Knoyle"
Date: 1/17/2004 8:00 PM Central Standard Time
Message-id:


"B2431" wrote in message
...
From: "Jim Knoyle"
Date: 1/17/2004 3:48 PM Central Standard Time
Message-id:


"Tarver Engineering" wrote in message
...

"Jim Knoyle" wrote in message
...

"Tarver Engineering" wrote in message
...

"Jim Knoyle" wrote in message
...

Hey, Splaps. Next time you are ever near a DADC or it's diagram,
check out what they have at the other end of the tubing connected
to the fitting labeled *TOTAL*. Only ONE pitot tube!

Yep, the term Total means they added two sensors.

Nope, the pitot tube detects static pressure + impact pressure.
Read the book(s).

I have been writing that to you for years, Knoyle. That is why you
seem
such an idiot when you insist a pitot port is a pitot tube.

Total means there is more than one sensor, nothing more.

You really don't understand how that one little opening on the end
of that pointy thing up front can detect static pressure (altitude)
as well as impact pressure (airspeed), do you. That's sad!


The hole on the front only detects pitot pressure. If there are holes on
the
side are for detecting static pressure.


No, sorry Dan, you'll have to refer to a more modern air data computer.
When the label at the top of the ADC switched from pitot to total, the
definition for Total Pressure (Pt) was given as:
"This is a pressure input (from the aircraft pitot probe) which varies
both with altitude and aircraft speed. (Range 3.11 to 42.50 in. Hg.)"
*This was a direct quote from a Honeywell HG280D DADC guide*
The book goes on to explain how the delta Ps is removed to arrive at
a more accurate airspeed. The Ps, whether obtained from the static
port(s) on the probe or flush mounted ports on the fuselage, is fed
through another fitting on the DADC (labeled static) and is something
else entirely. It does factor in to the math.

JK

OK, I see where you are coming from. The pitot pressure DOES vary by altitude.
To compensate for that when measuring airspeed you use static pressure to give
you altitude. Some aircraft detect static pressure from holes on the side of
the pitot tube and others have the static ports located elswhere.

I would be interested in seeing a schematic of your aircraft's pitot-static
systems including DADC. I have never worked on DADC. I did work on the CADC
abomination on the F-4E.

Dan, U.S. Air Force, retired

(B2431) wrote:



OK, I see where you are coming from. The pitot pressure DOES vary by altitude.
To compensate for that when measuring airspeed you use static pressure to give
you altitude. Some aircraft detect static pressure from holes on the side of
the pitot tube and others have the static ports located elswhere.



But you need BOTH Dan, you cannot measure airspeed AND altitude
unless you have BOTH pitot pressure AND static pressure...
--

-Gord.

From: "Gord Beaman" )
Date: 1/18/2004 12:48 AM Central Standard Time
Message-id:

(B2431) wrote:



OK, I see where you are coming from. The pitot pressure DOES vary by
altitude.
To compensate for that when measuring airspeed you use static pressure to
give
you altitude. Some aircraft detect static pressure from holes on the side of
the pitot tube and others have the static ports located elswhere.



But you need BOTH Dan, you cannot measure airspeed AND altitude
unless you have BOTH pitot pressure AND static pressure...
--

-Gord.

That's what I said.

Dan, U. S. Air Force, retired

On 18 Jan 2004 08:08:50 GMT, (B2431) wrote:

From: "Gord Beaman" )
Date: 1/18/2004 12:48 AM Central Standard Time
Message-id:

(B2431) wrote:



OK, I see where you are coming from. The pitot pressure DOES vary by
altitude.
To compensate for that when measuring airspeed you use static pressure to
give
you altitude. Some aircraft detect static pressure from holes on the side of
the pitot tube and others have the static ports located elswhere.

But you need BOTH Dan, you cannot measure airspeed AND altitude
unless you have BOTH pitot pressure AND static pressure...

That's what I said.

Did you also say that you can't correct them without OAT, outside air
temperature? That's the third element of a pitot-static air data
system.

Mary

--
Mary Shafer Retired aerospace research engineer

"Mary Shafer" wrote...

Did you also say that you can't correct them without OAT, outside air
temperature? That's the third element of a pitot-static air data
system.

What is required -- static air temperature (SAT) or total air temperature (TAT)
for the OAT correction?

If TAT, how is it measured, and how many thermocouples are required, in what
configuration?

From: "John R Weiss"
Date: 1/19/2004 2:05 PM Central Standard Time
Message-id: _LWOb.85390$sv6.201965@attbi_s52

"Mary Shafer" wrote...

Did you also say that you can't correct them without OAT, outside air
temperature? That's the third element of a pitot-static air data
system.

What is required -- static air temperature (SAT) or total air temperature
(TAT)
for the OAT correction?

If TAT, how is it measured, and how many thermocouples are required, in what
configuration?


It's OAT. Air speed measured with just pitot and static pressure is referred to
as indicated airspeed, IAS. If you temperature compensate it becomes true air
speed, TAS.

Basic mechanical analog TAS indicators use one of two methods of temperature
compensation: one uses a capillary tube from a bulb mounted on the exterior of
the of the aircraft , the other uses a knob where you can manually dial in OAT.
The C-130s I worked on had the capillary type.

Thermocouples are not used for electrically detected OAT. What is used is a
temperature bulb usually mounted flush to the skin of the aircraft. If you look
at a C-130 you will see a 2"(?) disk on the skin on either side ofthe nose
wheel well. Those are temperature bulbs. They vary in resistance due to
temperature change.

For the life of me I can't remember if the resistance increases or decreases
with temperature drop.

Dan, U.S. Air Force, retired

(B2431) wrote:



It's OAT. Air speed measured with just pitot and static pressure is referred to
as indicated airspeed, IAS. If you temperature compensate it becomes true air
speed, TAS.


Well, it's been many years but ISTR that there's another step
here. Isn't there such a thing as RAS?, maybe Rectified Air
Speed?...IAS corrected for temp? (or maybe CAS?). I thought TAS
was IAS corrected for altitude?

Man!...it was something like 27 years since I last stepped down
that six foot ladder under the tail of an Argus...and about 50
years since the F/E course where I learned this stuff (so cut me
some slack guys!).
--

-Gord.

"Mary Shafer" wrote in message
...
On 18 Jan 2004 08:08:50 GMT, (B2431) wrote:

From: "Gord Beaman" )
Date: 1/18/2004 12:48 AM Central Standard Time
Message-id:

(B2431) wrote:



OK, I see where you are coming from. The pitot pressure DOES vary by
altitude.
To compensate for that when measuring airspeed you use static pressure
to
give
you altitude. Some aircraft detect static pressure from holes on the
side of
the pitot tube and others have the static ports located elswhere.

But you need BOTH Dan, you cannot measure airspeed AND altitude
unless you have BOTH pitot pressure AND static pressure...

That's what I said.

Did you also say that you can't correct them without OAT, outside air
temperature? That's the third element of a pitot-static air data
system.


Yes, but would you believe that this whole squabble began by trying
to correct Tarver's misconception that the "Total" fitting of the two
fittings on an air data computer (labeled Static and Total) referred to
two or more pitot gizmos (Tarver hates to call them tubes) instead
of altitude pressure plus impact pressure?

JK

"B2431" wrote in message
...
From: "Jim Knoyle"
Date: 1/17/2004 8:00 PM Central Standard Time
Message-id:


"B2431" wrote in message
...
From: "Jim Knoyle"
Date: 1/17/2004 3:48 PM Central Standard Time
Message-id:


[ snip ]

The hole on the front only detects pitot pressure. If there are holes
on
the
side are for detecting static pressure.


No, sorry Dan, you'll have to refer to a more modern air data computer.
When the label at the top of the ADC switched from pitot to total, the
definition for Total Pressure (Pt) was given as:
"This is a pressure input (from the aircraft pitot probe) which varies
both with altitude and aircraft speed. (Range 3.11 to 42.50 in. Hg.)"
*This was a direct quote from a Honeywell HG280D DADC guide*
The book goes on to explain how the delta Ps is removed to arrive at
a more accurate airspeed. The Ps, whether obtained from the static
port(s) on the probe or flush mounted ports on the fuselage, is fed
through another fitting on the DADC (labeled static) and is something
else entirely. It does factor in to the math.

JK

OK, I see where you are coming from. The pitot pressure DOES vary by
altitude.
To compensate for that when measuring airspeed you use static pressure to
give
you altitude. Some aircraft detect static pressure from holes on the side
of
the pitot tube and others have the static ports located elswhere.

In another recent part of this thread that didn't get cross-posted from
a.d.a.
(is that cheering I hear? ) I mention how the 727, 757 & DC10 use the
flush mounted static ports whereas the 737, 747 & 767 use the combined
pitot/static probe. Since Tarver seems to infer that the combined
pitot/static
probe is somehow better, I couldn't resist getting in a jab as to how the
777
uses the seperate pitot tubes on the nose and the flush mounted static ports
on the fuselage. Seems the Boeing Engineers ignore his mud bee warnings.
They do use analog/digital conversion right at the probe or port and run
wiring instead of plumbing. Sounds like a good idea to me.

I would be interested in seeing a schematic of your aircraft's
pitot-static
systems including DADC. I have never worked on DADC. I did work on the
CADC
abomination on the F-4E.

In this long running sparring with Tarver, I've placed a couple diagrams on
"his" page: http://home.att.net/~j.knoyle/the_ta...hronicles.html
The DC10 plumbing diagram at the bottom of this came from the DADC book
mentioned above: http://home.att.net/~j.knoyle/mechtest.html
There is a 767 plumbing diagram at the bottom of this page:
http://home.att.net/~j.knoyle/pitot.html
Somewhere I came across this great 777 presentation:
http://euler.ecs.umass.edu/ece655/Boeing777.ppt

JK