Why are TE probes so long?

d b wrote:

I'm sure somebody may correct me, but as I recall, the TE probe produces
a signal equal and opposite of the pitot (total pressure).

Not exactly, total pressure is static + dynamic, TE is static - dynamic.

In article , Robert Ehrlich wrote:
d b wrote:

I'm sure somebody may correct me, but as I recall, the TE probe produces
a signal equal and opposite of the pitot (total pressure).

Not exactly, total pressure is static + dynamic, TE is static - dynamic.


Let's put it this way. The indicator reads the difference in pressure between
the hole called P and the hole called S. When I hook the hole called P to a
pitot tube and the hole called S to a perfect static source, I get a number,
let's say 70.

Now I hook a TE probe to the hole called S and the perfect static source to
the hole called P. The indicator again reads 70. Obviously, the TE probe is
the exact opposite of the pitot tube.

It is agreed that the pitot is the total energy static + dynamic
The obvious conclusion is that the TE probe is - (static + dynamic)

It is NOT static - dynamic, it IS -(static+dynamic)

Kinda sucks, doesn't it?

d b wrote:
In article , Robert Ehrlich
wrote:
d b wrote:

I'm sure somebody may correct me, but as I recall, the TE probe
produces a signal equal and opposite of the pitot (total
pressure).

Not exactly, total pressure is static + dynamic, TE is static -
dynamic.


Let's put it this way. The indicator reads the difference in
pressure
between
the hole called P and the hole called S. When I hook the hole called
P to a
pitot tube and the hole called S to a perfect static source, I get a
number,
let's say 70.

Now I hook a TE probe to the hole called S and the perfect static
source to
the hole called P. The indicator again reads 70. Obviously, the TE
probe is
the exact opposite of the pitot tube.

It is agreed that the pitot is the total energy static + dynamic
The obvious conclusion is that the TE probe is - (static +
dynamic)

It is NOT static - dynamic, it IS -(static+dynamic)

Kinda sucks, doesn't it?

Yes it IS (static - dynamic). Go study your fluid dynamics again
Cheers, John G.

Perhaps it isn't obvious. The airspeed indicator is a DELTA pressure guage.
It is not an absolute pressure guage. If the indicator reads the same delta
pressure, the two devices have to be producing the same delta pressure.
One sucking, the other blowing.


In article , "John Giddy"
wrote:
d b wrote:
In article , Robert Ehrlich
wrote:
d b wrote:

I'm sure somebody may correct me, but as I recall, the TE probe
produces a signal equal and opposite of the pitot (total
pressure).

Not exactly, total pressure is static + dynamic, TE is static -
dynamic.


Let's put it this way. The indicator reads the difference in
pressure
between
the hole called P and the hole called S. When I hook the hole called
P to a
pitot tube and the hole called S to a perfect static source, I get a
number,
let's say 70.

Now I hook a TE probe to the hole called S and the perfect static
source to
the hole called P. The indicator again reads 70. Obviously, the TE
probe is
the exact opposite of the pitot tube.

It is agreed that the pitot is the total energy static + dynamic
The obvious conclusion is that the TE probe is - (static +
dynamic)

It is NOT static - dynamic, it IS -(static+dynamic)

Kinda sucks, doesn't it?

Yes it IS (static - dynamic). Go study your fluid dynamics again
Cheers, John G.

d b wrote:

Perhaps it isn't obvious. The airspeed indicator is a DELTA pressure guage.
It is not an absolute pressure guage. If the indicator reads the same delta
pressure, the two devices have to be producing the same delta pressure.
One sucking, the other blowing.

Or, if you have a good static system, one that neither blows nor sucks,
but just sits there!
--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

d b wrote:

In article , Robert Ehrlich wrote:
d b wrote:

I'm sure somebody may correct me, but as I recall, the TE probe produces
a signal equal and opposite of the pitot (total pressure).

Not exactly, total pressure is static + dynamic, TE is static - dynamic.

Let's put it this way. The indicator reads the difference in pressure between
the hole called P and the hole called S. When I hook the hole called P to a
pitot tube and the hole called S to a perfect static source, I get a number,
let's say 70.

Now I hook a TE probe to the hole called S and the perfect static to
the hole called P. The indicator again reads 70. Obviously, the TE probe is
the exact opposite of the pitot tube.

It is agreed that the pitot is the total energy static + dynamic
The obvious conclusion is that the TE probe is - (static + dynamic)

It is NOT static - dynamic, it IS -(static+dynamic)

Kinda sucks, doesn't it?

No, the reading of your indicator is P - S, converted into whatever speed
unit you like. If P is connected to a pitot tube and S to a perfect static
source, P - S is total - static = (static + dynamic) - dynamic) = dynamic).
When P is connected to a perfect static source and S to a TE probe,
P -S = static - (static - dynamic) = dynamic again, so the reading are the
same.

Robert Ehrlich wrote:
...
P - S is total - static = (static + dynamic) - dynamic) = dynamic).
...

correcting myself, should read:

.... P - S is total - static = (static + dynamic) - static = dynamic.