Why a static port?

I can understand why pressurized aircraft need static ports,
but why do unpressurized airplanes have them? I wouldn't think
the pressure difference between the inside and the outside of
the airplane wouldn't differ by that much. (When I open the alternate
static port in my C185, the altimeter changes by just a couple
of feet.)

Without the static ports, we could get rid of all that silly
tubing and just leave the static port connection to the instruments
open to the air. (Of course there is no getting around needing
a tube for the pitot port.)

~Paul Mennen

On Sun, 17 Aug 2003 02:57:45 GMT, "Paul Mennen" wrote:

I can understand why pressurized aircraft need static ports,
but why do unpressurized airplanes have them? I wouldn't think
the pressure difference between the inside and the outside of
the airplane wouldn't differ by that much. (When I open the alternate
static port in my C185, the altimeter changes by just a couple
of feet.)

I was once goofing around in my airplane, and disconnected the static line
so the static source was the cockpit. When I did the runup, the altimeter
acted just like a tachometer...indication when up when I pushed the
throttle forward, and then back when I pulled it back.

Needless to say, I taxied back.

Ron Wanttaja

In article ,
Paul Mennen wrote:
I can understand why pressurized aircraft need static ports,
but why do unpressurized airplanes have them?

The venturi effect makes the pressure in the cabin lower than
the outside pressure. The same thing must affect the static ports
but instruments can be calibrated for the effect.

Look up the procedures for activating alternate static in an
airplane equipped with it. That is opening the static system to
the cabin pressure which causes airspeed and altitude to misread
(the POH will have an estimate of how much).

--
Ben Jackson

http://www.ben.com/

Paul..

Some airplanes successfully use cabin air for the static source. I know many
want "significant" answers, but whether a plane can or cannot use interior air
depends on how leaky the are.

For new, tight planes, the introduction of all that volume of heat or outside
ram air for people cooling can drastically change the pressure inside.

Some can, Some do.

Neal

******The venturi effect makes the pressure in the cabin lower than
the outside pressure.******

Not always, and particularly not in Paul's Cessna 185. These Cessnas have
two scoops on the aft fuselage that provide ram air to the cabin. The slight
pressurization reduces the risk of exhaust entering the cabin.

Karl

******The venturi effect makes the pressure in the cabin lower than
the outside pressure.******

Not always, and particularly not in Paul's Cessna 185. These Cessnas have
two scoops on the aft fuselage that provide ram air to the cabin. The
slight
pressurization reduces the risk of exhaust entering the cabin.

Karl

I didn't know that. (Nice to know.)

I think Bonanza's must be the same, since I flew in a Bonanza once
that had a small opening in the side window which was closed by
a hinged flap held in place only by the higher cabin pressure.
If the cabin pressure were lower than the outside pressure as Ben
suggested there would have been no way to close that flap.
(I don't know if all Bonanza's have that opening - this was the only one
I've flown in.). Ben might be correct for most aircraft however.

From: "john smith"
Subject: Why a static port?
As I recall from my Physics classes:
PV=nRT

I don't think that equation has much relevance here.

~Paul

Paul Mennen wrote:
PV=nRT

I don't think that equation has much relevance here.

It most certainly does!
since nR=(P1V1)/T1=(P2V2)/T2
Where P1, V1, T1 can be the exterior conditions, and
where P2, V2, T2 are the interior conditions
it shows the relationships between the variables
changing any one variable, alters the other five

So what the hell is P, V, and T? And nR for that matter.

Seems like total crap, put it in english would ya
Wayne

It most certainly does!
since nR=(P1V1)/T1=(P2V2)/T2
Where P1, V1, T1 can be the exterior conditions, and
where P2, V2, T2 are the interior conditions
it shows the relationships between the variables
changing any one variable, alters the other five

As I recall from my Physics classes:

PV=nRT