location of altimeter intake

[gravity32]

Can anyone tell me exactly where the air intake orifice is for the pressure altimeter on a Boeing 757? How high above ground when parked? How far lengthways from some identifiable feature on the body, for example the nose?

[zondaracer]

The correct word you are looking for is "static port".

[skkm]

Static ports

The "altimeter intakes" are the unpainted areas under the 'hol'.

Photos: Boeing 757-23A Aircraft Pictures | Airliners.net

[henry_crun]

Good question. The static port is never perfect, its reading is vulnerable to aerodynamic effects which may vary with speed and attitude. Static port calibration used to be a significant feature of test flying and presumably still is.


skkm - is that a 'selfie'?

[skkm]

henry_crun

Negative on the 'selfie' – The closest I've been to MAN is transiting LHR once!

[gravity32]

Thanks zondaracer for the correct term.

Thanks skkm, so there are two static ports, it seems. Why is that?

henry_crun, could the second port help correct problems with air flow?

[Intruder]

There are more than 2 static ports, but there are 2 primary static ports. They are there both for redundancy and (as you surmised) for balancing different pressures when in a sideslip.

[barit1]

This is pedantic, I know, but the location of the static port(s) is not the theoretical pressure level measured in an aircraft.

In a perfect world, you would discover that the elevation of the pressure transducer that is really what is measured. (For steam gages, the elevation of the altimeter instrument)

The difference is the weight of the air in the tubing between the port and the transducer. This weight is added algebraically to the pressure at the static port.

[gravity32]

I wasn't thinking about side-slip when talking about air-flow, but of course you would need ports on both sides for that purpose. I happened to look at some photos of 757s and found one facing the other way, and indeed there are matching ports on the starboard side:
ET-AMT - Ethiopian Airlines Boeing 757-200 at Delhi - Indira Gandhi Int | Photo ID 351638 | Airplane-Pictures.net
This photo also has the advantage that it was taken close to perpendicular to the body, thus allowing more accurate estimation of the location of the ports relative to the windows.

I also came across this report which states there are three ports on the left side:
ASN Aircraft accident Boeing 757-23A N52AW Lima, Peru

It seems there must be 6 ports, though the photos appear to show only 4. I wonder where the other two are. It seems likely that there are two in one of the darker areas, possibly the larger, more forward one, which appears to be elongated vertically.

[737Jock]

3 static systems, 1 for captains instruments, 1 for co-pilot instruments, 1 for standby instruments.

Each static system has 2 static ports and they are interconnected, to compensate for sideslip. So yes 6 static ports in total.