Test aircraft probe?
 

Hello,

most of test aircrafts have a probe fixed on the top of rudder... I guess it's for measuring the dyn pressure behind the aircraft, static pressure, angle of attack or sideslip angle.

anyone knows exactly what is it?

thank you.

http://img44.imageshack.us/img44/4851/probe2.jpg

http://img36.imageshack.us/img36/5663/probe1t.jpg

It's a trailing static cone, used to measure static air pressure away from the airframe and independently of the aircraft's own sensors.

arigato gosaimas :)

The cone is there to ensure that the pipe flies steady and straight. The static vents are usually a few feet ahead of the cone. What I would like to know though is how far Boeing reel the cone out. The one I had involvement with was 80 feet being the aircraft.

Don't forget the Nose Boom
 

A lot of test aircraft also have a seperate Nose Boom which carries a Pitot head well ahead of the aircraft plus an OAT probe and two pairs of sideslip & angle of attack vanes. You can see them on both the CRJ-1000 prototype and our CRJ-100 test aircraft on here http://www.pprune.org/flight-testing...en-flight.html

Jimmy,
Beleive we've used both 80 & 100 foot for the trailing cone - best (most stable) length for a particular aircraft seems to vary a bit so we have an internal capstan with appropriate markings on the tubing & the FTE just runs it out as required before the testing starts.

Thanks for that. We used to reel the cone out but more recently it has been deployed to its full length on the runway. When the power increased the cone started to fly anyway.
Do you know if there different cone calibration corrections for different trail lengths?

Jimmy,
Sorry you're talking to the Self Loading Ballast (well an Avionics engineer) but Mick (Flight Tester) is a real FTE & can probably help you as to corrections.

We also use the runway launch method for our smaller jets - the hose length looks to be closer to 50 feet (or less) on those.

You should do tower flyby's with the cone in order to calibrate it at whatever trail length you're going to use. In my insignificant experience, the trail length variation is inconclusive so you're probably not going to use it as a calibration parameter.

Air Data
 

All the info you need can be found here.


spaceagecontrol.com : Main > Data Sheet - 100101 Trailing Cone










Charlie

When I was involved in air data and RVSM certification we certainly calibrated the cone installation using tower fly-bys. We used a constant pipe length (and trail length) regardless of aircraft series and the calibration was usually the same. The overall pipe length being the variable rather than trail length.

We designed our own but that looks familiar.

Machdiamond
 

the small static ports few meters upstream of the cone measure the absolute static pressure at flying altitude, so I cannot understand the need to calibrate through tower fly-by, probably it was the aircraft static ports which were calibrated and compared to cone static port pressure.

However, for stall tests, in order to appreciate the difference between the pitot tube pressure indication and the 'true' static pressure measured 50 meters behind the aircraft, with its lag in reading due to the length of the small pipe, we used to calibrate the two systems recording the two pressure peaks resulting from exploding a toy balloon in close proximity to the two pressure sources (pitot and cone static pressure ports)
Regards
D.

You need to confirm somehow that the trailing cone sensors are far enough behind the a/c that they really are measuring the "absolute static pressure at flying altitude". If there's a wake effect because the cone is too short, this is the only way to find out.