Honeywell Primus 660 weather radar tilt

[darkbarly]

The Honeywell Primus 660 AWR Pilot manual (rev 3) states that

"The stabilization system uses the aircraft attitude source as a reference" for tilt setting. Furthermore; "hold the elevation of the antenna beam relative to the earth’s surface constant at all azimuths, regardless of aircraft bank and pitch maneuvers".

Can anyone confirm the 660 AWR TILT, at ZERO degrees, is aligned with the pitch attitude? (inferring that the "aircraft attitude source" quoted above does not refer to a gyro/platform/AHRS etc). A reference for same would be appreciated.

Been elsewhere on this forum and found some conflicting opinions which don't help me to explain away some erroneous tilt returns from my aircraft.

[Fursty Ferret]

"The stabilization system uses the aircraft attitude source as a reference" for tilt setting. Furthermore; "hold the elevation of the antenna beam relative to the earth’s surface constant at all azimuths, regardless of aircraft bank and pitch maneuvers".

Looks to me like it maintains the attitude selected on the control panel irrespective of aircraft attitude. As it's meant to...

[darkbarly]

Do not understand your answer. Question is underlined.

[JRBarrett]

Originally Posted by darkbarly

Do not understand your answer. Question is underlined.

I'm away from my office at the moment and can not give you a chapter and verse manual reference for the Primus 660 in particular, but I can tell you that the radar stabilization system does receive its input from the aircraft's primary attitude reference system. Depending on the model aircraft, that reference may be an IRU, an AHRS or a remote mechanical horizontal/vertical gyro.

Tilt is referenced to the earth's surface. If the aircraft is flying perfectly level, with the AWR tilt set to zero, the angle of the antenna pitch axis (as it sweeps side-to-side) will be parallel to the horizon.

If the aircraft pitches up 5 degrees in a climb, the AWR antenna will simultaneously pitch down 5 degrees to keep the sweep aligned with the horizon. Likewise if the aircraft pitches down 5 degrees, the antenna will pitch up 5 degrees.

If, from level flight, the aircraft enters a 20 degree left bank, The antenna horizontal sweep will change to an upper left to lower right path ( referenced to the wings), again to keep the antenna sweep aligned with the horizon.

What kind of tilt problem are you having that spurred your question? Stabilization issues are a very common symptom of a malfunctioning AWR. Sometimes due to problems with the input from the aircraft's attitude reference system, but more likely due to issues with the motors or gearing used to drive the antenna vertically or horizontally.

[darkbarly]

What kind of tilt problem are you having that spurred your question?

Today at 27000agl, beam bottom earth return at 30 miles required -3 deg tilt. Geometrically this angle should be 5.6 deg tilt down selection(8.4-1/2 beam width or 2.8 in my case)

Or lets say then we use TIP, a well known method for establishing tilt. 27000/30 = 9. Therefore -3+9 = +6 tilt to give beam bottom horizontal.

However, if beam width 2.8 deg for my 18" RTA is correct then it appears zero tilt out by +3.2 deg(which, if my sums are right, would mean not seeing a return 9000'ish above my level at 30nm)

I notice various sources mix the terms 'reference to horizon', 'parallel to earth surface' and 'attitude referenced'. These can all have different meanings for tilt I believe.

I understand that the tilt will not alter when manoeuvring with a stabilized system, but need to address where exactly ZERO TILT is referenced to when a calibrated LRU is fitted to the aircraft(Embraer 190).