Proper radar tilt management can save your hide, you need to understand what the tilt does and how to best use it to detect weather.
What follows are quotes from the sources listed below, as well as my comments in blue.
Figure: Radar beam illustration high altitude 18-inch radiator, from Honeywell Primus 880 Pilot's Guide, figure 5-5.
[Honeywell Primus 880 Pilot's Guide, pgs. 5-5 to 5-6]
The Primus 880 Pilot's Guide illustrates beam widths for 12" and 18" radar plates, not for the 24" plate in the G450. The larger the plate, the narrow the beam. The 18" plate has a 5.6° beam, the 24" plate narrows that to 4.2°. The illustration shows the beam width off center, really just half the beam width. For the G450 in this illustration would show a distance of 11,119' at 50nm and 22,269" at 100 nm. More about this: Procedures & Techniques / Radar - Beam Width.
Figure: Radar beam illustration low altitude 18-inch radiator, from Honeywell Primus 880 Pilot's Guide, figure 5-7.
Here again the numbers need to be compensated for the narrower beam of the G450's 24' plate:
Table: Approximate tilt setting for minimal ground target display 18-inch radiator, from Honeywell Primus 880 Pilot's Guide, table 5-2.
[Honeywell Primus 880 Pilot's Guide, pgs. 5-7 to 10]
You can estimate the tilt needed to paint the ground using level flight tilt as a starting point:
Figure: Beam width level flight tilt, from Eddie's notes.
If you know the width of your beam in degrees, you can figure it in feet with a little math.
In the case of the G450, we know our 24" plate produces a 4.2° beam that equates to 44,537' at 100 nm. Armed with this knowledge, if we were flying along at 44,537', we could adjust the tilt so the ground paints right at 100 nm. Raising the tilt 2.1° from that point will point the radar along level flight. With a little more math we could come up with the correct distance to paint the ground for various altitudes:
|Aircraft's Altitude (FL)||Distance to paint edge of ground clutter|
Table: G450 distance to pain ground clutter for level flight tilt adjustment, from Eddie's notes.
So let's say you are in your G450 at FL 350. Adjust your range scale to put 100 nm on the outer ring and adjust your tilt to show the ground clutter just starting at around 80 nm. Raise your tilt half the beam width, 2.1°, and know that the center of your beam is now point along level flight.
Figure: Ideal tilt angle, from Honeywell Primus 880 Pilot's Guide, figure 5-8.
[Honeywell Primus 880 Pilot's Guide, pgs. 5-11 to 15] Tilt management is often misunderstood. It is crucial to safe operation of airborne weather radar. If radar tilt angles are not properly managed, weather targets can be missed or underestimated. The upper levels of convective storms are the most dangerous because of the probability of violent windshears and large hail. But hail and windshear are not very reflective because they lack reflective liquid water.
The ideal tilt angle shows a few ground targets at the edge of the display.
Figure: Convective thunderstorms, from Honeywell Primus 880 Pilot's Guide, figure 5-10.
Convective thunderstorms become much less reflective above the freezing level. This reflectivity decreases gradually over the first 5000 to 10,000 feet above the freezing level:
Figure: Low altitude tilt management, from Honeywell Primus 880 Pilot's Guide, figure 5-15.
At low altitude, the tilt should be set as low as possible to get ground returns at the periphery only:
[Honeywell Primus 880 Pilot's Guide, pg. 5-15] The antenna size used on the aircraft alters the best tilt settings by about 1°. However, tilt management is the same for either size:
[Honeywell Primus 880 Pilot's Guide, pg. 5-15] A 1° look down angle looks down 100' per mile and the bottom of the beam is 1/2 beam width below tilt setting.
At 40,000', setting 0° tilt on a 24-inch radar grazes the ground at 90 nm.
At 30,000', setting 0° tilt on a 24-inch radar grazes the ground at 70 nm.
In a nutshell you want to aim all of the beam into the strongest part of the thunderstorm. For techniques on how to do that:
Portions of this page can be found in the book Flight Lessons 1: Basic Flight, Chapter 28.
Honeywell Airborne Weather Radar Training, Rev E, 12/09/02, Honeywell Inc. Commercial Flight Systems Group, Phoenix, AZ.
Honeywell Primus 880 Pilot's Guide, Pub. No. A28-1146-102-03, Revised January 2006, Honeywell International Inc. Commercial Electronic Systems, Glendale, AZ.