Radar antenna elevation when aircraft pitched up, both BMS and real world
I’m trying to help answer this question about fighter jets radar scan elevation on Aviation.SE.
(See the answer i gave as user scrontch)
Btw, feel free to post your own.
The question is: How does radar antenna elevation behave when the aircraft is flying pitch up?
Will it be corrected compared to level flight so that same absolute volume is scanned or will it pitch up with the airframe.
Let’s assume plain RWS without any bugged targets.
It is my assumption that no correction is taken and the antenna always scans the same volume relative to the airframe longitudinal axis vector. Thus if the plane is pitched up, antenna scans a volume of higher altitudes and might no more see lower altitudes.
This means you can just use the airframe pitch to scan higher or lower altitude volumes by pointing your nose higher/lower.
Is this right?
My question is both about BMS and the real world:
- How is it in the real F-16?
- How is it implemented in BMS?
- How is it in real other fighters, especially latest generation ones with AESA radars?
Any links to sources?
I never looked, but are FCR radar cursor altitude gates updated when i pitch up?
Constantly corrected to take into account aircraft roll and pitch… and no aircraft doesnt do this, because it would make it impossible to lock otherwise
Depends on the mode, but CRM modes and ACM-Slew are Space Stabilized. No matter your pitch and roll, they will look at the same portion of the sky. The only exception, of course, is if that potion of sky is outside the antenna gimbal limits, e.g ordered to scan 60° down when the aircraft is 20° pitch up.
Same in BMS and the real thing. And I’m pretty sure AESA stuff does it too. That’s not an antenna style problem, that’s a basic geometric “where to point my beam” problem.
I disagree that every fighter radar does that : you need an internal INS unit with precise angular measurements to be able to, I don’t think that e.g. a Mig-21 can.
Hmmm, okay. :?
Can we give any sources for this?
I dont see why it wouldn’t be possible to lock. The FCR could recalculate/correct the already identified positions on the scope, but still the antenna scan sweep could be free of corrections.
What i mean is:
The radar return for a given target at a given time gives the FCR system a certain point in 3D space. This point is mapped onto the B-scope display taking into account current pitch/roll state of the airframe. When pilot selects this point for locking, the FCR knows its 3D location and could again calculate the new antenna angles for any new pitch/roll state that might have changed.
T.O. 1F-16CM-34-1-1 would be a good first start if looking for reference material.
Or a quick observation in game : the cursor altitude numbers don’t skyrocket when you pull the stick.
Depends on the MiG-21. The older RP-21 was airframe centric (three bars of spin-scan with some overlap for 60x20 total FOR). The newer RP-22 was stabilized 80 in roll and within 30 of pitch (60x17.66). You don’t need an INS to do stabilization, just some form of attitude gyro.
I am curious what the F-16 radar does when its antenna can’t reach any portion of its normal field of regard. Does it shut down? Does it radiate at all? If it happens to detect something does it display it even if it’s at a weird angle?
My guess is that the antenna stops radiating and steers to the closest region of sky in the normal search envelope in order to be as ready as possible to resume scanning.
How much roll can the antenna do?