Monday, February 22, 2016

F-35 May not be VLO to X-Band Radar in the Front Quarter

Hey guys, this is snippets of a conversation I've been monitoring and I might have to take it down if the principals get pissed but check this out....
F-35 JSF May not be VLO to X-Band Radar in the Front Quarter
First, let's look at the way AESA Fighter radars are configured. The radar beam can be steered about 60 degrees around the vertical to the antenna back-plane. Because target of interest - opposing enemy fighters - might be higher, the practice is to tilt the back-plane at (say) 20 degrees up. Now the AESA beam can be steered +80 to -40 degrees to the horizontal which is the usual flight angle when searching.

Next, look at (say) a Sukhio T-50 at 55,000 feet engaging a F-35 at 35,000 feet head-on. If we do the trigonometry, at 25 NMi, the F-35 is looking up about 7.7 degrees. So the F-35 APG-81 beam will be looking at a T-50 AESA back-plate tilted up and most of the radar energy will be reflected skyward.

Looking the other way, the Sukoi T-50 will be looking down 7.7 degrees at the F-35 APG-81 so the T-50's radar will be painting the APG-81 back-plane 12.3 degrees off its bore-sight. The Laws of Physics suggest that there will be a good return to the T-50 AESA radar.

The possibility of not so VLO.  Effects of Plasma in the Radome

I raised this as the concept of 'stealthing' radars with plasma has been around for some time. Generating a radome full of cold plasma is feasible and is claimed to have been flight tested on the Su-35S:

There is a DTIC PDF on the subject but I can't get it to load:

So, here is the tactic. When 'cold-nose', the T-50 fill the radome with plasma. Now, the F-35 is both looking up at an angled AESA back-plane AND into a radome with plasma acting as RAM.

I don't know if you have noticed, by the T-50 is now quoted as having an OLS-50 IRST with a QWIP sensor.

Tactics could be flying 4 * T-50 widely spaced, one radiating, the rest looking with IRST and 'blinking' the active radar across the formation.

The physics suggests the X-Band on X-Band through Frequency Selective Surfaces could result in a compromise of the F-35 head-on VLO.
I say monitoring because to be blunt I don't know enough on the subject to participate in their discussion.  Is something as basic as an optimized flight envelope at 35K instead of 55K that most air superiority aircraft operate at, along with some basic trigonometry with regard to AESA arrays (not to mention some hardcore science with regard to plasma, IRST detection capability etc..) really that big an achilles heel for the F-35?

I don't know but from reading the above it sure looks like it.

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