Stealth and Aero Shaping: F-35 Versus F-22

The F-35 compared with other modern jets.
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sprstdlyscottsmn

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Unread post01 Aug 2013, 19:33

to be fair on the engagement circles, the T-50 will more likely be flying at M1.6 than M0.8. Good job showing relevance on flight altitude. Also remember that a M4 missile does not spend the whole flight @ M4.
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munny

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Unread post02 Aug 2013, 12:21

sprstdlyscottsmn wrote:to be fair on the engagement circles, the T-50 will more likely be flying at M1.6 than M0.8. Good job showing relevance on flight altitude. Also remember that a M4 missile does not spend the whole flight @ M4.


Still, stealth gets an advantage over speed.

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sprstdlyscottsmn

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Unread post02 Aug 2013, 13:55

Oh of course it does, not being seen is the best defense.
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Unread post09 Nov 2013, 11:34

munny wrote:Perhaps these can help with understanding side aspect stealth a little better.

Image
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Except for the sweep angle of the wings, there's no reason the F-35 can't have a similar or better frontal RCS than the F-22 as far as shaping.

i dont quite understand the picture , what they mean ? why the t-50 pic is so different from f-35 , f-22 even thought they looked the same ? :?
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Unread post26 Apr 2014, 13:15

munny wrote:Perhaps these can help with understanding side aspect stealth a little better.

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RCS polar charts of stealth features of the 3 aircraft shown. As you can see, due to the more shallow surface angles of the F-22's side panels, the main RCS lobe is angled further downward than the F-35 and a LOT further down than some features on the PAK FA. You can see the cross sections of the F-35 airframe were quite lumpy and bumpy, but because of the consistent adherence to the 65 degree surface angle rule, the lumps have little effect on RCS at the angles that matter.

The T-50 on the other hand is a god awful, horrible mess. Its has roughly 5 separate main lobes on it bottom hemisphere which Carlo Kopp acknowledges in an RCS test he did as well. Keep in mind, the component models used for the above polar charts were all to scale. The scale on the rear chart for the PAK FA is 10dBSM different to the others due to the massively higher RCS. A little issue with APA's analysis (complete garbage actually) is that they say that the T-50 profile may be "preferable" to the f-35's.

The impact of those main lobe angles is as follows. When flying past ground or low flying radar at each aircraft's typical operating altitude, this is how exposed they are within a 10-15 degree sector perpendicular to their flight path.

From left to right:

F-22 at 55kft
J-20 or F-35 at 30kft
J-20 or F-35 at 55kft
T-50 at 55kft

Image
This image is not as to scale as the others below.

If you look top down on the aircraft, this 15 degrees of bad beam RCS (in straight and level flight) exposes the aircraft like so. A bad result here equates directly to being exposed to radar for longer periods of time = able to be engaged by networked interceptors from a longer range.

Top to bottom:

F-22 at 55kft
J-20 or F-35 at 30kft
J-20 or F-35 at 55kft
T-50 at 55kft

Image

Something interesting I just worked out. I did a comparison of the T-50 vs the F-35 in a networked environment where any radar can guide any weapon. A couple stats based on the depression angle of their high RCS lobes being illuminated by ground radar from maximum range as they fly past.

F-35 at 35kft: -25 degree lobe extends to 22km and can be tracked for a maximum of 6km of its flight ( 25secs at M0.8 ). Can be engaged by M4.0 missiles (9sec accel time) within 23km of its location at the end of the 25secs.

T-50 at 55kft: -7 degree lobe extends to 136km and can be track for a maximum of 35km of its flight ( 152secs at M0.8 ). Can be engaged by M4.0 missiles (9sec accel time) within 164km of its location at the end of the 152secs.

F-35 and PAK FA at M0.8 Passing radars at the widest part of their worst side aspect. The circles roughly show the range at which the aircraft can be engaged from by networked launchers.

Image

Seems it doesn't pay to cheapen up on your stealth in a networked environment and this is why conventional fighters are soon to be 100% obsolete against any medium tier IADS.

Carlo Kopp
The F-35 JSF exhibits similar, but in some respects more severe beam aspect specular RCS behaviour than the T-50. This is a direct consequence of the use of multiple complex double curvature convex and concave shaping features in its lower fuselage design, and lower wing root area, and a much shorter fuselage. The ventral shaping features were introduced in the SDD aircraft and were not part of the X-35 demonstrator design. Another unfortunate feature of F-35 shaping is the depression angle of the slab sides of the engine inlets, which is shallower than the F-22 and J-20 designs, and similar to the T-50, as a result of which the associated mainlobe peaks at a lesser depression angle, in turn degrading performance against long range surface based threats.


Tsk tsk Mr Kopp, so many mistakes in one analysis.
1. The F-35 side features are nowhere near as impacting as the T-50's as shown above.
2. The J-20 has the same angles as the F-35.
3. The double curves you mention have very little effect on specular return from the side aspect. All aircraft are radar beacons when they bank.
4. The T-50 has numerous surfaces a lot more vertical than the F-35's including some corner reflectors. Factored with the differences in operating altitude, it is FAR less exposed.

Except for the sweep angle of the wings, there's no reason the F-35 can't have a similar or better frontal RCS than the F-22 as far as shaping.

yo man!where is this RCS estimated picture come from?
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