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

Unread postPosted: 09 Nov 2010, 11:30
by stereospace
I'm surprised by how differently the F-35 is shaped when compared to the F-22. Beyond the obvious difference of comparing a twin engine aircraft to a single engine, there are a number of differences in plan form and shaping.

One would think, having spent many years and tens of thousands of hours during F-22 development evaluating various designs for stealthiness and aerodynamic performance, LM would apply that (highly successful) model to the F-35 more fully.

Plan view comparison:

Unread postPosted: 09 Nov 2010, 11:32
by stereospace
Take a look at these features and compare to the F-22 above:

The one difference I can account for is the air inlet change, which is due to the boundary layer diverter on the F-35. The differences in the wing shaping and horizontal stabs throws me. Ditto for the nose proportions and overall nose shape. I can't account for those things at all.

Unread postPosted: 09 Nov 2010, 11:43
by stereospace
Also, compare the bottom views of the two aircraft, in particular the F-22's overall flatness versus the shaping on the F-35:

Unread postPosted: 09 Nov 2010, 12:40
by shep1978
Interesting topic, from the top looking down on them they look pretty similar apart from as you've pointed out the intakes and a few other areas. The underside is where the biggest difference seem to be but i'd trust LM knows what they're doing enough to make sure its stealthy down there.
You should throw in some frontal, rear and side shots to compare those. I'm pretty sure Paul Bevilaqua (I think thats the right chap) said the F-35 was designed as a mini F-22 or something like that in a video shown on Av Week not to many months ago but I guess they couldn't scale it down perfectly and still meet all the requiments for the three services as that'd be impossible.

(I wonder if that plonker who claimed the Typhoon has better underside values RCS will show up here to teach us a thing or two...)

Unread postPosted: 09 Nov 2010, 15:12
by exorcet
The reason for the differences is pretty simple, two planes with two different missions. The F-22 is going to fly around up high at M 1.5 behind enemy lines looking for fighters. The F-35 will either be loitering at a lower speed looking for fighters, or concentrating on finding ground targets.

I wasn't involved in the design of either plane, so I can't give you justifications for everything, but I can make some guesses (and use some of LM's claims).

The F-35's inlet is a simpler cheaper design than the F-22's. Since the 35 isn't expected to fly as fast as the F-22, there’s no reason to have high Mach inlets.

Lowering wing sweep goes along those same lines, the F-35 won’t spend the majority of its time in supersonic flight, so the wing is probably designed to maximize range at subsonic speed (though the maneuverability is probably strong through all speeds). The lower sweep also gives the F-35 a higher effective aspect ratio, which lowers induced drag (will probably lower cruise drag, but may not lower drag when maneuvering) and increases lift performance, this goes double for the F-35C big wing.

The F-35 seems to have a very “plain” wing compared to the 22. The F-22 has obvious washout and the tip trailing edge is clipped. This is probably in use to control the lift distribution and stall characteristics at high angle of attack. For whatever reason, the F-35 didn’t need these. It could be for costs reasons.

As far as stabilizers go, the F-22 probably has bigger verts because it’s a supercruiser. I don’t know why the horizontal stabs are different. I don’t see one as better than the other aerodynamically, but maybe the F-22’s is stealthier, while the F-35’s is cheaper and easier to make.
I have no idea why the underside is so curvy.

Unread postPosted: 09 Nov 2010, 15:46
by Lightndattic
This is the difference between all-aspect stealth and front focused stealth. Also, the benefits of the F-35 are seen vs. legacy aircraft carrying external stores; not vs. the F-22.

Unread postPosted: 09 Nov 2010, 15:48
by Conan
Image

Image

Image

Image

Signature management features have evolved over the last 30 years as computing power has increased and understanding has improved...

Unread postPosted: 09 Nov 2010, 17:03
by Prinz_Eugn
I really like the blanket assumption that the F-22 is automatically better... because it's the F-22!!!1

Look at the planform alignment- those wingtip notches on the Raptor create another RCS spike (It's for antennae coverage, the YF-22 did not have them). Look at the horizontal stabs- the F-35's trailing edges are simpler, and the joint gap is much better hidden. The F-35 looks more refined from an aerodynamic perspective, the F-22 fuselage is really just a glorified brick with little wing-body blending to speak of.

Unread postPosted: 09 Nov 2010, 17:32
by shep1978
Prinz_Eugn wrote:I really like the blanket assumption that the F-22 is automatically better... because it's the F-22!!!1


I'm pretty certain LM or the DOD (or some official body) have actually said the F-22 is stealthier. Edit:

"According to November 2005 reports, the US Air Force states that the F-22 has the lowest RCS of any manned aircraft in the USAF inventory, with a frontal RCS of 0.0001~0.0002 m2, marble sized in frontal aspect. According to these reports, the F-35 is said to have an RCS equal to a metal golf ball, about 0.0015m2, which is about 5 to 10 times greater than the minimal frontal RCS of F/A-22. The F-35 has a lower RCS than the F-117 and is comparable to the B-2, which was half that of the older F-117. Other reports claim that the F-35 is said to have an smaller RCS headon than the F-22, but from all other angles the F-35 RCS is greater. By comparison, the RCS of the Mig-29 is about 5m2."

Source is that Global Security site, I might go try and find the actual reports if i've got the time but I doubt global security would lie in the first place.

Unread postPosted: 09 Nov 2010, 18:09
by Prinz_Eugn
So it's stealthier from the front but also ten times bigger? Open sources aren't going to be that helpful here. The golfball thing was always just a convenient invention for explaining a complicated concept the non-technical people that control the money.

The truth is that both designs are compromised somewhat for various reasons, and were designed to completely different requirements, so "better" is not a relevant term. Your original post might as well be asking why McDonnell-Douglas didn't just make an F-4 with bigger engines for FX (F-15) back in the day, since the F-4 was the best fighter of its time. Different requirements and different technology equal different airplanes.

In fact, we should all be more surprised the F-22 and F-35 look more alike than not.

Unread postPosted: 09 Nov 2010, 19:47
by shep1978
I don't understand, why is it so incomprehensible to think that the F-22 has better 'stealth' levels than the F-35?
Sure the F-35 may be newer but perhaps the powers that be didn't want the F-35, which will be sold to foreign nations, to have better stealth than the F-22 which is perfectly understandable.

Unread postPosted: 09 Nov 2010, 20:28
by spazsinbad
shep, the term is 'exportable stealth' often confused to mean that F-35 has different levels of stealth for different countries, when all F-35 variants have the same level of stealthiness for reasons you state.

Unread postPosted: 09 Nov 2010, 21:18
by exorcet
Prinz_Eugn wrote:I really like the blanket assumption that the F-22 is automatically better... because it's the F-22!!!1

Look at the planform alignment- those wingtip notches on the Raptor create another RCS spike (It's for antennae coverage, the YF-22 did not have them). Look at the horizontal stabs- the F-35's trailing edges are simpler, and the joint gap is much better hidden. The F-35 looks more refined from an aerodynamic perspective, the F-22 fuselage is really just a glorified brick with little wing-body blending to speak of.


It’s not assumed, it’s been stated publically. I’m fitting what I know to the public info. On the 22’s clipped wings, the YF was a prototype, so expect shortcuts. Just because the YF didn’t have the clips does not make them aerodynamically superior. The YF-15 lacked sawtooth stabilizers, and it was a grave weakness. That said, I’ve confirmed the use for antenna coverage, though they may also be there for aerodynamic reasons.

I can see some of your points on the horizontal stabs, but you comment about the F-22 being a brick is a bit absurd. Care to explain? I don’t really see anything on the F-35 that looks “more refined”.

Prinz_Eugn wrote:So it's stealthier from the front but also ten times bigger? Open sources aren't going to be that helpful here. The golfball thing was always just a convenient invention for explaining a complicated concept the non-technical people that control the money.

The truth is that both designs are compromised somewhat for various reasons, and were designed to completely different requirements

Who says the F-22 is only stealthier up front? The golfball isn’t only what you say, but it’s also a way to tell someone something without actually telling them, so to speak. The F-22 seems to be stealthier, we just don’t know where/when/how.

You are completely right on these designs being made to fit their specifications. On that front, we think the same. But not, a plane may be required to be worse than another, apparently, this is the case with the F-35’s stealth vs the F-22’s.

Unread postPosted: 09 Nov 2010, 22:22
by Prinz_Eugn
It would not be terribly surprising the F-35 has a lower overall RCS, but you also talk about aerodynamics in your post. That is easily addressed by the different regimes in which they fly. Making it more like the F-22 would also make it worse at what it's supposed to do.

One would think, having spent many years and tens of thousands of hours during F-22 development evaluating various designs for stealthiness and aerodynamic performance, LM would apply that (highly successful) model to the F-35 more fully.

Actually, they did, but adapted the basic design to JSF requirements. Look at the X-32 to see what a truly different design would be like.

The F-22 block fuselage was a deliberate design decision early on in the program, mostly for simplicity reasons (cheaper to produce, get to RCS target). Take a gander at the YF-23 or even the PAK FA and see how blended those designs are. Pretty much every non-stealth design in recent memory has had more wing-body blending than the F-22, which should tell you there is a reason for it. . Getting away with more complex fuselage features like that (better airflow at normal flight regime) and still meeting RCS requirements is why I think the F-35 shouldn't be thought of as a half-baked F-22 design.

Unread postPosted: 09 Nov 2010, 23:03
by exorcet
Well, in the end, the X-32 wasn't that different

http://en.wikipedia.org/wiki/File:Boein ... tarmac.jpg

I'm still not seeing what's wrong with the F-22's fuselage, which is what I was aksing you about. Where is the F-35 more refined specifically?

Other than a few bumps on the underside, they're pretty similar, ie wide flat lifting bodies. Where they truly differ is wing and control surface design.

On blending, from the top, the YF-23 and PAK look pretty blended, but so does the F-22. From the bottom, you can see where the wings meet the fuselage.

http://upload.wikimedia.org/wikipedia/c ... flight.jpg

http://static.panoramio.com/photos/original/4634883.jpg

http://tinypic.com/view.php?pic=241jl11&s=5

Unread postPosted: 10 Nov 2010, 00:23
by stereospace
Prinz_Eugn wrote:The F-22 block fuselage was a deliberate design decision early on in the program, mostly for simplicity reasons (cheaper to produce, get to RCS target). Take a gander at the YF-23 or even the PAK FA and see how blended those designs are. Pretty much every non-stealth design in recent memory has had more wing-body blending than the F-22, which should tell you there is a reason for it. . Getting away with more complex fuselage features like that (better airflow at normal flight regime) and still meeting RCS requirements is why I think the F-35 shouldn't be thought of as a half-baked F-22 design.


So, if I understand, you're saying the complex blending on the underside of the F-35 results in, "better airflow at normal flight regime", correct? Interesting. I would think the flat surface of the F-22 would experience less turbulence. It's obvious it would be cheaper to build since it's less complex, and it seems a flat surface would be stealthier (angle of incidence equals angle of reflection). The aerodynamic gains must be worthwhile, though it seems counterintuitive.

Unread postPosted: 10 Nov 2010, 01:52
by popcorn
I can see a strong family resemblance between the 2 jets.

Unread postPosted: 10 Nov 2010, 04:10
by jeffb
stereospace wrote:
Prinz_Eugn wrote:The F-22 block fuselage was a deliberate design decision early on in the program, mostly for simplicity reasons (cheaper to produce, get to RCS target). Take a gander at the YF-23 or even the PAK FA and see how blended those designs are. Pretty much every non-stealth design in recent memory has had more wing-body blending than the F-22, which should tell you there is a reason for it. . Getting away with more complex fuselage features like that (better airflow at normal flight regime) and still meeting RCS requirements is why I think the F-35 shouldn't be thought of as a half-baked F-22 design.


So, if I understand, you're saying the complex blending on the underside of the F-35 results in, "better airflow at normal flight regime", correct? Interesting. I would think the flat surface of the F-22 would experience less turbulence. It's obvious it would be cheaper to build since it's less complex, and it seems a flat surface would be stealthier (angle of incidence equals angle of reflection). The aerodynamic gains must be worthwhile, though it seems counterintuitive.


Early mockups of the F-35 had a flat bottom as well. APA pointed to the new "bumpy" bottom to claim that ah-ha, some of the stealth aspects of the F-35 have been compromised to fit everything in. Without access to an F-35 on-a-stick to do radar comparisons it's hard to say if that's true or not. As you point out LM claim that the changes to the bottom surface don't adversly affect it's stealth characteristics, if that's true then you might be looking at the evidence that stealth isn't about shape, shape, shape and coatings anymore. I assumed, as soon as I saw the F-22 years ago, that they'd improved the coatings dramatically over those used on the F-117, obviously the technology is evolving very quickly. Makes you wonder how the opposition is doing with it.

Unread postPosted: 10 Nov 2010, 04:50
by jimraynor
Regardless of whether the "bumpy" bottom adversely affects stealth, every source out there says the F-35 is less stealthy than the F-22.

Unread postPosted: 10 Nov 2010, 06:53
by Tinito_16
Remember that the F-35 was designed to be mass-produce-able, i.e. by definition it wasn't going to have all the bells and whistles as far as stealth and speed that the F-22 has. Those are among the most expensive elements of a fifth-generation fighter. Not that it isn't stealthy or fast, it is. Just not to to the all out extreme that the Raptor was designed to be. And anyways, they probably got some of the stealth back just on improved computers and simulations. Remember, the F-22's design was finalized about 10-15 years before the F-35's was. Following Moore's Law, computer processing power increased exponentially (x1,000 +) in that time. You tell me that doesn't make a difference in cost to stealthiness...

Unread postPosted: 10 Nov 2010, 17:09
by Prinz_Eugn
I don't really think the F-35 is stealthier than the F-22, it would be completely surprising if it was from more than a couple angles. The problem I have is that the F-22 is put on a pedestal and the F-35 is just assumed to be worse (worse aerodynamics particularly). The F-22 has various design boo-boos they didn't predict until they actually started flying them (clipped wingtips, reshaped stabs), just like the F-15 (clipped wings, dogtooth on the h. stab), and the F-4 (just... just look at an F-4).

As people have pointed out, the F-35 was designed over a decade later, which entails magnitudes of difference in the computing power available, plus all the lessons from the F-22 program. Thinking that the F-35 does not have any design improvements and the F-22 is the absolute pinnacle of everything aircraft design is kind of ridiculous to me.

Unread postPosted: 10 Nov 2010, 18:52
by wrightwing
Prinz_Eugn wrote:I don't really think the F-35 is stealthier than the F-22, it would be completely surprising if it was from more than a couple angles. The problem I have is that the F-22 is put on a pedestal and the F-35 is just assumed to be worse (worse aerodynamics particularly). The F-22 has various design boo-boos they didn't predict until they actually started flying them (clipped wingtips, reshaped stabs), just like the F-15 (clipped wings, dogtooth on the h. stab), and the F-4 (just... just look at an F-4).

As people have pointed out, the F-35 was designed over a decade later, which entails magnitudes of difference in the computing power available, plus all the lessons from the F-22 program. Thinking that the F-35 does not have any design improvements and the F-22 is the absolute pinnacle of everything aircraft design is kind of ridiculous to me.


You also have to factor in the cost of implementation. Just because you can design something, doesn't mean that it will be cost effective. The F-35's stealth advantages are in ease of maintenance more than in lower RCS than the F-22.

Unread postPosted: 10 Nov 2010, 19:24
by Prinz_Eugn
Exactly. Which I think is an example of substantial improvement over the F-22's design- a practical level of Stealth that doesn't devour the MX budget.

Unread postPosted: 10 Nov 2010, 22:38
by f35phixer
Prinz got to it before me, Who says F-35 ISN'T Better!!!!!!!!!! You Might be surprised :devil:

Unread postPosted: 10 Nov 2010, 23:08
by exorcet
stereospace wrote:
Prinz_Eugn wrote:The F-22 block fuselage was a deliberate design decision early on in the program, mostly for simplicity reasons (cheaper to produce, get to RCS target). Take a gander at the YF-23 or even the PAK FA and see how blended those designs are. Pretty much every non-stealth design in recent memory has had more wing-body blending than the F-22, which should tell you there is a reason for it. . Getting away with more complex fuselage features like that (better airflow at normal flight regime) and still meeting RCS requirements is why I think the F-35 shouldn't be thought of as a half-baked F-22 design.


So, if I understand, you're saying the complex blending on the underside of the F-35 results in, "better airflow at normal flight regime", correct? Interesting. I would think the flat surface of the F-22 would experience less turbulence. It's obvious it would be cheaper to build since it's less complex, and it seems a flat surface would be stealthier (angle of incidence equals angle of reflection). The aerodynamic gains must be worthwhile, though it seems counterintuitive.

Now that I think about it, the curved surface under the fuselage could just be there to shape the area distribution for supersonic drag.
Subsonic, I don’t see any obvious benefits, but they may do something to the boundary layer. A long flat surface usually just lets the BL build up.
f35phixer wrote:Prinz got to it before me, Who says F-35 ISN'T Better!!!!!!!!!! You Might be surprised :devil:

Well, the two planes have two different purposes, and price was a bigger concern for the F-35. It would be surprising if the F-35 was better than the F-22 in the supersonic regime considering that that is what the F-22 specializes in. The reverse is true as well.

Unread postPosted: 11 Nov 2010, 00:34
by stereospace
exorcet wrote:Now that I think about it, the curved surface under the fuselage could just be there to shape the area distribution for supersonic drag.


Could you explain/expound on that a little? Thanks!

Unread postPosted: 11 Nov 2010, 05:08
by exorcet
It's the area rule

http://en.wikipedia.org/wiki/Area_rule

http://www.aerospaceweb.org/question/ae ... f102-1.jpg

To minimize the supersonic drag coefficient, the change in area along the length of the aircraft should be smooth (example, having a tubular fuselage with a pair of wings jutting out of the sides is much worse than having a fuselage that narrows along the chord of the wing).

There are a number of ways to control the area distribution. The F-102 used the method I described above, but the inverse it also true; instead of narrowing some section of the plane, you can make a different section wider. The bumps on the underside of the F-35 might make the area distribution more like the "ideal" curve in the F-102 photo (though the ideal shape changes slightly with different Mach numbers). I'm pretty sure that the bumps on the underside of the F-22's wings are there for supersonic drag reduction.

Unread postPosted: 11 Nov 2010, 09:28
by Rapec
Hello

exorcet wrote:Subsonic, I don’t see any obvious benefits, but they may do something to the boundary layer. A long flat surface usually just lets the BL build up.


I'm no expert in aerodynamics but on the other hand those "bumps" may leadto BL seperation, which increased drag and IMHO is far more worse situation than slow BL build up along fuselage.

exorcet wrote:I'm pretty sure that the bumps on the underside of the F-22's wings are there for supersonic drag reduction.


I've never heard of applying the area rule to aircraft's wings. In my opinion those bumps serve as fairings to ailerons and flaperons drives.

Regards

Unread postPosted: 11 Nov 2010, 09:31
by Rapec
Double post, my fault.

Unread postPosted: 11 Nov 2010, 15:50
by exorcet
Rapec wrote:I'm no expert in aerodynamics but on the other hand those "bumps" may leadto BL seperation, which increased drag and IMHO is far more worse situation than slow BL build up along fuselage.


That's certainly possible, although I don't know how that would slip through the design process unnoticed/unchanged.

I've never heard of applying the area rule to aircraft's wings. In my opinion those bumps serve as fairings to ailerons and flaperons drives.


The rule applies to everything, as long as the area along the lenght varies smoothly, you're good. You don't really apply the area rule to the fuselage, or to the wings, it has to account for the entire plane.

Unread postPosted: 12 Nov 2010, 21:39
by energo
Do the bumps on the F-35s underside provide hot spots? Consider the following speculation:

* would it be significant? (technical analysis)
* under which conditions? (operational analysis)
* RAM/RAS; would likely be applied to key areas to minimize unwanted effects
* it's speculated that electrical wires are embedded in the fuselage to absorb or scatter e-m and traveling waves; note absence of traditional saw-tooth features around around access panels, wing/tail trailing edges etc. -- could it be applied to "trouble spots" as well?
* what about the F-35's record breaking skin manufactoring tolerances?

B. Bolsøy
Oslo

Unread postPosted: 17 Nov 2010, 19:44
by linkomart
exorcet wrote:It's the area rule

http://en.wikipedia.org/wiki/Area_rule

http://www.aerospaceweb.org/question/ae ... f102-1.jpg

To minimize the supersonic drag coefficient, the change in area along the length of the aircraft should be smooth (example, having a tubular fuselage with a pair of wings jutting out of the sides is much worse than having a fuselage that narrows along the chord of the wing).

There are a number of ways to control the area distribution. The F-102 used the method I described above, but the inverse it also true; instead of narrowing some section of the plane, you can make a different section wider. The bumps on the underside of the F-35 might make the area distribution more like the "ideal" curve in the F-102 photo (though the ideal shape changes slightly with different Mach numbers). I'm pretty sure that the bumps on the underside of the F-22's wings are there for supersonic drag reduction.


I'd say that slenderness is more important than area ruling, ie it is more important to minimize the max cross section area for low supersonic drag. Also, the area distribution varies with different mach numbers, so it is really hard to get a good area distribution att all speeds, usualy the area distribution looks good at some Mach number, and then you just call it the desired design speed.. :)

Unread postPosted: 17 Nov 2010, 19:54
by linkomart
energo wrote:Do the bumps on the F-35s underside provide hot spots? Consider the following speculation:

* would it be significant? (technical analysis)
* under which conditions? (operational analysis)
* RAM/RAS; would likely be applied to key areas to minimize unwanted effects
* it's speculated that electrical wires are embedded in the fuselage to absorb or scatter e-m and traveling waves; note absence of traditional saw-tooth features around around access panels, wing/tail trailing edges etc. -- could it be applied to "trouble spots" as well?
* what about the F-35's record breaking skin manufactoring tolerances?

B. Bolsøy
Oslo


Knowing that LM knows more about LO than me, I'd still say that the RCS contribution from the bumps are significant, especially since they are so small (Wich means they scatter the waves). I guess that the operational analysis made by LM shows that with proper tactics, the most important is the frontal RCS, and that is unaffected by the bumps.
I'll leave the RAM and electrical wires for now, but I'll say that the tolerances are very important for RCS, in my humble opinion.

Unread postPosted: 18 Nov 2010, 04:53
by exorcet
linkomart wrote:I'd say that slenderness is more important than area ruling, ie it is more important to minimize the max cross section area for low supersonic drag. Also, the area distribution varies with different mach numbers, so it is really hard to get a good area distribution att all speeds, usualy the area distribution looks good at some Mach number, and then you just call it the desired design speed.. :)


You can only make your plane so small while carrying X missiles and Y pounds of fuel. A brick is less draggy than a fighter, but it's not going to meet any payload requirements. The F-35 is probably as small as it can get, or close to it. So instead of shrinking it down, they need to change the shape.

Remember, drag is CD*A, there's a component from size and one from shape. You want to minimize both always.

Unread postPosted: 18 Nov 2010, 17:48
by linkomart
exorcet wrote: A brick is less draggy than a fighter, but it's not going to meet any payload requirements. The F-35 is probably as small as it can get, or close to it. So instead of shrinking it down, they need to change the shape.



Don't know about your bricks, but the ones my house is made from is definitely more draggy than any airplane :-)
You're probably right that the F-35 is as small as it can get, I can not comment on the shape of the F-35, it probably looks that way for good reasons (to fulfill the requirements), but it does not look slender to me.

exorcet wrote:
Remember, drag is CD*A, there's a component from size and one from shape. You want to minimize both always.


I'm not an aerodynamics, bu as far as I know drag is devided in to:
*friction drag, depending on reynolds number, if it is laminar or turbulent flow and the wetted area
*induced drag wich is dependent on the lift generated by the object
*shape drag wich is drag depending on the shape of the object
and for supersonic objects there is
*wave drag wich depends on the area distribution trough the mach cone, Mach number and the slenderness.

I agree that minimize drag is always a priority, at least if you want to have a high performance airplane.
My five cent.

Unread postPosted: 18 Nov 2010, 18:52
by exorcet
Well, actually a brick should be less draggy than a fighter, as in less drag force generated. It's because it's so small. In terms of CD, a brick is far, far worse, which is what you are probably referring to.

You're correct on drag classifications, but all of that is usually condensed into a CD (you can approximate this as constant over a small range of conditions).

Unread postPosted: 19 Nov 2010, 19:41
by linkomart
exorcet wrote:Well, actually a brick should be less draggy than a fighter, as in less drag force generated. It's because it's so small. In terms of CD, a brick is far, far worse, which is what you are probably referring to.

Ah, you managed to fool me on that one..
exorcet wrote:You're correct on drag classifications, but all of that is usually condensed into a CD (you can approximate this as constant over a small range of conditions).


Well, I'm mostly interested in the whole envelope so I need to divide the drag, a single Cd don't work. (Actually, the computer does everything for me, but still...)

Unread postPosted: 03 Jun 2013, 10:24
by hornetfinn
shep1978 wrote:
Prinz_Eugn wrote:I really like the blanket assumption that the F-22 is automatically better... because it's the F-22!!!1


I'm pretty certain LM or the DOD (or some official body) have actually said the F-22 is stealthier. Edit:

"According to November 2005 reports, the US Air Force states that the F-22 has the lowest RCS of any manned aircraft in the USAF inventory, with a frontal RCS of 0.0001~0.0002 m2, marble sized in frontal aspect. According to these reports, the F-35 is said to have an RCS equal to a metal golf ball, about 0.0015m2, which is about 5 to 10 times greater than the minimal frontal RCS of F/A-22. The F-35 has a lower RCS than the F-117 and is comparable to the B-2, which was half that of the older F-117. Other reports claim that the F-35 is said to have an smaller RCS headon than the F-22, but from all other angles the F-35 RCS is greater. By comparison, the RCS of the Mig-29 is about 5m2."

Source is that Global Security site, I might go try and find the actual reports if i've got the time but I doubt global security would lie in the first place.


It has been almost eight years since this information came about and I think it's time to revisit it. I think that by November 2005 there had been no real RCS tests done with F-35 and the metal golf ball reference was only speculative or maybe apprioximate RCS threshold size. F-22 RCS was definitely well known by then by the USAF but F-35 RCS was not. First production F-35 flew about year later than this report and a lot of things have changed since then.

I think there has been statements that F-35 has exceeded most expectations, including RCS: I think it's very probable that F-35 RCS is not significantly larger than in F-22. Of course RCS is very complex issue overall and there might well be certain areas (radar band and viewing angle) where either one is superior to the other. I see F-22 having certain advantages when it comes to stealth (no cost compromises, bigger jet with comparatively smaller internal fuel and weapons volume) while F-35 certainly has its own advantages (later design, newer materials, lessons learned from F-22).

Unread postPosted: 29 Jul 2013, 07:43
by Corsair1963
hornetfinn wrote:
shep1978 wrote:
Prinz_Eugn wrote:I really like the blanket assumption that the F-22 is automatically better... because it's the F-22!!!1


I'm pretty certain LM or the DOD (or some official body) have actually said the F-22 is stealthier. Edit:

"According to November 2005 reports, the US Air Force states that the F-22 has the lowest RCS of any manned aircraft in the USAF inventory, with a frontal RCS of 0.0001~0.0002 m2, marble sized in frontal aspect. According to these reports, the F-35 is said to have an RCS equal to a metal golf ball, about 0.0015m2, which is about 5 to 10 times greater than the minimal frontal RCS of F/A-22. The F-35 has a lower RCS than the F-117 and is comparable to the B-2, which was half that of the older F-117. Other reports claim that the F-35 is said to have an smaller RCS headon than the F-22, but from all other angles the F-35 RCS is greater. By comparison, the RCS of the Mig-29 is about 5m2."

Source is that Global Security site, I might go try and find the actual reports if i've got the time but I doubt global security would lie in the first place.


It has been almost eight years since this information came about and I think it's time to revisit it. I think that by November 2005 there had been no real RCS tests done with F-35 and the metal golf ball reference was only speculative or maybe apprioximate RCS threshold size. F-22 RCS was definitely well known by then by the USAF but F-35 RCS was not. First production F-35 flew about year later than this report and a lot of things have changed since then.

I think there has been statements that F-35 has exceeded most expectations, including RCS: I think it's very probable that F-35 RCS is not significantly larger than in F-22. Of course RCS is very complex issue overall and there might well be certain areas (radar band and viewing angle) where either one is superior to the other. I see F-22 having certain advantages when it comes to stealth (no cost compromises, bigger jet with comparatively smaller internal fuel and weapons volume) while F-35 certainly has its own advantages (later design, newer materials, lessons learned from F-22).



Well, said and I am sure one day we will see F-35's flying with the Finnish Air Force! :wink:

Unread postPosted: 31 Jul 2013, 10:28
by hornetfinn
Corsair1963 wrote:Well, said and I am sure one day we will see F-35's flying with the Finnish Air Force! :wink:


I'm sure too, because Finnish Air Force is planning to replace the our C/D Hornets in 2025-2030 time frame after 30 years of service. At that time there are not many worthwhile alternatives as Typhoon, Rafale and Super Hornets are on the very end of their service lives. Chinese or Russian aircraft are a very remote possibility and JAS Gripen NG is not very competitive with F-35.

Unread postPosted: 31 Jul 2013, 11:51
by munny
Perhaps these can help with understanding side aspect stealth a little better.

Image

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.

Unread postPosted: 31 Jul 2013, 16:24
by SpudmanWP
Dear Lord....

Are those simplistic shapes on the bottom of the image what was used for the RCS measurement?

Unread postPosted: 31 Jul 2013, 19:14
by sferrin
SpudmanWP wrote:Dear Lord....

Are those simplistic shapes on the bottom of the image what was used for the RCS measurement?


Well it is Carlo Kopp we're talking about. :lol:

Unread postPosted: 31 Jul 2013, 20:05
by SpudmanWP
Is it just me, or does it look like Carlo has a boob fetish (lowest series of three images, especially the center one)?

;)

Unread postPosted: 31 Jul 2013, 22:50
by munny
SpudmanWP wrote:Dear Lord....

Are those simplistic shapes on the bottom of the image what was used for the RCS measurement?


No they are mine in the absence of model design ability. Kopp has a report on the PAK FA on his web site which pretty much shows the same results but they used a proffessional built T-50 model.

The angles of the surface were taken from numerous reference images. The shapes give an idea of where the main specular reflections are going to be.

....and what's wrong with B(o)(o)bies?

Unread postPosted: 01 Aug 2013, 19:33
by sprstdlyscottsmn
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.

Unread postPosted: 02 Aug 2013, 12:21
by munny
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.

Image

Unread postPosted: 02 Aug 2013, 13:55
by sprstdlyscottsmn
Oh of course it does, not being seen is the best defense.

Unread postPosted: 09 Nov 2013, 11:34
by rafale12345
munny wrote:Perhaps these can help with understanding side aspect stealth a little better.

Image
:


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 ? :?

Re:

Unread postPosted: 26 Apr 2014, 13:15
by taog
munny wrote:Perhaps these can help with understanding side aspect stealth a little better.

Image

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?