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

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.

I can see a strong family resemblance between the 2 jets.

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.

Regardless of whether the "bumpy" bottom adversely affects stealth, every source out there says the F-35 is less stealthy than the F-22.

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...

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.

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.

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.

Prinz got to it before me, Who says F-35 ISN'T Better!!!!!!!!!! You Might be surprised

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.

Prinz got to it before me, Who says F-35 ISN'T Better!!!!!!!!!! You Might be surprised

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.

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!

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.

Hello

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.

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

Double post, my fault.

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.