Is an stealthaircraft with round wing edge possible?

[malipa]

And would it give aerodynamic advantage.

 

[Avimimus]

I wonder what the stealh properties of a fully elliptical wing would be like?

 

[overscan (PaulMM)]

Pretty poor, and its pretty obvious why.


A round edge will return energy in a wide range of directions. Therefore a rounded wing is incompatible with VLO stealth, which aims to concentrate all reflections into a very small number (typically 4-8) of spikes.


"Rounded" planform stealth could potentially give reduced RCS in all directions, but not the dramatic "4 orders of magnitude" reduction needed for true VLO.

 

[bipa]

Actually I think this is a very very good question (the first one).
Of course Overscan's explanation is valid, although it related more to the second question (Avimimus).
However, playing with wave diffraction can pretty much lead to such unexpected solutions.
Sometimes, certain pictures make me wonder whether some (Northrop) engineers could be playing this game more seriously than others:
http://www.secretprojects.co.uk/forum/index.php/topic,2563.msg92587.html#msg92587
(or maybe this is just too far fetched)

 

[Kryptid]

The Lockheed A-12 Blackbird had such a wing tip design, and is often considered to have a low RCS (not as low as a modern stealth aircraft, however). Dan Raymer's aircraft design book quotes its RCS at 0.014 square meters. I imagine this is from head-on in some X-band frequency. A rounded wing tip can probably be used consistently with what qualifies as a VLO RCS from head-on. However, this will result in RCS penalties from other angles (as explained before by Overscan). There are aerodynamic benefits for curved wing tips, but the overall RCS benefits from an angular wing tip apparently outweigh those of its curvy cousin. The current design trend proves that.

 

[chuck4]

How about a two layer wing consisting of an external aerodynamic rounded airfoil shell made up of dielectric radome material, enclosing and supported by an internal, radar reflecting structure shaped for VLO characteristics?

This way much of the radar emission will pass through the aerodynamic, but unstealthy, shape, and any reflection will be controlled by an non-aerodyanmic, but stealthy, support structure underneath.

 

[malipa]

Thats a genius solution if the improvement of aerodynamics efficiency is sufficient, i dont know how much it would improve aerodynamic preformence.

 

[Mike Pryce]

Lockheed have tried a rounded leading edge on a VLO design, Dark Star:

http://upload.wikimedia.org/wikipedia/commons/thumb/4/46/DarkStar_Tier_III.jpg/300px-DarkStar_Tier_III.jpg

 

[quellish]

How about a two layer wing consisting of an external aerodynamic rounded airfoil shell made up of dielectric radome material, enclosing and supported by an internal, radar reflecting structure shaped for VLO characteristics?

This way much of the radar emission will pass through the aerodynamic, but unstealthy, shape, and any reflection will be controlled by an non-aerodyanmic, but stealthy, support structure underneath.

http://www.google.com/patents?id=d3UjAAAAEBAJ&pg=PA4&source=gbs_selected_pages&cad=4#v=onepage&q&f=false

Getting the impedance of the outer structure correct is a bit of a challenge.

 

[bipa]

http://www.google.com/patents?id=d3UjAAAAEBAJ&pg=PA4&source=gbs_selected_pages&cad=4#v=onepage&q&f=false

Strange... Last time I saw this patent, it was filed in 1963...
This is the holy grail of stealth engineering, just like designing a perfect aerodynamically "transparent" grating that's completely opaque to radar waves.

 

[quellish]

Strange... Last time I saw this patent, it was filed in 1963...

"This patent application is a divisional application of U.S. parent application Ser. No. 295,644 filed on Jul. 17, 1963, now U.S. Pat. No. 4,924,228."

This is the holy grail of stealth engineering, just like designing a perfect aerodynamically "transparent" grating that's completely opaque to radar waves.

It's (very) difficult to do if you want a big reduction or a reduction across a wide range of frequencies, but not impossible if your needs are outside that. There are emerging materials and techniques that make this closer to practical.

Darkstar's signature was not optimized for the frontal aspect, which is why the airfoil is shaped the way it is.

 

[sferrin]

Watch the perfect stealth aircraft end up being a flying saucer and equipped with EMP weapons. The kind that make your car stop running before you get beamed up for a probe.

 

[malipa]

MWCNFRP? Multiwalledcarbonnanotubefibereinforcedplastics?

 

[Stargazer]

Forgive if I'm wrong, but I'm under the impression that the topic's title has led to some confusion. Some understand "round wing edge" as the shape of the wing section (which obviously IS round on most aircraft), others discuss the shape of the forward fuselage (as with the Lockheed RQ-3A) while I think the question pertained more to the shape of the wing tips, according to the image posted in the first post.

Rounded wing tips have certainly been associated with quite a few stealth concepts. Allow me to remind you of a handful of them (I have selected only designs which have been acknowledged as real industry projects):

• The McDonnell Model 226 QAA (Quiet Attack Aircraft) of 1973.
• The so-called "Marshmallow" pre-ATF design.
• The Northrop/Loral "F-19" proposal (the so-called "Specter").
• The Northrop THAP from circa 1981, an allegedly built and flown sub-scale demonstrator that predated the B-2 and TACIT BLUE.

This being said, the fact that these rounded wing shapes can be found only in early stealth programs could indicate that the result on stealthiness may not have been as satisfying as planned.

 

[quellish]

Forgive if I'm wrong, but I'm under the impression that the topic's title has led to some confusion. Some understand "round wing edge" as the shape of the wing section (which obviously IS round on most aircraft), others discuss the shape of the forward fuselage (as with the Lockheed RQ-3A) while I think the question pertained more to the shape of the wing tips, according to the image posted in the first post.

Rounded wing tips have certainly been associated with quite a few stealth concepts. Allow me to remind you of a handful of them (I have selected only designs which have been acknowledged as real industry projects):

• The McDonnell Model 226 QAA (Quiet Attack Aircraft) of 1973.
• The so-called "Marshmallow" pre-ATF design.
• The Northrop/Loral "F-19" proposal (the so-called "Specter").
• The Northrop THAP from circa 1981, an allegedly built and flown sub-scale demonstrator that predated the B-2 and TACIT BLUE.

This being said, the fact that these rounded wing shapes can be found only in early stealth programs could indicate that the result on stealthiness may not have been as satisfying as planned.

From "RF STEALTH (OR LOW OBSERVABLE) AND COUNTER- RF STEALTH TECHNOLOGIES: IMPLICATIONS OF COUNTER- RF STEALTH SOLUTIONS FOR TURKISH AIR FORCE":

"The design included hidden inlets and a blended shape which avoided all vertical surfaces and contained no straight, leading, or trailing edges. However, the edge returns resulted in a contradiction. Entire curved platform edges produced a flare spot, which resulted in a relatively strong diffracted return from part of the edge, perpendicular to the line-of-sight [13] at nearly every viewing aspect."

This is in reference to the Model 226, but sums up some of the problems with rounding the edges of VLO aircraft well.

 

[overscan (PaulMM)]

THAP (a design of still unknown origin, published in an USAF Aeronautical Systems Division report) and QAA are real projects but more reduced RCS than stealthy using a basic understanding of RCS reduction techniques.


"F-19" and Marshmallow are both totally fictitious so not the best support to your argument :


Marshmallow was designed as a "cover design" for the A-12 trangle configuration, and hence was as unlike that aircraft as possible to avoid betraying its secrets. Its roundedness comformed to the public expectation of stealth, not the reality.

 

[Stargazer]

Thanks quellish and PaulMM for the great input!