The Struggle to Achieve Laminar Air Flow

Interesting explanation.

Great artificial.

Parasitic drag, also known as profile drag is one of the challenges the SR71 had to deal with with the heat created by it.

I recall an the development 30-40 years ago of having a perforated skin on the wings to help induce? Laminar flow. I just google it, and found it. And it does have its drawbacks.

I worked at a shipyard where we had majority of Naval contracts. We did a Special Operations Craft for the Navy Seals. And hired a UK company (Cougar Limited) to develop the design, it was one of the most interesting on the design, sharp corners such as the trailing edge of a chine is preferred. And the naval architects would use turbulent flow for control.

It seems to me that getting the greatest lift from the wing, and the least turbulence, are two goals that are diametrically opposed...It's an interesting problem that seems like it could be achieved with just a little tweak of the shape of the wing....

This is difficult, I’ve felt that the boundary layer between turbulent and laminar flow. I’ve felt that controlling that is the issue, when it starts breaking down, from laminar flow to turbulent, it tends to propagate. But that’s my opinion.

What if the wing could change shape during flight....? This way you could tune the wing for the speed, balance the lift and drag....

https://www.mdpi.com/2226-4310/6/10/109/htm

No, I mean the profile of the body of the wing, and the rigidity and flexibility of the skin...

..."The shape of an aircraft’s wings will affect its performance. Wing shapes are often defined by their aspect ratio - the length of the wingspan divided by the mean of its chord (the distance between the leading and trailing edge). Different aspect ratios will affect the amount of light-induced drag that a wing will create. Wings with lower aspect ratios will have more induced drag than those with high aspect ratios. An increase in wing aspect ratio would result in an increase in both range and endurance. Aircraft with large wingspans have good range and fuel efficiency but are slower and less maneuverable. Aircraft with low-aspect ratio wings are faster and more maneuverable but have poor aerodynamic efficiency.

Aircraft designers have therefore varied the shape of an aircraft and its wings depending on their intended use – for example, slow-flying gliders have long thin wings while fighter aircraft have short tapered wings for fast flight. The result is an aircraft shape which can fly close to its optimum in certain flight conditions but at sub-optimal performance for other conditions.

In addition, aircraft also have to be able to take-off, land and maneuver and so the designs have incorporated moveable control surfaces in the rudder and wings, as well as flaps or slats to change the geometry of the wings."....

https://www.aerosociety.com/news/shape-shifters/

https://me.engin.umich.edu/news-events/news/nasa-tests-shape-changing-aircraft-wing/

..."A team of engineers has built and tested a radically new kind of airplane wing, assembled from hundreds of tiny identical pieces. The wing can change shape to control the plane’s flight, and could provide a significant boost in aircraft production, flight, and maintenance efficiency, the researchers say."...

https://news.mit.edu/2019/engineers-demonstrate-lighter-flexible-airplane-wing-0401#:~:text=A%20team%20of%20engineers%20has,maintenance%20efficiency%2C%20the%20researchers%20say.

Actually, aspect ratio is not the key to reducing induced drag. Span loading is.

To prove this, imagine two rectangular wings, both ten feet in span. One wing has a two-foot chord, giving it an aspect ratio of five. The other has a one-foot chord, giving it an aspect ratio of ten. Assume they both support the same weight. Plug the dimensions of the two wings into the induced drag equation. They will both have the same induced drag, regardless of the difference in aspect ratio. This is because they have the same span loading.

https://www.sciencedirect.com/topics/engineering/spanwise-loading

Though not my words, I knew this but just copied off the www.

the the effects of dimples on a golf ball.

’”Dimples on a golf ball create a thin turbulent boundary layer of air that clings to the ball's surface. This allows the smoothly flowing air to follow the ball's surface a little farther around the back side of the ball, thereby decreasing the size of the wake.’

Same goes with the low air pressure behind a semi trailer, or any box van.

Race car drivers do that also, called drafting.

https://www.ijedr.org/papers/IJEDR1803068.pdf

https://www.quora.com/Why-dont-plane-designers-put-golf-ball-dimples-on-aircrafts-to-increase-the-efficiency

https://journals.indexcopernicus.com/api/file/viewByFileId/154876.pdf

What about dimples on demand for a shape shifting option?

I wonder if sections of the wing could have hard or soft surface area controlled by electrical fields like MagneRide...

https://en.wikipedia.org/wiki/Magnetorheological_fluid

An excerpt…

” That’s a myth that the dimples reduce drag, they don’t, they actually increase drag. This is why you don’t see missiles, submarines, high speed trains or anything else use dimples.”

what about scales on a fish. I heard back in the 80’s that the Australians were working on the surface similar to that for their boat, to hold onto Americas Cup.

Really neat stuff.

Actually, aspect ratio is not the parameter that matters. You can prove this to yourself by imagining two wings of equal span and supporting the same weight, one with an aspect ratio of, say, 2, and the other with an aspect ratio of, say, 4.

Run the numbers, and you'll find that they both have the same induced drag, because they're span loading is the same. That span loading is what matters.

It's true, to get the most lift at a given airspeed requires a higher angle of attack, and thus turbulence. But if you're after efficiency, you need the least amount of energy generating turbulence, or the highest lift-to-drag ratio.

https://en.wikipedia.org/wiki/Lift-to-drag_ratio

The amount of lift required varies with air speed though, so at cruising speed we would want nearly total laminar flow...The weight to wing shape and surface area also critical...There are so many variables, and conditions are also changing all the time....add to that the availability of new materials being introduced, and the possibilities seem endless...

In the years prior to World War 2 Major DeSeversky experimented with the same propulsion technique. It was reported on at the time in the "populars."

OK now this is a little more like it.....

Has anyone seen Mike Patey's variable wing geometry design?

Yes, interesting design...seems to work as seen in his later video...good for slow efficient flight...job well done