Supersonic Airfoils in Subsonic Flight

Supersonic Airfoils in Subsonic Flight

Supersonic Airfoils in Subsonic Flight

Many issues surround supersonic flight. Counter-intuitive aerodynamics, airframe issues, fuel burn, engines, the list goes on and on. Perhaps a lesser-known problem, but still one to recognize is the shape of supersonic airfoils and what they mean for subsonic, and even slow flight. Sleek as they may be, they pose incredible problems for pilot wanting to land their airplanes: an activity widely regarded as important to flight.

A discussion on how to make an airplane's wings is important in seeing the larger issues and understanding the solution. In many airplanes, especially sport aircraft, a wing with a large surface area and large camber increases the 'upward' lifting force due to the increased speed the fluid (air) needs to travel. Air pressure is in direct proportion to the speed at which that fluid is traveling. The faster the air travels over the top portion of the wing versus the lower surface the more lift is created. Thus, in order to increase lift, even at slower speeds, some wing patterns can be modified. Airplanes today lack the ability to increase the wing camber once manufactured. Wing area can be modified by use of certain types of flaps. Slower aircraft can afford this extra lift but supersonic airplanes cannot enjoy the luxury of increased camber and often have stall-inducing sharp leading edges.

The reason supersonic aircraft have sharp edges is to decrease drag caused by the compression of the air ahead of it. A blunt surface increases this drag and so a compromise is needed. Supersonic aircraft have sharp edges to minimize this drag; however, doing so makes stalling the aircraft more abrupt as the air is disturbed more readily. Because no known practical way exists to morph the leading edge to smooth, nor to morph the camber to positive on the upper surface, such development has not taken off. Supersonic aircraft cannot fly slow because supersonic capabilities are not practical in slower flight.

Slower flight for supersonic aircraft is desirable for a number of reasons. At many busy airports aircraft speed limits are imposed to increase safety and to reduce noise. Slower approaches also allow for shorter landing distances and also allow for pilots to scan for hazardous obstacles in front of them. Slower speeds also allow for steeper descents and add another aspect to landing area scans. At any rate, flying slowly at take offs and landings is desirable for aircraft due to increased safety and better performance. Supersonic flight cannot fly slow because it is too easy to get into a stall that might be hard to recover from due to their sharp leading edges and their minuscule camber. It is for this reason supersonic aircraft have fast approach speeds.

Morphing an Airfoil

For most people the idea of creating a wing that changes camber and thus increasing lift seems absurd; however, such a wing design is not out-of-the-question with today's advances in composite engineering. Composite materials today show incredible flexion without compromising structural integrity. Using such materials strategically would allow for aircraft maneuverability not seen until the near future. So how would it be possible to make a wing that morphs in whilst in flight? The idea stems from a technology already in place. Pneumatics.

Current deicing 'boots' use compressed air to increase the surface area on the leading edge of wings. Air is diverted from the compression stage of the power plant and diverted into the wings. Such capability in essence increases the surface area of the wing; however, it is minuscule. An interesting proposal would be to overhaul the pneumatics and divert the air into bladders that are located at the center of pressure on an airplane. By using compressed air from super-sonic engines (at subsonic speeds) and diverting them in to these bladders, the airfoil, increases surface area, camber, and ultimately, lift. The same ability could be diverted to the leading edges to 'dull' the leading edge, decreasing stall speed.

Conclusion

Supersonic aircraft have an inherent issue of high stall speeds and inability to fly slowly. Up until now it has been the opinion and educated guess of aerodynamicits that morphing an airfoil is impossible. Using pneumatic pressure in the same way deicing methods are currently used would make such capabilities possible and even desirable. The application could be implemented in many other aspects of aviation; increasing safety, increasing capabilities, and showcasing innovation.

Supersonic Airfoil

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Comments 2 comments

dallas93444 profile image

dallas93444 6 years ago from Bakersfield, CA

Basic question: Given a plane is apparently sucked up, why is there pressure underneath the wing pushing down? Example, when landing the plane adjust to the "cushion."


Gabrieel 21 months ago

glad you like the music:-) You can find more releases in the dischgrapoy section (and they all should be on discogs.com) New albums are coming end of the year and early next year. I look forward to your mix!

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