Why do jets have swept wings?

[OverTemp]

	Quote:
	Wow... don't me out to be such a bad guy... If you have a 50 foot long wing, and turn it back 45 degree angle, you have a 50 foot wing and X number of frontal area. You have increaced the cord, and hidden some frontal drag. Now... that does not mean I believe that to be the case here.... but please don't be so harsh. Well put OverTemp.

Thanks man.

In modern designs 22.5 degrees seems to be the optimum sweep to maximize critical mach number and minimize the adverse effects. I'm talking mainly about subsonic aircraft here. Fighters and other supersonic aircraft have a completely different set of problems to deal with.

teryn is right... aero is often counter-intuitive. For example... you can't make a wing shorter to minimize drag. Drag is actually lowest on a long slender wing (called high aspect ratio... like a glider). A short stubby wing with the same surface area as a long slender wing will produce more drag and less lift. This is true up to certain transonic speeds... then you once again get into compromises...

Airliners have all sorts of features on them (shape of wing, turbulators, strakes, etc) that increase drag at lower airspeeds. At design cruise speed, however, they greatly reduce drag due to the compressibility and sonic effects desbribed in the pages posted by Tommy321.

[KrisW]

Actually, swept wings do a number of things. . . .

They look REALLY cool ! !

They make the plane look like it's doing 1000 knots when it's sitting still

You can make a paper airplane with swept wing, it's really easy to do

Dragons have swept wings, so the design is proven aerodynamically.

You can park the planes next to eachother, facing opposite directions, and have a lot more of them in the same length of runway.

They sweep them so that the pilot does not have to see them when he looks out the canopy.

Actually, sweeping wings is a bad idea, you should use the proper cleaning solvent, and then wax them with Simonize.

However, a swept wing IS devoid of most snow, making it easier to fly in the Winter.

Now. . as for Myth busters: Drag. .

The F-104 Starfighter was a Mach-2 aircraft with a LE on the wing that was straighter than the wing on a P-51. It was also only 3" thick at it's thickest point, and had a razor sharp LE. . so much for drag reduction due to sweep. The Bell X-1 also had a straight wing.

Actually, the reason wings are swept is because along the LE the pressure buildup as you approach Mach is extremely high in the transonic speed range. By sweeping the LE of the wing, the onset of Mach pressure increase is delayed, and the actual airflow is "split" going both over the wing along it's chord, and traveling down the wing's sweep angle, helping to reduce overall drag and prevent pressure puildup along the LE area. It does not effectively shorten the wing panels overall length, though it does reduce span, so it's the angular and airfoil changes attached to the swept wing design that affect the best drag reduction and prevention of pressure buildup. Refer to Reynolds numbers, airflow charts, Guru Maharaji Jai's inflection of pseudo dynamic humanism, Newtons laws, Einsteins relativity theories, and other technical stuff for exactly how this occurs.

I'd start a discussion on "Swing Wings" but the Gay Rights community and all the Swingers organizations out there might get angry. Also, all the kiddies on the playground would get confused. . .

[Propstriker]

You also have to remember, aerodynamics change going from subsonic, transonic to supersonic.

Bernoulis Principle works well when a wing is Subsonic, these aerodynamics are pretty straight foward and easy to understand. Bernoulis Principle creates major problems the faster we go....

A Straight wing Can't go Transonic due to the shock wave and Wave Drag that will be created by the leading edge, Therefore, loss of efficency. It was found that sweeping a wing, results in airflow traveling a greater distance from leading edge to trailing edge, and thus the air pressure is distributed over a greater distance. In other words, As the speed increases toward transonic, aft sweep is required to have a subsonic leading edge.

At Supersonic Speeds, aerodynamics change again, and create shockwaves that have to be controled by the shape of the leading edge, thickness, sweep of the wing and shape of the fuselage. The placement of the shockwave has to be controled, and the airflow after the shockwave is actually traveling at subsonic speeds to create lift. As Overtemp points out, the airfoil and aircraft shape can cause problems, He calls it local sonic flow....I believe the term is compressability, which is the effect that acts on the wing as it approaches and passes through the speed of sound and the airflow over the top of the wing is allowed to go supersonic.


Keith, are'nt you glad you asked the question?, there really is no "Simple" answer due to the complex changes in aerodynamics for a given speed. And yes, every configuration is a compromise...thats why slats, flaps, slots, vortex generators, and swing wings are used, the plane can go fast as hell, but slow it down and the wing wont produce lift at landing speeds.

[Roll'nCircles]

Wow, suddenly everyone is an aerodynamicist. Send Burt Rutan and email, will ya?

No need to write a book or quote college text books.

Why swept wings you ask?

The straight forward answer over a dinner table conversation is that the wings are swept so that they do not come in contact the shockwave coming off the nose as an aircraft as it approaches and passes through the speed of sound. If the shock wave (that looks more like a cone) were to meet the wing (or the vertical stab), the wing would experience aerodynamic loads that would eventually rip it off. This basic principal was discovered at Muroc Air Base (now Edwards AFB) following WWII.

lets not make a mountain out of a mole hill, fellas.

[Propstriker]

The straight foward answer at Dinner would be in direct proportion to the amount of drinks served!

Find that in a textbook

[KrisW]

	Quote: Originally Posted by Propstriker
	The straight foward answer at Dinner would be in direct proportion to the amount of drinks served! Find that in a textbook

You mean there's other stuff besides drinks at a dinner??? Absolutely amazing.

Why didn't the F-104 have swept wings then. Huh??? Cmon mr. dinner host. .I wanna know ! ! !

[Roll'nCircles]

Good observation! The Starfighter would not benefit from swept wings, the designer knew this (Kelly Johnson). The nose of the 104 is far enough out in front of the wing so that the shockwave coming off the nose at mach 2+ would not come near the wingtips (small straight wings that are far behind the nose)

So, there is no reason to sweep the wings on this design to keep them from flying through the shockwave - the shockwave that is coming off the nose of the aircraft.

As the aircraft flys faster and faster through Mach 1, the angle of the cone decreases bringing the shockwave closer to the aircraft structure - aka the wing.

hope that helps

Ever heard a 104 in flight? Its the most awesome sound ever!

[Propstriker]

Missile with a man in it

[ilovemetro]

	Quote: Originally Posted by GremlinX
	Thats what I said last night, had to be frontal area... Thanks.

I take it you watched the thing with alexsander yakovlev and army stuff

[KrisW]

	Quote: Originally Posted by Roll'nCircles
	Good observation! The Starfighter would not benefit from swept wings, the designer knew this (Kelly Johnson). The nose of the 104 is far enough out in front of the wing so that the shockwave coming off the nose at mach 2+ would not come near the wingtips (small straight wings that are far behind the nose) So, there is no reason to sweep the wings on this design to keep them from flying through the shockwave - the shockwave that is coming off the nose of the aircraft. As the aircraft flys faster and faster through Mach 1, the angle of the cone decreases bringing the shockwave closer to the aircraft structure - aka the wing. hope that helps Ever heard a 104 in flight? Its the most awesome sound ever!

Actually the 104 does have swept wings, though only slightly.

Just busting your chops, Roll'n. . good explanation.

[Toro]

"man in a missle" one of my favs... still be-wilders me on HOW DO IT FLY ?

Reminds me of many of my early models... Big motor little wings, go fast.

[GremlinX]

Wow, this thread has gone crazy...