Swept wing design

UnAnswerd

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Seems like all the faster (jet) aircraft use a swept wing design. I know we could get heavily involved with disscusions of areodynamics, physics, etc....but is there any general answer???
 

9GClub

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UnAnswerd said:
Seems like all the faster (jet) aircraft use a swept wing design. I know we could get heavily involved with disscusions of areodynamics, physics, etc....but is there any general answer???

Answer to what? Your observation is correct. That's the most efficient design for aircraft that cruise in the high-subsonic regime.
 

labbats

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A straight wing design would create too much drag at the higher mach numbers jets fly at.
 

typhoonpilot

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The easy answer is that a swept wing gives you a higher critical mach number therefore allowing a faster cruise speed, usually somewhere between .76 and .86 Mach. With a straight wing you would be down at Citation speeds :eek: ( excluding the X of course )


TP
 
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GravityHater

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is it reduced frontal area that lowers the drag, or the actual sweep which allows the air to kind of roll off laterally?
 

typhoonpilot

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Easy answer:

When the wings are swept back the airflow is accelerated less as it flows over the wing. Only the component of the airflow perpendicular to the wing is actually accelerated at all. Therefore, a swept wing will have a proportionally higher critical mach number.

More complex answer:

Mcrit is the lowest mach number at which the airflow at any point on an aircraft becomes sonic (mach1). The speed of airflow at any point on an aircraft is the freestream speed plus whatever acceleration the aircraft has given to it. So Mcrit is mach 1 minus the greatest acceleration found at any point on the aircraft. If for example the greatest acceleration is mach 0.2 then Mcrit is 1 - 0.2 = 0.8. So if we can reduce this acceleration we will increase Mcrit.

The critical Mach number is not the absolute Mach number, it is the local Mach No, perpendicular to the leading edge of the wing. So, if you resolve the triangle of velocities, for the "ambient" Mach number to be that parallel with the wing centreline, then we get a lower apparent Mach number perpendicular to the wing leading edge. (It's a bit like calculating crosswind component). So, the greater the sweep, the lower the perpendicular Mach number for the same flightpath Mach number.


TP
 

furlough-boy

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typhoonpilot said:
Easy answer:

When the wings are swept back the airflow is accelerated less as it flows over the wing. Only the component of the airflow perpendicular to the wing is actually accelerated at all. Therefore, a swept wing will have a proportionally higher critical mach number.

More complex answer:

Mcrit is the lowest mach number at which the airflow at any point on an aircraft becomes sonic (mach1). The speed of airflow at any point on an aircraft is the freestream speed plus whatever acceleration the aircraft has given to it. So Mcrit is mach 1 minus the greatest acceleration found at any point on the aircraft. If for example the greatest acceleration is mach 0.2 then Mcrit is 1 - 0.2 = 0.8. So if we can reduce this acceleration we will increase Mcrit.

The critical Mach number is not the absolute Mach number, it is the local Mach No, perpendicular to the leading edge of the wing. So, if you resolve the triangle of velocities, for the "ambient" Mach number to be that parallel with the wing centreline, then we get a lower apparent Mach number perpendicular to the wing leading edge. (It's a bit like calculating crosswind component). So, the greater the sweep, the lower the perpendicular Mach number for the same flightpath Mach number.


TP

No disrespect intended, but is this what you Cathay guys talk about over beer and dinner? :)
 
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