Scimitar shaped planforms
Thread Starter
Joined: Oct 2007
Posts: 2,515
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From: A better place.
Scimitar shaped planforms
I note that scimitar shaped (curving) propeller blades are found on both aircraft and submarines - due I assume to benefits in reducing turbulence and cavitation respectively.
Why have scimitar shaped aircraft planforms not been developed?
By this I mean aircraft that when viewed from above, have a curved leading edge terminating in a sharp tip, and a trailing edge that curves inwards to mirror the leading edge.
Ie, from above they would look like a crescent moon.
The Spitfire had an elipitical planform, but I know of no aircraft with scimitar shaped wings.
And the intial design for the 787 had a scimitar shaped tail.
Manufacturing difficulties aside - would any aerodynamic advantage be conferrred, or conversely any major difficulties created?
I suspect since it hasn't been done - it's not a good idea....
Why have scimitar shaped aircraft planforms not been developed?
By this I mean aircraft that when viewed from above, have a curved leading edge terminating in a sharp tip, and a trailing edge that curves inwards to mirror the leading edge.
Ie, from above they would look like a crescent moon.
The Spitfire had an elipitical planform, but I know of no aircraft with scimitar shaped wings.
And the intial design for the 787 had a scimitar shaped tail.
Manufacturing difficulties aside - would any aerodynamic advantage be conferrred, or conversely any major difficulties created?
I suspect since it hasn't been done - it's not a good idea....
Joined: Oct 2002
Posts: 372
Likes: 7
From: Surrey
Off the top of my head, a scimitar-shaped wing might impose a high torsion load on the attachment to the fuselage, in addition to the usual bending load. Thus the wing box would have to be heavier, and the extra weight might undo any advantages that the planform itself contributed.
Also, it is significant that scimitar-shapes are hitherto found on rotating components, the fluid speed over which varies with distance from the hub. LM has got it right. This doesn't apply of course to a wing.
Also, it is significant that scimitar-shapes are hitherto found on rotating components, the fluid speed over which varies with distance from the hub. LM has got it right. This doesn't apply of course to a wing.
Joined: May 2000
Posts: 3,204
Likes: 2
From: Seattle
Wings have a relatively constant velocity profile across the span. Propellers have a significant velocity change profile from root to tip. That means a "low" speed airfoil chord near the root, transitioning to a "high" speed chord at the tip will be advantageous in distributing the load across the blade span.
Joined: May 2000
Posts: 3,204
Likes: 2
From: Seattle
The key word is "relatively"... I did NOT say or mean to imply that local airflow across a wing is constant-speed.
Every chord section of a wing is moving through the air at the same speed when in stable flight, since it is in linear motion.
Outer chord sections of a propeller are always moving at significantly higher velocities through the air than the root sections, due to the propeller's rotational motion. In fact, tip speed is a limiting factor in propeller design.
Every chord section of a wing is moving through the air at the same speed when in stable flight, since it is in linear motion.
Outer chord sections of a propeller are always moving at significantly higher velocities through the air than the root sections, due to the propeller's rotational motion. In fact, tip speed is a limiting factor in propeller design.
