"Saw Tooth" leading edge
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"Saw Tooth" leading edge
G’day All,
Just doing a little aerodynamics review and came across a reference to a “saw tooth leading edge”, used to prevent the inboard movement of a vortex on a swept wing. Could someone enlighten me on how it works, and what it looks like? What aircraft have used this design feature?
Thanks in advance,
SW
Just doing a little aerodynamics review and came across a reference to a “saw tooth leading edge”, used to prevent the inboard movement of a vortex on a swept wing. Could someone enlighten me on how it works, and what it looks like? What aircraft have used this design feature?
Thanks in advance,
SW
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The Phantom is fitted with a saw tooth leading edge,the notch in the leading edge stops span-wards flow of air along the leading edge at high airspeeds to reduce tip losses and vortices.
Have a look at the pic`s on the following link;
http://www.airliners.net/search/photo.search
Regards DDG
Have a look at the pic`s on the following link;
http://www.airliners.net/search/photo.search
Regards DDG
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One of the first fighter aircraft to use sawtooth was the Swift circa 50s.
Hunter and Swift suffered pitch up when pulling G sonic/supersonic.. My first experience was in a Hunter. Stick hard forward and still pitching to about 4 G was not pleasing.
Swift suffered worse than Hunter and lost reputation too late to be revived with modified saw tooth wing.
Flew a sawtooth Swift and did not encounter pitch up, but didn't try for it either.
Hunter and Swift suffered pitch up when pulling G sonic/supersonic.. My first experience was in a Hunter. Stick hard forward and still pitching to about 4 G was not pleasing.
Swift suffered worse than Hunter and lost reputation too late to be revived with modified saw tooth wing.
Flew a sawtooth Swift and did not encounter pitch up, but didn't try for it either.
It works by inducing a vortex behind it. The vortex acts similarly to a structural fence (an aerodynamic fence, if you like), inhibiting the spanwise flow tendency of the airstream.
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the saw tooth leading edge is one of the devices designers could employe to prevent spanwise flow and or separation on airfoils. Typically this could occur with A/C with high sweep angles. The Avro Arrow utilised leading edge notches for this reason,
D.
D.
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Great, thanks everyone.
The F4 and Hunter pics were just what I needed, I was unsure as to whether there was one notch or a series of notches.
However, I’m still a bit confused, is it a low speed or a high speed design feature, or both? I thought that the increased span-wise flow on a swept wing encouraged a larger vortex at the tip, as such creating a large increase in induced drag (a low speed problem). Reducing the span wise flow would therefore reduce the induced drag.
Or does the vortex created by the tooth flow over the top of the wing energizing the boundary layer (like a vortex generator) and as such delay boundary layer separation that occurs in the transonic region?
I guess it makes sense that it does both, does it? Or have I got it all wrong?
SW
The F4 and Hunter pics were just what I needed, I was unsure as to whether there was one notch or a series of notches. However, I’m still a bit confused, is it a low speed or a high speed design feature, or both? I thought that the increased span-wise flow on a swept wing encouraged a larger vortex at the tip, as such creating a large increase in induced drag (a low speed problem). Reducing the span wise flow would therefore reduce the induced drag.
Or does the vortex created by the tooth flow over the top of the wing energizing the boundary layer (like a vortex generator) and as such delay boundary layer separation that occurs in the transonic region?
I guess it makes sense that it does both, does it? Or have I got it all wrong?
SW
It works at high AoA, not speed.
Hence pulling 'g' in an early Hunter, the inboard movement of the Centre of Pressure caused the a/c to pitch up. The saw tooth wing effectively stopped it; the later Mk 4s (I think?) had the wing modded - and the big engined Mk 6s all had the new wing with the notch and certainly had no pitch up vices! Set full power, pull to the buffet, then milk the flaps to 23 deg to increase turn rate.....
Hence pulling 'g' in an early Hunter, the inboard movement of the Centre of Pressure caused the a/c to pitch up. The saw tooth wing effectively stopped it; the later Mk 4s (I think?) had the wing modded - and the big engined Mk 6s all had the new wing with the notch and certainly had no pitch up vices! Set full power, pull to the buffet, then milk the flaps to 23 deg to increase turn rate.....
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I have been pondering this since last week. on swept wings and maybe taper wings the airflow is from the root toward the tip, hence the fences and other devices. What then of the Hansa with the swept forward wing. It also had wing fenced as I remember. It liked to dutch roll in cruise also.
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I know they lost HFB-320 No.1 in a deep stall due to the T tail I was told. The folks that flew them here in Fort Lauderdale said they had very nice slowflight characteristics. Back then I didn't get to fly but I went on 10 or so training flights when the company I worked for sold them. American Hansajet Industries was based at Walkers Cay Air Terminal.
Put simply, (I can do 'simply') a swept wing generates pretty big vortices. Two small ones give less drag than one big one. A notch or sawtooth starts another vortex from it's position on the wing, and cancelles out the vortex that starts from the root. A fence has the same effect, but generates more drag. As BEagle mentioned, a slow speed thing.
