Is it possible to use a symmetric diamond (double-wedge) airfoil instead of a cambered airfoil in missiles moving at subsonic speed?
double edge profiles are suitable for supersonic flows. you may increase drag in subsonic flows.
The sharp corners typical to double-wedge geometries tend to encourage separation in subsonic flows at low angles of attack. Subsonic aerofoils on the other hand, have smoother and more gradual curves, this decelerates flows in a gentler fashion, delaying separation.
Using a double-wedge aerofoil in subsonic flow will likely result in early stalls.
Thank you all to take your time to answer the query. Dear Krishnaraj, I had already read the article myself before you provided here, and it is a good text on the subject, thank you. I am using the double-wedge for rolling-airframe-missile (RAM) which is typically supersonic. the other question is how the double-wedge airfoil behaves in rolling motion?. Does it have a bad effect on the rolling motion of fuselage. I need a uniform constant roll-rate spinning motion.
Dear Bilal. Thanks. I should add it that the missile is assumed to have a constant speed probably near Mach=2 (the more the better). What is your idea if this is taken into account. please also comment that whether the airfoils must be placed with similar incidence as a drill bit (a section of that) to ease spinning motion and not to resist roll?
You misunderstood, pardon. I do not need spin stabilization or spin stop. The missile intensely rotates in launcher canister and then is released shot. Hence, there is a constant roll rate or spinning motion. The missile has a screw motion as it moves in the atmosphere. I need to sustain this spinning motion or to keep missile screwing. I want to know how I should attach the fins not to confine rolling motion of the missile. The missile should screw or revolve or rotate as it moves and the fins should not be an obstacle for free spinning.
Subsonic flows don't like at all sharp edges...In the case of the symmetric diamond airfoil (which is suitable for supersonic flows), there will be :
- at zero angle of attack : separation will occur at the upper and lower wedges, which is not very sympathic for a drag point of view...
- if the airfoi is at some angle of attack, there will also be separation at the leading edge.
However, it is clear that before reaching supersonic speeds, the body will fly in subsonic...and it flies...although performances are not ideal.
Yes, but should have blunt edges, also instead of diamond one can opt for sweep back.
Thank you Mr. Quraishi. Please also let me know if there is any text on a suitable selection of sweep angle? What is the qualitative role of sweep angle?
You can kindly refer the books on "Wing Theory" by
1) R.T.Jones &
2) Abbot & Doenhoff.
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