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I've been experimenting with 3D printed fins using symmetrical airfoils. Something other than flat plate materials for fins.
The NACA/Munk M-1 airfoil is fairly effective for subsonic flight.
This kind of airfoil is great for subsonic flight, where air stays in laminaar flow along the surface of the fin, and reduces turbulence and therefore drag. It's has about a 6% thickness to length at a 30% chord, and makes a fairly strong fin. It also lets your rocket go higher (less drag). I've flown this kind of airfoil with success, printed from my 3D printer and reinforced with a layer of fiberglass.
While doing some research on supersonic profiles, I realized that laminar flow airfoils don't work because they produce a big shock wave at the leading edge. Current wisdom seems to prefer sharp knife edge leading and trailing edges. The double wedge airfoil used with the NIKE sounding rocket is an example, but many rocketeers use a trapezoidal cross section, sharp at the leading and trailing edges, flat in the middle. The other cross section used in supersonic research is the symmetric circular arc airfoil, which also has sharp leading and trailing edges. The idea is to reduce primary shock waves at the leading edge, and reduce the influence of secondary shock waves.
The symmetric circular arc airfoil got me thinking. What other shape do we use made from intersecting circular arcs? An Ogive nose cone!
An ogive nose cone isn't the most efficient shape for supersonic flight, but there are a number of other choices, like the Von Karman nose cone based on research in fluid mechanics. While different nose cones have advantages and disadvantages, the Von Karman profile is a good all-rounder, efficient at subsonic and upper supersonic speeds, somewhat less at transsonic speeds. You can see where this is going, huh?
Why not make a long thin supersonic fin with a Von Karman profile at front and back, like a Von Karman nose cone glued to a Von Karman tail cone, but then very long and thin? That might be pretty efficient.
Research on supersonic airplanes in the 70's seems to point to an optimal thickness of the airfoil between 4% and 6% of the length. Higher speeds favor the thinner airfoils at speeds higher than Mach2, so it'll be 4%.
So, are my hunches right? Feedback is welcome.
The NACA/Munk M-1 airfoil is fairly effective for subsonic flight.
This kind of airfoil is great for subsonic flight, where air stays in laminaar flow along the surface of the fin, and reduces turbulence and therefore drag. It's has about a 6% thickness to length at a 30% chord, and makes a fairly strong fin. It also lets your rocket go higher (less drag). I've flown this kind of airfoil with success, printed from my 3D printer and reinforced with a layer of fiberglass.
While doing some research on supersonic profiles, I realized that laminar flow airfoils don't work because they produce a big shock wave at the leading edge. Current wisdom seems to prefer sharp knife edge leading and trailing edges. The double wedge airfoil used with the NIKE sounding rocket is an example, but many rocketeers use a trapezoidal cross section, sharp at the leading and trailing edges, flat in the middle. The other cross section used in supersonic research is the symmetric circular arc airfoil, which also has sharp leading and trailing edges. The idea is to reduce primary shock waves at the leading edge, and reduce the influence of secondary shock waves.
The symmetric circular arc airfoil got me thinking. What other shape do we use made from intersecting circular arcs? An Ogive nose cone!
An ogive nose cone isn't the most efficient shape for supersonic flight, but there are a number of other choices, like the Von Karman nose cone based on research in fluid mechanics. While different nose cones have advantages and disadvantages, the Von Karman profile is a good all-rounder, efficient at subsonic and upper supersonic speeds, somewhat less at transsonic speeds. You can see where this is going, huh?
Why not make a long thin supersonic fin with a Von Karman profile at front and back, like a Von Karman nose cone glued to a Von Karman tail cone, but then very long and thin? That might be pretty efficient.
Research on supersonic airplanes in the 70's seems to point to an optimal thickness of the airfoil between 4% and 6% of the length. Higher speeds favor the thinner airfoils at speeds higher than Mach2, so it'll be 4%.
So, are my hunches right? Feedback is welcome.