All rockets get banged up in use, transport, and storage. However, air foiled three ply aircraft plywood holds up surprising well, and can even be transplanted to new rockets.Older rocket books and instructions will tell you to put airfoils on the leading and trailing edges of fins. I have some very old rockets done that way but they get banged up with launching, storage and travel. I think a square edge would also be somewhat fragile, at least the corners would be, and it would be hard to do and keep it uniform. A rounded edge is fairly easy to do and I think it the most resistant to damage that would make it look bad.
I don't know how much difference this makes to aerodynamics, probably not enough to matter unless you are going for altitude.
I'm not an aeronautical engineer but that statement just sounds dead wrong. A tapered leading and trailing edge and tapered outward edge would seem to be the best aerodynamically.Pretty sure rounding the trailing edge is worse aerodynamically than leaving it square. I would just do what you think looks best.
round LE and sharp TE is the lower drag option that is an approximation of an airfoil on a flat fin
sharp TE tend to get dinged up easily on landing
http://sargrocket.org/documents/Resources/Centuri/dm-1.pdf
View attachment 523110
depending on the kit and fin thickness, the aesthetics may look better with some flat edges. Cardstock or fiberboard fins don't really shape that well and are usually left with square edges.
Yup. Go print up a bunch of shrouds templates on Payload Bay and practice. It's not hard.Gotta learn how to make a boat tail...
It's just a transition pointed the "wrong" way, no?
Payloadbay.com is awesome!Yup. Go print up a bunch of shrouds templates on Payload Bay and practice. It's not hard.
If you want a curved boattail, like a on a V2, then that's usually a plastic ogive nose cone with the tip cut off.
Tapered is the best, yes. I wasn't comparing that, though.I'm not an aeronautical engineer but that statement just sounds dead wrong. A tapered leading and trailing edge and tapered outward edge would seem to be the best aerodynamically.
Cool pics! Where do I have to drive to in order to view this classic sounding rocket?I saw an Orion in a museum and it had pointy leading edges and square trailing edges. I was wondering if this aids in unguided stability by creating drag?
I try to make my fins look like airplane wings. Every fin is airfoiled.
If you are going fast enough the trailing edge will cavitate ( if square) and at a certain speed this will create LESS drag than trying to keep the water attached BUT will affect the load the rudder can take.
I think the rule of thumb is water doesn't like filling at more than 12 degrees hence all the work on NACA profiles.
I often intentionally airfoil my fins with a semi-symmetrical airfoil intentionally to induce v-e-r-y s-l-i-g-h-t spin for more strait-off-the-direction-of-the-launch-rod flights, it seems to work really nicely and it cancels out the almost unavoidable other un-noticed mis-alignments that can happen.How do you get all sides of the foil to be exactly the same? Do you have a jig?
If they are not the same, the rocket will have some roll.
I'm guessing that Orion is flying more than Mach 1, and to quote Tim Van Millican(sp?) at Apogee "Speed changes everything", and our Low Power rockets fly considerably slower than that. We're comfortably in the subsonic rounded leading edge, tapered trailing edge zone. Cool pictures! Thanks for posting that!I saw an Orion in a museum and it had pointy leading edges and square trailing edges. I was wondering if this aids in unguided stability by creating drag?
The sharp LE on that grate is lower drag when encountering buffalo on the tracks!View attachment 523202
Nice try with the leading/trailing edges, they just got it backwards.
I tried to find a better picture of the 1909 McKeen "Streamlined" self-propelled railcar which had a knife-edge front and a rounded backend.The sharp LE on that grate is lower drag when encountering buffalo on the tracks!
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