re post 27:
Why worry about rail guides when the fins are squared off?
Who cares about the fins being squatted off when your rail guides are square?
re post 27:
Why worry about rail guides when the fins are squared off?
Yes, but that is really not material to the discussion of rail guides.If you want to fly low, use a smaller motor.
I have a sign that I print off thing verse that is similar.I don't know if you would call them unique, but I use the ACME rail guides on just about everything that is bigger than low power. I do modify them a bit though.
I like them for a number of reasons, not all of them practical. For one, I think they have a nice "scale" look that makes them look like something that should be on the side of a sounding rocket or missile. They also are very easy to install, not requiring any mounting blocks or hardware inside the tube, and since I cut each one in half, a package of two will outfit two rockets.
To mount them I Dremel a crosshatch pattern in the mounting surface and drill two holes down between the lugs and through the tube. The tube gets heavily scuffed and the guides glued on with JB Weld classic (Not the quick). The holes in the guide and tube allow the JB to squish through and form a chemical rivet.
4" (very) semi-scale Spartan missile. You can sorta see the JB Weld rivets between the lugs.
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"Nike-ized" Estes Majestic. Added a few epoxy drop rivets on the sides for looks.
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Another pseudo-scale sounding rocket thing with more phony rivets,,,
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That was University of New South Wales - my team. Here's a CAD screenshot and photos of the bottom and top rail guides (slightly different designs due to the bottom assembly pulling double duty as a centering ring.) RASAero suggests it makes a 1-2k ft difference.One of the Australian teams had retractable rail guides at last year's Spaceport America Cup. Magnet pulled it out; a plastic clip sort of like the relevant part of the rail held it out until it was put on the rail at which time the rail pushed it out of the way; a spring pulled it in when it cleared the rail. Very cool but I'm not sure if was worth the effort.
I'd never have guessed it makes that much difference -- totally worth it!That was University of New South Wales - my team. Here's a CAD screenshot and photos of the bottom and top rail guides (slightly different designs due to the bottom assembly pulling double duty as a centering ring.) RASAero suggests it makes a 1-2k ft difference.
Sure it is. Aren't we trying to affect the height the rocket gets to? In the case of squared off rail guides, we're trying to make it go lower. In the case of streamlined or retracting ones, we're trying to make it go higher. If budget matters, using a streamlined guide and a small motor is cheaper than using a draggy, ugly, abominable rail guide and a big motor.Yes, but that is really not material to the discussion of rail guides.
I should think that this guide would have separation at the back. It would probably be lower drag to extend the "boat tail" part further back at a gentler angle, or just use a gentler taper at this length and cut it off sharp and square. Extending the front might help a little, too, but I doubt anywhere near as much. That's for subsonic speeds. Maybe for supersonic, it should be diamond shaped or something? I'd guess the shape shown would have some pretty strong shock waves, even a bit below Mach 1.
Of course it does. Low Reynolds number, terrible shape making for a high drag coefficient.... Unless it's low enough to hide in the boundary layer. Of course, one wonders, one or two k out of what?I'd never have guessed it makes that much difference -- totally worth it!
Out of 30k.Of course it does. Low Reynolds number, terrible shape making for a high drag coefficient.... Unless it's low enough to hide in the boundary layer. Of course, one wonders, one or two k out of what?
Just as with bevelling the fins, an improvement, but still: drag.
I'd like to see retractable rail guides. I've got an idea how to do it. The cool factor might outweigh the weight penalty.. Pun intended.
It is my understanding that conformal guides are designed to closely adapt to the airframe on which they're affixed so as to provide a thin, uniform layer of epoxy, both maximizing grip while minimizing air turbulence.I have often wondered which is better:
Solid rail guides like I made in post 34 or the conformal rail guides. Based on many videos, the more external walls there are, the stronger the guide. Why do people put a grove in the center?
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It is for flexion or expansion?
No idea on the axial groove. When 3D printing, the more layers you have on the parameters, the stronger the print. Infill can help but less than the parameters.It is my understanding that conformal guides are designed to closely adapt to the airframe on which they're affixed so as to provide a thin, uniform layer of epoxy, both maximizing grip while minimizing air turbulence.
"More external walls" = stronger? I don't see that (please explain).
Correct me if I err, but the central axial groove, I think, is to minimize the chances of a rocket locking up on a rail by allowing slight 'collapse' of the rail guide upon takeoff.
3D printing and rocketry: many do it, but I think it's right up there with elastics and rocketry. John Coker has it right.No idea on the axial groove. When 3D printing, the more layers you have on the parameters, the stronger the print. Infill can help but less than the parameters.
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