Who cares about the fins being squatted off when your rail guides are square?
Unique Rail Guides
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Who cares about the fins being squatted off when your rail guides are square?
lr64
Well-Known Member
If you want to fly low, use a smaller motor.
Yes, but that is really not material to the discussion of rail guides.
Design #1:
King size Unistrut:
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.
"Nike-ized" Estes Majestic. Added a few epoxy drop rivets on the sides for looks.
Another pseudo-scale sounding rocket thing with more phony rivets,,,
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.
"Nike-ized" Estes Majestic. Added a few epoxy drop rivets on the sides for looks.
Another pseudo-scale sounding rocket thing with more phony rivets,,,
I have a sign that I print off thing verse that is similar.
olivermpb
Big motor enthusiast
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.
Attachments
I'd never have guessed it makes that much difference -- totally worth it!
lr64
Well-Known Member
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.
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 have designed several now. I will start posting a few tonight.
lr64
Well-Known Member
Can you give the cross section dimensions that are customary? It might be fun to do a 3D body in CAD.
olivermpb
Big motor enthusiast
Out of 30k.
Just as with bevelling the fins, an improvement, but still: drag.
Why fly-aways (and some towers) exist, and retractables/etc. fill imagination.
lr64
Well-Known Member
On supersonic rockets, one could just use a low temperature plastic. Canadians could use reinforced ice.
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The issue w/ retraction is that it leaves a weight imbalance on one side of the vehicle (as do rail guides), assuring coning if the vehicle spins. The solution to that issue is to add counterweight on the opposite side of the rocket.
My simulations for the particular rockets I am working on indicate that the weight penalty results in lower performance than fly-away guides or a four rail launcher.
Bill
lr64
Well-Known Member
One could always shift something over, assuming there's any room, rather than adding a counterweight.
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?
It is for flexion or expansion?
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?
It is for flexion or expansion?
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.
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.
3D printing and rocketry: many do it, but I think it's right up there with elastics and rocketry. John Coker has it right.
lr64
Well-Known Member
A preliminary idea for a rail gulde that might be low drag. Obviously it needs a couple of mounting holes, and some of the edges might need to be radiused or broken. But ain't it swoopy? I've drawn it with .010" clearance. The swoopy comes from cutting away what's outside two ellipses. Three if you want to be fussy about it, I suppose, but I actually drew only a quarter of it and then mirrored.
Not having the proper equipment to fabricate them myself, I'd certainly pay someone for numerous sets of these - well-done, indeed!
Ramjet64
Member
I was thinking about this yesterday.
Something along the lines of a landing gear bay door that is spring actuated.
Now you've got me thinking about it again, I'll try and draw something up..
That is the great part about rocketry. There are many ways to do it safely. The best part about 3d printing is going from idea to reality in 24 hours.
I like it.
lr64
Well-Known Member
If you had a regular rail guide of reasonable length, you could make something like this by attacking it with a file. Or a scroll saw.Not having the proper equipment to fabricate them myself, I'd certainly pay someone for numerous sets of these - well-done, indeed!
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Incidentally, it seems to me that, for BFR's, it might be handy to have rail guides that could be inserted into the rail and THEN attached to the rocket somehow. Maybe rare earth magnets?
Not sure I understand the mechanics of a scroll saw to effectuate construction, as much as I like your proposed design. A file? I already hate sanding; please don't add filing to the mix.
(Maybe, though, a sanding disk on a lathe...)------------------------
A) how is that an advantage, except for loading the BFR onto the rail?
B) and when the BFR exits the rail, do not those rare earth magnets then stay on the rocket (or is a blockage for the magnets' escape at the top of the rail, but somehow they do not influence the planned trajectory of said BFR?)?
NOT trying to thwart your idea(s), as I think it's/they're quite good, just trying to think them through (proof I'm not a government employee. . .).
Please don't quit with your imagination and suggestions!!
lr64
Well-Known Member
The shape I've shown could be acheived with 3 or 4 cylindrical cuts starting from an extrusion. Not cylindrical as in round, but cylindrical as in of constant cross section. The CAD system calls these extruded cuts. When you sand, do you always use fresh paper and a sanding block? I've run into a kind of sandpaper from 3M that is purple, and clogs more slowly than other types. A nice feature is that you can wet sand with it, keeping it cleaner, cutting faster, and keeping the dust under control. The ideal tool might be a miniature surform. Maybe some cheese graters would be up to the task.Not sure I understand the mechanics of a scroll saw to effectuate construction, as much as I like your proposed design. A file? I already hate sanding; please don't add filing to the mix.
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A) how is that an advantage, except for loading the BFR onto the rail?
B) and when the BFR exits the rail, do not those rare earth magnets then stay on the rocket (or is a blockage for the magnets' escape at the top of the rail, but somehow they do not influence the planned trajectory of said BFR?)?
NOT trying to thwart your idea(s), as I think it's/they're quite good, just trying to think them through (proof I'm not a government employee. . .).
Please don't quit with your imagination and suggestions!!
A clever person might figure out a couple of jigs to use with a router, enabling a new part every few minutes, but routers are noisy and dusty.
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A) Making loading easier is what I had in mind.
B) I hadn't thought of leaving the magnets or the,hardware on the rail, but that could be arranged.
