- This topic has 15 replies, 8 voices, and was last updated 19 years, 2 months ago by
Conway Stevens.
Conway Stevens.-
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Anonymous
Is there a good, clean way to take ~80-100 thousandths off the span of some G10 fins that are already on a rocket? I know I could get out and Dremel or power sander, but I’m not into the dust thing. I’d like to cut the fins back a bit on a 29mm H rocket and try and get an extra couple hundred feet of altitude. Last Saturday I exceeded the TRA “H” record, but not by 2%. Aaaagggghhhhh.
I might just re-build the booster, but I *know* these fins are on straight, and if I can just modify this one, there is some merit to going that route. Perhaps I get some really coarse sandpaper and wet sand them? I’m concerned about uniformity, and it will be tough to do by hand.
The airframe is 29mm, and the fins are 1/16″ thick. Chopping of the tippy-tips of the fins may be a tall order….
denverdoc
John,
Wish I could help, if the fins have a square tip, IMO doubt shaving .08″ off the span will gain 200′ in all cases. But a straighter boost would–I guess the H268 went sideways by at least 10 degrees. Thats 200′, potentially more as I recall seeing it fly at a decent cant to the south,Alternatively, shaving most of the fin down to to less than .04 thickness might help.
Just a notion, but as i have suggested before a beau coup tower of 10′ long that carries levels with it dialed in would do it in spades. I’m happy to look for some high quality tubing to use with the tower. Can punch the holes and we give it a go. What do you think?
JEd Dawson
How about a planer and a jig clamped in place to control the cutting depth?
Anonymous
But a straighter boost would–I guess the H268 went sideways by at least 10 degrees.
Just a notion, but as i have suggested before a beau coup tower of 10′ long that carries levels with it dialed in would do it in spades.
Gotta tell you, I thought it was pretty straight up… Even if it did go 10 degrees off of vertical, if you employ the Pythagorean Theorem, (A squared + B squared = C squared) and use my altitude for “A” (10,674′), and figure it was 1000′ downrange when it deployed (call that “B”), that would not get me the extra 200’… in this case, it only yields another 50′ of altitude.
The tower I used was 8′ tall. I don’t think an additional 2 feet of rail would do me much good… It was most assuredly moving fast enough when it left the tower :-O I’m traveling this week and don’t have the rocksim file on this computer… but my hunch is that removing .80″ from the span would make a pretty big difference. It would also cost me some stability.
This is very near the proverbial “envelope”. To illustrate this, consider my J570 shot — which also broke the TRA record, but also not by that stinking 2% 😡 . I rebuilt that rocket with the fins about 5% smaller, and shortened the airframe by 1/2 inch… and it shredded. It is a very fine line at this point. The differences between my first J570 rocket and the second J570 rocket were tiny.
I was actually thinking of going to a shorter tower, thinking I might have lost a wee bit of punch rubbing on 8′ of rail. That said, the rocket wasn’t really scratched up. It is in terrific shape.
Gotta find another 200′ without slipping outside the envelope. I’m close to the edge right now… I’ll try again, hopefully getting a hotter motor, straighter boost, warmer temps, blah blah blah…
Anonymous
How about a planer and a jig clamped in place to control the cutting depth?
First of all, I want to publicly say THANK YOU to Ed Dawson for his help on my boost. He lent me some internals that allowed me to fly this shot, and I appreciate it! (I’m glad they didn’t land in the river!)
Planer and jig… I’m a man of few tools (that is an understatement!) If I go that route, I’ll need some adult supervision 😯
Someone else suggested that I consult a buddy who might mill the tips down for me, so I’ve sent him a note… his milling machine is a thing of wonder. That might just work?
JW
Doug Gerrard
JW,
Why not use an edge sander? I don’t know how precise you have to be but you should be able to get in the range between 0.080 and 0.100. If you send me the rocket, I’ll sand them off for you.
Doug
Ed Dawson
John,
I heartily agree with the shorter tower. Less length, less friction on the initial boost. I imagine that you reach a stable velocity pretty quick with that little bird.
One extra millisecond bump on the rails could easily cost a lot. I’m too lazy to do the math, but it seems 200 feet is doable.
edward
I don’t know how much this would help, but how about enclosing your rails on your tower with a tube. Kind of like a piston launcher but it just acts a on the rocket. I know we are talking small amounts (80 grand off a fin is small) so I’m wondering if this would be enough coupled with the fin adjustment to make the 200′? Is there anything against putting some BP in the bottom of an arrangement like that to get some more umph?
Edward
Anonymous
JW,
Why not use an edge sander? I don’t know how precise you have to be but you should be able to get in the range between 0.080 and 0.100. If you send me the rocket, I’ll sand them off for you.
Doug
Doug, that is a wonderful offer, and I very much appreciate it. I’m going to sit down with a buddy who has a mill next week, and see what he suggests… He thinks he can mill the tips down quickly, easily. I’ll let him see it before he commits…
I have a chronic lung issue, hence my resistance to anything G10 dust related.
Thank you again,
JW
Anonymous
I don’t know how much this would help, but how about enclosing your rails on your tower with a tube. Kind of like a piston launcher but it just acts a on the rocket. I know we are talking small amounts (80 grand off a fin is small) so I’m wondering if this would be enough coupled with the fin adjustment to make the 200′? Is there anything against putting some BP in the bottom of an arrangement like that to get some more umph?
Edward
I’m not sure what effect that may have. Right now, I’m looking at everything… 0.080″ – 0.100″ is an arbitrary number I came up with. I will run some sims to see.
Regarding BP to get some “oomph”… if you scorch fins, bubble up fiberglass (or primer – I don’t use paint), etc. you can lose some footage. I don’t think one could use enough BP to get enough boost…
Here’s a thought- going to a 4:1 conical cone vs. 5:1 conical? Might help.
I played a lot of baseball, and that was always a “game of inches”. This, too, is a similar scenario. I appreciate everyone’s suggestions!
Anonymous
denverdoc
Ed Dawson
Doug Gerrard
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