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Minimum diameter and rails

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bclark989

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Hi gang,

I'm starting my first MD build soon and wanted to get the peanut gallery's opinion on rail buttons. Here are the options I have seen so far:

  1. Buttons screwed directly into BT; screws filed down on the inside.
    Example: From page 18 of the Wildman Blackhawk 38 build instructions: "If using rail buttons mount one at rear of fin & other at front after grinding excess screw length off to fit flush with inside of airframe. A drop of CA will insure they stay put."​
  2. T-nuts laminated to the OD of the body tube; button screwed into T-nuts
    Example: Wilson Alness' Great BALLS of Fire build page. You can see the technique about 3/4 of the way down the page. He even states that it is overkill, but its cheaper than a tower, gives you more threads of engagement than the Wildman method, and it allows you to change them out without risking damage.​
  3. Fly-away rail guides
    I have zero experience with these, but they seem popular. Anyone have any arguments against them?​
  4. To hell with buttons, build a tower
    Not sure a tower is in my budget. Anyone have a link to what they think is the cheapest / simplest MD tower, or alternatively, a modular one that can be used for multiple OD's of MD rockets.​

Also feel free to point out any options I have not captured here.

Thanks all!

Brian
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NateLowrie

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Apogee has conformal rail guides that glue on with JB Weld. I just used them on my L2 cert and they work really well. Minimal drag profile and easy to install.
 

REK

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Fly away rail guides from AMW
Agreed here, this will be my choice now as it seems to be the best option rather than setting up a tower or at the very least spending lots of money to make one.


Alexander Solis - TRA Level 1 - Mariah 54 - CTI-I100 Red Lightning Longburn - 6,345 Feet
 

mpitfield

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Fly away rail guides from AMW
I suppose there is an argument to be had that in the true spirit of MD, less is better. I would go with a tower or the fly-away rail guides. I use both and the two flights I used the fly-away rail guides on, with my 54mm MD, they worked flawlessly.
 

smapdiage9

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I've used the flyaways from 38mm G motors up through 75mm MD full M- no issues, they work great.
 

delta22

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My one experience using a fly-away rail guide allowed the rocket too much play as it traveled up the rail:
https://www.rocketryforum.com/showt...-gt-Clusters-are-Fun-lt&p=1469220#post1469220

I prefer to surface mount T-nut rail buttons, laying 3 layers of thin (1-2oz) fiberglass, approx 2in squares, to secure T-mount rocket:
https://www.rocketryforum.com/showt...-gt-Clusters-are-Fun-lt&p=1470006#post1470006
Has worked like a charm for several mach-busting flights/projects.

Assuming that your are going to push the MD rocket fast, precise control going up the rail is critical.
 

Buckeye

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What diameter is your minimum diameter? Buttons will give you a serious performance penalty at 2" and below. Try it in RASAero, and you will see. As mentioned, you are violating the spirit of MD by sticking rail buttons on it.

#3. +1 on fly away guides. I used them just once on my 38mm MD, and I was happy. I need more friction to grab the rocket, though. I think I mistakenly ordered regular size when I really needed thin-wall size.

#4. Towers add a cool, new dimension to your launch day experience. Here are my trials and tribulations in building a non-adjustable tower using only big-box store parts and basic shop tools. It works, but clunky.

https://www.rocketryforum.com/showthread.php?69413-Jawstand-tower&highlight=tower
 

bclark989

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What diameter is your minimum diameter? Buttons will give you a serious performance penalty at 2" and below. Try it in RASAero, and you will see. As mentioned, you are violating the spirit of MD by sticking rail buttons on it.

#3. +1 on fly away guides. I used them just once on my 38mm MD, and I was happy. I need more friction to grab the rocket, though. I think I mistakenly ordered regular size when I really needed thin-wall size.

#4. Towers add a cool, new dimension to your launch day experience. Here are my trials and tribulations in building a non-adjustable tower using only big-box store parts and basic shop tools. It works, but clunky.

https://www.rocketryforum.com/showthread.php?69413-Jawstand-tower&highlight=tower
I have a Go Devil 38 and a Mongoose 75FG. The Go Devil is first obviously, so that is the current need. If I did a tower though, it would be great if it worked for the Mongoose eventually.

Seems like the fly-away guides are a good bet. I like the look of the conformal guides as well, but I imagine it has a similar negative impact to performance on a 38mm rocket as the buttons.

Thanks all for your input!
 

ksaves2

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Fly-away guides. I have some of the older ones without buttons. They work. Got a 54mm guide for an "onsale" mongoose that Madcow or RW had and look forward to completing that build and flying it.
I think the 38mm ones are "mandatory" for MD rockets of that range or put up with the nuisance of a tower. Sure, if record hunting, the tower is almost mandatory. Kurt
 

Swissyhawk

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The only downside I have with fly-away guides is that you have to remember to go pick them up. I know that sounds obvious, but when you start focusing on where your rocket is coming down, it is easy to forget about the rail guides.
 

rms

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Fit away guides but Gregg is right about remembering to pick them up. Last launch I had to turn around and drive back from 5 miles when I remembered I had forgotten to retrieve them.

image.jpg
 
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T34zac

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Fly away rail guides are probably best if you can't build a tower. Use some rubber bands on the clamps of it to get some extra gripping power on your rocket if it's too loose.
 

watermelonman

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I like the idea of fly away guides, but they never seem to work well when I see them in person. Witness the lawn dart two stage attempt at XPRS last weekend, attributed to either faulty guides or maybe they were simply not up to the forces at play.
 

NateLowrie

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I would recommend using ACME conformal rail guides from Giant Leap. I have used them on 38, 54, and 75mm minimum diameter birds. If you do use them, scuff them up a lot and adhere to airframe with JB Weld.

View attachment 302050 View attachment 302051 View attachment 302052

https://giantleaprocketry.com/products/components_launch_systems.aspx#Acme_Conformal_Launch_Guides
These are good. I like the plastic 3D printed ones from Apogee better. Identical shape, just a different material and a tad cheaper. For any rocket under 30 lbs I normally use these (though that may change with the minimum diameter birds.
 
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