Rail and Button sizing?

[ThreeJsDad]

For those of you flying smaller stuff how do you determine if a rocket can be flown on a Micro Rail or if a larger rail is a better choice.

Here is my thought process. It is not uncommon to fly a G powered rocket on a 1/4" rod. My Micro Rail is quite a bit stiffer than a 1/4" rod so it makes sense it should be able to handle a G powered rocket with no issues.

It does occur to me that a heavy rocket on a micro rail might not be a good idea.

I did fly my Bird Of Prey off my micro rail with a less than ideal motor and there were no issues. Well none with the pad anyways....LOL That rocket had massive fins and it was under powered.

I am asking to make sure I am not over looking a factor that needs to be considered.

I will say I am so impressed with this system I will be building another pad for the Mini Rail at some point. Even my little 18mm stuff has micro buttons.

 

[NateB]

I switched over to rails. My unscientific method was to use micro buttons on 18mm motors, mini buttons on 24mm motor mounts and standard 1010 on 29mm and up. I have no basis for this other than the buttons look right on each size of rocket.

 

[ThreeJsDad]

I have had good luck with the micro buttons on my 24mm stuff but I build pretty light rockets. I think I will follow your lead and fly my 29mm rockets on the 1010 rail. A 29mm G is a decent motor and the 1010 rail is probably the right choice.

 

[dr wogz]

Ideally, there should be no issue, except:

The length of the mini rail. Most "little" rockets only require a rod that is 36" or 48" long; usually 1/8" dia or 3/16". We do have a short length of 1010 rail at our club, and we have launched a few "light" 29mm rockets off it. the 1/4" rods I've seen have been in the 6' length range. But most of our 29mm MPRs use the 1010 rail, the full 6' of it. The velocity off the end of rail is important here.. Longer rails allow for more speed at the end of the rail.. Some (most?) clubs are starting to implement policy that all rockets over an F motor are required to be on a (6') 1010 rail.

Depending on the structure the little screws used to hold the mini button on might not have enough 'meat' to properly hold the rocket. This can lead to the screw / connection point failing, such as a gust of wind will try to turn the rocket on the rail; twisting it off the rail at the buttons. if you've used a good backer on the button, this shouldn't be be an issue. But if you just rely on a screw into cardboard & a bit of CA, i'd be concerned.

 

[ThreeJsDad]

I have come to think of it similarly.

When I watch videos though it seems like quite a few clubs fly with shorter 10/10. This doesn't make much sense to me. Our clubs 10/10 and bigger rails are all 8'.

My new saucer and all my rockets with a 29mm MMT are getting the 10/10 buttons. I am reserving the micro buttons for my 24mm and smaller powered motors. I have a longer micro rail I will also start using.

I can assure folks that CA and a nylon screw into a fiberglass frame is really solid, the screw breaks before it will release.

 

[Arsenal78]

I've never seen a micro rail in use. The mini (size above it) is what our club is starting to use in place of 3/16 rods. Rod whip is not nice and rails are safer. I've launched up to an F on the 4ft mini rail we have. I do hope you mean a metal screw and not a nylon screw (shear pin) for buttons. Unless I can get a backing for the button or if the centering rings are 1/8" thick and enough distance between them, I dip the screw into 5 minute epoxy and screw it into the frame, turn it over and let the epoxy create a fillet around the screw. Works every time. I can assure you that CA will fail and if an RSO finds out you're using CA and nylon screws to hold the buttons on, they'll be breaking NAR/TRA rules and allowing an unsafe rocket to fly.

 

[ThreeJsDad]

I've never seen a micro rail in use. The mini (size above it) is what our club is starting to use in place of 3/16 rods. Rod whip is not nice and rails are safer. I've launched up to an F on the 4ft mini rail we have. I do hope you mean a metal screw and not a nylon screw (shear pin) for buttons. Unless I can get a backing for the button or if the centering rings are 1/8" thick and enough distance between them, I dip the screw into 5 minute epoxy and screw it into the frame, turn it over and let the epoxy create a fillet around the screw. Works every time. I can assure you that CA will fail and if an RSO finds out you're using CA and nylon screws to hold the buttons on, they'll be breaking NAR/TRA rules and allowing an unsafe rocket to fly.

Thanks for your thoughts.

 

[rharshberger]

I go with the theory if it uses a 1/8th rod then the micro button are used and yes I mount them with a nylon screw. 3/16" rod then 20mm rail buttons are used usually with . If my model would have used 1/4" rod then its 1010 buttons. Another option for the mini rail is Plastruct H-beam (cant remember size) that I cut into section and glue to body tube similar to an Acme Conformal rail guide.

 

[ThreeJsDad]

I go with the theory if it uses a 1/8th rod then the micro button are used and yes I mount them with a nylon screw. 3/16" rod then 20mm rail buttons are used usually with . If my model would have used 1/4" rod then its 1010 buttons. Another option for the mini rail is Plastruct H-beam (cant remember size) that I cut into section and glue to body tube similar to an Acme Conformal rail guide.

Pretty much the same approach I have adopted. Right now I have the only rail below a 10/10 so if in doubt I go with the 10/10. My new saucer l used 10/10 because it is draggy and might be fun with a G138. I will look into those plastic H pieces, cool idea.

 

[NateB]

Another option for the mini rail is Plastruct H-beam (cant remember size) that I cut into section and glue to body tube similar to an Acme Conformal rail guide

I ended up using the 5/16" size with my Exiter based on your suggestion. It has worked well on A and B flights. I haven't tried a C or D in that little rocket yet.

https://evergreenscalemodels.com/co...278-312-7-9mm-opaque-white-polystyrene-i-beam