Rail button mounting questions

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Luv2launch

Luv2launch

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HI all,
I have just finished building my first high powered rocket for my level 1 cert, a Loc HyperLoc 835 and I would like to know how best to mount rails buttons?At this point I am almost kinda gonna go with the 1/2 inch lugs that came with it but I really wanna launch it off a rail so is it best to mount the rail buttons into the fore and aft centering rings?Or one in the aft ring and one farther up on the air frame?I am only gonna fly it single deploy so the main chute is gonna be in the bay where the drogue should be everything fits I swapped out the elastic that came with the kit for a 25 foot piece of TN with a nomex chute and shock cord protecter on it along with some quicklinks.It mostly complete all filits are done its just down to rail buttons or lugs JB weldings my aeropack retainer in and priming/painting gonna wait to put on the aeropack till after its painted.
Also one more question it weighs in at about 4.8 pounds which I am just gonna call it 5 pounds and having to keep it to a 1500 foot cert flight what do you guys think would be a good motor for it?I had the recomendation of maybe an H268 or maybe an I218R but some other input would be helpful.
 
It's not really neccesary to screw them into the CR's. A little CA around the hole will toughen up the tube plenty.

I went with an H180 on around a 5lb rocket for my cert. I wanted to stay low so I could observe the ejection and deployment.
 
I would strongly discourage using the lugs. Fit it with buttons only.

I'd use three buttons: one at the bottom & one a few inches above the fins (about 12-14" max between the two buttons). This config will work great for when you fly it without the payload. I'd add a third button on the payload bay. By adding one here you (1) make it easy to align with the other two since you can simply turn the payload bay to line them all up (2) provide support/stability for the taller rocket.

I have never nor will ever use lugs on a high power rocket. I've seen too many bad things happen with rod whip and/or lugs sticking/binding on the rod. Buttons are for high power, lugs are for Estes and midpower.
 
I just put my buttons in the forward and aft rings. You can even go just above or below if you prefer, and soak the tube in CA to stiffen it up a bit, as was already suggested. There's generally not a tremendous amount of stress on the buttons for that size and weight of rocket, so either or should be fine.
 
Probably the minimum motor for a safe flight would be an H123 or an H148. Both should keep it low and have a 5:1 thrust weight raito assuming a loaded weight just under 6 pounds.

Al
 
I usually put one guide in or near the aft CR, and another on the CP. I think that's what blacksky used to recommend, plus you'll always remember where your CP is.
 
I put mine through the body tube and use a nylon lock nut and a washer on the back side. You have to get out the BFH and smash the washer to the approx. curve of the tube. Then put epoxy over the nut.
 
In addition to what's been said here, I have also attached railbuttons to the tube with T-nuts and cap nuts. I prefer T-nuts because they sit nearly flush with the inside of the tube, and they make the railbuttons easily replaceable. They also act as ~1/8" standoffs, so they keep the rail from scratching the paint.
 
I'm really glad this post got posted. I was going to post my own rail button question, but I guess I'll ride along here so all the answers are in one place.

I'm planning an L2 rocket, 4" OD, 80" tall, 54mm MMT for a 54/2560 case(22" total length). This means a J or K motor. I was going to do a zipperless design with the fin can 18" tall and a 4" coupler extending from that to the top centering ring. The fin root would be 12" so mounting a rail button in the two CRs above and below the fins would put them 3/4" and 13 1/4" from the bottom.

If I put one rail button at each of those locations, should I add a third just below the e-bay lower end (approx. 35" from the bottom edge)? Would the two locations on the fin can be enough, I wouldn't think so, but greater minds then mine might have a better answer.
 
Handeman said:
I'm planning an L2 rocket, 4" OD, 80" tall, 54mm MMT for a 54/2560 case(22" total length). The fin root would be 12" so mounting a rail button in the two CRs above and below the fins would put them 3/4" and 13 1/4" from the bottom.

If I put one rail button at each of those locations, should I add a third just below the e-bay lower end (approx. 35" from the bottom edge)? Would the two locations on the fin can be enough, I wouldn't think so, but greater minds then mine might have a better answer.
Click to expand...

I don't know about the "greater minds" thing, but it might be better to mount the forward button closer to the CG with the motor loaded that you're going to fly. That would give the rocket better support on the rail than having them only 12.5 inches apart. It's not a lot of difference (maybe 5"), but you may find your CG with a K270 loaded is around 19 inches from the tail end.

That's my 2 cents.
 
Sound reasonable Joe, that was my thinking too.

Next questions, since the upper rail button will go on the tube between the fin can and electronics bay and that tube will be attached to the e-bay, not the fin can, how tight does the tube to fin can connection have to be to prevent it from rotating as the rocket is leaving the rail? Or is a snug fit to prevent seperation at motor burnout enough to prevent any rotation when coming off the rail?
 
Handeman said:
Sound reasonable Joe, that was my thinking too.

Next questions, since the upper rail button will go on the tube between the fin can and electronics bay and that tube will be attached to the e-bay, not the fin can, how tight does the tube to fin can connection have to be to prevent it from rotating as the rocket is leaving the rail? Or is a snug fit to prevent seperation at motor burnout enough to prevent any rotation when coming off the rail?
Click to expand...

This is exactly how I mount my third rail button and set up my DD rockets. I shear pin the tube to the fincan coupler. That way there is no rotation and I'm not risking the possibility of drag separation at motor burnout. Simple 1/16" styrene rod works great for shear pin material
 
MarkM said:
This is exactly how I mount my third rail button and set up my DD rockets. I shear pin the tube to the fincan coupler. That way there is no rotation and I'm not risking the possibility of drag separation at motor burnout. Simple 1/16" styrene rod works great for shear pin material
Click to expand...

I've never used shear pins before. What do you use to stop the styrene rod from slipping out of the hole? I would assume the fit gets a little loose after repeated use. Do you leave the pin extend out from the outer body tube?

Sounds like I'll have to start doing some ground testing. I just picked up a pound of FFFFg today for $14.95 at Gander Mountain, so I'm ready to go.
 
Handeman said:
I've never used shear pins before. What do you use to stop the styrene rod from slipping out of the hole? I would assume the fit gets a little loose after repeated use. Do you leave the pin extend out from the outer body tube?

Use a brass insert in the body tubes. Or use fiberglass tubes. Or just use masking tape to friction fit the tubes together.
Click to expand...
 
Handeman said:
Sound reasonable Joe, that was my thinking too.

Next questions, since the upper rail button will go on the tube between the fin can and electronics bay and that tube will be attached to the e-bay, not the fin can, how tight does the tube to fin can connection have to be to prevent it from rotating as the rocket is leaving the rail? Or is a snug fit to prevent separation at motor burnout enough to prevent any rotation when coming off the rail?
Click to expand...

Why would it rotate coming of the rail? If the fit is solid enough to survive motor burn out and not drag separate it should be good to go.
Another benefit of the third rail button on a "movable" part of the tube is you can ensure that the electronics arming switches cannot be in line wit and blocked by the rail at the pad.:surprised: I know this not from personal experience but from observation at LDRS.:)
 
That is kind of what I was asking. I don't see why it would rotate. As long as it is tight enough to not drag seperate, it should be fine. At least I can't think of any reason it wouldn't be.

I like the idea of always having the electronics facing away from the rail. I was going to put the second rail button on the tube between the alt bay and the fin can. I'm not sure that would keep the alt bay facing the right direction, but that is an assembly issue and should be taken care of before I ever get to the pad.
 

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