Help with Button Placement

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Martin Vrstal

Well-Known Member
Aug 3, 2002
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The Jayhawk I'm building over in the Scratch section will be my first useage of rail buttons. What would you guys do here.....put the buttons in the CR's as in this picture?
Or move the top button up about 12" as in this pic?

Also...what to use for screws? If I moved it up 12" I would need to use a nut on the inside of the airframe.

Give me your 2cents worth gang.
Id say 1 about 3" from the top of the bodytube & 1 2" from the bottom . It doesn't realy matter where you put them (IIRC) , but IIRC I remember reading something about placing one on the CG?
If you use the woodscrews
can you glue a block in?
Andy.....saw that on your V-2...way cool by the way. So you just glued the block in and the screw just screws in and out?

Also...if I drill holes I just put an extra screw in the hole in order to paint?...Remember...first time for everything.
do the second one. I Generally put on button as far down as i can (in a bottom CR) and the second on as far up as I can, usually in another CR, or a little bit higher. you dont want to put them too high (someone mentioned 3") because your shockcord will get hooked around them, I have seen this happen alot of times, once on an L1 cert
Originally posted by Karl
Id say 1 about 3" from the top of the bodytube & 1 2" from the bottom . It doesn't realy matter where you put them (IIRC) , but IIRC I remember reading something about placing one on the CG?

I wouldn't put one that far forward. remember that once the first (assuming you only have two) button leaves the end of the rail, their not doing their job any more.

I prefer to put one at the aft end of the rocket, and one at the CG. But, I'll shift them around a little if it means I can screw them into a centering ring.
one near the bottom and one near the cg(or nearest centering ring is good)

on the block I rounded it to fit the ID than I epoxied it in.. I installed the screws after I did most of the finishing work
I drilled a pilot hole and used wood type screws.

I like to put the buttons in CRs if I can. I just like the extra backing/strength/security I think it gives and doesn't interfere with recovery devices. I've never CA'ed or epoxied one in place because they do occasionally need to be replaced as the buttons wear. I've always screwed them in place with a stainless steel wood screw, too, for a better bite into the wood. On my Big Horizon I used honeycomb composite board for the CRs. That stuff is basically air in the middle. To overcome that problem I drilled a clearance hole for a piece of 5/16" wooden dowel and epoxied that in place then drilled and screwed the button into the dowel. The dowel is easily sanded to the contour of the BT so it worked just fine.

One other thing I recently discovered is that a Sharpie pen will color a stainless steel screw's head. It isn't permanent but does last for a while and lessens the visual distraction of the stainless head - if you care about such things. I believe Sharpies come in several colors too. info says to put one button as far aft as possible to get max. use of the length of the rail. A second button at the top CR should be good, too. On my big heavy rockets I use three in the CRs mostly to handle the weight. My 10' Big Horizon has one in each CR with the fore most button 28" from the aft end and it seems to work just fine.
remember that the further back the top button is, the more active guidence you get. I personally like buttons really close to the back end of the rocket. I put the top one maybe a caliber or two from the bottom button. Another option is two really close together at the bottom, with a third way up the rocket.
I second Dan's post. I'll usually go 2 calibers below the CG, at the very least. So far, so good.
Since this Jayhawk has a boat tail, I can't go all the way to the bottom of the rocket. The bottom button will go into a CR. It's the top one I've been wondering about. I only have 2 buttons on hand, so I'm useing what I have.

Also I haven't ballanced the rocket out yet, so I don't really know the true CG.

Do I install these suckers now or wait till it's painted?
Are those the Nylon buttons or the Derlin Buttons? I ask because they look white... and as far as I know, the Derlin Buttons are only in black, and for a rocket that size... I would recommend using the Derlin buttons... They are more durable than the nylons. Your choice :).

While I agree that buttons to the aft end is the best for the most useable rail length don't get too caught up in this. Most rails are at least 6' long and that length ought to be enough to get the Jayawk moving fast enough to be stable. If not, your motor is probably too 'small' anyway.
One thing I have been using lately to install rail buttons are well nuts. These are little rubber fasteners that when you tighten them they expand a lot. Kind of like a boat drain plug. I put a block of wood behind where I want the buttons and epoxy it in place. Then after drying I drill a hole the size of the well nut. Insert well nut and tighten down. This works really nicely. Also, it makes it easy to swap buttons if you break one. Just pop it out and install a new one. Never had a problem yet.

Originally posted by Martin Vrstal

Also I haven't ballanced the rocket out yet, so I don't really know the true CG.

I think that now could be a good time to find out!
I usually try to hit c/r's as well, however I have also followed the Blacksky instructions and drilled the proper sized hole for the screw and ca the screw into the body tube, no backing nut. Shouldn't be a problem on a rocket < 8 lbs. with a glassed airframe. BTW, you know where the cp is located yet?

No...infact I've just been building this thing and haven't got to that point yet. No known CP,CG, and no WT in the NC.

I'm still hopeing to find someone with the newer Roc sim program who can figure things out for me.....any takers?