Improvising a stand-off for rail buttons???

[Murrill]

I'm about half-way through construction of a PE Honest John; with 4 boys under the age of 11, construction tends to be a very drawn out process. Anyway, the PE kit calls for one of the launch lugs to be mounted on the nose cone itself; because the diameter of the HoJo nosecone is greater than that of the airframe, the lower lug is mounted directly on one of the fins, away from the airframe.

I'm not thrilled with the configuration of the lugs, and several earlier threads have suggested the alternative approach of using two stand-offs on the airframe to mount rail buttons.

Can anyone give me some specific guidance (pardon the pun) on constructing the stand-offs? My biggest concern is that I would like to launch the rocket with a Pro38 "J," which is a large motor for this rocket; and while I am not a physicist (I only play one on TV), I am concerned that as the rocket travels up the rail, a tremendous amount of pressure is going to be exerted on the stand-offs. If I glass some strips onto the joint between the airframe and the stand-off, should the stand-offs hold up? Also, is there any minimum thickness I should use for the stand-offs? Are there any commercial stand-offs available?

As always, any info would be helpful.
Thanks.
John

 

[Austin]

Murrill,

One of the best setups I saw was a launch lug mounted on the body tube at the fin joint and the upper lug was drilled lengthwise through the nosecone, using the length of the nosecone as the lug which was lined with a tube...it worked well and looked very cool as you didn't see any lugs sticking out. Of course, he used a rod rather than a rail.

Carl

 

[utahrc]

The Polecat Aerospace Honest John and Nike Smoke kits that I saw at Hellfire used a couple of nuts under each rail button as stand-offs.

 

[xenon]

What I did on another transition rocket was take a long 8-32 bolt and screw it into the airframe.
Railbuttons.com's rail guides fit right onto the bolt, so you just need to put a nut on to hold the button on. This was on a 3 pound rocket with only about an inch to stand off, so it may not work for you.I'll try to post pics later.

 

[jetra2]

Agreed - the railbuttons from Railbuttons.com are mounted using a standard screw/bolt. Use a long version of the same size and some nuts, and that should hold it up just fine. If you wanted to keep the button from coming off, you could put another nut on the inside of the body tube which will keep it from pulling out.

Jason

 

[DynaSoar]

Originally posted by murrill

I'm not thrilled with the configuration of the lugs, and several earlier threads have suggested the alternative approach of using two stand-offs on the airframe to mount rail buttons.

The outer end of the stand offs need only be as big as the buttons. But for strength, the root edge (against the body) should be long. Think: two long, narrow trapezoid fins, in line, an inch at the outer end and maybe 4 inches at the root. I'd think that would hold up. But it's look clunky and you'd probably take a hit on performance. I'd think it would arc towards the side with the stand offs.

What don't you like about the nose-and-fin mounting?

 

[lalligood]

Originally posted by jetra2
Agreed - the railbuttons from Railbuttons.com are mounted using a standard screw/bolt. Use a long version of the same size and some nuts, and that should hold it up just fine. If you wanted to keep the button from coming off, you could put another nut on the inside of the body tube which will keep it from pulling out.

Jason

Along with jetra2's excellent suggestion above, you should also take a look at https://www.railbuttons.com/rb/surfacemount.asp which is an article on the Railbutton's website about surface mounts. (It has pictures & should help to visualize what you're looking to do.)

I never thought about doing that with railbutton but I might have to design a project just so I can And please post pictures of your work!!

 

[Murrill]

Thanks for the responses, everyone. I'm beginning to think about a standoff along the lines of DynaSoar's suggested trapezoid shape (which was similar to what was recommended in the article at railbuttons.com). I have not yet put the calipers to the nosecone and airframe, but my rough initial measurements suggest the stand-offs would need to project about six-tenths of an inch from the airframe.

My remaining concern is about the effect on performance. I'm not so much worried about altitude; with a "J" in that rocket (or even an "I"), I'm going to get all the altitude I want. But I am worried about DynaSoar's concern that the stand-offs might cause the flight path to arch over because of the asymetrical design.

What do you think??? Do you believe the stand-offs will have a significant effect on the "straightness" of the flight???

I would appreciate your input.
Thanks.
John

 

[rstaff3]

I have used both longer bolts with nuts underneath and wooden standoffs. As the standoff gets longer the extra footprint probably is a good thing.

0.6 inch is not that large, you wont have any problems with your flight profile. Make sure the lower button is near the bottom of the rocket.

 

[astrowolf67]

On the one rocket I've built that needed a stand off for the rail buttons, I used epoxy, and laminated some popsicle sticks together, then cut what I needed, mounted the "stack" on the airframe with epoxy, then installed the button screw into that.

 

[DynaSoar]

Originally posted by astrowolf67
On the one rocket I've built that needed a stand off for the rail buttons, I used epoxy, and laminated some popsicle sticks together, then cut what I needed, mounted the "stack" on the airframe with epoxy, then installed the button screw into that.

I did much the same, but with basswood and a lug. That was just for the upper lug. The lower went on the fin/body joint. With fillets the upper made a nice smooth hump. More frontal surface area, but far less likely to come loose.

 

[ClusterWiz]

I’ve seen two setups with buttons. One we glued a T-nut to the inside of the nosecone and screwed the button into that. And on the bottom we just made a wooden standoff ourselves. The second one was with the same configuration with the nose cone but he used a extreme rail button for the standoff. Both had the botom screw go into the botom CR. I can’t remember if he used anything else. Measure and find out. I would strongly say to use buttons and not lugs. There smaller, easier, look better and more reliable. You wont have any problem wiht your flight path. Your rocket will probly spin anywase. And listen for a whisle!