6 inch diameter scratch-built rocket...number of rail buttons and separation?

[Tad]

So, I'm building an L-Class 6 inch diameter rocket with 3 notched centering rings (aft, middle and forward) housing four 11 inch root chord trapezoidal fins and total rocket height of 94 inches. I've always used two rail buttons for my other rockets (4" & 3" diameters) but I'm not sure if I should still go with two rail buttons or possibly a third. Is there a rule of thumb here? If so, what should be my separation? I've got good anchor points at the aft and forward rings with 11 inch separation but would that be enough for a 6 x 94 inch rocket? Thanks in advance.
Tad

 

[manixFan]

Need more info - 1010 or 1515 rail? And what is the liftoff weight? If you are using 1515 rail and liftoff weight is less than about 30 lbs, based on my experience, 2 buttons is enough. I’ve flown 2 rockets that size on M and N motors with just two 1515 buttons into a wood backer. Typical button placement should be fine, one at about CG and the other at the rear.

But maybe someone with more experience can chime in and provide some more feedback.

Tony

 

[OverTheTop]

Three buttons will just overcomplicate matters. Two of sufficient strength are sufficient.

Personally I locate one close to the CG and the other as aft as practicable.

 

[FredA]

Three buttons will just overcomplicate matters. Two of sufficient strength are sufficient.

You're building ROCKETS and you can't put three holes in a row????
Not very complicated and well worth it.

Put one at the aft end.
One at the top of the fincan.
And one as high up as possible but not where it interferes with the recovery space.
The aft two do the real work - the forward button holds the rocket nice and vertical on the pad during side winds.

Rail guidance ends when the second-to-last button leaves the rail.
That's pretty quick on a two-button rocket.

 

[mtnmanak]

Agree with a 2-button config with an aft placement and one near the CG. I have built rockets with 3 buttons in the past and it wasn't complicated, but I found it to be unnecessary.

For large 5" diameter rockets and above, I install two 1/4"-20 Rotaloc nuts in the booster which allows me to switch between unistrut and 1515 airfoils very easily. You usually don't need unistrut, but the clubs I fly at have unistrut on their away cells, so it is easier than asking them to switch out a rail on the hydraulic lift.

Here is the installation on a 6" Wildman Darkstar Ultimate that ended up being about 45-70 pounds on the pad:

 

[Michael L]

I install two 1/4"-20 Rotaloc nuts in the booster

I suppose I could google it but I'll ask first- where does one find Rotaloc nuts. I have my first 4" fiberglass build coming up ( prelude to my L2 attempt rocket) and I need a better way to install rail guides.

 

[mtnmanak]

I suppose I could google it but I'll ask first- where does one find Rotaloc nuts. I have my first 4" fiberglass build coming up ( prelude to my L2 attempt rocket) and I need a better way to install rail guides.

You can find them at the one rocketry store that none of us can live without - McMaster-Carr

Here is the link:

https://www.mcmaster.com/perforated-base-nuts/nut-type~adhesive-mount/
You can get them in many thread sizes and hole patterns/base sizes. The ones I showed above are part #98007A029

https://www.mcmaster.com/98007A029/
For smaller rockets, I often use the 8-32 versions. I found some 1010 buttons that work with an 8-32 screw, so 8-32 is great for switching back and forth between 1010 and 1515.

 

[Tad]

Yes, 1010 rail. Mtnmanak, your pics were super helpful. Thank you. I think I'll go with the 2 button config, and as the consensus agrees, one near the CG and the other furthest aft anchored in the aft centering ring. The 11 inch forward ring will not bring me to the CG so I'll go further up and I like how you secured it. Was that JB weld?

 

[Tad]

Lift off weight is estimated at at 27 lbs with about half the weight being EX motor and sugar propellant.

 

[neil_w]

I like to be extra careful

 

[Michael L]

You can find them at the one rocketry store that none of us can live without - McMaster-Carr

No kidding!

 

[David Schwantz]

I use 3 buttons on a lot of rockets. On a rocket that is over 90" tall, 11" apart for the buttons is NOT enough. Good you are placing the upper one higher. I like to put the lower one as far down as I can, usually lower CR. 2nd one in booster section just below Av Bay. 3rd one in payload section as far up as practical. This not only gives good stability off the rail but also lessen the chance the rocket might pivot on the rail, especially in wind. I have seen one button break off before and the rocket get stuck on the rail. I have done this on both 1010 and 1515 rails. Good luck.

 

[tfish]

I have a 6" rocket that is 41 pounds on the pad. It has two 1010 buttons on it. I get about 4 flights out of a set of buttons before they need to be changes out do to wear. The rocket is a bit wobbly ...side to side with the 1010 buttons.. I'm going to change them to 1515 buttons.
The buttons are 39" apart and the top button is 9" above the CG.

Here is a short vid of the rocket after a flight.



Tony

 

[Tad]

I use 3 buttons on a lot of rockets. On a rocket that is over 90" tall, 11" apart for the buttons is NOT enough. Good you are placing the upper one higher. I like to put the lower one as far down as I can, usually lower CR. 2nd one in booster section just below Av Bay. 3rd one in payload section as far up as practical. This not only gives good stability off the rail but also lessen the chance the rocket might pivot on the rail, especially in wind. I have seen one button break off before and the rocket get stuck on the rail. I have done this on both 1010 and 1515 rails. Good luck.

Thanks, David. Will consider. One thing is for sure, this L-Class won't get "stuck" on the rails. Wouldn't be pretty.

 

[UhClem]

My scratch built 6" diameter L3 cert rocket started with 3 buttons but I removed the top one because it wasn't doing what I wanted. There were rail marks on the rocket below it.

Locations near the CG and CP will minimize stress in the buttons and have other benefits.

 

[mtnmanak]

Yes, 1010 rail. Mtnmanak, your pics were super helpful. Thank you. I think I'll go with the 2 button config, and as the consensus agrees, one near the CG and the other furthest aft anchored in the aft centering ring. The 11 inch forward ring will not bring me to the CG so I'll go further up and I like how you secured it. Was that JB weld?

Yep - JB Weld. I completely fill up the threads with JB Weld and put some more on top. The Rotaloc nuts are good, but I have had the nut separate from the plate before, so now I JB weld the whole thing inside and out, top and bottom and then just tap the JB weld later. Works like a charm and since I started doing that, I have not had one of those nuts fail on me, even on a 100 pound rocket.

 

[DAllen]

You're building ROCKETS and you can't put three holes in a row????

Learn some tact please. Nothing in OverTheTop post says he couldn't drill three holes in a row - that's your assumption.

Plus, most of the time three buttons is completely unneeded but hey, if that's what you want to spend your time on and gives you all warm and fuzzies on the in side knock yourself out.

 

[Tad]

MtnManak, that looks great. I'm going with that. Thanks, again.

 

[Tad]

My scratch built 6" diameter L3 cert rocket started with 3 buttons but I removed the top one because it wasn't doing what I wanted. There were rail marks on the rocket below it.

Locations near the CG and CP will minimize stress in the buttons and have other benefits.

Completely agree. Thanks, UhClem.

 

[Tad]

Coming along.

 

[OverTheTop]

You're building ROCKETS and you can't put three holes in a row????

You severely underestimate my engineering skills. You are also insulting me. Unnecessary.

Rail guidance ends when the second-to-last button leaves the rail.
That's pretty quick on a two-button rocket.

To a first-order approimation, yes. Remember the rocket will be trying to rotate around the CG and the rear button will still be reasonably effective at reducing induced yaw caused by side winds. If you need three buttons to get every last ounce of guidance you could consider a longer rod or waiting for surface winds to subside to suitable levels.

 

[Tad]

You severely underestimate my engineering skills. You are also insulting me. Unnecessary.

Over the Top,
Don't even consider it an insult. Notice that I did not even acknowledge the comment. Move on. Build.

Thanks for your input.

 

[David Schwantz]

It was a M motor that got stuck, so anything can happen. Good luck and great flight.

 

[mtnmanak]

You severely underestimate my engineering skills.

I am lucky when I can get two of them straight, but then again, I have been told I am a little crooked...

 

[David Schwantz]

When there is only 2, they are ALWAYS in line with each other

 

[mtnmanak]

When there is only 2, they are ALWAYS in line with each other

True! As long as the pointy end is somewhat oriented to the sky, I am happy.

 

[Tad]

Lol

 

[OverTheTop]

Don't even consider it an insult. Notice that I did not even acknowledge the comment. Move on. Build.

You were not the one insulting me . Move on with your build.

 

[Tad]

You were not the one insulting me . Move on with your build.

Yes sir. Moving on.

 

[mtnmanak]

Yup, getting back to Tad's build - looking good!

If you do use the Rotalocs, one more tip - the base plate is flat and doesn't sit against the tube ID very well. I gently bend them in a vise to curve them out a bit. This is an operation that has the most likelihood of weakening the weld between the nut and the baseplate, so care should be taken. You don't need to bend the plate much at all. I just bend it a little bit, check it, bend it a little more, etc. It is fairly easy to get it to fit perfectly against the tube.