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When do I use 3 rail guides?

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cwbullet

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I have seen some builds that use 3 rail buttons or guides.

When do you use three buttons?

If using unistrut or 1515 buttons, when is there a need to use 3 buttons?

Where would you place them if you use 3 buttons?
 

troj

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I'd use three if I had a really long rocket that I wanted to help keep from swaying.

Only time I've ever used more than 2 is on rockets in the 20 foot tall and several hundred pound range.

Others will likely have differing philosophies.

-Kevin
 

cwbullet

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Thanks. I am doing a write up for my level 3 and have never used 3 launch rail buttons.

It will weigh 45-55 lbs. I plan on using a unistrut rail. It is 10 inches in diameter and about 12 feet tall. The center of gravity is 7 feet 8 inches from the tip of the nose or 4 feet from the base of the rocket.

Some people have said to use 3 buttons. I have seen both and juste wanted soem opinions on the matter.
 

JimJarvis50

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I like to use three buttons, but I am always ready to remove one of them if the rocket binds on the rail. I usually use two placed closer together near the bottom of the rocket with the third button higher up. This uneven placement with the middle buttom closer to the bottom button helps to minimize binding.

One reason I like three buttons is redundancy. The rocket can fly on any two of the three. Having the lower two buttons allows the rocket to be guided the longest before the point where the rocket is attached by only a single button. Having two button further apart is a problem in this respect if it's windy. On the other hand, two buttons further apart makes it less likely to have a button come off while loading the rocket. Three buttons gives both advantages.

I fly a lot of minimum diameter rockets, and the buttons can not be a securely attached on those rockets as compared to rockets with centering rings or bulkheads to screw in to. I think that's one reason I favor having three. Two very secure buttons closer to the bottom is fine too, and should work for you.

Jim
 

Crazyrocket

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I sometime use 3 buttons. Like Jim, I put to close together at the bottom and 1 up higher. I typically install on my ebay as I can rotate that at the rail to prevent binding.
 

cjl

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I would only do it on an extremely long, skinny rocket, or similar. For normal rockets, I only use 2.
 

sylvie369

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I vote "never" as well, though I've never built a rocket that weighed more than 16 pounds.
 

Ted Cochran

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Never is such a strong word :)

I have a rocket that uses four, myself--two on each stage of a Quantum Leap. The sustainer needs them for when I fly it by itself. The booster uses them because I wanted 6' of rail guidance, which means there need to be two buttons down low. Could have used one, I guess, but there's a chance for weathercocking if the top starts to tilt off before the bottom button gets free.

--tc
 

FredA

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Remember, the rail stops "functioning" as soon as there is only one rail button left in the rail.
Your effective rail length is the length from the top of the rail down to the second rail button from the bottom (aft) end.
So....you want two button as far aft on the rocket as possible to maximize time on the rail.
If your rocket is heavy, or your launch conditions windy, you might want to consider a third button close to the Cg of the rocket.

I've seen rockets with two buttons spaced 3 feet apart loaded on 6' rails resulting in less than 3 feet of net guidance --> pretty short --> better be a good push to get it going fast!
 

ben_ullman

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Remember, the rail stops "functioning" as soon as there is only one rail button left in the rail.
Your effective rail length is the length from the top of the rail down to the second rail button from the bottom (aft) end.
So....you want two button as far aft on the rocket as possible to maximize time on the rail.
If your rocket is heavy, or your launch conditions windy, you might want to consider a third button close to the Cg of the rocket.

I've seen rockets with two buttons spaced 3 feet apart loaded on 6' rails resulting in less than 3 feet of net guidance --> pretty short --> better be a good push to get it going fast!
BINGO!

If your on unistrut rail the use of a 3rd button is usually just to bear weight, not really to help with guidance. Put 2 of them really low and once the mass is moving it wont need to bear as much weight and will be used just for guidance.

Ben
 

cjl

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BINGO!

If your on unistrut rail the use of a 3rd button is usually just to bear weight, not really to help with guidance. Put 2 of them really low and once the mass is moving it wont need to bear as much weight and will be used just for guidance.

Ben
Somewhat true. The bottom rail button still allows for some guidance after the top one leaves the rail, as the rocket cannot significantly weathercock with the bottom of the rocket held to a vertical track. It's not as good as having two buttons in the rail, but believe me, having 6 feet of rail and two buttons is MUCH better than having 3-4 feet of rail and 3 buttons, even if the two buttons are 3 feet apart.

As for unistrut? I've noticed you guys really like that stuff out on the east coast, and I'm not entirely sure why. Yes, it's great for huge projects, but some people I talked to at LDRS seemed to be under the impression that anything >10-12 lbs needed a large (1515) rail, and anything L3 sized or so needed unistrut. To be honest, unistrut is completely unnecessary until you get to several hundred pounds, and 1010 rail is fine up to 40lbs or so (believe me - I've flown a 35lb rocket several times off a 16 foot 1010 rail).
 

Handeman

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As for unistrut? I've noticed you guys really like that stuff out on the east coast, and I'm not entirely sure why. Yes, it's great for huge projects, but some people I talked to at LDRS seemed to be under the impression that anything >10-12 lbs needed a large (1515) rail, and anything L3 sized or so needed unistrut. To be honest, unistrut is completely unnecessary until you get to several hundred pounds, and 1010 rail is fine up to 40lbs or so (believe me - I've flown a 35lb rocket several times off a 16 foot 1010 rail).
I agree with you. A lot of rockets flown off unistrut would be just fine off 1515. The real issue isn't the size of the rail, it's the size of the pad. We have 1010 rail pads that only have 8ft rails and would never work with 16ft. Anything over about 20lbs would be too much for the pad even though the rail would be fine. Our general rule is over 20lbs or over a K motor, goes to the 1515 pads. Anything over 40 lbs or an M would go to the trailer with the unistrut. That isn't because of rail requirements, but the strength and structure of the pads themselves.
 

cjl

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That's a decent enough reason. The pad definitely needs to be up to the task of supporting the rocket, regardless of rail size. Here's a shot of loading my L2 rocket (4" AMRAAM, 75mm MMT, 35lbs loaded) onto a 16 foot 1020 rail - you can see the pad is much stronger than the ones typically used with 10 series rails. I believe this flight was on a full L, but I can't remember for sure which flight this image was from.

http://i27.photobucket.com/albums/c183/chris_lapanse/L2 build/IMG_9200.jpg
 

JDcluster

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what happened to the blast deflector?

That's a decent enough reason. The pad definitely needs to be up to the task of supporting the rocket, regardless of rail size. Here's a shot of loading my L2 rocket (4" AMRAAM, 75mm MMT, 35lbs loaded) onto a 16 foot 1020 rail - you can see the pad is much stronger than the ones typically used with 10 series rails. I believe this flight was on a full L, but I can't remember for sure which flight this image was from.

 

ben_ullman

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Somewhat true. The bottom rail button still allows for some guidance after the top one leaves the rail, as the rocket cannot significantly weathercock with the bottom of the rocket held to a vertical track. It's not as good as having two buttons in the rail, but believe me, having 6 feet of rail and two buttons is MUCH better than having 3-4 feet of rail and 3 buttons, even if the two buttons are 3 feet apart.

As for unistrut? I've noticed you guys really like that stuff out on the east coast, and I'm not entirely sure why. Yes, it's great for huge projects, but some people I talked to at LDRS seemed to be under the impression that anything >10-12 lbs needed a large (1515) rail, and anything L3 sized or so needed unistrut. To be honest, unistrut is completely unnecessary until you get to several hundred pounds, and 1010 rail is fine up to 40lbs or so (believe me - I've flown a 35lb rocket several times off a 16 foot 1010 rail).
To piggyback off of what handeman said, The unistrut pads at the club I fly at (MDRA) are hydraulic so it makes it way easier then trying to lift 80+lb rockets.

We also have 1515 away pads that are built plenty strong, but no 1010.

Ben
 

Handeman

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That's a decent enough reason. The pad definitely needs to be up to the task of supporting the rocket, regardless of rail size. Here's a shot of loading my L2 rocket (4" AMRAAM, 75mm MMT, 35lbs loaded) onto a 16 foot 1020 rail - you can see the pad is much stronger than the ones typically used with 10 series rails. I believe this flight was on a full L, but I can't remember for sure which flight this image was from.

http://i27.photobucket.com/albums/c183/chris_lapanse/L2 build/IMG_9200.jpg
How many hundreds of lbs does that pad weight? Looks like 1/2" plate steel with 2" x 4" steel tubing. Do you set it up every launch or does it stay in place for the season?
 

ben_ullman

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How many hundreds of lbs does that pad weight? Looks like 1/2" plate steel with 2" x 4" steel tubing. Do you set it up every launch or does it stay in place for the season?
Battleparks are made from 1010 rail themselves :p I think a full pad is like 45-50lbs maybe?

Ben
 

cjl

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How many hundreds of lbs does that pad weight? Looks like 1/2" plate steel with 2" x 4" steel tubing. Do you set it up every launch or does it stay in place for the season?
That's one of our bigger pads - we bring it to every launch (we don't have anything permanently set up), but we only set it up if people need it for a larger rocket. Usually, that means summer launches plus our large spring and fall events (Mile High Mayhem each may, and Oktoberfest each October). During the smaller fall and winter events, as well as many early spring launches, there's not enough demand to warrant dragging the larger pads out.
 
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Handeman

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Battleparks are made from 1010 rail themselves :p I think a full pad is like 45-50lbs maybe?

Ben
The 1010 pads are lucky if they're 20lbs each. Mike and I moved all ten of them and they're not heavy at all.
 

cjl

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The 1010 pads are lucky if they're 20lbs each. Mike and I moved all ten of them and they're not heavy at all.
Yeah - that pad in my pic is a LOT more than 20lbs. It does break down into several pieces for transport though, so it's not too bad.
 

powderburner

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When there isn't room for 4?

I agree with someone's earlier comments about placing two guides close together near the rear of long rockets, and placing a third somewhere up front to support and steady the rocket on the launcher. (Only I do it the low-power way, with launch lugs on a launch rod.)

While true that a single aft rail guide would theoretically allow a rocket to start turning after the fwd rail guide clears the launcher, I am not sure how bad this effect is in real life. Yes, it can happen, but long rockets have relatively greater pitch/yaw inertia and don't repond as fast to forces that might try to turn the rocket. (If it is too windy, maybe you shouldn't be launching with any number of rail guides.)
 

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