Largest Rocket for 1515 Rail

[AlexBruccoleri]

Hi All, Can folks comment on what they think is the largest rocket that can be safely flown on a 1515 rail using the Aero Pack style of weld nut through the air frame. I am hoping for a 100 pound rocket but it would be helpful to get some feedback on what other people have done or had issues with. Thanks, Alex

 

[Handeman]

Mounting the rail guides on the rocket is one thing. The other is how much can the pad itself handle. We have some 1515 pads we won't allow over 40 lbs. on. We have another that 100+ lbs. is OK.

Before you finish building your rocket, contact the launch site people and find out what their GSE can support.

 

[cwbullet]

Hi All, Can folks comment on what they think is the largest rocket that can be safely flown on a 1515 rail using the Aero Pack style of weld nut through the air frame. I am hoping for a 100 pound rocket but it would be helpful to get some feedback on what other people have done or had issues with. Thanks, Alex

Alex, 1515 will handle 100 pounds. We have 1515 on several of our away cell pads. They can handle 100 pounds. I hear a lot of conjecture but I have seen anyone text the limits of 1515. That being said, they will handle 100 pounds.

 

[TheTank]

I've seen them handle over 100lbs on fiberglass rockets. But I have also seen clubs stop someone from flying when the rocket was 65lbs on 1515. I'd check with the club you are looking at flying it at. The one good thing is that with a 1/4-20 weld nut installed, you can quickly and easily swap out the 1515 to Uni-strut if needed.

 

[mtnmanak]

Agree that the pad is the limiting factor (assuming you mounted the buttons on your rocket in a way that they won't rip out of the frame - especially while the rail is horizontal and the rocket wants to roll left or right...).

At URRG, for example, I would not want to fly a 100 pound rocket off the normal 1515 pads. The 1515 pads are not robust enough to handle a 100 lbs rocket safely (would be concerned a nice gust of wind on the somewhat non-flat farm dirt would push the pad over) - and when the rail is horizontal, it is likely you could damage the pad or rail when you try to load the heavy rocket. Also the rails on those pads are a bit short for a heavy rocket. For most of my big rockets, I plan for a 12 foot rail minimum and that length is unlikely to work well with an unsupported rail.

Many of the hydraulic lift trailers at clubs are perfectly good for 1515 rails. They can easily handle the weight, the rails are usually 12 feet or more, and the rail itself is backed by a metal frame that ensures your rocket doesn't whip the rail around or bend the rail when you try to load the rocket. However, if I remember correctly, the trailer URRG has at their normal launches only has a unistrut rail on it (they bring in other trailers for URRF that include 1515). If you go to MDRA Higgs launches, though, they almost always have a trailer with 1515 available.

I build my heavier rockets with the capability to switch out the buttons for 1515 or Unistrut. Not because 1515 can't handle the job, but so I can be prepared to fly whatever the club has available.

 

[AlexBruccoleri]

I've seen them handle over 100lbs on fiberglass rockets. But I have also seen clubs stop someone from flying when the rocket was 65lbs on 1515. I'd check with the club you are looking at flying it at. The one good thing is that with a 1/4-20 weld nut installed, you can quickly and easily swap out the 1515 to Uni-strut if needed.

It was my hope to use a 1/4-20 weld nut. Unfortunately the barrel diameter is .313” which exceeds the 1515 button inside diameter. If I want to go swappable I believe I need a 10-32 weld nut and the flange can fit either a 1515 or unistrut rail. This is my current plan given others have confirmed 1515 is fine for 100 pound rockets.

 

[cwbullet]

I have to agree that limitation will likely be the pas and your local rules.

 

[thzero]

Agree that the pad is the limiting factor (assuming you mounted the buttons on your rocket in a way that they won't rip out of the frame - especially while the rail is horizontal and the rocket wants to roll left or right...).


I build my heavier rockets with the capability to switch out the buttons for 1515 or Unistrut. Not because 1515 can't handle the job, but so I can be prepared to fly whatever the club has available.

Yeah I noticed the left/right roll on a 8" that I helped prep on the pad over the weekend. Was a bit concerned.

Do you have a reference to the unistrut? Quick search turned up items, but not that seemed appropriate.

 

[FredA]

I've flown 320# off of 1515.
But:
- you need to fully support the rail with some sort of spine - none of this hold at the base monkey biz.
- clearly the pad needs to accommodate the weight - while loading and upright.
- we use a 2x2 sheet of quarter-inch steel as a blast plate on the ground.

 

[mtnmanak]

It was my hope to use a 1/4-20 weld nut. Unfortunately the barrel diameter is .313” which exceeds the 1515 button inside diameter. If I want to go swappable I believe I need a 10-32 weld nut and the flange can fit either a 1515 or unistrut rail. This is my current plan given others have confirmed 1515 is fine for 100 pound rockets.

FYI - The through hole on the 1515 airfoil buttons is bigger - they easily handle a 1/4"-20 screw and may/should fit the weld nut barrel? Also, if you have a drill press, you could easily bore out the bottom portion of the through hole enough to fit the barrel of the weld nut.

I have been using Adhesive-Mount nuts from McMaster: https://www.mcmaster.com/98007A029/

I JB Weld the snot out of them on the inside plate and on top and don't even worry about getting JB Weld in the threads. I find it easier to just JB weld inside and outside, sand it flat to the body tube and drill/out re-tap the threads of the nut. It sounds more onerous than it is. For my big rockets, I even make a little JB weld platform on the outside of the body tube - makes a nice base, especially for the large round unistrut buttons.

Here is a mount on an 8" tube:

Inside:



Outside:










Unistrut Button:

Yeah I noticed the left/right roll on a 8" that I helped prep on the pad over the weekend. Was a bit concerned.

Do you have a reference to the unistrut? Quick search turned up items, but not that seemed appropriate.

The picture above is of the Unistrut button from Aerocon: https://aeroconsystems.com/cart/launch-recovery/rail-button-unistrut-style-each/


But, lately, I have been using the Unistrut air foils from SCP or Onebadhawk.

 

[Titan II]

Do you have a reference to the unistrut? Quick search turned up items, but not that seemed appropriate.

https://unistrutstore.com/1-58-meta...Er-uIEr19hajnkmtkdH_JcZV5DBi5tKwaAsszEALw_wcB


https://aeroconsystems.com/cart/launch-recovery/rail-button-unistrut-style-each/
https://www.rocketryforum.com/threads/unistrut-rail-question.90222/

 

[AlexBruccoleri]

FYI - The through hole on the 1515 airfoil buttons is bigger - they easily handle a 1/4"-20 screw and may/should fit the weld nut barrel? Also, if you have a drill press, you could easily bore out the bottom portion of the through hole enough to fit the barrel of the weld nut.

It is the barrel that is the issue. I was talking to Mike Fisher about it and the barrel of a 1/4-20 will not fit in the button. If I want to go 1/4-20, I will need to do something like your setup where the threads are flush with the airframe. It is worth noting that the weld nut design with a 10-32 such that the barrel is inside the button, might be stronger than a 1/4-20 screw going into a mount that is flush. (I am not sure on this.) A 1/4-20 weld nut going into unistrut would be even more secure, but that precludes using a 1515.

 

[AlexBruccoleri]

I've flown 320# off of 1515.
But:
- you need to fully support the rail with some sort of spine - none of this hold at the base monkey biz.
- clearly the pad needs to accommodate the weight - while loading and upright.
- we use a 2x2 sheet of quarter-inch steel as a blast plate on the ground.

Okay this example is what I was looking for.... It is worth noting that the planned rocket will weigh 40-50 pounds dry. For smaller motors I plan to just use the standard rail at local clubs. My concern is for the larger motors. I would expect the rail to be supported by a truss for that.

 

[cwbullet]

I build my heavier rockets with the capability to switch out the buttons for 1515 or Unistrut. Not because 1515 can't handle the job, but so I can be prepared to fly whatever the club has available.

That is actually a good idea.

 

[TheTank]

It was my hope to use a 1/4-20 weld nut. Unfortunately the barrel diameter is .313” which exceeds the 1515 button inside diameter. If I want to go swappable I believe I need a 10-32 weld nut and the flange can fit either a 1515 or unistrut rail. This is my current plan given others have confirmed 1515 is fine for 100 pound rockets.

gotcha. I don't typically run the weld nut up into the button but I see how that could be an issue if you do. That said, I would just counter-sink the back of the button to accept it. Plenty of meat on there when using good buttons.

 

[jsdemar]

The weight limit isn't only about the button attachment. An unsupported rail or a flimsy base attachment will cause rail-whip and an unknown liftoff direction.

I've launched 150 to 200 pound rockets off of 1515 rails. But, the rail was backed with a heavier support, such as a steel pipe or steel U-channel. Also, there were guy wires (tightened with turnbuckles) to keep the rail from whipping or tipping.

Don't forget the effect of an angled blast deflector near the nozzle. The initial blast will torque the rail & pad, causing the rail to whip and oscillate as the rocket clears the rail. Worst case is an un-backed rail with angled blast deflector attached... I've seen 45 degree tip offs. It's better to put a flat plate on the ground a good distance below the nozzle.

 

[reddrock]

As others have noted, the 1515 rail guides themselves are not the limiting factor. It's how you mount them to the rocket, how your keep the rocket from rocking on the rail, and having a good strong stiff backing to the rail.

In 2009 a 450 lb 1/3 scale X-15 was launched on a 1515 rail attached to a triangular radio tower. Takeoff went fine, unfortunately the rocket was WAY overweight and did not get enough altitude to fully deploy the chute.

But the point is the rail guides were not a problem.

 

[AlexBruccoleri]

Thanks to all for the replies. This is really helpful! Special thanks as well to @mtnmanak for the build pictures.

 

[cwbullet]

@mtnmanak Which side of the adhesive nut do you place toward the tube? Are you a big hole for thee nut? My question could be answered with a picture of the inside of the tube. ​

 

[FredA]

Except for while loading, your railbuttons don't see a lot of stress.
They are JUST GUIDANCE during ascent.
Sure, they need to hold against the side load of the wind while the rocket sits on the pad, but that's sub-20 mph.
The weight of the rocket itself should be supported by something under the rocket.

I just use T-Nuts. Installed from the back with a dab of epoxy on the rim. Trimmed not to protrude past the outer surface.

 

[mtnmanak]

@mtnmanak Which side of the adhesive nut do you place toward the tube? Are you a big hole for thee nut? My question could be answered with a picture of the inside of the tube. ​

I have been installing them with the hex nut facing outwards, through the hole.

When you place them, you have some options if you want to control how much of the nut protrudes on the outside of the body tube.

If you leave the metal plate flat, you can see that there is a lot of space between the plate and the inside of the body tube and the nut is well below the outer edge of the body tube:



I like to gently bend a curve in the metal plate using a vice:



If you bend only slightly, you can get it so the nut is flush with the outside of the tube and then you can fill in the inside with a big mess of JB weld to secure it all in place. Usually, I like to bend it so the plate is flush against the inside of the tube:, but this means the nut protrudes quite a bit on the outside of the tube. Since I build up a little platform with JB Weld, I don't mind. Either way, you can dial in how much you want the nut to protrude:



Then, JB weld as in the photos in the previous thread.

I have not tried it with the nut on the inside, but it may be worth it to give it a shot. It would keep the outside of the body tube flat. I have a couple projects in the works, I may try it on my next build.

It should also be noted that these things come in all kinds of shapes and sizes, so you can use them on smaller rockets too. Here are the ones I keep on hand for a variety of rocket sizes:



From left-to-right, you have:

• 1/4"-20 x 1-1/2" plate
• 1/4"-20 x 29/32" plate
• #10-32 x 1-1/2" plate
• #8-32 x 1-1/2" plate
• #8-32 x 29/32" plate