What side for rail when launching on angle

[CrazyDiamond]

Hey Fellas,

Quick question that I can't seem to find an answer to anywhere. Is there a particular side the rail/rocket should be on when using an angled launch (such as wind adjustment).
So if launching on an angle, should the rail be above/beside/under the rocket, relative to the Earth, and why? Does it make a significant difference?

Hope that made sense! Thanks

 

[mikec]

Interesting question. I always let the rocket hang (rail above) but I'm not sure how much it matters. https://nar.org/member-only-reports/rd/NARAM-61/N61-Simulation-Testing-Rail-Launchers-Flanigan.pdf didn't look at the top, just bottom and side configurations and the side was clearly worse, but he was looking at it in the context of wind loading.

 

[heada]

I've never heard of a rule/suggestion before. For me, I load onto the rail and tilt so that the rocket is resting on the rail (above I guess?) My theory is that the rail buttons aren't designed to take the full load of the rocket, only guide it. SO if the rocket needs to be supported I'd rather the weight be taken by the rail and not the rail buttons.

 

[neil_w]

I've never heard of a rule/suggestion before. For me, I load onto the rail and tilt so that the rocket is resting on the rail (above I guess?) My theory is that the rail buttons aren't designed to take the full load of the rocket, only guide it. SO if the rocket needs to be supported I'd rather the weight be taken by the rail and not the rail buttons.

I would think that, at a typical launch angle, the buttons would only be taking a very small fraction of the weight of the rocket (sine of the rail angle, or whatever). Either above or below seems OK to me, maybe above is slightly better. Would definitely avoid side.

 

[blackbrandt]

Personally, I always let it hang from underneath. On top feels like it would put more torque on the rail button installation and it just makes my warm fuzzies feel better on the bottom side.

 

[CrazyDiamond]

How is this not something that someone has already science'd to death?

Added a poll!

I would think that, at a typical launch angle, the buttons would only be taking a very small fraction of the weight of the rocket (sine of the rail angle, or whatever). Either above or below seems OK to me, maybe above is slightly better. Would definitely avoid side.

Above as in the rail above or rocket?

 

[mikec]

How is this not something that someone has already science'd to death?

I think there are a lot of unknown variations in how the rail guides fit in the rail that would be hard to analyze. If you're a NAR member, you should look at the NARAM link I included above.

When the rocket is hanging, it's a stable configuration. If it's on top of the rail, it has a tendency to tip sideways with the slop in the rail guides/buttons.

 

[neil_w]

Above as in the rail above or rocket?

I was thinking rocket above but @mikec has me thinking that maybe rocket below is better because it's a stable configuration.

 

[UhClem]

For small angles it should matter almost not at all. For some value of small which is probably something less than the 20 degree maximum but more than the recommended 5 degrees away from flight line.

Unless your buttons are located far away from the CG and CP in which case the forces will be greater.

 

[GlueckAuf]

When I first slide the rocket onto the rail, if the rocket's on top of the rail, the wear inflicted on the buttons will be primarily to their inboard surface. No matter how worn thin that inner flange may become, the rocket is still not going to break loose from the rail, as the outboard flange, the screw, and the air frame will still hold it to the rail, albeit loosely.

When sliding the rocket on the rail while it hangs from it by the buttons, the wear inflicted is mostly, if not exclusively, against the buttons' outboard flange. If this half wears too thin and fails, the rocket could indeed break loose from the rail upon launch and cause untold havoc.

When the rocket launches, it's anyone's guess which flange might receive the most wear, as there are far more variables in play than gravity alone, including the button/air frame alignment, rail angle, thrust vector, launcher deflection, etc.

Of course, one should regularly inspect the buttons and replace them long before they become dangerously worn. But that's my rationale for preferring the rocket to lay on the rail rather than hang from it. In the great scheme of things, it probably matters little which way the rocket is racked--so long as it's not leaning off the side of the rail whether hanging or laying.