Tower Launcher Design

[GrossApproximator]

Hi all. I think that most tower launchers guide the rocket by constraining the body tube with a few guides. Are there any tower launchers that guide the rocket by constraining the fins, or can such a tower launcher be built? It seems to me that if the rocket is guided by its fins during flight, then it should be possible to guide the rocket by its fins in a tower launcher.

 

[BLKKROW]

Hi all. I think that most tower launchers guide the rocket by constraining the body tube with a few guides. Are there any tower launchers that guide the rocket by constraining the fins, or can such a tower launcher be built? It seems to me that if the rocket is guided by its fins during flight, then it should be possible to guide the rocket by its fins in a tower launcher.

It could certainly be done. But I think it is going to be more difficult. Think about it, all you need to three struts running up to keep when using the body. But if you use 3 fins you need 6 struts on on each fin, or 4 fins would be even more.

Plus if you build a tower with the fins being guided that could cause a lot of issues, especially with the torque of the body if it pushes or prefers the push in a different direction other then vertical it could tear one or all the fins off. I don't know if that makes sense.

 

[Neuport]

I don't think it would be stable. If the rocket tips at all it would abrade or possibly shred the fins and there is a good chance the rocket would come out of the tower other than vertical. When it is sitting on the pad any wind or other tipping force would create a large moment on the fins.

However, I have considered adding a c-channel to a conventional tower to capture one fin to make sure the rocket doesn't rotate such that a fin would catch on the upper support structure. This would allow a larger rocket to be safely launched from a tower with for example a triangular frame.

 

[Frozenferrari]

Yeah I dont think that would work very well either.
Think about these things -
1. Everybody's fillets on every rocket arent all exactly the same
2. You could still wiggle the nose with that kind of design. As soon as the motor lights its gonna wiggle around like crazy. It will come out of that tower anything but straight. And it will also tear the crap outta your rocket on takeoff.

during high speed flight, you have the air passing over the body itself helping keep that nose from wiggling around, and at high speeds the fins are effect. Sitting on the ground at 0-30mph the fins dont do much. So why would trying to mechanically force them into action be any different?

Very interesting concept tho.

 

[GrossApproximator]

I didn't have much faith in the idea of guiding a rocket by its fins, but I'm trying to figure out how to guide a rocket that has many fins. 10, 11, or 12 fins spaced around a rocket don't leave much room for typical guidance methods like rods or rails, but, then again, perhaps I will realize that a conventional launching method will work once I actually build the rocket. Maybe a sufficiently large rail-guide standoff will work.

 

[Neuport]

If you have that many fins, there probably is not a performance reason for elliminating a couple of rail buttons or lugs.

How about a sabot on the rocket and launch it out of a tube? That would be cool! Maybe a foam cylinder with a diameter a little bigger than the fin span and cored to the BT diameter. Split the cylinder in half lengthwise. To load you put the halves together around the rocket and then slide the assembly into the launch tube which is a nice slip fit with the cylinder. On launch, when the rocket clears the tube the sabot falls away. You might need to experiment with a polyethylene skin on the cylinder so it slips easily in the tube. You might also want to segment the cylinder into more pieces so they are lighter/smaller and have less interference with the rocket.

 

[MClark]

I have a video of a minimum diameter on a Kosdon 38mm fast J coming out of a tube like you discribe. I was going to post it but it is 30 meg
We had some bowling ball rockets launched out of tubes

Mark

 

[MClark]

Here it is
https://www.ahpra.org/OBrienJ.mpg

 

[GrossApproximator]

Here it is
https://www.ahpra.org/OBrienJ.mpg

Awesome video!

 

[GrossApproximator]

If you have that many fins, there probably is not a performance reason for elliminating a couple of rail buttons or lugs.

Yes, I would like to use lugs or rail buttons, although that tube launcher in MClark's video is pretty cool, and I wouldn't mind having one for myself! It's just that I don't know if a rocket with 10-12 fins would fit over a launch rail. A launch rod would be easy enough for small rockets, but what if I wanted a larger (i.e. MPR) rocket with 10-12 fins? Then I would want to use rail buttons, and the fins on the rocket may interfere with the cross-section of the rail.