Shearing Rail Buttons...on purpose

[G_T]

IIRC Nylon properties depend on temperature and moisture. https://www.toray.jp/plastics/en/amilan/technical/images/ami_tec_002.gif To my mind that would make Nylon a poor choice of material for the job. I would think a frangible fuse bolt or something similar would be better.

Also IIRC, didn't NASA do this with some sounding rocket or other? I forget where I ran across this but it isn't new to shear the lugs at the top of a rail.

Gerald

 

[beeblebrox]

What about having a flyaway button just below the fins, it would not hit them. Just need to figure out a way to hold it on, small notch or holes for pins on the flyaway part. And a retractable button above the motor where there is room for it to fit... Just trying to think along the wall of the box...lol, not outside the box or inside the box... In that grey area...my brain hurts now.

 

[retortec]

How about a cutter on the top of the rail? That way you could still have a button capable of launch and cross wind loads. Max velocity at the end of the rail hopefully would provide enough stability.

 

[Sabrina]

Does anyone have any experience shearing rail buttons off on purpose? I was thinking using nylon machine screws to hold them to my rocket and then two hose clamps at the top of the rail to remove the rail buttons.

I would score the nylon machine screws at the rail buttons/airframe joint so they would snap off easier.

I've seen fly away guides, but have also seen them doink fins when coming off and I don't want that to happen.

Rocket is 104" tall, 3" diameter, N1100.

Edward

I have seen the fly-away guides at Midwest power- used on some flights I assisted with... So this topic got me thinking... if you want to shear the buttons - nylon is probably a good choice

... you must be concerned about drag ... so how high can an N1100 fly anyway??? So I took a look at the Tripoli Altitude records... 41,000+ ft. Oh My!

That made me start thinking even more... where are you gonna fly this thing???

There are pictures on the Tripoli records page (you know I like pictures, right ) - So I totally swiped some pictures from the records page ( at least I'm an honest thief )

This is a photo of Greg Morgans rocket (photo credit: Scott Yow) flown in July 2018 on an N1100 to 41,042'. Looks like it launched from a tower... I can see why you don't want to build a tower... where are you flying this again??? Maybe someone at that launch has a tower you could use??? - just a thought... -just one more question, are you really planning to fly the N1100 in a 3" rocket, or is that just a typo?

 

[DaveW6DPS]

Why not just use a tower?

 

[cbrarick]

So, it's baaack!

I think if you're really interested in doing this I'd talk to the club and get permission.

My personal opinion is that cutting rail buttons is a very bad idea. Bring it to my club and you'll be hauling a pad very, very far away. I'm not saying I absolutely wouldn't launch it, but you'd have to prove the pad is far enough away that in "cruise missile" flight - eg your cutter making it go parallel to the ground and directly towards the flight line, won't actually get to the flight line. Depending on the motor you might want binoculars in order to see the launch......

towers, fly away devices, tube launchers all proven technology and not dependent on shearing something at the top of the rail which may affect the physics of the flight....

JMHO take it for what it's worth, or ignore it completely

 

[BLH]

I have been watching this thread and also agree its a sketchy idea on many levels... Its going to be hugely variable, not really gain that much (energy will be lost during cutting, maybe allot), and many questions that could have bad results.

IE: Once first button is cut off, is there anyway possible it can jam the second button causing big problems? Also it seems "cutter" will have to be close to rocket and rockets get a little rattley going up rails so I wouldn't put very nice paint on the rocket as it seems very possible that one could "cut" a big strip of paint off the side of the rocket and maybe some body tube material. That will kill altitude.

 

[cerving]

I always thought that an interesting idea would be to have some kind of spring-loaded retractable rail buttons... of course it wouldn't work for a MD project, which is most likely where you care the most about rail button drag.

 

[AlphaHybrids]

If you've read this thread you'll see that I'm look for this at alternatives for a tower. A tower is a large piece of specialized equipment and rails are ubiquitous. I'm just testing to see if this can be an alternative. I also fully expected the negative reaction of 'THIS IS THE END OF ROCKETRY AS WE KNOW IT'.

For those that haven't read the thread, the rocket is 3' diameter, N1100 motor, 104" tall and the velocity at the end of a 16-foot rail is 125 feet per second. Also, you'd see I'm just not pursuing this blindly, but I'm actually going through quite a bit of testing to quantify when the buttons shear, how they shear and what kind of forces they resist in different planes.

I've seen fly away guides cripple a rocket before and don't want to take the chance with this flight profile. For a regular 4" rocket, 4FNC, J/K motor, I'd use fly away guides hands down, if I didn't want buttons on the rocket.

For the last of the box of set screws I went the opposite way on the next tests. I was able to find a place where I could cobble together almost 30 feet of 1515 rail vertically for drop testing. I used 2.5" PVC that was 6 foot long and made the total weight 30 pounds, what my rocket will most likely come in at. Math says somewhere near 40 ft/s at the end of the drop. The first time I totally blanked on cushioning the fall and it hit the concrete and shattered the PVC and lead balls went all over the place. D'oh!

After that mishap I placed some cardboard boxes with pillows inside and the 'airframe' fared much better. No problems shearing the buttons, came off very cleanly as the buttons stacked up. It does tend to add small flat spots to the buttons. I haven't had a lot of time lately to pursue further testing, but I do have another two boxes of set screws on order. I just need to find the time to give this method a proper write up.

Edward

 

[gwh]

Sounds like a great application for 3D printed parts, PLA filament in particular.
Hobby grade 3D printing is quite weak in shear planes parallel to the print bed - the layer to layer adhesion is the weakest part. I find PLA has pretty poor ductility as well, a knife edge impacting that weak plane should make really short work of it. Really easy to test and iterate on.

 

[Cnorm]

This is the end of rocketry as we know it!

 

[mbeels]

I always thought that an interesting idea would be to have some kind of spring-loaded retractable rail buttons... of course it wouldn't work for a MD project, which is most likely where you care the most about rail button drag.

Or similarly, what about a pop-out fairing? Not as good as a retractable rail button, but maybe compatible with MD.

 

[OverTheTop]

For those that haven't read the thread, the rocket is 3' diameter,

3' or 3" ?