New 24 foot rail, comments please

My 21 foot Mean Machine needs a long rail, not always available at launches. I also like long burn motors and low and slow flights that I can see. These also could use a very long rail to reach stable speeds.
I designed a rail using 20 feet of aluminum antenna tower and 24 feet 15-15 with a 10-10 that could attach to it.
I showed it to my son, a mechanical engineer, for comment and he tweaked it a little, then a lot, then redesigned it from scratch. This is what he came up with.

The legs are all adjustable with telescoping tubing for uneven ground. There are pads for stakes at the 3 center posts and the leg ends. The 15-15 rails are attached to the tower with shaft collars welded to plates that bolt to the 80-20. A 10-10 rail would have 80-20 brackets to slide on and bolt to the 15-15. The blast plate also has welded collars to attach to the tower but is removable. I can put a winch on the back leg to raise the tower.

After removing the top half of the tower and rail, and blast plate, the rest folds up for transport in one piece. It has wheels at the bottom and middle to roll onto the trailer. It still weighs over 100 pounds so I'm not sure I like that part. The legs may need to be removable instead.
Here are links to his PDF files. Both are too large to post directly.
The second is a 3D PDF that can be zoomed, rotated and taken apart.

https://www.dropbox.com/s/soqws1sdozjn8cd/Launch Tower - Set up.PDF

https://www.dropbox.com/s/nqnkdycpjelwait/Launch Tower 3D- Set up.PDF

I would appreciate any comments, suggestions, warnings etc before we start building it.
Thanks
Dan Schwartz

Some general comments:

• avoid loose parts (which always seem to escape)
• rocket exhaust is corrosive
• if you fly in the desert, the playa dust is corrosive
• precise joints are a bad idea, since they will often not fit in the field
• every extra pound of weight will feel like 10 out in 100° heat

We set up a super-nice 30' rail out at Black Rock a couple of weekends ago. It was beautifully designed, but after only two seasons, things were already starting to rust and not fit properly. Not to mention, hauling heavy steel pieces around in the desert is no fun.

I don't know if I'll ever make it to Black Rock, but the parts will certainly be painted, cleaned and oiled as needed after launches. The legs are removable with a single pin, almost 20# each so the wheeled part would be about 60. Still heavy but to launch a big rocket, I think that's what it has to be. It would be hard for one person to set up but with a little help, it should be OK. All the joints have enough play that they should not be a problem.

What do you think of the overall design, structure, anything that needs to be added?
How heavy a rocket do you think it would support?
Thanks

24 feet is a lot of rail; I'm not sure I've ever seen anyone use something quite that long.

Depending on your definition of "big" projects, you may find that this design makes it very difficult to get the rocket vertical. Take all the weight of the tower itself, plus the rail, and add a 60 pound rocket to it. Now, try to push it up to vertical. Even with a group of helpers, it's difficult as people run out of ability to reach and help push before the rocket gets vertical.

You also want some way of keeping it from coming down hard when it reaches the point where gravity starts to pull it to vertical.

Finally, those long legs will prove to be an issue unless you're always launching on pretty darned flat ground. You want something shorter, or you'll find they're an absolute pain to get level. You also want adjustments on two of them, or you need to bring blocks to put under one, to help level the pad.

-Kevin (who has flown a few in the 250+ range)

I see you are from Illinois, where do you intend to launch this?

LDRS which was held at Bong has several large projects flown, one was a 22ft tall 2-stage. There were 3 pads there, capable of very big rockets, obviously cause several were flown.

Rather than build, I would explore the "where am I flying it" avenue first, contact the clubs and see if a pad will be available . If it's for MWP, I'm sure one will be there. Same for ThunderStruck.

There are at least 4 pads in the Quad cities club [QCRS} area I know of capable of this project.

There is a hand crank winch under it to help pull it up. Most of the weight is in the base and legs, only the antenna tower is aluminum-20 feet is 20# - plus the 15-15, and the rocket which is close to the pivot, to lift. I hadn't thought of the last drop to vertical from gravity - have to consider that.
All three legs are adjustable with telescoping tubing and pins on the upper arm of the leg.

I flew the 21 foot mean machine on the 20 foot tower at LDRS. I'm planning on going to Airfest and they said the longest 15-15 rail was 12 feet - not long enough for my mean machine.
My intent was for enabling rockets that otherwise have borderline thrust to weight, especially with some long burn motors, some AMW have low initial thrust. some flights are just low and slow. With 24 feet of rail, they can achieve a stable flight speed. This will give people a lot more options in motor choice.
Same with very tall rockets - my mean machine rail guides are 5 feet apart.
I'm not planning on 100# plus rockets, though I'd like opinions on what this rail would support. If I bring it to a launch, someone will ask how big a rocket can they put on it.

Thanks for all the comments. I will start building soon and post pics of the actual pad

I believe Dan does fly with QCRS as well as showing up at Thunderstruck.

I was at Dan's house and saw these piece parts. Any one piece of aluminum strut isn't too heavy but all together over 100 lbs, wow...

I guess my suggestion would be to get rid of the legs all together. Large size rails are usually trailer mounted, and for good reason, they are heavy. Maybe your son could get work up a trailer mount using a readily available frame (e.g., https://www.northerntool.com/shop/tools/product_200612543_200612543, or https://www.harborfreight.com/1720-...duty-utility-trailer-48-in-x-96-in-69897.html). You would then just have to add stabilization legs on each corner of the trailer--typically just a rod/pipe with foot that you can drop down to ground level and tighten in place.

Tim,
Only the antenna tower and rail is aluminum. The base and legs are all steel tubing. We considered a trailer mount, but at some fields you can't drive off the road. I've been in corn fields, soybean fields, cotton fields and it seems, most were muddy. We decided on the mounted wheels and if it won't roll in the mud, it can be at least partly disassembled and carried by a couple of young guys.

pythonrock said:

There is a hand crank winch under it to help pull it up.

Click to expand...

Winches don't work well as rockets get heavier and being near a cable that's under tension from 200+ pounds of rocket is downright scary.

Been there, done that, didn't like it. If the cable lets go for some reason it's not going to be pretty.

Putting the pivot point higher up on the tower helps significantly. Having it at the bottom makes life difficult for heavier rockets.

-Kevin

The pivot is at 30 inches above ground, so the rail is about 40 inches above ground to slide on the rocket. The bottom of the rocket should be about a foot or so below the pivot point, about 15 in. above the ground, when upright. I don't think I could make the pivot much higher without making it difficult to load the rocket on the rail.
With the lever arm from the pivot, there will be significant tension on the winch cable, though I'm not planning on any rockets over about 70-80 pounds. This winch previously loaded a 800 plus pound "battlebot" arena onto a trailer, (which was pretty scary to me) so I think it can handle it OK and there is a steel bar at the base of the tower to attach the cable.

Oh, and Tim, I have the Harbor Freight 4 x 8" folding trailer. That's the one that carries the battlebot arena, and that I'm using to go to launches.

Please look at this thread. https://www.rocketryforum.com/showthread.php?65458-Large-High-Power-Launch-Pads

There are several good design features presented here. The aluminum launcher described in the thread would easily launch the rocket you are planning for. It is based on this design https://www.jcrocket.com/prorailbase.shtml and is totally scalable. It can be made from aluminum or steel box tubing or from 1010 or 1515 based extrusions (you might use 3030 versions of the 1010 or 1515 systems or for really large launchers 4545 elements).

Vertical posts that are 4' high make it easy to mount the rocket to the beam and permit a high pivot point for a 60 harbor freight electric winch. URRG has 2 similar units in steel with a rigid T-base and they have demonstrated lifting a 160 test human and have launched many L3 rockets larger than yours.

Whatever unit you make should be able to use 10/10, 1515 or unistrut rails in the 20-25' range.

Bob

Bob,
Actually that thread is a shortcut on my desktop. How long a rail can go on that pad?
I started with 80/20 extrusions, but for the strength they needed to be larger and got very expensive. Also, I couldn't see the hundreds of tnuts and bolts for a design that would be as stable as I wanted. I could have done large aluminum tubing, still expensive and it seemed, not all that much lighter.

The vertical posts on this one are 30" and with the antenna tower and rail mounted, the top is at just about 40 inches. If I raise the pivot, the rail will be to high to comfortably slide the rocket.

The hand winch will need alitle more cranking force to start but with a little lift at the top, it will certainly not be too dificult. As I said, I wasn't planning 200# rockets, If they do start getting very heavy, I may switch to eletric winch, but that needs a big battery- more weight to carry and I worry about the speed and overshoot. We have also added a simple elastic system to hold the tower as it passes top so there is no sudden drop at the end.

One of the main considerations for the design was to make it very solid. Many of the recent videos, some with long threads attached, regarding "rod whip" actually seem to show the whole pad rocking back and forth, almost bouncing from recoil of the legs not the rod bending or "whipping" at all. I think the antenna tower will keep the rail from bending. I know, I have some unsupported rail at the top, which I might have to cut off if that seems to be a problem. I plan to have cross stakes at each center post and the end of each 8 foot leg. I don't think this pad will rock like those videos.

This pad is certainly more complicated than many others,( partly my sons fault- see first post ) and I have never built one before. I've always had a problem doing things the usual way though, obviously that way usually works very well. I also tend to get carried away and overbuild. I may have to wait till it's in the field to see if it works any better or is just heavier.

How have people dealt with that gravity drop at the end mentioned above, when using an antenna tower? Has it been a problem?

Thank you all for your comments so far.

pythonrock said:

One of the main considerations for the design was to make it very solid. Many of the recent videos, some with long threads attached, regarding "rod whip" actually seem to show the whole pad rocking back and forth, almost bouncing from recoil of the legs not the rod bending or "whipping" at all. I think the antenna tower will keep the rail from bending. I know, I have some unsupported rail at the top, which I might have to cut off if that seems to be a problem.

Click to expand...

Dan,

You shouldn't have to cut it off -- just stiffen it up a bit. It appears that your diagram shows that top part of the rail to extend about 5 feet beyond the tower (24'-20'+1' (appears slight offset at bottom)) - which I *would* try to reinforce a bit -- see this post over on Wilson's tower project:

https://www.rocketryforum.com/showt...t-A-Build-Thread-of-sorts&p=725808#post725808

(get your son to read it over, too)

This is a real simple problem to solve -- just 'truss it up' a bit. (I use 'truss' deliberately -- as one fundamental principle of structural design is "Triangles are good" - look at all those roof trusses you see in houses under construction - all those triangles in the large electrical transmission towers, etc. etc. Structural engineers are a frugal lot (as are their clients) and they don't do *anything* if it is wasteful or inefficient - and the truss is one of the most *efficient* structural shapes there is - and that is why you see it used everywhere - and the basis of that is the triangle).

You can prove this for yourself really simply with 4 soda straws and 4 toothpicks. Make a square frame by punching through the ends of the straws with the toothpicks (connecting two adjacent struts with a toothpick). Square it up and then try to deflect it sideways (in its own plane) --- it will take almost no force at all to deflect that square into a rhombus. Now, take one side of this square out and reconnect the remaining to make a triangle frame - try to deflect this one (again, *in the plane of the frame*). Pretty amazing, huh? That is the principle of the truss.

That's why your tower is triangular, too. All you have to do to extend that structural efficiency to the rail at the top is simply provide two struts up to near the top of the rail -- about a foot down from the tip down to the two 'back' chords of the tower - just some simple 1/2" stainless tubing (I used some from McMaster - something like 0.030" wall thickness). Get your alignment correct and then crush the ends of the tubing in a vise (a little touch up grinding to round the sharp edges) and then drill a hole thru these flattened ends - to bolt to the tower chords and the back side of the rail. (You can see an example from my tower in the above-referenced thread - post #19 - look close at the top of the first picture). You will be surprised at just what a little bit of triangulation will do to the stiffness of that rail - and maybe $35 worth of parts -- see:

https://www.mcmaster.com/#standard-stainless-steel-hollow-tubing/=ta76b8

If you want to test the concept out before committing funds, find two old broom handles, drill some holes to align (this might be easier to bolt these to each *side* of the rail, instead of the back side) -- a cheap way to gain an appreciation of the power of trussing.

==========

Only other comments on your tower would be to make those wheels as big as you can - big wheels roll easy and negotiate rough terrain better (even some 20" bicycle wheels, if the design could accommodate it).

From what I could tell, it appears the outstanding legs are hinged and demount through pins - assume this would allow folding up the legs to stow beside the tower (some anchorage there?) and then just wheel the whole thing back to the trailer.

-- john.

jcato
I know about trusses and that's a good idea that I hadn't thought of. The wheels - bigger is better. I'll see how these work, they already hang over the back of the trailer. If I have to go bigger, I may make them double wide and I think I can fit a little bigger.

The legs are hinged with a pin that is offset enough that they fold without detaching them. The concern with that is the weight. Removing one pin from the bottom and one at the telescoping section will remove the legs to carry separately if it's just too heavy all together. I only have to remove the top half of the antenna tower and rail to fit the trailer. I hope, it's still being built. Probably put my rocket on it to test Mon. or Tues.

I don't remember following that tower build, wish I did before I started this one, there's some good ideas there. That is one of the videos I was talking about above. That one does look like both flexing and rocking of the whole pad. Since the rocket went straight, how much of that flex etc was while the rocket was still on the rail, how much a rebound or bounce of the whole pad after it left the rail? It certainly didn't "whip" the rocket before it left.

Thanks

[YOUTUBE]YAVpn8QNgw0[/YOUTUBE]

This video shows a 120 pound M-impulse rocket launching from an URRG Coker style pad at URRF 1 - 2013.

At various time in the video, you will see a 350 pound O-impulse class trailer mounted hydraulic tower on the left, the loaded manual 150 pound N-impulse class Coker style pad in the center, and a large 100 pound M-impulse class "Weasel" pad on the right. Since URRF 1 both the hydraulic tower and Coker style pad have been total rebuilt and reconfigured. The trailer and the hydraulics on the tower launcher has been totally rebuilt and stiffened to allow for 400+ pound P-impulse class rockets, and an electric cable winch has been added to the Coker pad along with new bushings to eliminate joint movement to permit 200+ pound O-impulse rockets.

[YOUTUBE]e-zFF07ySYk[/YOUTUBE]

This video shows a ~300 pound 16' x 12" rocket with an O-impulse rocket launch of the unimproved URRG trailer mounted hydraulic tower at URRF 1 - 2013.

I really don't think you need a tower launcher for your rocket as the weight and thrust is not going to generate any significant whip with a 1515 rail mounted on a 2"-3" square beam Coker type launcher. 1515 rail is very stiff even without backing.

Bob

heres how I made mine its a 15 x 15 1/2 in steel plate that the legs bolt on and the tower or launch rod adapter are held by a 1/2 pin and the tower is pivoted up. I built mine 10 + yrs ago and its going to make its 4th trip to BALLS and has been at all Plaster Blaster Launches. it s flown a 400 lb + X-15, a 10x mars lander. and multiple M clusters, most of the big launches at Plaster have been off my pad, and several P motors also. built it simple and durable, only thing Ive had to replace has been the rocket stand-offs from the P motor blasts. its color coded so that when people borrow it they can put it together. I can assemble the whole 20 ft tower and 22 ft of 15 15 rail in about a 1/2 hr by myself. people have tried to suggest other things to me about what might work but this things a battleship, I also use up to a 1in launch rod that I have for my 14 ft tall Dart

So..
Finished building the pad yesterday, still not painted and left it at 20 feet for now. Will probably go to 24 with trusses as jcato suggested but didn't have time. Leaving today for Airfest.
Legs are pretensioned, so center actually doesn't touch the ground, but will stake center and leg ends.
Standing on the tower - it didn't budge at all.
Sets up in 20 minutes but does take 2 people because of weight and size. Putting it on the trailer is the hardest part.
Still a few tweaks planned - need to improve winch and attachment, mechanism to prevent drop at end of raising tower, add top 4 ft, clean up and paint...

Yeah.. way overbuilt for my rockets so far, but who knows in the future, and anybody can use it at the launches for a low and slow, or low initial thrust etc. flight.

I do like how the rocket sits low to the ground on your tower. Many designs have the rocket so high that prep becomes difficult.

This was a really fun build and worked beautifully. Can't wait to see how it handles the launch.

I need to give credit --- My son designed it and did virtually all the machining and a coworker of his, Gene, did all the welding.
They did a great job.!

I like the super wide footprint. Should help out with stability. Now, are the legs adjustable to account for uneven ground?

Adrian

jd2cylman said:

I like the super wide footprint. Should help out with stability. Now, are the legs adjustable to account for uneven ground?

Adrian

Click to expand...

The legs fold from completely vertical as shown in the photo of it on the trailer, to 15 deg (22") below the horizontal. It's hard to see in these photos but when set up the center frame is actually off the ground by a bit over an inch putting all the weight on the legs and adding to the stability. During setup the tower was initially leaning back a few degrees, we pulled the clevis pin and extended the leg down a bit and it was level.

Be sure to post video... I want to see something launch off it...