My launch tower design

[BobO]

I’ve started giving some design thought to my home-made launch rig.

The cyan colored outer rings are to be 1/8” thickness steel plate bent into 12 segments with 150 degree bends. This allows me to tack bolts to each of the flat faces so that a threaded rod will always be centered on the assembly whether using 3 or 4 fin rockets. Plus the segmented surfaces will be easier for me to make than a round will be. The internal diameter will be 16”. The 1/8” plate will provide good rigidity and is easier to weld to, for me. The upper ring will have eyelets for guy-wire attachment.

The yellow support rods are ¾” square aluminum tube stock and will be bolted to the steel rings with thumb screws. At this point I’m thinking a 60” height.

The green “rocket bars” are ½” square aluminum tube stock and will be mounted via a threaded rod assembly to the outer ring. This should allow for leveling and diameter adjustment. Would round stock be better here, the contact area of the square to the rocket is higher, but not significantly?

The things not shown are;
1. Steel base plate / blast shield, I want to use a ¼” aluminum plate for rigidity and hold-down with a thin steel blast shield for the area of direct heating.
2. A sliding standoff for the rocket to set elevation on each of the “rocket bars”.

The whole thing should be easy to assemble and disassemble for transport. I believe the 16” diameter would be suitable up to 6” diameter rockets, or should I up the size on that for future expansion. I probably need to have spike holes in the base plate to prevent sliding, do I need more ballast at the bottom end.?

Edit- I just noticed an error in my drawing, the bottom ring will be several inches up off the base plate.

 

[BobO]

Here's what I'm thinking for the rocket bar adjuster. The bottom of the vertical bars will sit on the base plate so I'm not worried about vertical load with this assembly.

 

[BobO]

Here is a detail at the base

 

[MarkII]

The tower launchers that I have seen are not disassembled in between launches. The entire thing is transported and set up as a single unit.

 

[troj]

Your design would definitely work; it's similar to the tower Giant Leap sells, but because of the top ring, a bit stiffer.

At the same time, rings limit fin and rocket sizes, so there's a trade-off.

That said, the flexibility and stiffness is great. But it comes at the expense of having to adjust numerous nuts and try to get them all relatively even. It's doable; I've done it -- the tower I use is adjusted that way. It can just get a bit annoying.

That's why I'm interested in the Versa-Tower, or a version thereof, that's in the other thread -- no nuts to adjust.

-Kevin

 

[Micromeister]

I believe your going to need some sort of stake & cables or outrigger braces to secure the tower in the vertical position. Otherwise you will have major troblems on light breeze days. Long skinny things just don't like to stand alone on uneven ground with winds blowing from one direction. 16" diameter base is not a very wide stance for anything outdoors even only 5 feet tall.
An easy way to figure "turnover pressure" is to use 15 to 25 psf (Pound per Square foot) against your tower structure & contents mulitplied by the average wind speed encounted at your launch site. You'll soon see it doesn't take a lot of area to tip heavily based loaded things

I've used adjustment systems sort of like your discribing off and on for many years. Over time you'll learn this type set up is a real PITA to work with.

Since your looking at rockets up to 6" in diamater I'm not sure 5 feet is even close to being long enough rails. I'm using 36" on my competition Tower, I'd go at least 72" for a sport MPR/HRP type tower, 8foot sound like more the norm.

heres a similar rail adjustment system I use on MICRO models Up to BT-50 in dia. Note the spring tension and thumbnut adjustments. These are STILL a PITA to get right, taking a lot of time to check for binding.
Hope this helps a little.

PS: Mark-II is correct most competition and sport flying towers do not disassemble for transport. most are either fold-up (like mine) or strapped on top of the car or trailer.

 

[BobO]

Being able to dissassemble is more for being able to store it at home.

I have always assumed there will be 3 guy-wires. The overturning moment on a tall slender apparatus would be difficult to compensate for otherwise. I'm not certain however, if sliding at the base is a concern when the top is fixed against rotation?

I wonder if there is some sort of sliding bar clamp arrangement that could be used for adjustment?

 

[MarkII]

Being able to dissassemble is more for being able to store it at home.

Yeah, that might be necessary for a larger tower. The towers that I have seen were for LPRs and competition rockets. Some had their own tripod legs, but others were simply clamped onto the launch rods on the regular pads. (One member of our club has the lightweight aluminum launch tower that BMS used to sell, and that version has a truly slick design.) I wonder if it would be feasible, and sufficiently stable, to design yours to be bolted onto the rail of a regular HP pad? It could be installed and removed as needed, and wouldn't need to have its own base.

The LPR/competition towers that I have seen were something like 8"-10" in diameter and 48" tall. The club member with the all-aluminum BMS tower just carries it fully assembled in the back seat of his car. I've picked it up and it only seems to weight a few ounces.

 

[BobO]

Based on my quick calcs, the base diameter would have to be 3 feet to resist overturning in a 20mph wind, more if it were a tripod arrangement. I could reduce the surface area some to reduce the wind load, but that would the MOI which may be counterproductive. I don't know about the rails, I'd have to know the structural properties of a section to calc it.

 

[Micromeister]

Yeah, that might be necessary for a larger tower. The towers that I have seen were for LPRs and competition rockets. Some had their own tripod legs, but others were simply clamped onto the launch rods on the regular pads. (One member of our club has the lightweight aluminum launch tower that BMS used to sell, and that version has a truly slick design.) I wonder if it would be feasible, and sufficiently stable, to design yours to be bolted onto the rail of a regular HP pad? It could be installed and removed as needed, and wouldn't need to have its own base.

The LPR/competition towers that I have seen were something like 8"-10" in diameter and 48" tall. The club member with the all-aluminum BMS tower just carries it fully assembled in the back seat of his car. I've picked it up and it only seems to weight a few ounces.

Unfortunately the Apogee Tower that BMS used to sell suffered from the same basic design flaw that the Old Versa tower and others had.
That is a lack of positive parallel alignment of the launch rails supports or frame.
Apogee/BMS towers thin .080" folded aluminum "gold anodized" attachment frame was easily bent out of adjustment by use, or just by carring around. The Old Versa towers thin band PVC (1-1/2" or 2" if memory serves) support rings, glued to a single upright allowed the heat of the day to warp the rings causing binding in the adjustable rails. These conditions can only be solved with use of some form of permanent vertical attachment at the 1/4 points to maintain proper alignment of the internal adjustable guide rails. Once the two main support rings, triangles or what-have-you are secure and stable, then an adjustable guide rail system can be attached and shimmmed that will retain its adjustment indefinitely as long as the unit is not badly abused.

Base slip while the upper portion is cabled to the ground is not an issue at all. We use this method to erect freestanding 20foot flag poles with simple 3 point rope attachment anchors at the 6 foot above grade with the ropes spread approx. 6 feet. This is a Great use of the taut-line hitch adjustable knot which has kept these flag poles with 3 flag flying erect in 40mph and higher gust windy weather days.

 

[MarkII]

Unfortunately the Apogee Tower that BMS used to sell suffered from the same basic design flaw that the Old Versa tower and others had.
That is a lack of positive parallel alignment of the launch rails supports or frame.
Apogee/BMS towers thin .080" folded aluminum "gold anodized" attachment frame was easily bent out of adjustment by use, or just by carring around.

Oh, so it was an Apogee product, then? I don't know anything about those issues and I'm not even that familiar with all of the details of its construction. He has had it for a number of years and I have even used it a few times during our meets. It seems to have held up quite well. What I liked about it was that the guides could be adjusted without loosening up and retightening anything. The adjustments are made by pushing the guides up or down or back and forth by hand. The pivots were loose enough to allow this without much force, and yet they had enough friction to hold that adjustment subsequently. I thought that was pretty cool. The vertical guides are mounted on horizontal pivot arms that swing up and down in an arc. The arc brings them closer together or farther apart. (I think that there are three pivot arms, located at the top, middle and bottom of each guide.) The pivot arms also allow the guides to be tilted to fine tune the parallel alignment if necessary. Adjustment is made by sliding the rocket down until it is about halfway along the rails, and then pivoting each rail in or out (by pulling it up or down) until it just contacts the airframe. The guides then simply remain in place with no wingnuts to retighten. You then slide the rocket up and down the tower a couple of times to check for alignment and make any other fine adjustments that might be necessary. I really like the fact that the adjustments can be made entirely with one hand while you hold the rocket in various places along the path of travel with the other. This was why I was so taken by it.

 

[MarkII]

Another member's version that I have used at club launches is a home-built unit that consists of a long, sturdy triangular wooden crate-like frame wooden beam and a pair of wooden triangles, with aluminum tubes mounted inside on long horizontal carriage bolts (or maybe they are all-thread) that extend out through horizontal cross members that are mounted in between the stanchions on the outer frame through the sides of the triangles, which are horizontally mounted at the top and bottom of a vertical wooden beam and offset a short distance from it by small blocks. The threads are bolted to one side of the tubes on one end and are held in place by a pair of wing nuts, one on each side of the support, on the other end. They extend through the supports sides of each triangle and beyond for a few inches. Adjustment is made by loosening the wing nuts, sliding the bolts in or out horizontally, and then retightening the nuts. As with the first one, this tower is affixed to an existing launch pad which provides the stable base for it. The frame is constructed largely out of 1x1 hardwood members with 1x2 for the cross members The tower is built with 1x3 or 1x4 hardwood planks for the two triangles and what appears to be a 2x4 for the beam. It is bull strong and massive, a good deal heavier than the all-aluminum tower, yet it too can be carried by hand and bolted onto the pad. The frame is put together with deck screws bolted together and glued, so there is no dismantling it between launches.

Mounting the tubes midway between the stanchions between each corner of the triangles provides more room for the fins without requiring a very large diameter frame. Each fin points toward a corner of the triangle made by the frame. For 4-finned rockets, he built a similar tower with a square frame pair of squares mounted on a beam.

The mount that attaches the tower to the pad includes a bolt on one of the middle cross members. By unhooking the tower's lower attachment, the entire frame can be pivoted on this bolt to a horizontal orientation parallel to the ground. This makes it easier to load a rocket into the tower.

 

[Micromeister]

Yeap! I agree the swing arm adjustable guide rails are without doubt very desireable.

My Competition tower has exactly that type 2 point pivot system with 6 rails so I can choose just about any fin configuration I choose. 3, 4 and 6 fin models are a snap. By adding Stainless Wingnuts to the adjustment pivot points each rail can be locked in postion or left a touch loose for those Odd-shaped birds. Not sure if the wingnuts are visable in the views below but you should be able to pick up the swing arms and channel rails.

Mark the wooden triangular frame towers are a NOVAAR invention from back in the dark ages LOL! The plan for this tower is available through NARTS, and on the NAR website or was. Somewhere I have a couple pic of one from the early 80's out at a Scout Expo in Manassas, Va. They are indeed very sturdy while remaining fairly light weight. Novaars version usually stood on the ground with a couple wire U-loop stakes holding it in place over the outer wooden triangluar framework. I seem to recall one of the Novaar guys telling me they were 4'-0" long but I could be mistaken?

I've never really liked attaching a tower to a single suspended point as it puts unnecessary stress on one side of the tower that can cause binding and/or heat warping during the days use. That's precisely way I chose a Tripod leg arangement for my tower. the legs give me complete azmuth adjustability without adding undue stress to any critical component of the rail support system. If needed each leg has a hole the will except a 1/4" dia stake that are stored in the vertical capped tube along with a 8' - 16/2 microclip extension for short lead launch systems or racks.
I think the last upgrades I did to my tower was the addition of 1/4" round Teflon facing rods to each channel rail to reduce contact surface & drag. and a drop-down adjustable height Piston mounting bracket that doubles as a blast deflector base for the 6" x 6" x 16ga deflector plate.

 

[MarkII]

I liked the wood frame design because it makes it quite simple to build without requiring a hunt for large diameter pipe to make the outer rings. I think that I could build it without looking at any design plans. The fact that it is nearly indestructible is another good point. Each one of our launch pads consists of a steel fence post driven into the ground; I'm sure you know the type. They are topped by adjustable rod holders. The blast deflectors are just flat steel plates that slide onto the rods. The crate-style tower just clamps onto the fence post, which provides a very stable support. Perhaps I wasn't clear about the attachment; it is attached in two places to the post. To rotate it (similar to lowering a rail) for loading, the lower clamp is temporarily released which allows the entire frame to rotate into a horizontal position. I don't know very many of the finer details of the design, so if there is a way to adjust the tower for windage, I don't know how it is accomplished.

Our range consists of 3 such pads, plus a Mantis pad nearby for mid-power launches that require a 1/4" rod.

 

[MarkII]

Yesterday I found some photos on my club's Yahoo group that showed a small part of the tower that I described in post #12 above. I was relying on memories of some brief experiences with it during launches that were held months ago when I wrote that. The photos don't show much, but they do show that I got a few things right about the tower design and a whole host of things wrong about it in my write-up. So I've gone back and corrected some major errors in my previous post.

 

[Ez2cDave]

Yeah, I know it's an old thread . . .

 

[Ez2cDave]

Last One . . .

Dave Fitch

 

[powderburner]

That looks very nice, clean, sturdy, and useful!
What does that thing weigh (by itself) and did you find some sort of special heavy-duty tripod for that mount?

And can you say what material you made those green rings from? (Are those slices of a giant PVC pipe?)

 

[[POW]Eagle159]

I’ve started giving some design thought to my home-made launch rig.

The cyan colored outer rings are to be 1/8” thickness steel plate bent into 12 segments with 150 degree bends. This allows me to tack bolts to each of the flat faces so that a threaded rod will always be centered on the assembly whether using 3 or 4 fin rockets. Plus the segmented surfaces will be easier for me to make than a round will be. The internal diameter will be 16”. The 1/8” plate will provide good rigidity and is easier to weld to, for me. The upper ring will have eyelets for guy-wire attachment.

The yellow support rods are ¾” square aluminum tube stock and will be bolted to the steel rings with thumb screws. At this point I’m thinking a 60” height.

The green “rocket bars” are ½” square aluminum tube stock and will be mounted via a threaded rod assembly to the outer ring. This should allow for leveling and diameter adjustment. Would round stock be better here, the contact area of the square to the rocket is higher, but not significantly?

The things not shown are;
1. Steel base plate / blast shield, I want to use a ¼” aluminum plate for rigidity and hold-down with a thin steel blast shield for the area of direct heating.
2. A sliding standoff for the rocket to set elevation on each of the “rocket bars”.

The whole thing should be easy to assemble and disassemble for transport. I believe the 16” diameter would be suitable up to 6” diameter rockets, or should I up the size on that for future expansion. I probably need to have spike holes in the base plate to prevent sliding, do I need more ballast at the bottom end.?

Edit- I just noticed an error in my drawing, the bottom ring will be several inches up off the base plate.

Just a quick question for me... why do you need the yellow support rods and cyan rings. It looks like that they aren't really doin' any thing

BUT don't ask me..... I have only heard about them....:eyeroll:

 

[Ez2cDave]

That looks very nice, clean, sturdy, and useful!
What does that thing weigh (by itself) and did you find some sort of special heavy-duty tripod for that mount?

And can you say what material you made those green rings from? (Are those slices of a giant PVC pipe?)

Sorry for the L-O-N-G delay in this reply . . .

(1) It is a large, commercial tripod that I had lying around.

(2) The rings are 9" diameter thick-walled PVC . . . Holes were cut with a "doorknob hole-saw" to help lighten things up.

(3) The Tower, by itself, weighs near 9.5 lb

I have additional 9" dia PVC and PVC up to 12" dia if anyone is looking to buy some !

 

[steveh.jae]

Last One . . .

Dave Fitch

View attachment 55553

 

[steveh.jae]

Hey Dave, any update on the TIAMR electronic version yet?