Swing Project - Engineering Advice Needed
 

So the kids want a tree swing. None of the trees on our property have an outward branch, fit to hang a swing from. The style of swing is the classic, single-seat, wood bench with rope on either side. My plan is to stretch a line between two trees and hang the swing from that. We'd like to keep it natural looking, so trying to avoid cable or straps. I was thinking about using a 1" diameter hemp rope (or similar style) wrapped/looped around each trunk, and secured with knots (bowline, taught line hitch, timber hitch, etc.). I was even thiking about doubling the line between the trees (two passes of rope) and using U-bolts to keep them joined together. The U-bolts could also double as stops to keep the swing ropes from sliding along the horizontal line, between the two trees. I'll alo be sure the tree trunks are protected from chaffing.

Here are some pics of the trees in question. Additionally, here is a napkin sketch of the plan. Both trees have a branch that I could utilize as a vertical stop for the rope. I will also be sure to check the forward and rearward travel distace of the swing, to ensure there's clearence...don't want anyone to hit the fence!

An additional requirement: this needs to support the weight of teenagers and adults.

So what say you? Will this work? I'm trying to keep it simple. I thought about running a beam between the two trees, but that might be overkill. I want it to be safe, but not over-engineered or overly complex. My one concern is even with a taught line, how much sag will there be on the center of the line, with weight on the swing?
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Also, to help reduce friction on the horizontal line, maybe can employ some carabiners on the ends of the swing ropes...

without doing the math.

no it wont work. two things. it will be a B to get that horizontal line tight enough. and when you pull down from the center, you add force to that horizontal line exponentially.

extreme (magic) example..if a truck was stuck in the mud..you could feasibly get a long enough strap..lonnnggg...like miles long. assume zero stretch in this magic strap. tie the end to something rigid..hike the many miles to the exact center length..grab that strap and pull it off to the side and you could pull out that stuck truck. i remember this problem in school when we were solving vectors.

Math? Aw man, nobody told me there'd be math...:D

You know, in looking at my first picture, that one limb might be strong enough...

just for fun.

how far apart are the trees and how much does your heaviest kid weigh :D ??

i think i have my old math book around here somewhere.

As a redneck engineer who didn't go to NCSU, I'd rig a good thick chain between the trunks above the branches....use an O-ring or nut through the links to take out slack....one run across. Take pics ;)

Yeah, that's why in that crappy napkin drawing I had the smaller tree staked to the ground to help oppose any bending forces. But "X'd" it out...

HHHMMM, chain! Yeah I know it goes against the "natural" requirement (women :rolleyes:), but might have to use something like that

Camo paint ;)

So, now re-thinking how to employ a beam...

Seriously, why not try a taught chain....easy to rig up. If one end comes loose, I didn't study law at Duke either....so this ain't legal advice ;)

this was way more interesting than what i am doing at work.

i just did a free-body diagram.

assuming the trees are 10 feet apart. and a kid weighs 50lbs. pulling down in the middle, when that rope displaces 3" (assuming no stretch - like a chain). you are pulling one tree to the side 1000lbs.

(unless i forgot how to do vortex problems...but i think it is just a similar triangles thing)

Sorry, I meant to respond. Yes, trees are 10' apart and assume an adult of 190lbs (I might want to have a go).

LOLz! And I haven't stayed at a Holiday Inn...

Why not just put the rope from one branch to one side of the swing and then the other side to the other tree? That way the force vector is not horizontal between the trees but angled to the swing/ground and you won't snap the rope/pull the beam out when the wind blows the trees around.

Why not this (in yellow)?

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Interesting. Is that what flipper35 was getting at?

that would make holding on to the chains odd feeling no? not bad of an idea tho..

how tall are those anchor points. ?

You could put a chain/rope across 4' above the seat to pull them together to hold onto easier.

Yes, that pic is what I was getting at.

The anchor points are about 18' up. And I was trying to obtain a very natural (that word again) swinging motion.

So now, we're thinking about cutting and using one of those smaller trees in the left corner to use as a horizontal beam.

this changes everything. this would work.

hey flipper i think we are hiring!! wanna job? :D

I think you could go with your original idea with a big thick rope across the span. A few loops around each trunk (above the small branch nook) and cinched good & tight in some fashion...Cliff can engineer the knot :)

So I'd have to make the swing ropes extra long so that when I pulled them together, I'd end up with the correct final length.

This just looks bad:
https://www.etsy.com/listing/467203899/swing-hanging-kithanging-a-swings?gpla=1&gao=1&utm_campaign=shopping_us_WoodS wings_sfc_osa&utm_medium=cpc&utm_source=google&utm _custom1=0&utm_content=5432904&gclid=Cj0KCQjw1-fVBRC3ARIsAIifYOO002ij7a6tO3upkK7hyyA3SLBkrEjE9QnF S0Fec3SC6rpTD7DMVR4aAogiEALw_wcB
https://img.etsystatic.com/il/73f481....jpg?version=1

You need something rigid between the trees. It will take a lot of Viagra to make that rope work.

I'm an IT Business Analyst and Product Owner! I have used this cartoon in more PowerPoint presos than I care to admit! LOL!

Not an engineer here, but a mechanical mind none the less. Wouldn'there be two different pivot points (one a few feet above the riders head, and another at the knots on the tree 18' off the ground) on the swing above, which might make the swinging experience a little awkward ? It would just seem to be a two-stage swing that might give a not so smooth effect ?

That is EXACTLY the image I thought of when I opened this thread!

A piece of pipe spanning the trees would work better. I'll let Cliff determine the size of the pipe needed. Then either drill it for some eyelets or weld some on at the desired spacing

A pipe would solve the sagging/sideways tension, while you could still run the rope through the pipe to attach to the tree trunks in a loop. Screw on a round floor base flange to each side to lessen the damage to the tree, and tie a rope through the flange holes tightly.

A pipe is an excellent idea! I had not considered that!

You could also run 5/16" wire rope between the trees using Crosby clamps to secure it to itself once looped around the branches. Fit a rubber sleeve over the wire rope where it contacts the branches to prevent it from digging into the wood. Tension as necessary, and use (2) additional Crosbys on either side of each swing rope(total of (4) to keep the swing centered on the cable, use oversized washers between the swing hangers and Crosby to allow smooth movement, and use a carabineer to attach swing rope to wire rope.

Yes, I think "crosby clamp" is what I was really thinking when I said "U-bolt". Thank you for the correction.

OMG, I'm an engineer, and you guys are way over thinking this. Tie a rope to each tree, a tire in the middle, and let the kids have fun. If you really want a classic swing, connect a 4x4 to both trees and attach swing to it.

How much of a hill is there? It's best to swing out over the hill.

Or tie a cable to a tree on the hill about 10' high, other end to the house or a lower tree, and attach a pulley to a T handle.

Again, those trees are going to move a great deal when there is wind so any beam or pipe attachment will have to account for that movement.

Personally I would do a zip line also.

Wrapping anything around the trunk or a branch may, in time, kill the tree or the branch.... aka "girdling" (the tree's vascular system runs just inside the layer of bark). I might consider this, instead. Boring through the trunk of a tree will not kill the tree. It would be easy to try and you'd know quickly whether the tree could withstand the forces of unfettered swinging.

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