LPR Technique: Cutting Hexagonal Parachute Using Protractor and Ruler

[brockrwood]

I need a 10 inch (face to face) oarachute for a Custom Rocket Company “Sport” rocket that lost its parachute. (OK, it didn’t lose the paracute, I did.).
I don’t have a form, or another chute to trace, so I am just cutting it out of an old, plastic shopping bag from the local hardware store. I am just using a ruler, a protractor, a ball point pen, and a cutting mat. I will let you know how it turns out.
The hardest part so far is getting the faces to be exactly 120 degrees from each other.

 

[brockrwood]

There’s the center of the hexagon. Not too bad. Only off by about a 1 mm.


Now that I look at the cutting mat grid, I see it is pre-printed with useful lines at just the angles I needed. And I can see them right through the parachute. Doh!

 

[brockrwood]

Spill hole done.

 

[brockrwood]

I need a 10 inch (face to face) oarachute for a Custom Rocket Company “Sport” rocket that lost its parachute. (OK, it didn’t lose the paracute, I did.).
I don’t have a form, or another chute to trace, so I am just cutting it out of an old, plastic shopping bag from the local hardware store. I am just using a ruler, a protractor, a ball point pen, and a cutting mat. I will let you know how it turns out.
The hardest part so far is getting the faces to be exactly 120 degrees from each other.

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Rats. Hobby knife blade went askew on one side.

 

[brockrwood]

I need a 10 inch (face to face) oarachute for a Custom Rocket Company “Sport” rocket that lost its parachute. (OK, it didn’t lose the paracute, I did.).
I don’t have a form, or another chute to trace, so I am just cutting it out of an old, plastic shopping bag from the local hardware store. I am just using a ruler, a protractor, a ball point pen, and a cutting mat. I will let you know how it turns out.
The hardest part so far is getting the faces to be exactly 120 degrees from each other.

View attachment 517796
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Shroud line attachment holes cut and reinforced with clear, plastic, packaging tape. Now to cut and tie on some shroud lines…

 

[neil_w]

There’s the center of the hexagon. Not too bad. Only off by about a 1 mm.

Uh oh, I fear that everyone is going to point and laugh at the club launch.





(nice work)

 

[brockrwood]

Uh oh, I fear that everyone is going to point and laugh at the club launch.





(nice work)

I embrace the “homemade” look. The sneers of those who have never turned a plastic shopping bag into an LPR parachute mean nothing to me. ;-). In India, the culture of “make it work with what you have” is known as “jugaad”. I wholeheartedly endorse jugaad!

 

[bjphoenix]

Do you have a way to reinforce the material around those holes?

 

[neil_w]

I have only one serious comment: that parachute is... well, grass-colored. That would concern me a bit. Green seems like a non-optimal chute color.

 

[brockrwood]

Do you have a way to reinforce the material around those holes?

Little rectangles of plastic packaging tape. .

 

[brockrwood]

I have only one serious comment: that parachute is... well, grass-colored. That would concern me a bit. Green seems like a non-optimal chute color.

Dang. I didn’t think about that. I usually prefer dark colors for parachute matetials because it is easier to see against a light blue sky or white clouds.
The rocket is mostly a light yellow-green color. Maybe that will help? Or tie a fluorescent pink streamer to the shock cord?

 

[brockrwood]

First shroud line tied on. Using “size 8 needlework thread” I got at the recycled art supplies place. Not super strong, but each shroud line only needs to supply 1/6th of the strength so it should be ok. Easy to tie knots using this thread.

 

[neil_w]

Dang. I didn’t think about that. I usually prefer dark colors for parachute matetials because it is easier to see against a light blue sky or white clouds.
The rocket is mostly a light yellow-green color. Maybe that will help? Or tie a fluorescent pink streamer to the shock cord?

Your call. Anything (within reason) to improve visibility of the rocket in the air and on the ground is good.

 

[brockrwood]

Your call. Anything (within reason) to improve visibility of the rocket in the air and on the ground is good.

I was hoping the “return for reward” on the ‘chute would help. . Also, I fly rockets near a dog park. Canine rocket return service?

 

[brockrwood]

I need a 10 inch (face to face) oarachute for a Custom Rocket Company “Sport” rocket that lost its parachute. (OK, it didn’t lose the paracute, I did.).
I don’t have a form, or another chute to trace, so I am just cutting it out of an old, plastic shopping bag from the local hardware store. I am just using a ruler, a protractor, a ball point pen, and a cutting mat. I will let you know how it turns out.
The hardest part so far is getting the faces to be exactly 120 degrees from each other.

View attachment 517796
View attachment 517798
View attachment 517799
View attachment 517801

Completed parachute hooked to loop in the shock cord. I read somewhere that attaching the parachute to a loop near the top of the shock cord helps prevent tangled shroud lines. We shall see!

 

[Kelly]

There's an easier way to draw a hexagon, all you need is the compass and a straightedge. Set the compass to the distance from center to one of the points, and draw a circle. Then mark a point on the circle - that is your first vertex - and put the needle point of the compass there. Swing the compass to mark the next vertex - it will be exactly one radius away, along the circle's edge. Put the needle point on this new mark, and repeat until all six vertices are marked. Connect with a straightedge and cut along the lines. Took me longer to describe than it would to do. Easier and more accurate than a protractor.

 

[GlenP]

I usually just fold the plastic in half, then in half again to find the center point. Using the center point I told one part over at 60 deg then flip it over and fold the other part 60 deg, kind of like an S fold. Then this gets folded in half. Then I just have to make one straight cut through all the layers, or can slip around a little, but you can do it with scissors if you are careful.

https://www.rocketryforum.com/threa...apped-recycle-bin-rocket.169834/#post-2219928

 

[brockrwood]

There's an easier way to draw a hexagon, all you need is the compass and a straightedge. Set the compass to the distance from center to one of the points, and draw a circle. Then mark a point on the circle - that is your first vertex - and put the needle point of the compass there. Swing the compass to mark the next vertex - it will be exactly one radius away, along the circle's edge. Put the needle point on this new mark, and repeat until all six vertices are marked. Connect with a straightedge and cut along the lines. Took me longer to describe than it would to do. Easier and more accurate than a protractor.

Thanks! Yes, I have used the compass method. As shown here: https://www.wikihow.com/Draw-a-Hexagon

Problem: I don't have a compass at this location that has jaws wide enough to draw a circle for a 10 inch parachute. To construct a hexagon using the "draw a circle and arcs with a compass" method, you need to first draw a circle that will totally enclose the hexagon. In my case, I have to draw a circle that has a radius of 5.774 inches. So the compass has to have jaws that open up to 5.774 inches. I don't have a compass with jaws that open that wide (not at this location, anyway).

I have tried the "pencil attached to a piece of string attached to a tack" type of compass, but the string stretches and I can't get it to draw a nice, round circle. Or the tack comes loose. Or both. Frustration sets in.

Hmm. Lowe's has a document that shows how to construct a hexagon using parallel lines: https://www.lowes.com/pdf/npc/creative-ideas/pdf/2016_01/Spring-Content/Hexagon-Layout-Guide.pdf

I am going to try the Lowe's method and see if that works.

 

[brockrwood]

I usually just fold the plastic in half, then in half again to find the center point. Using the center point I told one part over at 60 deg then flip it over and fold the other part 60 deg, kind of like an S fold. Then this gets folded in half. Then I just have to make one straight cut through all the layers, or can slip around a little, but you can do it with scissors if you are careful.

https://www.rocketryforum.com/threa...apped-recycle-bin-rocket.169834/#post-2219928

Wow, that is a neato trick! I am going to try it!

 

[brockrwood]

Ah! There IS a type of compass that can draw really big circles. It is called a "beam" compass. It can be had for less than $10 on Amazon. Hello Amazon, here is my credit card number...

https://www.amazon.com/Dasco-1405-G...t=&hvlocphy=9028818&hvtargid=pla-806535151383

 

[brockrwood]

I usually just fold the plastic in half, then in half again to find the center point. Using the center point I told one part over at 60 deg then flip it over and fold the other part 60 deg, kind of like an S fold. Then this gets folded in half. Then I just have to make one straight cut through all the layers, or can slip around a little, but you can do it with scissors if you are careful.

https://www.rocketryforum.com/threa...apped-recycle-bin-rocket.169834/#post-2219928

I did something wrong. I got an octagon!

 

[GlenP]

I did something wrong. I got an octagon!

Sorry, once you find the center point from the twice folded sheet, unfold it once. Then you make the S-layer folds at 60-deg, using the center point as the reference. I just eyeball the first fold, flip it over and fold again, then make adjustments so the two folds are identical 60-deg folds. This has one fold on the top and one fold on the bottom, layered like a letter S, of the once-folded sheet.

Then you can fold that in half and make a cut at 90-deg to the opposite side of that fold.

 

[Sooner Boomer]

https://www.rocketryforum.com/threads/how-to-make-a-hexagon-for-a-parachute.59719/
https://www.rocketryforum.com/threads/how-to-make-an-octagon-for-a-parachute.59720/
or even https://www.rocketryforum.com/threads/one-more-parachute-form.60103/

Works best if you make a cardboard template then cut your parachute material using it, but will work if you can draw directly on the parachute material.

 

[lakeroadster]

I have only one serious comment: that parachute is... well, grass-colored. That would concern me a bit. Green seems like a non-optimal chute color.

Well, depending on where he launches here in Colorado... it's dryer than a popcorn fart. So it'll probably be landing on tan colored terra firma.

No worries.

 

[brockrwood]

Sorry, once you find the center point from the twice folded sheet, unfold it once. Then you make the S-layer folds at 60-deg, using the center point as the reference. I just eyeball the first fold, flip it over and fold again, then make adjustments so the two folds are identical 60-deg folds. This has one fold on the top and one fold on the bottom, layered like a letter S, of the once-folded sheet.

Then you can fold that in half and make a cut at 90-deg to the opposite side of that fold.

Thank you!

 

[GlenP]

Thank you!

Since we are folding, the better letter description of the cross section would be a Z but where the diagonal and the top and bottom folds are all the same length when flattened down on top of each other.

 

[brockrwood]

Well, depending on where he launches here in Colorado... it's dryer than a popcorn fart. So it'll probably be landing on tan colored terra firma.

No worries.

The dry conditions in summer are starting to be a real problem for us model rocketeers here on the front range in Colorado. Summer heat sets in, the fire bans get issued, and there is no place to launch. :-(. I might have to become a winter launcher. Easy to find the rocket if it has recently snowed.

 

[caveduck]

Ultra-cheat 60 second method to make a nice (even competition) LPR parachute without templates or fancy measuring: grab a point in your cleaner bag material, pull down with the other hand to make a "spike" of the desired radius. Cut off with sewing shears. You now have a reasonably decent circle with some jaggies. Trim off the jaggies with the scissors. Fold in 8ths and mark locations for 8 shroud lines (8 being considerably better than 6). Tape down fly-tying nylon shroud lines with 1-mil mylar or kapton tape. Voila, you are done.

Fast way to cut the shroud lines: cut a single piece of line 8 times the desired shroud length. Fold in half, fold in half again, then cut off both ends of the bundle. Shazaam, you now have 4 lines of exactly the same length that can be stuck down to the parachute.

 

[brockrwood]

Ultra-cheat 60 second method to make a nice (even competition) LPR parachute without templates or fancy measuring: grab a point in your cleaner bag material, pull down with the other hand to make a "spike" of the desired radius. Cut off with sewing shears. You now have a reasonably decent circle with some jaggies. Trim off the jaggies with the scissors. Fold in 8ths and mark locations for 8 shroud lines (8 being considerably better than 6). Tape down fly-tying nylon shroud lines with 1-mil mylar or kapton tape. Voila, you are done.

I always wondered about 8 versus 6 shroud lines!

 

[caveduck]

Eight seems to give more uniform deployment and reduces oscillations, though it does weigh just a bit more. The competition crowd sometimes uses 12 lines on larger chutes (30-36"). It's also a lot easier to mark 8 positions on the rim of the canopy just by folding