Level-3 high-performance design and build thread

Adrian, I saw a demo flight of an AT M770 this past weekend. It was in a 75/7680 case. Pretty cool.

Tony

tfish said:

Adrian, I saw a demo flight of an AT M770 this past weekend. It was in a 75/7680 case. Pretty cool.

Tony

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Interesting. Do you have a link with more information on it?
Google is coming up empty.

Thanks.

Adrian, McMaster Carr sells a machine screw that has a self locking nylon patch on it that might work well for securing the avbay to the motor closure.
https://www.mcmaster.com/#machine-screw-fasteners/=e4yhvk
Regards,
Charles

op: Can't wait. Make sure you film the launch in Hi-Def video.

I don't. I did see a thrust curve of it. It looked similar to the M650. Normally they demo motors and release them the following season. You could contact karl at Aerotech.

Tony

tfish said:

I don't. I did see a thrust curve of it. It looked similar to the M650. Normally they demo motors and release them the following season. You could contact karl at Aerotech.

Tony

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Reading up a bit on the M650's construction, I would guess that the M770 would be a moonburner like the M650 but with 6 grains glued together instead of 5. If so, the impulse should be about 7150 Ns, similar but a bit smaller than the CTI M840, which has 7521 Ns with a similar burn profile. The CTI M840 was just certified this spring and there don't appear to be any flight reports using it on this forum. Anyone flown it yet? Maybe someone at LDRS?

Edit: More motor research:

The old M record by Curt Von Delius was set with a KBA M1450, using a case that's 40" long. The CTI 2020 has a bit more impulse and it's 36" long. Only downside of the M2020 for records are that it has about 20% shorter burn time, so top speed heating would be slightly worse. It also has a bit larger base diameter of 3.125 because of the thrust ring integrated into the case, compared to the flush case (if you don't use an external snap ring) of the 75-7600 Animal/KBA case.

Other comparisons to Curt's rocket, from the Rocketry Planet article announcing his record: His rocket weighed 4.5 lbs empty. I think this one will come in between 3-4 lbs. His rocket's length was about 60", vs. about 58" planned so far. From the pictures, it looks like he used a conical nosecone, and I'm planning significantly larger fins than he used.

I picked up the motor case from the post office today (Thanks, Kevin!), and I'm glad I have one in person to get a better feel for the size and the mass of the thing. It's a beast, it seems like it weighs about twice the 4.5 lbs that my shipping scale is telling me. Enough so that I checked the calibration with some reference masses. I get the feeling that anything I don't build strong is going to be crushed by this thing. It was fun doing some show-and-tell with friends at work.

I have some fiberglass tubing on the way for the rocket internal structures. There's some 3" OD FWFG from Giant Leap that I'll check out when it gets here. I've also been shopping around for some odd-sized fiberglass tubing for the version of the design that would have a reduced diameter for the av-bay so that a nosecone shoulder could sit all the way down onto the end of the motor. I came across a nice deal for a sampler pack of telescoping fiberglass pieces that could work well if they turn out to be strong enough: https://www.mgs4u.com/fiberglass-tube-rod.htm This company makes fiberglass masts for radios and flagpoles. Their sampler pack has every possible size in 1/4" increments, and it all nests inside each other to make it perfect for pistons. Cheap, too. It might be an inexpensive source for 38mm FG tubing, if you don't mind 1/8" wall thickness.

In case you're wondering why I don't just use metal or CF tube for that, it's all about RF transparency. I really want rocket telemetry and GPS reception before apogee as well as on the way down.

As I play with the geometry of the front end closure, and try to figure out the best place to support the electronics and everything else, it occurs to me that round may not be the best answer. I may want to make my av-bay a square prism with a 3" dia donut-shaped flange on the bottom. Then I could bolt the electronics directly onto the interior sides. Hmmm...

Adrian A said:

I've also been shopping around for some odd-sized fiberglass tubing for the version of the design that would have a reduced diameter for the av-bay so that a nosecone shoulder could sit all the way down onto the end of the motor. I came across a nice deal for a sampler pack of telescoping fiberglass pieces that could work well if they turn out to be strong enough: https://www.mgs4u.com/fiberglass-tube-rod.htm This company makes fiberglass masts for radios and flagpoles. Their sampler pack has every possible size in 1/4" increments, and it all nests inside each other to make it perfect for pistons. Cheap, too. It might be an inexpensive source for 38mm FG tubing, if you don't mind 1/8" wall thickness.

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The biggest challenge is that tubes for these purposes tend to be pretty thick walled, so it'll take up a lot of space.

Since you're using it internally, the lack of a smooth exterior won't be an issue.

BTW, if timing works, I don't mind loaning you the case for the flight, as well.

-Kevin

Adrian A said:

https://www.mgs4u.com/fiberglass-tube-rod.htm This company makes fiberglass masts for radios and flagpoles. Their sampler pack has every possible size in 1/4" increments, and it all nests inside each other to make it perfect for pistons. Cheap, too. It might be an inexpensive source for 38mm FG tubing, if you don't mind 1/8" wall thickness.

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Let me know if a 38mm motor fits inside of this tubing. $21.00 for 8' of this tubing is outstanding, assuming it's strong enough, to make a nice hefty 38mm minimum diameter that I have been contemplating.

troj said:

The biggest challenge is that tubes for these purposes tend to be pretty thick walled, so it'll take up a lot of space.

Since you're using it internally, the lack of a smooth exterior won't be an issue.

BTW, if timing works, I don't mind loaning you the case for the flight, as well.

-Kevin

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Thanks a lot, Kevin. The flight will be at BALLS next year if enough things go right. Have you thought about buying a 75mm 6G-XL case? :duck:

patelldp said:

Let me know if a 38mm motor fits inside of this tubing. $21.00 for 8' of this tubing is outstanding, assuming it's strong enough, to make a nice hefty 38mm minimum diameter that I have been contemplating.

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I'll let you guys know when I get it.

Adrian A said:

Thanks a lot, Kevin. The flight will be at BALLS next year if enough things go right. Have you thought about buying a 75mm 6G-XL case? :duck:

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BALLS next year shouldn't be a problem. As for the 6XL, no, I haven't, but that doesn't mean it won't happen.

Those things (6XL) were like gold at LDRS this year

-Kevin

Adrian A said:

Thanks a lot, Kevin. The flight will be at BALLS next year if enough things go right. Have you thought about buying a 75mm 6G-XL case? :duck:

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I have one of those if you want to borrow it...

cjl said:

I have one of those if you want to borrow it...

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Thanks, I may take you up on that. Looking at the CTI hardware dimension drawing, I'm wondering if there was a mistake on the 6GXL dimension "A". All of the other increments from one case size to another are 5.33", but that one is 5.83. There is a 0.5" thrust ring at the bottom that's not supposed to be included in dimension A, but does add to the length a person would naturally measure.

I believe that is a mistake, since the spacer for 6xl to 6 is the same as the spacer for any other case in the Pro75 line.

It may be that the 6XL grain is longer than the other grains. I don't know; that's a question to ask CTI, to verify.

-Kevin

troj said:

It may be that the 6XL grain is longer than the other grains. I don't know; that's a question to ask CTI, to verify.

-Kevin

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It can't be though, since a 6xl case with a standard spacer fits a 6g load.

cjl said:

It can't be though, since a 6xl case with a standard spacer fits a 6g load.

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unless there is an allowable play?

ClayD said:

unless there is an allowable play?

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If Chris has his case handy, he could measure it to answer the question. I bet the full motor case length is 40.46", and not 40.96".

I did some chute calculations. I looked up my old build thread on my first 38mm scratch carbon rocket, because it had a nice long descent from which to measure the descent rate for my existing chute, and even the mass and dimensions:

https://www.rocketryplanet.com/forums/showthread.php?t=2808&page=11&highlight=I600

From there I calculated that the chute has a Cd (based on the chute opening area) of 1.7. If I were to use the same chute, I'm calculating that an 8 lb descent mass would have a 41 foot/second descent rate, which is more than I want, even for the soft ground of the playa.

The chute I have is made from a single sheet of 1.3 oz ripstop nylon, turned into a nearly hemispherical shape by starting with a large circle of fabric and cutting curved wedges from the perimeter and sewing them closed. I used a hot knife to cut the edges, so I don't need any hems. The result is a nice hemispherical chute that packs about as small as possible. In this case, it's a 35" chute that packs into a 3" long section of 38mm tube.

I ordered a couple of yards of the same day-glow yellow fabric, which has a 60" width. If I start with a circle of that full width, I calculate that my 8 lb mass would come down in about 24 feet/second. The canopy area ratio is just under 3x compared to what I have now, so I estimate that I would need 9" of 38mm chute holder to accommodate it. That's a bit more than I had planned, but I think I can still fit that.

Looking at it the other way, with that size chute coming down fast, it would open with 322 lbs of force at 150 feet/second. That would be a 40 G chute opening event. I think I'd like to do some research to find out what speed other drogueless descents reach. If 150 feet/second is about right for the speed at main chute opening, then that would put about 40 lbs on each of the 8 bridle lines if it were all even. So for some margin I think I'll want my bridle lines (and chute attachments) to be able to handle at least 100 lbs, each. The braided polyester masonry line I usually use may not be up to the task.

Adrian A said:

If Chris has his case handy, he could measure it to answer the question. I bet the full motor case length is 40.46", and not 40.96".

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I highly doubt there'd be 1/2" of play.

I ordered a couple of yards of the same day-glow yellow fabric, which has a 60" width. If I start with a circle of that full width, I calculate that my 8 lb mass would come down in about 24 feet/second. The canopy area ratio is just under 3x compared to what I have now, so I estimate that I would need 9" of 38mm chute holder to accommodate it. That's a bit more than I had planned, but I think I can still fit that.

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Packing technique may help on that; it all depends on how tightly you're getting them, today.

Looking at it the other way, with that size chute coming down fast, it would open with 322 lbs of force at 150 feet/second. That would be a 40 G chute opening event. I think I'd like to do some research to find out what speed other drogueless descents reach. If 150 feet/second is about right for the speed at main chute opening, then that would put about 40 lbs on each of the 8 bridle lines if it were all even. So for some margin I think I'll want my bridle lines (and chute attachments) to be able to handle at least 100 lbs, each. The braided polyester masonry line I usually use may not be up to the task.

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Take a look at Paragear for various line options.

Something else to consider is whether or not the stitching on the seams of the parachute can handle the opening shock, as well.

-Kevin

Adrian,

If you switch to 1.1 oz calendared ripstop you can pack a lot into a little area. I've got some very nice line that rips out at just over 25# per shroud line with a 3:1 safety factor. I packed a 60" toroid into just under 5" of space in 2.5" tubing. This included double chute protectors and 16 lines that were 72" long each.

Edward

AlphaHybrids said:

Adrian,

If you switch to 1.1 oz calendared ripstop you can pack a lot into a little area. I've got some very nice line that rips out at just over 25# per shroud line with a 3:1 safety factor. I packed a 60" toroid into just under 5" of space in 2.5" tubing. This included double chute protectors and 16 lines that were 72" long each.

Edward

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The fabric that I got is here: https://www.rockywoods.com/Fabrics-...cs/1-3oz-Silicone-Coated-Ripstop-Nylon-Fabric

I have tried several types of cloth, and if I remember correctly, this is my favorite type, very low friction and virtually impossible to crease. I got some 0.75 oz spinnaker sailcloth from a kite-making website once, and it seemed so creaseable and likely to para-wad that I didn't dare try to make a real parachute out of it.

What does calandering do for the fabric?

So your line breaks at 75 lbs? Today I broke some of my usual shroud line with about half my weight, which is around there. I also came across remains of a chute that showed that the chute fabric failed well before the shroud line did. I think I should consider using more, rather than stronger, shroud lines to increase strength. Of all of the extras that pro chute manufacturers add on to strengthen their chutes, (hems, taped seams, etc) I wonder which ones are most effective. I would imagine that sewing the shroud lines a longer distance along the canopy would be one of the more efficient ways to add strength.

Adrian A said:

The fabric that I got is here: https://www.rockywoods.com/Fabrics-...cs/1-3oz-Silicone-Coated-Ripstop-Nylon-Fabric

I have tried several types of cloth, and if I remember correctly, this is my favorite type, very low friction and virtually impossible to crease. I got some 0.75 oz spinnaker sailcloth from a kite-making website once, and it seemed so creaseable and likely to para-wad that I didn't dare try to make a real parachute out of it.

What does calandering do for the fabric?

So your line breaks at 75 lbs? Today I broke some of my usual shroud line with about half my weight, which is around there. I also came across remains of a chute that showed that the chute fabric failed well before the shroud line did. I think I should consider using more, rather than stronger, shroud lines to increase strength. Of all of the extras that pro chute manufacturers add on to strengthen their chutes, (hems, taped seams, etc) I wonder which ones are most effective. I would imagine that sewing the shroud lines a longer distance along the canopy would be one of the more efficient ways to add strength.

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Adrian,

Calender or calendering -- A finishing step where the cloth is subject to heat and pressure to improve bias stability. (ref: https://www.dimension-polyant.com/en/Aktuelles_Tipps_Glossar.php)

I don't know, if it were me (and it isn't, but I'll state it anyway), I would not be worrying about the parachute. You have enough other variables and challenges. I would take my specs and go to Julie Blehm at Spherachutes who already make some of the most compact packing designs and welcomes custom work and see if she could do something for you in a thin-mil fabric like Top Flight uses.

-Tim

Adrian A said:

The fabric that I got is here: https://www.rockywoods.com/Fabrics-...cs/1-3oz-Silicone-Coated-Ripstop-Nylon-Fabric

I have tried several types of cloth, and if I remember correctly, this is my favorite type, very low friction and virtually impossible to crease. I got some 0.75 oz spinnaker sailcloth from a kite-making website once, and it seemed so creaseable and likely to para-wad that I didn't dare try to make a real parachute out of it.

Click to expand...

Silicone-coated fabric tends to be more bulky than calendered.

What does calandering do for the fabric?

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It's a process where the fabric is run through hot rollers, which in the case of nylon, makes it zero porosity. So, a parachute made from calendered ZP fabric has a higher Cd than a parachute made from an identical weight standard fabric. And because it's not a coating, it adds neither weight nor bulk.

Now, I will tell you one downside -- it's slicker than snot, and takes a little more practice to work with. It sounds like a trash bag when you rustle it. Great stuff for what you're trying to accomplish.

Of all of the extras that pro chute manufacturers add on to strengthen their chutes, (hems, taped seams, etc) I wonder which ones are most effective. I would imagine that sewing the shroud lines a longer distance along the canopy would be one of the more efficient ways to add strength.

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Run the lines up the seams and sew them on there. Most high-quality chutes have the lines running up and over the apex of the canopy. Some of the smaller ones use tape over the top of the canopy, but sew 12" or so of line onto the canopy.

-Kevin

Kevin is spot on, the 1.1 oz calendered stuff I have is very slick and harder to sew but when you need performance it is definitely worth it. I have some of that 1.3 and it is very bulky. You'll notice in the bottom that the fabric started out as 1.3 oz and then the nominal weight is 1.95 oz finished, meaning there is .65oz of coating on the fabric.


I agree with Kevin - 12" of shroud line is plenty sewn into the seams. I had one of my parachutes deploy when the rocket was returning ballistic and it was unharmed - zippered the rocket really bad and then drug it across the plains from the wind, but the chute stayed intact.



I have some of the calendared stuff if you want some - I have pink and black.

Edward

dixontj93060 said:

I don't know, if it were me (and it isn't, but I'll state it anyway), I would not be worrying about the parachute. You have enough other variables and challenges. I would take my specs and go to Julie Blehm at Spherachutes who already make some of the most compact packing designs and welcomes custom work and see if she could do something for you in a thin-mil fabric like Top Flight uses.

-Tim

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This is very reasonable advice, but I'm a little crazy, and maybe I'm applying my smaller rocket experience where I shouldn't. In the smaller chutes, the construction method I have used results in much smaller packing volume than any commercial chute I have seen. For example, the 35" chute I keep talking about has a packed volume of 5.2 cubic inches. The equivalent Spherachute packed volume is 13.5 cubic inches, according to the dimensions on their site. It could be that they're using techniques and materials that are more appropriate for larger chutes than what I have been doing, so I need to be careful here. But I have over a year before the cert flight, so I have some time to test things out.

The chute packed volume is a major design driver for this rocket, so I will need to design it starting from the inside and work my way out like I have done for my other record attempt rockets.

Adrian A said:

This is very reasonable advice, but I'm a little crazy, and maybe I'm applying my smaller rocket experience where I shouldn't. In the smaller chutes, the construction method I have used results in much smaller packing volume than any commercial chute I have seen. For example, the 35" chute I keep talking about has a packed volume of 5.2 cubic inches. The equivalent Spherachute packed volume is 13.5 cubic inches, according to the dimensions on their site. It could be that they're using techniques and materials that are more appropriate for larger chutes than what I have been doing, so I need to be careful here. But I have over a year before the cert flight, so I have some time to test things out.

The chute packed volume is a major design driver for this rocket, so I will need to design it starting from the inside and work my way out like I have done for my other record attempt rockets.

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Fair enough. I just think if you didn't want to worry about it and had the specs, Julie could get the job done for you.

The chute design is following a trend for me on this build thread. I started out planning to use almost all off-the shelf parts, including the nosecone and tube. I was going to make a scratch-built chute holder/av-bay and make my own fins, but that was about it.

Now the more I look into it, the more customization I want to do. I did some research last night on basalt fibers as an alternative to fiberglass for the nosecone, and did some design on the layup I would use for scratch airframe tubes. Now it's looking like this will probably be about as scratch of a build as it's possible to do. I'm not really sure I want to commit that much time to this project, but as long as the inspiration and motivation are there, I'll keep doing what I enjoy doing, which is design optimization.

Adrian,

Have you considered the pull-down toroidal chute (Iris I think) made by Fruity Chutes? The CD is phenomenal, 2.2!! It looks as though you could use a chute with less material which means less weight and smaller packed space. They don't list a small version of their chute on the website, but Gene Engelgau is a member of the forum, and he might be willing to work with you to get you what you need.

G.D.

troj said:

Run the lines up the seams and sew them on there. Most high-quality chutes have the lines running up and over the apex of the canopy. Some of the smaller ones use tape over the top of the canopy, but sew 12" or so of line onto the canopy.

-Kevin

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The chute remains I found last night were from my April 2010 I record attempt, where the chute deployed at Mach 1 due to pressure/drag separation. I had the risers sewn onto the chute seams about 2". The risers and the sewing were o.k., because there was a chunk of canopy nylon still attached to each line. I'm thinking about using the Apogee 100 lb shock cord for the risers and running it over the top of the canopy and down the other side.