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6" scale of Blue Origin's orbital New Glenn (and L3 build thread)

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jmattingly13

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I'm working on a number of exciting new rockets to bring to NSL this year, but the one I'm most excited about is the scale model of Blue Origin's yet-to-be-built New Glenn rocket, since this would be my Level 3 cert. The New Glenn rocket is going to be pretty big [citation needed], so I scaled it down from the photos out there such that the majority of the airframe would be the size of a 3" PML tube. After looking at it for a while, I figured I might as well double the size and stick an M in the back of it to make it an L3 rocket, so most of it is the size of a 6" PML tube. At just over 77" in length, it's not the tallest rocket on the block, but it still should be pretty awesome. I've baselined the rocket to use an AT M1350 motor, but the motor mount is a 98mm mount, so I can add more power later if I want (and have the $$$). Projected altitude is just over a mile because I believe in low and slow cert attempts.

javaw_2017-04-23_14-52-10.jpg

So what's the construction plan? The only thing that fits well into a standard tube size is the 6" airframe and the 98mm motor mount, which will both be PML phenolic tubes (no glass). Unfortunately, it seems that Blue Origin did not have rocketry component scales in mind when designing this rocket, so I'm getting a bit more creative with the payload fairing and the aft section. In both cases, I am attempting to cast a polyester resin mandrel (4.9" for the payload fairing and 7.1" for the aft section), from which I will then use to create a short section of fiberglass airframe. If the cast mandrels don't work out, I may have to 3D print the mandrels (which I don't want to do) or find a way to turn a mandrel (I don't have a lathe). A lot of other things are actually already 3D printed--the nose cone and both transitions, as well as some internals. The canards and strakes will both be 1/4" laser cut plywood, and I've added four additional acrylic fins (1/4" laser cut as well). Most of the centering rings and bulkheads are stock from PML, but I also got a couple of custom ones laser cut to TTW fin locking and for the non-standard diameter airframe sections.

Recovery will be standard dual deploy (36"/96") with redundant altimeters. I'll probably fly with my Raven as a primary and possibly use the Eggtimer I recently built as secondary. (I could also use the RRC3, HiAlt45k, or Eggtimer Quark.) I will likely leave my Eggfinder off, as I don't anticipate too many issues finding a low-flying rocket in the desert, but will play it by ear on launch day. I will also fly with a 2kg dead weight payload for added stability and decreased altitude.

More pictures to be posted as the build continues. Questions, comments, and critiques are welcome.

View attachment New_Glenn_6.ork
 

neil_w

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:pop:

By the way, if I read that side view correctly, I *really* like what you've done with the tail. Gives me some ideas...
 
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Incongruent

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I would go with polycarbonate rather than acrylic for the clear fins, since acrylic is more brittle.
 

jmattingly13

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I made the decision to 3D print the transition sections using white ABS. My printer, a FlashForge Creator Pro, is a pretty nice unit with a fairly large build area--approximately 8.9 inches by 5.7 inches on the base, and 5.9 inches vertically--but this is also a really big rocket. Neither of the transitions could fit on the print bed, and even if they could, there still would not be enough room in the Z direction. My solution to this problem was to divide each transition into four segments. Additionally, the nose cone, while it could fit on the base, was too tall for my printer, so it too got sliced in half.

The immediate question that arises after splitting up a large print is how to join the pieces. Joining with an adhesive (say, epoxy), plastic welding, and melting the mating surfaces together with acetone were all viable options, but left some risk of the joint failing catastrophically, especially given that being such a large print, there was an increased probability for a wavy surface. (I'm still working on dialing in the bed level and print settings, but generally the mates are pretty good.) My solution was to employ one of these methods (leaning towards acetone melting), but also to design in alignment pins, which would relieve some mechanical strain from warping and other deformations. This would also allow for the optimal alignment of the parts for better surface continuity at the segment interface. Below are the pre-joined nose cone, forward transition, and aft transition.

IMG_4839.jpgIMG_4840.jpgIMG_4842.jpg

After printing, I bored out the holes a bit with a 9/64 drill bit so the 1/8 pins would slide in. The pins (1.5 inch long steel) are secured into one of the segments with a drop of CA glue and then the opposite (horizontally) segment is mated to it. I have not joined these segments together yet; that will occur once I verify they fit snugly into their respective airframe tubes. For the transition units, the top and bottom halves will be mated such that the horizontal interface planes of each are perpendicular. This should theoretically increase the strength (or, rather, decrease the weakness) of each transition unit. I noticed when trying to join the top and bottom halves of the forward transition that the pins did not align and the diameters at the mating plane may have been slightly different. I figure I made an error when breaking up the forward transition, so this will have to be re-printed. Below are the aft transition, forward transition (the horizontal mates looked nice), and the nose cone when joined together.

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I noticed that there is a little bit of sag in the prints, so I will have to do a bit of cosmetic work (sand and coat with epoxy) to the top-bottom mating interfaces. I anticipated this might happen, so that dictated the decision to print all components with the top-bottom interface at the bottom of the print. This meant that I would not compromise the circularity of the transition shoulders or the effective diameter, since the mate into the airframe tube is a far more important mate (and more difficult to repair) than the mate between each segment.
 

jmattingly13

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As previously mentioned, the payload bay and aft section airframes are not of a standard size, so I will have to make those tube sections myself. In order to make the airframe tubes, I will also have to make the mandrels, which are to be the subject of this post. I previously printed a few mandrel negatives so I could cast the mandrels with polyester resin. I think I made an error printing the aft mandrel negatives, so I will have to re-evaluate and try again. Each negative is 3 inches tall (to save on printer material), so mandrels will be cast over multiple sessions. I bought a couple of 2 foot segments of 4-inch PVC piping to reduce the amount of resin I would need to cast. I did a sample pour with the forward mandrel to prove my concept and noticed a few things. First, it was difficult to maintain a good seal at the bottom. This could probably be solved by planting the PVC and mandrel negatives in a base of clay or something similar. I also imagine this would only be an issue in the first pour. Second, the fumes from the polyester resin were overwhelming. I think the only properly-ventilated place to do this task is outside. The fumes also stick around a bit after the resin has cured, so I'm not a big fan of this method. The results of my first pour were pretty encouraging, though. I only used a few ounces of resin (so as to avoid waste from rookie mistakes), which is why the segment in the photos is so short.
IMG_4848.jpgIMG_4849.jpgIMG_4851.jpgIMG_4854.jpg
As you can see, the alignment between the mandrel and the nosecone (which will fit into the tube made by this mandrel) is pretty good, so I am encouraged by the results. Following the casting of this short segment of mandrel, I purchased some air-dry modeling clay, which I think will actually be much faster to cast and have no fumes. To increase the hardness of this clay mandrel, I will glaze the clay mandrel with a thin layer of polyester resin (outside), which should also give a a few thou of tolerance between the manufactured airframe tube and the parts that mate into it.
 

Mushtang

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I have ZERO experience with canards, so I'm only asking for my own education and not trying to make suggestions. I've always heard canards make a model rocket much less stable, which makes sense because they add drag in front of the center of pressure. Are you expecting them to be a problem here?
 

gwh

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This looks awesome! Really looking forward to seeing your build progress, I am hoping to do my own at 1:88 scale someday.

Why not a Blue Thunder motor though? A New Glenn just really needs that sexy bright blue flame IMO.
 

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Neat build so far. Subscribed.
 

jmattingly13

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As it may have been deduced thus far, this was not finished in time for NSL. I'm having a bit more trouble than anticipated making mandrels for the payload fairing and aft section. I'm also considering descoping the two strakes since I got them cut to the wrong dimensions and I also failed to include fin-lock slots for them in my centering rings (and I prefer not to rework that). Stability margin will decrease a smidge, but I'll still be good in that department.

Why not a Blue Thunder motor though? A New Glenn just really needs that sexy bright blue flame IMO.
It was going to be cheaper to buy a 75mm DMS rather than buy a motor+case, which was the primary driver. I had an AT blue backup (and try to rent a case), and now I may have an option to get a Loki blue + case (which would be pretty cool because I did L1 on AT, L2 on CTI, and could finish L3 with a different brand entirely).

Anyhow, I'll be getting back into build mode, so look for more updates in the near future.
 

jmattingly13

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Obviously, it's been a while since last posting, and a few things have changed (but not the incredibly small amount of time I have to work on stuff like this). I modded the design a bit to match the 7 meter fairing only configuration. This did not change the height of the rocket, but it did make my life a whole lot easier not having to make more weird tube sizes. The aft body tube layup experiment has not been going well, so I decided to make the aft transition and airframe section a single 3D print out of PETG. Pictures to come when it is complete. The next few posts will cover the progress on other bits of the rocket.
 

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jmattingly13

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To put it simply, there are a lot of aerodynamic surfaces on my New Glenn model. The most important are the main fins, which are located at the aft end of the rocket. These fins are 1/4" thick clear acrylic fins (currently still in their protective blue plastic cling wrap). They are of a through-wall design, so they will be epoxied to the motor mount tube as well as to the inside of the aft module. A small fillet of epoxy will also be used on the outside joint. They have a root chord of approximately 10.8 inches, a tip chord of 5 inches, and a height of 8 inches (measured from the 6 inch primary airframe). The root chord is contoured to match the profile of the rocket as it transitions from the 6 inch primary airframe to the 7.7 inch aft module. While alignment is handled primarily by the slotting, the fins also utilize locking tabs, which fit into laser cut notches in the middle and aft centering rings. The primary function of these tabs is to keep the fins square with the airframe during construction, but do provide an extra level of assurance for minimizing fin cant.

The second set of fins are the forward canards. Located 29.5 inches from the nose end of the rocket, these fins actually provide a destabilizing force. For this reason, the rocket will have to fly with at least 1 kg of payload. Each of the four canards has a root chord of 4.3 inches, a tip chord of 1.4 inches, and a height of approximately 1.8 inches to maintain the scale of the rest of the rocket. These are made from 1/4 " thick plywood and are painted white and blue. Unlike the main fins, the canards are surface mounted so as not to interfere with the main parachute, to whose bay they are mounted. To provide additional attachment strength, each canard will be held by two pair of 3D printed PETG brackets with 10-24 binding posts. These brackets will be epoxied onto the airframe and provide approximately 1 square inch of bonding surface per bracket pair. Due to launch rail considerations, these canards will be mounted 45 degrees off their intended position, aligning with the main fins.

The final set of fins are the strakes. These two fins are also made from 1/4" thick plywood and painted white and blue. Like the main fins, they are contoured to match the profile of the transition in the aft module. They have a root chord of approximately 14.9 inches, a tip chord of approximately 2.8 inches and a height of approximately 2.6 inches to maintain scale. Like the canards, the strakes are surface mounted, but this is because they were not originally considered for inclusion in the model, so the appropriate accommodations were not provided. To provide additional attachment strength, each strake will be held by two pair of 3D printed PETG brackets (same as used for the canards) with 10-24 binding posts. The strakes, each 180 degrees apart, will be mounted 45 degrees off of the main fins and 90 degrees off from the launch rail.

Aerodynamics were not a major consideration (or rather, more drag was considered better to lower the max speed and apogee for a certification flight), so all fins will keep their square leading and trailing edge profiles. This also has the benefit of decreasing the work required on the fins and maintaining the same standard of quality for each fin.

View media item 346454
 
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jmattingly13

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The main airframe structure is built from 6-inch PML phenolic tubing. Three segments of this tubing make up the rocket body--a 29 inch segment which serves as the booster airframe and drogue parachute bay, a 24 inch segment which serves as a main parachute bay, and an 11 inch segment which serves as the payload fairing. There is also a 1 inch segment on the coupler between the booster and main parachute airframes which serves as a switch band, but more on that in another post. The booster and main parachute airframes have notches cut out and glued to the avionics bay to enforce a single clocking of these two sections.
View media item 346455View media item 346457
Four slots of length 2 inches and width 0.25 inches were cut to accommodate the forward fin tabs on the main fins.
View media item 346456
The aft transition and airframe are now an integrated component. This assembly was 3D printed with PETG plastic. Wall thickness is 0.2 inches throughout with 25% infill. The transition has a 2 inch shoulder and there is a thrust takeout ring near the aft against which the aft centering ring sits. The transition expands from 6.155 inches in diameter to 7.706 inches in diameter over a length of 1.69 inches. The straight airframe section is 5.14 inches long. Four slots are designed into the part to accommodate the main fin aft tabs. The slots extend 0.25 inches beyond the top of the aft tabs to allow enough slop to successfully integrate the fins, mid centering ring, booster airframe, and aft section.
View media item 346490View media item 346491
The motor mount is a 24 inch long segment of 3.9 inch PML phenolic tubing. This model was designed to fly on 75mm and 98mm motors, though the plan for certification is with a 75mm AT M1350. The motor mount is located with three centering rings. The forward centering ring (not yet installed) is a 0.5 inch plywood ring and also has a 2 inch stainless steel U-bolt to serve as a tie-in for the the recovery system. The middle centering ring is a 0.25 inch plywood ring and is laser cut with key ways to mate with the locking features on the main fin forward tabs. It also rests against the top of the aft section shoulder. The aft centering ring is two stacked 0.25 inch plywood rings and is laser cut with key ways to mate with the locking features on the main fin aft tabs. It also features a 98mm flanged AeroPack motor retainer.

Integrating the main fins was no trivial task due to the tight tolerances. Ultimately, the aft section was secured to the booster airframe with epoxy. Additionally, the forward and aft tabs were epoxied to the motor mount tube. The mid centering ring was wood glued to the motor mount tube. Fillets were applied to the joints between the fin tabs and motor mount tube as well as between the fin tabs and the inside wall of the aft section and booster airframe. (External fillets are forthcoming.) The aft centering ring was glued to the motor mount using wood glue and to the aft section using epoxy. The balance of the 2 fluid ounces of epoxy that was mixed was used at the join between the mid centering ring and the aft section. The wood glue used was Titebond II Premium wood glue and the epoxy used was US Composites thin epoxy. To thicken up the fillets, aluminum tryhydroxide powder was added to the epoxy, mainly because it was close by. Due to the time sensitivity of this process, no images of a struggling builder were able to be obtained.
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jmattingly13

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I actually did fly this at AirFest in 2018 and completely forgot to put in the final updates. It was a great flight, but after landing, the wind kept catching the main, which dragged the rocket across the field and also slammed the nose cone into the ground multiple times. The end result was that the nose cone broke in half (there was also a 2 kg deadweight), which was no bueno.
 

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gwh

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Oh cool, have any finished pics other than the launch pad one?

Now that the real rocket is taller, you could always add a little height to reduce the ballast required :D
 

jmattingly13

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Here's the only other photo I can find. I think I'm going to wait until the real deal flies before I completely rebuild since the design seems to change often enough. I'll also have to re-decal, which is a bummer.
upload_2019-3-3_15-54-53.png
 
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jmattingly13

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This one flew on seven BE-4's and two BE-3U's an M1350. The sim had it doing ~5900 ft and the data shows it was closer to 5500 ft. The sim also showed a max speed of ~820 ft/s whereas Raven thinks that number was closer to 640 ft/s. The sim does account for individual component weights, which I measured for each component, so this isn't a paint weight issue (and unlikely to be a glue issue, either). I'm going to chalk up the discrepancies to the unusual aerodynamics. Honestly, though, I'm fine with the lower and slower flights.
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