I save all my drawings like that. Might be cool to frame a collection of them at some point. It's art! Abstract impressionism?
Taking a shot at the G record
- Thread starter Adrian A
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When I tried sanding the 1-layer tube that I made last year (a few posts upthread), I pretty much sanded through. It also had a significant wrinkle that turned into a slit after trying to sand it off, so I decided to try again today.
Here is the mandrel, covered with mylar, and the prototype tapered rear closure I helped CTI develop a long time ago, covered with flash tape, with a bunch of grease in between. I always wonder if I am getting the mylar on snugly enough.
For the layup, I'm going with an inner layer of slightly-overlapped 0/90 cloth strips about 1.5" wide, covered by a biaxial sleeve that I expect to mostly sand off. The sleeve is also there to make sure I can get the rear taper without wrinkling. I spiral-wrapped two layers of peel ply that ran out before I got good coverage over the tapered part, so I decided to add some shrink-wrap sleeve. I forgot that it shrinks in both directions, so it too ran out before I got to the tailcone. I added another 6" or and shrank that down, pulled it tight and twisted:
Now it's in the oven at 160F.
Here is the mandrel, covered with mylar, and the prototype tapered rear closure I helped CTI develop a long time ago, covered with flash tape, with a bunch of grease in between. I always wonder if I am getting the mylar on snugly enough.
For the layup, I'm going with an inner layer of slightly-overlapped 0/90 cloth strips about 1.5" wide, covered by a biaxial sleeve that I expect to mostly sand off. The sleeve is also there to make sure I can get the rear taper without wrinkling. I spiral-wrapped two layers of peel ply that ran out before I got good coverage over the tapered part, so I decided to add some shrink-wrap sleeve. I forgot that it shrinks in both directions, so it too ran out before I got to the tailcone. I added another 6" or and shrank that down, pulled it tight and twisted:
Now it's in the oven at 160F.
Interesting using a motor casing as a mandrel. I would be afraid of not getting the carbon fiber off my motor casing.
The mylar sleeve makes it easy to slide the motor casing out after curing, as long as you make it longer than your layup so that the epoxy can't sneak in underneath. Today since I was using flash tape for release on the tailcone closure, I had the mylar end at that joint, and I put a bunch of grease in there to keep the epoxy out. That didn't work for me today, and I had to cut off the carbon tapered end and a bit of the tube, to be able to break the motor case loose. The motor case probably isn't usable any more, unfortunately.
The tube came out great, with no wrinkles. It's about 17 grams before I cut it down to length. I may sand it a little more first, since there are still some spiral waves from the carbon strip overlaps, and it's a bit stronger than it needs to be. The tube needs to be about 1.8" longer than the G12 shown in the photo.
Not a lot to look at in the photo, but it feels light and strong and has a nice ring. I used the 820 epoxy from Soller. I really like that epoxy for all applications 220F or lower, because it cures hard and strong, has a long working time and very low viscosity. And it’s 1/6 the price of the Cotronics.
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What's the OD of your tube?
1.17"
Parts and pieces for the av-bay.
I'm planning to use a 150 mAhr battery for the tracker and a 110 mAhr battery for the 29mm Blue Raven. The green circuit board is a 29mm bulkhead with three brass/zinc unthreaded spacers soldered on. That part will get glued and maybe fiberglassed into the BlueTube coupler to form the seal for the deployment charge. I'll solder some small silicone extension wires onto the heads of the brass screws, and use them to install the 29mm Blue Raven onto the bulkhead along with some nuts using the Apo and Arm+ terminals. The third hole that would normally be used for Main, I'll use as a pass-through for the shock cord that I'll glue into the tip of the nosecone and thread through the tracker.
I'm planning to use a 150 mAhr battery for the tracker and a 110 mAhr battery for the 29mm Blue Raven. The green circuit board is a 29mm bulkhead with three brass/zinc unthreaded spacers soldered on. That part will get glued and maybe fiberglassed into the BlueTube coupler to form the seal for the deployment charge. I'll solder some small silicone extension wires onto the heads of the brass screws, and use them to install the 29mm Blue Raven onto the bulkhead along with some nuts using the Apo and Arm+ terminals. The third hole that would normally be used for Main, I'll use as a pass-through for the shock cord that I'll glue into the tip of the nosecone and thread through the tracker.
Adrian --
Is that the Apogee 29mm PNC 29MM Nosecone in your photo ?
Apogee: PNC 29MM
According to Apogee ( and they're usually very accurate with weights and measures ), the diameter is 1.176 inch and your carbon tube is 1.17 inch.
Does the nose match your airframe tube as well as it sounds like it would ?
Thanks !
-- kjh
Is that the Apogee 29mm PNC 29MM Nosecone in your photo ?
Apogee: PNC 29MM
According to Apogee ( and they're usually very accurate with weights and measures ), the diameter is 1.176 inch and your carbon tube is 1.17 inch.
Does the nose match your airframe tube as well as it sounds like it would ?
Thanks !
-- kjh
Yes, it's the Apogee nosecone. It's not a perfect fit, but close enough.
I just put all the electronics in and did a range test with the antenna folded over in half inside the cone. The RSSI was -94 dBm at 740 feet range. If -128 dB is the lower limit then I have sqrt(34 dB) of range margin. That's a nice even factor of 50x, which means that the link would support 37 kft of range in this configuration, if the losses are the same. The receiver will be in a quieter location and the test would have had some ground losses that wouldn't apply to flight, so I know LoRa range won't be an issue. Next is to see how long the transmitter lasts on a 150 mAhr cell. I turned on the transmitter at 2:00 and it's 2:30 now, and the battery is down to 3.8. A half hour is pretty much all I really need for this record attempt, since it's a small launch with nonexistent LCO lines, but it's on track for over an hour of transmission, probably two.
On the other end, I took a shot at using another nosecone to help make a tailcone for this bird. I'm concerned that it's not tapering down quickly enough, so to get a decent area reduction, it might interfere with the motor exhaust. What does everyone think? I did cut it back far enough so that the trailing edge is outside of the exhaust cone angle by a little bit. Maybe I should ask this question in the propulsion sub-forum.
It feels like I'm forgetting something...
I did a little forum research and found someone who did some testing, and found that the threshold the problem for a cylindrical back end was when the motor was recessed 1.0 body diameters from the end. The back of the nozzle with this tailcone is recessed 0.877" from the tailcone exit, and the tailcone exit ID is 0.95." Maybe it's o.k. as is?
The tests I've seen in the past used a straight body tube. Unless the study you found was with a tailcone, I'd be inclined to be a little conservative and trim the tailcone a bit more. But that's just a hunch on my part, with no data to back it up.
James Keller
Well-Known Member
Any chance you can link the forum you read. I've been toying with the idea of printing a tailcone for my Min 38mm that I'm building and if I make a tailcone it gives me a few thousand more feet of altitude.
@Adrian A --
Hmmm ... Base Drag reduction due to a Boat Tail -vs- Krushnic ?
There is some old research on Base Drag and Boat Tails in Estes TR-11 - Aerodynamic Drag of Model Rockets.
And the Krushnic effect is discussed in NAR Technical Review Volume 1.
I don't know ...
I guess it all boils down to: is there a net altitude gain when you add a Boat Tail to a rocket where the Boat Tail MAY reduce thrust of your G12 due to the Krushnic Effect ?
Another thing I wonder is: will the Apogee styrene boat tail melt during the 12.7 sec burn time of the G12 ?
-- kjh
EDIT: I wonder how @Neutronium95 constructed the boat tail on his H13 for Highperion - My attempt to break the Tripoli H altitude record ?
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I’d look at fabbing a 5-degree taper and end it at a 90-degree cone outward from the perimeter of the nozzle boss. Just as a guess that feels right. You could always build a test stand and burn some motors.
I think he 3D-printed it.
When I do my sims in RASAero now, the altitudes are high enough that I think I'll start next weekend with an F10 to go for the F record, and then if the altitude is in line with the RASAero predictions, see how the prefect feels about exceeding the FAA waiver with a rocket that doesn't need a waiver. If I want to stay under the waiver, I may end up skipping the tailcone, to help keep the altitude lower and more predictable.
When I do my sims in RASAero now, the altitudes are high enough that I think I'll start next weekend with an F10 to go for the F record, and then if the altitude is in line with the RASAero predictions, see how the prefect feels about exceeding the FAA waiver with a rocket that doesn't need a waiver. If I want to stay under the waiver, I may end up skipping the tailcone, to help keep the altitude lower and more predictable.
@kjhambrick found the same material that I did.
Why not ask the prefect in advance, just for your peace of mind and to simplify your planning? Some clubs are cool with Class 1s doing Class 1 things, but others won't countenance the waiver being exceeded, no matter by what.
James Keller
Well-Known Member
Curious when/where do you plan on flying? Isn't NCR doing 1 more launch at their north site or are you trying to launch sooner?
Just different styles I guess. I’d rather reduce other uncertainty first, like will I get my rocket back intact after an F attempt. I’m also leaning against going for the G record under circumstances that are questionable, anyway. If the rocket underperforms the sim on the F flight and I’m confident it would stay under 14200 on the G, I’ll probably go for it. The Tripoli launch site is the highest in the country, but every site has its challenges and limitations, so it feels more fair to set for the record at NCR or NSL in Alamosa next year if it wouldn’t stay under the Hartsel waiver.
There is another NCR launch scheduled for Nov, but all the fuel on the ground is just getting drier, so I’m not expecting it will happen.
What a kool idea, @SolarYellow !
This is an AT 29mm nozzle with a 0.180 inch throat and a 30-degree exit cone from The RCS Site: 29/38mm Nozzle, 0.180" Throat.
I don't know if this is the same nozzle as the G12 but it might be fun to make a composite attachment for the nozzle-end that extends the exit cone out to the circumference of an ogive boattail that matches the airframe.
Note that the nozzle is only 1.000 inch in diameter where the OD of the 29mm motor casing / ID of the airframe are about 1.14 inches so the ogive boattail would be wider and longer than suggested by the nozzle dimensions.
EDIT: about like the tailcone in Adrian's photos above ...
Eyeballing the RCS blueprint, it looks like the ogive boattail L/D ratio could be long enough to actually reduce base drag more than a little bit !
So, I wonder if @AeroTech has published the actual specs of a G12 nozzle ?
What fun !
-- kjh
EDIT: After studying the blueprint a little longer, I see I should have included the table of part numbers -vs- throat diameters:
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NTP2
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FAR?
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Adrian --
My rough sim puts a similar 65 gram rocket at Hartsel at over 8k feet ...
What do you mean by 'underperforms on the F flignt' ?
Thanks for sharing this thread !
-- kjh
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For clarity, this is what I was thinking. When I wrote the above, I was thinking of the green line, but I suppose an argument could be made for the orange line as well.
This is just to illustrate the principle. Obviously, the OD of the boat tail would start at the airframe OD, not the motor OD. (Okay, I was thinking "sub-MD/flying case" when I drew it.)
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I'm talking about the pad altitude. About 8800' for the Tripoli CO Hartsel site.
Ideally the exhaust plume when it passes the nozzle exit diameter will be expanded to atmospheric pressure. If it is over-expanded then you can get a loss of thrust and motor efficiency. And anyway, modifying the nozzle in a propulsion-changing way is a motor mod that I wouldn't want to do for a commercial motor record attempt.
A couple of days ago I found a larger nosecone that I used to cut out a more traditional boat tail. This one tapers down to 0.95" diameter over 0.9" length.
The F10 sims to right around 8900 with a boat tail. If I fly it and it goes straight but to 7000 feet, then the sim says I would only expect 12,750 feet on the G and I would fly it with confidence. But if the F10 goes to 9000 feet, then I would expect over 15k on the G if I use the same boat tail. In that case I probably would fly it without the boat tail or not at all.
The sim parameters that get the rocket to 14,400 on the G12 without a boat tail get the rocket to 8045 on an F10 without a boat tail or 8421 with a boat tail. So my current plan is to fly on the F10 with a boat tail, and if all goes well and the altitude is under 8421, I'll reload with a G12 without a boat tail and go for the G record.
The F current record is 7989 feet, launched from about 4500 feet ASL in Oregon. I've seen Kelley's beautiful work on the rocket, especially the nosecone, and it paid off with an impressive flight. If I were to fly this rocket from 4500 feet RASAero says it would only get to about 7600 feet. I'm glad that the new Tripoli record search implementation shows the data from the previous records also, so that Kelley can continue to get credit if I beat his record partly due to a higher launch site.
Thanks for pointing out Kelly Bruland's TRA F Record, Adrian.
The TRA Record entry includes a link to @kbRocket's Effed Up Build Thread here on TRA which also points at the build threads for Eyelash and Gee Willikers (*).
Wow !
I really missed a lot while I was gone from rocketry ...
Very nice techniques that even I might be able to pull off in my garage with my stone knives and bearskins !
And there are enough study materials in Kelly's build threads for DAYS of fun !!
Thanks again, Adrian !
-- kjh
(*) - GREAT names for rockets, by the way, @kbRocket !
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NTP2
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I thought he was talking ffa waver.
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I have many questions regarding this build. Why is a high-strength Carbon Fiber tube required when the motor is a G12? I would imagine the low-thrust, long burn motor would allow you to use a cardboard tube. In my mind, you could take a standard Estes "Star Orbiter" BT-60 kit, build it without the second tube so it's only half the length, and still fly pretty damn high on a G -- a low thrust G12 should not cause the tube to fail.
It seems to me that the Carbon Fiber requires heavier adhesives such as epoxy to keep the fins attached, when you could go cardboard and balsa, and keep the whole thing fairly light. Or am I not thinking this through?
It seems to me that the Carbon Fiber requires heavier adhesives such as epoxy to keep the fins attached, when you could go cardboard and balsa, and keep the whole thing fairly light. Or am I not thinking this through?
I took some photos a couple of days ago that I haven't posted yet:
This one shows the tracker, tracker battery, and Blue Raven battery installed into the cone on the left, and on the right is the 29mm Blue Raven with the shock cord threaded through the tracker board and the Blue Raven's main deployment terminal. The other 2 terminals with the nuts attach the Blue Raven to the glued-in bulkhead and electrically connect the board to the Arm+ and Apogee channel deployment wires that are soldered onto the brass screws in the next photo, which shows the other side of the glued-in bulkhead:
My current plan for sealing this is to put a blob of vacuum sealing putty on the shock cord at a location that will provide enough room to pull the av-bay apart and then I'll tuck the slack in when I stick the coupler back into the nosecone.
Below shows everything tucked into the Apogee nosecone. The glued-in bulkhead is right near the front of the coupler.
This one shows the tracker, tracker battery, and Blue Raven battery installed into the cone on the left, and on the right is the 29mm Blue Raven with the shock cord threaded through the tracker board and the Blue Raven's main deployment terminal. The other 2 terminals with the nuts attach the Blue Raven to the glued-in bulkhead and electrically connect the board to the Arm+ and Apogee channel deployment wires that are soldered onto the brass screws in the next photo, which shows the other side of the glued-in bulkhead:
My current plan for sealing this is to put a blob of vacuum sealing putty on the shock cord at a location that will provide enough room to pull the av-bay apart and then I'll tuck the slack in when I stick the coupler back into the nosecone.
Below shows everything tucked into the Apogee nosecone. The glued-in bulkhead is right near the front of the coupler.
