An ingenious solution for securing the fin tabs at that angle. Thumbs up!!
Fall 2023 batch of 5
- Thread starter bjphoenix
- Start date
Help Support The Rocketry Forum:
Slight setback- my order of tubes and cones came in today but the tubes are all damaged so I've asked for replacements. I did weigh the 2 nose cones and they came in close to what the website says, just a tiny bit lighter. This means my open rocket file is pretty close. Build #5 already has the fins cut out and in the process of sanding and so forth. Build #4 was more critical for stability. Now that I know the weight of the cone I can modify the sim and verify if the fin design will work.
- Joined
- Aug 27, 2011
- Messages
- 11,627
- Reaction score
- 6,266
I’ll go you one better. Cut a 3/8” length piece of whatever motor Mount tube is, cut a lengthwise segment out (just enough so it will roll up INSIDE the same size tube without overlap. Slightly too BIG a cut is better than too small, you don’t want overlap.
figure out the depth you want, and mark it on a used motor casing. Practice placing it a few times until you can reliably do it in a Smooth in and out motion with the casing. Use WHITE glue (or epoxy if you like, white glue has always worked fine for me.)
it is easy (for those without an electric saw, far easier than cutting a motor casing, then peeling out the insides), it’s lightweight, and while it doesn’t seem like much, in over a decade I have yet to have one fail on the motors I use, 13 mm through 24 mm black powder E.
I haven’t used a standard motor block for years, even on kits that include them I usually save the supplied block to use as a centering ring for another project.
- Joined
- Aug 27, 2011
- Messages
- 11,627
- Reaction score
- 6,266
both true, not necessarily a deal killer.
the fins may not be PERPENDICULAR to the body surface as seen in AXIAL plane, but assuming The slots are correctly cut, they SHOULD still be perfectly aligned with the LONG axis of the rocket, which is the critical part.
if the are slightly off perpendicular in the AXIAL plane the only effect is they will be slightly less efficient. Unless design stability is marginal, they should work just fine. Meaning they should NOT induce any roll or corkscrew.
ALL of my helicopter models back to Gyskelion have fins which are waaaaaay off perpendicular to body centerline in axial plane (because they are integrated into the blades) and they work great.
pretty sure the X-wing Star Wars Rockets also have fins that are not aligned axially with the centerline.
@Dotini ‘s birds also have radically NON-perpendicular fins (they are curved only in the AXIAL plane), again as long as they line up parallel to long axis you are good.
note this also means the fins do not have to be evenly SPACED around the rocket. So for 4 fins, rather than 90-90-90-90, you can go 70, 110, 70, 110. Lots of room for variation as long as performance is not your main goal.
all the above should still “fly straight and true.”
If you want a walk on the wild side, and you can view corkscrewing as a “feature” rather than a defect, even more radical fin placement is perfectly flyable, a lot of fun, and often gets great attention from spectators, usually positive!
Last edited:
Never implied it was a deal killer, just that the fins would intersect the motor tubes at an angle to the surface of those tubes which would be difficult to glue properly as they could deflect off the side of the tube. Difficult but not impossible to do. BJ Phoenix came up with a great solution by installing a plate across the sides of the tubes which provided a groove for the fins to seat into.
I got my tubes and cones in the mail so builds #4 and #5 are making more progress. Build #4 is BT-70, build #5 is BT-80.
Build #5 is going to have fins extending to the motor tubes so I marked and cut slots in the lower section of tube. In the photo is a piece of aluminum angle that I use for marking tubes. I don't remember when I got this but it is very old. I even broke out a new blade for the XActo.
Build #5 is going to have fins extending to the motor tubes so I marked and cut slots in the lower section of tube. In the photo is a piece of aluminum angle that I use for marking tubes. I don't remember when I got this but it is very old. I even broke out a new blade for the XActo.
Rocketarium cones?
I think they both are, from erockets.
Aha, just checked and see the Rocketarium cones there. I hadn't known erockets carried them.
I've been posting in the "what are you doing today" thread, I'm circling back to fill in this thread.
In this photo I have added more fillets to the motor mount assembly for build #5 and I've started cutting out the fins for build #4.
At first I had intended for build #4 to have a long motor tube with centering rings front and back. I decided I would add another ring closer to the location of the thrust ring. I cut a couple of pieces that can slide over the motor tube and glue to each other.
This photo shows all of the pieces for the fins of build #4. I seem to keep coming up with the designs that require a lot of fins. 3 rockets of this build were simple- 3 or 4 fins each. build #3 took 6 fins, build #4 took 12 pieces to make 3 fins.
This photo shows the fin pieces in place on an impromptu jig I made to align everything while I glue the pieces together. The resulting assembly will probably barely be strong enough for handling but I thought I could place one large assembly better on the outside body tube rather than trying to piece everything together. The larger pieces are papered with thin cardstock for strength. Because of the way I'm putting these together on a flat surface I decided I needed to paper the little pieces too just to make them the same thickness.
In this photo I have added more fillets to the motor mount assembly for build #5 and I've started cutting out the fins for build #4.
At first I had intended for build #4 to have a long motor tube with centering rings front and back. I decided I would add another ring closer to the location of the thrust ring. I cut a couple of pieces that can slide over the motor tube and glue to each other.
This photo shows all of the pieces for the fins of build #4. I seem to keep coming up with the designs that require a lot of fins. 3 rockets of this build were simple- 3 or 4 fins each. build #3 took 6 fins, build #4 took 12 pieces to make 3 fins.
This photo shows the fin pieces in place on an impromptu jig I made to align everything while I glue the pieces together. The resulting assembly will probably barely be strong enough for handling but I thought I could place one large assembly better on the outside body tube rather than trying to piece everything together. The larger pieces are papered with thin cardstock for strength. Because of the way I'm putting these together on a flat surface I decided I needed to paper the little pieces too just to make them the same thickness.
I built a new fin jig. This is based on a design someone else has posted inn these forums in the past. I have a smaller one I built out of some scrap wood. I decided I'm building some bigger rockets now so I'll build a bigger jig out of better material. I had bought a piece of 1x6 primed trim material for another project so I cut off a 16" piece for the jig. In the photo is actually my build #5 from my ongoing build thread, it has a BT-80 main body tube. Someone may spot in the second photo that I have not yet put in the spacer to match the thickness of the fin material that I'm using.
Here it is in action putting the fins on build #5.
Here is how the fins fit through the slots and on to the motor mount assembly. The fin tabs were made long so I had to sand and hand fit each one into its respective position which is the reason for the tape and numbers on the tube.
Here it is in action putting the fins on build #5.
Here is how the fins fit through the slots and on to the motor mount assembly. The fin tabs were made long so I had to sand and hand fit each one into its respective position which is the reason for the tape and numbers on the tube.
The BT-80 pieces for build #5 only come in short lengths so I needed a coupler. I made a couple out of the damaged tube from previous shipping problems. I cut to short lengths of tube and cut slivers out of each to compensate for the reduced diameter inside the tube. I stuck a piece of thin plastic inside the main tube at the gap so there wouldn't be a gluing problem and the tubes would get stuck together. I put one tube inside, coated its inside surface with glue and put the other tube inside it. It's not as tight as a real Estes coupler but will work and isn't as likely to get stuck to the glue while sliding it in place.
This is the rear end view of build #5 with all of the fins in place. I don't build rockets with 4 fins unless I have to because the fin alignment is much more critical. I like to see the opposing fins perfectly aligned. I didn't get that here partly because I didn't do enough sanding to get them to fit the motor tubes. Next I will have to add internal fillets between the tabs and the motor mount, then I can put on the rear bulkhead and add its fillets.
I now have enough finished to mock up all of the pieces of build #5 and show the overall design. My goal was to build a larger rocket that would perform well on a pair of D12. I think under good conditions I could launch it on a pair of E12 and still keep it in sight. It is essentially the size of an Estes Executioner. The fin design is based on the Estes Nova so I'm calling it the Double Nova. It now gets to join the pile that is waiting for paint. Ignore those cans of paint in the back. Both cans of white are nearly new and neither one works anymore. I bought a can of Ace Hardware brand to use on these builds.
This is the rear end view of build #5 with all of the fins in place. I don't build rockets with 4 fins unless I have to because the fin alignment is much more critical. I like to see the opposing fins perfectly aligned. I didn't get that here partly because I didn't do enough sanding to get them to fit the motor tubes. Next I will have to add internal fillets between the tabs and the motor mount, then I can put on the rear bulkhead and add its fillets.
I now have enough finished to mock up all of the pieces of build #5 and show the overall design. My goal was to build a larger rocket that would perform well on a pair of D12. I think under good conditions I could launch it on a pair of E12 and still keep it in sight. It is essentially the size of an Estes Executioner. The fin design is based on the Estes Nova so I'm calling it the Double Nova. It now gets to join the pile that is waiting for paint. Ignore those cans of paint in the back. Both cans of white are nearly new and neither one works anymore. I bought a can of Ace Hardware brand to use on these builds.
When I use spray paint I always dip a small brush in varsol and dab the nozzle of the can to clean the small opening and channel the paint comes thru. Never had a can dry up yet. You may be able to pull the top button off and stick a pin thru it to clean and do the same to the top of the can. Watch out for paint coming out though!
Also really like your solution to the four fin cluster engine mount.
Motor mount fillets dried enough that I could start putting fins on build #4 so here it is looking somewhat complete. I borrowed the fin design from another thread, and found that it derived from several commercial kits. So far I've been calling this one "Subatomic". After fin fillets it will be ready for paint.
All things considered it turned out to be more work and problems than I wanted. If I had not gotten so far into it I would have probably rotated the pattern 45 degrees so that 2 of the fin tabs were longer and extended to the valley between motor mount tubes. But I already had the fins made and papered by the time that came up.
This is becoming a batch of 6. I picked up an old kit for the Estes Alien Probe, not a collector kit because it has some water damage, and I've been aching to kit bash it into a FatBoy so I started working on that yesterday. I cut and papered fins yesterday and started on the motor mount. Today I attached the fins to the motor mount to build a fin can. After the photo I put on the rear centering ring then later tonight I'll fillet everything with Titebond Quick and Thick. Tomorrow I'll slot the tube to match the fins, slide the fin can in and fillet the fins with Quick and Thick. I should have it ready to fly at our launch Sunday even though it will still be naked.
In this photo you can see how I attached and reinforced the engine hook. I wrapped the BT20 with a strip cut from an old piece of tube, put the hook over it, then put another strip of old tube over that. The piece underneath helps keep the engine hook from pulling out, the piece on top holds it in place. This makes it a little hard to fit the fin tabs. The downside of building the fin can this way is that it doesn't allow me to use my nifty neato fin jig. I've built MPR and HPR fin cans this way before, this is the first time for an LPR.
In this photo you can see how I attached and reinforced the engine hook. I wrapped the BT20 with a strip cut from an old piece of tube, put the hook over it, then put another strip of old tube over that. The piece underneath helps keep the engine hook from pulling out, the piece on top holds it in place. This makes it a little hard to fit the fin tabs. The downside of building the fin can this way is that it doesn't allow me to use my nifty neato fin jig. I've built MPR and HPR fin cans this way before, this is the first time for an LPR.
I put on fillets yesterday- internal fillets with Titebond Quick and Thick, external fillets with Titebond II. I was in a hurry to put the fin can in the body tube and forgot to install the kevlar leader for the shock cord so I had to retrofit it. I have a few odd long drill bits so I drilled through both centering rings, stuck a piece of wire there there, stuck the end of the kevlar to it with a bit of glue, and pulled it through. It is ready to launch tomorrow, naked.
The Fat Boy got to fly naked yesterday. I flew it on a B6-4 which simmed at about 200', I don't think it flew that high. I would have been better with more like a 3 second delay but it recovered high enough for the parachute to deploy and let it float down most of the way. I was concerned that at our small field if I flew it on a C6 and it weathercocked off the rod it would travel beyond the limits of our field before it deployed.
It was warm enough yesterday afternoon to get some paint on builds 1 and 2, and the Fat Boy got some primer after we got home. Thursday and Friday this week I should be able to get some more painting done.
It was warm enough yesterday afternoon to get some paint on builds 1 and 2, and the Fat Boy got some primer after we got home. Thursday and Friday this week I should be able to get some more painting done.
I had some weather cooperate and had some success with paint. Everything is not perfect, my red didn't give a very smooth finish so ultimately I need to sand it and try again. The Lil Hustler is patterned from a photo in the 1971 Centuri catalog and still needs a red stripe just in front of the single black stripe to be complete. The Sprint XL has Rustoleum yellow on top of Ace Hardware white and the yellow didn't stick very well. When I removed the masking tape it took some yellow with it, hints of that are visible in the photo. I'll have to do more sanding and respray the yellow. The Fat Boy at least is complete.
I have finalized the paint scheme for the Yellow Sapphire and the paint for build #5 so just waiting for weather and time to get those done. I haven't finalized the paint scheme for build #4 yet. It got launched a week ago in just its primer.
I have finalized the paint scheme for the Yellow Sapphire and the paint for build #5 so just waiting for weather and time to get those done. I haven't finalized the paint scheme for build #4 yet. It got launched a week ago in just its primer.
I just finished the paint on build #3 although there is an issue with the black on the back that I may have to correct. This one is called the "Pink Sapphire". It is my own take on the Blue Sapphire so had to be a different color, and I already had a can of pink.
In other news the Fat Boy is probably still hanging from a very tall tree in Arlington. It has a kevlar shock cord so it probably won't come down anytime soon. Build #4 has all of the paint on it but needs some small black stripes, I'm thinking about buying some pinstripe tape for that. Build #5 is waiting for me to buy a new can of red which I'll try to do in the next few days.
In other news the Fat Boy is probably still hanging from a very tall tree in Arlington. It has a kevlar shock cord so it probably won't come down anytime soon. Build #4 has all of the paint on it but needs some small black stripes, I'm thinking about buying some pinstripe tape for that. Build #5 is waiting for me to buy a new can of red which I'll try to do in the next few days.
Lovely Sapphire. Re. Fat Boy, I wonder if there's a market for water soluble shock cords and shroud lines.
mh9162013
Well-Known Member
Probably not, at least for LPR rockets. As the rockets themselves are usually made of water soluble materials (cardboard, paper and wood).
Eventually the body of that one will come down, by then nothing will be usable except for the engine hook. The nose cone might come down then, or the kevlar might be tangled around branches enough that it would never come down. That rocket body is built with big glue fillets and fins extending to the motor tube so it won't come apart very fast.
I fished an Estes Nova out of a lake a year or so ago. It had been in there a couple of hours and the fins were already coming off of it.
I finally put the finishing touches on #4 so it deserves a new photo. I'm calling this one the "Subatomic" after another thread here somewhere that inspired me. The paint scheme is taken from a photo of a WWII fighter. The intent was always to have thin black stripes to separate the colors. I decided it would take me forever to mask and paint black, and I had to order some new Tamiya masking tape anyway, so I ordered some pinstripe tape. The cost of the tape by far offset the amount of time it would have taken for me to do all of the masking. This has already flown a couple of times on D12 motors, the next launch day with good conditions I'll try it on an E12 (fingers crossed). OK maybe I'll try to get some more good flights with D112 first, just in case it gets unlucky with an E12.
I was finally able to launch the Double Nova today on a pair of D12-5. This turned out to be a great combination with the rocket flying straight and to a decent altitude for my purposes. My sim said 875 feet and it seemed to get all of that. It didn't seem to get off the pad as fast as I expected considering it was a very light rocket on essentially E24 power. I built it to also fly on a cluster of E12 if I get brave enough, with sim altitude of 1350 feet. It was hard enough to see at approximate altitude of 875' so I will not worry about E12 power unless conditions are perfect. Maybe I need to paint the front of it a darker color, but then it wouldn't have the Red Nova paint inspiration.
I haven't flown a cluster in many years and I didn't want this one to fail so I careffully prepped the motors a few days ago. I pulled out some igniters and tested them with a VOM, picking 2 with similar resistances. I put the igniters in the motors and tested them again, then I twisted the leads together and tested the combination to see that it had proper parallel resistance. I really have very few igniter problems these days, the few problems I've had were bridge wires broken or the 2 leads touching inside the motor. Either one of these issues I could rule out if I was getting proper resistances.
I haven't flown a cluster in many years and I didn't want this one to fail so I careffully prepped the motors a few days ago. I pulled out some igniters and tested them with a VOM, picking 2 with similar resistances. I put the igniters in the motors and tested them again, then I twisted the leads together and tested the combination to see that it had proper parallel resistance. I really have very few igniter problems these days, the few problems I've had were bridge wires broken or the 2 leads touching inside the motor. Either one of these issues I could rule out if I was getting proper resistances.
Sorry I missed seeing that flight. Was once again too busy to make it to the launch. That's a beautiful liftoff, and I'm sure the whole flight was spectacular.
