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And here's a quick vid...
Unexpected builds
- Thread starter Y3kankerous
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Correction: That last flight was actually a B6-2 centre with 4x A10-0T.
I had an altimeter (JLA2) in both the first (C6-3+2xA10) and last (B6-2+4xA10) flights. These gave altitudes of 58m and 78m respectively.
According to the C/F-M equations the first flight made 67% of prediction, while the second made 97%.
My naive interpretation was that this was due to a truer flight with the 3off spin tabs, but I realise there are many other factors which could influence this (including altimeter accuracy).
In this video of the first flight I think there is a pronounced pitch/yaw, I don't believe there was enough wind to cause this through windcocking, but again various other factors.
A couple of these flights have been my first D impulse launches, and more generally this build has been a big progression for me. I have learned a lot, in one or two cases, the hard way!!
I am now wondering about launching this model on a Klima D9-3. If I add boosters, then I can get into mid-E range, which is a prospect! Overall, the peak thrust from the boosters (even with some very slight non-simultaneity) will have likely exceeded the peak thrust of the D9 giving some confidence, nonetheless, recalling the mount failure I’m planning go back over and run a few more glue fillets on the internals to be sure.
There is also the possibility to put three extra boosters into the tube fins, but I feel like this is asking for trouble as they do not point to the CG and are a long way out from the main axis, so I think this one is not on the menu...
I had an altimeter (JLA2) in both the first (C6-3+2xA10) and last (B6-2+4xA10) flights. These gave altitudes of 58m and 78m respectively.
According to the C/F-M equations the first flight made 67% of prediction, while the second made 97%.
My naive interpretation was that this was due to a truer flight with the 3off spin tabs, but I realise there are many other factors which could influence this (including altimeter accuracy).
In this video of the first flight I think there is a pronounced pitch/yaw, I don't believe there was enough wind to cause this through windcocking, but again various other factors.
A couple of these flights have been my first D impulse launches, and more generally this build has been a big progression for me. I have learned a lot, in one or two cases, the hard way!!
I am now wondering about launching this model on a Klima D9-3. If I add boosters, then I can get into mid-E range, which is a prospect! Overall, the peak thrust from the boosters (even with some very slight non-simultaneity) will have likely exceeded the peak thrust of the D9 giving some confidence, nonetheless, recalling the mount failure I’m planning go back over and run a few more glue fillets on the internals to be sure.
There is also the possibility to put three extra boosters into the tube fins, but I feel like this is asking for trouble as they do not point to the CG and are a long way out from the main axis, so I think this one is not on the menu...
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Moving on to the second rocket in this thread (or third including the small prototype)... which was also started a bit by accident. This was because I didn’t check some motors I was ordering and got a pair of 24mm C11-3’s without noticing they were not 18mm. These mistakes happen and sometimes can lead on to good things, as I had been a bit unsure about getting into the larger motors, so maybe needed a nudge.
Having got the motors through I realised my mistake but also decided that I might as well find a way to use them…
From the experiences in building and optimising the Gran Cohete, I liked the idea of making another large model, but more streamlined.
I had got some 42 mm dia tube (BT-60) and used the nosecone from a Loadstar I got back in the 90’s to save some scratch build time.
I made a set of narrower and proportionally longer fins more similar to a conventional medium power design, but because I’ve not got into the simulations yet, decided to play it safe and go for 5 fins for extra surface area. And because I had not made a 5 fin rocket!
This made a nice arrangement and led me to protrude the motor mount again, and make a sort of boat tail with the fins extending onto the mount. Debatably this might bring a little aero benefit but I think really this would need a smoother transition, rather than a step, but I liked the aesthetic! I did a few trials in painting highlights on the fins and found a pattern that I was very pleased with that brought out this geometry without emphasising the length too much. This time I used a wire loop as a strong point for the shockcord and again used large drinking straws for launch lugs.
Having got the motors through I realised my mistake but also decided that I might as well find a way to use them…
From the experiences in building and optimising the Gran Cohete, I liked the idea of making another large model, but more streamlined.
I had got some 42 mm dia tube (BT-60) and used the nosecone from a Loadstar I got back in the 90’s to save some scratch build time.
I made a set of narrower and proportionally longer fins more similar to a conventional medium power design, but because I’ve not got into the simulations yet, decided to play it safe and go for 5 fins for extra surface area. And because I had not made a 5 fin rocket!
This made a nice arrangement and led me to protrude the motor mount again, and make a sort of boat tail with the fins extending onto the mount. Debatably this might bring a little aero benefit but I think really this would need a smoother transition, rather than a step, but I liked the aesthetic! I did a few trials in painting highlights on the fins and found a pattern that I was very pleased with that brought out this geometry without emphasising the length too much. This time I used a wire loop as a strong point for the shockcord and again used large drinking straws for launch lugs.
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I also made a payload bay as an extension to the main rocket. This was a further ~46 cm length of the same body tube, but with a DIY ply bulkhead at one end, which ran another wire loop for the NC end of the recovery, plus a wire pair so I could put in some LEDs or something like that at some point. The idea is that when the payload section was used, the whole front section including the NC (friction fitted tightly) would separate, possibly with a different recovery to avoid the two halves crashing into each other from shock cord twang. I kept the coupler quite long to prevent any play which might introduce flex at the join, and sanded the coupler back in the mid part to reduce friction, along with a good coating of pencil graphite. I am still a bit tentative about launching it with the payload and want to do a simulation because its too long to do a swing test.
Once it was all finished up, I named this model “Razzo”… can you spot the theme?
I inked on the payload section the second part of the name, so that when it is launched in this extra-long configuration, it is “Razzo Oltraggioso”! Well it is by my standards anyway!
Once it was all finished up, I named this model “Razzo”… can you spot the theme?
I inked on the payload section the second part of the name, so that when it is launched in this extra-long configuration, it is “Razzo Oltraggioso”! Well it is by my standards anyway!
First and foremost, congratulations on successful flights.
Can you provide a reference to these equations. Just because I"m curious.
Where are you? The Klima engines are not available here in the US, much as many of us wish they were.
I'm with you there; I would not do that.
Another nice one. I love the look of five fins. (So why don't I make some of them?) I think that step in diameter will increase your drag, not decrease it as a boat tail does. But you're not building for competition, and it seems you're building what you like, so who cares? Since you've got the 24 mm motor mount, I think you'll like how this goes on a D12.
Good, expanding your experience, I like it.
How would you deploy that payload's recovery device (parachute, I assume)?
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Thanks for the interest and comments!
What I refer to as C/F-M is the re-derivation by Randy Culp of the Fehskens-Malewicki equations (see Estes TR-10 but the version I have does not give the equations) I'm sure you may know these by a different name but I've not yet seen them with a consistent title (other than *not* being what is usually called "the" rocket equation). They are very concisely explained and laid out in a practical way at
http://www.rocketmime.com/rockets/rckt_eqn.htmlI think there are online calculators based on these but i've found it useful to do the calcs myself and understand the sensitivities a bit better.
Yes indeed, I am in the UK and fortunate enough to have a few boxes of different Klima motors.
Definitely!! This is next on my list of things to do once I am in a big enough field!
I have read threads for a couple of models which separate at a mid point where each section has its own recovery and the two chutes are carefully (!) packed one behind the other and simply separate on ejection. Because the fore is streamlined compared to the aft section, it should decelerate more slowly and separate rather than entangle. I was considering using a streamer for the front section to aid this process but haven't worked this through yet and a small chute may be better.
What I refer to as C/F-M is the re-derivation by Randy Culp of the Fehskens-Malewicki equations (see Estes TR-10 but the version I have does not give the equations) I'm sure you may know these by a different name but I've not yet seen them with a consistent title (other than *not* being what is usually called "the" rocket equation). They are very concisely explained and laid out in a practical way at
http://www.rocketmime.com/rockets/rckt_eqn.htmlI think there are online calculators based on these but i've found it useful to do the calcs myself and understand the sensitivities a bit better.
Yes indeed, I am in the UK and fortunate enough to have a few boxes of different Klima motors.
Definitely!! This is next on my list of things to do once I am in a big enough field!
I have read threads for a couple of models which separate at a mid point where each section has its own recovery and the two chutes are carefully (!) packed one behind the other and simply separate on ejection. Because the fore is streamlined compared to the aft section, it should decelerate more slowly and separate rather than entangle. I was considering using a streamer for the front section to aid this process but haven't worked this through yet and a small chute may be better.
Let me see if I've got this. One might place a bulkhead at the bottom of the upper section, with a parachute attached to the underside thereof. Then pack both parachutes in the lower section. Is that the idea? It's clever. If that's the idea, my hat's off to whoever thought of it. If that's not it, well, hats off to me I guess. 
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Yes that's it exactly, I can't claim the idea though! Credit to other threads on TRF. My main consideration in building the bulkhead was to reinforce this well so it wouldn't blow out and stifle the separation.
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So, to date I have done two launches with the main “short” section of Razzo, using those two C11-3s I (accidentally) bought. Both these worked very well, probably the only minor improvement being that ejection looked to be a little before apogee so possibly the 5 second delay would be better. One flight with an altimeter clocked an altitude of 87m, which is just over 80% of my C/F-M prediction, I'm very happy with that esp given the slightly early ejection.
View attachment TRIM_20220302_123451.mp4
I'm feeling pretty confident about launching this on a D impulse in the short configuration (once the storms finish...), but there are a couple of other things I could certainly appreciate any advice on....
1. I would like to try the long configuration with the payload but need to assess its stability. Is it too long? I have seen plenty of skinny rockets on threads, and my guess is this rocket is fairly stable with 5 fins, but am aware that care is needed. I can't swing test, so I need to simulate, but this is a new thing to me...
2. Launching on a reloadable casing and venturing into mid-power. I am hoping to soon have a 24mm one-grain Cesaroni casing and am considering whether I can launch this rocket on a low thrust (white/smokey) composite E motor. As well as doing the calcs for a higher thrust and checking the build quality, I realise I will need to modify the mount to accommodate the thrust from the base of the mount rather than the thrust ring at the top. I have some phenolic 24 mm mount tube and my simple idea is to add a ring of this then bond and reinforce onto the existing mount, then add a better retainer. Is this a reasonable approach, are there simpler ways?
View attachment TRIM_20220302_123451.mp4
I'm feeling pretty confident about launching this on a D impulse in the short configuration (once the storms finish...), but there are a couple of other things I could certainly appreciate any advice on....
1. I would like to try the long configuration with the payload but need to assess its stability. Is it too long? I have seen plenty of skinny rockets on threads, and my guess is this rocket is fairly stable with 5 fins, but am aware that care is needed. I can't swing test, so I need to simulate, but this is a new thing to me...
2. Launching on a reloadable casing and venturing into mid-power. I am hoping to soon have a 24mm one-grain Cesaroni casing and am considering whether I can launch this rocket on a low thrust (white/smokey) composite E motor. As well as doing the calcs for a higher thrust and checking the build quality, I realise I will need to modify the mount to accommodate the thrust from the base of the mount rather than the thrust ring at the top. I have some phenolic 24 mm mount tube and my simple idea is to add a ring of this then bond and reinforce onto the existing mount, then add a better retainer. Is this a reasonable approach, are there simpler ways?
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To have a go at the simulation, I have just downloaded OR and put in a simple geometry for the two configurations (edit: ie, with and without the payload section), using a manual mass entry. The short version matched pretty well with the altimeter data and the CGs for both versions seem close.
This gives a high stability... possibly too high! From reading a couple of threads on this topic previously, one consideration seems to be to avoid launching with any appreciable cross-wind.
Any thoughts on this would be very helpful.
For info, here are the fin dimensions which are probably the only part not described above, but just let me know if any other variables would be useful.
This gives a high stability... possibly too high! From reading a couple of threads on this topic previously, one consideration seems to be to avoid launching with any appreciable cross-wind.
Any thoughts on this would be very helpful.
For info, here are the fin dimensions which are probably the only part not described above, but just let me know if any other variables would be useful.
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Well you've learned what happens when you add length to an otherwise unchanged design: the static stability margin goes up. And yes, the major, perhaps only downside to a very high margin is the weathercocking. To say you shouldn't launch "with any apreciable crosswind" is probably overcautious, but you do want to be more careful about wind than you'd be without the payload section.
That said, any payload you place up there will raise the CG even more, and then you might really get into the "no appreciable wind" territory.
You can fight this by adding canards to the payload setion. You'd keep your original short configuration with its original static margin, then the payload section's canards would raise the CP just as the added length and elevated payload raise the CG.
What I would do in your shoes is decide where I'd like the canards aesthetically, then size them to get the margin where I want it. My off the cuff, complete WAG of a guess that's probably wrong is that canards of somewhere between half and a quarter of the area of the main fins, placed about 2/3 of the way up the payload tube, might be somewhere near right.
Fiddle around with it in OR and you'll learn a lot more than you would by reading what I have to say, even if I knew what I was talking about.
As for modifying the motor mount to take E motors, you'd be surprised at how complex that does not have to be. Use a wrap of masking tape on the case to get a tight friction fit, another wrap around the tube and thrust ring for additional retention, and launch that puppy. You'll be fine.
That said, any payload you place up there will raise the CG even more, and then you might really get into the "no appreciable wind" territory.
You can fight this by adding canards to the payload setion. You'd keep your original short configuration with its original static margin, then the payload section's canards would raise the CP just as the added length and elevated payload raise the CG.
What I would do in your shoes is decide where I'd like the canards aesthetically, then size them to get the margin where I want it. My off the cuff, complete WAG of a guess that's probably wrong is that canards of somewhere between half and a quarter of the area of the main fins, placed about 2/3 of the way up the payload tube, might be somewhere near right.
Fiddle around with it in OR and you'll learn a lot more than you would by reading what I have to say, even if I knew what I was talking about.
As for modifying the motor mount to take E motors, you'd be surprised at how complex that does not have to be. Use a wrap of masking tape on the case to get a tight friction fit, another wrap around the tube and thrust ring for additional retention, and launch that puppy. You'll be fine.
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Brilliant, this is the sort of advice I like!
But will in any case take it easy on the reloads to avoid shredding the whole thing
Thanks for the ideas. Canards would be a nice addition and a good thing to work up on OR as well.
Will update with experience from the next launch!
But will in any case take it easy on the reloads to avoid shredding the whole thing
Thanks for the ideas. Canards would be a nice addition and a good thing to work up on OR as well.
Will update with experience from the next launch!
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OR sim updated with optimised canards...
Designed to keep the stability below 3 cal, compared to getting on for 6 cal without canards, and a little over 2 for the short version.
Slightly against my expectation I have actually found OR to be quite fun to use... hopefully that doesn't mean I am doing it all wrong!
Designed to keep the stability below 3 cal, compared to getting on for 6 cal without canards, and a little over 2 for the short version.
Slightly against my expectation I have actually found OR to be quite fun to use... hopefully that doesn't mean I am doing it all wrong!
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Cut sanded and glued in quintuplicate
Oh, no no, it's definitely supposed to be fun.
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I added a wire loop to allow the motor casing to be cable tied assuming it would not be compatible with the engine hook, as per the pro29 casing I already have.
But when my new pro24 casing arrived I was delighted to find it has a neatly designed slot in the rear closure so works fine with the original hook.
Having made the loop will probably cable tie over the top of the hook and into the loop anyway... Belt and braces!
I've run extra glue fillets on the fins and accessible parts of the motor mount, also sealed the tube spiral.
Planning to try a D12 with the extra section and my first reload flight on a E31 with the short config.
All painted and RTF!! Flying day Sunday!
But when my new pro24 casing arrived I was delighted to find it has a neatly designed slot in the rear closure so works fine with the original hook.
Having made the loop will probably cable tie over the top of the hook and into the loop anyway... Belt and braces!
I've run extra glue fillets on the fins and accessible parts of the motor mount, also sealed the tube spiral.
Planning to try a D12 with the extra section and my first reload flight on a E31 with the short config.
All painted and RTF!! Flying day Sunday!
waltr
Well-Known Member
I lost a reload casing upon ejection once when only using the motor hook. Now I tape the hook onto the casing to hopefully ensure the casing stays in the rocket.
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We had an epic flying day at the weekend, fantastically sunny (particularly for the UK in March!) and a mild cross wind. I flew both models from this thread gradually increasing impulse and thrust.
First up was Razzo Oltragiosso in the long configuration with payload bay, on a D12-5. I noticed as I was setting up that the main section of the body tube had warped ever so slightly, whether from gluing the spirals, or from sitting in the sun for an hour, I don't know, but got some advice from experienced members and was reassured that it was not a big issue.
View attachment TRIM_RO.mp4
I was very happy with how the rocket looked on the pad and it went off a storm on my first D motor! As well as a successful flight, the bit I was particularly interested in was the ejection to see how the payload separation went. What I was secretly hoping for was something like this separation of this amazing HPR Soyuz model. Happily it just missed crossing the sun and I had a good visual on it for ejection, and that was exactly what happened! Don't think its visible in the video but it was a great image that I will remember well. The front part was on a streamer and this was the one bit that could have been improved, as I sized it for a front ejection where I suppose the streamer primarily makes the tube drop with some lateral aspect and so breaks the aero, whereas for a rear ejection (esp on a section with canards!), it was fully aero and came down pretty fast... but due to being light and thanks to some quality west country mud, the damage was limited to a small crack at the very fore of the tube and also the nosecone hook. As I had superglue and some kevlar braid handy I was able to repair the NC attachment point easily in time for the next Razzo launch.
Next was GC, on a D9-3 centre and two A3-Ts, ignited with an indirect method so the boosters ignite via tape match from the centre composite (this directly ignited by ematch), to avoid any potential fast BP jump-n-stall effect. This was my first composite and also first E impulse - it went off very well and got a decent altitude then came back in with an ideal recovery.
Thanks to @PhilC for these cracking action photos and advice as well.
Then towards the end of the day I went whole hog and did my first reload and E motor on the short configuration Razzo. Had some more great advice from experienced flyers on getting the reload set up just right (the reloads having arrived in hand only that morning via the club) - very grateful for this as they don't look quite the same off of a youtube video. This was a CTI Pro24-1G 26E31 white thunder on a 6 second delay. I was very stoked with this and great to see how differently the same rocket (minus payload bay) behaved launching on nearly three times the thrust, altimeter clocking effectively double peak acceleration and not far off three times velocity. The pre-launch OR sim said 313 m and it made 302 m, so 96% of prediction and well near enough 1000 ft. Minor tangle in the chute meant it dropped slightly fast but saved a long walk (or worse!) and again no damage done thanks to the mud.
Many other great flights on the day, plus my nipper launched her first (very nearly) entirely self constructed model, a 5-fin Baby Bertha and successfully completed the first stage of the model achievement programme, so she was well happy too. Credit to everyone on the field, especially the RSOs.
This thread has been a major progression for me, from models that I had never contemplated launching on mid power, using SIMs and much more technical motors, with great satisfaction! Thanks to everyone who has chipped in, and especially @jqavins for advice, ideas and encouragement which have really helped a lot.
First up was Razzo Oltragiosso in the long configuration with payload bay, on a D12-5. I noticed as I was setting up that the main section of the body tube had warped ever so slightly, whether from gluing the spirals, or from sitting in the sun for an hour, I don't know, but got some advice from experienced members and was reassured that it was not a big issue.
View attachment TRIM_RO.mp4
I was very happy with how the rocket looked on the pad and it went off a storm on my first D motor! As well as a successful flight, the bit I was particularly interested in was the ejection to see how the payload separation went. What I was secretly hoping for was something like this separation of this amazing HPR Soyuz model. Happily it just missed crossing the sun and I had a good visual on it for ejection, and that was exactly what happened! Don't think its visible in the video but it was a great image that I will remember well. The front part was on a streamer and this was the one bit that could have been improved, as I sized it for a front ejection where I suppose the streamer primarily makes the tube drop with some lateral aspect and so breaks the aero, whereas for a rear ejection (esp on a section with canards!), it was fully aero and came down pretty fast... but due to being light and thanks to some quality west country mud, the damage was limited to a small crack at the very fore of the tube and also the nosecone hook. As I had superglue and some kevlar braid handy I was able to repair the NC attachment point easily in time for the next Razzo launch.
Next was GC, on a D9-3 centre and two A3-Ts, ignited with an indirect method so the boosters ignite via tape match from the centre composite (this directly ignited by ematch), to avoid any potential fast BP jump-n-stall effect. This was my first composite and also first E impulse - it went off very well and got a decent altitude then came back in with an ideal recovery.
Thanks to @PhilC for these cracking action photos and advice as well.
Then towards the end of the day I went whole hog and did my first reload and E motor on the short configuration Razzo. Had some more great advice from experienced flyers on getting the reload set up just right (the reloads having arrived in hand only that morning via the club) - very grateful for this as they don't look quite the same off of a youtube video. This was a CTI Pro24-1G 26E31 white thunder on a 6 second delay. I was very stoked with this and great to see how differently the same rocket (minus payload bay) behaved launching on nearly three times the thrust, altimeter clocking effectively double peak acceleration and not far off three times velocity. The pre-launch OR sim said 313 m and it made 302 m, so 96% of prediction and well near enough 1000 ft. Minor tangle in the chute meant it dropped slightly fast but saved a long walk (or worse!) and again no damage done thanks to the mud.
Many other great flights on the day, plus my nipper launched her first (very nearly) entirely self constructed model, a 5-fin Baby Bertha and successfully completed the first stage of the model achievement programme, so she was well happy too. Credit to everyone on the field, especially the RSOs.
This thread has been a major progression for me, from models that I had never contemplated launching on mid power, using SIMs and much more technical motors, with great satisfaction! Thanks to everyone who has chipped in, and especially @jqavins for advice, ideas and encouragement which have really helped a lot.
I'm touched. You're welcome. Great job!
