More Half-Baked Designs Thread

[BigMacDaddy]

I made this thing -- even if I cannot make it stable it will make a nice display piece. My first print failed (but I learned some issues from what printed). I wound up splitting off ring fins/wings to print separately. Printed the rear ejection pod parts today.

Yeah, what he said. To be a little more specific, I think making the aft part of the wings into that "squashed ring tail" was a good move,

Cool... My mind sim may be getting better training...

but the forward part that remains flat constitutes large canards on a short rocket; that's going to be really tough. And that on top of the fact that flying cones are not stable to begin with unless they rely on base drag. (Put a nose cone alone into OR and look at where the CP is; it's not pretty.)

Yeah, I am skeptical about this -- just not long enough and a host of other issues.

The yaw stability pods should probably be shorter, coming from the base up only as high as the front edge of the ring.

The first thing I would do in your shoes to get rid of the mini motor cluster. Just use faux nozzle bells. That'll take a lot of mass out of the bottom.

I hope you can make it work, 'cause it's definitely cool looking.

Thanks -- I did angle the yaw-stability-pods more into the rocket to basically shorten them and make rear portion a bit larger. I also scrapped the cluster and went with a single 18mm engine. Depending on how heavy this is and how much weight I need to jam into the nosecone I may need to go up to a D engine (but then will need more weight and may not have enough space and length).

I am going to have so many crazy rockets to launch the next time I get out to the field.

 

[Bill S]

BigMacDaddy,
If you get that rocket flying straight, please put up some video. Pretty cool idea, if you can get it to work.

 

[Cape Byron]

I like the 16 motor MicroMaxx cluster...

 

[jqavins]

If you can't get it stable, you might try leaving off the parts you have here in wood. I bet that would do it, with a tolerable amount of nose weight. That makes it less like the inspiration pictures; whether or not that makes if less cool looking is a matter of taste.

 

[BigMacDaddy]

If you can't get it stable, you might try leaving off the parts you have here in wood. I bet that would do it, with a tolerable amount of nose weight. That makes it less like the inspiration pictures; whether or not that makes if less cool looking is a matter of taste.

Thanks Joe -- definitely something to consider. I was wondering about making them swivel as well but could not figure that out.

By the way -- for some reason I think this rocket looks a bit like a chicken (less cool than the prototype with that stuck in my head)...

 

[BABAR]

Thanks Joe -- definitely something to consider. I was wondering about making them swivel as well but could not figure that out.

By the way -- for some reason I think this rocket looks a bit like a chicken (less cool than the prototype with that stuck in my head)...

for some reason, everything looks like chicken somehow.

 

[BABAR]

thinking about Obi Wan's ship in one of the earlier (episodes 1-3) Star Wars movies, where it attached to a big ring in orbit, took off at light speed, then detached planetside. At least I think it was something like that. You could rig your wood sections to fall off at launch (they're PAD stabilizers, yeah, that's the ticket.) Alternatively and more challenging would be for them to SLIDE BACK at launch and hang out the back, so they go from being DE-stabilizing to STABilizing. Would be a challenge to make that reliable. As presented here, I think unless you can put a piece of a black hole in the nose, no earthly element is going to be heavy enough to provide enough nose-weight to make that stable and it's going to go head over heinie. I have been proven wrong before, and I would love for this to be another of those times.

Regardless, it's a cool design.

 

[BigMacDaddy]

Alternatively and more challenging would be for them to SLIDE BACK at launch and hang out the back, so they go from being DE-stabilizing to STABilizing. Would be a challenge to make that reliable.

That is interesting... Actually there is an internal tube that the motor is sitting in so I could mount the fins to a ring that would fit around that and could slide back. This version is all glued together now but I could definitely think about doing the moving fins model with those canards sliding back through the ring wings to become rear fins. Not impossible at all -- but maybe that is late night optimism...

 

[jqavins]

Maybe lightly spring them toward the rear, with strings holding them forward. Much the way some glider's use ejection charges to burn through strings, you could one of two extra igniters and a cluster whip to burn through at launch.

OK, now that's half baked.

 

[BigMacDaddy]

Maybe lightly spring them toward the rear, with strings holding them forward. Much the way some glider's use ejection charges to burn through strings, you could one of two extra igniters and a cluster whip to burn through at launch.

OK, now that's half baked.

Or go the other way and have them spring forward at ejection... maybe I can make it glide for recovery? haha... that is fully unbaked...

 

[BigMacDaddy]

A rocket with a camera on a selfie stick?

Not mine or anything but definitely a creative / half-baked idea... Some good failures and testing / iteration here...

 

[BigMacDaddy]

I was able to test my finless streamlined rocket today... Not perfect (quite a bit of wiggle) but flew upwards on C5-3 and deployed its chute. Too much nose weight was needed to make this really worth flying in my opinion but looks cool and glad I got to fly it once...



EDIT: We had hypothesized that the rear ring tail might get singed or even catch on fire. Field I launch at is really wet and swampy so figured I was pretty safe (I launched next to a massive swampy puddle). Anyway, I forgot all about that worry after the launch but just went back to check -- little to no damage and only a tiny amount of soot. I did not do anything to protect it other than priming it.



EDIT #2: FWIW - I remember various concerns about where to put the wadding - either above or below the chute buffer that kept the parachute towards the front of the rocket. I had not left much room for the parachute above the frame I attached inside the body tube. Given this I did push some of the dog barf down below the chute buffer to sit on top of the engine and also put another thin layer on top of the buffer (right under the parachute). Anyway, ejection worked fine but I noticed that the dog barf from below the buffer was stuck pretty good to underside of buffer after the launch.

 

[BigMacDaddy]

Here is a 2nd angle on the launch of the Streamlined Finless Ringtail rocket...



It is pretty interesting if you look at how the fire seems to consume (or at least overwhelm) the ringtail -- I assume this is a trick of the camera since the ringtail is not singed at all.

 

[jqavins]

Interesting, and those are some pretty awesome moment-of-launch pictures.

Thanks for the report. It motivates me to make another try at mine.

 

[BigMacDaddy]

Interesting, and those are some pretty awesome moment-of-launch pictures.

Thanks for the report. It motivates me to make another try at mine.

Thanks! C5 engine puts out some good fire trail (also it was getting a little dark so optimal time to get good blast pictures).

I was reading the Apogee report from 2014 (https://www.apogeerockets.com/education/downloads/Newsletter379.pdf) and I think that I would need to make my ring tail much longer to optimize the stabilizing effect of engine-driven dynamic stability. Currently my ringtail is a little less than 2 body-tube diameters long (75mm long vs. 40mm for body tube diameter). That write-up suggests that 4 body tubes long is optimal (would likely see more ring tail burning then). Then I would need to optimize the gap between main body tube and ring tail so that it is the same as the area inside the body tube.

I messaged Apogee to see if I can get Tim to weigh in.

 

[jqavins]

So you're moving toward GDS. That's a good idea, and not what I want to do. Remember, if the stability is created by the exhaust plume then the rocket becomes unstable after burnout.

I had thought that yours looks rather long, and shorter might work better. For a conventional ring tail - a.k.a. a ring fin, i.e. acting as a lift generating fin where GDS is something entirely different - as the length increases past some point (relative to the diameter) air stops going through. I don't remember what that limiting L/D ratio is. I don't think you're there, but maybe you're in a range where flow through the ring is diminished.

RockSim has shown me stability from some surprisingly short ring tails; it could be that a half inch is all that this design needs. I'm thinking a half inch long ring held off the back by three or four CF rods.

 

[BigMacDaddy]

Going back to another build -- I cannot find my roll of Kevlar line so did not get to finish the Arrowhead Spaceship and test it this past weekend. However, was also wondering about incorporating some rear fins to make this more likely to be stable. Can skewers work for this or should I do mock flame fins?

Can do as many as 8 of these and still stay around outer area of rear of rocket. I am guessing I will get maximum CP shift w/o influencing CG too much if I just did 4 of these fake fire blasts. How long and wide should I make them? Should I put them angled towards center of rocket or angled around outer circumference?

 

[boatgeek]

Going back to another build -- I cannot find my roll of Kevlar line so did not get to finish the Arrowhead Spaceship and test it this past weekend. However, was also wondering about incorporating some rear fins to make this more likely to be stable. Can skewers work for this or should I do mock flame fins?

Can do as many as 8 of these and still stay around outer area of rear of rocket. I am guessing I will get maximum CP shift w/o influencing CG too much if I just did 4 of these fake fire blasts. How long and wide should I make them? Should I put them angled towards center of rocket or angled around outer circumference?

I think for best effect they'd be on radial lines coming out of the central motor tube. I don't think they'll have much effect unless they extend into the free air stream outside the body tube, though.

 

[jqavins]

Six or eight (or more) skewers angled outward, outlining a cone, would be in interesting look, probably not for this. Sputnik-like, but with more than just a ball for the body. I bet they'd oscillate, which I bet would make lots more drag than they would if the don't. It might make noise, so I'm thinking a name with some pun on Buzz Lightyear would be good. With all that drag it wouldn't go high; one hundred feet is about 100 light-nanoseconds. If it would get to 1000 feet that would be Buzz Light-microsecond, but I don't think such a thing would ever get that high.

 

[boomtube-mk2]

Here's one of my half-baked designs I built and flew.
The booster used one D12-3 and one D12-0 with a D12-7 in the sustainer.
Or a D12-5 if it was lofting an egg, the payload section is a BT65. Thank You BMS for having those parts available.

 

[jqavins]

I like it. But if it's flown, isn't it fully baked?

 

[boomtube-mk2]

I like it. Bu if it's flown, isn't it fully baked?

The rocket might be "Fully baked" but the builder is most certainly half baked.

 

[lakeroadster]

I was able to test my finless streamlined rocket today... Not perfect (quite a bit of wiggle) but flew upwards on C5-3 and deployed its chute. Too much nose weight was needed to make this really worth flying in my opinion but looks cool and glad I got to fly it once...



EDIT: We had hypothesized that the rear ring tail might get singed or even catch on fire. Field I launch at is really wet and swampy so figured I was pretty safe (I launched next to a massive swampy puddle). Anyway, I forgot all about that worry after the launch but just went back to check -- little to no damage and only a tiny amount of soot. I did not do anything to protect it other than priming it.

View attachment 489041

EDIT #2: FWIW - I remember various concerns about where to put the wadding - either above or below the chute buffer that kept the parachute towards the front of the rocket. I had not left much room for the parachute above the frame I attached inside the body tube. Given this I did push some of the dog barf down below the chute buffer to sit on top of the engine and also put another thin layer on top of the buffer (right under the parachute). Anyway, ejection worked fine but I noticed that the dog barf from below the buffer was stuck pretty good to underside of buffer after the launch.

Discussion?

 

[BigMacDaddy]

View attachment 489356

Discussion?

Fair enough -- and the ring tail also probably counts as a fin in some way... not sure how to say that there are no fins that stick out past the body tube...

 

[jqavins]

It's a fine line, sometimes, between aerodynamic fins and structural pylons. I believe that in this case the latter was the intent. A well designed ring tail can make a rocket stable even if the pylons are just tooth picks. The matter under investigation is whether or not a "well designed ring tail" can be achieved with the ring no larger than the body tube.

 

[lakeroadster]

Pretty cool.

 

[lakeroadster]

I couldn't get a finless rocket to simulate as successful in Open Rocket, but interestingly enough I did get a Red Nova style design to work, by stretching the length and using a large transition at the end.

 

[jqavins]

It won't simulate as stable, and I think I've figured out why it won't but does seem to have flown well in the video.

It has to do, I think, with body lift. Look for a Peak of Flight article called "What Barrowman Left Out". In that article it's explained that the body lift moves the CP forward from what the Barrowman equations predict. Now, what I think is going on is this:

If you put a nose cone by itself into OR or RS it will show a CP that's forward of the part, and that's not wrong. If you add a body tube, the CP is still forward of the rocket, because the software ignores the body tube when computing the CP. No matter how much nose weight you add, you can never get the CG forward of the rocket (obviously) so the rocket will never simulate as stable.

The body tube's CP (that has been ignored) is at its center. For a rocket with fins, the CP is generally far below the middle, so considering the tube raises it. In this case, with the CP far forward, considering the tube brings it down. With enough nose weight, the CG can be brought forward of it, but the software will never show that.

The video seemed to show the rocket beginning to lose stability as it coasted, saved by the parachute deployment. I think I understand that too. The builder kept saying that the CP would be at the mid point of the tube, but that's not true. The nose cone does bring the CP up from the middle. He added enough nose weight to put the CG two calibers forward of the mid point, and two calibers of static margin should be OK. But because the CP is not where he thinks it is his rocket was actually marginal.

Until yesterday I had accepted that finless doesn't work without GDS or some similar method. But you can't argue with empirical results (as long as the experimenter's methods are valid) so I had to try to think this through. I think I've got a viable answer. Now I want to try to replicate the result, but with better tubes that won't be crushed and bent so easily, with a better estimate of the CP accounting for the nose cone^*, and with a greater static margin.

* I don't know how I'll compute a better estimate. I'll have to look into that. Rereading the PoF article will probably help, or may even have the whole answer. If it doesn't have the whole answer, I'll start by going back to the Barrowman equations, which is something I've never done for myself; why bother when RS does it for me? This time I'll see the method for figuring not only the location of each component's contribution to the CP, but the strength of that contribution. If I can get the strength of the tube's contribution, then it shouldn't be hard to add the body lift in. Of course, it won't be that easy, or Barrowman wouldn't have left it out, would he?

 

[BigMacDaddy]

It won't simulate as stable, and I think I've figured out why it won't but does seem to have flown well in the video.

It has to do, I think, with body lift. Look for a Peak of Flight article called "What Barrowman Left Out". In that article it's explained that the body lift moves the CP forward from what the Barrowman equations predict. Now, what I think is going on is this:

If you put a nose cone by itself into OR or RS it will show a CP that's forward of the part, and that's not wrong. If you add a body tube, the CP is still forward of the rocket, because the software ignores the body tube when computing the CP. No matter how much nose weight you add, you can never get the CG forward of the rocket (obviously) so the rocket will never simulate as stable.

The body tube's CP (that has been ignored) is at its center. For a rocket with fins, the CP is generally far below the middle, so considering the tube raises it. In this case, with the CP far forward, considering the tube brings it down. With enough nose weight, the CG can be brought forward of it, but the software will never show that.

The video seemed to show the rocket beginning to lose stability as it coasted, saved by the parachute deployment. I think I understand that too. The builder kept saying that the CP would be at the mid point of the tube, but that's not true. The nose cone does bring the CP up from the middle. He added enough nose weight to put the CG two calibers forward of the mid point, and two calibers of static margin should be OK. But because the CP is not where he thinks it is his rocket was actually marginal.

Until yesterday I had accepted that finless doesn't work without GDS or some similar method. But you can't argue with empirical results (as long as the experimenter's methods are valid) so I had to try to think this through. I think I've got a viable answer. Now I want to try to replicate the result, but with better tubes that won't be crushed and bent so easily, with a better estimate of the CP accounting for the nose cone^*, and with a greater static margin.

* I don't know how I'll compute a better estimate. I'll have to look into that. Rereading the PoF article will probably help, or may even have the whole answer. If it doesn't have the whole answer, I'll start by going back to the Barrowman equations, which is something I've never done for myself; why bother when RS does it for me? This time I'll see the method for figuring not only the location of each component's contribution to the CP, but the strength of that contribution. If I can get the strength of the tube's contribution, then it shouldn't be hard to add the body lift in. Of course, it won't be that easy, or Barrowman wouldn't have left it out, would he?

It would be easy enough to swing test a number of variations and change variables till you get a stable spin/swing... I know that is not the end-all be-all but would be faster and cheaper than crashing a bunch of rockets.

 

[jqavins]

I've read, not experienced, that swing tests are really hard to perform on very long rockets. And I think this would have to be very long (as shown in the video) in order for the body lift to be much greater than nose cone lift working against you. If I can satisfy myself with calculation (which remains to be seen) then I hop to crash only one or two rockets.