Of cabbages a spools

[Borderline Sci]

I was playing a round with RockSim (7.0.4.5) to see if I could come up with at high-speed high altitude spool. In the old 5.0 version of RockSim I could use tube sleeves to simulate a disks. But on the 7.0 sleeves are not considered for calculating the CP. So I used transitions as the disks and what I came up with.

 

[Borderline Sci]

Here is a Jpeg for you-ns that do not have RockSim 7
it simmed at over 7000ft and 907 mhp on a H48

 

[KermieD]

From my understanding, spool rockets only work with a plate on the front as well as the back end, but I could be 100% wrong on this. I think rstaff3 did some experimentation using a CD on the back of a rocket and some odd stress squishy as the nose and had some stability problems. Hopefully he'll chime in.

 

[rstaff3]

Spools have been discussed at length in other threads, and people have reported taht they will work with either the top or the bottom plate. I think these 'one platers' all used CD-ROMS. The thing I built had a foam PC on the end of the tube and a CD on the bottom. The odd shape of this 'nose' may have had something to do with its instability.

The design Borderline presented looks to me to be...well...borderline. The bottom plate looks pretty small compared to typical spool, cone-stabilized, or even ring-fin designs. Rocksim probably isn't that accurate for this type design. If it were me I'd try it on a smaller motor for its first flight and fly it from the HPR racks so it's far away from the crowd.

 

[KermieD]

Toldja I could be 100% wrong!! So, rstaff...you're telling me you can do a rocket with only a TOP plate on it?

 

[rstaff3]

Stymye reported it here https://www.rocketryforum.com/showthread.php?s=&threadid=4126 and I've seen other reports on rmr. Like you said, my one 'experiment' went awry.

I do have a nice plastic HPR spool..review is on EMRR.

 

[lalligood]

Originally posted by KermieD
Toldja I could be 100% wrong!! So, rstaff...you're telling me you can do a rocket with only a TOP plate on it?

As much as I hate calling a 1 disc rocket a "spool rocket", they do in fact work with only one disc. I have built & flown two made from a single CD, 18mm MMT tube, & launch lug. One had the disc at the forward end of the tube, the other had the CD at the aft end. Both flew straight as an arrow. They (along with other "true" spools) are stable because the CP is at least 4/3 the diameter behing the aft plate (this is according to teflonrocketry1 & a report that he recently acquired). I have never built one (singel disc spool rocket) that was larger, but it would definitely work as long as all dimensions were scaled up...mostly because they look like a wounded duck during recovery. (Yeah, I'm a spool purist--if there is such a thing! )

But back to the original issue. RockSim does not properly deal with high drag designs (I know that teflonrocketry1 will chime in agreement with me on this). I feel that I have proved it in the real world though by building what is essentially a high power funnel rocket, which really is little more than a saucer with a long central body tube/MMT. Check out my scratchbuild design called "Black Dragon". Even with an I motor, this rocket wasn't going to get anywhere near 1000ft. Heck, I don't think it would hit 1000ft with a decent J motor! While it doesn't slow down nearly as quickly as a true saucer, it unquestionably coasts much, much shorter than a "traditional" rocket design. I guess what I'm trying to say is that there is no such thing as a high altitude spool.

High velocity OTOH is somewhat possible because spools typically have a much smaller mass than a comparable "traditional" rocket. Proportionately speaking, high thrust + low mass will always equal high velocity. Just don't expect that velocity to stay high for any significant length of time

HTH,

 

[rstaff3]

All true...I don't know why the 'probably' was added to the post above. Rsim is way off on many of my weirder designs.

Teflon...tell me more about this report. If it was discussed in another thread I missed it. Link will suffice.

 

[Borderline Sci]

Ya more links

Thanks for the responses.
I was thinking of this design as more of a funnel fin then half a spool. That was the only way I could fib to RockSim 7 to get it to make the rocket stable. I have the nose flat because with any normal nosecone shape, RockSim will push the CP forward.
When I was using RockSim 5, I could put real looking disks on the body tube by using short outer sleeves with large OD’s but RockSim 7 will not see the sleeves as drag elements for calculating the CP. Now I know that the CP is ¾ the diameter behind the disk. I can make this work.
No fears mate, I launch my dangerous stuff out in the desert miles away from everyone.

 

[rstaff3]

For tube and ring fins, see the Apogee newsletters with articles by teflonrocketry1. Links to these can be found here https://www.rocketreviews.com/rocksim_library.shtml

Remote desert launches are great for this type of thig

 

[powderburner]

Originally posted by Borderline Sci
I have the nose flat because with any normal nosecone shape, RockSim will push the CP forward.

So, if I read these posts correctly, this is a 'paper' design and has not flown?
If you *DO* try to launch this thing, I hope you pick a day in your desert that is not very busy (no bystanders).
I think you have stumbled across a 'glitch' in Rocksim. Just because you do not select a nose cone shape does not mean that the front end of your rocket will not have some aerodynamic effects. If Rocksim leaves off (or zeroes) the nose cone contribution (which would act to de-stabilize your design if it is included) it will calculate an artificial c.p. that is too far aft. I think you have a fiction (fantasy?) answer that resulted from your Rocksim inputs.
A better approach would be to ask Apogee how to simulate a bluff nose shape.
I think you will get a completely different c.p. result.

 

[Borderline Sci]

Powdreburner
If you have RockSim 7.0 you can open the file and see that the body tube is hand rolled two-layers of 5oz carbon. And front and rear disks are fiberglass. This is just an idea that has been rolling around in my head for two years. It will be some time before I could make this. I’m still working on my 4.5inch carbon fiber L2.
As far as glitches go I have a habit of finding them in every bit of software I work with. This is why I put this here so I could get you smart guts to give me some info on calculating this manually.
I would prefer to have a cone shaped nose but then you will just have a flat funnel fin. I put a flat nose to simulate a small front disk.
I just down loaded Pete Lilja’s RockSim file to see how he did it. The cp is good until I touch the front disk and change the size. Then the cp moves to the front the rocket. This leads me to believe that there is something wrong with my copy of RockSim.
Has anyone seen this problem?

Rstaff3
Got the Rocket reviews newsletters, not much there in links for spools. Do you have a link to the article from Teflonrocketry1?

 

[rstaff3]

I don't have the spool article, teflon...hellooooooo....

BTW I changed the front transition to a similar shaped cone and the stability went bye-bye. And, I just remembered something. I have seen cases in the past where I made very short, wide cones an the results went haywire. When I made them just a skosh longer it started working. I don't think yours has a bug, they prolly all do.

 

[teflonrocketry1]

Boderline Sci what are you trying to simulate? Please post or PM me the diameters and thicknesses of the front and rear plates for your spool rocket. I can't figure this one out. As drawn in the RockSim file its not stable. If you give me the details I will do my best to get back to you with a good RockSim simulation. Please be patient since I am actively searching for a new job. The 38 mm half spool is a no go. Not enough base vortex (as drawn) for stability not enough funnel fin area for stability.

The scratch 12 inch spool is a very stable design. The CP is no where near the location RockSim states; according to John Cipolla's wind tunnel data it should be about 1.5 plate diameters behind the actual rocket. To purchase a copy of the "Spool Rocket" report visit: https://www.aerorocket.com/spool/spool.html To reduce the drag to a minimum make the rocket be 18 inches in length!

Bruce S. Levison, NAR #69055

 

[daveyfire]

Doesn't work...

https://www.pacificpropulsion.com/events/launch_12-19-04.htm#pencil

{g} was pretty spectacular though!

 

[urbanek]

I did the simulation work for my Wife's level 3 spool rocket. I used RockSim 7.0.

First off, I ignored any stability information from the simulation. It's just a simulation, after all. She conducted a series of flights with scale models of her spool. In one series of tests, whe tried to move the CG car enough back by adding weights to the underside of the aft disk. She found that she could not move the CG back far enough to make the spool unstable. Stability was proved through flight testing of a scale model.

What she wanted me to determine was timer settings. She was flying with 2 timers because Level 3 required electronic deployment and redundancy.

The central tube was just a normal tube. The forward and aft disks were simulated as Sleeves with the dimensions of the disks. A 'nose cone' was added at the front which was as wide as the disk and had a length of .001".

I used mass override to assure the simulation would 'fly' the rocket correctly. I made the mass of the rocket equal to the full scale rocket.

Since a flat disk flying through the air has a Cd of 1.00, that's what I used for the Cd in the simulation. When we launched the simulation with the M1419, the simulation predicted about 1800' altitude and that the rocket would pretty much stop dead when the motor burned out.

Our flights with the scale models lead us to believe that the spool would carry enough momentulm to continue upward for at least 2 seconds before descending, so my wife set the first channel to go off at 2 seconds after burn out.

When she flew the beast, it looked every bit like 1800 feet to my uncalibrated Mark I eyeball. The rocket stopped dead after the motor burned out and the rocket tumbled for about 2 seconds before the chutes were deployed. The simulation was right.

Julia's WizKid 3 was one of the more interesting level 3 flights I've ever seen. The rocket looked like it was easy to construct, easy to transport and easy to recover. The flight could have beem done at just about any flying field in the country.

It was 48" long and 5 1/2" in diameter. The disks were 24" diameter and 3/4" thick. It split in the middle. The two sections had their own chutes. The lower section has the 98mm motor mount. The top of the foward section had the electronics bay with two Missile Works Pet2 timers. The thing I like the best was the fact that all the switches were on the top of the electronics bay. All she did was climb a ladder and flip the switches. No hatches or anything. Very 'outside the box'.

Right now the rocket sits in the corner of our back bedroom, with a children's blanket over the top disk, and a cat bed on top of that. It's Alyssa's favorite place to sleep.

urbanek

 

[teflonrocketry1]

Welcome to the Forum Urbanek! Would you be David Urbanek who inspired me to figure out how to simulate odd things like tube fins and ring-tail fins?

John Cipolla did some wind tunnel testing on Spool rocket designs and has written up a report that he is selling through his company AeroRocket.

(https://www.aerorocket.com/spool/spool.html)

I fnally purchased a copy of the report and it confirms the fact that the CP of spool rockets is behind the aft plate. Included in the report are several mathematical models to fit the limited set of data that was generated. I have been looking at extending these results to use in RockSim simulations of short fat rocket designs. Extending the wind tunnel data using a linear fit, indicates the CP of a single flat plate in a perpendicular air flow is about 2.1 plate diameters behind the plate. The linear fit gives the most conservative CP value of all the models of the wind tunnel data. I use a massless transition in RockSim to bring the CP aft behind the base of the rocket for these types of simulations. If you make the conical transiton pi times the base diameter long, and the same width at its base as the base of the rocket (tip diameter as small as possible without crashing the software) the CP indicated behind a single flat plate is 2.1 base (or plate) diameters from the tip of the nose cone.

Bruce S. Levison, NAR #69055

 

[rstaff3]

At first this result surprised me. But it is totally consistent with the fact that a spool with only a top plate is stable, and that you can CHAD stage a saucer with a D12 'staged' to an empty casing, hence moving a lot of the initial mass behind the shroud.

 

[urbanek]

Originally posted by teflonrocketry1
I fnally purchased a copy of the report and it confirms the fact that the CP of spool rockets is behind the aft plate.

How much did he charge for just the report? I've seen his software and it's really cool, but I don't have a practical use for most of it. OTOH, I have no trouble paying for the report. When I told my wife that someone had done some solid research on spools, she definitely wanted to get the report. I was about to email to find out how much he charged for just the report.

urbanek

BTW, same Dave Urbanek

 

[teflonrocketry1]

Dave,

I bought $150.00 in software to get the report. I plan on writing and article about how to simulate short wide designs using an extension of the data from the report.

Bruce S. Levison, NAR #69055