Somewhere, Over the Rainbow

I've done a few "interesting" builds - check these links if interested
https://www.rocketryforum.com/threads/skeletar-another-mega-mosquito-bash-done.121462/
https://www.rocketryforum.com/threads/eye-catching-design-launch.67599/
https://www.rocketryforum.com/threads/pix-thats-nuts-or-i-am-new-rocket-concept-build.58170/

I have a new crazy thought for a rocket, inspired by the Fliskits ACME Spitfire.

That kit proved you don't need a rocket tube to be straight to fly right.......

Attached is my crazy concept. A rocket curved like a rainbow. The fins will be cloud shaped.

802high (AKA Casey) was offering to do custom laser cutting for just material and shipping costs - can't beat that!

These arrived today (there are actually 2 sets). He did a FANTASTIC job cutting these.



They assemble as follows:



I have to admit, we agreed on using 1/8" ply, but the weight is a bit more than I like. I'm probably going to cut out some material to make them lighter.....

"RSO, this one will be a heads up..."

Interesting idea! Following...

I've had issues printing cutting templates that are larger than standard 8.5" x 11" paper (and this needed to be at least 12.3716"), so I went "old school" so I could make the template in halves. To have a 15deg angle I'll be cutting each end to 7.5 deg. Going to be fun on the thin BT101 tubes I'll be using...........

OK - I've come to realize that the thin wall BT101 won't do. I need to order some LOC tubing........

Here's a tune for you to listen to while you build this...

Got my LOC tubing and couplers.

Figuring out how to join the tubes with the angles. The coupler can't extend into the next tube directly without hitting the tube wall (see right side), so I will cut the couplers at and angle as well.

First tube cut & coupler. Test fit of coupler in the tube and the scrap piece installed

More cutting, and dry fitting the pieces together. The center tube is a bit longer than the others, and the 2 end pieces are a bit shorter

It seems like a minimal requirement would be for the center of mass to be perfectly aligned with the motor tube and thrust. So I’m wondering if this is simulated or measured physically.

Decided to try a new technique....

I want to lighten the "fin" weight. Fortunately, I had a spare piece to experiment with.
First I drilled a few holes, then papered one side.


Once the glue dried, I mixed and put some (too much) two-part expanding foam in the large cavities (I wasn't worried about the smaller ones). I suppose I could have left the holes empty but 1) I didn't want to worry about pushing through the paper and 2) having the foam to fill the gap will add some strength.


I then trimmed the excess. I used a razor saw for the main part and then sanded flush to the wood.


And then finally papered the other side


This technique did remove about 25% of the weight. Unfortunately, the battery on my accurate scale died so I had to use my bigger and less accurate scale.

Based on my results, I'm going to work the other other pieces (unfortunately I need to order more foam).
I also need to get the final weight so I can decide how big a motor tube I will need. I initially hoped for a 24mm mount, but I think I will need more power for this.
Definitely 29 - possibly even a 38...........

Spent some time making Swiss cheese of the fin pieces. I didn't get as much weight out as I was hoping for. I may make a few more holes....
Trying to reduce weight without significantly impacting the structural integrity. The biggest piece carries the entire load, so I hesitated to make too many holes - but I may add a few more small ones.

RSO: No funny looking rockets. No asymmetrical designs with crooked or flexible or telescoping body tubes. Motor and fins on the back of the rocket. No kite tails or trailing streamers or canted motors to offset asymmetry around the thrust centerline. Computer simulation required; if you can't sim it, don't fly it.

Hello Sir. I would like to fly my rainbow rocket today!

Silly oddroc flyer's, when will they ever learn. Get them a one way ticket to the rocketry reeducation camp in rural North Korea!

Could make a nice macaroni & Cheese rocket. A fun little rocket for the kids! Name it Mr
Noodle and put an Elmo sticker on it.

Daddyisabar said:

RSO: No funny looking rockets. No asymmetrical designs with crooked or flexible or telescoping body tubes. Motor and fins on the back of the rocket. No kite tails or trailing streamers or canted motors to offset asymmetry around the thrust centerline. Computer simulation required; if you can't sim it, don't fly it.

Hello Sir. I would like to fly my rainbow rocket today!

Silly oddroc flyer's, when will they ever learn. Get them a one way ticket to the rocketry reeducation camp in rural North Korea!

Click to expand...

No asymmetrical designs, canted motors, fins must be on the back...these rules would probably ground a large portion of my fleet. Especially some of Shrox and Fliskits designs....

BTW - I'm taking the original quoted post as a joke.......

suggestion, skin the fins w/ tissue paper, then 'paint' the skin w/ white glue.
Rex

Funkworks said:

It seems like a minimal requirement would be for the center of mass to be perfectly aligned with the motor tube and thrust. So I’m wondering if this is simulated or measured physically.

Click to expand...

... (I don’t want to shout)

Not sure why you’re posting all this. But assuming someone was interested in reproducing the build, what would assure that person the flight is safe?

Simulation?
Measurements?
Prior testing by someone else?

(Someone let me know if I’m off-topic.)

I bought the ACME Spitfire because it was proven. I see no proof here yet.

Funkworks said:

Not sure why you’re posting all this.

Click to expand...

Is this a trick question? It's a build thread.

But assuming someone was interested in reproducing the build, what would assure that person the flight is safe?

Click to expand...

Who said anything about anyone else reproducing the build? @les is documenting his own build.

Certainly the ability of this rocket to fly properly is... TBD. We shall see.

les said:

No asymmetrical designs, canted motors, fins must be on the back...these rules would probably ground a large portion of my fleet. Especially some of Shrox and Fliskits designs....

BTW - I'm taking the original quoted post as a joke.......

Click to expand...

The Shrox and Fliskit designs are fine since they fall under the exemption of a "rocket kit from a trusted manufacturer. " Made to look funny but they are not too extreme.

It will be interesting to see how the curved body tube will fly. What type of nose cone are you thinking of? I would think that critical to help stabilize the airflow over the curved tube.

Yes this is all a joke because you can't sim the turbulence a curved body tube would create, at least with software commercially available. Have fun on the away pad. Always fun to see how far you can push the envelope! As always fly in good conditions with a long rod or rail.

In my opinion dragging it up with canted tractor motors would be preferable to trying to push it from the back with one powerful composite motor. Any find on the back would be for show. Silly oddrocs sometimes require backward thinking.

Daddyisabar said:

The Shrox and Fliskit designs are fine since they fall under the exemption of a "rocket kit from a trusted manufacturer. " Made to look funny but they are not too extreme.

Click to expand...

Maybe not Shrox, but I'm sure Jim had to do some experimenting to get his kits to work.....

Daddyisabar said:

The Shrox and Fliskit designs are fine since they fall under the exemption of a "rocket kit from a trusted manufacturer. " /QUOTE]

Click to expand...

Say WHAT? What "exemption"???????????? "Exemption" by who?

There's been way more far-out safe-flying models over the years from many many individuals than from companies.

And here's a big "secret", many of those oddball models by those companies likely crashed a few times before they worked the bugs out. They had to have been flight tested, before being kitted. What you posted sounds too much like nobody should try anything unusual of their own design, leave that to the manufacturers. But there is never going to be a manufacturer that is going to come up with a design that is exactly like someone else has designed for themselves, short of a "design to order" contract kind of thing. Many are into this hobby to design their own.

Now I'm not advocating "anything goes - put an "L" into a finless real snowmobile" kind of thing. Don't do a Big Bertha with Alpha-sized fins on the nose cone and expect that to fly straight. But the idea of leaving unusual models to the companies, "banning" modelers from doing it, is nonsense.

Now to get back to the real point, the OP's design process could use some feedback to try to improve its' chances. But to say "forget it - leave the unusual designs to the kit-sellers", that's not the hobby I've known for nearly 50 years.

Um, just to be clear, the ACME Spitfire first proto flew very well. While we did proto testing as a matter of course (we did on all of our designs), we were testing more the math/science that told us it should be stable, more so than the model. This testing DID highlight some modifications to help assure other builders would assemble it successfully, but we had a very good understanding of how it would fly before we put her on the pad.

As for an “exemption”, we did have one, but not because we were “FlisKits”, rather it was because as a KIT being mass produced there was a HISTORY of success with the design. Early in the ACME production I heard many tails of RSO’s refusing the allow the ACME on the pad until the flyer could prove it was a kit...

georgegassaway said:

Say WHAT? What "exemption"???????????? "Exemption" by who?

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D'isaBar just talks like this. Satirically and facetiously. He has a long history of unconventional rockets and on the forum enjoys mocking the standard practice of RSOs trying to turn away Odd-rockets because they don't match the "standard rocket shape (3/4 fins and and a nose)"

Nytrunner said:

D'isaBar just talks like this. Satirically and facetiously. He has a long history of unconventional rockets and on the forum enjoys mocking the standard practice of RSOs trying to turn away Odd-rockets because they don't match the "standard rocket shape (3/4 fins and and a nose)"

Click to expand...

Well, I don't blame him then. Fortunately I've not run into close-minded RSO's that want to stifle creativity.

There are the kind of models that you'd fly at a public demonstration, which is a smaller subset of the kind that you fly at a normal launch. I'd never fly an unusual model at a public demo, that had not been thoroughly tested and proven to be very reliable, nor would I want anyone else to at a public demo launch. But then where does one test a unusual model to find if it works and is reliable, if not at a regular launch?

Again I'm not advocating "anything goes", or letting "obviously unsafe" models fly. But "the must be NORMAL (or a kit) or it is banned" mentality is, again, NOT the hobby I've known for the last 50 years.

Speaking of “explaining a joke kills it”...

georgegassaway said:

Say WHAT? What "exemption"???????????? "Exemption" by who?

There's been way more far-out safe-flying models over the years from many many individuals than from companies.

And here's a big "secret", many of those oddball models by those companies likely crashed a few times before they worked the bugs out. They had to have been flight tested, before being kitted. What you posted sounds too much like nobody should try anything unusual of their own design, leave that to the manufacturers. But there is never going to be a manufacturer that is going to come up with a design that is exactly like someone else has designed for themselves, short of a "design to order" contract kind of thing. Many are into this hobby to design their own.

Now I'm not advocating "anything goes - put an "L" into a finless real snowmobile" kind of thing. Don't do a Big Bertha with Alpha-sized fins on the nose cone and expect that to fly straight. But the idea of leaving unusual models to the companies, "banning" modelers from doing it, is nonsense.

Now to get back to the real point, the OP's design process could use some feedback to try to improve its' chances. But to say "forget it - leave the unusual designs to the kit-sellers", that's not the hobby I've known for nearly 50 years.

Click to expand...

Good to see some oddroc passion around here Geoge! As an oddroc flyer I have flown with one of the safest clubs around, very strict RSO who doesn't tolerate much crazy oddroc flying. You have to really convince him of flight worthiness before he assigns you a pad. So anything funny looking is an automatic no fly until he says otherwise. Then there are additional dry weather rules here imposed by the club. At least the old guys here are not afraid of 1/4 inch rods, but we do have a lot of Flis Kit and Dynastar models at the launch. Therefore it was agreed by the club that funny looking kits from an established and trusted kit manufactures would only need normal scrutiny and need not go through the same process as scratch builds. Thus we see Night Whispers, Spitfires, Nantuckets, Goddard scale, Estes MIRV, Sirus Ventris and Dynastar SHX are flying high.

Then there is the black list of kits from trusted manufacturers that do not enjoy exempted status. Those include Estes Cosmos Mariner, Spaceship One E, Quest X 30 bugs, Noris kits and I think the Dynastar Lexjet is still on the list.

Same goes for these kits if they are modified, say someone glues plastic army soldiers on top of a Nantucket and attaches bombs on the sides. Kitbashing and PMCs also receive the treatment.

But the harshest inspections go to the scratch builds like this one. A crooked body tube is his biggest NoNo! He is not a fan of mindsim. So one like this would be DOA. But fortunately there are still places where you can safely have fun, just don't put it on cable TV.

Such is the real world of oddrocs. High power ones really get the "Stink Eye." That is why a rainbow is interesting. Got a little bend in the tube there do ya!

Also helps if it has a nice paint job on the first flight. Shows confidence and confidence is key.

My lingering concern with the stability of this rocket is that the air hitting the top of the rainbow will tend to push it to the right, while air hitting the bottom will push it left, creating a (significant?) torque attempting to rotate the rocket. In the best case this will simply cause it to arc a bit in flight, in worst case it will arc a *lot*, or tumble.

I have no idea how significant this force is compared to the stabilizing force of the fins, though. I could almost imagine small canards up top, canted to offset the force from the diagonal body tube, but again I would have no idea how to size them or determine the cant.

CFD or a wind tunnel would be mighty interesting with this one, or else a much more sophisticated mindsim than I have to offer.

neil_w said:

My lingering concern with the stability of this rocket is that the air hitting the top of the rainbow will tend to push it to the right, while air hitting the bottom will push it left, creating a (significant?) torque attempting to rotate the rocket. In the best case this will simply cause it to arc a bit in flight, in worst case it will arc a *lot*, or tumble.

Click to expand...

My thoughts are the air hitting the top will try to push it to the right, but that will get the cloud fins to push it back to the left to stabilize it. I plan to mount the fins so the CG is either in line with the center of thrust, or perhaps a bit to the left.

My initial mindsim, performed while grasping an old school slide rule and invoking the spirit of Kelly Johnson, is that a lot of slower moving turbulent in the inner arc will produce a lot of lift as the faster moving air on the outer arc becomes turbulent at the bottom, making any fins on the back nearly useless. I would put the buttons/guides on standoffs on the outer arc and tilt the rail as much as possible into the wind , which is away from the flight line. I would name it something like imminent failure so the LCO will announce "imminent failure going in 54321. " A smoky motor will do. Get some video because like Jim Carey says "there's still a chance. " If it works then load another motor and fly again!

A good thing is all the prelaunch banter you can use for the Spitfire is applicable. Have fun and be safe!