Questions on the code

[skybuster]

Hey everyone!

After taking a look at "never been done before in rocketry" I saw the awesome picture of the third stage of a Saturn V, and it got my teenage mind going with many different things besides girls, cars, and other things. So I got to thinking, that picture was so detailed, I wonder if it would be possible to build a multi stage model of a Saturn V. First firing off 5 engines, then through gap staging, 5 more smaller ones, and finally, igniting the final stage, and the capsule would return to Earth (if still in orbit) like on the classic models. However, two things about the code have me a bit confused, the first one being about metal parts. Now, in my Estes catalog, it states "non-metal parts for the nose, body, and fins". Since this would be about scale, each stage would have the "bells" around the engine mount(s) however, with gap staging the engine is being lit within which should surely melt the plastic that's used for them (I could easily be wrong on that). If one was to use a lightweight metal like tin in the shape of the bells just for durability, would that go against the code?

Second question, there's also the weight limit for propellant of 4.4 oz. Is that just for LPR, or for all types of rocketry? As this could be a potential 11 engines, that could void it. Does this apply to the entire rocket, or is it 4.4 oz per stage?

As I currently lack skills to build something of this magnitude, it'll still stay in the back burner of my subconscious, but the clarification would be much appreciated.

Thanks for the help!

[Rocketbuilder]

I could be wrong, but I think if you used a very thin, lightweight metal for the bells, it wouldn't be a problem, especially since it's in the back of the rocket. Think of it like metal engine hooks, or for that matter, screw-on metal motor retention systems.

The issue of total propellant weight has surfaced multiple times recently, both with clusters and multi-staged rockets. (Yes, it applies to the whole rocket, not just each stage.) If it exceeds the limit you mentioned, then it becomes a high power rocket, regardless of total impulse or average thrust. So, you have to be certified (L1, I think-- again, I could be wrong.) to fly it.
Of course this also affects the answer to your question about the metal engine bells; because it is technically a high power rocket, the NAR model rocket safety code no longer restricts it. Instead, the builder must follow the high power safety code: http://www.nar.org/NARhpsc.html (TRA has one too.) The NAR HPR safety code states,

Materials. I will use only lightweight materials such as paper, wood, rubber, plastic, fiberglass, or when necessary ductile metal, for the construction of my rocket.

Hope this helps!

[blackbrandt]

What they mean is no major parts of the rocket can be metal. So you can't use a metal nose cone, but you can use eyebolts, metal leaders, fishing weights for nose weight, etc. Here is what the code says:

Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

And on the weight of the propellant, once you get above 4.4 ounces, you have to have an FAA waiver. You also have to have the waiver if you have a rocket above 3.3 pounds. I am not sure on the total propellant. Oh wait, here it is:

Size. My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse.

So your entire rocket has to have less that 4.4 ounces of propellant, weigh less than 1500 grams, or have less than 320 N-sec to just be able to launch by yourself. Once you join a club, they will typically get the waiver for you.
Thanks for asking,
Blackbrandt

[Zeus-cat]

I think your biggest problem, other than this most likely being a high powered rocket, is lighting the 5 second stage motors. I wouldn't trust gap staging to light 5 motors. And if you use electronics the current draw would be quite high to power 5 ignitors. I am sure there is a way to do it, but this would be a very challenging project.

[luke strawwalker]

And why would you WANT metal bells on the upper stage motors?? You're certainly not going to see them, ESPECIALLY on the S-II stage... paper nozzles coated with epoxy would be safe from melting... should be sufficient for the time of the flight. I could *kinda* see having the nozzle on the S-IVB, but then again, it should be so much higher at staging you can't see it anyway...

Later! OL JR

[Tarasdad]

There are high plenty of other materials he nozzles could be made from since they would be purely cosmetic. High temp plastics, nylon, moulded carbon fiber - the list is practically endless.

[MarkII]

If I am not mistaken, a "fully functional" Saturn V scale model rocket was flown at NARAM (or was it the WSMC?) some years ago, by George Gassaway I believe. I'm not sure, but I think it even had motors for the SM and LM, and they all fired correctly during the flight.

Something approximating a "fully functional" flying scale model of a historic launch vehicle is something that you might see at the World's.

[adrian]

I can't see how it's going to be a 100% accurate scale model. For one thing, each stage will need a set of fins to stabilise it. Also, if you look again at those pictures of the Saturn V third stage, look how narrow the nozzle throat is compared to the bell end and the stage body tube - I don't see a 100% accurate nozzle as being practical. The fins can be transparent so the model looks reasonable when it's on the pad and you're at a safe distance for launch, at which point you're not going to see the second and third stage nozzles anyway.

I'd have just plain motor mounts for flying. For display, build something to insert into them consisting of a dummy or expended motor with a scale nozzle stuck on the end.

[skybuster]

And why would you WANT metal bells on the upper stage motors?? You're certainly not going to see them, ESPECIALLY on the S-II stage... paper nozzles coated with epoxy would be safe from melting... should be sufficient for the time of the flight. I could *kinda* see having the nozzle on the S-IVB, but then again, it should be so much higher at staging you can't see it anyway...

Later! OL JR

Had no idea that epoxy was that durable! For anything, it'd just be for display reasons, but this is just a crazy thought that I got, definitely something I can't build...at least in the meantime

[skybuster]

I can't see how it's going to be a 100% accurate scale model. For one thing, each stage will need a set of fins to stabilise it. Also, if you look again at those pictures of the Saturn V third stage, look how narrow the nozzle throat is compared to the bell end and the stage body tube - I don't see a 100% accurate nozzle as being practical. The fins can be transparent so the model looks reasonable when it's on the pad and you're at a safe distance for launch, at which point you're not going to see the second and third stage nozzles anyway.

I'd have just plain motor mounts for flying. For display, build something to insert into them consisting of a dummy or expended motor with a scale nozzle stuck on the end.

Great idea!

[JStarStar]

A fully-staged Saturn V is another one of these dream-world projects which has indeed been done.

However, in order to do it, sizable clear-plastic fins must be put on each stage (including very big ones on the first stage).

Guess what: Clear plastic fins are not really "invisible" -- anybody seeing such a model launched would see it had big fins on all three stages.

Since the general point of building a "scale model" is to end up with a rocket that looks somewhat like the original vehicle in flight, isn't there some point you pass at which the "scale model" looks nothing like the real rocket, and you scratch your head and say, "what's the point."

[luke strawwalker]

Had no idea that epoxy was that durable! For anything, it'd just be for display reasons, but this is just a crazy thought that I got, definitely something I can't build...at least in the meantime

The RS-68's on Delta IV use ablatively-cooled nozzles... basically they are nozzles made of composite materials built up in layers and overlaid with layers of epoxy-like resins... the nozzle slowly burns away, just like the resin heat shields on the old Apollos, Gemini's, and Mercury capsules, taking the heat with it.

Epoxy coated parts aren't flame-PROOF, but they are flame RESISTANT... IOW it WILL char and burn away if exposed directly to too high a heat for too long... but for paper nozzles surrounding the motor tube of a model rocket motor... (don't bury the motor TOO deep in the epoxy-coated paper nozzle!) it'll work pretty good...

Epoxy is commonly used to coat ejection baffle parts, as the resin can greatly strengthen and protect the paper or fiberboard disks and even balsa disks used in certain baffle designs-- it's quite resistant the the intense but short heat pulse from the ejection charge firing off and being exposed to the erosive hot gases. Of course it's only exposed to the worst of it for a few milliseconds...

Later! OL JR

[luke strawwalker]

A fully-staged Saturn V is another one of these dream-world projects which has indeed been done.

However, in order to do it, sizable clear-plastic fins must be put on each stage (including very big ones on the first stage).

Guess what: Clear plastic fins are not really "invisible" -- anybody seeing such a model launched would see it had big fins on all three stages.

Since the general point of building a "scale model" is to end up with a rocket that looks somewhat like the original vehicle in flight, isn't there some point you pass at which the "scale model" looks nothing like the real rocket, and you scratch your head and say, "what's the point."

Going with fixed clear fins IS *one way* of doing it, but not necessarily the best way. Apogee's "Peak of Flight" newsletter recently covered doing retractable pop out fins for just such a project, in three different styles no less, depending on what you're trying to do and which ones work best in what part of the rocket. For instance, they used radially pop-out fins (that fold down against the motor tube when stowed, and flip out sideways on hinges and lock into place after deployment.) They used fins that extend out behind the third stage on wooden legs, hinged at the bottom, which fold tips up when stowed and then flip down and out into the airstream at staging. They also had a design for "flip forward" fins that were hinged at the leading edge root, which folded back and tips down against the motor tube and then swung forward into the airstream when deployed, but gee forces and aero forces are working against you in this method... swing back uses those forces to your advantage. Moving the fins that far aft behind the upper stage means they have a MUCH greater effect on CP for thier size, meaning the fins can be a LOT smaller than they would otherwise have to be. (be sure you check your stability margins by Barrowman, Rocksim, or whatever before flying!)

So huge honkin' clear fins sticking out insn't NECESSARILY the only way to go, and certainly not the best way...
Check the Apogee "Peak of Flight" newletter archives for the details...

Later! OL JR

[JStarStar]

Retractable popup fins are also prominently visible during flight, so the model in flight looks nothing like the original rocket.