Newbie questions

[noahnott]

Seems easy enough....the words of a true rocketeer. *edit* come to look at it again, your right. It isnt too bad.

I think if im going to do something ill stick with the 5 leds without the strobes and xenon lamps. ...or will I?


I launched my first cluster rocket! Had 3 A10T size motors in it. =) Great stuff, all three fired suprisingly!

-Noah

 

[f16fan12]

What'd you end up doing for the ignition system??
Oh yeah, and congrats on the cluster. I remember my first cluster...on a scratch built. Just two motors. Beautiful flight, got stuck in one of the evil government trees though at the FDA.
Uh oh, sorry Mr. Bush.

 

[noahnott]

Can anyone point me to a thread/site on electronic staging remotly? Ive been looking for 30 mins and cant find anything that tells me *how* to do it.

Hey, gotta loft something heavy in the air if you have a cluster rocket =) ...eggs dont count

Thanks,
Noah

 

[powderburner]

Originally posted by noahnott
Looking through the NAR rules for rockets, i didnt catch anything against night flights. .... So can i?

I think you must have an FAA clearance, maybe a few other strings attached to the deal also.
Check the old threads here on TRF, there is a bunch of info already posted especially by Micromeister
There are indeed some serious rules about night launches that you should follow

 

[noahnott]

*edit* Just realized my next question wasnt worth asking.

 

[ben]

are you sure?? I am more than happy getting my post count up by answering I am sure everyone else is too

thanx, Ben

 

[f16fan12]

yeah, come on, give ben a chance to get his half-grand post.

 

[noahnott]

Lol. Fine fine. Were doing a vacuum tube rocket project in school, and was wondering about a few things...

First, its being propelled by a vacuum which sucks a rocket (or some other projectile) and shoots it out the other end. But....This isnt the same as a rocket which uses motors is it? Since we are trying to get the most distance its best if it is small in diameter, short preferable and what not. Im just giving the general idea of how it works.

My question is: do i even need to use fins(!) and just stuff in a lot of weight? This is basically the same as taking a baseball and hitting it, just that i'll make it more aerodynamic. Of course it may rotate side to side sometimes, but is it worth the drag of adding fins?

I was thinking of taking an easter egg, stuffing it with weight, then taking a carbon fiber tail boom (which i still have from other projects) and glueing on some fins! Simple and easy =)

Hey, or i could do what other people are doing: retractable fins!

My second question is: Know any ways to give me an advantage? =P *this here is somewhat on the cheating side*

Off topic, but i just launched my paper rocket for the 7th time. Still going good! Had to replace the streamer though, it was getting a little crumpled up.

Thanks,
Noah

 

[cjl]

Well, what you want in this case is a small rocket with a very high ballistic coefficient. You want it fairly dense, but small, and you DEFINITELY want fins (a tumbling rocket without fins has a LOT more drag than a rocket flying straight with fins). Use small fins, though not miniscule, and keep the weight central to the rocket to prevent any coning or wobbling. Ensure that the fins are as straight as possible, and keep it to the smallest size possible. What you want is a fairly dense and very low drag small rocketlike projectile. If you can sneak a rocket motor into it, then it won't hurt either

Another thing - if you can get a reliable seal with the launch tube (sabot?), then make it have a full tail cone. Since there does not need to be a motor mount, the tail cone can taper the whole way down to a point, and practically eliminate base drag. The nose should be an elliptical shape, though the nose shape will probably not make a statistically significant difference in the flight distance of a otherwise well designed projectile.

With a little effort, you should easily be able to destroy anyone else's design, and you can make it look cool too

 

[noahnott]

That helped me A LOT!...though i did think about sneaking in an RC igniter for a rocket motor.

So my redisigned rocket: Rocket like shape, elliptical nose, conical tailcone (because if its elliptical on the tail the air will form a little eddie, but if conical the air will merge together better?), spray painted for smoothness, straight fins (so no spinning rockets?) [about 1in x 2in?], and CG basically in the center of the rocket.

For weight if your curious I'm going to use steel filings....oh but wait, not allowed to use metal. Maybe i should ask him to make an exception for weight.....

Would it be good to use my carbon fiber tail boom just to get rid of the huge surface area the main part of the rocket will use up?

The only other thing im afraid of is that when the rocket comes out of the vacuum tube (im using another cylinder to push the smaller diameter rocket out so its like a 2 stage rocket! ) it wont be able to break the paper cover the end. The paper there is so there is better suction, so will putting a toothpick there do the job?

Thanks for all the help, and i hope you like my run on sentances
Noah

 

[cjl]

Well, you've basically got it, though I would use an ogive rather than conical for the tailcone for smoother transition. As for the puncturing - I wouldn't add anything, other than perhaps a very short spike to the very tip of the nose. Keep in mind that the earlier you puncture it, the less acceleration time the rocket will have. As for spinning rockets? You could do that, but it will not go as far as a straight flying one will (the spinning will reduce the amount of energy that propels it forward, and use some energy to give it the spin). The size of the rocket is up to you, but I would make it rather small, but also long and skinny relatively. I would go for about .3" by 3" or so, to keep it small and relatively light. Somewhere around the 8:1 or 10:1 length/diameter ratio will work nicely. You definitely want it to be weighted well, to maintain speed both breaking through the paper seal and to minimize the effects of aerodynamic drag on the vehicle. Good luck

 

[noahnott]

Well I think ill start on it tomorrow. I'm running out of my perfect nose cone material: styrofoam!

When you said short spike, for some reason i had the idea of a mace-like nose. .

Thanks again,
Noah

PS. ppl here arnt to big on staying up past 10. That or the time zones.

 

[cjl]

Haha - yeah, past 11:00 PM or so, it kind of dies (that's mountain time). Yet here I am at 12:37

There's school tomorrow too (actually today).

 

[noahnott]

You said put the weight near the center. Would it be better if in the front so it pulls the rocket forword rather than making it wobble in the air (less stable because my fins are going to be tiny)?

Thanks,
Noah

 

[cjl]

It won't necessarily pull the rocket forward regardless of the location, and with the weight at the nose, I'd be more concerned about the wobbling than with it centered.

How small are you talking relative to the rocket size (for the fins)?

 

[noahnott]

Not really tiny (fins), just to fit in the tube we are using which is about 1 1/2in in diameter.

I mean since if the weight in the front has more mass it wont slow down as fast as the rear would causing it to fly practically straight, since it is decelerating.

If it was in the middle then it would be less stable. But wouldent this design "glide" farther rather than diving into the ground?

*edit* would it also be good to put small fins near the CG to make it "fly" in a way?

Thanks
Noah

 

[cjl]

Once it is in flight, the fins will be keeping it straight. The "pulling" principle won't contribute to it at all, and putting "wings" near the CG is asking for problems IMO. I would go with the CG as central as possible, with an overall shape something like this:

(note: rough model only, meant to show basic concept).

 

[noahnott]

Suprised you actually put it in rocksim to show me =D

So i decided to do the same with mine. I like yours because you can put the weight in the center; mine on the other hand requires me to put it in the front, however it has less drag.

*edit* im starting to forget that is my project. Your starting to do a lot of the work....I call it research

*more edits* I know this is not really "low powered rocketry" But its still rockets, that are launched by low powered means.

Thanks for helping,
Noah

 

[cjl]

Haha - no problem

Your design looks like it would work, though I would still go with the design I showed you (mostly for the sturdier fin attachment, as well as less difficulty of launching it). Definitely either of these will be better (lower drag) than the standard rocket shape - I get a Cd on mine in the .3-.45 range, depending on speed (standard rocket in the .5-.75 range). What kind of Cd does yours have?

 

[noahnott]

.175-.375...i dont know if this is right. I just looked at the plot. (is that what im supposed to do and just look at the min and max)...

Im still thinking about this..hmm hmm

-Noah

 

[noahnott]

Interesting because i try and try again to reporduce the rocket i posted in the picture...i cant get my CD that low again. (lower is better right?)

Came up with other ideas, mixes your idea with mine, which i think im going to use.

Noah

 

[noahnott]

My Alien8 just arrived in the mail! (actually it arrived a long time ago but my parents were waiting for my bday) Anyways, I'll start building it sometime. =) ...but i have something else to build first, in which my dad will do most of the work.

Ah, im spoiled,
Noah

 

[noahnott]

Hey again,

Still on my vacuum tube rocket design, not really part of this forum..but since im not allowed to use metal, what is a really dense nonmetal!? I cant think of anything...

I fired my first rocket design today, it was a 4mm in D carbon fiber rod with a metal head (illegal)...it almost went on the otherside of the fense beating every1's elses by about 4x...easy. (They are stuck on the idea of more weight=good, when im stuck on the idea that smaller=good with a little tiny weight).

About the CG being the in the middle, yes your right. It will cause the rocket to "float" longer because it is pointing more parrellel to the ground.

My only problem is, im not using fins because when the rocket (with very little mass) goes through the paper, a lot of energy is lost there. So if i take of the fins it will easily pierce through the paper. (i just tested this idea and its true). The only problem with not using fins (fletches) is that my CG will have to be a lot more forward to still be stable (which is the only reason my rocket went so far and was stable).

So since I have to move the CG very far forward I need a heavy non metal to keep it way up there. Otherwise, my rocket design is down the toilet....ummm, maybe litterally.

My other fear now is that others will use the small diameter idea and come up with something even better =O

Oh, since its a vacuum tube rocket, i use a pingpong ball as the airseal since the rocket is too small (so this is why they make their rockets larger).

Just thought I should let you know...im on step 8 of the alien8 thing, somewhere just after I cut the ping pong balls. =) ..and my "favorite" scratch built rocket is still going good, now its noseconeless, and flies just as good!

Thanks,
Noah

 

[f16fan12]

I can't really visualize this thing, but maybe try some modeling clay?

 

[noahnott]

Let me help you visualize. Lets say im using a PVC pipe (1/16th in normal PVC pipe). The PVC pipe is 2 ft long and only 1-2in thick. Now imagine its only 10in long and 4mm thick (sorry about the change in units). Now instead of a PVC pipe, its a tiny fiberglass tube.

Now imaging that tube being pushed by a pingpong ball through a tube....no fins...and maybe a little nose.

Modeling clay might work, (would epoxy putty do the job?), but another prob is the ID is only 2 mm thick. So that doesnt do me anygood.

 

[powderburner]

I vote for modeling clay also
There might be something else out there that is slightly more dense but clay is probably going to be much easier to find

I understand you are afraid to use rigid fins for stability because you think they will "hang up" on the paper seal. Try archery fletching (available at many sporting goods stores). Use the real feathers and not the plastic vanes. If you cannot find fletching, try your local craft stores for other kinds of feathers.

Feathers can be easily glued at their root, they are ****extremely**** light, they can be trimmed with a sharp scissors, they fold back out of the way if they strike any objects (like your paper seal), and they spring right back into position. Just keep them dry.

 

[noahnott]

Your feather idea sounds good, and i thought about it b4. The reason i didnt want to use them is because feathers have a lot of drag(?)? If this is only my own myth, plz let me know...

Also, modeling clay? Lol, what does it look like and where can i buy it?

Thanks,Noah

 

[powderburner]

Most archery fletching comes pre-cut and shaped, ready to be glued onto the shaft. It is often available in pkgs of 12 pieces for only a few dollars. Or, go to the park and pick up some pigeon feathers.

If you split the feather shaft and cut it down (straightedge and Xacto knife, just like working with balsa sheet), and then attach the feather just like on an arrow, you will get very effective fin area (just as good as any other rigid material like balsa, G10, etc) and just as low drag.

Modeling clay can be found in craft stores, and in the school supplies section of your local W-mart

 

[noahnott]

Alright, thanks for the help.

But just to let you guys know, i found a place where i can buy rockets and rocket motors in this town! ...yup, they have A's all the way up to E's. They also have a bunch of rocket kits there (estes and quest). But they also have 10 boxes (as in the larger boxes, not the small boxes motors come in) filled with rocket motors stored right on the shelf, is that legal!? So now i can make a multi stage rocket =D

-Thanks noah

 

[RandyM]

Sounds like he's hooked now!