Rocketry of Central Carolina

I thought I'd post a threaqd in case anyone wanted to discuss April Contest stuff. Anything contest related is OK, such as tips, questions, strategy etc.

Please feel free to get involved. I'll try to keep up with the topic often in case something comes up.

Sandy.

Steve,

Thanks for asking! I'm new to all this, so I'll try not to lead you astray.

As far as clustering/staging goes, the total impulse is what determines the class of the flight. For example:

B impulse is between 2.51 and 5 N-s. A 2X A8 would get you 2X2.3N-s=4.6 N-s, so it would be within the requirements of flying in the B class, clustered or staged.

Using your example, 3X C6 would be 3X 8.8N-s =26.4N-s. That is over the limit for D impulse (20N-s) but well within an E class flight, but it would be a small E for sure. If you were flying that, you would have to be in a contest for E class rockets, not C. To boot, you'd have a pretty small E in the scheme of things, so you might want to cluster even bigger, adding a 4th C engine to get closer to the maximum allowed for E class rockets of 40N-s.

I'm not sure if you've seen the website www.thrustcurve.org or not, but it is a neat resource for information about specific motors. From the competition standpoint, any C motor that is approved for contest use counts as a C, so flying a C6 or C11 is completely OK. The thrust profile for those motors is completely different, though. A C6 has an average thrust of 4.7N for 1.9 seconds, while a C11 has 10.9N for only 0.8s. I'm far from a contest expert, but I do know a few places where picking one motor over the other would be a good idea. Specifically, C eggloft (not one we're doing this time) usually works much better with a C11 than a C6. First, you don't get a aerodynamic drag penalty for having to use a 24mm body tube due to the size of the egg and second it 'hits really hard' and gets the rocket going, whereas the C6 doesn't have much kick compared.

I don't know what the monthly theme will be, but I don't think it is necessarily contest related.

Hope that helped. Any other questions are welcome!

Sandy.

The contest flights are not all held at one time. Basically you make your flights at whatever time during the 2 day contest you want to. I think it will be best to limit contest flying times from 11:00am to 4:00 pm each day to give time for scoring etc.

Note there are a few limitations on the order that flights can be made. I'll re-read that section to make sure of all the details and post more later, but spot landing must be the first event flown by each participant. You don't have to fly it at a specific time, but it has to be the first one you fly, if you are participating in that event in the contest.

Also, I have just finished a tower launcher for specific bodytube sizes. It will be available for anyone who would like to use it in the contest. As this is my first version, I made a few mistakes, but it seems workable. Downside is that the smallest size BT it can use is BT-20 (18mm). I didn't think about 13mm! Also, I omitted BT-56, as that isn't too common of a size, but if you have a rocket that is BT-20, 50, 60, 70 or 80 with 3 or 4 evenly spaced fins, this should work for you.

Keep the questions coming!

Sandy.

After reviewing the rules a bit more here's some info.

B-Altitude: May have multiple flights during the day, but only one official flight that must be declared and flown with the proper flight slip.

C-Payload Altitude: May have multiple flights during the day, but only one official flight that must be declared and flown with the proper flight slip. The dimensions of the payload are 19mm (+/- 0.5mm) x 70mm (+/- 10mm). The dimensions specified will not allow the payload to fit in a standard BT-20 tube. In fact, they are being made from a BT-20 tube, which is what I imagine the NAR was 'shooting' for. The approximate weight will be 28 grams and I should be done with these tonight or tomorrow, so I'll have the actual weights for sure. If you're trying for something that is the most minimum diameter, you might want to go with card stock wrapped around a BT-20 tube as a mandrel to make a custom payload section, as the payload must be completely contained within the rocket. I do have a question about this, so check back later for an update in case I am misinterpreting the rules!!!

Precision Duration may have multiple flights during the day, but only one official flight that must be declared and flown with the proper flight slip. One rule for this competition (that doesn't count for us) is that this must be the first TIMED event flown during the competition. Since this is the ONLY timed event, you can fly it whenever you want, but if we had multiple duration events, this one would come first.

On all of the above contest events, if you want to practice a few flights earlier in the day etc, that is fine.

Spot Landing, however is one flight only on that rocket during the competition and there are no practice flights allowed. Also, the rocket must not separate into more than 1 piece. Lastly, I didn't clearly specify in the original post, but this is 'open' spot landing (not specifically parachute or streamer). The rules state (and I quote): "Any type of recovery device allowed." I interpret it to mean that there must be an actual recovery device of some sort deployed. I think it if fair to say that if the deployment charge causes a shift in stability (like some gliders do) then that could be considered a deployment device. The only one that doesn't seem to sit well with me is a ballistic type of recovery. In my mind, a regular Estes Mosquito (the small one) would not qualify, as it uses tumble recovery without deploying the nosecone at all. If the rocket used tumble with nose blow recovery, that would seem fine. If anyone would like to call that interpretation into question, that's fine. Please provide some source of additional information for me to hone my understanding and I'll be glad to.

Again, the 'pinkbook' is available for on-line viewing or as a pdf at http://www.nar.org/pinkbook/index.html .

Keep 'em coming. Still have a few weeks before the competition!

Sandy.

******************UPDATE******************

I clarified the rules in Payload Altitude and have confirmed that the flier can supply his/her own payload if it meets the requirements. If it would be beneficial to your design, feel free to supply your own payload that meets the following requirements:

19mm dia +/- 0.5mm
70mm long +/- 10mm
Minimum mass 28 grams

The payload may not have holes drilled in it etc. It must be put inside of your rocket. It must be permanently sealed to prevent the mass from changing. If you supply your own, it will have to be weighed before flight and verified after flight.

If this is helpful to you, feel free to bring it with you. If you want to use one that is provided, that's OK too.

Just wanted to make sure I got that information out there.

Sandy.

I will be bringing flight slips, so nothing special to do there. Just reiterating that when you fly your official flight, it has to be done on the proper card so it is obvious that it is the planned flight and not some sort of test flight. Probably more important for big contests, but no reason not to go through all of the motions, right?

Feel free to make one that uses a BT-20 (18mm tube) or slightly larger in diameter. If your rocket is made from BT-20 tube, the standard payload won't fit, so you'll have to be a teeny bit larger than that. The Quest 20mm tube might be good for the rocket.

No form of motor modification is allowed. With Estes type BP motors, there's really nothing at all that is allowed. If it were an Aerotech type of reload, scraping the flashing from the nozzle etc would be OK, but actually changing the nozzle size is also a no-no. Tons of rules about safety are out there for a reason.

Anyway, I don't imagine you'll have to try too hard to do well in the contest. . .

Sandy.

PS: This is the camp out launch as well.

Oh. Yeah, that should be OK. Sometimes you have to sand that down just to get it to fit!!

Sandy.

Brad: The payload must be removeable for inspection. It must be a cylinder per the stated dimensions and must not have any holes etc in it.

Steve: This tower design has fixed positions for the guides. It is 'somewhat' loose, but I don't know if it is 'that' loose. I don't have any 20mm tubing on hand. Can you measure the OD and I'll check to see if it works or not?

Sandy.

I'll check the tower and get back to you.

As far as streamer dimensions go, since we're not launching any contests with specific recovery specified, I would think you are free to use any streamer configuration you'd like.

As far as nose-blow recovery (i.e. no streamer etc) I see no issue with using this method.

Keep the questions coming - doesn't bother me a bit!

Sandy.

Steve,

I wrapped a tube to make it a little over .800" dia and it slid easily down the tower about 2 1/2 feet but then got stuck. If your tube is very round and just .787", it might work out and go all the way. If not, we might be able to put a stop on the tower so it doesn't get stuck. Otherwise, it might be best to plan for some other method to launch it. Apogee has an article about making 'pop-lugs' which self eject after a rocket leaves a regular rod. Never made one, though, so I don't know if they work well

Sorry.

Sandy.