Just Jerry

I have seen a lot of TARC and UKAYROC posts but rarely if ever HOW they did it. What rocket style, what motor combo, etc.

Jerry

William Slaughter

My son's team made the finals in 2007 & 2008 with a lightweight BT-70 x approx 2.5 ft rocket on an Aerotech F39. Four basswood fins,a plastic ogive nosecone, and due care to not be over-stabilized. Ballast the rocket to get the altitude, then adjust the parachute as needed for flight duration. Egg damage has been a total non-issue. The nearby middle school has also made the finals the last two years with a similarly sized BT-70 rocket flying on a 2x Estes E9 cluster with an elliptical nose cone. Black powder cluster (2x & 3x) and F powered rockets were well represented at the finals, but quite a few teams were flying larger and/or heavier rockets on G motors. Electronics for deployment are starting to make some inroads.

edk

I've heard of altimeters being used to deploy the parachute while the rocket is still ascending - to me that takes much of the science out of it. Ed.

heada

Ed,

I'd disagree. In this case, you'd have to design the rocket to withstand deployment forces while traveling greater than non-zero (apogee). Also, you'd have to figure out when to deploy so that the altimeter reaches the desired altitude because even after deployment, the rocket will move "some" and the body tube that contains the altimeter may be connected to a significant amount of recovery bridle. For example, if you set the electronics to deploy at 740 feet when your goal is 750 feet, the parachute has to come out into the airstream, stop the rocket and still hold the altimeter to within 10 feet of where it deployed the parachute. This is no small task.

Also, if not thought of before hand, you could have very serious failures by using electronics for your ejection. If the rocket is designed for electronic deployment only (no motor ejection) and you don't reach your deployment altitude, the deployment may never happen and the rocket would come in ballistic. Granted, this failure mode should only happen once but that one failure could be a season ending event.

There is also something to be said about making a complex task even more complex by adding a new element to the mix. If the rockets were weighted in judging, I would give a rocket that used electronic deployment a higher weight simply because it would be more difficult to repeatedly get working correctly.

Anyway you look at it, it is very impressive feat that these teens are doing and I'm sure not all us old rocketeers, with all our years of experience, could do as well as they do.

-Aaron

Just Jerry

When people started using piston launchers in competition there was a bit of an outcry it gave an unfair advantage. They are now allowed. When people come up with innovative strategies within the rules like this one or superstructure superroc rockets or the like, this is the exact sort of innovation we should encourage. It might work, it might not. Usually the complaining only occurs if it does!

Encourage innovation. The rules should be a level playing field. The methods and outcomes should not.

Jerry

H_rocket

The Wethersfield High School team has been using that approach for three years and made the finals with it the first year. It is a very difficult engineering challenge as the students needed to not only design the airframe, they also need to design a deployment system that fires at a specific altitude. Remember most of our altimeters are apogee detect, not altitude detect. Further they need to predict how far below the target altitude to deploy so they stop on time. Also designing a recovery harness to slow the rocket down is way different from designing one to simply survive the deployment forces.

This year's challenge is really a new stretch. The teams can no longer depend on the natural strength of a hens egg in the axial position. Now they have the additional challege of protecting their "pilot"

Bravo to Trip and the AIA for continuing to grow TARC into a true breeding ground for our next generation of engineers and scientists.

n5wd

Ya know, I remember you asking basically the same thing a couple of months ago, and I was going to respond with some details, but got sidetracked. Sorry 'bout dat!

I sponsored three teams at the high school where I teach engineering and multimedia (digital photography, digital video, a little bit of webmastering and desktop publishing, etc.). One of the teams was rocket-rookies, only one of the eight guys had flown anything but the basic Estes/Quest type rockets and that was an X-15! The other two teams had kids that had participated in TARC a couple of years earlier, while they were in middle school, so they had some experience.

My all-girls team (two of the girls from my engineering class plus another young lady with previous TARC experience) made it into the finals, the only one of our three teams to do so.



Their rocket was a BT-80 based 4-big fin that weighed somewhere in the range of 720 grams loaded with a RoadRunner F60-7 and the two eggs. They adjusted ballast to right at 750 grams for the final flight weight with fishing weights and rolls of electrical tape (the wieghts fit quite snugly in the middle of the tape to keep things from sloshing around in flight).

The design was pretty straightforward (I've attached the Rocksim file for anyone that's interested).... body in three pieces:the chute and shock cord was shared between the booster and the bottom of the payload section - their objective with that was to get the laundry into the air quickly. Seemed to work. The payload contained (from the bottom) some shock-absorbing material, the two eggs, packed in styrofoam cradles, some more shock absorbing material (high density rubberized foam) the altimeter sled, and the ballast. The nosecone was taped on as shown in the first picture.



During practice, they were nailing the altitude within 5 feet consistently. The variable was the descent rate. During the finals, though, the descent rate was right at 44 seconds (the goal was 45 seconds), but the darned rocket took off like a scalded bandit and flew 30 feet higher than it had been (780 feet versus the goal of 750). So they didn't make it into the second round of the finals and wound up 32nd overall. Interestingly enough, of the 18 teams that did make it into the finals, 11 had second round scores that were worse than our first round flight.. so conditions definitely got a bit more squirrely as the day wore on.

On the girl's team, only one of the three (the one not pictured - just coincidence) was a senior and not returning this coming year. One other member of the 'varsity' was a senior, so there are four returning members there, and there are six returning members of the 'junior varsity' team (one of the JV members was a foreign exchange student from Germany - now trying to get something similar started there!). Should have a lot of experience going for them in this year's contest.

Just Jerry

They are invited to my big motor rocket tests anytime. Good job all!

Jerry

Ashad729

I am one of the four members of the UKAY-RoC/Farnborough winning team. We used a simple design with four base fins, laser-cut following Space-CAD simulations. Our final rocket used four Estes D12 motors with staggered ejection charges, as early on in our project we had a lot of problems with the sheer force of four simultaneous ejection charges. Our motors were ignited by quickmatch using a single ignitor.

In addition to the mass of our components we added a permanent 40g of mass to our engine block to lower the centre of gravity of our rocket, and attached a compartment to our nose-cone for a variable amount of ballast weight.

Fins, bulkhead and engine block were made from acrylic, as we found it to be much stronger than balsa wood, and with four motors we had to make up some extra mass.

If there's anything else you'd like to know about our design, I'd be happy to post it!

By the way, I'd love to see some high-powered rocket tests, Jerry, although I think being in the UK limits what we can do and see.

Ashley

ddmobley

Ashley, welcome to Rocketry Planet. Thank you for posting this information, and congratulations on your accomplishments. Do you think it would be possible to post some photos of your rocket's components and assemblies? I know everyone would like to see how you did it.

H_rocket

What he said....

Bravo to the Brits for a job well done! Fear not though, the colonies will be back next year for a rematch so don't get too attached to that trophy!

Ashad729

A shot of most of our rocket's components before completion




My calculations to find an approximate ideal parachute size



Our engine cluster and fins close-up



And... one of our launches at the Farnborough fly-off! - this picture was taken from Raytheon's website. They were a very important sponsor of both competitions and the Farnborough fly-off.

Thanks for the support! Hopefully we will be entering the competition next year, although we are also considering mentoring a younger team instead. Either way, we will definitely continue with rocketry.

ddmobley

Excellent stuff, Ashley. And you consideration of mentoring a younger team is just wonderful. Keep up the great work.

(P.S. The parachute calculation shot made me really appreciate the online calculators. )