Jeff's Rocketry Postal Contest Entry

January 2011 -- FAI S3A A Parachute Duration

Jeff with his S3A PD model.

January 2011 -- FAI S3A A Parachute Duration

This month's event was FAI S3A, aka "A Parachute Duration flown with Big Berthas." :) I didn't really plan to fly the postal event this time. The weather in upstate NY in January (and February and March...) isn't really conducive to rocket flying. We had a three week period were the temperature did not reach freezing (normal high is around 31 degrees F) and we had 34 inches of snow for the month (about double the normal), very little of which melted away.

But I like the idea of the postal contest and I wanted to support it. I had been able to win the contests the first two months with entries of varying quality, so I really hated the idea of not even trying to make an entry for this event. As the end of the month approached, we got above freezing for a few days and I couldn't resist it.

Another reason I wasn't too excited about flying this was that I didn't have a handy off-the-shelf model to fly. The last Internats flying I did was about twenty years ago (has it been that long? :), so any models I had leftover were for the 30mm diameter formula, nothing to meet the current 40mm rules. I didn't have a 40mm mandrel (or fresh resin), so I couldn't make a competitive body. I could have placed an order with Venus Rocketry for an FAI kit if I had planned ahead, but time was short. I decided to go with a paper body, as detailed on George Gassaway's web pages:

Now, paper isn't the choice material of the regular US FAI flyers. Fiberglass (or more exotic materials) gives you a stronger body for a lower mass. Everything is a nicely finished single piece, versus paper parts joined together. Also, fiberglass is waterproof, handy if you have to fly in the rain or snow. But paper has the advantage of providing a serviceable model for a minimal investment of time, materials, and tools and techniques. (As far as the time investment, most of the work was done over 2-3 hours the night before I flew it.)

I used 24 pound inkjet/laser printer paper. I had a Quest 40mm tube, which was handy to form the main body tube around. I created a jig similar to what George shows to glue a 2" piece of BT-5 one inch into a 6" paper tailcone (the 10mm end of George's tailcone has to be trimmed a little to fit the 13mm motor tube.) Then I joined the 11" main body to the tail (I cut 1/8" slits around the circumference of the body tube and slid it into the tailcone and joined it with CA and scotch tape.) The 3" long nose is also paper, printed by the shroud printing function of VCP. The base of the nose is a one inch thick piece of blue styrofoam, hand-trimmed to fit. Fins were 1/16" balsa, designed to strict TLAR principles ("that looks about right." :) I actually did do a VCP analysis after the model was built but before it was flown to make sure the CG was far enough forward; it was stable without any added mass. The model utilized launch lugs and a 1/8" launch rod. The shock cord was 15 pound kevlar line. The parachute was an old eggloft duration 'chute I've had around for many years (complete with authentic singes and welds. :) It was about 31" in diameter, made from dry cleaner's bag (approx. 1/4 mil polyethylene), colored with magic markers, and using eight shroud lines.

The empty mass of this model was 9.5 grams. Way better than a Big Bertha! (which IIRC is about 55 grams), but the regular Internats guys get their fiberglass models down to 5-6 grams. The parachute was 9 grams. Total liftoff mass was approximately 29 grams.

Now, in consideration of the weather conditions (uncomfortable to be out long), recovery conditions (which likely involved trekking across deep snow), the FAI rules (which, strictly speaking, don't require a return to qualify), and my model material choice (i.e.: non-waterproof), I decided to make this a one-shot deal. One model, one flight, and if I did recover it and it was flyable again, I could always take it home and re-prep it (although I'd cross that bridge when I came to it.) I choose a local park, instead of the local school field, because it had several plowed roadways through it. Normally I don't fly from paved areas, because of the chance of damaging my models. But now, landing on the ice-coated snow wouldn't be much different than pavement, so I took used the parking lot to fly from. Another disadvantage of the park was more trees around, but considering my one-shot plan and the minimal investment of time and materials in this model, it was a fair trade-off.

The forecast for the next few days was partly cloudy skies, high temperature around freezing, no precipitation, and winds around 5 mph. I did most of the model prep at home (aside from 'chute packing) and I went out and flew on Friday, January 28. The temperature was about 30 degrees F and the wind was from the SSE at about 8 mph -- enough wind chill to bite into bare skin after 5-10 minutes. I set up the model with an Estes A3-4T in the parking lot and away it went. The launch and flight was good and vertical, the model ejected at apogee, and the 'chute deployed after only a slight delay. The descent seemed neutral, no lift, but not a great duration. One problem was that the tape holding the shock cord at the body's CG must have torn loose, since the model hung in a nose-down attitude, reducing descent drag somewhat. I had hoped the wind would be a touch more easterly and carry the model over the main park area, but it drifted over the parking lot and the adjacent tree-lined area. The model ended up about 30-40 feet up in those dense trees, so it is likely that it will be staying there for some time. Flight time was 1:35.90.

It was fun building this model from paper (something I haven't done much of before) and the low-pressure postal competition lets you try something new and not be too worried if it will work or not. Fiberglass would still be my material of choice if I was serious about Internats models, but I was impressed by the relative ease-of-building and performance of a paper model. If you want to try flying these types of models, paper is a good way to break in and get your feet wet without worrying about mandrels, epoxy, and fiberglass.

Future postal contests include:

February 2011NAR 1/2A Superroc Duration
March 2011NAR 1/8A Streamer Duration Multi-round
April 2011FAI S6A (multiround A Streamer Duration)
May 2011NAR 1/4A Parahute Duration
June 2011NAR C Rocket/Glider Duration
July 2011FAI S9A (multiround A Helicopter Duration)

See Rocketry_Postal_Contests Yahoo Group for more details.

Photo Gallery

(click on an image to view a larger version)

Jeff's paper S3A model. It looks ugly and it feels flimsy, but it does the job. :)

Detail of the motor end of the model. I only used a small single piece of tape (not visible here) to secure the shock cord at the CG (versus wrapping the tape all the way around the tube), which cost some flight time.

At the pointy end, showing the nose cone (not a misnomer this time :), a peek of the the foam nose block, and the upper launch lug. I used black magic marker to add some color to the model.

The parachute I used, about 31" across (although it varied depending on previous 'chute damage, note the welds and singes.)

Here I am with the model prepped to fly.

It's been quite a change from month to month, with plentiful snow banks in the background.

The model sits on my trusty old Porta Pad, ready for it's flight.

Motor choice was an Estes A3-4T.

The model in flight.

You see (top to bottom) the parachute canopy, the conical nose, and the main body section in a nose-down attitude. The duration would have been a bit better if the model hung horizontally.

The item at the right was some Estes recovery wadding (I filled the tailcone with it for 'chute protection.)

The model found a tall, dense grove of deciduous trees and it's not coming down anytime soon.

You can see the 'chute dead center in the photo; the body is a bit down and to the left.

A zoom shot of its final resting place.

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Last modified February 14, 2011