Jeff's Rocketry Postal Contest Entry

May 2011 -- NAR 1/4A Parachute Duration

A 1/4A Parachute model floating along.

May 2011 -- NAR 1/4A Parachute Duration

This month's event was 1/4A Parachute Duration (PD.) Novices may laugh at such a "wimpy" event, but veteran competitors know that just about any PD event flight is tough to recover, so 1/4A is one of the most-pleasant / easier-to-recover impulse classes. In my early contest days, I never really did that well in PD, usually having deployment problems or scorching mylar 'chutes. When I teamed up with Chuck Weiss, he usually flew PD for our team, so I haven't had much practice. I find it a fun event when it works, but it usually doesn't work that well for me. :) This time around I found out once again just how tricky a simple event can be, especially when you are trying unfamiliar things and trying to push the envelope.

With my experiences with FAI models and 1/2A SRDur, I planned on an oversize model that would easily carry and deploy a large 'chute. I thought the 40mm FAI would be too big, but I got a chance to experiment at an ASTRE sport launch May 1st at our Guilderland flying field. It was great weather, with almost no wind. I hadn't had any time to build anything new for the event yet (which explains why the weather was so good :), but I pulled out an old 1991-vintage fiberglass 30mm Internats model and flew it several times. Empty model mass was 11 grams; loaded with an Estes 1/4A3-3T and a 26" red plastic 'chute (5.6 grams), the model was 24.5 grams. I flew it from a piston launcher. The model slightly staggered off the piston (I guess it looked pretty wimpy after flying piston-launched A's a couple of days before :), boosted to a decent altitude (100 feet?) and deployed the 'chute for a 41 second flight. A second flight was not as successful -- a similar boost, but this time the 'chute did not fully leave the body tube for a 9 second DQ. Oh, well...

(Click on an image to view a larger version)

Jeff with his old 30mm Internats model, masquerading as a 1/4A PD.

The model perched atop the piston launcher.

Post flight 2, with a DQ for no deploy.

Note the soon-to-be-notorious blue Quest wadding featuring prominently at the scene of the crime.

Based on those flights, I decided I was on the right track, but wanted to downsize the model a bit and use the paper model technology I've been working with. I decided to go with a 25mm body, using BT-50 as a form to roll the body around and a balsa BT-50 nose cone (a partially-hollowed BNC-50KP provided by Semroc.) I created patterns for the body tube (two per sheet of paper) and the tail shroud (four per sheet). I again used Wausau Astrobrights paper for the body parts. The body pattern is a full 11" long, you can cut it to a shorter length if you like (either before or after rolling.) I originally had the 25mm section at 9", but later cut it down to 8".

Once I got the bodies built and a nose on them, they started to look familiar... Estes Sprint! Christening these the "Super Sprint," I decided to go right to the source and pinched the original Estes Sprint fin templates for this model, with a bit of an angle at the trailing edge root to fit the exposed 1" of 13mm motor tube (fins were 1/32" balsa.) A bit of Design Master ColorTools flat black (just as virtually massless and stinky as spray dope :) on the balsa parts and we had the "Super Sprint." It has the basic size and shape of an Estes Sprint, but the "super" part was that it was 6.5 grams empty (versus 28 for the original Estes model with a crepe streamer.)

25mm Patterns
Body tube SVG file PDF file
Tail shroud (13mm motor) SVG file PDF file
Fins (Estes Sprint courtesy JimZ's) TIFF file PDF file
Patterns created with Inkscape, an open-source, multi-platform, vector-based drawing program. I've included both the .SVG vector graphics files and .PDF Acrobat documents above. (The .SVG file is good if you have Inkscape installed and/or if you want to edit the files, like add change the NAR number. I haven't tested the printing of the PDF file, so use caution, and be sure you are printing 1:1 and not "shrink to fit".)

Two raw bodies (with full 11" length straight sections) and two completed models (with 9" straight sections.)

Pondering the incomplete deploy at the start of the month, I thought that there might be several possible causes and cures. First, I usually fill the tail cone and some of the straight section of the tube with wadding, but this time I packed it more loosely (I was short on wadding and I also wanted to save a bit on weight), and I thought this looseness might have absorbed some of the mighty 1/4A pop. (On the topic of wadding, most FAI flyers use a plug made from styrofoam insulation as a plug/piston to protect/eject the recovery device. I didn't have the tools on hand to easily create these plugs, which is why I didn't go that route.)

Second, this model had four small pinholes at the top of the tailcone (I had originally threaded string through here to hold up the wadding and not allow/require any in the tailcone), which may have been enough of a gas leak to prevent full deployment.

Third, the first time I flew the model, I forgot my binoculars, and it flew well. Before the second flight, I remembered to bring my binoculars, and it failed to deploy. Coincidence, or cruel conspiracy of fate? :)

We had wet weather for the first three weeks of May, but the last ten days of the month were warm and dry. The first good flying opportunity was Wednesday afternoon, May 25, with temperatures in the low 70s and the all-important light and variable winds. I flew at the Elm Avenue Town Park. The fully loaded model with an Estes 1/4A3-3T and a 26" 'chute was 20.8 grams. I put one of the new models on the piston launcher and let her rip. The boost was better, but the results were similar -- a partial 'chute deploy and a 14 second flight. :( When I recovered this model, I found the problem: I had used a piece of blue Quest wadding as a wrapper around the bottom of the 'chute, a sort of final flame barrier to protect it. Unfortunately, this wadding is stiff and takes a set -- it was still formed around the bottom of my packed 'chute and didn't allow it to fully deploy! (This had also happened on my failed 30mm model flight, but since the 'chute and wadding hadn't left the tube, it wasn't clear to me that they would be inseparable. :)

I prepped a second flight and used only Estes wadding, filling the tailcone and a little of the straight tube. This had a nice boost, a good deploy (alright! :), and floated down after 64 seconds to an easy recovery.

My mom and I took a break for dinner, then I prepped a model at home and came back to the field for a last flight attempt. With a good qualified and returned flight under my belt, putting a model into a thermal would result in a good event score. Up it went, and down it came, just as quickly -- an 8 second no deploy flight. Like the 30mm model, this one did not eject the 'chute from the tube (and I couldn't blame wadding anomalies this time.) Back to the drawing board...

Jeff with a shiny new "Super Sprint", ready for PD action.

The model perched atop the piston launcher.

In the background, my mom puts on her track shoes and prepares to chase down my model for me. :)

First flight deploy thwarted by the dreaded blue wadding.

Is there ever such a pretty sight as a fully deployed 'chute at apogee?

The second flight was picture perfect, 64 seconds...

... and an easy return.

A final attempt late in the day resulted in another no deploy (8 seconds.)

I spent a few more days thinking about how to fix this. One idea which occurred to me is that perhaps these paper models might be more porous than thicker, more-finished tubes to the ejection gases and might lose some pressure that way. I decided I would be better off using an ejection plug like other flyers use. I ended up building some plugs from a 1" piece of BT-50 and a 1/64" plywood cover plate.

Also, perhaps the 'chute was a bit on the large side, so in consideration of that, I decided to go with a smaller 'chute. The 26" 'chute I had used was the famous "Canadian Red" plastic, a 1/4 mil polyethylene sourced by Taras Tataryn of Canada in the '80s for contest flying. I found some gold mylar-like gift wrap at the local Michael's and made some 20" 'chutes from it, but the more I handled it (it was more like 1/2 mil), the more convinced I became that slinky 1/4 mil material would be necessary for these light models to be able to open them. Lacking any 1/4 mil mylar, I went back to the Canadian Red, using an old 18" 'chute of that material (2.7 grams.) Since I was downsizing the 'chute, this is when I decided to cut the body tube from 9" to 8". I also did a stability check, since my intuition felt the CG and the CP were getting close to each other -- all was well.

Tuesday, May 31 was my last shot at this event and the winds were cooperative -- light and variable. Less cooperative was the temperature, heading for the upper 80s that afternoon. I headed out relatively early and tried to make my flights. With the smaller 'chute, these models were 17 grams ready to fly. I used just a minimum of wadding above the motor and in the tailcone, and planned to let the new ejection plug do most of the work. So, onto the piston it went, waited for favorable air, hit the button, up it went (just a little bit higher), out came the 'chute and... it didn't deploy fully again!... (will this ever end?!?) 18 seconds, qualified and returned, but not very competitive.

So I walk over to the model and interrogate it. "Old failure mode with new equipment," it says. When I made the plugs, they had a flat face and a hollow side. I put them in with the plywood face down. The hollow side up, towards the bottom of the 'chute. So the 'chute could be pushed into the hollow plug, never to emerge again! Yup, the plug swallowed the tip of the 'chute and wouldn't let it go. (I guess that's why the Internats guys use solid styrofoam plugs. :)

I prep the model again, this time with the solid face of the ejection plug up, facing the parachute. Up, out, beautiful! A clean deploy, floating gently on the breeze, not much lift to speak of, but a nice 60 second flight with another easy return. Hmmm, I just might be getting the hang of this. :)

The wind was establishing itself in an unfavorable direction, so I moved to another section of the park, out to the parking lot where I flew S3A and 1/2A SRDur. And if there was some lift formed off the parking lot, I wouldn't refuse that either... :) My last flight and finally caught a bit of lift. This one hung for 119 seconds. See, this can be fun when it works! :) It drifted and landed in the middle of the main road in front of the park, but traffic was light and it was recovered without any damage.

A shot of one model with two of the ejection plugs.

Ever the optimist, Jeff is prepped and ready to go again. (And so is his rocket. :)

With the smaller 'chute, these models were cut down an inch to 8" straight section length.

The model perched atop the piston launcher.

Deja vu is setting in... :)

More deja vu, when the hollow end of the ejection plug tries to digest the end of my 'chute. Partial deploy for 17 seconds.

Yet another pre-launch shot.

A good deploy, 60 second flight time...

...and the easy return.

A final pre-launch shot, after moving from the lush parkland to the barren but thermal-rich (I hope) parking lot environment.

Success! A clean deploy and a bit of lift to float the model along.

Floating down to land in the middle of the road, but it was successfully recovered. Flight time was 1:59.

So that was my PD adventure. This is only the second time I made additional flights to improve my score (I also flew a full set of 1/8A SD MR flights twice.) In the past, things have been fairly fool-proof and worked right the first time; this time I had to work at it. I think I learned a few pitfalls which I (and you, from sharing the experience) can avoid in the future. It's a good example of how, no matter how good something looks on paper, you actually need to build and test it to learn all of its secrets.

One good thing about these flights was that I was able to recover and examine these paper models after multiple flights. They held up pretty well to the wear and tear. They showed some spotty burn-through damage (burn-spots often show up as a black area on the paper before they burn all the way through the paper), but that can be patched for reflight by a piece of masking tape.

Future postal contests include:

June 2011NAR C Rocket/Glider Duration
July 2011FAI S9A (multiround A Helicopter Duration)

See Rocketry_Postal_Contests Yahoo Group for more details.

Back to Jeff's Rocketry Postal Contests page


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