DART’s “Geezer TARC” Event: My entry

[smstachwick]

Well, I had a build pile before, but for the first time I can remember I also have a building pile.



Okay, a little backstory:

My local low-power club, DART, hosts a number of ARC (formerly TARC) teams and a number have advanced to finals. San Diego is well-represented in competition. But why should high-schoolers have all the fun?

Thus, DART created the “Geezer TARC” event, an unofficial precision egg lofting event for all ages and affiliations but with different design requirements so that TARC teams are generally unable to use the data and must gather their own. I think the target altitude is different, and entries can come from any source. There are no body tube requirements like there are for TARC teams this year.

Full rules here:

https://www.nar.org/site/section317/geezer-tarc/
On DART’s Facebook page, I described the concept for my entry:

“Currently I’m looking at converting a Quest/AeroTech Courier with a 29mm mount, single-piece recovery, 1010 rail buttons, and an extended body tube with payload bay to meet the contest requirements. A modest E motor should hit the altitude target. Single-motor operation makes the E35W Q-Jet more viable.

(snip)

“Currently I’m only looking to qualify and score, not to beat Chris [Flanigan, DART Director] and any other competitors that may show.”

Now, the Courier is a classic egg lofter, but these are not necessarily simple conversions, especially not with the kind of time I have and the rapidly approaching 11/11 deadline. I’m hoping to have the guts all sorted out and the thing ready for a test flight by Saturday. You can bet there will be a few manic episodes dumped into the work on this rocket!

Here’s the first update I posted:

“G-TARC update: After half-a-dozen shopping excursions, three or four engineering challenges solved, and a few experimental subassemblies put together and validated on a preliminary basis, I feel confident and ready to begin assembly.

“First though: A weigh-in. I don’t expect this figure (253g) to stay static but I did need to know what kind of headroom I’d be looking at. A minimum length (650mm) and maximum mass (650g) makes you really think about the limits and discourages you from trying anything extreme.



“In this case I need not have worried. The preliminary figure is encouraging. I have more than enough length and I’m not even close to the mass limit.

“For added context: The motor mount is glued in place, probably dried and curing by now. The forward centering ring is just a masking tape shim held in place by wood glue, the rear centering ring is the stock one, cored out *not quite enough* and butting up against the end of the body tube instead of slipping inside. That joint got CA superglue. A preliminary breath test indicates a good gas seal but I will likely apply some more glue later to act as a sealant. The aftmost portion will be cut down a bit to accommodate an Estes 29mm retainer.

“The brown-colored tube is a BT-55 and that will be the extension, and I’ve stuffed both of the stock Quest polyethylene sheets for chute assembly inside, plus a length of Estes elastic shock cord (the Pro Series II stretchy fabric kind also found in some AeroTech kits). The Quest T35 will be cut in two for the BT-55 to serve as middle component/payload bay. The nose will slip into the forward segment of the T-35. I’ll still need to fashion a bulkhead and shock cord attachment point of some sort but I don’t expect that to eat up all my room for weight gain.

“The rail standoff has been beefed up a bit, constructed out of a bit 1/4-inch birch ply cut to similar dimensions, and another 1/4-inch plate held on with wood glue, which will hold the rail buttons. In addition to the attachment screws I have some pretty serious JB Weld in my supply, which will be applied liberally on all remaining joints in that assembly and I may make some fillets on the existing glue joint as well.

“The fins will probably stay stock balsa unless a test flight reveals that they break, in which case they’ll be replaced. I probably won’t fly the Quest chutes, more likely I’ll get a stronger, more compact nylon one from the Discount Rocketry trailer or use one I happen to scrounge up from my own supply.

“A few more grams of dog barf, glue, and one or two minor structural components will give me a final weight. Part of me wonders if I can get away with flying this on less-thrusty motor like an F23.

“Either way, my only goals are to qualify and score. I’ve seen how hard TARC can be and I have no illusions as to my skills as a builder!”

That mass figure includes a Jumbo-sized egg in the nose, by the way. If you look closely you might be able to see the bit of condensation that formed since I had just taken it out of the refrigerator.

One thing I’m realizing from this build is that I don’t really like the Gorilla brand of wood glue, at least not until it has sat for about 10 minutes and become somewhat more tacky. I refuse to turn this into a glue thread, but you can rest assured that I will be trying something else soon!



@fyrwrxz was kind enough to recommend that I get into contact with Discount Rocketry for custom laser-cut centering rings, which appear to just not exist commercially for this combination of diameters. I’m reasonably happy with my solution though, so I might have a spare set lying around at some point, maybe for some improvements to this project.

 

[smstachwick]

“This will be the approximate appearance and dimensions of my G-TARC entry. Only the motor retainer, rail standoff/buttons, and a few internals remain. If all goes well I should be able to figure those out in time for a Saturday test flight. If it comes back in qualifying fashion, I’ll make my official flight.



“Note the tape over the shock cord knot for better gas seal, as well as the tape serving as an extension tube shoulder.”




“My epoxy joint is pretty messy because I used my finger to try to create a fillet, which was only sort of successful. I then eyeballed it on the line I drew.

“I’m guessing that I’ll lose one or both buttons or the lower body tube will start tearing/twisting apart before the standoff itself breaks loose from the tube. That’s some rough plywood and a big, heavy joint.

“But I think the most probable failure of all is a fin breaking on touchdown, more than any kind of rail issue.

“I still have a few internals to sort out but I think I can install them at the field.”

 

[smstachwick]

Actually, part of me now wonders if I may have been better off turning the stand-off into some kind of combo standoff/rail guide. Maybe I’ll buy a rail to prototype this idea and figure out what dimensions and tolerances I’d need.

 

[neil_w]

"Geezer TARC" wins best competition name, if nothing else.

 

[smstachwick]

Geezer TARC or: How I Snagged the Top Spot with an Automatic Disqualification!

Well, my Geezer TARC rocket got completed at the range with some generous assistance from Jim and Ruby Myres of Discount Rocketry. I bought a BT-55 bulkhead to form part of a shock cord attachment and Jim was kind enough to give me one matching coupler instead of me being on the hook for a whole bag’s worth. Ruby gifted me an 18” chute after learning from Mindy Kay Powers that my birthday was a week ago. I would have been happy to purchase both outright (and I did spend quite a bit on motors and adapters, more on this later) but who doesn’t like free stuff?

After assembling the mount to my satisfaction, I spoke to DART director Chris Flanigan about using a loaner altimeter and he was kind enough to make available and show me how to use a PerfectFlite P-Nut. I secured this in the payload bay with a dog barf wadding cushion and a plastic bag for to keep the dog barf it out of the sensor. I bit a small hole in the bag to take static pressure and give an altitude reading.

I protected the egg with a little bit of dog barf in the top and bottom of the Courier’s egg capsule, and secured it shut with Frog Tape.

After testing out my L1 rocket on an F67W motor, I purchased a pair of Enerjet by AeroTech E30-4T motors from the trailer to make my flight(s). I also purchased an Estes 24mm-to-29mm motor adapter so that I could avoid overpowering the rocket even with the oversized mount.

The practice flight was spectacular, SCREAMING off the pad to 769ft and smashing through 200mph. The rocket was recovered with no damage to itself or the payload, and the altimeter happily beeping out the flight data.

With a successful test flight under my belt, I decided to make an official flight and get on the scoreboard.

My official flight did not go as well. I can’t tell if the delay ignited before the propellant or if it simply did not perform to spec, or if the booster separated prematurely due to drag forces and the recovery gear being compressed pretty tight in the tube. In either case, the recovery system ejected prematurely at high speed. Despite the reefed parachute for this attempt, aerodynamic forces pulled the shock cord through the mounting slit and separated the rocket in two, an automatic disqualification.

The booster and payload sections were both recovered safely, more or less intact. The altimeter beeped out a 492 ft apogee and another high airspeed figure that I also cannot recall, but I believe it was also above 200mph.

A final inspection of the egg payload revealed that even this wild ride was powerless to harm it. I marked it with the flight info and put it back in the carton.

During my crash course on the P-Nut altimeter, Chris mentioned that I was the first contestant to make an official flight, and he seemed pretty surprised that I’d be so hasty about it, with good reason apparently. A few other club officers and longtime members are also competing and will move me to the bottom of the rankings in short order, but as the rankings currently stand, I am ranked #1 with an apogee over 200 ft below the target on a DQ flight!

Special thanks are due to Mindy Powers and Eric Quilkey, without whose help this dubious feat would have been much more difficult or impossible. You can hear them working the controller in the videos [which I annoyingly cannot upload!] but having their extra pairs of hands and feet around made things simpler!

I’ll keep flying this beast of a rocket, just with a little less thrust to combat the possible drag separation and subject egg payloads to less stress. I think a Q-Jet by AeroTech E26W would be a good selection next time I’m out.

 

[smstachwick]

Another photo of the eggs upon return. They will make a tasty breakfast very soon.

 

[smstachwick]

This rocket is currently in sick bay. I’m currently working on some better centering rings, which are not available commercially in this combination of sizes as far as I’m aware.

PayloadBay has a centering ring tool, I ripped the dimensions from the Apogee’s RockSim file for the Courier and the specs of BMS’s 29mm tube I have lying around. The results are understandably messy, as I’m just thinking of it as a proof-of-concept right now and not fully expecting to get usable centering rings the first time. Gotta start somewhere!



The outside edge of the template was cut out with kitchen shears and traced lightly with a pencil. The interior was cut with an X-Acto knife, but after starting to trace the interior edge I elected to do the rest freehand. I don’t anticipate that mistakes will throw me too far off centerline with the rings being this thin.

That’s 1/4inch markerbpard, it’s just what I have on hand and will probably be overkill. I’ll probably go at it with a scroll saw and try to sand to fit.

If a next attempt is necessary, I’ll try to go at it with more precise tools and materials.

 

[neil_w]

This rocket is currently in sick bay. I’m currently working on some better centering rings, which are not available commercially in this combination of sizes as far as I’m aware.

PayloadBay has a centering ring tool, I ripped the dimensions from the Apogee’s RockSim file for the Courier and the specs of BMS’s 29mm tube I have lying around. The results are understandably messy, as I’m just thinking of it as a proof-of-concept right now and not fully expecting to get usable centering rings the first time. Gotta start somewhere!

View attachment 632596

The outside edge of the template was cut out with kitchen shears and traced lightly with a pencil. The interior was cut with an X-Acto knife, but after starting to trace the interior edge I elected to do the rest freehand. I don’t anticipate that mistakes will throw me too far off centerline with the rings being this thin.

That’s 1/4inch markerbpard, it’s just what I have on hand and will probably be overkill. I’ll probably go at it with a scroll saw and try to sand to fit.

If a next attempt is necessary, I’ll try to go at it with more precise tools and materials.

For a ring like that I'd be inclined to build it up with wraps of cardstock, rather than trying to actually cut something like that.

 

[smstachwick]

For a ring like that I'd be inclined to build it up with wraps of cardstock, rather than trying to actually cut something like that.

Hmmm…maybe…

As it stands I’m having issues with the scroll saw. I’m working on getting the blade detached at one end to go through the hole I just drilled and saw the inside. I just can’t remember how I got it free last time…

Maybe I’ll see if I can get some thicker paper to go through the printer and give that a go if I can’t figure it out in the next 10 minutes.

 

[smstachwick]

Hmmm…maybe…

As it stands I’m having issues with the scroll saw. I’m working on getting the blade detached at one end to go through the hole I just drilled and saw the inside. I just can’t remember how I got it free last time…

Maybe I’ll see if I can get some thicker paper to go through the printer and give that a go if I can’t figure it out in the next 10 minutes.

I got it. It was the tensioner at the back.

It didn’t take long for me to see a drawback to this method. I’ll go see about that cardstock, maybe I have some office folders lying around or something.



At least the template works ok!

 

[neil_w]

I think you could even just build it up using masking tape, save the trouble of gluing all the layers.

 

[smstachwick]

I think you could even just build it up using masking tape, save the trouble of gluing all the layers.

That’s probably less messy. It’d be great if I can get tape wide enough to just draw it on, but I could do it in seams if I really needed to.

I did use tape for the last one, taking advantage of air bubbles to make a binding surface and gluing it in, but doing it as an actual ring would be lighter.

 

[smstachwick]

I think I figured out my centering ring problem. That’s a BT-55, an Estes coupler, and the 29mm tube. They slip easily over with one another but can probably be glued nice and snug



I could just put tubes within tubes like a matryoshka doll, but I’ll probably chop a BT-55 tube and coupler real thin to make actual rings.

 

[BEC]

First of all, good luck beating Chris Flanigan! You can tell him I said that if you like.

Second, yeah, I'd just wrap the motor tube with masking tape in a couple of spots to make it a snug fit in the BT-55 coupler and then glue the two parts together. Then glue the coupler into the BT-55. That's essentially how I put a 29mm mount in my Enerjet 1340 clone that was based on an Estes Eliminator (BT-56-based model).

There is both an NAR event and an FAI event that are also tARC-adjacent. The NAR event is called Precision Fragile Payload - one egg, 300 meters, 60 seconds. Scores is 1000 points minus factors for both altitude and time. This event was flown at NARAM last summer and is up again this year.

The FAI event is S2/P and is similar to the NAR event except that you fly THREE times and only check the egg after the third flight. Scoring is more like tARC with zero being perfect.

Chris came in 7th at both the World Spacemodeling championships last July and NARAM last August in the FAI and NAR events respectively. I was part of the altimeter-wrangling team at the Worlds and came in 9th at NARAM myself. At NARAM last year I flew an essentially stock Estes Olympus in Precision Fragile Payload and intend to use the same model at NARAM this year with a couple of very minor tweaks. For whatever that's worth (not much). I used the Q-Jet E26s last summer and had more than enough performance.

 

[smstachwick]

First of all, good luck beating Chris Flanigan! You can tell him I said that if you like.

Second, yeah, I'd just wrap the motor tube with masking tape in a couple of spots to make it a snug fit in the BT-55 coupler and then glue the two parts together. Then glue the coupler into the BT-55. That's essentially how I put a 29mm mount in my Enerjet 1340 clone that was based on an Estes Eliminator (BT-56-based model).

I forget the results except for the fact that he and Ross Iwamoto (side note, he always has really cool, beautifully detailed stuff at the range) both beat the snot out of me simply by making qualifying flights.

Still, this was a very fun little contest and a neat challenge that keeps on giving long after it’s decided. Every flight seems to present some new thing to think about or tweak. I’m really looking forward to stuffing something like a G74 in it and just letting it absolutely rip!

My goal for the next round is to post an actual score.

 

[smstachwick]

The first ring is cut. I’ve put it on the tube for safe keeping but I haven’t actually glued it.

I put the a coupler in another length of tube to start on the other one, currently waiting for the TiteBond to turn solid so I can cut it. I don’t know if I’ll accomplish installation today but I should get pretty darn close.

 

[smstachwick]

The motor tube is cut just shy of 200mm and the forward centering ring is installed. This length will be plenty for a G80 and it might accommodate an RMS 29/180 casing at a pinch for a G75J flight. It will certainly accommodate CTI G casings. Currently I’m looking at installing the AeroTech gas baffle/anchor point at the forward end and relocating the shock cord attachment point there. I wonder if I could slide some more BT-55 into the body tube to seal up the slit I made to accommodate the original…



I cut off the Estes retainer threads from the original mount. It’s currently soaking to loosen the paper before I go to war with my old epoxy job.



Currently I’m thinking to install the rear centering ring and retention threads at the same time and use the same epoxy job to secure them both butted together.

 

[smstachwick]

Can anybody think of a good way to reduce the diameter of the AeroTech baffle/shock cord mount? Some kind of hot knife, maybe?

 

[Initiator001]

Can anybody think of a good way to reduce the diameter of the AeroTech baffle/shock cord mount? Some kind of hot knife, maybe?

View attachment 633824

Use a belt or disk sander.
The aroma that comes off of high speed sanding plastic parts can be intense.

 

[smstachwick]

Use a belt or disk sander.
The aroma that comes off of high speed sanding plastic parts can be intense.

Possible. I’m definitely saving that for when I can open the garage and set up a fan.

I might also consider using that scroll saw again. It doesn’t have to be a perfect match, it just has to fit inside the tube.

 

[smstachwick]

I flew the rocket today, using masking tape to hold the motor mount in place. The objective was just to test the gas seal generated by my centering rings and the Estes retainer, which is butted up to the rear ring and the end of the body tube.

I kind of like this arrangement with the removable mount, since it allows me to pack wadding directly into the extra space in the motor mount tube instead of having to stuff it in all the way from the front of the rocket. It marries the virtues of traditional wadding and more elaborate cooling systems closer to the motor (such as AeroTech’s Labyrinth).

I do not plan to keep it that way though, since using tape every time doesn’t seem like a good idea. I’m just waiting on my AeroTech baffles/shock cord mounts to get here. I ordered like 10 so I have zero chance of losing them, they were $.69 apiece and I figured I could justify quick shipping with a larger order. So far they have failed to materialize, UPS might have gotten confused.

The E30s were a bit overpowered for this site when allowed to coast for 7 seconds. I’ll likely be down-powering to E26s for the next flights at DART, since they’ll trim a bit of impulse without sacrificing a ton of thrust. I’ll save 29mm motors and overachieving 24s for desert trips.

And of course, the eggstronaut survived both missions to fly a third, or become breakfast tomorrow!

Flight video
View attachment IMG_1194.mov

 

[smstachwick]

Well, this rocket is basically complete the way I want it. I so thoroughly enjoyed yesterday’s build session that I neglected to get photos of my modification to the baffle, but it and the rest of the motor mount are installed, the shock cord mount is moved to a screw eye screwed into the baffle, and the slit is plugged up with a short section of BT-55. The remainder of the tape seal has come off, and the exterior displays a lot more soot than I expected.





The gas seal passed the breath test so now all that’s left is to wait for my E26s and let her loose at ROCStock. I’ll probably start painting today if conditions are favorable.

If I had one wish-list item from AeroTech it would be for a baffle that’s better suited for smaller-diameter rockets like this one. I really don’t like creating microplastics if I can avoid it. I’m also open to suggestions for third-party substitutes.

 

[smstachwick]

So, I don’t have the paint I wanted to use. Bummer. But my E26s finally showed up!



I noticed the nozzle has a small chip in it, but I don’t expect issues since it doesn’t extend to the nozzle throat.



All of my projects are basically ready to fly, but my head is still swimming with rocket stuff. Maybe now would be a good time to go shopping for my next kit…

 

[smstachwick]

In preparation for the next Holtville launch, I went out and bought payloads. A fit test revealed that precisely half of the Large eggs I bought were skinny enough to fit in the compartment. They are labeled and the rest will be used for my late lunch/early dinner today.



Because motors in this rocket’s size range typically come in two-packs, I’m going to see what I can add to a two-egg dish to make it tastier, more nutritious, and more filling. Grilled sweet onions, salsa, and a couple of other things on the side might work. As with actual rocket flight, I’m prepared for a spectacular failure, in this case a gross or under-portioned meal.

Never thought rockets would get me into cooking but here we are.

 

[smstachwick]

I kinda like it.



It’s half a grilled sweet onion, two eggs, and some salsa. Melon and plain yogurt on the side complete the meal.

Like anything else I have a few tweaks in mind. I won’t bore everyone with the details because it works! I’m very proud of myself and I can very easily see that as a range dinner.

 

[smstachwick]

The rocket flew at Tripoli San Diego’s April event. It looked a little slow off the rod and weathercocked a bit, but at least it’s clearly staying under 1000ft. Fellow DART member Frank Killion wondered aloud why I couldn’t make the flight at Fiesta Island, which is good enough for me.

The flight ended with the rocks tearing up the balsa fins. I’ll have to do some work fixing them back up and strengthening them, or replacing them completely. I might also attach another parachute, the descent rate seems a bit on the high side and I have plenty of length in the tube. It’s packing diameter that’s in (relatively) short supply.

I also cracked the eggshell but didn’t actually break it clean open. An additional chute might also fix that.

The only thing to watch out for is the weathercocking, I’ll have to fly the E26 in calmer winds or look for something with more initial thrust, while also bringing down the total impulse. The D22W Q-Jet looks promising, it delivers a little bit more initial thrust a little bit quicker. It’s rather unfortunate I don’t have an option for something like an E30 that’s just less impulse and perhaps 75% of the initial thrust spike. ~50% seems a tad low. Every convenient option to lower the impulse has a relatively flat curve. That’s the E30 in the green.



I’ll keep playing around with it and maybe look at acquiring or borrowing some hardware to open up more motor options.