TARC frustration: advice needed

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At least nobody suggested Jelutong.

I had to Google that one, Fred . . . LOL !

https://en.wikipedia.org/wiki/Dyera_costulata

They could always make laminated fins . . . 4-axis, 1/32" Balsa . . . Balsa or Bass with 1/64" plywood "skins" . . . Alternating layers of 1/32" balsa and 1/64" Plywood, etc . . . It would be great to teach them vacuum-bagging with a food-saver ( a little fiberglass ) !

Dave F.
 
You can laminate fiberglass on either side of balsa without too much trouble if you are so inclined. Pressing them between two tiles makes a nice surface. 1/8” balsa and very light fiberglass makes a durable fin.

This is far beyond what Neil’s team needs, though!
 
Not from my perspective . . . As I see it, Neil's team needs a miracle !
As I have tried to convey, the goal at this point is to simply attempt some qualifying flights.

Todo list right now looks like this:
1) Secure the payload section (and possibly shorten it)
2) Mount the altimeter and punch air holes in the BT They have a Firefly.
3) Add recovery to bottom section. I have a parachute to give them, along with shock cord materials.
4) Find some motors. Some forum members have graciously offered to supply these if we can't find any in time.
5) Go fly

None of this requires a miracle, just some applied effort at getting it all done in the allotted time.
 
As I have tried to convey, the goal at this point is to simply attempt some qualifying flights.

Neil, that sounds like a good goal to aim form. The two teams that I was a witness for took several years before they had 2 qualifying to submit officaily to the TARC organization. Technically, there is a form to fill out for the two qualifying flights which must have two timers/witnesses. The TARC teams can make as many practice flights as they want. I've seen TARC teams add or subtract lead shot to the rocket and change the parachute size on practice flights. However, keep in mind that for any official qualifying flight the TARC team leader must declare before the launch that the flight is a qualifying flight. Naturally, if the team picks up some good flights along the way that would have been qualifying flights is good to know and is a worthy goal in itself.
 
Well, if I were a TARC-age kid ( teens ), this is what I would be building for 2019. Bear in mind that I started flying rockets at age 6 and already had 8 years of building & design experience by the time i was 14, back in 1975. Yes, I would have been able to construct this, by myself, back then ( the carbon-fiber components would have been wooden dowels, 44 years ago. ).

Each egg has it's own compartment with a rigid divider in between and each egg would, naturally, be padded. The payload section "shroud" would slide over the framework and be retained either by a friction fit or small screws.

Since this design is smaller in diameter and less bulky, a 24mm motor MIGHT be capable of reaching the 856 ft target altitude ( up to 881 ft in the Finals ). However I believe that a 29mm motor is the better choice ( ballast required ).

The "Giant Leap" name refers to Neil Armstrong's words on Apollo 11. "That's one small step for a man . . . One giant leap for mankind".

The clipped delta fins are reminiscent of the Saturn V first stage fins. Four fins were chosen, since they are less prone to "coning" than three fins would be.

The paint scheme would be "Saturn V-ish" ( Silver fins, black & white roll patterns, USA, United States, & USA flags, etc ), in honor of the 50th Anniversary of Apollo 11.

The Booster section might need minor lengthening ( 1"-2" ) to accommodate three parachutes. Similarly, the Payload might require similar lengthening to properly accommodate the eggs.

Dave F.

TARC - 20191.jpg
 
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Well, if I were a TARC-age kid ( teens ), this is what I would be building for 2019. Bear in mind that I started flying rockets at age 6 and already had 8 years of building & design experience by the time i was 14, back in 1975. Yes, I would have been able to construct this, by myself, back then ( the carbon-fiber components would have been wooden dowels, 44 years ago. ).

Each egg has it's own compartment with a rigid divider in between and each egg would, naturally, be padded. The payload section "shroud" would slide over the framework and be retained either by a friction fit or small screws.

Since this design is smaller in diameter and less bulky, a 24mm motor MIGHT be capable of reaching the 856 ft target altitude ( up to 881 ft in the Finals ). However I believe that a 29mm motor is the better choice ( ballast required ).

The "Giant Leap" name refers to Neil Armstrong's words on Apollo 11. "That's one small step for a man . . . One giant leap for mankind".

The clipped delta fins are reminiscent of the Saturn V first stage fins. Four fins were chosen, since they are less prone to "coning" than three fins would be.

The paint scheme would be "Saturn V-ish" ( Silver fins, black & white roll patterns, USA, United States, & USA flags, etc ), in honor of the 50th Anniversary of Apollo 11.

The Booster section might need minor lengthening ( 1"-2" ) to accommodate three parachutes. Similarly, the Payload might require similar lengthening to properly accommodate the eggs.

Dave F.

View attachment 375359

It’s a fairly reasonable design. The only serious flaw is that your tube diameter is way too small. BT70 is the practical minimum to fit eggs and padding. If I were your mentor, I’d also say that you are overthinking the padding and framework. The foam padding systems available from Apogee are plenty for the job with no framework required.

Do you fly Aerotech or CTI?
 
It’s a fairly reasonable design. The only serious flaw is that your tube diameter is way too small. BT70 is the practical minimum to fit eggs and padding. If I were your mentor, I’d also say that you are overthinking the padding and framework. The foam padding systems available from Apogee are plenty for the job with no framework required.

Do you fly Aerotech or CTI?

I grew up flying eggs in NAR competition in vac u-formed CMR capsules, in 1975 onward ( slightly larger diameter than a BT-60 ) and the sport-flying the Astron Scrambler with a 1.65" diameter payload tube.

The 1.88" OD is sufficient ( a 2.04" OD could easily be substituted ) . . . I don't know why TARC started off with BT-70 & BT-80 type models, as they are quite draggy and add unnecessary mass.

The use of rigid divider plates between the eggs is a lesson learned decades ago. They prevent the eggs from impacting each other, either under thrust or upon landing. Remember that NAR competition, for the most part, is about maximum performance, which means minimum diameter & optimum weight, etc. NAR does not have a "triple eggloft" event.

Yes, I have seen the Apogee foam egg protectors, including the ones which allow for eggs to be carried horizontally. Most of them are for BT-70 and BT-80 diameter rockets . . . Overkill.

Unless TARC includes a minimum diameter clause in the rules, there is no reason to be handicapped by large, draggy rockets.

My design uses three of these "egg protectors" from Apogee . . .

https://www.apogeerockets.com/Building_Supplies/Payload_Protection/Egg_Protector_for_Vac-Form_Capsule

The "framework" is very lightweight and is virtually 'bulletproof" in protecting the eggs. In addition to the foam egg protectors, each egg is surrounded by "dog barf".

The rocket in this pic weighs 3.2 oz empty . . . Minimum liftoff weight w/ 3 eggs & padding, minus motor & ballast is 10.4 oz.

Dave F.



triple-egg-lofter-01-jpg.374658
 
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TARC rules give a maximum egg diameter of 45mm or 1.77”. If your carbon rods are big enough to be useful, they and the eggs won’t fit in a 1.88” tube. You do get some choice of eggs at finals but I wouldn’t want to be at the table with a set of calipers.

TARC rules have developed over time to help students be successful. They are not intended to be maximum efficiency. I suspect that they start with BT70 because smaller tends to lead to more broken eggs.

So I’ll offer a challenge to you. Tell us how high your planned rocket will go on a specified motor using hand calcs of your choice and then see how close that comes to a sim from Openrocket or Rocksim.
 
Agreed . . . I respect your wishes on this . . . Can't speak for others, though !

Dave F.

Funny. The guy who interjects his family history, his contempt for computers, his plans for L3, how he is smarter than a 5th grader, and other meaningless anecdotes now blames everybody else for derailing this thread.
 
Funny. The guy who interjects his family history, his contempt for computers, his plans for L3, how he is smarter than a 5th grader, and other meaningless anecdotes now blames everybody else for derailing this thread.

Well, what's your plan to help these kids ?

Please enlighten us . . .

Dave F.
 
can I just use regular plywood instead of airplane plywood to make my fins; or if not where can I find airplane plywood?
 
can I just use regular plywood instead of airplane plywood to make my fins; or if not where can I find airplane plywood?

You want the plywood to have as many layers as possible. If you can’t find aircraft plywood locally, Baltic birch is a good substitute. You can find that at a good woodworking store like Rockler Hardware. That’s what I use. If you can’t find Baltic, get the highest grade plywood you can find at a hardware or craft store.

[edit] sorry for previous derailment—sticking to answering questions that have been asked.
 
can I just use regular plywood instead of airplane plywood to make my fins; or if not where can I find airplane plywood?

You can use any plywood you want/ can get...
It's your rocket!
Don't let these guys convince you other wise.. sure, airplane ply is optimal for rockets but not necessary...
 
First of all, you need to encourage them to fly a rocket that is safe.

It doesn't sound like this team has any chance of qualifying for the TARC finals so I suggest you jump in with both feet and show them how to build a rocket and how OR works. Help this team get ready for next year. Taking a completely hands off approach in hopes that this inexperienced team somehow builds a rocket that qualifies seems more likely to result in a team that won't even try next year. They need to learn how to build a rocket and what is safe and what isn't. That will help them get ready for next year.
Man, the first part of this thread is really helpful for me at least, I'm in my second year for being a tarc mentor to a great group of afrotc cadets and they've started late both years. Thanks for some great advice here.
 
I found in being an mentor/advisor that the most common problems for TARC teams was breaking fins and detaching parachutes. Attaching the parachute with a strong connection will save a lot of trouble. Having a way to modify the chute by size or possibly by reefing can tune in the target flight time. Of course, you cannot use the Apogee Egg Storminator. It is not the right design configuration, which changes every year, but it shows a light but sturdy through-the-wall fin configuration made out of strong wood.
 
You can use any plywood you want/ can get...
It's your rocket!
Don't let these guys convince you other wise.. sure, airplane ply is optimal for rockets but not necessary...

I prefer to give sound advice, rather than say "do whatever you want". With the latter, he might as well not have asked, at all.

To the young man who asked . . . There are many different materials and construction methods available for making fins. I recommend building "strong & light".

Personally, I like the using what I call the "Sandwich Method" . . .

https://www.rocketryforum.com/threads/how-would-you-laminate-fins.88962/

https://www.rocketryforum.com/threads/core-material-for-lightweight-fins.130879/


Dave F.
 
One of the TARC teams I mentored switched exclusively to tube fins years ago. All their problems related to fins ended.

What material did they use for the tube fins? The team I work with tried tube fins from BT70/80 and they got beat up pretty quickly.
 
Maybe, but I just loved seeing how the students would solve problems. Much of the time they did things that I “would” do differently. They learned from their mistakes and I learned from their successes.

Steve,

Unfortunately the "window of opportunity" is very truncated for this team. Time is short, options are few, and experienced people to teach them are not in place. Frankly, I would have started with them back in September.

My best general suggestion to the team, at this late date, is to scrap the existing rocket, pick up some slotted BT-70, a coupler and two bulk-plates (Altimeter Bay), a new nose cone, a 29mm motor mount, and 3 BT-70 foam "egg sarcophagus" ( 1 double / 1 single ) units from Apogee. Use 1/4" C-Grain balsa, make either Clipped Delta or Trapezoidal fins, and start flying, ASAP !

These kids deserved a lot better . . .

Dave F.
 
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