TARC frustration: advice needed

[neil_w]

Hi,
Could use some advice here. My friend's daughter (8th grade) is part of a just-formed TARC team at her school. There are only 3 girls in it. To make a long story short: the advisor, a science teacher at the school, has no rocketry experience. All the girls built rockets based on a previous year's design (dunno where that came from), using parts apparently from Apogee. No simulation of any sort was done, no theory was taught. Some very minimal technique was taught, and everything was build with Home Depot epoxy, so presumably some 5 minute variety.

Two rockets were launched so far: one was lost, another crashed. My friend's daughter's rocket was not launched yet, and tonight I had a chance to look it over. Considering the lack of rocketry knowledge that went into it, it's almost flyable, with a few exceptions:

1) Lower half lacks any form of recovery
2) Payload section is not secured shut (either the nose cone or the transition at the bottom)
3) I am hoping to sim it to check stability. The fins are quite small, although it's possible they're fine. I have no idea where CG will be.
4) The rail buttons are secured to the body tubes with a standard nut in the back, rather than a T-nut or anything like that. They felt a little flimsy but I'm not sure if it's OK.
5) The MMT centering rings are foam. Is there a recommended maximum thrust for these (it's a 29mm mount inside BT80) or are they pretty much fine for an F or G motor? They felt pretty flexy to me but that doesn't mean they won't hold. I tend to overbuild anyway.

I have no intention of "fixing" the team or becoming an advisor, just want to help them make sure their rockets are safe and flyable until they learn enough to be able to ensure it on their own. But I have zero TARC experience and almost all my own experience is with LPR, so there are an assortment of techniques here that I certainly know of but have never actually used (e.g. I've never used a rail button before).

My understanding is that for TARC the kids are supposed to do all the work? Exactly where does "advice" end and "work" begin? I figured the least I could do was help them get some OR sims going so they could verify stability and figure out their ejection timing. Also, in case it's not obvious, this is just a learning project; no one will be seriously competing with these rockets. So is it bad if I give them a little hands-on help just for the learning, or should I keep my paws off?

I guess I'm just trying to figure out what I can do that is helpful without "making trouble", as it were. Any advice appreciated.

 

[JJSR]

Neil it's kind of late in the competition to start from scratch for them. Qualifying flights have too be done in April. If they want, have then come out to a club launch. We have 5 teams launching, I'm sure they could get some pointers from them and our club mentors.
Give them my email and I'll see what can be done to help them.

 

[BEC]

This year's challenge involves 3 eggs (this is a first for TARC) so it's not going to take too much fin area to make the thing stable. This year it is supposed to come down in two pieces - the part with the eggs and the altimeter must use two or more parachutes. Clearly if it's not secured well enough to not spill the contents at ejection that's a problem.

The recovery system on the booster is optional but there has to be one or an official flight will be DQ'd as unsafe.

TARC is limited to 80 N-s (full F). What time/thrust curve as well as total impulse up to that point is up to the team in order to hit the target.

I'd guess the rail buttons will likely be OK. Not sure about the centering rings. It kind of depends on what motor they're planning to use.

Joe is quite right that they are kind of late to the game - though if they're starting to fly now they are still better off than a number of teams I've dealt with over the last few years with almost two months left until qualifying scores are due.

 

[aerostadt]

In addition to launching 3 eggs unbroken with a motor no greater than 80 N-s, the rocket target altitude is 846 feet and a total flight time of 43 to 46 seconds. You need 2 witnesses or timers for the flight, one of which needs to be a NAR member. The full 2019 rules can be found here:

https://3384f12ld0l0tjlik1fcm68s-wp...loads/2018/08/Event-Rules-TARC-2019-FINAL.pdf

and the official website is here: https://rocketcontest.org/

I agree with the other posts that now is too late to really compete. However, the team could build and practice to gain experience, to have fun, and possibly compete next year. To some extent the rules change every year. I have seen mentors and school advisors guide with different degrees of participation. I have seen some mentors/advisers be strong drivers and others be very non-participating. The rules advocate that the students do the bulk of the work. If a team makes it to the finals, the rules do not allow the mentors/advisors at the launch pad. Apogee offers a basic kit the Egg Storminator. I bought one last year. I think that the kit, especially the single egg compartment, might be too complicated, but it might be a way to introduce the students to the basics. If you have a model that is close to be in good flying condition, by all means finish it up. You could put an egg or eggs or simulated weight in the payload compartment. If you do use an egg, put it in a sealed plastic bag.

 

[BEC]

The students are to do all the work on the models used in competition. At the finals mentors/teachers/any adults outside of those tasked with running the finals are not allowed in either the rocket prep area or down on the field at the pads.

Getting an official score in to the AIA is something to strive for, even if it's not a score that gets the team invited to the finals (the best 100 sum-of-two-flights' scores among all those submitted). It is not impossible to do that in the remaining two months... but it isn't easy as there are only so many practice/adjustment flights that can be done before flying the official ones by the deadline.

I think aerostadt typo'd a bit above - this year's target altitude is 856 feet. The second flight at the finals will be either 25 feet higher or lower depending on a coin toss at the flyers' meeting the day before the finals are flown (and the duration target is adjusted to match the increase or decrease in target altitude).

 

[mikec]

Apogee offers a basic kit the Egg Storminator.

Keep in mind that you can't use this kit, or any kit, for TARC competition.

Each student member must make a significant contribution to the designing, building, and/or launching of the team's entry. No part of any of these
activities for a rocket used in a qualification flight or at the Finals may be done by any adult, by a company (except by
the sale of standard off-the-shelf components available to the general public, but not kits or designs for the event), or
by any person not a student on that team.

 

[Rex R]

in response to the foam centering ring question, the answer is it depends on the fins. if you have TTW fins firmly affixed to the motor tube and the airframe, then they become the means by which the thrust loads are transferred to and from the motor tube. I have flown a 2.6" dia. rocket on a small H that had the rings made from 5mm foam (the fins were made from papered balsa), I named the rocket 'mostly harmless' because of its lightweight construction, sure surprised some folks when it leapt off the pad . from your comments I suspect that the bird you're talking about might not have TTW fins.
Rex

 

[neil_w]

Thanks for the replies. A few clarifications and additional items:

1) Thanks Rex for the reminder re: centering rings. The fins *are* TTW (they're using the pre-slotted tubes from Apogee), so they should be OK, assuming they got a good glue joint in there. I *always* forget about that.

2) I agree they're very late to be competing. I have thought that they would do great just to build working rockets that come close to meeting the TARC requirements. The rocket I looked at is very close to being flyable. But I don't to run afoul of the rules in case they do get to the point of being able to do any official flights. I don't know what the plans are for the team (I know almost nothing except the rocket I was shown). Perhaps their next step would be to build the official competition rocket together?

3) If I help them with building an OR model, is that within the rules?

4) What method would typically be used to secure the payload compartment? They've got the Apogee foam nose cone and a blow-molded plastic transition on the bottom. Right now the nose is medium-snug and the transition is very loose.

5) How would you attach a chute to the bottom section? I'm thinking a tri-fold mount is the best after-the-fact option (couldn't tie a shock cord to the foam ring anyway). They're using some sort of nylon for the upper section shock cord, I'm thinking Kevlar for the bottom or maybe even some 3/8" elastic or something like that (the bottom isn't too heavy).

6) I learned that they did their epoxying without gloves.

 

[samb]

Definitely get them to Joe's club launch asap so they can see what flying rockets is like.

1) Lower half lacks any form of recovery

An upscaled Estes teabag attached shock cord should do the trick.

2) Payload section is not secured shut (either the nose cone or the transition at the bottom)

Glue the transition and tape the nose code.

3) I am hoping to sim it to check stability. The fins are quite small, although it's possible they're fine. I have no idea where CG will be.

Most def.

4) The rail buttons are secured to the body tubes with a standard nut in the back, rather than a T-nut or anything like that. They felt a little flimsy but I'm not sure if it's OK.

Epoxy them in place.

5) The MMT centering rings are foam. Is there a recommended maximum thrust for these (it's a 29mm mount inside BT80) or are they pretty much fine for an F or G motor? They felt pretty flexy to me but that doesn't mean they won't hold. I tend to overbuild anyway.

To me, this is the kicker. I would create another ring from cardboard (like a USPS priority box) or 1/16 inch ply and laminate it to the aft ring. Can you access the forward ring ? If so do a lamination there as well.


Your a good man Charlie Brown ! Help those youngsters.

 

[Zeus-cat]

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.

 

[neil_w]

Additional note: I *did* take them to a launch last Spring, when the news of the team forming first hit. Gave them a Crayon rocket to launch. They enjoyed it. There was also a TARC team there already testing their 2019 rocket, so they got to see a bit of that as well.

 

[anbhtblr]

Neil: I've not been involved with TARC, but I was a Destination Imagination (DI) team manager for years (decades), and DI has the same rule about the team doing the work (DI makes the team sign a statement that no outsider [parent, sibling, teacher...] interfered [helped] the team). So what I did as a team manager with teams of 5th graders through HS seniors, was to teach skills, e.g. how to measure, cut, sketch your ideas, debate alternatives/variations, use hand tools, use power tools... The teaching (demonstrations and practice) always used scrap materials, never the actual project materials. I expect the TARC approach should be the same.

 

[Tobor]

Another suggestion for teaching aids, do a group build session (You included) with some Micro Max kits. Smaller can be harder which could help teach patience. This is often an overlooked "skill".

 

[Ez2cDave]

To make a long story short: the advisor, a science teacher at the school, has no rocketry experience. All the girls built rockets based on a previous year's design (dunno where that came from), using parts apparently from Apogee. No simulation of any sort was done, no theory was taught.

It's a shame that the kids got "short-changed" like that. As for the teacher, you can't teach skills that you do not possess yourself. The late start is a real handicap, too.

I have mentored several TARC teams in the past. They got a "crash course" in competition rocket design and construction techniques, plus a LOT of Flight Testing.

My approach to TARC this year would be to teach the kids :

(1) Assume that the eggs are all max weight ( 61 grams each ). Everything is weighed on a digital scale before EVERY flight.

(2) Chute sizes are optimized to provide the desired descent rate, with a given weight. If the eggs were all 55gr, 18 gr of ballast would be added to the Payload Section.

(3) "Jettison-able" Ballast ( loose sand in a paper sleeve - blown out at ejection ) is added to the booster, above the parachute, if needed, to achieve the optimum Liftoff weight needed to hit the target altitude. Thus, both Boost and Recovery performance are separately "tunable". This is critical when flying at different elevations at different launch sites.

(4) Parachutes are packed the SAME way, EVERY time. ( One or two members of the team are assigned this task )

(5) Efficient design, repeatable performance, reliability.

(6) Launch from a TOWER only !

(7) The only variable you can't control, other than wind and thermal conditions, is motor performance, which varies from motor to motor.

The end result would, likely, resemble the 25.7" rocket in the pics below ( Yes, three eggs, plus an altimeter, will fit in this payload section )

Dave F.

 

[neil_w]

Their rocket currently looks like this:


I thew the OR model together based on rocket dimensions provided to me; weight and CG are still to be measured (I hope to get that info today).

Bottom section is BT80, payload is BT70, each 18 inches long. One thing I immediately said was that the payload section is needlessly long, but I'm guessing they just didn't do any tube cutting, just used the 18" BT sections direct from Apogee. So shortening up the payload section, gluing and/or securing the nose and transition to the payload section, and adding recovery to the bottom section were the changes that I recommended they make immediately just to make it flyable (although I guess payload section length isn't a flyability issue).

Once I have the weights and CG we can check stability and also figure out proper delay. I don't know exactly what motor they're using; it's an Aerotech single-use F motor but not sure which, and heaven knows what the delay is.

I should have taken a picture of the harness for the payload section; I'm not too enthusiastic about how it was done but it's probably good enough to at least function.

Oh: for TARC do you guys generally get a Nomex blanket or just throw in a lot of wadding? I've never tried to load a BT-80 with dog barf before but I assume it should work.

It's possible I might have a session with the girls on Sunday, but not sure how I should spend it. Could do some building, or I could give them an intro to basic concepts and how to use OR to build a sim. Then just maybe hit on a few general build techniques based on mistakes I saw. I don't think I have time to figure out a whole big rocket build day.

One last thing: Is there any reason not to use something like 1/8" balsa for the fins on these things? They're not gonna go that fast. Basswood at most. Right now they have 1/8" plywood on there, which seems pointlessly heavy and hard to cut.

 

[afadeev]

Oh: for TARC do you guys generally get a Nomex blanket or just throw in a lot of wadding? I've never tried to load a BT-80 with dog barf before but I assume it should work.

For repeated flights (which is what they should be doing now), Nomex blanket is FAR easier to manage than repeated stuffing of dog barf (another weight variable to manage).

It's possible I might have a session with the girls on Sunday, but not sure how I should spend it. Could do some building, or I could give them an intro to basic concepts and how to use OR to build a sim. Then just maybe hit on a few general build techniques based on mistakes I saw. I don't think I have time to figure out a whole big rocket build day.

Neil,
Do whatever you think will keep their interest in TARC alive!
If I was them, I would be both nervous and lost at this point. They don't know what they don't know, and you don't have the time to teach them everything in one session.

Observation #1: that BT70/55mm diameter payload section looks dangerously narrow to allow for sufficient egg padding. The eggs in my fridge are 1 3/4" in diameter. That leaves scan 5mm room for padding on the sides. Will it be enough? Only one way to find out - FLY!

One last thing: Is there any reason not to use something like 1/8" balsa for the fins on these things? They're not gonna go that fast. Basswood at most. Right now they have 1/8" plywood on there, which seems pointlessly heavy and hard to cut.

Since this is not an altitude event, survivability would be a big consideration for rocket that needs to fly dozens of times. If plywood fins are already precut - use them as-is. If not, make fins out of whatever materials you have handy, and go out to FLY!

Observation #2: There are many things that don't look right about the rocket, as-is. But if it's flyable, the best and only way to teach the kids at this point is to go out into the field, and demonstrate. Discussing theoretical short-comings of their model will just demoralize them further. If you don't have a tower or a rail, glue some 1/4" lugs to the model, and spend the Sunday flying it with them at the local park/baseball field. Validate that as-is rocket is at all usable, stable, and fit for purpose (eggs survive, chute deploys). Then collect altitude & descent time data, and explain to them how to adjust it to optimize for TARC goals.

Long story short - my vote is to go out and FLY the rocket with them, and use theory to help them optimize it, as necessary. Not the other way around.

HTH,
alex

P.S.: If the rocket is not even built yet, and you can't fly, then take them out for ice-cream.

 

[samb]

I agree with Alex, get’um flying ASAP. The thing I noticed in the design is that It’s too long for this years contest, which specifies total airframe length of 25.6 inches. There is an overall weight limit too. I would sort that out, probably shorten both payload and airframe sections and use the 1\8th inch balsa. I think it’s important to get them to a point where they can do an official qualifying flight and send the results in. They will learn a lot from that effort. Like reading and following the contest rules !

 

[neil_w]

Once I have the weights and CG we can check stability and also figure out proper delay. I don't know exactly what motor they're using; it's an Aerotech single-use F motor but not sure which, and heaven knows what the delay is.

You can't make this stuff up. I just found out what motor they've been using:


Not sure yet what it weighs without eggs, so I can't pick a good test flight motor yet.

Fully loaded with eggs the rocket weighs in at about 16 oz, so we're comfortably in F territory. Not gonna worry about that yet at all.

that BT70/55mm diameter payload section looks dangerously narrow to allow for sufficient egg padding. The eggs in my fridge are 1 3/4" in diameter. That leaves scan 5mm room for padding on the sides. Will it be enough? Only one way to find out - FLY!

I strongly doubt I'll be able to take them flying this weekend.

For what it's worth, they're using the Apogee egg protectors, which fit in BT70.

Since this is not an altitude event, survivability would be a big consideration for rocket that needs to fly dozens of times. If plywood fins are already precut - use them as-is. If not, make fins out of whatever materials you have handy, and go out to FLY!

They appear to have been messily hand-cut. I'm not sure exactly how.

Validate that as-is rocket is at all usable, stable, and fit for purpose (eggs survive, chute deploys). Then collect altitude & descent time data, and explain to them how to adjust it to optimize for TARC goals.

Unclear if they even have an altimeter. I need to find out. My priority first is to get the rocket into safe flying shape. One step at a time.

I agree with Alex, get’um flying ASAP. The thing I noticed in the design is that It’s too long for this years contest, which specifies total airframe length of 25.6 inches. There is an overall weight limit too.

Modifying that one down to 25" would be a pretty good challenge. Certainly it should be possible. Weight limit (650g) shouldn't be a problem. But I'm not really thinking of these rockets as intended for competition, just learning vehicles. Dunno how these builds were originally framed, though, since I wasn't there.

Lest I seem *too* critical and frustrated, I repeat that I am impressed they got as close to a working rocket as they did.

 

[mad4hws]

While we are probably too far for you to travel, we'll have several teams flying over the next several Saturdays in Durham, CT. They still have 6 weeks left, so a lot can still be accomplished, even if they don't get the requisite number of practice flights up. Send me a note if you're interested and I'll give you a call.

 

[mad4hws]

[QUOTE="neil_w, post: 1860207, member: 23964]
Modifying that one down to 25" would be a pretty good challenge. Certainly it should be possible. Weight limit (650g) shouldn't be a problem. But I'm not really thinking of these rockets as intended for competition, just learning vehicles. Dunno how these builds were originally framed, though, since I wasn't there.
.[/QUOTE]

There are several mis-interpretations of the rules throughout this post. The minimum length is 25.6", so they should be fine.

I have plenty of spare parts, altimeters, motors, etc. I don't think I can make it down to NJ though. send me a note if I can help in any way.

 

[neil_w]

There are several mis-interpretations of the rules throughout this post. The minimum length is 25.6", so they should be fine.

Whoops, my bad. That's what I get for trying to sort through too many things at once.

As a quick reminder to all, I'm not the advisor here, just an interested party. I'm trying to fill in some sorely missing education and guidance, but I can't just jump in and take over everything.

I have plenty of spare parts, altimeters, motors, etc. I don't think I can make it down to NJ though. send me a note if I can help in any way.

Appreciate the offer. At this point I'm just trying to get this rocket flyable.

 

[afadeev]

You can't make this stuff up. I just found out what motor they've been using:
View attachment 374672
Not sure yet what it weighs without eggs, so I can't pick a good test flight motor yet.

Fully loaded with eggs the rocket weighs in at about 16 oz, so we're comfortably in F territory. Not gonna worry about that yet at all.

OK, -0 part of E16-0 is not helpful.
Is the motor mount actually 29mm in diameter (not assuming anything now)?
If yes, and if you don't mind funding them for the weekend, go pickup a few F15's and a stop-watch from Hobby Lobby, and you should have a decent starting point.

I strongly doubt I'll be able to take them flying this weekend.

Unclear if they even have an altimeter. I need to find out. My priority first is to get the rocket into safe flying shape. One step at a time.

You can borrow any of my altimeters (Estes, JL2, JL3), if needed.
I also should have F15's in the range box, if you want to go flying this weekend. At last weather looks to be cooperating.

If you are sure they are not in a shape to fly, then ice-cream party it is, with a sprinkling of rocket theory!

a

 

[neil_w]

F15 is actually slower off the rod than an E16, doesn't help.

It's a genuine 29mm mount. Rocket is 294g dry weight, which is actually just light enough for an E16, but according to my sim it is not stable without some weight in nose, so when all is said and done it'll probably be too heavy for any BP motor. I just don't think flying this weekend is any sort of realistic possibility.

 

[mad4hws]

Appreciate the offer. At this point I'm just trying to get this rocket flyable.

Totally understand. The offer stands, so please don't hesitate to call me. having something with a little more initial thrust than the F15 would be advisable, since they are so close to being unstable. getting TARC type motors at this point is difficult. I have a good assortment and would be willing to meet you to do a hand off. not sure that the F15 would meet the 5:1 rule, suspect it's pretty close. I definitely wouldn't go there on a day that has any meaningful wind.

 

[afadeev]

F15 is actually slower off the rod than an E16, doesn't help.

It's a genuine 29mm mount. Rocket is 294g dry weight, which is actually just light enough for an E16, but according to my sim it is not stable without some weight in nose,

Does your sim include the weight of 3 eggs in the nose?

so when all is said and done it'll probably be too heavy for any BP motor.

You are probably right.
Almost all TARC teams flew on Aerotech F's last year:
https://3384f12ld0l0tjlik1fcm68s-wp...ads/2018/05/TARC-Results-2018-Flight-Data.pdf

I just don't think flying this weekend is any sort of realistic possibility.

 

[Rex R]

for my 3:16 (sport)scale patriot I used 1/8" balsa papered (cardstock) fins, they seem to be holding up. I also used 1/16" plywood centering rings. it seems to favor F52s .
Rex

 

[neil_w]

Does your sim include the weight of 3 eggs in the nose?

294g is without eggs, but it occurs to me I don't know if it includes the protectors (no idea how much those weigh).

All in with the eggs is 466g.

Regarding flying this weekend: it occurs to me that not only do we have no motors, or a (yet) flyable rocket, I also don't have a 1010 pad, and don't have a 12v launcher. So let's just put that thought to bed for now.

 

[Zeus-cat]

The TARC teams I have seen all use Aerotech F motors. BP is just not feasible with the weight and time profile the rocket must meet.

 

[samb]

[QUOTE="neil_w, post: 1860207, member: 23964]
Modifying that one down to 25" would be a pretty good challenge. Certainly it should be possible. Weight limit (650g) shouldn't be a problem. But I'm not really thinking of these rockets as intended for competition, just learning vehicles. Dunno how these builds were originally framed, though, since I wasn't there.
.

There are several mis-interpretations of the rules throughout this post. The minimum length is 25.6", so they should be fine.

...[/QUOTE]

OUCH ! "... must be no less than... ". Reading is fundamental . Good thing I'm not a TARC mentor.

 

[afadeev]

As a quick reminder to all, I'm not the advisor here, just an interested party. I'm trying to fill in some sorely missing education and guidance, but I can't just jump in and take over everything.

Truth is - if you want to drive this wreck of a team out of the ditch, you will HAVE TO take over as the de-facto adviser/manager/team lead.
Anything else will not move the needle.
There is no other way around it.

Regarding flying this weekend: it occurs to me that not only do we have no motors, or a (yet) flyable rocket, I also don't have a 1010 pad, and don't have a 12v launcher. So let's just put that thought to bed for now.

I can loan you all of the above, including AT F's.
I have 3 launch sites lined up around 07901, if you need them.

a