TARC frustration: advice needed

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Ez2cDave

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Neil,

Not a bad start . . . What were their comments throughout the day ? Did they ask questions ? Did they have fun ?

I really hope they get a chance to do this again in high school, with the right kind of help, right from the start .

Good job . . . Keep the updates coming !

Dave F.
 

neil_w

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Well they said they had fun, and seemed to be telling the truth, so I'll take their word for it. :)

Not too many questions, though. They were pretty well occupied (a) trying to keep warm (it was pretty blustery early on) and (b) keeping track of all the things they needed to do before each flight. Questions would be more likely to come when things are more relaxed and they have time to think. I'm gonna try to get them to a launch or two in the summer so they can relax and enjoy.

They are planning to attempt their qualifying flights this Saturday, fingers crossed for good weather. Motors for these attempts will be F42s, which should give them a bit more altitude although still not close enough to target for a good score. I think the fin can (solid but very messy) is adding a *lot* of drag to the rocket, and causing the motors to underperform. No matter, getting a good score wasn't a serious objective for this year; getting *any* score is, and that is now within striking distance.
 

boatgeek

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I'm glad they got out in the field and that you had fun.

If you can get them in, the CTI F51 blue motors (24mm 2-grain) are just about perfect for a BT-70 rocket this year. The extra thrust off the pad gives them a pretty straight flight.

[edit] Forgot to add, out TARC team had a couple of fun interactions when we were out flying yesterday. First was a guy who works at the local SpaceX office flying a Falcon 9 model. Second was a ~5-year old visiting from Paris who happened to be on the field (not sure why?). The kid asked the SpaceX guy where the booster was, I'm pretty sure wondering why it wasn't staged and/or a Falcon Heavy. It was pretty cute.
 

JJSR

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Its always fun seeing the little guys at a launch. We do a lot of cub scouts and it NEVER gets old watching their faces brighten with smiles. Once they get the hang of the count down,,,,, it gets LOUD!!!
LOL
 

neil_w

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Well, it looks like life has conspired to make true qualifying flights impossible. There simply will be no opportunity for the team before the deadline.

However, it's not that bad, considering that making the nationals wasn't a serious goal. Based on what we learned from the practice flights, there would be almost no way of getting a good score anyway; can't make the altitude.

Instead, the girls will come to a Rad Rocks launch with me one day in the spring or summer, and do their flights as if trying to qualify, and we'll calculate their score. I'll give them some LPR rockets to fly as well if they want. So at that point they will have completed the year's journey, maybe not quite what was originally hoped for but definitely better than it could have gone. I think they're coming out of this with a positive feeling. No clue yet if they're going to try to get a team together for next year, can't worry about that yet.

Thanks for all the advice and help along the way. I'll report back here with the results of the "qualifying flights" whenever they happen.
 

boatgeek

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Well, it looks like life has conspired to make true qualifying flights impossible. There simply will be no opportunity for the team before the deadline.

However, it's not that bad, considering that making the nationals wasn't a serious goal. Based on what we learned from the practice flights, there would be almost no way of getting a good score anyway; can't make the altitude.

Instead, the girls will come to a Rad Rocks launch with me one day in the spring or summer, and do their flights as if trying to qualify, and we'll calculate their score. I'll give them some LPR rockets to fly as well if they want. So at that point they will have completed the year's journey, maybe not quite what was originally hoped for but definitely better than it could have gone. I think they're coming out of this with a positive feeling. No clue yet if they're going to try to get a team together for next year, can't worry about that yet.

Thanks for all the advice and help along the way. I'll report back here with the results of the "qualifying flights" whenever they happen.
Sounds like everyone has their heads screwed on right. Good luck!
 

Ez2cDave

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Neil,

At least they got to fly . . . Hopefully, they will keep coming out to launches and be interested enough to try again, next year .

This is the time to teach them everything they need to know and actively design & build competitive "TARC-style" rockets with them.

Maybe you could get other club members to participate in "pseudo-TARC" contests ( nothing "extravagant", to keep costs down ) ?

Looking forward to the updates !

Dave F.
 

aerostadt

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The TARC finalist have been announced. The cut-off score was a little bit better than last year, but there were more DQ's this year, which is probably a reflection of the tougher requirement to fly 3 eggs. Trip Barber noted that any team making it to one or more qualification flights did a significant accomplishment.
 

firpisto34

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Hi everyone, I'm not sure if this thread is still active but I'm leading a TARC team for the first time this year and I had a few questions.

1. We are using OpenRocket to model the rocket and everything looks fine but the flight time looks a little unrealistic. We are using two body tubes and the weight of the rocket is around 300g right now. According to the software, it goes up to around 280m but has a flight time of around 40 seconds with only one 30 cm diameter parachute. The parachutes are set to come out at apogee and there is a shock cord attaching the two parts body tubes together. Is there something we have to specify to make sure that it thinks both parts are coming down together with the one parachute or what are we doing wrong?

2. We are also trying to find a good E- class rocket motor that's reliable and easy to find with an impulse of around 33. We can adjust the design to make sure that it fits a rocket motor that won't be difficult to find or use. Any recommendations?
 

rocketaholic

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Hi everyone, I'm not sure if this thread is still active but I'm leading a TARC team for the first time this year and I had a few questions.

1. We are using OpenRocket to model the rocket and everything looks fine but the flight time looks a little unrealistic. We are using two body tubes and the weight of the rocket is around 300g right now. According to the software, it goes up to around 280m but has a flight time of around 40 seconds with only one 30 cm diameter parachute. The parachutes are set to come out at apogee and there is a shock cord attaching the two parts body tubes together. Is there something we have to specify to make sure that it thinks both parts are coming down together with the one parachute or what are we doing wrong?

2. We are also trying to find a good E- class rocket motor that's reliable and easy to find with an impulse of around 33. We can adjust the design to make sure that it fits a rocket motor that won't be difficult to find or use. Any recommendations?
What motor are you currently using in open rocket to achieve that altitude?

You can also double check your specs utilizing the ThrustCurve app or website for a sanity check on altitudes:

http://www.thrustcurve.org/
 

neil_w

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Hi everyone, I'm not sure if this thread is still active
It is now! :)

1. We are using OpenRocket to model the rocket and everything looks fine but the flight time looks a little unrealistic. We are using two body tubes and the weight of the rocket is around 300g right now. According to the software, it goes up to around 280m but has a flight time of around 40 seconds with only one 30 cm diameter parachute. The parachutes are set to come out at apogee and there is a shock cord attaching the two parts body tubes together. Is there something we have to specify to make sure that it thinks both parts are coming down together with the one parachute or what are we doing wrong?
Can you post the file?
 

firpisto34

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Thanks everyone so much for the quick responses.
What motor are you currently using in open rocket to achieve that altitude?

You can also double check your specs utilizing the ThrustCurve app or website for a sanity check on altitudes:

http://www.thrustcurve.org/
We are using an E11J motor right now but the optimum delay is 5 seconds even though every motor I found online comes with a 3 second delay. The E20 also works but its a single use motor and we want to use a reloadable one.
Can you post the file?
sadly, our sponsor has told us not to post our design online.
 

neil_w

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In that case, can you just post a screenshot of the details dialog for the parachute? That doesn't reveal anything important.
 

Zeus-cat

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An E11 seems pretty small for a TARC rocket. To be fair, I have not looked at the requirements for this year. The TARC teams I have seen use F motors.

Usually it is better to slightly overpower the rocket; especially based on sim data. Sims are notorious for overestimating altitude. Better to have more power and then add weight or drag to lower the altitude. It is easier to reduce altitude than to add it.
 

boatgeek

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A 30cm (12") parachute seems a little small to me. You might try 15"-18" and see how that looks. You can always reef the shrouds a little to bring it down faster if you need to. You are definitely on the light and low impulse side of TARC designs. Do you have a built rocket yet to confirm that this is a real weight? Everyone (and especially students) tend to build heavy until they have lots of experience.

Aerotech's master order list (here) only shows a 3-second delay for the E11, so there's probably no 5-second delay available. On the plus side, the 24/40 case has lots and lots of options for you. You might look at the E18 or E28 instead--they both have 4s and 7s delays available in similar total impulse and weight motors. Higher thrust off the pad also tends to make the rocket weathercock less in winds, making flights more predictable.
 

Ez2cDave

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We are using an E11J motor right now but the optimum delay is 5 seconds even though every motor I found online comes with a 3 second delay. The E20 also works but its a single use motor and we want to use a reloadable one.

sadly, our sponsor has told us not to post our design online.
Based on what you have said:

280 meters ( 918 feet ) . . . 30 cm Chute ( 11.81 inches ) . . . 300 gram ( 10.58 ounce ) Rocket Mass ( Liftoff Weight, Empty Weight, or Recovery Weight is unstated ) . . . TOTAL Flight Time of 40 seconds ( Including Motor Burn Time and Delay ) . . . Sim-generated, Optimal Delay of 5 seconds.

There are a lot of "problems" here :

(1 ) The use of a 30 cm (11.81") chute, in a 300 gram (10.58 oz.), descending from 280 meters ( 918 ft.) will have a Descent Rate of 9.28 meters/sec. (30.45 ft/sec.)

(2) The "Optimal Delay" is the "800 lb. Gorilla in the room" . . .

(3) Without having any idea of the design, "guesswork" is a bad thing, especially when "precision" is called for.

***************************************************************************************************************************

Where are you located and who is your Sponsor ( did you mean "Mentor" ) ?

Without any physical data to work from, you will only get a bunch of "WAG's" ( Wild Azz Guesses ).

***************************************************************************************************************************

The next part is directed at your Sponsor . . . ( Not you, or the Team, at all )

This may sound a little "snarky" ( not intended ) but, if your Sponsor has such a "Whiz-Bang" design
that is must be kept "top secret", why isn't he satisfactorily answering the questions being asked here ?

***************************************************************************************************************************

Back to the Team, now . . .

I and, I am sure, many others would love to help you out, but more information is needed.

Ask your Sponsor to post here !

Dave F.
 

rocketaholic

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[
Thanks everyone so much for the quick responses.

We are using an E11J motor right now but the optimum delay is 5 seconds even though every motor I found online comes with a 3 second delay. The E20 also works but its a single use motor and we want to use a reloadable one.

sadly, our sponsor has told us not to post our design online.
An E 11 is under powered. There are other more powerful e reload motors that would be a better option. When you are lofting a payload such as an egg you really need a motor with a quicker thrust at ignition and the E 11 would not do that. Something more like an E18W-4,8 which is on the TARC list of apporved motors for 2020: https://rocketcontest.org/wp-content/uploads/2019/10/Rocket-Motors-Approved-for-TARC-2020.pdf
 

rocketaholic

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Attached is an idea based on your specs and the 2020 TARC rules. Technically you can up in weight to 450 grams since the weight limit is 650 grams under TARC 2020 rules.
Ideas Support TARC 2020.jpg
 

firpisto34

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I will try to answer everyones questions here:

An E11 seems pretty small for a TARC rocket. To be fair, I have not looked at the requirements for this year. The TARC teams I have seen use F motors.

Usually it is better to slightly overpower the rocket; especially based on sim data. Sims are notorious for overestimating altitude. Better to have more power and then add weight or drag to lower the altitude. It is easier to reduce altitude than to add it.
Yes, thanks for the advice but we did change it to an Aerotech E20-7 engine. The TARC rockets this year are actually much lighter than previous years because instead of carrying 2 or three eggs, we only have to carry one egg for the payload which cuts the mass down by about 15% - 20%. According to openRocket, the apogee will be 295m which is way more than 243m we're aiming for in qualifications(it's overpowered on purpose like you suggested until we can see how it really flies at our first launch).

A 30cm (12") parachute seems a little small to me. You might try 15"-18" and see how that looks. You can always reef the shrouds a little to bring it down faster if you need to. You are definitely on the light and low impulse side of TARC designs. Do you have a built rocket yet to confirm that this is a real weight? Everyone (and especially students) tend to build heavy until they have lots of experience.

Aerotech's master order list (here) only shows a 3-second delay for the E11, so there's probably no 5-second delay available. On the plus side, the 24/40 case has lots and lots of options for you. You might look at the E18 or E28 instead--they both have 4s and 7s delays available in similar total impulse and weight motors. Higher thrust off the pad also tends to make the rocket weathercock less in winds, making flights more predictable.
First off, I want to be conservative and say the rocket will weigh around 330 grams. Also will be trying to do the rocket launch with a 15 or 18 in parachute before we try with the 12 in that openrocket is telling us fits our rocket.
I've also tried putting the rocket motors you suggested in the OpenRocket but according to it, the apogee becomes around 345m (over 1,000 ft) which is way too high for TARC even if we're trying to slightly overpower the rocket. As I mentioned above, we have changed to an E20-7 and we'll see how it flies with that motor.

There are a lot of "problems" here :

(1 ) The use of a 30 cm (11.81") chute, in a 300 gram (10.58 oz.), descending from 280 meters ( 918 ft.) will have a Descent Rate of 9.28 meters/sec. (30.45 ft/sec.)

(2) The "Optimal Delay" is the "800 lb. Gorilla in the room" . . .

(3) Without having any idea of the design, "guesswork" is a bad thing, especially when "precision" is called for.

***************************************************************************************************************************

Where are you located and who is your Sponsor ( did you mean "Mentor" ) ?

Without any physical data to work from, you will only get a bunch of "WAG's" ( Wild Azz Guesses ).

***************************************************************************************************************************

The next part is directed at your Sponsor . . . ( Not you, or the Team, at all )

This may sound a little "snarky" ( not intended ) but, if your Sponsor has such a "Whiz-Bang" design
that is must be kept "top secret", why isn't he satisfactorily answering the questions being asked here ?

***************************************************************************************************************************

Back to the Team, now . . .

I and, I am sure, many others would love to help you out, but more information is needed.

Ask your Sponsor to post here !

Dave F.
First, I want to clarify that using we are now using an E20-7 motor with a 15 inch parachute. The liftoff weight is about 330 grams. Total flight time, from launch to touchdown, is 46 seconds with the delay set to 7 seconds.
1) I did think it was too small so what we're most likely going to end up doing is trying an 18 or 15 inch parachute which works better with the E20-7 motor we're using right now. According to openrocket, the ground hit velocity is 7.5 m/s using the 15 inch parachute.

2) The optimum delay from openrocket is now 5.83(I dont really know why) but the rocket doesnt reach apogee until about 7.5 seconds which is why we've went with a 7 second delay.

3) I'm not really sure why he doesn't want us to share the design but I'm happy to answer any specific questions anyone has about the rocket.
[


An E 11 is under powered. There are other more powerful e reload motors that would be a better option. When you are lofting a payload such as an egg you really need a motor with a quicker thrust at ignition and the E 11 would not do that. Something more like an E18W-4,8 which is on the TARC list of apporved motors for 2020: https://rocketcontest.org/wp-content/uploads/2019/10/Rocket-Motors-Approved-for-TARC-2020.pdf
An E18 motor is would also be good for our design but our team has decided that single use motors would be more beneficial since they save time and we usually have a short amount of time to launch every few weekends.

Quick question tho for everyone: since we'll probably experiment with different motors after we're done building the rocket, is there a way to build a bottom section that can accommodate both aerotech motors which require an engine retainer and estes motors which require a back stop and a clip to hold them in?
 

neil_w

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Quick question tho for everyone: since we'll probably experiment with different motors after we're done building the rocket, is there a way to build a bottom section that can accommodate both aerotech motors which require an engine retainer and estes motors which require a back stop and a clip to hold them in?
Estes BP motors are probably not your best option for TARC, but if you want to use them, it's no problem... just wrap masking tape several times around the last 1/4" of the motor, enough to create a thrust ring. Use a knife to cut off all the excess tape hanging off the end. Works fine, and that's what pretty much everyone does. Works perfectly with retainers designed for composite motors, no hooks required.
 

rocketaholic

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Estes BP motors are probably not your best option for TARC, but if you want to use them, it's no problem... just wrap masking tape several times around the last 1/4" of the motor, enough to create a thrust ring. Use a knife to cut off all the excess tape hanging off the end. Works fine, and that's what pretty much everyone does. Works perfectly with retainers designed for composite motors, no hooks required.
Rocketarium has retainers for 24 mm retention which may be good to look at:


https://www.rocketarium.com/Build/Motor-Retainers/24-mm
 

firpisto34

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Thanks for the responses guys. I have a few more questions:
1) Last year, we had trouble getting the eggs out of the tube after the flight to check if they were cracked. This was because the foam protectors fit very tightly inside the tubes to protect the eggs. In the end, we just put a blukhead under the eggs and tied some rope on it that went to the top of the body tube so that we could pull up of the cord pushing out all the eggs. It didn't really work because half the time, the bulkhead would slide up onto one side tube or we would crack the egg on the bottom. Is there another way we can take easily take out the eggs?
2) Also, TARC requires both parts of the rockets this year to come down together meaning we have to use a shock cord. Should we attach the parachute to the bottom part of the rocket, top part, or to the shock cord itslef?
 

neil_w

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1) Last year, we had trouble getting the eggs out of the tube after the flight to check if they were cracked.
Poke a small vent hole or two (or three) in the body tube opposite to where the eggs are removed. This will eliminate pulling against a vacuum and should make it easier to remove them.

Should we attach the parachute to the bottom part of the rocket, top part, or to the shock cord itslef?
Commonly the chute is attached to the top part, or even better, to the shock cord about 1/3 the way down.
 

Ez2cDave

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Poke a small vent hole or two (or three) in the body tube opposite to where the eggs are removed. This will eliminate pulling against a vacuum and should make it easier to remove them.
It also provides a option for the use of "positive pressure" to extract the egg(s) . . .

Place your lips over the hole and blow ( If multiple holes are used, block off all but one of them ).

Be sure to place the holes opposite the end where the egg(s) will exit the airframe, either "above" or "below" the egg(s).

Dave F.
 

shreadvector

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Thanks for the responses guys. I have a few more questions:
1) Last year, we had trouble getting the eggs out of the tube after the flight to check if they were cracked. This was because the foam protectors fit very tightly inside the tubes to protect the eggs. In the end, we just put a blukhead under the eggs and tied some rope on it that went to the top of the body tube so that we could pull up of the cord pushing out all the eggs. It didn't really work because half the time, the bulkhead would slide up onto one side tube or we would crack the egg on the bottom. Is there another way we can take easily take out the eggs?
2) Also, TARC requires both parts of the rockets this year to come down together meaning we have to use a shock cord. Should we attach the parachute to the bottom part of the rocket, top part, or to the shock cord itslef?
The teams with girls on them solved that problem many years ago.

You slide the egg in the foam protector inside a nylon stocking (one leg cut from cheap pantyhose). You can then tie a knot in the open end on the top and you can pull the egg and protector out easily.
 

Rocket501

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Back in my TARC days, I never had any problems with the apogee foam egg protectors. They work really well. Even with tangled parachute and a 50fps descent rate, all eggs were undamaged. While the foam fits snuggly, you can just pinch it and yank it out.

I agree that single use motors are a good idea. However, I’d go with at least 30 newtons worth of average thrust. 20 will likely lead to excessive weathercocking that will ruin consistency, which is what gets you a good score. We used motors that tended to have around 50, but they were F’s.

12 inches seems small. Get two 15 and 18 inch chutes and then cut a larger spill hole until you get the right descent rate.

The sponsor sounds a bit iffy. While people do take good ideas from other teams, this is more along the lines of clever tricks to make life easier not literally stealing your design. Personally, that requirement would be a red-flag to me, but you do you. In TARC, you are all in it together and while you are competing, I both helped and was helped by my fellow TARC teams. The sponsor seems to be a bit ignorant of there TARC culture at best.

The parachute should be attached to the shock-cord, 1/3 of the way down from the nosecone. Use a shock cord of a least 5 body lengths long.
 
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