TARC frustration: advice needed

[Ez2cDave]

I have seen only one team recently flying clusters of Estes D12 motors. They did very well. In the first few years of TARC, clusters were fairly common.

Hmm . . . 4 D12's would yield 68 Nt-Sec . . . 5 stays under the Propellant Wt. Limit, but pushes them over 80 Nt-Sec.

A central D12, surrounded by C6's might be feasible.

1 D12 has 17 Nt-Sec and 21.1 gr of propellant . . .

1 C6 has 9 Nt-Sec and 10.8 gr of propellant . . .

1 D12, surrounded by 7 C6's will fit into a BT-80 . . .

Total for cluster is 80 Nt-Sec with a propellant wt. of 96.7 gr ( well below the 125gr. limit )

Dave F.

 

[dhbarr]

Very difficult to get that many AP/BP motors to light at once. Spiders aren't good for AP AFAIK, they work okay on Euro mix though.

 

[Ez2cDave]

Very difficult to get that many AP/BP motors to light at once. Spiders aren't good for AP AFAIK, they work okay on Euro mix though.

They're all BP . . . Josh Tschirhart's "PVC Spider" would be the most reliable method today. "Back in the day", I would have used AG-1 flashbulbs with Centuri "Sure-Shot" igniter wick.

Dave F.

 

[dhbarr]

My mistake, I was thinking 6+1 18mm, I should read more carefully.

 

[shreadvector]

Hmm . . . 4 D12's would yield 68 Nt-Sec . . . 5 stays under the Propellant Wt. Limit, but pushes them over 80 Nt-Sec.

A central D12, surrounded by C6's might be feasible.

1 D12 has 17 Nt-Sec and 21.1 gr of propellant . . .

1 C6 has 9 Nt-Sec and 10.8 gr of propellant . . .

1 D12, surrounded by 7 C6's will fit into a BT-80 . . .

Total for cluster is 80 Nt-Sec with a propellant wt. of 96.7 gr ( well below the 125gr. limit )

Dave F.

I need to see if Qjets are on the TARC list.

5 x D16-6 is very Saturn V like.

 

[Ez2cDave]

I need to see if Qjets are on the TARC list.

5 x D16-6 is very Saturn V like.

Fred,

The current Certified Motor List still shows them as "pending", but it's from January 3, 2019.

https://www.nar.org/standards-and-testing-committee/nar-certified-motors/

Dave F.

 

[neil_w]

It may be possible to use a hair dryer to soften the epoxy . . . Then, it can be "peeled" out.

Success! They held the rocket in front of the fireplace and were able to scrape it out with a knife.

Frankly it makes me a little worried about the durability of that epoxy in the motor mount, but I guess we'll find out.

 

[firpisto34]

Thanks for the tips but I'm a little nervous about using these larger motors cause they make the rocket a little more unstable. Im using Open Rocket and the stability is now 1.86 cal with the new F35W motor. Is this good or should I increase the size of the fins to make it 2 cal.

 

[Ez2cDave]

Thanks for the tips but I'm a little nervous about using these larger motors cause they make the rocket a little more unstable. Im using Open Rocket and the stability is now 1.86 cal with the new F35W motor. Is this good or should I increase the size of the fins to make it 2 cal.

You should be fine, as far as stability goes . . . The further the CG is ahead of the CP, the more prone to "weather-cocking" and "coning" the rocket becomes. Even at 1 caliber, stability would be fine

Dave F.

 

[shreadvector]

Fred,

The current Certified Motor List still shows them as "pending", but it's from January 3, 2019.

https://www.nar.org/standards-and-testing-committee/nar-certified-motors/

Dave F.

Not the same as the approved TARC motor list.

 

[boatgeek]

I would expect that the Qjets would be fine, but you can email the NARTARC Yahoo group to be sure. Trip Barber is very responsive on that list.

F50 is a Skidmark and would not be eligible for competition because the flyer needs to be over 18. The F51 (24mm CTI 2 grain Blue) may be enough power if you can find them. If not, the F79 (24mm CTI 3 grain Smokey) is probably your best bet but you’ll have to add a lot of drag to get back down to 856 feet. It will probably want to go to around 1000 with the rocket as is. Fortunately it’s easy to add drag.

Epoxy holds up fine in motor mounts. The outside of the casing doesn’t get all that hot and not for all that long.

 

[afadeev]

Success! They held the rocket in front of the fireplace and were able to scrape it out with a knife.

Frankly it makes me a little worried about the durability of that epoxy in the motor mount, but I guess we'll find out.

Wow indeed.
If they managed to scrape "epoxy" off without heavy sanding, it makes you wonder if they mixed properly, and whether it really cured?
But no matter, that is the least of their problems right now...

Very difficult to get that many AP/BP motors to light at once. Spiders aren't good for AP AFAIK, they work okay on Euro mix though.

+1.
Clusters are a b@#$ to light reliably.
This alone makes them a poor choice for competition settings (unnecessary complexity and cost are the other).

Thanks for the tips but I'm a little nervous about using these larger motors cause they make the rocket a little more unstable. Im using Open Rocket and the stability is now 1.86 cal with the new F35W motor. Is this good or should I increase the size of the fins to make it 2 cal.

1.86 is almost over-stable. 2.0 cal is excessive.
Anything over 1.0 calibers is more than enough, unless you are flying trans-/supersonic, which you should not be.

F50 is a Skidmark and would not be eligible for competition because the flyer needs to be over 18.

F50 is NAR certified, and is therefore perfectly eligible.
It may not have the desired thrust-profile for your needs, but skid-mark or not, you could fly it for TARC.

I am not aware of any motor-specific prohibitions for TARC, other than "must be powered only by commercially-made model rocket motors of “F” or lower power class that are listed on the TARC Certified Motor List":
https://3384f12ld0l0tjlik1fcm68s-wp...loads/2018/08/Event-Rules-TARC-2019-FINAL.pdf
https://3384f12ld0l0tjlik1fcm68s-wp.../uploads/2018/08/2019-Approved-Motor-List.pdf

An adult may be required to place the order for the motors (which is usually the case anyway, as the team mentor typically handles the money), but there is no restriction on flying them by the kids.
A few teams definitely flew F50s last year.

a

 

[neil_w]

Wow indeed.
If they managed to scrape "epoxy" off without heavy sanding, it makes you wonder if they mixed properly, and whether it really cured?

I'm no super optimistic about that. There is at least one spot on the fillets (don't ask) that is still tacky, although all the rest I touched seemed fully cured, to be fair.

It's one step closer to being able to fly, at least.

 

[boatgeek]

....

F50 is NAR certified, and is therefore perfectly eligible.
It may not have the desired thrust-profile for your needs, but skid-mark or not, you could fly it for TARC.

I am not aware of any motor-specific prohibitions for TARC, other than "must be powered only by commercially-made model rocket motors of “F” or lower power class that are listed on the TARC Certified Motor List":
https://3384f12ld0l0tjlik1fcm68s-wp...loads/2018/08/Event-Rules-TARC-2019-FINAL.pdf
https://3384f12ld0l0tjlik1fcm68s-wp.../uploads/2018/08/2019-Approved-Motor-List.pdf

An adult may be required to place the order for the motors (which is usually the case anyway, as the team mentor typically handles the money), but there is no restriction on flying them by the kids.
A few teams definitely flew F50s last year.

a

The Aerotech and Estes 29mm F50T are on the TARC list. The CTI F50SK is not on the approved list.

 

[shreadvector]

The Aerotech and Estes 29mm F50T are on the TARC list. The CTI F50SK is not on the approved list.

Correct. Any motor that is a High Power motor per the N.F.P.A. code is not allowed in TARC. Sparky motors are all HPR, even if they are in the "Model Rocket" power range.

Ditto for motors with over 80 Newtons of average thrust.

I know of one TARC team that is using the Cesaroni Skidmark for test flights because their teacher could not buy enough of the TARC approved motors. AND, since they are in CA, they must launch them on a military base with their own permission from the base fire authority and powers that be. On a non-military base in CA, you need to have a High Power Rocket launching permit to launch any Cesaroni motor, since they are all still classified as HPR. They could have the classifications of the non-sparky, lower than 80N average thrust G and below motors changed to Model Rocket Motor, but they have not done so.....

 

[shreadvector]

I need to see if Qjets are on the TARC list.

5 x D16-6 is very Saturn V like.

On the list:

https://3384f12ld0l0tjlik1fcm68s-wp.../uploads/2018/08/2019-Approved-Motor-List.pdf

 

[Ez2cDave]

since they are in CA, they must launch them on a military base with their own permission from the base fire authority and powers that be. On a non-military base in CA, you need to have a High Power Rocket launching permit to launch any Cesaroni motor, since they are all still classified as HPR.

There is much I could say about the State of California, but it would be way off topic and, most likely, get the thread locked.

Moving on . . . If they are going to potentially be flying clusters, is their launch system capable of doing so, safely & reliably ?

Dave F.

 

[shreadvector]

There is much I could say about the State of California, but it would be way off topic and, most likely, get the thread locked.

Moving on . . . If they are going to potentially be flying clusters, is their launch system capable of doing so, safely & reliably ?

Dave F.

They are not flying clusters. Q-jets are very easy to cluster.

 

[shreadvector]

Different teams in the past with D12 clusters had zero ignition failures. I sold them Estes igniters to use in place of the Starters and showed them how to do it. They did what I showed them and they worked every time. They were launched using our club launch system at our NAR section launches. We have a car battery.

I only have a bit over a thousand Estes igniters left......

 

[Ez2cDave]

They are not flying clusters. Q-jets are very easy to cluster.

They're also not getting to the target altitude on a single 24mm motor . . . They either need to go 29mm or cluster.

Dave F.

 

[shreadvector]

They're also not getting to the target altitude on a single 24mm motor . . . They either need to go 29mm or cluster.

Dave F.

I have seen several teams using 24mm F32 single use and 24/60 RMS have no problem reaching the target altitude with full payload.

They built like aerospace engineers using sane Model Rocket parts.

Teams that used heavy HPR parts or 3D printed large parts of their rockets need more total impulse (over 57 N-s) and run into the weight limit for TARC.

 

[Ez2cDave]

I have seen several teams using 24mm F32 single use and 24/60 RMS have no problem reaching the target altitude with full payload.

They built like aerospace engineers using sane Model Rocket parts.

Teams that used heavy HPR parts or 3D printed large parts of their rockets need more total impulse (over 57 N-s) and run into the weight limit for TARC.

Fred,

(1) Were those Teams carrying 3 eggs to 856 ft ? ( Also the "coin toss" in the Finals could be up to 881 ft ).

TARC Rules

"The altitude score for every qualification flight and for the first flight at the Finals will be the absolute difference in feet between the 856 feet (261 meters) target altitude and the altimeter-reported actual flight altitude in feet (always a positive number or zero). For those teams at the Finals that are invited to make a second flight based on their first-flight performance, the target altitude for the second flight at that event will be either 831 feet or 881 feet, determined by a coin toss at the student team pre-flight briefing at the Finals."

(2) Did they have a virtually "non-existent" Mentor and a totally inexperienced Teacher, as this Team does ?

(3) How did they learn to "build like aerospace engineers" ?

(4) We have all seen the "design" they are stuck with, do you still believe that a single 24mm motor will get them to a potential altitude of up to 881 ft ?

Dave F.

 

[boatgeek]

Fred,

(1) Were those Teams carrying 3 eggs to 856 ft ? ( Also the "coin toss" in the Finals could be up to 881 ft ).

TARC Rules

"The altitude score for every qualification flight and for the first flight at the Finals will be the absolute difference in feet between the 856 feet (261 meters) target altitude and the altimeter-reported actual flight altitude in feet (always a positive number or zero). For those teams at the Finals that are invited to make a second flight based on their first-flight performance, the target altitude for the second flight at that event will be either 831 feet or 881 feet, determined by a coin toss at the student team pre-flight briefing at the Finals."

(2) Did they have a virtually "non-existent" Mentor and a totally inexperienced Teacher, as this Team does ?

(3) How did they learn to "build like aerospace engineers" ?

(4) We have all seen the "design" they are stuck with, do you still believe that a single 24mm motor will get them to a potential altitude of up to 881 ft ?

Dave F.

I 100% guarantee that they’re rocket will reach more than 881 feet on a CTI F79 as long as its stable. I have personally seen a BT70 rocket at maximum TARC mass hit 1000 feet. The CTI 24mm 2 grains have as much impulse as the 29mm one grains at a lower weight. The 24mm 3 grains are 50% more impulse.

It’s not motor diameter, it’s impulse and thrust that matter.

 

[Ez2cDave]

It’s not motor diameter, it’s impulse and thrust that matter.

Fully understood . . . Greater impulse is available from 29mm motors than is available from 24mm motors.

The rocket is a big, clunky,( most likely heavy ) inefficient design . . . They have not even made any test flights yet.

Dave F.

 

[shreadvector]

Fred,

(1) Were those Teams carrying 3 eggs to 856 ft ? ( Also the "coin toss" in the Finals could be up to 881 ft ).

TARC Rules

"The altitude score for every qualification flight and for the first flight at the Finals will be the absolute difference in feet between the 856 feet (261 meters) target altitude and the altimeter-reported actual flight altitude in feet (always a positive number or zero). For those teams at the Finals that are invited to make a second flight based on their first-flight performance, the target altitude for the second flight at that event will be either 831 feet or 881 feet, determined by a coin toss at the student team pre-flight briefing at the Finals."

(2) Did they have a virtually "non-existent" Mentor and a totally inexperienced Teacher, as this Team does ?

(3) How did they learn to "build like aerospace engineers" ?

(4) We have all seen the "design" they are stuck with, do you still believe that a single 24mm motor will get them to a potential altitude of up to 881 ft ?

Dave F.

I'm probably getting lost since there are many teams being discussed. The teams that are building like engineers have good teachers with TARC experience and they use me as a Mentor.

My comments are not directly related to the team you are responding to which has no mentor and an inexperienced teacher.

The teams I have personally seen/mentored/RSOd that used 24mm 55 to 57 N-s motors have had the full 3 eggstronaut payload and some teams had to add bits to add drag and keep the altitude to the target. if they need to go higher, they will break off the drag bits.

The other teams at

 

[boatgeek]

Fully understood . . . Greater impulse is available from 29mm motors than is available from 24mm motors.

The rocket is a big, clunky,( most likely heavy ) inefficient design . . . They have not even made any test flights yet.

Dave F.

I was going to argue the first point but then I realized I was wrong. Aerotech has a few 29mm motors optimized to be 80 N-s to stay in the F range. CTI didn’t do that so their 3 grain 24mm motors can have more impulse than the 29s.

For the second point, a 90%-ish F will take any BT-80 sized or smaller rocket at 650 grams or less to well over the altitude required. Could you use a smaller motor and a more efficient rocket and still make altitude? Sure! But you don’t have to. TARC rewards consistency more than efficiency. As my old engineering prof said, engineering is the science of good enough.

 

[firpisto34]

what do you guys think about using plywood to make the fins rather than balsa wood? Any other types of wood or fin building materials are highly appreciated too

 

[neil_w]

For the second point, a 90%-ish F will take any BT-80 sized or smaller rocket at 650 grams or less to well over the altitude required. Could you use a smaller motor and a more efficient rocket and still make altitude? Sure! But you don’t have to. TARC rewards consistency more than efficiency. As my old engineering prof said, engineering is the science of good enough.

Indeed, sims of my friend's rocket (I assume comments about poor design were directed at this one; it is hard to keep track of which team is being discussed at this point) show it'll go well above target altitude with a legal F motor. Or, given unaccounted for drag (excess epoxy all over the place), maybe one of those Fs would just get you there. So as boatgeek says it really doesn't matter that the design is not ideal. As long as it flies stably and the recovery systems work it should be able to get in a qualifying flight, which is all that matters right now. Getting a very good score is unlikely if for no other reason then the lack of a sufficient number of test flights to dial in the correct motor and adjust drag and weight as needed.

This is one of those situations where I would be inclined to put in a 29mm mount even if intending to use 24mm motors since it's so easy to throw in an adapter, and it keeps things a lot more flexible.

 

[neil_w]

what do you guys think about using plywood to make the fins rather than balsa wood? Any other types of wood or fin building materials are highly appreciated too

Plywood would be very durable but a bit harder to cut and shape, and heavier. Basswood would be a good intermediate option if you want more durability than balsa. Papered balsa fins would be great, but I don't want to assume too much technique on the part of the builders who might be inexperienced.

Given all the weight in the nose from the eggs, the extra weight from plywood fins might not matter so much, you'd have to see whether your CG would end up in a reasonable place.

 

[shreadvector]

1/16" thick model airplane plywood is great for TARC fins. A bit heavier than balsa but WAYYY stronger. Basswood is nice, but it can crack along the grain with any hard impact (like hitting a rock on landing).

At least nobody suggested Jelutong.