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  #1  
Old 07-15-2006, 10:14 PM
Tau Zero's Avatar
Tau Zero Tau Zero is offline
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Thumbs up Jay's Tau Zero A-C Launch

Today I drove 70 miles one way to fly with the Tripoli Idaho guys at their summer flight range west of Fairfield, Idaho. The first of my rockets off of the low power (or "Estes") pads was my Tau Zero on an A8-3. Taping the motor in made all the difference on this flight, and the TZ hit about 300 feet before coming down on a streamer. The Tripoli Idaho crew offered several noises of approval for this one.

I slapped a C6-5 into my low-power (18mm) Sirius Rocketry Interrogator, and *that* impressed the gathered high-power rocketeers. The Interrogator made it to about 550 feet and nosed over for a picture-perfect ejection and recovery. (Now I'll *have* to try the mid-power 24mm Interrogator on some D's. ;-D)

I sent up my Prometheus with newly extended elastic shock cord on an A8-3. Nice performance to about 225 feet, with a good recovery.

Determined to test my Tau Zero on the entire A through C motor spectrum, I inserted a B6-4 motor and let it fly. The launch director asked me, "Did you notice it was a little less stable on that B motor?" I didn't, but the Tau Zero made it to about 600 feet, blew the streamer, and landed gently in the alfalfa field. (For you city dwellers, that's what us farm boys cut up and turn into hay. ;-D )

The Prometheus tore off the pad on B6-4, arrowed to about 550 feet, and ejected the chute shortly after apogee. Unfortunately, on this flight, I discovered a disturbing corollary to Bill Eichelberger's dreaded "Launch Fever." A teenage boy had been running like mad after rockets even before they'd landed. Partially as a joke, I sent him out to recover the Prometheus. This is when I found out (all over again) about "Inexperienced Tracker Syndrome." (I attribute the loss of my original 1.36X Estes Wolverine two years ago at the same flight range to this particular malady.)

In brief, the tracker went *way* too far, and even though I followed up his wake with a more sweeping eye, my original prototype for the "Prometheus" is now destined to become part of the next cutting of cattle feed. In other words, "Eez lost." And along with a perfectly good 12" ripstop nylon parachute, too.

The Tau Zero needed one final flight on a C6-5 to bring my launch day to a close. RockSim had estimated its altitude at more than 1100 feet, so I was ready for a lengthy recovery walk. Unfortunately, my wife noticed that the wind was blowing harder than it had been, and since she and my girls were ready to leave after 2.5 hours, she prayed, "God, don't let Jay have to walk a long ways for this rocket."

The Almighty was listening, and the Tau Zero pinwheeled off the pad, made it to an altitude of roughly 30 to 50 feet above ground level, and hit the gravel road about six feet in front of my car. The ejection charge blew the streamer, but a bit late. (Reminder to self: When taking wife to launches, remind her not to invoke Higher Powers to induce undesireable outcomes regarding rocket flights.)

Actually, this particular design does fine on A motors, but B and definitely C motors will require some sort of nose weight. (And I'm not particularly keen on extending the main body tube from 9" to 12", but that *may* be part of the solution.)

Here are pics of the rockets in question: Tau Zero and Prometheus and Interrogator from a previous thread of mine.


SUMMARY:

Interrogator on C6-5: *Smokin'!*
Prometheus on A8-3, B6-4: Unexpectedly high performance. Get yourself a professional tracker for B flights and above.
Tau Zero: Great on A8-3, wiggly on B6-4, performs terrifying cartwheels on a C6-5.

(Now I'm wondering how the heck Bill Eichelberger's TZ flights were so good on a B6-6 and C6-7, respectively. Okay, maybe it's because there wasn't anybody lurking nearby who was in cahoots with beings from a higher plane of existence.)

At least I remembered to put sunscreen on my face, neck, ears, and knees. My arms are another story, though.

Then I came home to see Scott Goebel's smiling face on my first official issue of Sport Rocketry.


All in all, a good day.
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"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

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Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014

Last edited by CenturiGuy : 07-15-2006 at 10:21 PM.
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  #2  
Old 07-15-2006, 11:01 PM
James Pierson James Pierson is offline
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Arrow Photo's Please.

Jay, Sorry to hear about the Prometheus as cattle feed. Been there and done that as well. Also about the Tau Zero, you have a few options as far as C flights go : larger ring fin, increase outter fin length from body, lengthen rocket body, add tailcone, increase fin number. Nose wieght is a double edged sword, increases stability for C flights yes, but will reduce altitude on smaller motors. Sounds like you get to play with Rocksim a bit.

Hope this helps, JP

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NAR# 77907
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  #3  
Old 07-16-2006, 01:01 AM
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Tau Zero Tau Zero is offline
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Thumbs up "No Steenkeeng Peectures..."

Quote:
Originally Posted by James Pierson
Photos please.
Click on the links (the underlined rocket names). Nothing new from today except for smoke trails.

Thanks for the "encouraging words," though.


Quote:
about the Tau Zero, you have a few options as far as C flights go : lengthen rocket body
I'll start with this one.

Cheers,
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"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014
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  #4  
Old 07-16-2006, 01:35 AM
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Tau Zero Tau Zero is offline
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Thumbs up Hard Knockin' in the Free World

Quote:
Originally Posted by CenturiGuy
needed one final flight on a C6-5 to bring my launch day to a close. The Tau Zero pinwheeled off the pad, made it to an altitude of roughly 30 to 50 feet above ground level, and hit the gravel road about six feet in front of my car.
Okay, kids, here's what I learned about RockSim and the real world.

After going back to my Bruce Levison-tweaked Tau Zero file, I compiled the following figures on stability. I lengthened the 9" long ST-7 body tube to 12" just for contrast:


Tau Zero 12" (ST-7120 body tube)

Motor / Stability factor (CG ahead of CP)

Empty -- 5.87 calibers
A8-3 -- 2.54
B4-4 -- 2.26
B6-4 -- 2.33
C6-5 -- 1.85


Tau Zero 9" (ST-790 body tube)

Motor / Stability factor (CG ahead of CP)

Empty -- 4.08 calibers
A8-3 -- 1.39
B4-4 -- 1.17
B6-4 -- 1.23
C6-5 -- 0.86 Marginal


*There's* my problem right there! (Funny how I didn't notice it in the computer until my real world model did cartwheels across the flight range.)

So it looks like my Tau Zero Prototype II will have a slightly longer main tube than the original.


Cheers,
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Jay Goemmer
"Centuri Guy"/"Tau Zero"
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Semroc SAM #0029
NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014
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  #5  
Old 07-16-2006, 03:15 AM
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andrew scott andrew scott is offline
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o no i just order the parts for tau zero from semroc !!!
ok i just go and order a BT 712
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Last edited by andrew scott : 07-16-2006 at 03:24 AM.
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  #6  
Old 07-16-2006, 07:03 AM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by CenturiGuy
Okay, kids, here's what I learned about RockSim and the real world. Tau Zero 9" (ST-790 body tube)

Motor / Stability factor (CG ahead of CP)

Empty -- 4.08 calibers
A8-3 -- 1.39
B4-4 -- 1.17
B6-4 -- 1.23
C6-5 -- 0.86 Marginal

Cheers,


Jay,

On one of my revision files, I got a 1.03 margin for the C6-3, so we're both seeing the same thing happening.

Try increasing the length to 10" instead of 12". The extra 1" should give you more than enough margin, and not alter the appearance much.

BTW, using the 10" length my motor selection is as follows:

A8-3 -- 2.05 -- 147' -- 27 FPS
B4-2 -- 1.81 -- 249' -- 11 FPS
B6-2 -- 1.87 -- 242' -- 13 FPS
C6-3 -- 1.47 -- 444' -- 18 FPS

See the attached RS file for additional data...

Addendum: Yes, I see the discrepancy in the altitudes. I need to look at all of the variations we came up with to see what the averages are...
Attached Files
File Type: rkt TauZero_Rebuild_B4_BARCLONE.rkt (44.5 KB, 124 views)
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Last edited by CPMcGraw : 07-16-2006 at 07:56 AM.
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  #7  
Old 07-16-2006, 08:37 AM
A Fish Named Wallyum A Fish Named Wallyum is offline
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Quote:
Originally Posted by CenturiGuy
(Now I'm wondering how the heck Bill Eichelberger's TZ flights were so good on a B6-6 and C6-7, respectively. Okay, maybe it's because there wasn't anybody lurking nearby who was in cahoots with beings from a higher plane of existence.)


Yeah, that's about it. Hanging with heathens will guarantee stability every time.
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  #8  
Old 07-16-2006, 05:25 PM
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Tau Zero Tau Zero is offline
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Question Too long, or not long enough?

Quote:
Originally Posted by CPMcGraw
BTW, using the 10" length my motor selection is as follows:

A8-3 -- 2.05 -- 147' -- 27 FPS
B4-2 -- 1.81 -- 249' -- 11 FPS
B6-2 -- 1.87 -- 242' -- 13 FPS
C6-3 -- 1.47 -- 444' -- 18 FPS
Craig,

That's an excellent layout to include the CG/CP differential (stability) figure.

On my initial "Rebuild" file (the one I consulted you on), I remember that all of the delays were 2 seconds, and the altitudes were around 100 feet.


Here's what I get using the Bruce Levison-tweaked file:

+++

Tau Zero 10"

Motor / Calibers / Max. Alt. / Dv

Empty - 4.67
A8-3 -- 1.77 -- 332' -- 22 FPS
B4-4 -- 1.52 -- 645' -- 20 FPS
B6-4 -- 1.59 -- 645' -- 24 FPS
C6-5 -- 1.19 -- 1176' -- 8 FPS


Tau Zero 9"

Empty - 4.08
A8-3 -- 1.39 -- 314' -- 20 FPS
B4-4 -- 1.17 -- 632' -- 22 FPS
B6-4 -- 1.23 -- 632' -- 25 FPS -- Wiggly!
C6-5 -- 0.86 -- [1180' -- 12 FPS] -- Cartwheels 30' high!!!


Tau Zero 12"

Empty - 5.87
A8-3 -- 2.54 -- 319' -- 20 FPS
B4-4 -- 2.26 -- 629' -- 20 FPS
B6-4 -- 2.33 -- 630' -- 23 FPS
C6-5 -- 1.85 -- 1160' -- 9 FPS

+++


I suppose that using comprehensive R&D methods would entail building a Tau Zero with a 12" ST-7, flying it on C engines, and gradually trimming back the length to 10" to see how it performs.

Last night, I kept wondering if I should add some detailing to the front end of the ST-712 to break up its (now seemingly) excessive length. I'm still thinking. (Hmm...)

Anyway, thanks for the feedback.
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Jay Goemmer
"Centuri Guy"/"Tau Zero"
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NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014

Last edited by CenturiGuy : 07-16-2006 at 05:44 PM.
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  #9  
Old 07-16-2006, 08:54 PM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by CenturiGuy
Craig,

That's an excellent layout to include the CG/CP differential (stability) figure.


I think I'll start including it in all future design posts. Thanks.

Quote:
I suppose that using comprehensive R&D methods would entail building a Tau Zero with a 12" ST-7, flying it on C engines, and gradually trimming back the length to 10" to see how it performs.


I had not started the construction of my TZ when you posted your tale of woe, so I located a spare 12" ST-7 and cut it back to 10". My TZ is now completed, pre-prime, with the ring and outer fins not glued in place. I'll try to get it primed tomorrow and glued together by Wednesday for a flight next weekend.

On your 9" prototype, just take a 1", 2" and 3" section of ST-7 and glue into each an HTC-7 coupler. Just run the shock chord through these to the NC and slip them into place. Now you can test out three combinations of length to see which works best.

Perhaps this is real reason why Carl hasn't set up a kit yet -- no actual flight data to prove the RockSim predictions. Maybe it's a good thing you've found this out early...

One additional note, concerning any kit that might be released. This design really needs to have a set of fin alignment guides laser-cut to get the angles correct. Even with a cardstock guide I didn't get one of those inner fins spot-on, and it shows. Carl's 0.05" fiberboard material would be much better. You need two guides for each set, so that you get the same angle along the full length of each fin.
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  #10  
Old 07-16-2006, 09:35 PM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by andrew scott
o no i just order the parts for tau zero from semroc !!!
ok i just go and order a BT 712


Andrew,

Don't worry too much about those parts, because Jay and Bill E. and I are actively working to test this design and find out what really happened. It just goes to show, you can't fully trust a computer to design something fool-proof...

Remember this passage:

"A common mistake that people make when trying to design something completely foolproof was to underestimate the ingenuity of complete fools."

Remember this one, as well:

"They're not complete idiots... Some parts are missing..."

Both of these statements occasionally apply to us here on the forum...
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