Estes 1/200 Scale RTF Saturn V

Discussion in 'Low Power Rocketry (LPR)' started by JumpJet, Jan 10, 2019.

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  1. Jul 25, 2019 #301

    jahall4

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    #2 Motors.
    I will use only certified, commercially-made model rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer.

    Estes own chart says: "Do not fly a rocket/engine combination whose lift-off weight exceeds the recommended maximum lift-off weight". C6 "Max Lift Wt." is 113g , but the rocket weighs at least 141g (ours weighed more). Note this has already been mentioned in this thread. Note specifically that the avg. T/W ratio 4.7/1.4 or 3.4/1

    https://estesrockets.com/wp-content/uploads/Educator/Estes_Engine_Chart.pdf
    Very nice!
     
    Last edited: Jul 25, 2019
  2. Jul 25, 2019 #302

    jahall4

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    3/1 is a minimum 4 or 5/1 is what I'm typically looking for as an RSO. The Estes 1/200 Sat V model is no better that 3.4/1. Ours was heavier won't be surprised if our second one comes in at 3/1. Get a motor that has a 10% thrust deficiency and you find a given flight at less than 3/1. :(
     
  3. Jul 26, 2019 #303

    shreadvector

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    This has been explained many times in the past.

    The motor table lists recommended max liftoff weights for people who design their own rockets and as a general limit for an average rocket.

    For kits, the listed motors ARE the recommended motors. They have many kits that exceed the weight limit in the table. These are usually models that have slow flights (ExoSkell, Venus Probe, 1:200 Saturn V....). YES, a 4 foot long steel launch rod would be better. Yes, a higher thrust motor would be better. BUT, the recommended C6-3 works GREAT. Just follow the instructions and make sure the motor is fully seated.

    I've seen several dozen of these fly from many different modelers. One was super experienced. I handed him the new revised instructions (printed in color). He expressed strong emotions about how he thought there was no need for these extra instructions and he thought they were 'stupid'. 2 week later he tried to fly his with a C12-4 and it went unstable. Post flight inspection revealed he did not insert it fully. It was at an angle. He self-flaggelated and then had many more successful flights last Saturday with many different motors.

    My opinion: Flies GREAT with C6-3, but it would be good to revise the design to make the motor mount fool-proof.
     
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  4. Jul 26, 2019 #304

    dhbarr

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    This thread is exhausting. Looks like a nice kit.
     
  5. Jul 26, 2019 #305

    jahall4

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    If you can show me where the linked PDF supports your assertion then I'll concede your point, otherwise you are arguing its okay to fly are rocket with a T/W ratio that could be less than 3:1.

    ... and BTE anecdotal success does not PROVE the design is NOT flawed, but the failures given the marginal T/W ratio do. Even you agree it would be a good idea to revise a design that can result in an unstable condition. That makes the design flawed.
     
    Last edited: Jul 26, 2019
  6. Jul 26, 2019 #306

    astronwolf

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    I flew this model with a B6-2, and had a completely safe flight. I agree that the model flies well with a C6-3.
     
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  7. Jul 26, 2019 #307

    BABAR

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    FWIW the ExoSkell and Venus Probe models ARE probably underpowered for 18 mm estes engines.

    I have both modified for 24 mm mounts and give perfect flights on D12-3s.

    Your argument seems to be that the recommended maximum lift weight Estes publishes is only for amateurs. Since Estes designers are professionals those limits do not apply to them. The new Saturn is a beautiful complex contoured rocket. Not exactly the sleek aerodynamic dart that I would expect would be "fine" for exceeding published weight recommendations, but Estes guys are the experts.

    I am delighted that many are getting good flights on the Estes C6-3 engines. Under optimal flying conditions seems like a nice rocket. At $70 list price would be nice to have something that has a bit more latitude for winds, a not fully seated motor, or a bit of drag on the rod, especially as it is sold as a beginner starter set.
     
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  8. Jul 26, 2019 #308

    jahall4

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    Yes, not surprised at all after looking at the thrust curves. Even Estes has in their table that the B6-2 has higher Max. Lift Wt. @ 127g compared to the C6-3 @ 113g. Even if this was a misprint the B6-2 has a slightly higher avg. thrust than the C6-3, suggesting that the B6-2 would make a better motor to use particularly for smaller fields since it burn time is less than half the C6.

    No surprise really (since both motors are end buring BP) that the C6 is just a B6 with a longer propellant "grain". The B6 is of course lighter, but with essentially the same burn profile over the first 0.8 seconds making the same rocket faster of the pad and potentially more stable than the C6. Also, don't forget the lighter B6 means the CG is farther forward making the same rocket inherently more stable. So it makes one wonder why Estes did not also recommend the B6-2 for the "first flight" as they do with other kits. Maybe the delay was a little long? Wolfram, what did you observe in your flight?

    ThrustCurve.jpg
     
  9. Jul 27, 2019 #309

    jadebox

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    Estes, the manufacturer of the C6-3, is recommending its use in the rocket. Therefore, using the motor in the rocket is using the motor for a purpose recommended by the manufacturer.

    There are rockets which fly quite well with lower thrust-to-weight ratios - even a few that fly fine with less than 3 to 1.
     
  10. Jul 27, 2019 #310

    jahall4

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    At 3/1 sometimes they will, sometimes they won't. Other variables involved besides the motor and the rocket, which is why 3/1 is an absolute min.
     
  11. Jul 27, 2019 #311

    jadebox

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    Joe Barnard and others have demonstrated rockets flying well with lower thrust-to-weight ratios. That's why absolutes are not written into our safety codes.

    I'm any case, the RTF Saturn V on a C6-3 is well over a 3 to 1 ratio.
     
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  12. Jul 27, 2019 #312

    jahall4

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    Funny you mention Joe, because I have been thinking about his thrust vectoring technology as the only way fly a rocket under 3/1 safely. In fact I was willing certify someone for their L1 using his thrust vectoring unit because the 3/1 ratio is obviously NOT applicable. So that argument is fallacious and you are wrong about the Sat V being well over 3/1, its not. The potential for a flight under 3/1 exists and was explained in post #302.

    BTW there are specific absolutes in our safety codes: winds, distances, and yes even thrust to weight. From the TRA SLP which is self described as being "a condensed version of Tripoli Safety Codes and policies" it states "The maximum lift-off weight of a rocket shall not exceed one-third (1/3) of the average thrust on the motor(s) intended to be ignited at launch." This was also explained in a prior post.
     
    Last edited: Jul 27, 2019
  13. Jul 27, 2019 #313

    jadebox

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    This is just a quick, back of the envelope calculation, but at liftoff the C6-3 produces about 14N of thrust for a thrust-to-weight ratio of about 4.5. Halfway through the burn, the thrust is about 4.6N and the propellant mass has dropped by about half. The thrust-to-weight ratio is about 3.3 (which increases a bit until burnout).

    So, the Estes C6-3 is not the ideal motor for the rocket, but is the best available from Estes and not a bad choice.

    I wish Aerotech had a White Lightning Q-Jet. That would be great for a Saturn V.

    I flew mine in a Q-Jet D16. The C12 might have been a better choice only because that July afternoon was really hot and walking to recover the rocket wasn't fun! :)
     
  14. Jul 27, 2019 #314

    jahall4

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    My calculation was actually a little higher at 3.4/1, so not "well over". When the effective thrust varies 10-20% on given motor you could end up with a flight at or below 3/1. So looking at only the thrust curve, the B6 may be a better option than the C6 because with less propellent the rocket is lighter at launch with a CG that is a touch more forward.

    If you want proof motors can vary that much you need to look no farther than the graph I posted earlier, the first 0.8 second of which should match, instead there is delta of about 15% in max thrust. Turns out this is corroborated using the latest curves from the Thrust Curve Beta site. Note that the curves match even better and that the max thrust of both closer to 12 (not 14) a 16% difference.

    upload_2019-7-27_10-19-12.png
     
  15. Jul 27, 2019 #315

    shreadvector

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    TRA safety code is for HPR.

    This is a Model Rocket intended to be flown under the NAR MRSC.

    There is no T/W ratio in the NAR MRSC.
     
  16. Jul 27, 2019 #316

    DEN

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    So does any one have the nerve to try a B6 motor to see if the math holds true in real world tests?? A actual B6 motor launch is the true test but risk factor is higher till actually proven in a flight. Im personally not that much of a risk taker lol
     
  17. Jul 27, 2019 #317

    jahall4

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    Appears to have already been done and why I took a closer look at the B6, but one launch does not make a "true test". A launch or two is anecdotal unless paired with "the math". Ultimately both the B6 and the C6 appear marginal, but the math and a successful flight suggests its a better choice.

    https://www.rocketryforum.com/threads/estes-1-200-scale-rtf-saturn-v.150276/page-11#post-1905547
     
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  18. Jul 27, 2019 #318

    jadebox

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    The B6 has a higher average thrust than the C6. So, based on the thrust-to-weight ratio, the B6 should work better. :)

    But, the B6 has a lower peak thrust and shorter duration. Both make it less appropriate for the rocket.

    Someone earlier, however, said they had flown the rocket successfully on a B6. It's not a recommended motor though and I would be concerned that it wouldn't reach a high enough altitude for the 'chute to reliably deploy in time for a safe recovery.
     
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  19. Jul 27, 2019 #319

    jahall4

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    This is fundamentally wrong, LPR rockets are flown at TRA launches by those holding only a NAR membership using commercial motors. The TRA SLP I cited explicitly lists A-G (LPR) Impulse motors.

    Who said? I'm confident Estes would not tell a flyer they should only purchase one if they are member of NAR flying at a NAR launch, besides the laws of physics don't change. Are you really suggesting the safety of a particular flight changes because it is under a different safety code? (rhetorical)
     
  20. Jul 27, 2019 #320

    jahall4

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    Are you sure (I'm not :)) take a closer look at the second graph I posted directly from Thrust Curve. The curve for the first 0.8 seconds or so should be the same, but in that one the B6 has a slightly higher peak. As I mentioned before a 10-20% variability is possible, which is what makes both the B6 and C6 marginal for this rocket. IOW 14n may be atypical and 12 more reasonable.
     
  21. Jul 27, 2019 #321

    shreadvector

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    Are you unable to read the Estes instructions???

    They do not say to fly per the TRA safety code.

    Go ahead and read the instructions.
     
  22. Jul 27, 2019 #322

    Eljay

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    At this point I honestly believe he's just trolling us.
     
  23. Jul 27, 2019 #323

    jahall4

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    Are you? They read as all Estes instructions do, "follow" the NAR code. Nothing about TRA code at all, and certainly nothing about NOT flying the rocket under TRA code. So I'll say it again because it is accurate "Who said? I'm confident Estes would not tell a flyer they should only purchase one if they are member of NAR flying at a NAR launch (because NRA code is less restrictive), besides the laws of physics don't change. Are you really suggesting the safety of a particular flight changes because it is under a different safety code? (rhetorical)"
     
  24. Jul 27, 2019 #324

    jahall4

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    Not at all, seems to me it is just the opposite. Anytime there is reason to inform and educate in the interest of safety and in the face of misinformation I’m going to do it. As a NAR advisor and club officer that is both a section (NAR) and a Prefecture (TRA) I have that responsibility.
     
  25. Jul 28, 2019 #325

    Cnorm

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    10-min-21-267x300.jpg
     
  26. Jul 28, 2019 #326

    shreadvector

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    Estes makes Model Rockets as defined by N.F.P.A. 1122 (and motors per N.F.P.A. 1125)

    They instruct their consumers to launch them following the NAR Model Rocket Safety Code which is in N.F.P.A. 1122.

    Estes NEVER said you had to join the NAR or be an NAR member to launch them. Sheesh.

    TRA website clearly states that their safety code is a High Power Safety Code.
    http://www.tripoli.org/SafetyCode
    "NFPA 1127 is the foundation of the Tripoli High Power Safety Code. All Prefects are provided a copy of NFPA 1127, and it is available to members for viewing on the NFPA website. If individual members wishes to receive a copy of NFPA 1127, they may purchase a copy from the NFPA."

    Perhaps you need to read your copy?

    You cannot use N.F.P.A. 1127 (or a flawed interpretation of it) to ignore N.F.P.A. 1122, which is THE fire code for Model Rockets.

    In the meantime, you should recuse yourself from any "safety" related reviews of Model Rockets.

    NAR has a High Power Rocket Safety Code as well:
    https://www.nar.org/safety-information/high-power-rocket-safety-code/


    *****

    We have people show up at our Model Rocket launches with rockets made using rigid fiberglass body tubes, nose cones and fins. Commercial kits. They can fly using a G motor, BUT they are not legally Model Rockets because of their construction materials. I pull out the smartphone and show them the website of their kit manufacturer, which identifies the rocket as a High Power Rocket. I provide them with info on the local club that hosts HPR launches. I explain the differences between the MRSC and the HPRSC(THPSC).

    We've also had HPR flyers at our Model Rocket launches SCREAMING at people who were catching their lightweight fluffy Model Rockets as they descended gently under their parachutes. The screamed that they were violating the Safety Code. NO, they were NOT. Again, we have to politely explain the difference in the safety codes.
     
  27. Jul 28, 2019 #327

    jahall4

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    No you should, because you are arguing that a rocket with a demonstrated safety issue be flown under a less restrictive code. Nothing about HPR applies here, but if you are flying at a TRA launch the 3/1 rules applies whether it LPR or HPR regardless of construction materials. There is no ambiguity here try reading the TRA SLP. Again the Estes instructions say nothing about NOT be able to flying under the TRA code as you originally implied and now are trying to walk back.
     
    Last edited: Jul 28, 2019
  28. Jul 28, 2019 #328

    shreadvector

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    :rolleyes:o_O;):confused:
     
  29. Jul 29, 2019 #329

    Ez2cDave

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    Fred,

    Item #1 does not exclude composite or rigid materials. "Lightweight" is not defined in the Safety Code. As long as the rocket is under 1500gr at liftoff, with no metal structural parts, it is in compliance. Not that I agree with the use of these materials in Model Rockets, but the Safety Code does not prohibit them.

    Here is a good example . . . Read the description ( note "nearly indestructable" ) . https://www.madcowrocketry.com/1-1-fiberglass-go-devil/

    Dave F.

    NAR Model Rocket Safety Code
    1. Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.
    2. Motors. I will use only certified, commercially-made model rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer.
    3. Ignition System. I will launch my rockets with an electrical launch system and electrical motor igniters. My launch system will have a safety interlock in series with the launch switch, and will use a launch switch that returns to the “off” position when released.
    4. Misfires. If my rocket does not launch when I press the button of my electrical launch system, I will remove the launcher’s safety interlock or disconnect its battery, and will wait 60 seconds after the last launch attempt before allowing anyone to approach the rocket.
    5. Launch Safety. I will use a countdown before launch, and will ensure that everyone is paying attention and is a safe distance of at least 15 feet away when I launch rockets with D motors or smaller, and 30 feet when I launch larger rockets. If I am uncertain about the safety or stability of an untested rocket, I will check the stability before flight and will fly it only after warning spectators and clearing them away to a safe distance. When conducting a simultaneous launch of more than ten rockets I will observe a safe distance of 1.5 times the maximum expected altitude of any launched rocket.
    6. Launcher. I will launch my rocket from a launch rod, tower, or rail that is pointed to within 30 degrees of the vertical to ensure that the rocket flies nearly straight up, and I will use a blast deflector to prevent the motor’s exhaust from hitting the ground. To prevent accidental eye injury, I will place launchers so that the end of the launch rod is above eye level or will cap the end of the rod when it is not in use.
    7. Size. My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse.
    8. Flight Safety. I will not launch my rocket at targets, into clouds, or near airplanes, and will not put any flammable or explosive payload in my rocket.
    9. Launch Site. I will launch my rocket outdoors, in an open area at least as large as shown in the accompanying table, and in safe weather conditions with wind speeds no greater than 20 miles per hour. I will ensure that there is no dry grass close to the launch pad, and that the launch site does not present risk of grass fires.
    10. Recovery System. I will use a recovery system such as a streamer or parachute in my rocket so that it returns safely and undamaged and can be flown again, and I will use only flame-resistant or fireproof recovery system wadding in my rocket.
    11. Recovery Safety. I will not attempt to recover my rocket from power lines, tall trees, or other dangerous places.
     
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  30. Jul 29, 2019 #330

    Eljay

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    Especially when we're in a world where you can get BT20 fiberglass rockets (with plastic nose cones). They're actually quite nice, don't have to worry about them getting wet, they're very light and you don't have to fill the seams. Our local club had a knee jerk reaction to fiberglass being "a high power thing" and not allowed but as smaller and smaller fiberglass rockets have shown up I think somebody actually read the safety code and they quietly dropped any objections.
     
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