An "R"-powered rocket build

Discussion in 'High Power Rocketry (HPR)' started by Rail Dawg, Nov 30, 2018.

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  1. Jul 17, 2019 #2101

    GalantVR41062

    GalantVR41062

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    I would fabricate a set of "sawhorses" that you use to display and assemble the rocket on the ground, then lift the rocket with a load leveler (beam with 2 straps to air frame and the single lift point from the center of the beam) or large enough single strap to handle the load with out damaging the air frame.

    Then find a tree, engine hoist, automotive hoist, rafters, come along, wench. To lift it high enough to determine CG.

    I have never tried to do anything on this scale, I have been watching and learning. I hope to see it in Kansas. Amazing work guys.

    ~John
     

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  2. Jul 17, 2019 #2102

    Rail Dawg

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    Here's some info and pics on the 1/2" sewn-loop Kevlar backup to the recovery system.

    Since the 3/4" forged-steel eyebolt that goes into the motor upper enclosure is a single-point failure part of the recovery system it was decided to have (2) extra Kevlar lines that are anchored into the rocket booster section and attached to the motor eyebolt. If for some reason the motor eyebolt unscrews itself the backup Kevlar lines will take the load.

    The pics show the 30" long top coupler in the booster section. This coupler is where both the 9.5' and 10' motor have their uppermost reach.

    I drilled holes in the CR's so the Kevlar could pass through them and then anchored the Kevlar loops with quick links as you can see. Then the Kevlar lines were epoxied inside of the coupler along with a good layer of fiberglass. A lot would have to happen before these backup lines failed. Pretty much the destruction of the booster itself lol.

    The aluminum plate you see is the motor retainer. The 3/4" hole in the middle is where the motor eyebolt will pass through and into the fwd bulkhead of the motor casing.

    This entire 30" coupler will be slid into place in the booster and epoxied in.

    With this done it's the drogue section which shouldn't take but a few hours to complete.

    It's coming along... having several hours on a day off to simply bang things out makes the progress happen.

    Chuck C.


    IMG_5096[1].JPG IMG_5097[1].JPG IMG_5098[1].JPG IMG_5099[1].JPG
     
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  3. Jul 17, 2019 #2103

    Theory

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    what size quick links are those? I know the scale of this is very different from "typical" rockets, but they look like they may be a weak point.

    also, and just asking a question here, why 1/2" Kevlar when stronger 3/4" is readily available?
     
  4. Jul 17, 2019 #2104

    Ez2cDave

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    Theory,

    Agreed . . . Every time I hear Chuck say, "1/2 inch wide Kevlar", I "cringe", on a project of this size.

    "From my Chair", 3/4" ( possibly even 1" ) Kevlar would "get the nod", without ever looking back !

    Dave F.

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  5. Jul 17, 2019 #2105

    Rail Dawg

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    The quick links used in the backup are there to keep the Kevlar from pulling through the CR. Combined with the fiberglass and epoxy for 2' that's plenty of anchor.

    The rest of the quick links in the system are 1/2" steel.

    Each 1/2" tubular Kevlar line has 5500 lbs of breaking strength. Using 2 of them takes it over 10,000 lbs.

    The chances of the 3/4" eyebolt unscrewing from the motor is very low as the eyebolt will be secured by the backup Kevlar lines. The backup recovery is almost not needed but is there to ensure the entire recovery system is bulletproof.

    We're comfortable with that. Increasing the size of the recovery system increases the weight of the rocket which requires an even stronger recovery system. You get the idea lol.

    Thanks though for the input!

    Chuck C.
     
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  6. Jul 17, 2019 #2106

    Theory

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    please do not read this as an argument, but I am not sure your math works out. 5500 + 5500 does = 11,000 (grater than 10,000) however this assumes that forces act on each at exactly the same time, in the same direction etc.

    yes, moving from 1/2 inch material to 3/4" or 1" increases weight and that weight would be considered "recoverable weight," however, this is increase (even for a pair of 75' harnesses) is relatively negligible is significantly less than the strength provided by the increase.

    again, just throwing this out there as in my experience the "down" part is significantly more challenging than the "up" part
     
  7. Jul 17, 2019 #2107

    Ez2cDave

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    Chuck,

    I am in complete agreement with Theory, regarding the use of 3/4" - 1" Kevlar for the recovery harnesses.

    I strongly recommend that you re-evaluate the recovery harness requirements.

    Weight reduction over strength has never been a primary factor in this project, up to this point.

    I'm not being argumentative, but I am expressing a genuine concern, which could affect the success of the flight, especially with multiple flights being involved in the scope of the project.

    Dave F.

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  8. Jul 17, 2019 #2108

    Rail Dawg

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    Good points guys.

    Have you looked at the recovery system as a whole I.e. where are your weakest links?

    3/4” Kevlar is great what about the rest of the system? Quick links to match the breaking strength of 3/4” Kevlar are very heavy. What about the drogue and parachute shroud lines?

    Now the AvBay connections need to be beefed up to match your Kevlar.

    With a significant amount of weight being added how do you handle the CG being pulled forward pushing the rocket well into over-stable territory?

    It’s a balancing act. Going to 3/4” Kevlar is easy to do but there are big negatives involved with that decision.

    Chuck C.
     
  9. Jul 17, 2019 #2109

    Ez2cDave

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    Hi, Chuck,

    "From my Chair" . . .

    (1) Drogue & Shroud lines - We must defer to Buddy Michaelson properly sizing these, since he is familiar with the mass of the rocket and his materials. I imagine he has a "Safety Margin" in place.

    (2) CG - The new, larger "R" motor has already added additional mass to the aft end of the rocket. I would be more concerned on the "Q" flight, with the original motor casing.
    Since the rocket will be reaching Mach 2.2+, have you calculated the CP-shift ( Forward ), as velocity increases, for both flights ? ( Static Test data will give the most accurate results ).

    (3) AV-Bay Connections - Naturally, ALL connections with have to be sufficiently strong, throughout the rocket.

    (4) Weakest Links - We have not seen the Recovery System in its entirety, nor all of the hardware & attachment points throughout the rocket..
    Without that, we would be "working in the blind" and, at best, we would only be guessing.

    (5) Balancing Act - "Literally" true, in this case. Of course, if a Recovery System component fails, the entire project can fail, catastrophically.
    Frankly, I think we need to take a brief, but thorough, look at the entire Recovery System. If we can evaluate the entire system, we will be able to make the best suggestions.

    Dave F.

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    Last edited: Jul 17, 2019
  10. Jul 17, 2019 #2110

    Rail Dawg

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    Let’s just say Dave that with LDRS six weeks away I’m quite comfortable with the build on this rocket. Now is not the time to redesign lol.

    It’s going through the Tripoli Class 3 Review Committee (C3RC) as we speak and all indications are they are satisfied. They are an important part of the process and if there were concerns they would be addressed.

    Your worries are noted.

    Chuck C.
     
  11. Jul 17, 2019 #2111

    Theory

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    that is good news to be sure!

    remember, the pointy end goes up ;-)
     
  12. Jul 17, 2019 #2112

    Ez2cDave

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    Chuck,

    My main concerns were, are, and will continue to be, the safety and success of your project. I have expressed my opinions but, ultimately, the final decisions are yours. I sincerely hope that my concerns are, in the end, unfounded.

    When will the Charge Cannons be tested and the Static Tests take place ?

    Dave F.

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  13. Jul 17, 2019 #2113

    Nytrunner

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    Unless your chair's in the wrong place

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  14. Jul 17, 2019 #2114

    Bat-mite

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    Looks like something out of a horror movie!
     
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  15. Jul 17, 2019 #2115

    troj

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    The C3RC is not an RSO check. It's not a flight-readiness check. An Analyst may make some recommendations, but they do not review your build and make the level of comments you are implying. The C3RC is mostly focused on making sure that sufficient (and accurate, based on what is provided) data is made available to allow the FAA to have confidence that we won't violate the waiver issued for the rocket (Class 3 rockets, in most cases, each get their own, individual waiver). Keeping an eye out for build/design issues is secondary and something for which the RSO is relied upon.

    The rocket must still be reviewed and approved by an RSO who can see and review things in person.

    -Kevin
    (C3RC co-chair)
     
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  16. Jul 17, 2019 #2116

    Rail Dawg

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    Ah very good.

    I stand corrected!

    Thanks.

    Chuck C.
     
  17. Jul 17, 2019 #2117

    Theory

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    Valuable information right there!

    Thank you
     
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  18. Jul 18, 2019 #2118

    Ez2cDave

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    Chuck,

    Based on the last information posted, a re-evaluation of the 1/2" Kevlar Harnesses seems to be in order. If an RSO says "no", after they are bonded in placed, a "nightmare scenario" could result, preventing the rocket from flying.

    As you are aware, I always tend to err on the side of caution . . . I feel that the 1/2" Kevlar is marginal, especially since you intend to make multiple flights with the rocket. If it were me, I would go 3/4" - 1", for the extra "peace of mind" . . . Of course, the final decision is yours, Chuck !

    Dave F.

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  19. Jul 18, 2019 #2119

    davdue

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    I see these 1/2” Kevlar as only Insurance to keep the 3/4” eye bolt from unscrewing. If each is connected to each side of the bolt I can’t unscrew. So even smaller would work for that.

    As far as the primary harnesses for the drogue and main being 1/2” I’m a little concerned but only because I am not clear yet on how they are connected and how much each piece they are connected to weighs. Are each of the 100’ harnesses connected in parallel on separate eyebolts?

    I know the full up weight on the pad is 850#. But what is the weight at Apogee? That weight is what needs to be known for how much force will be on the harness after deployment and also lets say it takes 5-10 seconds for the drogue to open. How fast will the rocket be falling by then and what will be the forces on the harness when it pulls tight. I don’t know how to do those calculations anymore. It’s been 30 years since I took dynamics in college and electrical engineers don’t use that stuff at work. Lol
     
  20. Jul 18, 2019 #2120

    Ez2cDave

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    Dave,

    The motor has approximate 200 lb of APCP . . . So weight at Apogee is 200 lb less than Liftoff weight.

    Dave F.

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  21. Jul 18, 2019 #2121

    Rail Dawg

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    Let me look into the 3/4" tubular Kevlar.

    Need almost 500' of it. Although I have confidence in the numbers for the 1/2" this is a big, heavy rocket and the added margin of safety won't hurt. For the record the R is about 560 lbs loaded with fuel and at apogee it's about 400 lbs.

    Lots on my plate so if anyone here can source the 3/4" tubular sewn-loop Kevlar I'd appreciate it. The first few places I looked it wasn't in stock.

    This stuff ain't cheap either dangit. Nothing seems to be in rocketry lol.

    Thanks gents.

    Chuck C.
     
  22. Jul 18, 2019 #2122

    neil_w

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    Not when you're building a 600 lb rocket. ;)
     
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  23. Jul 18, 2019 #2123

    jbr

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    I was on a case with the medical examiner and we had a body with shattered knee caps that the legs did bend the wrong way
     
  24. Jul 18, 2019 #2124

    Bat-mite

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    When I was a young teen, at the roller rink, there was a bad crash and ambulance called. Rumor was that some kid's kneecap was down on his shin, but I didn't see it. Eeeeeeeewwwww!!!
     
  25. Jul 18, 2019 #2125

    davdue

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  26. Jul 18, 2019 #2126

    neil_w

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    Seriously, go talk to Teddy an OneBadHawk and work with him to get what you need. That's about as safe a recommendation as going with StickerShock23 for the vinyl.
     
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  27. Jul 18, 2019 #2127

    davdue

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    I sent Teddy a FB message about this and told him to comment here.
     
    Last edited: Jul 18, 2019
  28. Jul 18, 2019 #2128

    Ez2cDave

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    Chuck,

    They both beat me to it . . . Definitely contact "OneBadHawk" !

    Dave F.

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    Last edited: Jul 18, 2019
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  29. Jul 19, 2019 #2129

    rcktnut

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    I say if that 1/2 in. Kevlar gives way you are going to kiss that rocket good by anyway, aint going to be the only thing that breaks. With a nominal flight what you have is good. You have to draw a line somewhere and trust in what you believe is sufficient.
     
  30. Jul 19, 2019 #2130

    TonyL

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    Chuck,
    two things:
    1. The two Kevlar cords are a good plan. While you can't assure equal load carrying, you also don't need to, and to some degree don't want to. If enough kinetic energy exists to break one cord, then it may break. The good news is that the energy consumed breaking the shock cord is now dissipated. If enough kinetic energy still remains to break the second cord, then the event was severe enough that some sort of catastrophic failure is probably expected. That said, if you break both the shock cords from the ejection charge, it is your own fault :).

    2. The sewn loops still seem like an unknown. They look properly made, however loops tested to some proof load [reasonably less than the ultimate load strength] would be desirable. What I have done lacking that, is to use the loop to double over on itself and create a knot on the quick link of at least some expected properties. Your loops in the picture are too small for that, but proof testing is still possible. Testing a sample loop to failure would be even better, maybe onebadhawk has already done this?

    br/

    Tony
     
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