An "R"-powered rocket build

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

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  1. Jul 19, 2019 #2,131

    Ez2cDave

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    Chuck,

    I believe the knot Tony is referring to is called a "Lark's Head" .



    ALL "knots" & "sharp bends" reduce strength . . . ( Including those "bends" your loops take around those quick links )

    I did some research before making the above statement.

    http://allaboutknots.blogspot.com/2010/11/knot-strength-structures-that-make.html

    http://itrsonline.org/wordpress/wp-...be.A-Review-of-Knot-Strength-Testing_2016.pdf

    https://www.rescueresponse.com/much-strength-rope-loose-tie-knot


    Please remember that my concerns are only the safety and success of your project, Chuck !

    Dave F.

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    Last edited: Jul 19, 2019
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  2. Jul 19, 2019 #2,132

    TonyL

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    Dave F,
    Indeed, the whole 'expected properties' concept.

    I favor the "figure 8 on a bight" or a 3-wrap noose, both are easy to tie, with the noose being the more likely to untie [in kevlar] after being heavily loaded. Either way, historically my 1/2 tubular kevlar shock cords have always broken in the middle for some reason...

    br/

    Tony
     
  3. Jul 19, 2019 #2,133

    jderimig

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    Chuck,

    The 1/2 kevlar is fine. If you have >5000# of tension on that line then you are going to have other bigger problems (other parts of the rocket are going to be breaking.....).
     
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  4. Jul 19, 2019 #2,134

    TonyL

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    So 400 lbs of recovery mass in say two equal sections means 5500 lbs / 200lbs for a 27.5 g strength limit when the cord pulls taught. This seems very easy to achieve with kevlar lines, especially with more aggressive ejection charges [to make sure it separates]. Personally I like having a breakable link to absorb energy before the limit is reached. Recovery in two sections makes all of this moot [I like two sections].
     
  5. Jul 20, 2019 #2,135

    Rail Dawg

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    Thanks guys for the replies on the 1/2” Kevlar.

    I must agree with over 5000# of protection the 1/2” will do the trick.

    This is a solidly-built rocket that is stable. It won’t be launched in any crosswind over 10 mph.

    Because LDRS is a major event with lots in attendance this rocket in particular has to fly as safely as possible. The high-altitude guys with KloudBusters are going to look at the recovery system. They are quite familiar with big projects and I’ll follow whatever recommendations they provide.

    That being said the ideas and suggestions on here are encouraged. Just as they have been from the beginning of this fun project!

    Chuck C.
     
  6. Jul 20, 2019 #2,136

    3stoogesrocketry

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    Chuck to help mitigate the shock load , how about using two drouge's , one one the payload and one on the booster . It will help slow each part down before the parts hit the end of the line .

    Eric
     
  7. Jul 20, 2019 #2,137

    jderimig

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    He has two attachment points, 5000# would require a 55g shock. That line is not rigid, 55gs is not happening. IMO.
     
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  8. Jul 20, 2019 #2,138

    Ez2cDave

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    That is a 55g load, based on the Kevlar being at 100% breaking strength.

    As pointed out in the data I previously supplied, in post #2131, every knot or sharp bend diminishes breaking strength. So, necessarily, that 55g number decreases, as well.

    Also, ask yourselves this question : " No matter how strong the Kevlar itself may be, how strong is the thread it is stitched together with ? "

    A relatively few strands of thread, compared to the total number of strands in the 1/2" Kevlar harness are actually all that stands between success and catastrophic failure.

    How much strength do the threads supply ?

    Are they stronger or weaker than the harness itself ?

    If the threads are weaker, then they are the "true measure" of the strength of the harness.

    Pics below show the stitching on a OneBadHawk 3/4" wide Kevlar harness.

    ( Note that Tubular Kevlar is used on their 3/4" harnesses, while Flat Kevlar is used on their 1/2 " harnesses )

    This pic is their 1/2" wide Kevlar harness ( Compare to the 3/4" )

    [​IMG]

    Dave F.

    [​IMG]

    [​IMG]

    [​IMG]

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    Last edited: Jul 20, 2019
  9. Jul 20, 2019 #2,139

    Flyfalcons

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    I, for one, trust Teddy's stitching and weight ratings.
     
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  10. Jul 20, 2019 #2,140

    Theory

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    One more data point is the intent of this project being a “multi flight” bird. Yes, 1/2” might hold up for the “Q” flight.

    But will chafing, wear from the flight, storage and prep take its toll and result in issues for the “R” flight?

    From the pictures the 1/2” is permanently bonded to the structure and cannot be replaced in the future should challenges arise.
     
  11. Jul 20, 2019 #2,141

    jderimig

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    Yes, but you don't have to be anywhere near 55g. 5g is achievable. Best practice is to dissipate the energy of the ejection charge while the harness is stretched.

    A method I use to add this dissipation is loops in the harness which are taped by layers of electrical tape. The electrical tape breaks as the harness extends. Vinyl electrical takes alot of energy with it when it breaks.
     
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  12. Jul 20, 2019 #2,142

    Ez2cDave

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    Theory,

    Your concerns "echo" mine.

    Dave F.

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  13. Jul 20, 2019 #2,143

    Ez2cDave

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    "Teddy" says this about his 1/2" wide Kevlar harnesses, " These are made from 2500 lb. 1/2" Flat Kevlar Webbing. These recovery harnesses are well suited to light paper tube airframe mid power rockets and some light high power rockets."

    That does not describe Chuck's rocket, in any manner.

    "Teddy" tells you the material they are made from , but not that they are rated for that amount, as he manufactures them !

    Dave F.

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    Last edited: Jul 20, 2019
  14. Jul 20, 2019 #2,144

    3stoogesrocketry

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    Wow , go back and re-read for a bit .
     
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  15. Jul 20, 2019 #2,145

    3stoogesrocketry

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    Chuck , if your in the slightest concerned with the Tubular Kevlar , you could sleeve the Kevlar with 2 inch Tubular Nylon from Strap Works. It's only $.65 per foot. A cheaper alternative to The 3/4 inch kevlat. The Kevlar will slid inside the nylon. The Nylon has a 5k breaking strength. It will also work excellent as a abrasion detergent on the Kevlar if it rubs the edge of your tube.
    Eric
     
  16. Jul 20, 2019 #2,146

    Ez2cDave

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    Eric,

    Finally, a "breath of fresh air" . . . Your suggestion has merit and Chuck should give it serious consideration.

    BTW - I believe you intended "deterrent", not "detergent" . . . LOL !

    Dave F.

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  17. Jul 20, 2019 #2,147

    rcktnut

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    On all my rockets with any body tubes other than cardboard, I "cut", round the inside edges of the tubes wherever the recovery harness comes into contact with them. It also helps couplers slide in easier. I would also round the holes of any bulkheads especially metal ones that the harnesses pass through. You could also add a few inch long pieces of wider tubular Kevlar/Nylon slid over the 1/2 in. Kevlar where it passes through bulkheads etc., just tape on, secure somehow. This will reduce or eliminate any wear and tear on the harnesses.
     
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  18. Jul 20, 2019 #2,148

    Rail Dawg

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    Again great stuff gents!

    I do want to steer away from the doom and gloom predictions of tragedy if 1/2" tubular Kevlar is used. The stuff is stout and is designed to handle some very hefty loads.

    Am also going to see what the high-altitude folks at KloudBusters have to say. Again they have seen plenty of big projects on their Rocket Pasture and their judgments are sound.

    It's $1000 to switch to the 3/4" Kevlar. Money never trumps safety but money does play into a decision to overbuild.

    But please... let's not get too overly-dramatic lol.

    Chuck C.
     
  19. Jul 21, 2019 #2,149

    Ez2cDave

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    Well, if the harness breaks . . . LOL !



    Dave F.

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  20. Jul 21, 2019 #2,150

    Rail Dawg

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    Posts like this aren't helpful lol.

    I can assure you Dave we are looking hard at the harness and will ensure it is 100% safe for both flights.

    You've made your concerns known and it's appreciated. Let us decide from here the safest course of action.

    Chuck C.
     
    Last edited: Jul 21, 2019
  21. Jul 21, 2019 #2,151

    Ez2cDave

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    Chuck,

    So, moving on to electronics testing, charge cannon testing, and static motor testing, what is the current timeline for those, Chuck ?

    Of the three items, motor static testing is my biggest priority, since it will provide "real world" performance numbers. Secondarily, I'm looking forward to seeing the Charge Cannons in action !

    Dave F.

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  22. Jul 25, 2019 #2,152

    Rail Dawg

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    Finishing up the drogue section... it's a pretty easy build there.

    The Q motor we wanted to use for LDRS has too long of a burn and not enough initial thrust to safely get the rocket off the pad. There are other routes to take but with time so short there's a chance this rocket will only see BALLS 28 this year...

    The rocket isn't that far from completion just a lot of details to add on like Delrin rail guides and the blind nuts for securing the AvBay to the airframe.

    While perhaps not making LDRS is a let-down safety trumps everything. Quite frankly this rocket is built like a tank and I have no doubt whatsoever that it will handle even a full R motor.

    Ordered the 3/4" Kevlar harnesses today. Definitely a robust recovery system!

    I'll post some pics later on. Hang in there with me guys these big projects will have setbacks. I'm already looking to start ordering parts for the 16" G-12 "S" powered rocket lol.

    Isn't building rockets fun?

    Chuck C.
     
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  23. Jul 25, 2019 #2,153

    Rail Dawg

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    I’m thinking of hauling the completed rocket to LDRS 38. Give the great folks at KloudBusters a chance to look her over for perhaps an AirFest flight down the road.

    KloudBusters is known for their big project flights. I’d thoroughly enjoy them crawling around this thing to see if it passes their muster.

    Nothing but respect for these guys.

    Chuck C.
     
  24. Jul 25, 2019 #2,154

    Nytrunner

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    I'm guessing the static test happened and revealed actual motor performance? Do you have permission from the motor folks to tell us about it?

    What prompted the change to 3/4?
     
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  25. Jul 25, 2019 #2,155

    FredA

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    What makes it safe to fly at Balls if it can't get off the pad in Kansas?
    Or are you going to bring the R to Balls-28?
     
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  26. Jul 26, 2019 #2,156

    Rail Dawg

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    Nope no static test yet. The 9.5’ Q motor casing is being shipped to me on July 29 and I plan to test a Q already built to see its burn time.

    I’d like to see a 6:1 thrust to weight ratio. If the rocket weighs 550 lbs then 3300 lbs of liftoff thrust would be great.

    Went with 3/4” Kevlar just because I always overbuild my rockets. The Chuck C mantra is Safety Trumps Altitude lol.

    Chuck C.
     
    Last edited: Jul 26, 2019
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  27. Jul 26, 2019 #2,157

    Rail Dawg

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    Good question. The BALLS 28 motor will have more power in a longer motor. Testing will tell us a lot.

    I don’t see any reason not to get at least a 6:1 ratio at BALLS 28.

    Chuck C.
     
  28. Jul 26, 2019 #2,158

    Theory

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    Given where your current project stands, I find statements like this concerning

    Or is the focus more on simply “building big things?”
     
  29. Jul 26, 2019 #2,159

    Rail Dawg

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    Not concerned with building bigger. The current R rocket is almost as solid as a telephone pole lol.

    Going from 12” to 16” isn’t too big of a step. Of course a lot will be decided once this current rocket flies.

    Chuck C.
     
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  30. Jul 26, 2019 #2,160

    Ez2cDave

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    Chuck.

    (1) Q Motor - Better to make that determination mow, than to let "go fever" cause a problem later.

    (2) I'm really intrigued by the idea of the "Charge Cannons" and I'm looking forward to when they are tested !

    (3) "Safety Uber Alles" . . . Words to live by and the sign of a man who is in control of the project, rather than the other way around. I applaud your decision, Chuck !

    (4) 3/4 Kevlar - A wise precaution, sir ! I know it's an expensive proposition, but you should either be able to use the 1/2" Harness on a smaller project, or sell it to recoup some of your investment !

    (5) The "S" - The experiences from building the UpChuckR should make the next project go even more smoothly . . . It's a wise precaution to order hard to find items or parts that will need to be custom-made, in advance !

    Dave F.

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