Big Daddy Lawn Darts... Show of Hands Please.

Discussion in 'Low Power Rocketry (LPR)' started by K'Tesh, Feb 1, 2016.

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  1. Feb 28, 2016 #61

    rharshberger

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    Probably has more to do with the BP motors ejection charge not being sufficient combined with the shape, AP motors have pretty stiff ejection charges (and can be adjusted) as they are usually used in bigger rockets like the Leviathan and Executioner.
     
  2. Feb 28, 2016 #62

    John Beans

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    Different cone. The Big Daddy has a unique cone with a big ramp to it on the base.
     
  3. Feb 28, 2016 #63

    rharshberger

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    Leviathan and Scion use the same NC as Big Daddy, the Executioner and PS Patriot may as well. I have at least 5 of the Estes 3" cones ( from Levithan, BD, ans Scion) and several of the ones Apogee, Mercury Engineering, and BMS sell ( they are slightly longer and have a shorter "ramp".
     
  4. Feb 29, 2016 #64

    Kruegon

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    The PS Patriot and the Executioner us the PNC-80K. Same as the V2 and the Phoenix. It's a completely different nose cone in shape and design. The BD, Scion, and Leviathan use the PNC-300K. I have heard word that it is the same as, or a redesign of, the Maxi Brute V2 nose cone.
     
  5. Feb 29, 2016 #65

    Viking

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    Last edited: Feb 29, 2016
  6. Feb 29, 2016 #66

    Kruegon

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    Hmm very interesting. The file I had on the PS Patriot had centering rings drawn out that were exactly sized for the BT-80. I had thought it was 3" originally. It was when I printed it out and it fit the BT-80 that I figured I had heard wrong.

    That explains why the 4x BT-50 were such an extremely tight fit.

    Now I need to find the correct specs for the kit. Obviously everything I have is wrong.
     
    Last edited: Feb 29, 2016
  7. Feb 29, 2016 #67

    Rex R

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    Jimz has the instructions (in Tiff format) look for 2066. I built mine w/o the boat tail (at 3" dia. the difference in tube sizes is pretty small). you will likely need some nose weight. the ork file I put together for mine. flies nicely on an F52.
    Rex

    View attachment rcrpatriotv3.ork
     
  8. Feb 29, 2016 #68

    Kruegon

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    I saw his once, but there's no info on the size of anything with it. Is your ork file to spec or have you modified anything?
     
  9. Mar 1, 2016 #69

    Rex R

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    overall length is correct as is the length of the slotted tube(the BD gets it's bt and nose from the pat) so if you want the tail cone and the correct length you will have to shorten the upper part of the booster(how much I am not sure, my guess is about an inch) the fins do not follow the cone. the payload/warhead section length is correct. I scaled all my measurements from the actual missile (as provided in the instructions) the color scheme is an early version. HTH
    Rex
     
  10. Mar 1, 2016 #70

    jrkennnedy2

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    Never had a lawn dart with my Leviathan. Then again I don't fly that with an E motor. Maybe the AT G-size motor has enough deploy charge to overcome the difficulties on the NC shape?
     
  11. Mar 1, 2016 #71

    rharshberger

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    That was part of my line of thought up in post #61, more gas, more pressure therefore it gets forced out faster.
     
  12. Mar 9, 2016 #72

    kevinkal

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    I've flown my Big Daddy 6 times, three on D12-5's and three on E9-6's. All went well. I think I'm a little under the stated build weight and thus should be getting upwards of 900' AGL possibly more with the E9-6.

    I've been reading about the concerns with the nosecone's angled shoulder allowing the ejection charge pressure to blow-by and not eject the parachute. This can only happen if the nose cone is pushed forward about 1 inch. I'm sure this has been mentioned somehwhere but I didn't find it, so I'll mention it here... It occurs to me that the pressure difference upon rocketing up to 900 ft could push out the nosecone. At 1000 ft AGL, the pressure difference vs. ground at sea level would be something like 14.7 psi - 14.16 psi = 0.54 psi. The area of the Big Daddy's Big nosecone is about 6.8 sq in. Thus for a "unvented" Big Daddy, the pressure force would be 0.54 * 6.8 = 3.67 lb. Without going through more calculations, it would seem quite possible that the nose cone could be pushed out all the way to the problematic angled shoulder where it would then vent pressure. If the ejection charge fired in that state... it would be less likely to eject the parachute properly, allowing the Big Daddy complete a ballistic lawn dart maneuver.

    My Big Daddy's nosecone is relatively loose. It differs slightly from the nosecone on my Leviathan in that it has 6 evenly-spaced circumferential raised plastic lines around the nose cone shoulder section that run from the seat to the bottom. These raised "lines" are what make contact with my body tube inside diameter. I'd guess it is a near perfect slip fit.. very little friction and very little side-to-side play. I do not have a vent hole in my Big Daddy, but I think the slip fit nosecone along with those slightly raised lines give it the ability to equalize pressure somewhat as soon as the nosecone moves slightly from its seated position. I suspect I'm lucky that the stock nose cone fit the way that it did. I imagine that after launch the internal pressure does push out my nosecone as the rocket decelerates toward apogee, and when the nosecone comes off it's "seat", the internal pressure vents to the outside without the nosecone moving more than a fraction of an inch. Still, I plan to add a vent hole. The Big Daddy has a big diameter which in turn generates more pressure force with altitiude.
     
    Last edited: Mar 9, 2016
  13. Mar 9, 2016 #73

    Kruegon

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    I can say this: I have yet to hear of a lawn dart happening on a composite motor. It has also been discussed on several occasions that the composite motors have more ejection charge. So I pose this question

    What motor were you using when your Big Daddy decided to lawn dart?

    I was using an Estes E9-6.
     
  14. Mar 9, 2016 #74

    rharshberger

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    Mine hasn't, but I don't fly it on BP (its too heavy due to the Av-Bay nose cone mod), but I have seen several lawn dart on BP motors (not sure which motors though).
     
  15. Mar 10, 2016 #75

    GlennW

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    Mine was on a D12-3 when it had its "final flight."

    Glenn
     
  16. Mar 12, 2016 #76

    KevinM

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    I lost a Big Daddy to an Aerotech D15, but in fairness my 'Daddy was modded with a baffle that probably negated any additional benefit of the stronger ejection charge of the composite motor.
     
  17. Mar 13, 2016 #77

    BDB

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    Here is my mod nosecone. I upgraded the MMT to 29 mm and added 5 oz of nose weight. It flew great yesterday on an F26-6.
    ImageUploadedByRocketry Forum1457901653.624697.jpg P3121683_ORF copy.jpg

    There were several other Big Daddy's at the RIMRA launch yesterday, two of which lawn darted.
     
    Last edited: Mar 14, 2016
  18. Mar 15, 2016 #78

    loopy

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    D12-5, E18-7. In all fairness, the E18 never ejected for some reason...Black powder was still in the casing, delay burnt all the way through...quite the mystery.
     
  19. Mar 15, 2019 #79

    K'Tesh

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  20. Mar 15, 2019 #80

    JERRYR708

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    I completed a Baby Bertha and spray painted it gloss black including the shoulder of the nose cone just 3 days before launching. The Summer day at ROC Lucerne was so hot and humid that the Baby Bertha's paint began to get a little tacky and even stuck to the side of one of my other rockets. After seeing what was happening, I tested the nose cone fit and it was stuck. (was loose before heading to the launch. I always believe in loose NC's and never had a lawn dart). The paint around the shoulder of the nose cone got tacky and was really difficult to remove. That rocket didn't fly that day until the problem was remedied. Some paints take a week to fully cure especially gloss and I only waited for 3 days after painting and clear coating. Now I just use masking tape around the nose shoulders. This would have been a Lawn Dart if I didn't catch it.
     
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  21. Mar 15, 2019 #81

    bill_s

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    No.

    My theory is the bit of masking tape to tighten the fit (no paint) should be slightly asymmetrical with extra drag between the bevel and shoulder. Also tape the standard retainer. The Estes ejection charge is mighty.
     
  22. Mar 15, 2019 #82

    Scotty Dog

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    My beautiful Underdog lawn darted at CMASS. Its fixable. Just haven't looked at it since it happened To bummed out .I'll post pic tomorrow.
     
  23. Mar 15, 2019 #83

    JERRYR708

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    If you are launching in Lucerne in August and the temperature is 112+ degrees, black rockets can warp, stick to each other and black paint on nose cone shoulders can heat and glue themselves to the BT. I have experienced all of it. I try to stay away from black paint or leave those models at home during the hot summer months. If I bring one, it will stay in the air conditioned truck in the back seat with a dowel running through the tube like a spit where no fins or BT touch anything.
     
  24. Mar 15, 2019 #84

    cwbullet

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    Aye. But, I have also had a lot of success.
     
  25. Mar 15, 2019 #85

    jnobels

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    I’ve had this happen twice now with slightly generous delays. My theory is that when the rocket arcs over, the bp falls away from the delay charge and with no contact, doesn’t light - or lights very late and/or randomly. The hole to the delay charge gets a little crufty over time and can keep then powder from settling down properly.

    I will be filling that forward empty space above the BP with wadding from now on and making sure there is good contact with the delay grain.
     
  26. Mar 15, 2019 #86

    bill_s

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    Yikes.. just was my theory on the beveled NC shank issue.
     
  27. Mar 15, 2019 #87

    DuctTapeandRocketFuel

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    I had a D12-3 turn into a D12-30, resulting in a lawn dart a few years back. Too much dog barf is the main culprit I have seen, and had happen to myself.
     
  28. Mar 16, 2019 #88

    goose_in_co

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    I didn't have a problem with the modification that I did. I cut a hole in the base of the nose cone and extended the motor mount into the nose cone, and then lined the inside of the nose cone with epoxy. It has the extra benefit of needing no wadding, and leaving a nice area for the parachute. Unfortunately I did not lengthen the shock cord, and I ended with an dent on the nose cone and a bent motor tube. Here are some pictures of the rocket. Flight and deployment otherwise were just about perfect.
     

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  29. Mar 16, 2019 #89

    JERRYR708

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    The extended motor tube through the nose cone is a great idea. Funny how the NC snapped back and hit the MMT dead center without nicking the BT. That was a slam swish.
     
    Last edited: Mar 16, 2019
  30. Mar 16, 2019 #90

    jbr

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    I just launch my daddys on h200, I400, and J600, the J barely fits
     

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