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  1. #211
    Join Date
    19th January 2009
    Location
    Branford, CT
    Posts
    1,653
    Love CTI, Hopefully this load and the 3G 75mm L1350CS I demoed will be certified soon! That load put my 23lb Gizmo XL slug to 6300' Love the 3G 75 loads.

    Gary Tortora
    TRA 11898 L3
    ProLine Rocketry Sales & Support
    sales@prolinerocketry.com

    203.836.4014

    Ns Burned 2010 - 76,344
    Ns Burned 2011 - 93,595
    Ns Burned 2012 - 71,386
    Ns Burned 2013 - 63,463
    Ns Burned 2014 - 43,271

  2. #212

    Confused about static port size for my Gizmo XL

    I want to accurately determine the static port size for my Gizmo XL to be built similarly to Gary T's rocket. e.g. With a 4" diameter tube glued into the nose cone with a centering ring 1/2" just the nose cone opening. The main chute goes into the 4" tube and the altimeter resides between the wall of the nose cone and the wall of the 4" tube. To figure out the internal volume of the altimeter compartment, I filled the empty nose cone with water to within 1/2" of the opening (where the centering ring will be glued). I came up with 464 fluid Oz. Using the formula 1 US fluid Oz = 1.8046875 cu inches, gives 837.4 cubic inches of internal volume for the complete nosecone.

    I then emptied the nosecone and inserted the 4" tube, then refilled with water up to the point where the nosecone and 4" tube meet. This gave 19 fluid oz or 34.3 cubic inches which must be deducted since this portion of the nose will be sealed off by the tube.

    Finally I measured the length of the 4" tube from the nosecone intersection point to the centering ring. This was 22.5". Using the formula Volume = Radius squared x Length x 3.14 gave me 282 cubic inches for the portion of the tube that stuffs the nosecone. This must also be deducted from the total nosecone volume.

    So I take the total nosecone volume (837.4) minus the sealed off portion of the nose tip (34.3) minus the volume of the 4" stuffer tube (282) which ends up totaling 521.1 cubic inches.

    The standard charts and formulas for determining static port size require inputting the internal avbay diameter and length to come up with a hole size or multiple hole sizes but I found a formula that states: Port diameter in inches = Volume in cubic inches divided by 400. (This gives a 1/4" hole for every 100 cubic inches of avbay volume which seems reasonable.) So to continue, 521.1 / 400 = a whopping 1.30275" diameter static hole!

    To reduce the hole diameter, we can go to multiple holes which is better anyway for avoidind wind induced problems.

    The formula for sizing multiple ports is: Hole size = Single port diameter/ [# of ports / 2] . For 3 ports (which I prefer) I get 1.30275/ [3 / 2] = a still whopping 0.8685" hole nearly 7/8" diameter. Something doesn't seem correct. Even going to 6 holes is 0.43425" or roughly 7/16". My rocket is going to look like Swiss cheese!

    Looking at Gary's rocket photos, I see a static hole that appears to be about 1/4" diameter although I can not see how many there are. Still that is way smaller than my calculations. On all other Gizmo XL photos in this thread, the static ports seem minuscule in comparison. Please chime in. I'm at a loss!
    L3 Certified
    NAR #90891, TRA #14994
    Clubs: CRMRC, METRA, MDRA

  3. #213
    Join Date
    25th August 2009
    Location
    Carol Stream
    Posts
    1,939
    Yeah, I was going to do all that too (NOT!!) but I just used 3, 1/4" holes and it worked fine. LOL!!!!
    L3-TRA 12636
    QCRS BOD/Prefect. Princeton, IL
    TWA Bong, WI
    Chicago Rocket Mafia "The Hot Tub"
    Public Enemy Aerospace
    Beep-Beep-Boop-Boop

  4. #214
    Join Date
    19th January 2009
    Location
    Branford, CT
    Posts
    1,653
    Dave:
    Not everything needs to be deduced by an equation , The rule of thumb is 1 1/4" static port hole per 100 cubic inches, Again that's just the rule of thumb.

    I've seen multiple 1/8" holes on a 4" bird and even 1! 1/2" hole work, Not what I would recommend but they did work.

    For my Gizmo XL I used (3) 1/4" holes and needless to say it works perfectly.

    Good Luck.

    Gary Tortora
    TRA 11898 L3
    ProLine Rocketry Sales & Support
    sales@prolinerocketry.com

    203.836.4014

    Ns Burned 2010 - 76,344
    Ns Burned 2011 - 93,595
    Ns Burned 2012 - 71,386
    Ns Burned 2013 - 63,463
    Ns Burned 2014 - 43,271

  5. #215
    Hi Griffin,

    I see you and Gary both got your Gizmo's back safely so I agree that smaller holes work! However I'm trying to get my Gizmo XL together for an L3 attempt and as you know my NAR L3 proposal is supposed to be filled with science, not conjecture.

    I tend to do things by the book so to speak which causes my builds to take longer but in the end I seem to be have doing things right.

    On this static venting issue, the only thing I can see happening with undersize holes is that there will be a latency in venting the avbay which will cause the altimeter to delay it's functions slightly. Probably nothing like the crapshoot we take when estimating motor eject delays!

    So let's see what others say. If I can't justify drilling huge holes in my Gizmo I'll just reference Griffin's Law in My L3 proposal.
    L3 Certified
    NAR #90891, TRA #14994
    Clubs: CRMRC, METRA, MDRA

  6. #216
    Thank's Gary. 1/4" x 3 it will be!

    I just booked for Red Glare so I'll see you there. Also going to NERRF and LDRS. I gotta start burning some of my AP!
    L3 Certified
    NAR #90891, TRA #14994
    Clubs: CRMRC, METRA, MDRA

  7. #217
    Join Date
    19th January 2009
    Location
    Branford, CT
    Posts
    1,653
    Dave:
    Yup I'll be at all three launches as well, Which launch are you planning to do your L3 at and what motor?

    Gary Tortora
    TRA 11898 L3
    ProLine Rocketry Sales & Support
    sales@prolinerocketry.com

    203.836.4014

    Ns Burned 2010 - 76,344
    Ns Burned 2011 - 93,595
    Ns Burned 2012 - 71,386
    Ns Burned 2013 - 63,463
    Ns Burned 2014 - 43,271

  8. #218
    Quote Originally Posted by GaryT View Post
    Dave:
    Yup I'll be at all three launches as well, Which launch are you planning to do your L3 at and what motor?
    I hope to do a shakedown flight on a K675-SK at NERRF with an L3 attempt with a M2250-CS at LDRS. I don't have my 75mm hardware yet.

    Curious, do you have a preference for piston or no piston on the Gizmo XL after flying both?
    L3 Certified
    NAR #90891, TRA #14994
    Clubs: CRMRC, METRA, MDRA

  9. #219
    Join Date
    25th August 2009
    Location
    Carol Stream
    Posts
    1,939
    Quote Originally Posted by DavieRockets View Post
    I hope to do a shakedown flight on a K675-SK at NERRF with an L3 attempt with a M2250-CS at LDRS. I don't have my 75mm hardware yet.

    Curious, do you have a preference for piston or no piston on the Gizmo XL after flying both?
    I would run some data (sims) on that K675. If yours comes out anywhere near the weight of mine, that will be a bit low on "umph" (no science behind that thought by the way). If you do fly it, let me know how it goes. I would love to know it can fly on things smaller than an L. (I have a 3 grain75 L Skid that I wanted to fly in mine, I think it's a bit underpowered for the 23 pounds......so did CTI)
    L3-TRA 12636
    QCRS BOD/Prefect. Princeton, IL
    TWA Bong, WI
    Chicago Rocket Mafia "The Hot Tub"
    Public Enemy Aerospace
    Beep-Beep-Boop-Boop

  10. #220
    Quote Originally Posted by GRIFFIN View Post
    I would run some data (sims) on that K675. If yours comes out anywhere near the weight of mine, that will be a bit low on "umph" (no science behind that thought by the way). If you do fly it, let me know how it goes. I would love to know it can fly on things smaller than an L. (I have a 3 grain75 L Skid that I wanted to fly in mine, I think it's a bit underpowered for the 23 pounds......so did CTI)
    I would in fact prefer an L motor for the shakedown. I was just looking at what I currently have and ran them through Rocksim. My estimated build weight without epoxy or paint is 22.9 lbs. This includes chutes, shockords, avionics, everything but the motor. At that weight rocksim shows 2600 feet on the K675 and 7320 feet on the M2250. A 3 grain 75mm L would be more appropriate for the shakedown. I'll run more sims as I get closer to launch time.
    L3 Certified
    NAR #90891, TRA #14994
    Clubs: CRMRC, METRA, MDRA

  11. #221
    Join Date
    25th August 2009
    Location
    Carol Stream
    Posts
    1,939
    Quote Originally Posted by DavieRockets View Post
    I would in fact prefer an L motor for the shakedown. I was just looking at what I currently have and ran them through Rocksim. My estimated build weight without epoxy or paint is 22.9 lbs. This includes chutes, shockords, avionics, everything but the motor. At that weight rocksim shows 2600 feet on the K675 and 7320 feet on the M2250. A 3 grain 75mm L would be more appropriate for the shakedown. I'll run more sims as I get closer to launch time.

    It's the speed leaving the rail that will be a bit "hairy" I think. Again. Let me know what you do, and post pics and vid.
    L3-TRA 12636
    QCRS BOD/Prefect. Princeton, IL
    TWA Bong, WI
    Chicago Rocket Mafia "The Hot Tub"
    Public Enemy Aerospace
    Beep-Beep-Boop-Boop

  12. #222
    Join Date
    25th August 2009
    Location
    Carol Stream
    Posts
    1,939
    Well, I flew it again. This time was AWESOME!!! a "clapping and cheering crowd pleaser"

    The central motor was a CTI 3 Grain 75 Vmax L3200 (lets all push Dr. J to cert this one)

    The outboards were going to be 2 single grain 38's (just for some smoke and noise)

    Wildman would not allow that. With lightly twisted arm, I picked up 2 6XL Skids (J520's)

    I air started the J's at 1.5 seconds after burnout. It was a nice delay in between motors and a real cool show. The bigger chute (Sky Angle CERT 3 L ) saved the fillets from cracking and the "Gary T" nose-ave bay- chute cannon worked like a champ.

    Here are some of the specs;

    Alt-7273'
    G's- 24
    MPH-516
    Main motor peak speed-438MPH
    1.5 second coast to - 345MPH
    Outboard boosted to - 514MPH+

    Next flight will be a "Jim Scarpine Trio" ....That's all Skids L820, 2 J520's all lit on pad.
    (Jim, That was an awesome flight in your Aquarius by the way)



    Attached Photo By David Reese.

    The rocket jumped off the pad so fast it caused "rail whip". The rocket is NOT weather cocking like the picture may look like.

    Video of the flight might just appear on the next JF Productions video
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    L3-TRA 12636
    QCRS BOD/Prefect. Princeton, IL
    TWA Bong, WI
    Chicago Rocket Mafia "The Hot Tub"
    Public Enemy Aerospace
    Beep-Beep-Boop-Boop

  13. #223
    Join Date
    26th February 2012
    Location
    Poultney , Vt
    Posts
    441
    The flame is twice a long as the rocket !!!!!

  14. #224
    Join Date
    16th January 2011
    Location
    Spring Green WI
    Posts
    1,315
    Hi Gary T
    Any news on the Performance Rocketry scale kits?? Any idea when they may be out?
    Thanks
    GP

  15. #225
    Here's a couple shots of my L3 flight at Thunderstruck. The CTI 2250 C-Star ripped off the pad so quick most of the photographers couldn't keep up with it. I can't wait to see the vidieo from Justin. The rocket got 8231', landed perfect.
    Click image for larger version. 

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    Click image for larger version. 

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ID:	78516

    Jenny

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