Quantcast
3 fins and a nose cone...

BuyRocketMotors.com Giveaway!



Results 1 to 7 of 7
  1. #1

    3 fins and a nose cone...

    hi everyone, i'm new here, (not to rocketry) and i am about to start on my "3fnc" build. a quick check with openrocket says its a go, but im not so sure, and dont know what to do about the recovery system in the small amount of space. help would be great, especially if you have done something similar. thanks
    Attached Files Attached Files

  2. #2
    Join Date
    16th August 2011
    Location
    Edmonton, Alberta, CANADA
    Posts
    2,912
    Well, It certainly is interesting! Kudo's for originality!

    I did a simulation with Altitude/total Velocity/vertical orientation and it did some "interesting" things: It appears to go into a tumble after about 4 seconds from Engine Burnout.

    My simulation parameters:

    Wind: 7.2 km/hr
    Wind deviation:1.2 km/hr
    Launch site elevation from sea level: 670 metres
    Launch rod length: 1.3 metres
    Launch rod angle: 1 degree
    Direction of launch rod in relation to wind: 180 degrees (tilted with the wind)
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Original Flight simulation.jpg 
Views:	39 
Size:	84.5 KB 
ID:	57738  
    Plays with wood, cardboard, and carpenters glue at home.

    "We have done the impossible and that makes us mighty"
    -rocketeers vs. BATF

    Ego intentio parumper perficio fuga , tamen Ego peto a perficio reverto.

  3. #3
    Join Date
    21st February 2011
    Location
    Tuleta, Tx
    Posts
    4,417
    I'm thinking rear ejection with a streamer or chute wrapped around the motor tube. Change the parameters of your fins to 3/32 rounded balsa and that will lighten up the rear a bit. That should help the CG some. Check your parameters on the nose cone and tubes as well. The overall weight seems a little bit high to me. Move your LL to about 14 degrees radial. I would also add a forward centering ring. You may still need a 1/4 ounce of clay in the tip.


    Very cool design. I've done a few of these in MMX scale for spot landing comp.
    Jeff Vegh
    TRA# 03011
    NAR# 92403

  4. #4
    Join Date
    16th August 2011
    Location
    Edmonton, Alberta, CANADA
    Posts
    2,912
    Here's just a thought here. Still in the spirit of a very short rocket, but considerably more stable and higher flying.
    Attached Files Attached Files
    Plays with wood, cardboard, and carpenters glue at home.

    "We have done the impossible and that makes us mighty"
    -rocketeers vs. BATF

    Ego intentio parumper perficio fuga , tamen Ego peto a perficio reverto.

  5. #5
    Join Date
    26th January 2010
    Location
    Northern California
    Posts
    10,654
    It looks to me like you just need to add a 1/2 ounce of nose weight to it.
    NAR 91107, Level 2

    PC's are more frustrating than paint.

  6. #6
    Join Date
    21st March 2011
    Location
    central America
    Posts
    1,020
    In my experience, it's a little light in the nose. OR says about .5 calibers stability. What I would do, is to glue a spent engine casing in the nose. The "inner tube" (as OR calls it) would slide over this. I would use a (flame-proof) streamer wrapped around the base of the inner tube as recovery. The engine casing in the nose (maybe a little extra epoxy...) will add weight and serve as a piston and protect the inside of the nose cone. I did something like this with my egg rocket (casing acrually fit *over* engine tube in egg). Also - you may experience tumbling just after thrust ends. I've seen several "odd ball" rockets that were stable under thrust, but tumbled before ejection (examples are the egg rocket, and some spools). Here's the insides of the egg...
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	egg1.jpg 
Views:	45 
Size:	22.5 KB 
ID:	57782  
    [ This Space For Rent ]
    [ Inquire Within ]


  7. #7

    Smile

    Wow, thanks for all the help. I did plan on adding a bit of weight to the nose, and now I just have to figure out some type of ejection method, probably piston/ streamer as sooner.boomer suggested. Will post pictures when finished.
    i love the Comanche-3.

    its the awkward moment when a sentence doesn't end the way you octopus it would

    Why is lemon juice made with artificial flavor, and dishwashing liquid made with real lemons?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •