Wildman Rocketry Giveaway!


Results 1 to 29 of 29

Thread: Grid Fins

  1. #1
    Join Date
    20th January 2009
    Location
    Williamsburg, VA
    Posts
    482

    Grid Fins

    Anyone tried to model grid fins?

    http://en.wikipedia.org/wiki/Grid_fin

    If so, what material(s) did you use and how did you attach them to the airframe?

    Tim Wilson

  2. #2
    Join Date
    18th January 2009
    Location
    Southeastern PA
    Posts
    4,022

    Re: Grid Fins

    I've never heard of the term or seen such fins. It's a very interesting concept, and I'd really like to know if anyone used these before.

    Josh

  3. #3
    Join Date
    18th January 2009
    Location
    Virginia - Central
    Posts
    2,722

    Re: Grid Fins

    Quote Originally Posted by wilsotr View Post
    Anyone tried to model grid fins?

    http://en.wikipedia.org/wiki/Grid_fin

    If so, what material(s) did you use and how did you attach them to the airframe?


    Oh yeah...seen 'em.

    And as soon as someone tells us how to do that eggcrate thingy 4x......I can build that Soyuz conversion for that Cosmodrome Vostok.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Sojus_100_Farbe-vorn.jpg 
Views:	112 
Size:	21.3 KB 
ID:	233686   Click image for larger version. 

Name:	Image-F1A5CBF2C7BE11D9.jpg 
Views:	78 
Size:	95.5 KB 
ID:	233687  

  4. #4
    Join Date
    18th January 2009
    Location
    Merrimack, NH
    Posts
    15,299

    Re: Grid Fins

    We have a CMASS club member who flew that very configuration this past year. It worked quite well as I recall.

    Not sure if he is on TRF or if one the other CMASS members knows more...

  5. #5
    Join Date
    18th January 2009
    Location
    Virginia - Central
    Posts
    2,722

    Re: Grid Fins

    the real thing.....
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	SoyuzTransport.jpg 
Views:	101 
Size:	35.4 KB 
ID:	233688   Click image for larger version. 

Name:	jsc2006e11350-lowres.jpg 
Views:	120 
Size:	34.5 KB 
ID:	233689  

  6. #6

    Red face Re: Grid Fins

    Our own Cesaroni Tech has experience with these grids fins.
    watch the flash based intro ad at:

    http://www.cesaroni.net/index.php

    it shows a grid fin rocket booster

    terry dean
    nar 16158

  7. #7
    Join Date
    18th January 2009
    Location
    west Ft Worth
    Posts
    7,361

    Re: Grid Fins

    The Russians have used grid fins on a variety of air-air and air-surf weapons for some time now.
    Knowing a little about how they do things, I can tell you that they would not be using these fins if they did not work well.
    Grid fins are starting to show up in lots of places now....
    This is the country that built the transcontinental railroads, the Hoover dam, the Panama canal, coast-to-coast interstates, and put men on the moon....but we can't build a fence.

  8. #8

    Re: Grid Fins

    Very timely post, I been thinking about doing a rocket with some now for a few months since seeing the concept. I planned on using plastic egg crate available at a local hardware store.

  9. #9

    Re: Grid Fins

    The MOAB is probably the best known Western interpretation of the Grid Fin, but the Soyuz stole the concept from the N1, which makes perfect sense given Russia's penchant for continuing to use a technique thats proven to work. (The grid Fin NOT the N1) 8)

    Grid Fins are used to change course, given their lack of torque when required to alter a missile/rockets course.

    So, heres the million dollar - or 2 cent question - your choice...

    Do you plan to build and test a design with Grid fins, using them in a regular - on axis configuration - instead of using them in their proper setup as control fins?

    I ask because about 8 years ago, the Scale freak came out in me and though my current work is on a high detail project - W.A.S.P., I've been studying these fins and have discovered they can be a fantastic alternative to traditional fin designs. No, I've not boilerplated a design yet, but have some links I can provide with more data for your perusal.

    The following pdfs give a detailed subsonic study on these fins, and perhaps will raise more questions, but they are a fantastic read:

    http://www.fluent.com/solutions/articles/ja136.pdf
    http://www.zju.edu.cn/jzus/2005/A0507/A050722.pdf

    This pdf is the most detailed, but also has great info.

    http://handle.dtic.mil/100.2/ADA383925

    I'm still searching for a document entitled "Grid Fins - A new concept for missile stability and control", by W. D. Washington, U.S. Army Missile Command, Redstone Arsenal, Alabama. It was presented at the 31st Aerospace Sciences Meeting & Exhibit. Jan. 11-14, 1993.

    It is directly referenced in a current patent approved in 1997 entitled:

    "Aerodynamic lifting and control surface and control system using same" by Ralph H. Klestadt. The full text of his patent can be found here:

    http://www.patentstorm.us/patents/5642867-fulltext.html

    Free membership is required to view the images included in the patent, but essentially Mr. Klestadt's patent is for an aerodynamic lifting and control surface comprising a wrapped grid fin for use with an aerodynamic vehicle. His idea will allow the fins to fold around the body of the vehicle to provide for a compact storage arrangement. (A little more research shows that Mr. Washington received a patent for a similar design some 7 years previous to Mr. Klestadt.)

    I digress....

    The problem that these fins have when used - as discovered after research at Eglin AFB in Florida, is they can cause excessive drag at Transonic speeds. So, while these would be a seemingly acceptable change from the normal fin on lower powered flights, I'd be hesitant to accept them as a clear choice on HP flights that are designed for high altitude attempts.

    More research to follow and once I get moved into the new house, I can start boilerplating some models to test this idea.

    Cheers,

  10. #10

    Re: Grid Fins

    Just found a bit of info on Mr. Washington's original 91 patent - with images at the same site linked above. A snippet of his idea:

    Accordingly, it is an object of this invention to provide a grid fin that is non planar and has open or porous structure.

    Another object of this invention is to provide a curved grid fin that is contoured to conform to the outer shape of a missile body to enable the fin to be stored within a portion of the missile body.

    Still another object of this invention is to provide a fin that has the ability to develop lift for stability when set at incidence and aligned perpendicular to the air flow direction.

    A still further object of this invention is to provide a curved grid fin that can be used as a drag brake on a missile.

    Lastly, hers another link with a bit more info, and pretty pictures.8)

    http://www.aerospaceweb.org/question...ns/q0261.shtml

    Cheers,

  11. #11

    Re: Grid Fins

    For starters, I plan to mount them as depicted--with the grid parallel to the airstream flow and the containment box normal to the airframe. They are begging to be made detatchable. One thought here that wouldn't require any specialized machining or assembly would be to use a CF tubular spar that runs down the center of the fin in lieu of the center plate and which ends in a rail button. The airframe would have attached at the motor end short "rail" segments that provide a sort of dovetail fit so that the fins would just drop into place. A bottom stop on the rail to keep them from falling out--a short screw that prevents forward motion could be used, but I'm guessing would be unnecessary as drag would provide a downward directed shear force at all times.

    Short of that, the innermost member could be cutaway and replaced with say 30 degree segments of FG reinforced body tube scrap and just glued to the AF. Along these lines a cool app would be to build a very short airframe say an inch long with the grid fins, and use it for CHAD staging. Just slip it over the motor hanging out the aft end and use masking tape above and below to keep it from moving.

  12. #12
    Join Date
    18th January 2009
    Location
    Maryland
    Posts
    9,447

    Re: Grid Fins

    Cool thread, guys! denverdoc, I'm anxious to see how your project progresses.

    My kludgey mind immediately thought of the plastic lattice from a fluorescent light. Not very sturdy, but if you had a supply and made the fins replaceable.....

    (For small versions only, of course.)
    Dick Stafford
    The Original Rocket Dungeon
    Volunteer compiler of product news for ROCKETS Magazine

  13. #13

    Re: Grid Fins

    Quote Originally Posted by rstaff3 View Post
    Cool thread, guys! denverdoc, I'm anxious to see how your project progresses.

    My kludgey mind immediately thought of the plastic lattice from a fluorescent light. Not very sturdy, but if you had a supply and made the fins replaceable.....

    (For small versions only, of course.)
    Just what I had in mind--cheap and easy to cut. Maybe FG the outside of the box..

  14. #14
    Join Date
    18th January 2009
    Location
    Maryland
    Posts
    9,447

    Re: Grid Fins

    I'll have to go dumpster diving
    Dick Stafford
    The Original Rocket Dungeon
    Volunteer compiler of product news for ROCKETS Magazine

  15. #15
    Join Date
    20th January 2009
    Location
    Williamsburg, VA
    Posts
    482

    Re: Grid Fins

    [QUOTE=rstaff3;507082]My kludgey mind immediately thought of the plastic lattice from a fluorescent light. Not very sturdy, but if you had a supply and made the fins replaceable.....
    QUOTE]

    Hmmmm ... a single fluorescent light panel would make a lot of grid fins. Gonna have to make a Lowe's run, I guess .....
    Tim Wilson

  16. #16
    Join Date
    29th January 2009
    Location
    Winnipeg, Canada
    Posts
    92

    Re: Grid Fins

    Does anyone have an explanation as to why these grid fins work so well and how would you simulate them in VCP or Rocksim etc.

  17. #17

    Re: Grid Fins

    Nick,

    As you may have read, these aren't your standard fin that we would normally use in our hobby, but are used as a braking/control system to alter course of a missile on its downward/target seeking cycle. It also allows the missile - in this example an air-to-air missile system - to have a tighter turning radius for a target that is highly maneuverable.

    Each fin has its own hinge/actuator network system, and when the missile launches they lay up against the body and only when needed are they dropped down into position. When this happens, they break up the airflow, and offer an advantage over conventional controls. They increase drag at Higher mach numbers (0.5 to 3.0) and give the ground station/computer more control over the missile than traditional methods.

    Currently a ton of research is being conducted - simulation, analytical, wind tunnel testing, and real world launches - all in the hopes that this system can be used.

    As to these fins being simmed - I'm not sure if its possible at this time with Rocksim - but perhaps Bruce Levinson or another of the Rocksimaholics can give you a better quantified answer than I.

    If you find out - or if one replies here, I'd be very interested in knowing if its possible.

    ******
    What I theorize is that these MAY work as an alternative to a standard on axis rocket fin, meaning that instead of a solid balsa fin - a lattice network fin might help guide the rocket the same way a standard fin does.

    I'm not sure at this stage if they have enough of a "lifting body principal/profile" to replace our standard fin, but its worth a closer investigation.

    Hmm, perhaps I have something that I can write up for my thesis...

  18. #18

    Re: Grid Fins

    Unless I miss my guess, there should be very little problem with using these up to transonic speeds. When deployed they likely function in pretty much the same manner as a conventional planar fin--by providing lift at a non zero angle of attack. That there are many parallel high aspect ratio "finlets" is actually advantageous in the sense that the Lift/Drag ratio is much better than a conventional low aspect ratio fin, and may account why their performance is comparable--at least at low speeds. Its not a lot different than using say a dozen equally spaced wing shaped fins around the AF, except that the grid design provides great structural rigidity that you would never see if you tried attaching high aspect ratio fins--they would likely flutter off in nothing flat.

    Where they have issues is the increased number of shock waves forming at the leading edge of each strip as mach is approached. So instead of 3 shock waves, one has 3 dozen! This causes a huge hit in the drag department. Other than that, and the T tail like equivalent shape built into each fin, the principles are not much different from planar fins--at least thats my read. As always I reserve the right to change my mind when confronted with real data.

  19. #19
    Join Date
    20th January 2009
    Location
    Williamsburg, VA
    Posts
    482

    Re: Grid Fins

    Quote Originally Posted by Silverleaf View Post
    Do you plan to build and test a design with Grid fins, using them in a regular - on axis configuration - instead of using them in their proper setup as control fins?
    Nope ... they would be installed perpendicular to the flow as they are on missiles and the Russian Soyuz launch escape system. One of the advantages of such fins is the convenient way they can be folded against the airframe for in-flight deployment ... I suspect that's why the Russians chose them for the Soyuz LES and ICBMs, many of which are silo-launched.

    I have a scale application in mind, but it seems that fold up option would be useful for a sustainer. You could fold the fins against the upper stage airframe and slide the whole thing into the booster, then deploy at separation.
    Tim Wilson

  20. #20
    Join Date
    18th January 2009
    Location
    Maryland
    Posts
    9,447

    Re: Grid Fins

    Just like the FlippiTwin. That would be neat.
    Dick Stafford
    The Original Rocket Dungeon
    Volunteer compiler of product news for ROCKETS Magazine

  21. Re: Grid Fins

    I know I've seen something over on EMRR that used the fluorescent light grid for fins, but I can't find it. Thought it was a DESCON entry, but I may be wrong.

    kj

  22. #22

    Aero breakers on Soyuz rockets are NOT fins !!

    Hello,

    The big four squares with the metal grid are not fins, but aero breakers.

    In case of an emergency, the top half of the white fairing with the soyuz
    capsule still inside, is pulled away by the big four red thrusters. The smaller
    ones in between them are for directional control. The big four aero breakers
    open and stabilize the capsule.
    As soon as the big thrusters finish burning ( about 5 seconds ) , a few seconds later
    the smaller rockets on top ignite and pull away the white fairing from the
    capsule.
    When the two have separated enough, the manned capsule separates from the
    rest and the parachute deployes, providing a safe landing for the 3 men
    inside, who may still be unconsious from the sudden 12 to 17 G blast, generated
    by the big four thrusters.

    Who said space flight was not exiting ??? ;-)


    If you want to build a similar grid and use them for fins, you might want to
    reconsider, because the accuracy you need is close to extreme.
    ALL metal strips have to be aligned perfectly along the rocket's axis.
    1 degree off and the fins will work as a aero breaker instead of a fin.....!!!

    Having that said, the Russian aero breakers are tilted down about 15
    degrees. The open mesh provides enough resistance to maintain stability
    and the right amount of decelleration.


    Erik.


    p.s. To this day, this escape system has only been used once, for real,
    Soyuz T-10, 1983.

  23. #23

    Re: Grid Fins

    I had e-mailed TIm at Apogee back in 2005-06?, about simulating grid fins on Rocksim. I wanted- er- stll might workup a Tochka missile. ( I forgot the NATO designation) TIm had advised me to figure up the overall frontal surface area of the grids, and simulate a big fat fin of that meaurement, with the actual depth. (length) Of course, I usualy find with my toys, it pays to just do the twirly round on a string thing.

    I like the Flourescent light grid idea- so much I may actually cheat and use it, instead not making a pattern for cardstock! NOT!!

    AX'E

  24. #24
    Join Date
    18th January 2009
    Location
    Maryland
    Posts
    9,447

    Re: Grid Fins

    That might be an approximation, however, I bet the induced base drag plays a big factor. From what I've read they act like solid plates at Mach rates and will probably cause a lot of drag at lower speeds. I saw a recent journal reference but could only get to the abstract.
    Dick Stafford
    The Original Rocket Dungeon
    Volunteer compiler of product news for ROCKETS Magazine

  25. #25

    Re: Grid Fins

    I've sen exactly that in my studies/reading. They were used for lift-off, trans-sonic, and then ejected?
    For low powered rocketry, though, I think they'd bean interesting addition, especialy if used on a 2 stage, as the lower stage fin? Eh- Somethingtothink about anyway- and almost totally unique in model use.

    AX'E

  26. #26

    Re: Grid Fins

    I was wondering about this when I first saw the "Canadian Arrow" X-Prize entry - that has these on its second stage.
    Grif

  27. #27

    Re: Grid Fins

    Quote Originally Posted by rstaff3 View Post
    That might be an approximation, however, I bet the induced base drag plays a big factor. From what I've read they act like solid plates at Mach rates and will probably cause a lot of drag at lower speeds. I saw a recent journal reference but could only get to the abstract.
    Dick,

    From what I could glean wading thru all the references, it looks like at subsonic, they are not bad, and at Mach2.5 in theory almost comparable to planar fins--provided they are tapered from root to tip. Otherwise they can be almost twice as draggy. Another interesting finding from the Chinese paper, is that the box thickness is much more important in terms of thickness wrt drag than the web members. Transonic is the biggest issue owing to choked flow--and behaving as you say.
    J

  28. #28

    Re: Grid Fins

    I have worked on a design for grid fins for a 'real' application (real = rent paying) at work. There were a few advantages to the grid fins for a missile or smart bomb application. The advantages were primarily that you can fold the fins against the body of the missile/bomb, and the torque required to actuate the fins is less than a conventional design.

    One of the disadvantages is the transonic drag, all of those intersections get really messy trans sonic. The attachment is also a bit more difficult in that there is a point load that sees bending (remember these are typically used with an actuator that wants a single attach point.

    Having said all that, I'm thinking of using them on a triangular body rocket with flat sides. This makes the mounting much simpler. I plan to make the fins out of graphite in a long section and then 'slice them' like cutting bread. It helps that I have a large band saw set up for cutting graphite composites.

    I plan to have the fins on hinges that allow them to fold flat along the rocket after the parachute deploys.

    Or i could do something that takes half the effort, works better, and avoids the 'told you so' if it doesn't work, but what is the fun of that....

  29. #29

    Re: Grid Fins

    This place is weird for sure - or rather it is me...

    I dreamt about grid fins last night!

    (I spent too much time on here!)

    They were mounted onto a rocket that looked a bit like the Big Bertha "Ares" rocket (can't find that thread right now though) and needess to say they worked great...

    Interesting thing was that they, once the rocket had gained enough speed to be drag stabilized, they folded up against the fuselage.

    Weird dream...

    (Yep, I spend WAY too much time on here! )


Posting Permissions

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