Register

If this is your first visit, please click the Sign Up now button to begin the process of creating your account so you can begin posting on our forums! The Sign Up process will only take up about a minute of two of your time.

Results 1 to 19 of 19

  1. #1
    bcovish's Avatar
    Join Date
    Feb 2002
    Location
    Austin, TX
    Posts
    4,710
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    CG'ing A Large Jet

    Need to help someone CG a large Jet. Need some ideas on how to do it. The plane is a little over 11 ft long and weighs in the 50+ pound range.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Wu60122.jpg 
Views:	4 
Size:	77.6 KB 
ID:	1804248  
    Bob-O
    I Crashed All My Planes, Can I Fly Yours

  2. #2
    invertmast's Avatar
    Join Date
    Dec 2003
    Location
    North Port, Fl
    Posts
    6,837
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    Bob,
    Normally I just weight the models and do some math Calc's per full-scale weight and balance methods to get the CG. I have sort of a "beta" spread-sheet I have been workin on for a few months that I can send you if you PM me your email address.

    Thomas
    Thomas W.
    Euro-sport Evo, Scratch built 1/7 F-14D Tomcat, 26.5% Gee Bee R2

  3. #3
    bcovish's Avatar
    Join Date
    Feb 2002
    Location
    Austin, TX
    Posts
    4,710
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    pm sent
    Bob-O
    I Crashed All My Planes, Can I Fly Yours

  4. #4
    Eddie P's Avatar
    Join Date
    Feb 2003
    Location
    Reno, NV
    Posts
    1,632
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    She's a beauty, love that paint job - perfect for it!
    Freedom is Flying

  5. #5
    wojtek's Avatar
    Join Date
    Dec 2001
    Location
    nj, NJ
    Posts
    4,073
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    I would string it up from a pulley (fore aft). Drop a plumb bob straight down from the pulley. when you tilt the plane to a level 0-deg incidence attitude, the plumb bob will be directly over the CG ... adjust weight distribution from there until you can get the plumb bob to hang directly over the CG ..


    all the best,


    ~V~
    www.facebook.com/allscale
    http://www.all-scale.com

    - working model MFD & HUD, 3D design & printing, CNC, Laser-cutting
    - Professional-Building
    - Metal-Morph Plating
    - CARF-Models Dealer

  6. #6

    Join Date
    Dec 2004
    Location
    Lisbon, PORTUGAL
    Posts
    992
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    Hi

    Does it matters where you string it in the for and rear position? Also I guess the lenght of the cable should be the same in both parts, right?

    The plane is beatifull. Is it a Airworld F5?

    Regards

    Nuno

  7. #7
    bcovish's Avatar
    Join Date
    Feb 2002
    Location
    Austin, TX
    Posts
    4,710
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    It's from Tomahawk
    Bob-O
    I Crashed All My Planes, Can I Fly Yours

  8. #8
    Henke Torphammar's Avatar
    Join Date
    Oct 2002
    Location
    Ljungby, SWEDEN
    Posts
    1,662
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    You can build a jig like this one in any size, or buy the finnished product in any size from HAB Electronic.

    /Henke
    www.youtube.com/henke2
    Ready2fly Yak-130 "Mitten", Lambert Kolibri T35 - Пенопласт летчик-истребитель

  9. #9

    Join Date
    Jan 2002
    Location
    Fayetteville, GA
    Posts
    93
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    Bob, check the JPO site at http://www.jetpilots.org/index.htm Go to members/weight and balance.
    Keith developed a spread sheet for use with scales complete with instructions. In addition, there are
    spreadsheets for some popular models already filled in with the distance measurements.

    Joe
    Team Horizon, BVM

  10. #10
    S_Ellzey's Avatar
    Join Date
    Aug 2002
    Location
    Grand Prairie, TX
    Posts
    493
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet


    ORIGINAL: bcovish

    Need to help someone CG a large Jet. Need some ideas on how to do it. The plane is a little over 11 ft long and weighs in the 50+ pound range.
    I did an artical in Contrails some years ago on how to do this using a scale. The artical even has pictures of this being done using the scales I borrowed from you. :-)

    Steven

  11. #11
    Erik R's Avatar
    Join Date
    Jan 2002
    Location
    Fogelsville, PA
    Posts
    953
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    Bob,

    I have had good luck with this.A little pricey,but worth it in the long run.Good luck,

    Erik


    http://dreamworksrc.com/catalog/ez-b...ii-p-1415.html

  12. #12
    lov2flyrc's Avatar
    Join Date
    Dec 2001
    Location
    Daytona Beach
    Posts
    5,925

    RE: CG'ing A Large Jet

    THIS makes it a breeze!
    Todd Witkoff
    Dreamworks Model Products LLC
    www.dreamworksrc.com
    Your Source For RC Jet Accessories!

  13. #13
    bcovish's Avatar
    Join Date
    Feb 2002
    Location
    Austin, TX
    Posts
    4,710
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    Thanks guys. Will give it go on trying to get it done.

    To answer a couple of the pm's that I received and as most of you probably know the F5 belongs to Scott Marr. Its a good thing that he has a 31ft trailer to haul things around. We will have it full for the trip to Best in the West next month. It's a good thing that I wasn't planning on taking my Boomerang to the event. Let's just say that the Boomer had 503 flights on it but there will not be flight number 504
    Bob-O
    I Crashed All My Planes, Can I Fly Yours

  14. #14
    geh3's Avatar
    Join Date
    Oct 2003
    Location
    wilmington, DE
    Posts
    1,332
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    I take the mfg recommended CG and put a mark on the side of the fuse where the wing joins
    this is typically at the front of the main spar for example. Then I get a strong cord and drape it under the fuse
    and up across the marks so it sticks up when the wings are attached. Then by lifting this cord with a simple set of pullys,I can determine
    exactly what weights etc has to be added and where it has to be added to make the plane sit exactly level while suspended on the strings.
    This only costs the price of the string and 2 small pulleys. MOST of the time CG is achieved by careful placement of running gear and batteries
    Sometimes small weights have to be added however. This method is very accurate.
    WREN TURBINES USA...GO GREEN!
    ALSO SEE: http://www.rcaircraft-specialties.com/

  15. #15
    wojtek's Avatar
    Join Date
    Dec 2001
    Location
    nj, NJ
    Posts
    4,073
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet


    ORIGINAL: jetnuno

    Hi

    Does it matters where you string it in the for and rear position? Also I guess the lenght of the cable should be the same in both parts, right?

    The plane is beatifull. Is it a Airworld F5?

    Regards

    Nuno
    it wont matter where its strung up, when level it will always hang directly under its CG .. with its weight wanting to find center, this will end up always directly under the pulley. The plumb bob is just a pointed that's always paralel with gravity


    ~V~
    www.facebook.com/allscale
    http://www.all-scale.com

    - working model MFD & HUD, 3D design & printing, CNC, Laser-cutting
    - Professional-Building
    - Metal-Morph Plating
    - CARF-Models Dealer

  16. #16
    DelGatoGrande's Avatar
    Join Date
    Mar 2004
    Location
    ATHENS, , GREECE
    Posts
    2,606
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    most "realtime" and ACCURATE way: hung it with cables from the wing tube,or where cg should be .Look it from the sides and add weight till it gets level .You are done..

    LOW WING AIRCRAFTS MUST BE BALANCED UPSIDE DOWN (L39 photo)

    my 2c

    Best Regards George
    www.rcjet.gr \"props are for boats\"

  17. #17
    David Gladwin's Avatar
    Join Date
    Feb 2002
    Location
    CookhamBerkshire, UNITED KINGDOM
    Posts
    3,014
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    Easy and accurate C of G calculation:

    Place model nose against wall, measure the distance of each wheel axle, main and nose, to wall. (you can use any other datum point you wish but a wall is often convenient) Place scales under each main wheel in turn and pack up nose so that the machine is level, note weights.

    Then measure weight on nosewheel.

    Multiply TOTAL weight on main wheels by distance from wall or other chosen datum. Moment A.
    Multiply weight on nose gear times distance from wall or datum. Moment B.

    Add A + B to obtain total moments.

    Divide value of A+B by TOTAL weight and that will give you exact distance of C of G from wall or chosen datum. eg nose.

    To adjust, I tape a paper cup to nose or tail and add fishing weights to get C of G exactly correct.

    Easy , quick, accurate and free, can easily be done by one person, and prevents hernias. Works on 747s too, (which are NEVER inverted !) honest !

  18. #18

    Join Date
    Jan 2002
    Location
    Everett, WA
    Posts
    36
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    Here is another method similar to Mr. Gladwins method.

    Remember that if you have to add weight to achieve balance, it would be an interative process.

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Ec87443.jpg 
Views:	7 
Size:	62.4 KB 
ID:	1804841  

  19. #19
    dbsonic's Avatar
    Join Date
    Oct 2005
    Location
    san jose, CA
    Posts
    516
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: CG'ing A Large Jet

    As some have elluded to, with full size aircraft it is done with scales and not outside, but in a hangar. You dont want wind messing up the readings. However it is important to set the attitude correctly to get an accurate measure. Sometimes the manufacturer will describe a wedge be created and placed on the fuselage with which you use to level by placing blocks under nose or tail wheel.
    P-40 Brotherhood #112


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
All times are GMT -6. The time now is 08:08 AM.

SEO by vBSEO 3.6.1 ©2011, Crawlability, Inc.