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Thread: balancing a bi-plane

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  1. balancing a bi-plane 
    #1
    does anyone know the formula for balancing a bi-plane? i used mr. robelen`s formula(Regarding the balance issue. Measure the chord (width) of the wing. Multiply that by .3, and use that as the distance back from the LE to balance the model.) but i ended up with way too much weight in the nose, it balanced, but it would never have flown.The model i`m trying to balance is a pitts s2a, it can be seen in the post your projects section of this forum. Any help would be greatly appreciated.


    this may not be the proper place for this subject but i would just like to express how much i like this site and it`s features, i found this site through a web search and i can`t tell you how invaluble the information on this site has been. when i first found this site , i had never flown before, since then i can honestly say that the experience(first flight) was aided by this site and it`s available information, i felt i had a definite advantage, real or perceived. I took the advise that was available on first timer flight( parked the bi-plane and got a trainer) very glad i did!!
    Finally, thanks to all that contribute to the forums. you help in ways you will probably never know................
     

  2.  
    #2
    Join Date
    10-05-2001
    Location
    Farmville, VA
    Posts
    2,291
    Hello rashadow,
    To find the desired balance point on your Pitts with the swept upper wing, start at a location 1/2 way out the upper wing. Measure from the leading edge of the upper wing to the trailing edge of the lower wing at this .5 span location. Take the total distance, multiply by .3, and measure back from the leading edge of the upper wing by this amount. This should be the location of the CG with an empty fuel tank. BTW, that is one lovely model. Even if it takes significant weight in the nose to balance a model, it is far safer than trying to fly it tail heavy.
    Regards, Dave
    Dave Robelen
     

  3. swept upper wing 
    #3
    thanks Dave, i really appreciate it. the model, although fine in appearance,doesn`t fly.I made some modifications to the plane that has had several unwanted effects( i guess you should not mess with an engineer`s work!!). the plane is so heavy when balanced correctly that it would take alot more motor than i presently have to get it off the ground! (290 cobalt brushed) unfortunatly i do not have an accurate scale YET!! so i can`t tell you exactly what it weighs in at when balanced(i`m guessing around 16 ounces) or slightly over a pound. it makes a great car but it`s not much of a plane!I went with a fma 20 amp esc (programable,so i could use lipo`s) a thunder power 7.4 v 1320 mah bat.and a futaba r156f for the receiver. I also added a servo to the ailerons to give me flaperons, all this seems to have made the plane a real brick!! i didn`t think the changes would have been that significant, i was wrong.i am presently in the process of moving every bit of weight i can move, forward including the battery and landing gear. i don`t know how much it will help but at this point i`m kinda at a loss for what to do..........perhaps a bigger heavier motor is in order...i`ll keep you posted, if nothing else , maybe it will make for a funny story someday.......
     

  4. Re-engineered 
    #4
    Dear Dave,
    Finished moving weight forward including ESC, bat, rec, and landing gear. It is not nearly as pretty as it was but it does balance. By moving these components I was able to loose approx. 8 oz of lead. Initial taxi tests indicate the plane is severely underpowered. WIll probably look into a new power plant. Any suggestions? Thanks for any info you can share.
    rahshadow.
     

  5.  
    #5
    Join Date
    10-05-2001
    Location
    Farmville, VA
    Posts
    2,291
    Hello rashadow,
    This size model is a bit out of my realm of experience. I have had excellent experience with the free download www.motocalc.com when it comes to matching models, motors, and batteries. This program is free for a trial period of 30 days, then you ante up or it goes poof.
    Regards, Dave
    Dave Robelen
     

  6. Talking thanks again dave 
    #6
    Thanks Dave, the program you suggested is exactly what i needed to answer all my questions, much appreciated!!

    Sincerly,
    rahshadow
     

  7.  
    #7
    Join Date
    11-25-2005
    Location
    Ft. Bragg
    Posts
    49
    Have you tried a 3 cell Lipo in it yet. my only electric plane right now is a modified Stryker(delta wing with ailerons).
     

  8. 3 cell lipo 
    #8
    hello, yes in fact i had to go from a 2cell 7.4v 1320 mah (wouldn`t support all 4 servos and the esc i wanted to run) to a 11.1v 2600 mah 3 cell lipo. i upgraded to 2 wing servos for flaperons, making the plane a 5 channel instead of a four channel. alot of work but worth it.thanks for the post let me know if i can help in any way, a friend of mine flys a stryker, says it`s a blast......sure looks fun!!
    keep your nose up!!
    rahshadow
     

  9.  
    #9
    Join Date
    11-25-2005
    Location
    Ft. Bragg
    Posts
    49
    I'm about to try to run a outrunner with a folding prop mounted to the nose. I'm tired of breaking motor shafts on my inrunner mounted in the back(20 bucks a shaft). I was going to mount the battery in the back to balance out the motor on the front. Any tips would be appreciated. Pack of choice is a 3cell 1500mah Lipo that also powers my blade cp.
     

  10. Bi Plane ballancing 
    #10
    Join Date
    06-29-2006
    Location
    Mexico City, Mexico
    Posts
    4
    Hello Rahshadow:

    Model Airplane News published a couple of articles on the subject of ballancing bi-planes, by Andy Lennon (1998?). Perhaps you can get them to post them on the web site for us.

    Regards,

    Javier
     

  11. Unhappy back issues 
    #11
    Hello everyone
    As far as getting ahold of the person that could help post a back issue, or any article contained within, i`m sorry to say i`m at a loss.
    Perhaps Dave Robelen could help? I myself am not affiliated with any magazine or website persay, i simply post here because it`s the most informative forum i could find on the web. And the help (I) you receive here is curtious and helpful. Answers to all your questions at your fingertips!!!
    What a great time to be alive!!


    Keep your nose up!!
    Rahshadow
     

  12. thats great 
    #12
    hi guys

    Iam thankfull for the suggestion on balancing topic, i got lots of help from the discussions.Thnx

    Regards
    Chronis Tsempelis
    Marketraise Corp.

    Suite 200 and 400,
    41-A East Merrick Rd.,
    Valley Stream,
    NY 11580
    Cell: 516-398-0996
    Tel: 516 887 1929.
     

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