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Author Topic: How does one determine the balance point of a c/l airplane?  (Read 1739 times)

Offline frank mccune

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How does one determine the balance point of a c/l airplane?
« on: July 26, 2013, 06:45:23 PM »
      Hi Folks:

     I recently picked up a Lieutenant airplane and I am wondering where should I balance it.  Right now, it balances at about the high point of the wing or almost one half of the chord.  Since it is similar to a Magician, perhaps it should balance farther forward on the wing.  The Magician balances at the spar or about 25% of the wing chord.

   The previous owner could not get it to fly with an older O.S. .30 or .35.  It was very unstable in flight.  Perhaps tail heavy? He had a difficult time doing the pattern as he complained that the maneuvers were quite large.

   This airplane has an elliptical shaped wing a la Spitfire.  Would this change the C/G?  The moments are about the same as the Magician.  If I get it balance where the Magician balances, I need about a 14 oz. engine.

    This is a great looking airolane and I would like to get it to fly well!

    The engines that I have to try include:

    Fox .36

    Fox .40 Stunt 1972

    O.S. .40S

    O.S .40 LA and FP

    S.T. .49 Sport

    S.T. G21/.46

    Any suggestions?

                                                                                                          Tia,

                                                                                                          Frank

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Online Trostle

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Re: How does one determine the balance point of a c/l airplane?
« Reply #1 on: July 26, 2013, 09:37:51 PM »
Quote from: frank mccune on July 26, 2013, 06:45:23 PM
      Hi Folks:

     I recently picked up a Lieutenant airplane and I am wondering where should I balance it.

     Any suggestions?
                                                                                                                                                                Frank

The Lieutenant has a straight LE.  The TE is "somewhat elliptical with rounded tips.  Neither the plans nor the magazine article (see my response to your other question on the Lieutenant above) mentins anything about the balance point.  This is a flapless airplane.  A "safe" CG for your initial flights would be no further back than 20% of the average chord.  (We could insist on the thing called the mean aerodynamic chord, but this 20% of the average chord will get you started safely.)  From the magazine plans, the root chord is about 13".  Given the swept forward nature of the TE of that airplane, you definitely do not want the balance point to be further aft than 2.5" from the wing LE.  A better CG location would probably be somewhere between 1.5 and 1.75" from the LE.

Keith
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Offline Tim Wescott

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Re: How does one determine the balance point of a c/l airplane?
« Reply #2 on: July 27, 2013, 06:40:50 AM »
What Kieth said about balance point.

It sounds like the plane is about the right size for one of your OS or ST 40's.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline frank mccune

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Re: How does one determine the balance point of a c/l airplane?
« Reply #3 on: July 27, 2013, 06:43:59 AM »
     Hi Guys:

    Thanks for the help!


                                                       Frank

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Offline frank mccune

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Re: How does one determine the balance point of a c/l airplane?
« Reply #4 on: July 27, 2013, 07:46:15 AM »
    Hi Keith and Tim et. al.:

    With my heaviest engine, O.S.40 LA with muffler, the balance point is 3" behind the leading edge. 

     How can this plane be so tail heavy? I have always built nose heavy planes that flew very well.  This one has me stumped!  I can not see this plane flying  well with a 14 oz. engine.  I think that the wing loading would become too high for good flight.

      The builder must have used a very heavy wood or metal for the fuselage and tail feathers!

      Any more suggestions? Can you say wall hanger?

                                                                                                        Tia,

                                                                                                        Frank

     
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Online Brett Buck

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Re: How does one determine the balance point of a c/l airplane?
« Reply #5 on: July 27, 2013, 11:29:14 AM »
Quote from: frank mccune on July 27, 2013, 07:46:15 AM
   Hi Keith and Tim et. al.:

    With my heaviest engine, O.S.40 LA with muffler, the balance point is 3" behind the leading edge.  

     How can this plane be so tail heavy? I have always built nose heavy planes that flew very well.  This one has me stumped!  I can not see this plane flying  well with a 14 oz. engine.  I think that the wing loading would become too high for good flight.

      The builder must have used a very heavy wood or metal for the fuselage and tail feathers!

      Any more suggestions? Can you say wall hanger?

     Lots of airplanes are like that. A former flying buddy of mine once build a Barnstormer that required *6 oz* of lead in the nose to balance. If the airplane it heavy it tends to also get tail-heavy because almost all the parts are behind the desired CG.

    MY suggestions - put in the best engine that will fit, add whatever weight it takes to get it to balance where Keith says, then fly it. People worry far too much about weight and give up too quickly. Maybe it won't be any good and then hang it up, but don't quit before you try it.

     Brett
« Last Edit: July 27, 2013, 03:10:01 PM by Brett Buck »
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Offline frank mccune

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Re: How does one determine the balance point of a c/l airplane?
« Reply #6 on: July 27, 2013, 01:53:31 PM »
    Hi Brett:

    Thanks for the tip!

    I think that I am going to start forming some wheel weights to form an air intake for the nose of this plane similar to a P-40 Warhawk! Lol

                                                                                                     Stay well.

                                                                                                     Frank
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Offline frank mccune

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Re: How does one determine the balance point of a c/l airplane?
« Reply #7 on: July 28, 2013, 06:29:24 PM »
    Hi All:

    I think that I have solved the problem! I have a ST .49 RC engine that has venturi and a ST n.v.a. that balances the plane! This is the Lieutenant that is so tail heavy!

   This engine is one of those "Sport" engines with the huge head and a single ball bearing.  If I need more weight, I will add the huge muffler! Lol  The engine alone weighs 12 oz.

                                                                                                   Stay well,

                                                                                                    Frank
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