CG location vs total weight

[Xavier Mouraux]

I have got a few interesting answers off line also and will think about it some more. Thank you all.
You are partially right Del about the weight lifting project. I start thinking about CG vs. weight issue before meeting these students but that project got the idea back. I plan to do the first few flights with a low weight but I would like to keep the plane behavior similar once loaded.
I have no intention to add weight to my pattern plane, don't worry :-)

Xavier

  ----- Original Message ----- 
  From: Del K. Rykert 
  To: discussion at nsrca.org 
  Sent: Monday, March 29, 2004 9:20 PM
  Subject: Re: CG location vs total weight


  Hi Xavier..
      Remember that elevator controls speed and throttle controls elevation.  The speed component is what need to be addressed to keep the wing from stalling more so in the 2# heavier plane. Pitch control is going to take much less elevator/drag input the more the CG is moved back.  If you truly want to make a pattern airplane 2# heavier than it needs to be I guess I am missing the fundamentals of why we normally strive so hard to keep our competition aircraft as light as possible. Speed is a factor that has to be increased for a heavier aircraft to stay in the air as wing loading is higher. C.G. I believe is primarily a factor within realistic flight parameters that different pilots choose to fly at different places to get the track and feel from their aircraft, not a component of carrying more weight. 
      I suspect this is part of your weight lifting project?

                           del 
                 NSRCA - 473

    ----- Original Message ----- 
    From: Xavier Mouraux 
    To: discussion at nsrca.org 
    Sent: Monday, March 29, 2004 8:23 PM
    Subject: CG location vs total weight


    Hello all,

    I am trying to clarify an idea about CG location for different weight of a same airplane. 

    Goals: 
    Minimize the effect of elevator trim /stab incidence on level flight, inverted flight and verticals.
    The airplanes need to fly at the same speed independent of its weight or the qty of fuel.

    Questions:
    Could it be that a heavier plane need a CG more AFT than the same plane with a lower weight to "set" in the proper angle of attack ?
    Could it be useful to locate the tank so the CG move FWD as the fuel is burned ?
    What about CG recommendation on plan or from other pilots with same plane but different weight ?
    How much change in angle of attack is required on a pattern plane for a 2lb difference in weight to fly at the same speed ?
    What would be the effect on elevator sensitivity ?
    Am I going too far ?

    Any opinion ?

    Xavier
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