Sr.Telemaster CG calculation, lifting tail airfoil.

I have an 8' Senior Telemaster because of its High Lift Capability.

And one argument I have is with the way common RC flyer's Balance the Telemaster's CG before flight.

I seek a solution for calculating the CG that provides input for the lifting tail of the Telemaster.  Because such a solution would allow the airframe to share lifting duties between the main wing and the lifting tail.

 

The "experienced flyers" at my airfield insist on balancing the plane as you would a non-lifting tail RC plane.  I feel they are not taking into account the lifting tail of the Telemaster.  Where CG balancing between the lift capability of the main wing and tail is achieved.

 

I believe that when balancing the CG on the Telemaster it should be tail heavy when balancing the "traditional" way.

 

Can anyone help me with this. I believe it would increase the actual lift capability of the plane.

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  • The replies by Beal and others describe how the cg position interacts with stability. A follow-on to the comment that the F/A-!8E/F landing with stabilator down deflection under control of the EFCS: A basic Ardupilot has the potential capability of stabilizing an unstable pitch loop(without increasing the max load). A knowledge of the pitch moment of inertia and other control loop parameters is required.

    Increasing power and angle of attack increases payload with a penalty of reducing the maximum g the airframe can sustain under maneuvers. Again an Ardupilot g-limiting control law could be written to keep the plane in a suitable g envelope. For F/A-18 fans, watch the rudders on take off.  They are each rotated to full inboard deflection, because the stabilator exerts insufficent aero moment to raise the nose on carrier take-off.  The pilot grabs the two grab bars, the EFCS goes off the cat with full control of the stabilator and rudder fade-out. The pilot does not take control until normal climbout is established.

     

    Some DIYer out there may have a wind tunnel under construction to build interesting and useful unstable aircraft.  Technology change is exponential.

     

    Mike Cowan

  • A "TAIL" heavy plane is harder to control. Most R/C planes have a CG range. I suggest to install what you want then "CG" the plane according to MFG spec.
  • Moving the CG will neither increase nor decrease the aircraft's lifting capacity, it may make the airplane more pleasant to fly. The only things that can affect its steady state lifting capacity are 1) motor power, 2) airfoil shape(s), 3) lifting area and to a tiny extent 4) tail vs wing incidence (by affecting parasitic drag).

     

    You can fly with a CG further back than normal however you will want to be careful. The easy way to test it is first make sure all the incidences are correct - this is important, use an hanger 9 angle pro or something similar. Then check that the airplane trim does not change much with airspeed - ie no elevator trim change from say 0% to 75% throttle, and no trim change from level flight to say a 45 degree dive. Once that is all correct check the actual elevator trim, ie look at the elevator surface, if its not flat then you can move the cg to improve the aerodynamics. Move it only a little at a time and check nothing else changes, ie the test's listed above are still ok. There will be some interaction with the above changes, for example changing the motor thrust line will change / mask changes in elevator trim - its an iterative process.

  • Developer

    The pitch stability is based on the CG being in front of the aerodynamic center.  Just because the tail is a "lifting tail" vice a negative lifting tail doesn't actually move the aerodynamic center.  It just makes the negative pitching moment that much harder to balance.  You can balance that moment by either extra elevator deflection or by moving the CG aft.  Moving the CG aft is making it more efficient for sure but still at the cost of Pitch stiffness. 

     

    This is definition of the F/A18 A/B vs the F/A 18 E/F  Look at pics of the Super hornet landing.  It it tail heavy to the point of requiring conventionally opposite elevator control deflection.  This makes it clearly unstable but the AFCS computer is flying, not the pilot. 

     

    So to answer your question....  Yeah move the CG aft to carry more of the load but know that the pitch stiffness will still decrease. 

     

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