WEIGHT AND BALANCE DATA

Mean aerodynamic cord (MAC) center of lift is at the midpoint between the forward and aft attach points of the cabane struts.


Ideal loaded center of gravity is 0 inch to 1 inch forward of the MAC center of lift.


Loaded center of gravity limits are 4 inches forward to 3 inches aft of the MAC center of lift.




Baby Lakes and Buddy Baby Lakes

MAC (Center of Lift)

NOTES

  1. The airfoil section is a modified M-6 for all except the last 18 inches of span where it transitions to a USA-15 on both upper and lower wing tips.

  1. Stagger between upper and lower wings is approximately 30% of the cord at the root becoming nil at the tips du to the upper wing sweep-back.

  1. The upper wing is set a 1 degree more angle of incidence (2 ½ degrees) than the lower wing (1 ½ degree).

  1. There should be no dihedral in the lower wing and from 0 degrees to 2 degrees dihedral in the upper wing.

  1. Flight testing has shown that the lift (pressure) profile resulting from this wing configuration produces the following results:

a) In cruise level flight at about 115-120 MPH, with a gross weight of 800 pounds, all lift is bring generated by the  
    upper wing with the lower wing being essentially streamlined with the relative wind.

b) In condition a) above, the mean aerodynamic cord center of lift is at midpoint between the forward and aft cabane
    attachments for the upper wing.

c) As the angle of attack (for both wings) is increased, the lower wing begins to generate lift aft of the upper wing
    center of lift. The combination of both upper and lower lift profiles has the overall effect of maintaining a combined
    center of lift that remains almost constant relative to the center of gravity at all angles of attack right up through
    full stall of the upper wing.

d) As the upper wing stalls, the center of lift is then (initially) well aft of position described in b) above (midpoint
    between forward and aft cabane attach points) which causes an immediate pitch down of the aircraft's attitude.

  1. The ideal loading (pilot, fuel, oil, etc) center of gravity is from 0 inch to 1 inch forward of the midpoint between upper wing cabane forward and aft attach points.

  1. Loaded center of gravity limits should be held to from 4 inches forward to 3 inches aft of the midpoint of the cabane attached points. (Even through the aircraft has been found to be controllable when the center of gravity was well outside these limits.)

  1. Before fabrication the engine mount for a Baby Lakes or Buddy Baby Lakes, a calculation should be made to determine how far forward of the MAC center of lift (for the upper wing) will the engine, cowl, prop, wheel pants, etc have to be in order to provide a plus moment that is about equal to the minus moment of (intended) pilot (and passenger in the Buddy Baby).

  1. It is important to use the cabane struts attachment mid point as the primary reference for weight and balance calculations since firewall (the usual datum) position and seat back position are often adjusted to accommodate pilot size and comfort considerations (see sheets on weight and balance)

  1. Loaded Gross Weight vs Structural G Limits

850 pounds max. for 9 G positive and negative.

1000 pounds max for 7.5 G  positive and negative

The Baby's C.G. range is sufficient to allow for a difference in pilot weights as much as 40-50 pounds either side of the 170 pound if its initial balance falls at the C.L. of M.A.C. With a 170 pound pilot. However, its overall performance is proportionally less as you approach the extremes of the C.G. range.


ADDITIONAL NOTES

  1. See some comparable weights and approximated C.G.'s for different engines in the table below. Differences in same models occur with different dash numbers and all are given with accessories except starter and generator.

MAKE MODEL                  WEIGHTS             ENGINE C.G.


Continental A-65               163 lbs                   6.2 inches

C-75                                   177-182 lbs.          6.2 - 4.6 inches

A-80                                   173-176 lbs.          6.2 inches

C-85                                   178-180 lbs.          6.2 - 4.6 inches

C-90-8                                184 lbs.                 6.2 inches

C-90-F                               188 lbs                   4.6 inches

0-200                                 190 lbs                   4.6 inches


Lycoming 0-235                 209-219 lbs.           7 inches

Lycoming 0-290                 230-250                  7 inches


C.G. measurements are taken forward of the rear face of engine mounting pads. Adaption of some of the heavier engines might require moving pilot aft or weighting the tail.


For horsepower rating above 90 HP the engine mount should be made to give up to 3 degrees down thrust to the prop shaft. (one way is to install a 1 inch spacer at top mounting points only). This improves the climb rates and also improves the take-off characteristics. Leave it to 0 degrees (standard) if you are going to fly it inverted for extended periods.  


 For an aircraft that is to be used for extensive inverted flying, the incidence of the lower wing should be reduced to 0 degrees with the top wing at 1 degree. This will give a more level fuselage attitude in both modes.   Actually, within reason (1-3 degrees) the exact incidence, relative to the longitudinal axis, is not too important as long as the relationship of 1 degree more on top wing than the bottom wing is maintained. Basic incidence merely establishes fuselage attitude in flight.

Have a great day!

Harvey Swack

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