WEIGHT AND BALANCE
Refer to the three weight and balance pages at the end of this manual,
these show how to do the computations.
A very heavy pilot might result in a forward C.G. An airplane with an excessive forward C.G. would need a faster than normal speed to take-off and would run out of elevator control before the wings would stall. Thus, with an excessive forward C.G., the pilot would need to fly much faster than normal to be able to have sufficient elevator control.
Pilots weighing 160 lb or more should not have any problem with a normally equipped 377 or 447 FireStar. Lighter pilots may want to consider putting some weight in the nose. (Some restore balance by placing a thick cushon behind their back - this moves their body weight several inches forward; many times this is all that is needed.) For 503 equipped airplanes, the 160 lb. figure might be 185 lb.
Balance Basics
The basic balance equation is:
WEIGHT X DISTANCE - MOMENT
The weight is measured in pounds, and the distance should be measured
in inches - all units must be consistent. The resultant moment is then
in inch- pounds.
Basic Procedure
If you have high capacity scales or have 5 scales at your disposal (2
for each main wheel), you can do the weight and balance as shown by the
first calculation sheet - weighing airplane, pilot and gas - everything
in one weighing. This is the easiest and you are less likely to make a
mistake this way. If you use 2 scales for each main wheel (bridge the 2
scales with a piece of lumber and place the wheel in the center of the
two scales; then simply add the 2 scale readings together).
If you are limited to 3 scales or less - your procedure will be to follow the calculations on the second calculation sheet:
1) Weigh each wheel with a separate bathroom type scale (3 scales needed).
2) Multiply each wheel weight by its distance from the datum point.
3) Add the 3 resulting moments together.
4) Divide the resultant moment by the total weight (the sum readings
of all 3 scales) this will give the resultant distance from the C.G
(of what you weighed) to the datum.
Bathroom scales generally do not weigh high enough to be able to weigh
the pilot along with the airplane (they read high enough typically,
but at such heavy weights the scales become less accurate, i.e. even if
your scale reads to 300 pounds, don't assume that it is accurate with
that much weight on it. It has been our experience that when you get
that much weight on a scale that it may not be very accurate.
5) The weight of pilot is then factored in as shown in the 2nd
calculation sheet. You could do all the weighing with one scale, but this is
a lot more work. You also need to have 2 blocks the exact thickness
of the scale to place under the other 2 wheels, so that the airplane
remains level and in the same attitude when the scale is shifted from
wheel to wheel.
The attitude of the airplane should be set so that the bottom of the
wing is set at 9 degrees angle of attack (hold a 4 foot level under the wing with one end on the rear spar, the front end of the level should be 7-1/2 inches below the front spar when the wing is at 9 degrees.
When you weigh the airplane, there should be no wind (if outside). Your main concern is to avoid a tailheavy loading condition. So make a C.G. calculation with the liehtest pilot with maximum fuel. A nose heavy condition does not normally occur - unless the pilot would be excessively heavy. Things like a parachute, electric start, and custom gas tanks, etc. affect balance of the airplane significantly depending upon the installed position - this is why it is important to do a weight and balance. The scale that measures the weight of the tailwheel should be very accurate. If the scale is only several pounds off, one way or the other, it can significantly affect the calculated C.G. If possible, verify the accurace of the reading. For instance, if the scale showed 45 pounds, then find 45 pounds of known weight and place it on the scale as a check.
