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Figure 33 Figure 34
(Refer to figures 33 and 34.) Calculate the weight and balance and
determine if the CG and the weight of the airplane are within limits.
Front seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 350 lb
Rear seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 325 lb
Baggage
. . . . . . . . . . . . . . . . . . . . . . . . . . 27 lb
Fuel
. . . . . . . . . . . . . . . . . . . . . . . . . . 35 gal
ANSWER: CG 83.4, within limits.
Total weight, total moment, and CG
must all be calculated. As in most weight and balance
problems, you should begin by setting up the schedule as
shown below.
Next, go to the Moment Limits vs. Weight chart (Fig. 34),
and note that the maximum weight allowed is 2,950, which
means that this airplane is 23 lb. under maximum weight. At a
total moment of 2,441, it is also within the CG limits (2,399 to
2,483) at that weight.
Finally, compute the CG. Recall that Fig. 33 gives moment
per 100 in. The total moment is therefore 244,100 (2,441 x
100). The CG is 244,100/2,927 = 83.4.
Moment/1000
Weight lb.-in.
Empty weight w/oil 2,015 1,554
Front seat 350 298
Rear seat 325 393
Fuel, main (35 gal.) 210 158
Baggage 27 38
2,927 2,441
Figure 33 Figure 34
(Refer to figures 33 and 34.) What is the maximum amount of
baggage that can be carried when the airplane is loaded as follows?
Front seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 387 lb
Rear seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 293 lb
Fuel
. . . . . . . . . . . . . . . . . . . . . . . . . . 35 gal
ANSWER: 45 pounds.
The maximum allowable weight on the
Moment Limits vs. Weight chart (Fig. 34) is 2,950 lb. The
total of the given weights is 2,905 lb. (including the empty
weight of the airplane at 2,015 lb. and the fuel at 6 lb./gal.),
so baggage cannot weigh more than 45 lb.
It is still necessary to compute total moments to verify that
the position of these weights does not move the CG out of
CG limits.
The total moment of 2,460 lies safely between the moment
limits of 2,422 and 2,499 on Fig. 34, at the maximum weight,
so this airplane can carry as much as 45 lb. of baggage when
loaded in this manner.
Moment/1000
Weight lb.-in.
Empty weight w/oil 2,015 1,554
Front seat 387 330
Rear seat 293 355
Fuel, main (35 gal.) 210 158
Baggage 45 63
2,950 2,460
Figure 33 Figure 34
(Refer to figures 33 and 34.) Determine if the airplane weight and
balance is within limits.
Front seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 415 lb
Rear seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 110 lb
Fuel, main tanks
. . . . . . . . . . . . . . . . . . . . . . . . . . 44 gal
Fuel, aux. tanks
. . . . . . . . . . . . . . . . . . . . . . . . . . 19 gal
Baggage
. . . . . . . . . . . . . . . . . . . . . . . . . . 32 lb
ANSWER: Weight within limits, CG out of limits.
Both the weight and the total moment
must be calculated. Begin by setting up the schedule shown
below. The fuel must be separated into main and auxiliary
tanks, but weights and moments for both tanks are provided
in Fig. 33.
Since 415 lb. is not shown on the front seat table, simply
multiply the weight by the arm shown at the top of the table
(415 lb. x 85 in. = 35,275 lb.-in.) and divide by 100 for
moment/100 of 353 (35,275 ÷ 100 = 352.75). The rear seat
moment must also be multiplied (110 lb. x 121 in. = 13,310
lb.-in.). Divide by 100 to get 133.1, or 133 lb.-in./100. The last
step is to go to the Moment Limits vs. Weight chart (Fig.
34). The maximum weight allowed is 2,950, which means that
the airplane weight is within the limits. However, the CG is
out of limits because the minimum moment/100 for a weight
of 2,950 lb. is 2,422.
Moment/1000
Weight lb.-in.
Empty weight w/oil 2,015 1,554
Front seat 415 353
Rear seat 110 133
Fuel, main 264 198
Fuel, aux. 114 107
Baggage 32 45
2,950 2,390
Figure 33 Figure 34
(Refer to figures 33 and 34.) Which action can adjust the airplane's
weight to maximum gross weight and the CG within limits for
takeoff?
Front seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 425 lb
Rear seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 300 lb
Fuel, main tanks
. . . . . . . . . . . . . . . . . . . . . . . . . . 44 gal
ANSWER: Drain 9 gallons of fuel.
First, determine the total weight to see
how much must be reduced. As shown below, this original
weight is 3,004 lb. Fig. 34 shows the maximum weight as
2,950 lb. Thus, you must adjust the total weight by removing
54 lb. (3,004 - 2,950). Since fuel weighs 6 lb./gal., you must
drain at least 9 gal. To check for CG, recompute the total
moment using a new fuel moment of 158 (from the chart) for
210 lb. The plane now weighs 2,950 lb. with a total moment
of 2,437, which falls within the moment limits on Fig. 34.
Original Adjusted Moment/100
Weight Weight lb.-in.
Empty weight with oil 2,015 2,015 1,554
Front seat 425 425 362
Rear seat 300 300 363
Fuel 264 210 158
3,004 2,950 2,437
Figure 33 Figure 34
(Refer to figures 33 and 34.) With the airplane loaded as follows,
what action can be taken to balance the airplane?
Front seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 411 lb
Rear seat occupants
. . . . . . . . . . . . . . . . . . . . . . . . . . 100 lb
Main wing tanks
. . . . . . . . . . . . . . . . . . . . . . . . . . 44 gal
ANSWER: Add a 100-pound weight to the baggage compartment.
You need to calculate the weight and
moment. The weight of the empty plane including oil is
2,015, with a moment of 1,554. The 411 lb. in the front seats
has a total moment of 349.35 [411 x 85 (ARM) = 34,935/100 =
349.35]. The rear seat occupants have a weight of 100 lb. and
a moment of 121.0 [100 x 121 (ARM) = 12,100/100 = 121.0].
The fuel weight is given on the chart as 264 lb. with a
moment of 198.
Moment/100
Weight lb.-in.
Empty weight w/oil 2,015 1,554
Front seat 411 349.35
Rear seat 100 121.0
Fuel 264 198.0
2,790 2,222.35
On the Fig. 34 chart, the minimum moment for 2,790 lb. is
2,243. Thus, the CG of 2,222.35 is forward. Evaluate A, B, and
C to see which puts the CG within limits.
Weight Moment/100
A +114 +107
B +100 +140
C +60 +56
-60 -45
0 +11
At 2,890 lb. (2,790 + 100), moment/100 of 2,362.35 (2,222.35 +
140) is over the minimum moment/100 of 2,354.
Figure 33 Figure 34
(Refer to figures 33 and 34.) Upon landing, the front passenger (180
pounds) departs the airplane. A rear passenger (204 pounds)
moves to the front passenger position. What effect does this have
on the CG if the airplane weighed 2,690 pounds and the MOM/100
was 2,260 just prior to the passenger transfer?
ANSWER: The CG moves forward approximately 3 inches.
The requirement is the effect of a
change in loading. Look at Fig. 33 for occupants. Losing the
180-lb. passenger from the front seat reduces the MOM/100
by 153. Moving the 204-lb. passenger from the rear seat to
the front reduces the MOM/100 by about 74 (247 - 173). The
total moment reduction is thus about 227 (153 + 74). As
calculated below, the CG moves forward from 84.01 to 81.00
in.
Old CG = 226,000 lb.-in.
2,690 lb. = 84.01 in.
New CG = 203,300 lb.-in.
2,510 lb. = 81.00 in.
Figure 33 Figure 34
(Refer to figures 33 and 34.) What effect does a 35-gallon fuel burn
(main tanks) have on the weight and balance if the airplane
weighed 2,890 pounds and the MOM/100 was 2,452 at takeoff?
ANSWER: Weight is reduced by 210 pounds and the CG is aft of
limits.
The effect of a 35-gal. fuel burn on
weight balance is required. Burning 35 gal. of fuel will reduce
weight by 210 lb. and moment by 158. At 2,680 lb. (2,890 -
210), the 2,294 MOM/100 (2,452 - 158) is above the maximum
moment of 2,287; i.e., CG is aft of limits. This is why weight
and balance should always be computed for the beginning
and end of each flight.
What is ground effect?
ANSWER: The result of the interference of the surface of the Earth
with the airflow patterns about an airplane.
Ground effect is due to the
interference of the ground (or water) surface with the airflow
patterns about the airplane in flight. As the wing encounters
ground effect, there is a reduction in the upwash,
downwash, and the wingtip vortices. The result is a
reduction in induced drag. Thus, for a given angle of attack,
the wing will produce more lift in ground effect than it does
out of ground effect.
Floating caused by the phenomenon of ground effect will be most
realized during an approach to land when at
ANSWER: less than the length of the wingspan above the surface.
Ground effect is most usually
recognized when the airplane is within one-half of the length
of its wingspan above the surface. It may extend as high as a
full wingspan length above the surface. Due to an alteration
of the airflow about the wings, induced drag decreases,
which reduces the thrust required at low airspeeds. Thus,
any excess speed during the landing flare may result in
considerable floating.
What must a pilot be aware of as a result of ground effect?
ANSWER: Induced drag decreases; therefore, any excess speed at
the point of flare may cause considerable floating.
Ground effect reduces the upwash,
downwash, and vortices caused by the wings, resulting in a
decrease in induced drag. Thus, thrust required at low
airspeeds will be reduced and any excess speed at the point
of flare may cause considerable floating.
Ground effect is most likely to result in which problem?
ANSWER: Becoming airborne before reaching recommended takeoff
speed.
Due to the reduction of induced drag
in ground effect, the airplane may seem capable of becoming
airborne well below the recommended takeoff speed.
However, as the airplane rises out of ground effect (a height
greater than the wingspan) with a deficiency of speed, the
increase in induced drag may result in very marginal initial
climb performance. In extreme cases, the airplane may
become airborne initially, with a deficiency of airspeed, only
to settle back on the runway when attempting to fly out of
the ground effect area.
What effect, if any, does high humidity have on aircraft
performance?
ANSWER: It decreases performance.
As the air becomes more humid, it
becomes less dense. This is because a given volume of
moist air weighs less than the same volume of dry air. Less
dense air reduces aircraft performance.
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