12 practice questions from the 330 in this chapter of StudyWren Aviation. Pick an answer and check it to see the explanation and its FAA source.
Weight Shift & Weight ChangePAR-10-180
An airplane's fuel tanks are located aft of its loaded CG. As fuel is burned during flight, the CG will
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The answer is B: move forward
Removing weight located aft of the CG removes positive moment faster than it reduces weight, so the CG moves forward (away from the removed weight). The pilot should confirm the landing CG is still within limits.
Removing weight located aft of the CG removes positive moment faster than it reduces weight, so the CG moves forward (away from the removed weight). The pilot should confirm the landing CG is still within limits.
An airplane weighs 2,300 lb. A 180-lb rear-seat passenger (arm 73.0 in) moves to the empty front passenger seat (arm 37.0 in). How far does the CG move?
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The answer is B: 2.8 in forward
ΔCG = (180 × 36.0) ÷ 2,300 = 2.8 in. The weight moved forward, so the CG moves forward. 5.7 in uses the rear-seat arm (73.0 in) instead of the 36.0-in distance moved.
ΔCG = (180 × 36.0) ÷ 2,300 = 2.8 in. The weight moved forward, so the CG moves forward. 5.7 in uses the rear-seat arm (73.0 in) instead of the 36.0-in distance moved.
A pilot moves a 50-lb box from the baggage compartment to the rear seat. What changes?
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The answer is C: The total moment and CG change, but not total weight
Shifting weight within the airplane changes its arm and therefore the total moment and CG location, but total weight is unchanged. Adding or removing weight changes total weight, moment, and usually CG.
The answer is C: The total moment and CG change, but not total weight
Shifting weight within the airplane changes its arm and therefore the total moment and CG location, but total weight is unchanged. Adding or removing weight changes total weight, moment, and usually CG.
An airplane weighs 2,510 lb with a moment of 121,190 lb-in (CG 48.3 in; aft limit 47.3 in). One 200-lb rear passenger (arm 73.0 in) moves to the empty front passenger seat (arm 37.0 in). What is the new CG, to the nearest 0.1 in?
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The answer is B: 45.4 in
Moment change = 200 × (73.0 − 37.0) = 7,200 lb-in. New moment = 113,990; weight unchanged at 2,510 lb. CG = 45.4 in, now within limits. 42.5 in uses the 73.0-in arm instead of the 36.0-in distance moved; 51.2 in moves the CG the wrong way.
Moment change = 200 × (73.0 − 37.0) = 7,200 lb-in. New moment = 113,990; weight unchanged at 2,510 lb. CG = 45.4 in, now within limits. 42.5 in uses the 73.0-in arm instead of the 36.0-in distance moved; 51.2 in moves the CG the wrong way.
An airplane weighs 2,510 lb with a moment of 121,190 lb-in. The pilot removes 40 lb of baggage stowed at an arm of 123.0 in. What is the new CG, to the nearest 0.1 in?
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The answer is A: 47.1 in
Removed moment = 40 × 123 = 4,920 lb-in. New weight = 2,510 − 40 = 2,470 lb; new moment = 121,190 − 4,920 = 116,270 lb-in; CG = 116,270 ÷ 2,470 = 47.1 in. Dividing by the old 2,510 lb instead forgets to take the bag's weight off, and 49.5 in adds the bag instead of removing it.
Removed moment = 40 × 123 = 4,920 lb-in. New weight = 2,510 − 40 = 2,470 lb; new moment = 121,190 − 4,920 = 116,270 lb-in; CG = 116,270 ÷ 2,470 = 47.1 in. Dividing by the old 2,510 lb instead forgets to take the bag's weight off, and 49.5 in adds the bag instead of removing it.
An airplane's takeoff CG is exactly at the aft limit, and its fuel tanks are forward of the CG. What should the pilot expect as fuel burns?
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The answer is B: The CG will move aft of the limit
Removing weight located forward of the CG moves the CG aft. Starting at the aft limit, burning fuel will put the CG beyond it, so the airplane must be loaded so that both takeoff and landing CG are within limits.
The answer is B: The CG will move aft of the limit
Removing weight located forward of the CG moves the CG aft. Starting at the aft limit, burning fuel will put the CG beyond it, so the airplane must be loaded so that both takeoff and landing CG are within limits.
An airplane takes off at 3,000 lb with its CG at 82.0 in (aft limit 83.0 in). Its fuel is located at an arm of 75.0 in. After burning 40 gal of avgas, what is the CG, to the nearest 0.1 in?
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The answer is C: 82.6 in
Fuel burned = 40 × 6 = 240 lb; moment removed = 240 × 75 = 18,000. New CG = (246,000 − 18,000) ÷ 2,760 = 82.6 in, still within the aft limit. 89.1 in removes the weight but not the moment; 81.4 in moves the CG the wrong way.
Fuel burned = 40 × 6 = 240 lb; moment removed = 240 × 75 = 18,000. New CG = (246,000 − 18,000) ÷ 2,760 = 82.6 in, still within the aft limit. 89.1 in removes the weight but not the moment; 81.4 in moves the CG the wrong way.
The datum of an airplane is the firewall. Its empty weight is 1,200 lb with a CG of 12.0 in. A 30-lb item is installed at an arm of −15.0 in (forward of the firewall). What is the new empty-weight CG, to the nearest 0.1 in?
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The answer is C: 11.3 in
Moment = 1,200 × 12.0 = 14,400; item moment = 30 × (−15.0) = −450, negative because the item is forward of the datum. New CG = 13,950 ÷ 1,230 = 11.3 in. 12.1 in treats the arm as positive, and 12.0 in ignores the effect: an item installed forward of the firewall reduces the total moment and moves the CG forward.
Moment = 1,200 × 12.0 = 14,400; item moment = 30 × (−15.0) = −450, negative because the item is forward of the datum. New CG = 13,950 ÷ 1,230 = 11.3 in. 12.1 in treats the arm as positive, and 12.0 in ignores the effect: an item installed forward of the firewall reduces the total moment and moves the CG forward.
What is the most hazardous effect of loading an airplane with the CG aft of the aft limit?
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The answer is A: Reduced stability and possible inability to recover from a stall or spin
An aft CG reduces longitudinal stability and leaves less nose-down elevator authority. If the CG is too far aft, the pilot may be unable to lower the nose for stall recovery, and spins may become flat and unrecoverable.
The answer is A: Reduced stability and possible inability to recover from a stall or spin
An aft CG reduces longitudinal stability and leaves less nose-down elevator authority. If the CG is too far aft, the pilot may be unable to lower the nose for stall recovery, and spins may become flat and unrecoverable.
Landing with the CG forward of the forward limit could result in
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The answer is C: insufficient elevator authority to flare
A CG ahead of the forward limit makes the airplane nose-heavy; at low landing speeds the elevator may not have enough authority to raise the nose for the flare, risking a nosewheel-first landing. Light control forces are an aft-CG trait.
The answer is C: insufficient elevator authority to flare
A CG ahead of the forward limit makes the airplane nose-heavy; at low landing speeds the elevator may not have enough authority to raise the nose for the flare, risking a nosewheel-first landing. Light control forces are an aft-CG trait.
