
Beginner's Guide
to Propulsion
Thrust to Weight Ratio and Excess Thrust
Activity
If so instructed by your teacher, print out a worksheet page for these
problems.
Choose the one
correct answer for each problem. REMEMBER: For some of the problems,
you must use the given information or information from prior problems.
WE
ARE GOING TO TAKE A TRIP ON A BOEING 747 THAT WEIGHS 800,000 POUNDS!!
 As we
are waiting to take off, what is the F/W (Thrust to Weight Ratio) ?
1)
0

2)
.5

3)
1

4)
Cannot
be determined.

 After our seat
belts are fastened, the plane begins going down the runway and starts
to accelerate. The drag is 10,000 pounds. What must be true about
the thrust?
1)
Thrust < 10,000 pounds.

2)
Thrust > 10,000 pounds.

3)
Thrust = 10,000 pounds.

4)
1,2,
or 3  depends on F/W.

 As we sit back,
relax, and dream about our vacation, the 747 climbs to it's desired
cruising altitude. What happens to the thrust?
1)
It
decreases.

2)
It
increases.

3)
It remains constant.

4)
It depends on the lift.

 When the jet reaches
it's cruising altitude, it's velocity is 540 mph. If the excess thrust
to reach this altitude averaged 100,000 pounds, approximately how
long did it take to reach this altitude? [Hint: weight
= m x a_{g} where a_{g}(acceleration due to gravity)
= 32.2 ft/s^{2} ]
1)
21 seconds.

2)
283 seconds.

3)
114
seconds.

4)
197 seconds.

 It takes the pilot
about two minutes to accelerate to 580 mph. What amount of excess
thrust did he have to use?
1)
12,145
pounds.

2)
58,440 pounds.

3)
84,520 pounds.

4)
125,830
pounds.

 For the remainder
of the flight as you are enjoying your food and drinks, the pilot continues
cruising at 580 mph. During this time,
1)
The thrust must be greater than the drag.

2)
The
drag must be greater than the thrust.

3)
The thrust must be equal to the drag.

4)
The
relationship between the thrust and the drag depends on the
cruising speed.

 As the aircraft
is landing, the pilot wants to decrease the speed by cutting back the
throttle. What has to happen?
1)
The F/W Ratio must increase.

2)
The excess thrust must increase.

3)
The drag must be greater than the thrust.

4)
The
thrust must be greater than the drag.

Now that you have
enjoyed your flight and safely landed, check to make sure you answered
the questions correctly. If all answers are correct:
1. The sum
of your numerical answers will be fifteen,
AND
2. the product
of your numerical answers will be seventytwo!
