Flight 4
Level Flight Performance
Gregory R. Whitney
David Hughling
TA: Eduardo Gildin
November 12, 2001
University of Texas at Austin
ASE 167M
Abstract
The level flight performance of the Beechcraft Bonanza A-36 were investigated with the use of CAT II simulator at the University of Texas at Austin. The level flight speeds were recorded by varying the engine settings at an altitude of 3,500 feet. It was found that as the engine power was reduced, the speed of the aircraft decreased. It was also found, form theory, that as the altitude increases, the power available decreases. Thus, the performance of an aircraft depends greatly on the power setting and the altitude.
Table of Contents
Objectives
Procedure
Discussion
Level Thrust
Power Required
Experiment Data/Test Results
Recommendations
Appendix A – References
Appendix B – Simulator Hardware
Objectives
The objectives of this experiment were to:
- Summarize the various level flight airspeeds, which result from various power settings at a given assigned altitude
- Explain the effects of altitude and power setting changes on aircraft performance based on cruising flight data from a production aircraft
Procedure
Once the pre-flight checklist was completed, we conducted a normal start and takeoff and climbed to an altitude of 3,500 feet.
At the designated altitude with full power and maximum RPM the level flight airspeed was determined. Then the manifold pressure was decreased to 20’’ Hg and the speed was determined. The manifold pressure was then decreased to 17’’ Hg and finally 15’’ Hg; airspeed readings were taken for each of these settings. This process was repeated for 2200 RPM, 1800 RPM, and 1500 RPM. For each engine setting, the altitude was kept constant and the airspeed was recorded after the aircraft had stabilized. The complete flight plan can be found in the ASE 167M lab manual on page 33, and the data can be found in table 1.
Discussion
The purpose of this experiment was to determine the level flight performance of an aircraft at several different engine settings at 3,500 feet. Since the aircraft is in steady level flight, the equations of motion reduce to:
L = W[1]
T = D [2]
where
L = Lift
W = Weight
T = Thrust
D = Drag
Level Thrust
Solving for L =W in terms of velocity gives
[3]
where
= density
V = Velocity
S = Wing Planform Area
CL = Coefficient of Lift
And substituting equation [3] into the thrust-drag relation gives
[4]
where
CD = Coefficient of Drag
After rearranging equation [4] it is seen that the thrust required to fly is:
[5]
Equation [5] can be rewritten as a function of velocity by using the parabolic drag polar and L = W to finally show
[6]
Graphically, equation (6) is represented by a quadratic graph that can yield two solutions for every required thrust. For the high velocity solution the angle of attack and required CL are small while the dynamic pressure, q, is large. This implies that the total drag is also very large because of the dynamic pressure term in its equation. However, for the low speed solution there exists a large angle of attack and required CL that lead to induced drag dominating the drag term.
Power Required
For aircraft, power can be found using the following equation
[7]
which follows the convention that power is equivalent to work per time. This relation can also be shown in terms of coefficient of lift and coefficient of drag
[8]
The above equation proves the intuitive idea that an increase in lift will reduce the power needed in any condition whereas an increase in drag always increases the power required. It is important to note that a linear relationship exists so that TR is like a slope. The minimum thrust required can be found at the minimum slope zero intercept line that intersects the PR curve.
Finally, using the conversion factor of 550, the thrust HP can be found the relation
[9]
Experiment Data/Test Results
During the experiment, the level flight speed was determined for several configurations. The configurations and the associated speeds are shown in table 1 below.
Table 1: Level Flight Speeds at 3,500 ft
Level Flight Velocities at Variable Power SettingsManifold Pressure (“Hg)
RPM / Max / 20” / 17” / 15”
Max / 175 knots / 170 knots / 160 knots / 150 knots
2200 / 178 knots / 165 knots / 155 knots / 145 knots
1800 / 175 knots / 155 knots / 142 knots / 138 knots
1500 / 175 knots / 150 knots / 140 knots / 125 knots
Table 1 shows that as the manifold pressure and engine RPM are reduced, the steady level flight speed decreases. It is important to see that as the manifold pressure decreases the flight speed doesn’t decrease by a large amount.
The power required for each of the level flight speeds is shown in table 2 This table was constructed using a parabolic drag polar with K=0.07 and Cdo = 0.02 and a weight of 3500 lbs.
Table 2: Thrust Horsepower Required at 3,500 ft
Thrust Horsepower in (ft-lbf/s) at Variable Power SettingsManifold Pressure (“Hg)
RPM / Max / 20” / 17” / 15”
Max / 83.73 / 81.02 / 76.44 / 73.02
2200 / 85.50 / 78.59 / 74.59 / 71.74
1800 / 83.73 / 74.59 / 71.12 / 70.45
1500 / 83.73 / 73.02 / 70.76 / 69.65
Table 2 shows that the amount of thrust horsepower (THP) decreases as the manifold pressure and the engine RPM decreases.
Conclusions
The goals of this lab were to demonstrate the effects that a reduction in power has on an aircraft simulated by the CAT II simulator. These data were attained by sixteen combinations of MP and RPM. These data were then verified by theory to show that a decrease in power would decrease the maximum velocity attainable by the aircraft. Another source of data that follows the theories behind level flight performance was the 1968 Cessna 182/Skylane operation manual.
Unlike the data presented with in this lab exercise, the Cessna data was attained at various altitudes. This provides a way to show the effects of altitude changes on the power available to the aircraft. In equation [6] density is in the numerator of the dominant term of the equation. This means that an increase in density helps the production of horsepower while a reduction acts conversely. Another, trend of the Cessna’s cruise performance is the engine setting for maximum endurance. The charts show that the amount of fuel consumed is much higher for higher power settings. The pilot would then be best advised to reach cruising altitude and then reduce engine RPM and manifold pressure in order to maximize range.
There is a tradeoff between range and safety. The aircraft would be able to travel longer distances if the pilot cruised at the low speed solution of the flight envelope, but flying at this speed is dangerous. The pilot should then fly at some speed higher than the low speed solution. Time is also an issue, so a pilot would not always want to fly at the low speed solution. In order to complete the flight plan safely, the pilot will have to decide the best conditions for flight.
Recommendations
There are no recommendations for this lab.
Appendix A – References
- "ASE 167M Lecture Eight Propulsion Flight 4 Briefing"
- "Introduction to Airplane Flight Mechanics" David G. Hull
Appendix B – Simulator Hardware
The simulator used in this lab was the CAT II simulator
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