Posted: February 16th, 2017

Exercise 5: Aircraft Performance

For this week’s assignment you will revisit your data from previous exercises, therefore please make sure to review your results from the last modules and any feedback that you may have received on your work, in order to prevent continuing with faulty data.

1. Selected Aircraft (from module 3 & 4):b17 bomber

1. Aircraft Maximum Gross Weight [lbs] (from module 3 & 4):65500 lbs.

Jet Performance

In this first part we will utilize the drag table that you prepared in module 4.

Notice that the total drag column, if plotted against the associated speeds, will give you a drag curve in quite similar way to the example curves (e.g. Fig 5.15) in the textbook. (Please go ahead and draw/sketch your curve in a coordinate system or use the Excel diagram functions to depict your curve, if so desired for your own visualization and/or understanding of your further work.)

Notice also that this total drag curve directly depicts the thrust required when it comes to performance considerations; i.e. as discussed on pp. 81 through 83, in equilibrium flight, thrust has to equal drag, and therefore, the thrust required at any given speed is equal to the total drag of the airplane at that speed.

Last but not least, notice also that, so far, in our analysis and derivation of the drag table in module 4, we haven’t at all considered what type of powerplant will be driving our aircraft. For all practical purposes, we could use any propulsion system we wanted and still would come up with the same fundamental drag curve, because it is only based on the design and shape of the aircraft wings.

Therefore, let’s assume that we were to power our previously modeled aircraft with a jet engine.

1. What thrust [lbs] would this engine have to develop in order to reach 260kts in level flight at sea level standard conditions? Notice again that in equilibrium flight (i.e. straight and level, un-accelerated) thrust has to be equal to total drag, so look for the total drag at 260kts in your module 4 table. (In essence, this example is a reverse of the maximum speed question – expressing it graphically within the diagram: We know the speed on the X-axis and have the thrust required curve; that gives us the intercept point on the curve through which the horizontal/constant thrust available line must go.)

1. Given the available engine thrust from A. above, what is the Climb Angle [deg] at 200kts and Maximum Gross Weight? (Notice that climb angle directly depends on the available excess thrust, i.e. the difference between the available thrust in A. above and the required thrust from your drag curve/table at 200kts. Then, use textbook Eq. 6.5b relationships to calculate climb angle).

1. What is the Max Endurance Airspeed [kts] for your aircraft? Explain how you derived at your answer.

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