Where can you get the drag polar of the A320 at cruise and TakeOff?
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1$\begingroup$ To have an idea of thrust you can check engine public data (Maximal thrust is usually during T/O) $\endgroup$– Acsed.Commented Aug 4, 2020 at 19:05
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1$\begingroup$ resource location is off topic as defined by the help center. You'd better directly ask for the polar instead of its location. $\endgroup$– Manu HCommented Aug 5, 2020 at 21:28
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$\begingroup$ Are you asking for the thrust or are you asking for the drag polar? Those are two different questions.... $\endgroup$– JanCommented Aug 6, 2020 at 5:49
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2 Answers
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A320 family's engine of choice is the CFM56-5B. Now there are multiple variants of this engine. But on average the takeoff thrust for the models -5B1/B2 and -5B3 are between 30,000 to 33,000 lbf.
Other variants have a lower thrust rating between 21,000 - 24,000 lbf and 27,000 lbf.
The cruise thrust is lower of course since the aircraft has already taken off and now in upper atmosphere, with low drag and running at its best efficiency. Cruise thrust is about 4,700 to 5,800 lbf, although these are the maximum rated cruise thrust, so the engine thrust is always lower than that. Say if the engine is rated for 5,800 lbs the actual thrust would be roughly about 5,300 - 5,500 lbs, maybe even lower.
Feel free to correct me if I'm wrong!
Reference
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Takeoff thrust depends on many factors and needs to be calculated carefully. You can take the max values from the manufacturer in orther to have an idea.
Cruise can be calculated roughly. Let's see an example. We know that during cruise phase all four forces are level.
Lift = Weight and Thrust = Drag
We also know that an airliner such as the A320 is very efficient and can easily have a glide ratio of 18:1 This is known as Lift / Drag (L / D) ratio. If the plane flies near its optimal L / D of 18 at cruise then the CD / CL is 0.055556. The airplane begins its cruise phase after the climb, but we can assume that its mass is close to that of the takeoff minus the fuel consumed for the climb. Say our weight is 44 tons.
With these data we see that the drag force is 1/18 of the force generated by the mass of the plane. Weight is mass multiplied by gravitational acceleration: 44,000 x 9.81 = 431,640 N. Therefore, drag would be 431,640 / 18 = 23,980 N in this phase.
Let's assume that at the end of the trip and before the descent, the plane could have burned 1.5 tons of fuel; in that case the drag will be 23,162.5 N. These calculated values are the total drag (induced and parasitic) of the plane, but in cruising flight it is also the same value as the engine thrust, since T = D. If we change in lbf we have values of 5,391 and 5,207, far from the maximum rated thrust for cruise.
