# How much energy is consumed by a aircraft to maintain a speed of sound? [closed]

Let's assume that the aircraft is 1000kg and it is flying in a air density of 1.225kg/m^3 at the speed of sound in air.

Just how much energy does it require per second to maintain flying at this speed.(Please make other necessary assumptions.)

Thank you.

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## closed as off-topic by Chris White, akhmeteli, Nathaniel, Dilaton, Qmechanic♦Jul 10 '13 at 12:40

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Questions that basically come down to "solve this numerical problem for me" usually aren't well received here... did you try to solve this yourself? What did you try? Where did you get stuck? – Kyle Oman Jul 9 '13 at 23:31
Sorry, and thanks for letting me know. – user26863 Jul 10 '13 at 8:44
"Other necessary assumptions?" Okay, the air craft is a long, thin rod about the diameter of a pencil, with tiny wings. No wait, it's a 500 kg jet engine, dragging behind it a large diameter open parachute made of 400 kg of nylon. – Kaz Jul 10 '13 at 22:37

## 1 Answer

Along the lines of what Kyle is saying, nobody is going to do the calculation for you, but I think the answer is conceptually more comlpicated that the other two clear regimes (supersonic and subsonic).

Supersonic flight and subsonic flight incur two different kind of airflow. Trying to travel at exactly the speed of sound would present a lot of difficulties in the first place, because the speed of sound is sensitive to air composition and temperature, which will change as you traverse the sky.

Regardless, this speed of travel, near Mach 1, is called "transonic" and encompasses a range where both supersonic and subsonic flows co-exist in complicated and chaotic ways: it can cause a lot of instabilities and put undesirable sheer forces on the aircraft, so the aerodynamic design of the aircraft is going to have a significant effect. Between the increased drag force associated with transonic speeds, the instabilities causing control problems, and possibly having to endure several shock waves, I speculate that it would take a lot more energy than traveling at either supersonic or subsonic speeds.

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Hello, I do agree that at transonic speed there are a lot more that need to be taking into account but if it was supersonic, would you say that considering the work done against the drag is a good approximation of the energy consumption? Thanks. – user26863 Jul 10 '13 at 8:47