Well, any speed above Mach 5 (5 times the speed of sound) is considered hypersonic. Planes with a triangular design are perfect for said speed, reducing fluid friction of the air around it and the immense heat it will generate.

I cannot give you a number without a specific speed or aircraft, but from what you are asking, it would be minute. Air is a fluid like water, and any aircraft is built to be aerodynamic.

Here's how you can figure it out. The friction force experience by a surface can be non-dimensionalized into a coefficient of friction. To do that, divide the friction force (measured in pounds-force or Newtons) by a reference area (measured in square feet or square meters) and a dynamic pressure (measured in pounds-force per square foot or Newtons per square meter).

For a fairly smooth surface in hypersonic airflow, the coefficient of friction might be something like 0.001 to 0.002 - seems like pretty small stuff!

Hypersonic aircraft are often designed to fly at dynamic pressures of about 1000 pounds-force per square foot. That's equivalent to Mach 5 at an altitude of about 80,000 feet (~24 kilometers), or Mach 10 at 110,000 feet(~34 kilometers) .

If you multiply these numbers, you'll find that a square foot of exposed surface will experience a friction force of 1 to 2 pounds-force ( about 4.5 to 9 Newtons). So, a hypersonic airplane with about 1000 square feet of surface area would have 1000 to 2000 pounds-force of drage due to friction.