An empty motorless 500 kg boat is drifting on a river. Current is moving at
2.5 m/s, so is the boat. How many H.P has the boat?
BQ
"Bruce Hoult" a écrit dans le message de
...
In article ,
"Jim Kelly" wrote:

"Todd Pattist" wrote in message
news |
| You add to that aerodynamic power any power required
| to climb. That power is climb rate times aircraft weight.
| The total of those two is power required to fly.

Hi Todd,

Would you mind extending this thought to declare a useful quote to
use in "Air Experience Flights" as to what "horsepower" we are
getting from a thermal showing 5 knots lift in a typical club
twin-seater (say a Janus B)?

That's pretty easy.

Call it 500 kg total mass, moving at 90 km/h (50 knots, 25 m/s), with an
L/D of 40, climbing at 2.5 m/s (5 knots).

Drag = 500 / 40 = 12.5 kgf = 125 N.
glide power = 125 N * 25 m/s = 6250 W = 4 HP

climb power = 5000 N (500 kgf) * 2.5 m/s = 12500 W = 16.75 HP


So total HP is about 20.

Change the numbers to suit your reality :-)

-- Bruce