What is windmilling drag?

Drag is a function of blade area for a stopped rotor and a function of disc area for a windmilling one.

Why does a windmilling prop create more drag?

It’s all related to blade angle. A windmilling prop turns, because the blades are at a flatter angle in relation to airflow, like a pinwheel. A stopped propeller’s blades are perfectly perpendicular to airflow, so no rotation, much less drag…

What does feathering a prop mean?

This process is referred to as feathering. The inflight feathering of the propeller, on an engine that has failed or has been intentionally shut down, greatly reduces the drag that would occur with the blade pitch in any other position.

Can a propeller create drag?

For example, although a propeller makes thrust to move you forward, it also produces drag that tends to hold you back and slow you down, and the amount of drag it makes depends on the angle of the blades. Unlike with a plane propeller, drag isn’t an issue, so it doesn’t really matter how big the blades are.

How do you use Prop feathering?

Most feathering systems for reciprocating engines sense a drop in oil pressure and move the blades toward the feather position, and require the pilot to pull the propeller control back to disengage the high-pitch stop pins before the engine reaches idle RPM.

Why is there a minimum feathering rpm?

All oil pressure is dumped from the governor, and the counterweights drive the propeller blades towards feather. As centrifugal force acting on the counterweights decays from decreasing rpm, additional forces are needed to completely feather the blades.

Why is propeller blade twisted?

There is a twist along the length of a propeller blade because the blade speed is much higher at the tip than it is at the root. The twist is necessary to maintain a more or less constant angle of attack along the length of the blade. As an example, increasing the aspect ratio of the blade will reduce drag.

What does feathering a prop do?

The inflight feathering of the propeller, on an engine that has failed or has been intentionally shut down, greatly reduces the drag that would occur with the blade pitch in any other position.

What is the benefit of a constant speed propeller?

Some of the benefits of a constant speed propeller: Optimum RPM is set with the propeller control, allowing the propeller to adjust automatically to the most efficient pitch angle. As airspeed increases, such as in a descent, propeller pitch is automatically increased keeping the RPM the same.

What do pilots do during engine failure?

If an aircraft suffered engine failure on takeoff, the standard procedure for most aircraft would be to abort the takeoff. In small airplanes, if the engine failure occurs before VR (Rotation Speed), the pilot should reduce throttles to idle, deploy speed brakes (if equipped), and brake as necessary.

How much drag does a windmilling propeller create?

Overall, the actual propeller parasitic (simple aerodynamic) drag increases by up to a factor of 3. Not orders of magnitude, but it’s significant. Since there’s no way for me to estimate how much of the total drag is due to the propeller, all I can say is that this is probably noticeable.

Why do wind milling blades create more drag?

The reason wind-milling blades cause more drag is because they’re going faster. An autogyro has huge blades and very little other drag. An aircraft has much smaller blades and lots of induced drag from the wing. So while the drag from the prop may be an order of magnitude higher, the total drag will not be.

What happens when you stop a windmilling engine?

If you are high enough when the engine stops, it’s a good idea to slow down a little so that the propeller stops windmilling. Once it has stopped, you can accelerate back to normal. The propeller will usually not start windmilling again, as it’s drag, and thus available power, is now much lower.

How does a feathering propeller reduce aerodynamic drag?

(Feathering props are used on multi-engine planes to reduce drag if one engine fails. Non-feathering props are used on single-engine planes so if the pitch control fails but the engine still works, you don’t lose all your power). Overall, the actual propeller parasitic (simple aerodynamic) drag increases by up to a factor of 3.