#### Jean Claude

##### Junior Member

- Joined
- Jan 2, 2009

- Messages
- 2,577

- Location
- Centre FRANCE

- Aircraft
- I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C

- Total Flight Time
- About 500 h (FW + ultra light)

**Title:**Negative Thrust and torque characteristics of an adjustable pitch-metal propeller

**Author:**Edwin P. Hartman

**Ref:**NACA report n° 464

**Comments:**This report can be used to predict the drag of a propeller accidentally freewheeling, due to a broken gearbox belt, or transformed into a windmill driving the dead engine, or simply idling.

How can we find the drag of a freewheeling propeller from this report?

Since level 0 of the torque coefficient (Q / ρV2D3) corresponds to zero torque, i.e. perfect freewheel operation, note the abscissa where level 0 intersects the torque curve corresponding to the pitch of your propeller (e.g. 22° at 0.75 R, top graph) (here, nD/V =0.83).

If your propeller has a diameter D of 1.65 m, then at a forward speed of 25 m/s it will reach :

n = 0.83*25/1.65 = 12.6 rpm or

**756 rpm**

On the lower graph, the drag coefficient curve corresponding to your 22° pitch gives a value of - 0.01.

Since the drag coefficient is Tc/ ρV2 D2 , the propeller thrust will be :

T = -0.01*1.22*252*1.652 =

**-21 N**

The propeller mentioned in this report have D= 9 fts (2.74 m), pitch 17° and V =100 mph (44.7 m/s) would have given

nD/V = 1.03 Hence n = 1.03*44.7/2.74= 16.8 t/s or

**1008 t/mn**

and T = -0.015*1.22*44.72*2.742 = 274 N or

**60 lbs as was well found**

It's very clear that rpm and drag increase dramatically as propeller pitch decreases.

It's very clear that rpm and drag increase dramatically as propeller pitch decreases.

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