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Reverse Engineering a WWI Wooden Propeller

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FokkerDVII

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Hello everyone. New guy here needing help. I have a set of plans drawn from an original WWI propeller that was used on Fokker D.VII aircraft. It shows angles of the various cross sections, but doesn't give the actual pitch of the propeller. From the following info is it possible to determine the prop's pitch?

Thanks Chris

Diameter2800mm
Radius %
Angle
10
-
2045º 20'
3034º
4026º 50'
5022º 02'
6018º 38'
7016º 08'
8014º 12'
9012º 40'
10011º 51'

 

Jan Carlsson

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Yes, whats the problem?

Here is a picture that show the helix drawn on a flat paper, where the hight is the pitch, and angle is the beta angle.

http://commons.wikimedia.org/wiki/File:Propeller_pitch.gif

P is Beta Tan * radius * 2 pi() simple as that.
1781 mm at 70%
1780,7 mm at 80%

Sounds little for a DVII
what does it say on the drawing? engine? RPM? Power ?

Jan
 
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FokkerDVII

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Sounds little for a DVII what does it say on the drawing? engine? RPM? Power ? Jan
Thanks Jan

There is no engine, RPM or HP info on the drawing. I did find this document and it agrees with your findings, but diameter is 5 cm smaller. (Wolff prop) The prop must be from a very early 160 HP version of the D.VII. Later models with a 200 HP engine using an Axial propeller had a 2120 mm pitch.

http://www.woodenpropeller.com/DVIIMercedes.html

http://woodenpropeller.com/DVII.html

Any idea why the pitch is so different between the Axial and Wolff propellers in the chart below when the HP, speed and RPM are the same?


 
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Jan Carlsson

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Good question,

one ansver would be that they have different airfoils, thickness or camber.
Mesuring the pitch at the flat bottom is just don because it is easier, it dos not represent the real pitch, that would be the zero lift pitch angle.

The beta also depends on the CL chosen, higher cl, higher pitch and narrower blade.
 

FokkerDVII

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Suppose we want to build the same prop with a different pitch, using the Wolff drawing above as an example. For any given cross section, if we change the blade angle, does the blade thickness and chord stay the same with the change being the shape of the planform (front and side view) or does the planform stay the same and the blade thickness and chord increase or decrease depending on the angle? Thanks
 
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Dana

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If you change the pitch, it's not the "same prop" any more, so you can change (or not) whatever else you want to. Typically, though, you'd keep the chord and thickness the same.

Dana

Scientists cause cancer in laboratory animals.
 

FokkerDVII

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Sorry I should have been more clear. Not so much what we can do. How was it done in 1918?
 

TFF

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The station thickness with angles will be different; they will not be a lot different unless you are changing 10" of pitch. When carving the stations, they will naturally assume the correct shape. The trick is more about matching the other side than exact shape, when hand carving. Machine carving can be perfected more as long as you are willing to remake the master blade.
 

FokkerDVII

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The station thickness with angles will be different; they will not be a lot different unless you are changing 10" of pitch.
If the side view and front view planform don't change, it doesn't take much of a pitch change to make the blade thickness increase or decrease drastically.




If we keep same thickness and chord, planform changes in both front and side view.

 
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TFF

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That is a big pitch change. You have to draw where the new leading edge and trailing edge are to get the new cross section; the blade airfoil will follow. It is one of those things where you need to let the chips fly to see how the cross section stays with the leading and trailing edge. With CAD you can force things that will not be natural if done by hand.
 
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