Axial prop question

Douwe · 10 November 2005, 05:56 AM

I am a bit confused by the results of my research into Mercedes/BMW props. I've assembled some sizes for different props from different HP engines and they don't make sense. Higher HP sometimes means a longer prop, sometimes not... sometimes they're pitchier, sometimes not...

Anways, my question is this. I have figures that show a 278 X 220 prop being used on both a 180 Mercedes, and a 160 Mercedes. The Oberusel 110 used a prop that is stated as 278 X 220 as well. WAS THIS THE SAME PROP as the mercedes mentioned above? The measurements are the same. Did the Merc just turn it up faster? OR was the cord on the Merc prop wider? As far as I can tell, those are the only two possible differences, except for a different airfoil, which I highly doubt. From a thourough study of photos, the props on the rotary and the smaller Mercs appear identical, I can observe no cord differences. I'm getting ready to build one and am very much in need of any help.

If anyone is interested, or cares to edify me, here is my list of prop sizes:

160 merc (pfalz DXII in France) 278 X 200
160 merc (Tallman's old DXII) 174 X 195
160 Merc 278 X 220
170 merc 300 X 275
180 merc 278 X 220
195 BMW 280 X 190
BMW 200 280 X 212

I can't figure these out. The sources are pretty good, though one never knows if the props are original to the plane/engine found upon. But unless there were cord differences, I can't see how some of these engines performed differently from their lower HP brothers unless they turned faster, which it doesn't seem like they did.

??

franzkait · 10 November 2005, 10:09 AM

the mercedes 160 is only the name, all this engines have moore hp. the normal diameter is 276 cm , but 270 is also possible. Oberursel Ur2 has 162 cm .

franzkait · 10 November 2005, 10:10 AM

262 cm !!!!!!!!!!!!!!

wulffo · 11 November 2005, 06:30 AM

Quote:

Originally Posted by Douwe

160 merc (pfalz DXII in France) 278 X 200
160 merc (Tallman's old DXII) 174 X 195
160 Merc 278 X 220
170 merc 300 X 275
180 merc 278 X 220
195 BMW 280 X 190
BMW 200 280 X 212

??

As Franzkait already statet the 160 / 170 denotes the engine and nominally the horsepower. The number with the d in your case the first number is the diameter or nominal length of the prop. The actual length has been known to vary by several centimeters. The second number should be the pitch of the props and here I believe lower numbers are for higher speeds hence fighters and vice versa. Hence: 160 Merc 278 x 200 should be a prop for the 160hp daimler engine (often the boss is stamped 160PS with PS the abbreviation for horse power... which differs though in the actual value from HP's). 278, often written D278 would be the nominal diameter. On averaverage the actual diameter should be within 3 cm.... otherwise you may be looking at a shortened/deactivated prop that has been refurbished. The last number should denote the pitch. I believe that on your list above: ''160 merc (Tallman's old DXII) 174 X 195'' should be 274 x 195 and I think that this could have easy added to your confusion.

Dave_Watts · 11 November 2005, 11:22 PM

Hi Douwe,

You may already have my information from my prop as I see a listing of the same type;

8644
AXIAL
160PS
D278
ST220
TP 95

Hope it is of help.

Best,
Dave W.