Prop blade markings

modeldad · Post by **modeldad** » Tue May 15, 2007 7:04 am

Does anyone know the purpose of the line on the back side of the prop blade? Seems like it would cause a stroboscopic effect.

Post by **Editor** » Fri Jun 22, 2007 7:59 am

Steven, try reading Stefano's article:

A Famous Torpedo-Bomber S.79 Carlo Emanuele Buscaglia's “281-5" - Part II

modeldad · Post by **modeldad** » Fri Jun 22, 2007 8:23 am

Didn't have to try, I could.

So the effect is like the speed adjustment on a turn table. Ever own a Dual turntabel?

I wonder if there was another registration marking against which the mark was set.

I think it would drive my crazy, if I was the pilot.

But what I found most interesting is that even as late as well into 1941 the undersides of the SM 79 were aluminum, not grey. This would be more circumstantial evidence that the Fiat Cr 42s that crashed landed in the UK , during the BoB, did have aluminum undersides, as reported by the British. Guess some aircraft makers didn't want to toss alt the unused aluminum paint. Or didn't care about the Table 10 specs, or any other specs.

Post by **Editor** » Fri Jun 22, 2007 8:35 am

I had no doubt you could

Never owned a Dual turntable but the effect is the same. The lines were used as measuring instruments for determining cyclic speed (rpm). A common use of stroboscopics (light) is to set the ignition timing of internal combustion engines.

Great question!

modeldad · Post by **modeldad** » Fri Jun 22, 2007 8:51 am

which raises another question. Was there a stroboscopic light mounted on each cowlings?

Seems all rather primative, considering RPM gauges were probably available.

Ah yes, I do now remember the days when setting the engine timing was a mechanical task. Now I dare not even look under the hood for fear of disturbing the computer. Besides, everything mechanical is pretty much covered.

Post by **Editor** » Fri Jun 22, 2007 9:20 am

I don't think a stroboscopic light was used (or that any kind of lighting device was mounted on the engine cowling). I think the speed was controlled via reflection since the strips were mounted against a black background. Rpm gaugues were in common use, however I don't think the rpm gauges were as accurate as the pilots would have liked (I'm only guessing here).

No easy task to service your own vehicle these days besides I think you null the warranty if you do, and as you mentioned everything is covered in either wire or plastic - you need an expensive service manual and costly instruments.