Brett brings up an important thought: the 'pitch' marked on the prop may not be the same as the measured pitch. Normally, the flat rear face of the prop is used to measure 'pitch.' Props have - usually- flat bottom airfoil blade cross sections; the 'effective pitch' of the blade is NOT the same as we can measure from the flat rear face.
A flat-bottom airfoil has a 'zero lift' angle of incidence above the angle of the flat bottom. (I.e., for the airfoil to produce NO lift, the LE must aim down a certain angle to the direction of airflow passing over the blade.) Back in the 1940's a guy named Raul Hoffman wrote a book to make understanding model airplane aerodynamics simpler...
(Yeah, right....)
One useful thing I retrieved from the wizard's mysterious mumbo-jumbo was that a flat-bottom airfoil's 'zero lift' angle of attack could be estimated as about half the angle at which the upper and lower surfaces meet at the trailing edge. A SWAG, sure, (emphasis on WILD) but it DOES suggest the idea that measuring pitch off the back face of the blade does not give us a realistic understanding of what the blade airfoil is trying to do.
Example: back in the 1970's, the Rev-Up EW props were considered very useful for stunt. Their back faces consistently measured 1/2 to one full inch less pitch than the labeled pitch. The EW (Extra Wide) Rev-Ups also spread the airfoil over a greater 'chord' (prop LE to TE at radius stations out from the hub) for the blade thickness, so the airfoils had a 'thinner' section - less drag? - than standard or "single-wide" Rev-Ups. I wonder: was the quoted pitch the result of observed/measured in-flight performance, or just factory claim?
(NOTE for our younger pals: Rev-Ups were wooden props, of decent but not perfect geometry and wood density from left to right. I miss them, but realize that props of that general quality today would need to be in the Bolly/Eather price range. ...And would still be subject to wood density variations.)
Back to the topic title: Has anyone measured the back-face pitch of available X-4" pitch props to check whether 'claimed' pitch might be 'observed performance pitch' rather than 'back-face measured pitch'? I wouldn't be surprised if nominal 4" pitch props occasionally measured (back-face) less than 4" pitch...
It wouldn't surprise me if the back-face measured pitch turned out to be less than the labeled pitch. except for some high priced, or APC moderate-priced, props. This is just another aspect to be considered.
Topic: 11/3 propellers (Read 1175 times)