In some respects, Germany had led the way in propeller design by introducing wide, broad chord blade propellers. If one looks at the narrow chord blades of the Luftwaffe’s Bf 109E fighter and compares these to the later Bf 109G, it is readily apparent that the latter’s propeller blades have widened considerable. The earlier VDM, variable pitch propeller worked reasonably well at converting the Daimler-Benz 601 engine’s power into thrust. However, as the weight and drag of subsequent models increased, so did the horsepower requirements. With the increased power came the need to utilize that power in a more efficient manner. Thus, German engineers looked to the propeller design as the solution to getting the power to the road, to use the common metaphor. Ultimately, these engineers decided to remain with three blades, rather than four (or more) as incorporated by British and American designers. It must be assumed that the efficiency of their design did not require more than three blades. Perhaps the penultimate example of the German three-blade design resides in those used on late war fighters such as the Fw 190D and the Ta 152. Indeed, the chord to span ratio of these propellers is dramatic in comparison to the “toothpick” blades used on virtually every fighter in the American inventory through 1942. Another noteworthy observation of the German designs shows us that the propeller blades were not “clipped”, or squared off. The blades have a semi-elliptical trailing edge that tapers to a tight radius at the tip. There can be little doubt that this shape was found to be acceptable. 3 blade vs 4 made interupter gear easier to work? is one thought/comment worth adding. & Russians were well impressed with the wide Dora prop. See if I can find the comment.
I wonder if it made a difference if the prop was metal or wood ? Also I know different manufacturers tried contra-rotating props but it usually failed in practice. Ducked fan props have been tried alot over the years but I don't know what their drawback is.
Good question. Dora prop was wood. Some late k-4 also had wood props. It's either lack of metal or lighter weight of wood increases performance somehow. Here's more... Ultimately, the propeller designers gradually turned to blades of greater chord. Moreover, that chord was extended closer to the propeller hub, blending into the cuffs on the Hamilton Standard 24D50-65 installed on the Mustang. Curtiss Electric props incorporated increased chord, but they narrowed down to the reverse taper of the cuff. By their appearance, the new prop blade designs did present more than a passing likeness to a canoe paddle. Hence the term, “paddle blades”. One striking difference between the American propellers and those of Germany was that the “paddle blades” were more of constant chord taper. Whereas the Germans utilized a more pronounced taper leading to the tip. It might be speculated that the German designers did not want to place the greatest width of the prop near the tip. Reasoning for this may be that it made little sense to do that because of the great loss of efficiency when the tip velocity approached the speed of sound. Therefore, the greatest width of chord can be seen at the mid-section of the blade. However, one must wonder how much thrust was sacrificed by tapering the trailing edge so much when the loss of efficiency was likely no greater with Aeroproducts constant chord, squared tip design. Certainly, by 1944, the Americans and British had not only caught up with the Germans in propeller design, but probably had surged ahead. Scroll to the bottom & some cool Dora prop shots can be seen. http://www.largescaleplanes.com/articles/WW2/JeffreyBrundt/Dora/Dora_2.html
