You might want to verify such claims because even in the case of Mike Arnold's AR-5 (with excellent aerodynamics) the spinner had marginal influence. From the data of his record attempt flight, I think that NO spinner allowed a slight speed INCREASE (less than 0.3%) than having a spinner. Torpedo and rocket engineers had similar conclusions, in some applications 'blunt nose' objects showed to have less actual drag than sharp nosed ones. This led Mike Arnold to form the nose of his AR-5 the same way a blunt nose torpedo is shaped and reach the high speed record of the time.Sinus ( 80 hp ) with bigger spinner is 110 km /h faster than more powerful ( 100 hp ) Zenair CH 701.
I think the spinner plays a role in it too.
Not true. Propeller designers don't spend time on the center third of the propeller for nothing. The whole blade is busy generating thrust; if it wasn't so, all you'd need would be short bits of airfoil near the tips.Almost the center 1/3 of the prop is dead (no thrust generated) so you can make the spinner as big as practical/beautiful you want.
Sure that almost the whole propeller generate thrust, I do not know if I could not explain well. What I am saying is that the percentage that the center third is small enough to neglected the area of the spinner, if we see the whole prop.
This is the result of the example 14-18 of the book General aviation aircraft design - Snorri Gudmunsson, page 643. It is blade theory with the limitations of this theory, however could give us a good idea.
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General Aviation Aircraft Design: Applied Methods and Procedures: Snorri Gudmundsson: 9780123973085: Amazon.com: Books
In the "normal" LSA category, the spinner hardly will be bigger that 1-2 ft, that will take us to the station +/- 5 of the X-axis. As we can see the percentage of thrust (Y-axis) is really few, so I won’t will spend too much time sizing the spinner looking for any major aerodynamic advantage, as long as it can help us with the general reduction of drag and the cooling of the engine, I will be satisfied.
Regards
Sinus and CH 701 are aerodynamically so different that it would be ridiculous to compare the two at level spinner versus no spinner.Sinus ( 80 hp ) with bigger spinner is 110 km /h faster than more powerful ( 100 hp ) Zenair CH 701.
I think the spinner plays a role in it too.
You might want to verify such claims because even in the case of Mike Arnold's AR-5 (with excellent aerodynamics) the spinner had marginal influence. From the data of his record attempt flight, I think that NO spinner allowed a slight speed INCREASE (less than 0.3%) than having a spinner. Torpedo and rocket engineers had similar conclusions, in some applications 'blunt nose' objects showed to have less actual drag than sharp nosed ones. This led Mike Arnold to form the nose of his AR-5 the same way a blunt nose torpedo is shaped and reach the high speed record of the time.
The Sinus is faster than the CH-701 because it has less drag, not because it has a bigger spinner.
This. In fact they are part of the entire cowling system. They set up the airflow through the prop and into the cowling ducts and fairing. But as a factor of streamlining, either in tractor or pusher, not so much until you get up into really high airflows. Most spinners are just there to make the airplane look pointy and fast.Spinners are often part of the cooling system. Take the spinner off some airplanes and the engine will overheat. The spinner guides the air into the cowl inlets in such airplanes and prevents cooling air from escaping back out at the prop hub. The equipment lists of certified airplanes will show whether the spinner on that design is an option or a required item.