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Bigger spinners !?

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Retroflyer_S

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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.
 

StarJar

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It may be a cheap way to raise performance instead of a prop extension. The larger circle will start getting above the cowling though, so you might need a cowling that looks like the hood of a supercharged dragster.
 

DangerZone

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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.
 

Dan Thomas

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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.
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.

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.
 

Eduardo Fadul

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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.

prop.jpg

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
 

DangerZone

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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.

View attachment 44217

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


It seems you and Dan are talking about different things. You are talking about thrust of the propeller and air passing around the cowling and he is talking about cooling the engine with the flow of air that slips around the spinner to enter into the cowling inlets past the propeller disc.
 

Dana

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I flew my plane a few times without the spinner and observed no difference, either in performance or cooling... granted it's a small spinner. OTOH, I saw a report from a guy who added a spinner to his powered parachute (pusher installation) and noted a significant thrust increase.

Dana
 

Retroflyer_S

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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.

I may have exaggerated the meaning of the spinner here...spinner is part of the completely aerodynamic fuselage...definitely bigger than in other planes in the market.


In AR-5 they have chosen not to use a spinnr and made a really smooth cowling.
 

Jay Kempf

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The AR-5 is a fine example of how in a question like this that it depends.

I am sure if you ran the P51 without a spinner you would lose a lot off the top end and you would hurt climb due to turbulence. The AR5 is using the air where the spinner would normally be to ram the cooling duct. But you could still use a spinner and shape the inlet and get some result.

Slower speeds on draggy craft aren't going to matter much. If you have a large engine to package and you don't do something to smooth the nose, prop and cooling you can create a lot of drag. I am sure some planes out there have 30 or more percent of their drag in bad cooling and horrible engine installations. Lots of people stuffing large engines in the root of the Long EZ wing. Some of those are hideous in terms of aerodynamics.
 

WonderousMountain

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I think we can get quite a lot of performance out of a less cheeky plane,
though, I've seen some really good examples of flat engine styling on this sight.

The size of the spinner makes almost no difference, however, with a small spinner and the ogive cone shape, you're looking at a prop extension, or a shaft.

So the larger spinner is a far more sensible approach. That said, it will impart a swirl to the air the spinner hits, as a surface at greater speed than free-stream.

The Sirius is a good rendition of the most common configuration.

LuPi
 

JamesG

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The size of the spinner is dictated by the size of the cowling behind it, which is dictated by the size (frontal area) of the engine within it.

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.
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.

One of the aerodynamics books goes into great detail of the NACA tests for all this. Can't remember which one...
 

karoliina.t.salminen

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Stemme has big spinners on them.
In small RC scale hotliners have large spinners
that leave no gap towards the fuselage.
Air does not like to do bends, so I have hard time
believing small spinner with a discontinuity with
shape would be advantageous to a continuous shape.
 
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