Bigger spinners !?

[JamesG]

 

[Daleandee]

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.

My Corvair powered Sonex needs a larger spinner to cover the size of the front mounted flywheel/starter setup. With the 13" spinner in the middle of a 54" prop some like to ask, "where's the rest of your prop?" - but in fact it is the same size prop that Sonex recommends for their aircraft with VW and Jabiru engines.

One builder with a 3300 Jabiru changed his cowling from the standard Sonex "pug-nose" cowling with the dinky spinner to the "Cleanex" style that uses the 13" Van's spinner and noted that both cooling and airspeed were improved. I understand that cooling engines involve more than just spinners but my 3.0 Corvair engine almost runs too cool using the large spinner in front of the cowling that Dan Weseman designed for it. Not to mention how much better the airplane looks ...

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
107.3 hours / Status - Flying
(Myunn is in the "Completions" section of Kitplanes for November 2015)

 

[Will Aldridge]

Mike Arnold noted that wind tunnel tests found that the air "piled up" I think was the term he used in front of the engine face on radial engined aircraft creating a natural spinner thus there was little to be gained by having a spinner except extra weight.

Obviously a significant difference between a corsair that needs cooling air going through the cowling and a mustang that doesn't. Btw I've seen pics of a corsair with a spinner on it (wartime not racer ) so I know Vought or the navy was looking for performance increases and obviously it didn't make enough of a difference to be considered cost effective.

 

[StarJar]

Have you guys/gals seen the new floater spinners that don't spin with the prop? They just sit there, or turn about 5 rpm.

 

[mcrae0104]

If you want to use a big spinner for better streamlining, by all means, do it. But, it shouldn't be too large in proportion to your prop diameter, and if you have air inlets on either side, you may find that the larger spinner pushes your cooling air outboard of where you want it to be. I have done some work looking at the largest spinner I could use but there is a point at which it will add cooling drag because the airflow inside the cowl will stall (bending sharply to get it back in line with the cylinder heads).

 

[Dan Thomas]

Have you guys/gals seen the new floater spinners that don't spin with the prop? They just sit there, or turn about 5 rpm.

They couldn't fit over the blade roots then. What would be the point to having it on bearings?

 

[StarJar]

They couldn't fit over the blade roots then. What would be the point to having it on bearings?

Ya, you're right. I was seeing if I could trick anyone.:emb:

 

[JamesG]

Only if its chromed and 21" in diameter.

 

[karoliina.t.salminen]

Watercooled engine enables Mustang scoop and no spinner size reduction
for inlets is necessary because there are no inlets in prop root. Literature
states that the prop efficiency is negatively
affected by any obstacles behind the prop. A large spinner would make the obstacles faired.
Faired typically is better than unfaired. Obviously use of old fashioned air cooled engines have negative impacts on freedoms for the designer as the engines used are inferior to those used already in 1940s in the Mustang.

 

[Aesquire]

The Stemme 10 series doesn't actually have a spinner. It's a nose cone. That is pushed forward to allow the folding prop to spin.

The 6 does have a large spinner. With feathering prop. Neither has cooling openings in the nose. The 10 loses a bunch of prop efficiency with the nose cone gap compared to the 6, but gains drag reduction when the prop is stowed and nose cone retracted.

I love the Stemme planes. Hard to pick better examples of where compromises are made.

The complexities of a mid engine P-39 drive system are used in both to provide "normal" sailplane visibility and drag reduction.

The additional complexity of a hiding prop system is used on the higher "performance"..... & cost model.

 

[Norman]

Have you guys/gals seen the new floater spinners that don't spin with the prop? They just sit there, or turn about 5 rpm.

If anybody is actually selling that it's just a gimmick. The spin of the nose cone only affects the boundary layer on the nose cone, the potential flow outside of the bounder layer is not strongly affected by the spin, certainly less than by the prop.

 

[Tiger Tim]

You might be on to something here. Although there was no propellor involved, the Apollo Command Module had an end like an enormous blunted spinner and it did over 17,000 miles per hour on re entry!

 

[Aesquire]

Yes, but it would have gone faster if it was pointy!

 

[Dan Thomas]

Yes, but it would have gone faster if it was pointy!

Yeah, but they didn't want speed. They had to slow it from 17,000 MPH to some speed where they could pop the 'chute.

I bet the engineers had fun coming up with a shape that wouldn't oscillate on descent.

 

[JamesG]

The smooth shape of the heat shield and the placement of CG (low and fwd) dampen out ossollation. Its a very dynamically stable shape.

 

[gtae07]

Yes, but it would have gone faster if it was pointy!

And gotten a whole lot hotter, too.

 

[H.Evan'sRV7A]

This will be a little controversial, but elements of it have been presented to several "experts" who were unable to deny the factual part. Here goes:

1. Contrary to most commonly accepted wisdom, IMHO, the air hitting the prop (front engine) is not actually slowing down or at least very little. Rather, it is hitting the prop at an angle to the free stream as it diverts to go around the cowl. Prop designers deal with this as if it were slowdown, using the leg of the triangle as the slower speed. The bug streaks on my prop are sufficient proof that the angled hit takes place. I'm seeing between 30 and 45 degrees.
2. In my view, the problem with this is simply that the air near the base is (thus) seeing an airfoil with a longer chord than if it were measured parallel to the stream. Different airfoils have different behaviors. Until very recently, prop designers did not handle this or at least not in they way that I think they should.
3. If the spinner could be made larger AND the prop designed to correctly handle the airflow, then I think some gain might be possible because the farther out on the prop you go, the higher the Q and the higher the Reynolds number. The mass of air hitting the prop disk is the same but how it is further accelerated is where there is room to improve.
4. Craig Catto is experimenting with fences on props in the middle area to alter the spanwise flow. He is seeing some improvement. He also pays a lot of attention to the inner or root area. You can speculate as I do that a larger spinner fits this view of potential improvement. Craig's gain may just be reduced loss to induced drag at the tips, though. In his recent work his prop was used to set another record. That airplane has a very long, pointy "nose". I really don't think that's an accident.
https://www.facebook.com/cattoprops/photos/a.303998146424926.1073741832.303902023101205/530160723808666/?type=3&theater

OK, flame away.

 

[StarJar]

I believe there is room for improvement. It may mean shifting several things around.

 

[Dan Thomas]

1. Contrary to most commonly accepted wisdom, IMHO, the air hitting the prop (front engine) is not actually slowing down or at least very little. Rather, it is hitting the prop at an angle to the free stream as it diverts to go around the cowl. Prop designers deal with this as if it were slowdown, using the leg of the triangle as the slower speed. The bug streaks on my prop are sufficient proof that the angled hit takes place. I'm seeing between 30 and 45 degrees.


OK, flame away.

Here's the flame.

Prop makers have known that for a long time. That's why the TCDS for certified airplanes specify which props may be used, and those props are very often designed to satisfy the airframe manufacturer's engineers. They might want more or less pitch in the center area for more or less cooling flow. They might even want more blade area in the center. If you sight down some propellers, especially along the trailing edges, you can see some fairly abrupt changes.

The other problem with the prop: it's travelling upward on one side and down on the other, so the two sides see different airflows, even in level flight. Pretty hard to design a prop to handle both sides well. If the airflow is moving outward and downward around the cowl, for instance, the upgoing blade has a higher AoA than the downgoing blade. At the bottom, the airflow is moving sharply downward, while at the top it's almost straight.

Wind tunnels with smoke streams have been used for a long time to see this. Computers can probably do it much more easily and cheaply now. But the problem of uneven divergent flow is still there unless you're flying a round engine.

 

[Marc Bourget]

Retroflyer said: "I may have exaggerated the meaning of the spinner here...spinner is part of the completely aerodynamic fuselage"

Exactly, and all portions should be coordinated with the others. John Thorp told me that he had to "coordinate" 5 pressure distribution curves from the spinner to the firewall on the T-18.

mjb