Radial Engines vs Inline Engines?

[bozon]

This is not a hijack, we are still on topic, as everyone will easily point out that one difference between radials and inlines is the frontal crossection area. The "frontal area means drag" often comes up in such debates and I wanted to point out that frontal area has little to do (directly) with drag. Surprising maybe, but this is physics. It is the big hole in the center, the edges of the rim around this hole, and labyrinth of airflow through the engine that makes the difference - also known as "cooling drag".

[pembquist]

It is also relevant that a boat travels in the boundary between 2 fluids and the major limitation on a conventional hulls top speed is simply the length of the thing. The shell benefits from a long length with a low wetted surface, hence the narrowness.

From my limited reading on aerodynamics I have realized that intuition changes with experience and that what Bozon is saying is accurate. The first time I read about supersonic aerodynamics it was a real expansion of intuition.

I'd like to know what the apogee of air cooled engine cooling design was, I read that it wasn't until 1949 that things were really improved on the design side (not counting the original NACA cowl.) And if there are inherent limitations with aircooled engines such that they will always suffer greater cooling drag than you get with a radiator.

[WaffenVW]

Aerodynamics and hydrodynamics are closely related. The two biggest differences are compressibility and cavitation. A conventional boat hull suffers all the same drag penalties as an aircraft fuselage (subsonic) including boundary layer drag.

[DaveBB]

Liquid cooled engines were able to harness the Meredith Effect and actually produce thrust.  For example, the P-51 produced around 1000 pounds of thrust from it's Merlin engine.  The radiator produced an additional 375 pounds of thrust.  So this dramatically offset the cooling drag.  While most WW2 aircraft used about 10% of their engine power for cooling, the P-51 only needed to use about 2%.

[pembquist]

Aerodynamics and hydrodynamics are closely related. The two biggest differences are compressibility and cavitation. A conventional boat hull suffers all the same drag penalties as an aircraft fuselage (subsonic) including boundary layer drag.

Yes, I am not disagreeing with you however a boat hull has the added complication of traveling within the boundary between two fluids, air and water; I didn't mean boundary layer drag. What is boundary layer drag? I know what a boundary layer is broadly speaking. Would this just be a more specific way of describing wetted surface drag? E.G. when the VariEze gets bugs on its canard the laminar flow is destroyed so the boundary layer drag goes up?

Anyway, I don't really think there is any disagreement here I think you are being misinterpreted as saying that the larger fuselage crossection of a radial powered airplane is a significant factor when compared to cooling drag when comparing the drag between a radial vs water cooled airplane that flew in WW2. But I don't think you mean that.

I think if there is a disagreement it would be that what Bozon is saying and I'm believing is that the increase in drag that would come with an increase in fuselage crossection would come mostly if not all from increased wetted area all along the fuselage and not so much from the increase in frontal area. This is assuming that the design of the fuselage does not create vortices that scale with an increase in dimensions.

[icepac]

Scoopless mustangs will eventually be dominating reno.

[hitech]

What you are saying is nonsense. We've hijacked this thread long enough and I'm not going to get into a major aerodynamics debate with you. I'll just end by pointing out that if you want something to go fast in air or water you'd better make it slender and pointy. And the less power you have the more important it becomes. There's a reason these guys aren't sitting two abreast.


(Image removed from quote.)

Waffen simply put, the shape (both front and back) is much  more important then the frontal area. It is about how you divide the air and put it back the way it was with out imparting any movement (energy/drag) to the air.

HiTech

[WaffenVW]

For sure Hitech, but my point was about two otherwise identical aircraft. This discussion has spilled over into general aerodynamics with people discussing all kinds of different points.

Yes it most certainly does. Two aircraft otherwise identical the one with the wider fuselage will produce more drag.

[earl1937]

Waffen simply put, the shape (both front and back) is much  more important then the frontal area. It is about how you divide the air and put it back the way it was with out imparting any movement (energy/drag) to the air.

HiTech

this is a "for what it is worth" comment! I was told once by a P&W engineer that the shape of the leading edge of the cowling has a lot to do with cooling and cutting drag. When pressed, he said the shape of the "cuff" is everything when trying to reach a compromise  between effective cooling and reducing drag! I don't really know, but after he told me that, I started looking at the "cuff" on different aircraft and there are a difference in them!

[FLS]

You can compare the Mustang and FW190 drag in the middle of the chart. The FW has more total drag but the percentage of total drag from the power plant is lower and the actual total profile drag figure is about .5 lower for the power plant. Maybe it's a D model. 

[Charge]

MP499 was an A3 variant.

http://www.iwm.org.uk/collections/item/object/205126940

-C+

[FLS]

MP499 was an A3 variant.

http://www.iwm.org.uk/collections/item/object/205126940

-C+

Thanks.   

[DaveBB]

That chart does not take into account the thrust the radiator produces to offset the drag from the P-51's power plant.