R4360, angle of the dangle...

[woodstock74]

I'm coming up with zeros in my search for this: Who can tell me the degree angle offset between the banks on the R4360 (is there an industry term for this?)? Looking head on towards the engine, Calling bank 1 "zero", what's the angle offset between bank 1 and bank 2? 2 to 3, etc, and is it consistent?

Also...do my eyes deceive me: looking top-down on an individual cylinder, using the leading pushrod as reference, they are obviously rotated to the left relative to airflow or centerline. I've eyeballed it as approximately 7 degrees (this is a wild-ass guess), assuming straight ahead is zero. The question here, as you step through the banks, does this cylinder-angle-relative-to-engine-CL change? I was looking at photos of a display engine and it appeared to me that this angle opens up slightly as you step through the cylinder banks. But it's subtle...maybe 1/2 degree relative difference per bank.

I'm in the process of drawing a 1/48 version, something very simple and not a faithful dimensional reproduction, just MkI eyeball good, to replace what comes with the Special Hobby/Accurate Miniatures kit (which isn't bad at all, it just bugged me that the last cylinder bank wasn't completely modeled). Plus I wanted one for display, so I'll draw up a display stand too. Having both the Special Hobby R4360 as well as the Engines & Things R4360 as reference, I'll then print up my version and then work out the kit integration. Long roads ahead, but fun.

 

[MiTasol]

How many cylinders in the first row?
Divide 360 by that and then by 2. That is the fixed offset for each row

 

[kmccutcheon]

Divide 360 by that and then by 2. That is the fixed offset for each row

That works for two-row radials; this is a four-row, which means:
(360 / 7) / 4 = 12.857142° cylinder angular difference from row-to-row.
The crankshaft throws are also rotated to compensate for the cylinder rotation, with each successive throw, aft to fore, being 192.857142° clockwise from the last.
Cylinder numbering, firing order and other details can be found at
P&W R-4360

 

[MiTasol]

Many thanks for the correction Kim.

 

[woodstock74]

Thanks for the info. Still early days with this, trying to get my head around the shape of the housing at the rear as there's lots going on there (but some pretty decent pictures online, sections, etc.). Need to determine what I want to do about the exhaust/intake/and cooling ducting as it obscures most of what I'm currently working on, and the detail in scale would be delicate and potentially problematic to locate, etc. For me it's a giant CAD headache too, this was to be a fun-draw!

 

[pbehn]

I'm coming up with zeros in my search for this: Who can tell me the degree angle offset between the banks on the R4360 (is there an industry term for this?)? Looking head on towards the engine, Calling bank 1 "zero", what's the angle offset between bank 1 and bank 2? 2 to 3, etc, and is it consistent?

.

On a pipeline it is called radial offset, same issue for different reasons.

 

[kmccutcheon]

Thanks for the info. Still early days with this, trying to get my head around the shape of the housing at the rear as there's lots going on there (but some pretty decent pictures online, sections, etc.). Need to determine what I want to do about the exhaust/intake/and cooling ducting as it obscures most of what I'm currently working on, and the detail in scale would be delicate and potentially problematic to locate, etc. For me it's a giant CAD headache too, this was to be a fun-draw!

Looking good!
By the way, in historical accuracy, it is R DASH 4360 (R-4360). A hundred years from now the dash will be important, even if Google omits it.

 

[Steve Hnz]

Thanks for the info. Still early days with this, trying to get my head around the shape of the housing at the rear as there's lots going on there (but some pretty decent pictures online, sections, etc.). Need to determine what I want to do about the exhaust/intake/and cooling ducting as it obscures most of what I'm currently working on, and the detail in scale would be delicate and potentially problematic to locate, etc. For me it's a giant CAD headache too, this was to be a fun-draw!

Hard to tell from your cad view but it is my understanding that the angle of the cylinders is the same in every bank. That is the impression I get from photos anyway.

 

[eljefe]

That works for two-row radials; this is a four-row, which means:
(360 / 7) / 4 = 12.857142° cylinder angular difference from row-to-row.
The crankshaft throws are also rotated to compensate for the cylinder rotation, with each successive throw, aft to fore, being 192.857142° clockwise from the last.
Cylinder numbering, firing order and other details can be found at
P&W R-4360

From R-4360: Pratt & Whitney's Major Miracle by Graham White, p. 59:

"After the basic concept of 28 cylinders in four rows had been established, Pratt & Whitney's next goal was putting all the parts together, making it work, putting out decent horsepower, and cooling effectively. It should be remembered that no one had, before or since, successfully put a radial engine in production with more than two rows. It had been tried, but all development efforts faded into the sunset and deserved obscurity. With 28 cylinders, even firing dictates that a cylinder fires every 25.714285 degrees (720 divided by 28). This number would have a profound influence on the R-4360's design. With seven cylinders per row, there is little choice for angular spacing between the cylinders on a particular row; it is 51.428571 degrees (360 divided by 7). Now the question of what offset angle to give between cylinder rows arises. This is arrived at by dividing 25.714285 degrees (half of 51.42857 degrees) by two, which gives 12.857142 degrees. This 12.857142-degree offset is what gives the R-4360 its characteristic spiral..."

I've eyeballed it as approximately 7 degrees (this is a wild-ass guess), assuming straight ahead is zero.

What proves that the Mk. I eyeball is a little off is this: pretend that there's a fifth row of cylinders, offset from #4 as much as #4 is from #3. Note that your fictional row 5 lines up exactly with row #1, of course offset by exactly one cylinder (cylinder 29 lines up with cylinder 2, not cylinder 1). That's what proves 12.857142 is correct, or as they would have said back then, 12 51'.

You can also look up US patent 2,426,879. Nice drawings.

 

[woodstock74]

The patent drawings are very enlightening, I'm surprised I haven't seen it referenced elsewhere. I'm pretty far down the CAD road, and the other issue, as this is a cosmetic drawing to create a printed part that will fit an existing model kit, compromises will be had.

And for what it's worth, my 7 degrees eyeball was in reference to an individual cylinder's angular offset from the airflow. Using the leading pushrod as a reference, it's obvious the cylinders are rotated relative to straight ahead, I just was trying to ascertain by how much. I've run with 7 degrees. I have no idea if that is correct. I've run with the 12.85 degree bank angular offset. So at least that is correct.

 

[woodstock74]

I've found the engine length online, something around 2600 mm. Does anyone know how that is measured, that is, is it to the very face of the (I'll call it...) the gearbox at the leading edge to the very rearward face of the supercharger housing at the trailing edge? More importantly...does it include the splined propeller shaft?

 

[kmccutcheon]

Does anyone know how that is measured?

Please see
http://www.enginehistory.org/members/images/PW_InstallationDwgs/R-4360.jpg

 

[woodstock74]

Please see
http://www.enginehistory.org/members/images/PW_InstallationDwgs/R-4360.jpg

Thank you for this, BTW.