Talk:Pratt & Whitney R-2000 Twin Wasp

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Aviation: Engines

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Displacement

Bore and stroke yield 1,999.5 cuin, not the 2,004 given. AMCKen (talk) 03:43, 26 December 2010 (UTC)[reply]

Source? - BilCat (talk) 08:21, 26 December 2010 (UTC)[reply]

It is not necessarily the displacement that is wrong, you need to find a ref to change this, not a calculator. - Ahunt (talk) 15:27, 27 December 2010 (UTC)[reply]

I just consulted the Type Certificate Data Sheet which is cited as a ref for the article and it says bore of 5.75" and stroke of 5.5" and displacement of 2004 cu in, so I think you are missing something there in your calculations. The TCDS is an approved engineering document prepared by the manufacturer and approved by the FAA. It is possible there is some error, but it is more likely you are missing some factor. You are going to need to find a very good ref to overturn the TCDS. - Ahunt (talk) 15:32, 27 December 2010 (UTC)[reply]

Of course it is wrong, because displacement is a strict function of bore,stroke and number of cylinders, it is exactly 14*PI/4*5.75^2*5.5 = 1999.7481 cubic inches (PI/4*bore^2*stroke).

The document comes from a time when typewriters made many mistakes.

And we can identify where the error comes from exactly:

R-2800 (larger model of this company) has a displacement 2804 inches (precisely 2004.0197) as you can see inhttp://web.archive.org/web/20161113123035/http://rgl.faa.gov/Regulatory_and_Guidance_library/rgMakeModel.nsf/0/1f78aa99851224c58525676a0067217f/$FILE/ATTB1RFZ/5E-5.pdf), so someone looked at the wrong cell in the table when creating this document and read it as 2004 that is very similar on old font types (there was the dash inside 0 to make it distinct from O). 62.148.84.67 (talk) 00:41, 8 December 2024 (UTC)[reply]

That's still original research. Unless you can cite a reliable published source which either details the error or provides the other figure, we can't change it. BilCat (talk) 03:57, 8 December 2024 (UTC)[reply]

Basically, the situation is analogous to the formulation "exactly two years before the outbreak of World War II" based on which someone determines the year to be 1937. And then a person appears who treats the arithmetic operation 1939 - 2 as original research!

This is not original research but basic knowledge in a domain at the level of primary school.

The source document correctly provides fundamental information that does not raise any doubts, because these are standard cylinder sizes also used in the R-2180 and in accordance with typical engineering practice of the era have round values, confirmed by many sources. And these values absolutely unambiguously determine the capacity, mathematics and conventions leave no room for any arbitrariness here. If you have any doubts in this matter, maybe Wikipedia will help:

http://en.wiki.x.io/wiki/Engine_displacement

Basically, you can and should add a template calculating engine capacities to avoid such nonsense in the future.

The explanation of the origin of the error in the document is only a bonus - an unsuccessful attempt to appeal to common sense.

And no, math hasn't changed in 80 years. And all working calculators give the same result. 62.148.84.67 (talk) 05:59, 8 December 2024 (UTC)[reply]

We still default to the source, as the other editors have explained here. As another editor said, "It is possible there is some error, but it is more likely you are missing some factor". BilCat (talk) 08:10, 8 December 2024 (UTC)[reply]

This would be a great joke if it weren't actually happening. For anyone with any technical background, the odds are strictly 0.

For anyone with any professional experience using historical sources, my explanation of the mistake allows the document's direct value to be completely ignored in the face of doubt.

So if you think the chances of this value being true are greater than the one calculated from the given cylinder dimensions, and apparently greater than 50%, could you please state which scenario you think is the most probable?

1) The document contains an incorrectly given stroke

2) The document contains an incorrectly given bore

3) The commonly used formula, which I also linked to in the Wikipedia article, is incorrect

4) The formula for the volume of internal combustion engines with round pistons does not apply to this model, unlike all other engines of this make or era 62.148.84.67 (talk) 17:56, 8 December 2024 (UTC)[reply]

Any or all of those options could be true, especially the first two, possibly due to rounding errors, odd piston configurations, etc. Please remember that Wikipedia is a general encyclopedia that reports what is in reliable published sources; it's not a technical journal. We don't do our own research and calculations. BilCat (talk) 19:33, 8 December 2024 (UTC)[reply]