P&W Wasp (R-1340) Super Charger

On a broader base – here is a listing for probably all the P&W radial engines.

http://freebee.ucoz.com/load

Truc

See this list from : http://www.enginehistory.org

Wasp Index 1956

Look at the Engine model , as soon as there is an S in the model the “normal” horsepower is given at a certain altitude.

For example :
D-1 –> 550 Hp at 2100 RPM at S.L ( Sea Level )
SD-1 –> 500 Hp at 2000 RPM at 7500 Feet

And you are right at a certain speed the Mixer will become a Blower

Guess

[QUOTE=Bulldogbuilder;2035896]Can anyone explain when,why or how the “S” was introduced into the engine designation of the Wasp engines?

Guess :
Being 1931 it was the transitional period from unsupercharged to supercharged as standard, as existing engines were adapted for altitude performance. Therefore 1931 literature, probably conceptualized in 1927, would have a foot in both camps. Probably an unsupercharged engine was was not commercial/in the race by the time 1927 tooling and assembly lines were financed, designed and commissioned and all engines came out supercharged. Bit like cooking pasta for yourself then Nigella Lawson knocks on the door looking hungry so you have to add some basil pesto to the original dish concept, though the literature on the side packet just said “add water”.

I am more familiar with this theme with the Bristol Jupiter- Mercury- Pegasus rather than this clumsy Yankee theft of ideas called the Wasp, but no doubt somebody in a 16 gallon hat at P&W would have slammed a cigar down on a desk in 1931 and said, “Dammit, we’re just gonna have to makem all with superchargers then!” and a guy that looked like a thin, scared bartender in a Western would have scurried of and written the equivocating paragraph.

There seemed to be this market segmentation at the time between flying boats (unsupercharged), transports (mildly supercharged) and fighters (blow the bolts off), so any prudent scale manufacturer would want to assure each segment that their tool could do the job. I can’t think of anything further to add so I am off to cook some pasta and wait by the door.

Almost all radial engines have some form of impeller or supercharger, initially primarily to improve mixture distribution to all the cylinders. One notable engine with mixture distribution problems is the Jacobs R-755, hence they were known as the “Shaky Jakes”. Radial Engines Ltd in Oklahoma have produced a fuel injection system for this engine to resolve this problem.
I would not be surprised if the conversion of the R-1340 Wasp from the “C” to “SC” was due to the change in step up ratio of the blower drive and therefore changing the function of the blower from merely improving mixture distribution to also increasing power, both at sea level and altitude.

Thank you Pim and cypherus . I have studied the afore mentioned info list on the Wasps, but as in most cases the more you read the more questions arise. I would love to find the source of the lists as there are a few mistakes and or questions regarding some of the models.
As every Wasp model was built with a compressor I can only surmise from Pim’s information that at some point the compressor (which originally was used as a fuel/air diffuser-mixer) went from charging to supercharging. Again the two pieces of information on the nomenclature of the Wasp labeling leaves much to be desired.
Thanks again.

Ed

The difference between Charged and Supercharged is that the compressor on a Supercharged engine can deliver more air on the ground then the engine can handle power wise ( so it can be overcharged – to high manifold pressure ). As such a super charged engine can deliver maximum horsepower up to a certain altitude because it can still deliver enough compressed air to reach maximum horsepower. A Charged engine reaches maximum power on sealevel and this power only decreases with altitude.

There is a lot of info available in Wiki along with a PDF scanned document from around 1956 covering the many variants of the in Military and civil variants along with specs and aircraft fitted with them.