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Post by kstlmike on Feb 15, 2009 22:16:48 GMT -5
I very much enjoy piloting the FSDZigns 049 Constellation and the L-1649A Starliner and I have a question regarding the R-3350 engines.
I have read up on the Blow-Down scavenging Turbo-Compounding device, (as on the Starliner) and I understand that it is an energy recovery system and has nothing to do with the engine intake supercharging.
My questions are: Were the R-3350 engines supercharged via a separate exhaust turbo-supercharger, or was the supercharger driven by mechanical means? How was the supercharger boost controlled?, did the engines have a supercharger waste-gate?
Thanks........Mike
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Post by Tom/CalClassic on Feb 15, 2009 22:49:05 GMT -5
The 3350's were indeed mechanically supercharged (not turbocharged on the airliners). I don't know about the waste-gate.
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Post by ashaman on Feb 15, 2009 23:12:37 GMT -5
This is a question that has intrigued me as well, from time to time, but really I was unable to understand how to cascade two different kind of exhaust superchargers ( regular ones and PRT) without losing every advantage this chain would give due to the clogging of the exhaust pipes they would oppose. I guess I always supposed the Turbo Compound R-3350 to be only mechanically supercharged, renouncing the superior MAP pressure a exhaust driven supercharger would give in exchange for another kind of exhaust energy recovery use.
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Post by kstlmike on Feb 15, 2009 23:57:36 GMT -5
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Post by emfrat on Feb 16, 2009 1:52:13 GMT -5
Early supercharged aeroengines use a primitive form of wastegate - if the boost gets too high, the cylinder heads lift to release the excess MikeW
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Post by kstlmike on Feb 16, 2009 10:46:23 GMT -5
Thanks again for all the input, and Mike W, I've seen that cylinder head lift concept demonstrated in race cars...LOL I may have found my "boost control" answer here: www.pilotfriend.com/aero_engines/aero_eng_dvmt.htmThe article has a basic concept diagram of how P/W & C/W mechanically driven two-stage supercharger design controlled boost by means of a hydraulic variable speed clutch (fig.13). It appears that "waste gate" boost control only applies to turbo-supercharging. .........Mike
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Post by sunny9850 on Feb 16, 2009 18:10:27 GMT -5
The Superchargers on the Starliner were gear driven through basically a 2 speed gear box. That is why you need to slow the engines / props to certain MP and RPM combinations before switching from LB to HB. In addition to the Supercharging these engines also use PRTs which are driven by the exhaust gas and then drive the engine crankshaft through a viscous coupling. I am still a little hazy on the whole thing myself....I would love to look at one of these engines up close and personal to see how it all fit together. But in principle the engine crankshaft in case of the R-3350 is both being driven (PRTs) and driving (Superchargers or Blowers). One system uses otherwise wasted energy to help turn the prop and the other system robs a little of the engines power to help it make more especially up high. This Wiki article is pretty good material: en.wikipedia.org/wiki/Wright_R-3350
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Post by Defender on Feb 20, 2009 4:38:42 GMT -5
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Post by ashaman on Feb 20, 2009 12:44:37 GMT -5
...if not Babelfish is your friend: babelfish.yahoo.com/ Even if the results are sometimes comical, it helps understand an unknown language.
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Post by sunny9850 on Feb 20, 2009 21:46:42 GMT -5
That is a great site Bill....I guess I should have browsed a bit more when we were discussing the weights on the 749 One trick that you can use to get the foreign sites to show up in english fairly easily is usually to copy the original link into Google and let it search. On the retrieved links there should be a field "translate this page" ...tried to copy the translated link ...but that does not work ;D
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Post by kstlmike on Feb 20, 2009 23:04:01 GMT -5
Bill, Thanks so much for the French Aviation link.
I don't speak French, but the diagrams and photographs were most helpful.
..........Mike
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Post by herkpilot on Feb 22, 2009 2:02:06 GMT -5
Here's a link to things going terribly wrong on the turbo-compound 3350 and really spoiling your day www.enginehistory.org/wright_aero.htmDescribes a catastrophic failure on an SAS DC-7C and a similar events on two NWA DC-7Cs that ditched as a result. The document has links to the official reports as well. In another comment about these engines Capt Bob Buck (Chief Pilot for TWA) says of the TC engined 1049 and 1649 "..problems dropped dramatically if you never shifted the supercharger... So we just flew lower and now we were down where more weather lurked, ice and turbulence, back to the DC-4 days..." So much for progress! Hy
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Post by ashaman on Feb 22, 2009 9:14:54 GMT -5
Well... in my abyssal ignorance I have at times idly wondered why not using a single speed blower geared only to high, with a pressure control system that would... "cut and throw away", in a sense, the excess pressure when it was not needed. I guess it would have been noisy... but at the same time the excess pressure could have been used for cooling, or whatever else... Mysteries that would never receive an answer. ;D
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Post by Tom/CalClassic on Feb 22, 2009 10:08:35 GMT -5
The simple answer was in the forum post above yours - high blower put extra stress on the engine, and it was best to use it only when needed.
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Post by ashaman on Feb 22, 2009 10:19:20 GMT -5
Wasn't the shift to High blower to add stress ( or at least I understood so)? I mean, if there was no shift, but the blower was a single stage single speed, simply capable of pressures akin to the High blower ( with a max pressure cap control system), would have there been stress? And if yes, would that stress been of the same level and kind of the shift from Low to High, ( and, I guess, from High to Low in descent)?
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