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Mixture control on a R-3350-57 engine.

 
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jschauer



Joined: 19 May 2004
Posts: 89
Location: Justin, Texas

PostPosted: Thu May 27, 2004 08:47    Post subject: Mixture control on a R-3350-57 engine. Reply with quote

Does anyone know why you only have three positions on the mixture control of a R-3350-57 (B-29 fuel injected engine), FUEL-CUTOFF, AUTO-LEAN, and AUTO-RICH? The flight manual says not to operate it in any other position other than these stated. In other words, you can't manually lean the engine out. I believe the later versions of the engine in the "Connies" had fuel injection and were able to manually lean those engines. I've been flying as FE on the CAFs B-29 for 5 years now and still don't know the answer.
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kmccutcheon



Joined: 13 Jul 2003
Posts: 193
Location: Huntsville, Alabama USA

PostPosted: Sat Jun 19, 2004 05:49    Post subject: Reply with quote

Quote:
Does anyone know why you only have three positions on the mixture control of a R-3350-57 (B-29 fuel injected engine), FUEL-CUTOFF, AUTO-LEAN, and AUTO-RICH?


Sorry it has taken so long to respond to this. I wanted to do a bit of research and run my answer by a carburetor expert before putting it into print.

This is a very complicated issue, the truth of which is just beginning to emerge through some of the research that is being done on the R-3350 service history. The short answer, though, is that mixture distribution in the carbureted R-3350s is so poor that C-W didn’t want the “green” flight crews to have any real control over it. Carburetors were built so that AUTO-LEAN and IDLE-CUT-OFF were so close together that it is practically impossible to lean manually.

Early R-3350s had a sharp corner in the induction passage leading to the supercharger impeller. This probably caused what we would today call duct rumble in a gas turbine installation. The resulting turbulence in the induction system led to unequal mixture distribution. The easy way around this, at least in theory, was to run all of the cylinders rich enough (even in AUTO-LEAN) so that no cylinder was lean enough to detonate.
We now know that the combination of bad mixture distribution and poor cooling design probably conspired to produce a very unreliable engine.

When the R-3350 went into airline service, four things happened to improve this picture:
1) Changes to induction air paths and the addition of fuel injection, coupled with improved cooling design fixed many of the basic engine flaws. Even then, air distribution was still less than ideal, as can be seen in this drawing of injection duration as a function of cylinder number.

http://www.enginehistory.org/images/FIduration.jpg

Note the ragged edges marking the start and end of the injection event. Notice also how they change as a function of power setting. This was the "improved" version!

2) Better instrumentation (BMEP gages, engine analyzers) gave flight crews enough data to accurately control the mixture and troubleshoot engine problems.

3) Better flight and ground crew training, combined with better record keeping, provided an environment conducive to steady improvement in operation and maintenance techniques.

4) Finally, airlines, with a limited supply of money (as opposed to Uncle Sam’s presumably unlimited supply), had an economic incentive to do all of the above.

This is a typical systems approach to solving a problem—combining the efforts of engineering, operation and management. And it worked. The TC18 became one of the most reliable and efficient piston engines ever, but not without an unbelievable list of “growing pains”, one of which you still live with in your inability to manually lean the -57s in the B-29.
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mmraz



Joined: 13 Jul 2003
Posts: 11

PostPosted: Mon Jun 21, 2004 20:10    Post subject: Fascinating Reply with quote

Kim, this is really amazing info. I hope you plan to write another book and that it's going to be about the 3350's history.

jschauer: I would give my you-know-what to fly FE on "Fifi." You are one incredibly lucky man!!!
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kmccutcheon



Joined: 13 Jul 2003
Posts: 193
Location: Huntsville, Alabama USA

PostPosted: Fri Jun 25, 2004 09:07    Post subject: Reply with quote

mmraz:
Quote:
Kim, this is really amazing info.


Kevin Cameron should get the credit, having been pondering this topic for over a decade. Kevin would probably disagree with my assessment that the TC18 eventually became “reliable” because he identifies a number of problems with it in airline service. Still, its efficiency enabled travel over great distances with a level of comfort never before possible. No one can argue that it wasn’t a thoroughbred requiring careful and intelligent handling. It certainly never achieved the dependability of the R-2800. However, I am of the opinion that it played an important, perhaps indispensable role in the waning days of aircraft piston engines.
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cconnacher



Joined: 13 Jul 2003
Posts: 4
Location: Pa.

PostPosted: Sat Jun 26, 2004 11:43    Post subject: Reply with quote

This is all very interesting, I would like to see a book written on the R3350's history also, including some history on the Curtiss-Wright Co. itself. It sounds like many of their problems were self inflicted but I have a partiality for Wright. My Dad worked for them in the fifties (51-58) as a tool designer at Wood Ridge, N.J. I was just a kid then. I guess the debate over the best or most important engine could go on for centuries. Everyone has their personal favorites for one reason or another just as in any area of interest or hobby. Railroad fans have their favorite roads & locomotives etc. When looking for an engine to restore I finally chose an R1820 when it became available because of Dad working for Wright. It may even have been built while he was there, I suppose with some research I could find out. While living there in Northern N.J. we were close enough to La Guardia & New York International that the propliners going west were still on their climb as they passed overhead. Dad taught me to differentiate between the Connies, DC3's 6's & 7's. Later in the fifties the Vickers Viscount turboprops appeared with a distinbctive "new" sound. But I liked the throaty roar of the piston engines better. One night while out in the yard a plane went over & Dad pointed out the exhaust flames from the engines. this all fascinated me as a youngster. Another item of interest from that era were the sky writers that flew over putting advertisements in the sky. They were single engine planes ( I'm guessing surplus WW2 fighters or trainers) that flew 5 wingtip to wingtip (don't know what that formation is called) & left puffes of smoke in perfect timing to make perfect letters accross the sky. I miss all those things that once were, including steam locomotives, that are all but gone today. Thankfully we have other people that feel the same & put so much effort (& expense) into restoration of all this so we can still experience & enjoy it & let the younger generations of today experience their heritage as it was before them.
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jschauer



Joined: 19 May 2004
Posts: 89
Location: Justin, Texas

PostPosted: Mon Jun 28, 2004 12:25    Post subject: Reply with quote

Thanks for the info. I don't know if you know it or not but "FIFI" has fuel injected engines, R-3350-57A. Your right about the small distance between Auto-Lean and Fuel-Cutoff, it is only about 1 1/2 inches of travel with the mixture control.

John
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mmraz



Joined: 13 Jul 2003
Posts: 11

PostPosted: Mon Jun 28, 2004 13:30    Post subject: TC18s in airline serivce Reply with quote

Anyone interested in the 3350 turbo-compound (or any other round engine) should visit John Deakin's AVweb site and buy a copy of the booklet he reprints, "Basic Theory of Operation, Turbo Compound Engine." It very clearly and concisely explains the principles behind mixture control in all internal combustion, spark-fired, gasoline engines. It was written by American Airlines (published by Curtiss-Wright) based on their service experience with the TC18 in their DC-7 fleet.

http://www.avweb.com/news/columns/182192-1.html
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kmccutcheon



Joined: 13 Jul 2003
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Location: Huntsville, Alabama USA

PostPosted: Tue Jun 29, 2004 07:21    Post subject: Reply with quote

John-
Quote:
"FIFI" has fuel injected engines, R-3350-57A


The fuel injected engines were a decided improvement over the older carbureted ones, but even fuel injection could not compensate for the uneven and unstable airflow. According to Kevin Cameron's research, this issue didn't get fixed until the TC18.
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mmraz



Joined: 13 Jul 2003
Posts: 11

PostPosted: Tue Jun 29, 2004 16:18    Post subject: B-29/3350 questions Reply with quote

I saw (from a distance) B-29-60-BW s/n 44-69729 "T Square 54" at the Seattle Museum of Flight and its 3350s had the front-row exhaust collectors mounted ahead of the front row of cylinders. Does anyone know if "T Square 54" has the correct engines installed? As I recall, B-29A-60-BN s/n 44-62070 "Fifi" does not have this exhaust-collector "feature."

jschauer, are Fifi's -57 engines the original dash number, or did the CAF replace them with a later version?
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jschauer



Joined: 19 May 2004
Posts: 89
Location: Justin, Texas

PostPosted: Wed Jul 07, 2004 07:20    Post subject: Reply with quote

Yes FIFI has the same exhaust, but my guess is the 29 in Seattle doesn't have the pieces of cowling that cover the fwd. facing exhaust collector as it does on FIFI. We have been talking for years to convert to a later version of the 3350 such as the -26 that was found on the Skyraider. The biggest drawback is that the 29 has a fwd. facing exhaust on the front row of cylinders as opposed to the normal rear facing exhaust on all the other versions. We would have to build a complete new exhaust system. All we need is cubic yards of dollars.
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jkinney



Joined: 13 Jul 2003
Posts: 11
Location: Washington, DC

PostPosted: Fri Jul 23, 2004 08:04    Post subject: Books on Curtiss-Wright History Reply with quote

cconacher:
cconnacher wrote:
This is all very interesting, I would like to see a book written on the R3350's history also, including some history on the Curtiss-Wright Co. itself.


Until a more comprehensive history of Curtiss-Wright is written, try these books:

Eltscher and Young, Curtiss-Wright: Greatness and Decline, 1998.

Fausel, Whatever Happened to Curtiss-Wright?, 1990.

Rubeinstein and Goldman, To Join With the Eagles: A Complete Illustrated History of Curtiss-Wright Aircraft from 1903 to 1965, 1974.

Sorry for the late reply.
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Dr. Jeremy R. Kinney
Curator, Aeronautics Division
National Air and Space Museum
Smithsonian Institution
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