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Why No Smokeless JT3Ds After So Many Years?  
User currently offlineHappy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Posted (6 years 7 months 2 days 13 hours ago) and read 3413 times:

Lots of JT3Ds still in operation today! Many, but not all, DC-8s were re-engined . . . lots of military 707 variants still using the JT3D today. Now, I love the old noisy classic engines as much as any red blooded aviation lover - but given the concern over the last 20+ years about emissions, including particulate emissions, I truly wonder why after nearly 50 years, the core of the JT3D engine has not been modified so that it would burn more cleanly at low altitudes.

Just going by what I've seen, it seems that the JT3D smokes least when operating in hot, dry conditions, and most when humidity is high and the temperatures are cool to cold. The heaviest smoke trails seemed to always form on damp winter days back when I'd see the classics coming in and out of YYZ.


May the wind be always at your back . . . except during takeoff & landing.
5 replies: All unread, jump to last
 
User currently offlineTimz From United States of America, joined Sep 1999, 6839 posts, RR: 7
Reply 1, posted (6 years 7 months 2 days 9 hours ago) and read 3344 times:



Quoting Happy-flier (Thread starter):
why after nearly 50 years, the core of the JT3D engine has not been modified so that it would burn more cleanly at low altitudes

They modified the JT8D to cut visible smoke, back around 1970-- do we know for sure they didn't do the JT3D too?


User currently offlineHappy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Reply 2, posted (6 years 7 months 2 days 1 hour ago) and read 3246 times:



Quoting Timz (Reply 1):
do we know for sure they didn't do the JT3D too?

Well, just judging by this very recent photo of a -63 smokin' in on final, I'd say that no, they didnt:

View Large View Medium
Click here for bigger photo!

Photo © Bruno Tucci


No modified JT8D that I know of ever belches that much, for example.



May the wind be always at your back . . . except during takeoff & landing.
User currently offlineG4Doc2004 From United States of America, joined Feb 2004, 123 posts, RR: 0
Reply 3, posted (6 years 7 months 1 day 13 hours ago) and read 3162 times:

I'd have to say that they haven't for several reasons. First, it's an old engine, who wants to dump that much R&D money into old technology? It would be like putting a smog pump on an old 50's era car....not really worth it! And, who would spend the money if someone offered to upgrade the engine at hot section or overhaul? Not me, unless required by some regulatory edict.
And, as mentioned, with all the re-engine programs available, if you are wanting to invest some new money in an old airframe, the only sensible thing is to put money in a newer engine that will be well supported.



"Failure to prepare is preparing to fail"--Benjamin Franklin
User currently offline113312 From United States of America, joined Apr 2005, 572 posts, RR: 1
Reply 4, posted (6 years 7 months 1 day 6 hours ago) and read 3097 times:

I would disagree. The JT-3D engines operating today are "smokeless" when you compare them to the smoke they belched prior to that mod. It is just that they still produce some smoke. Even the JT-8D and even some widebodies can be seen producing some smoke trail under the right conditions.

User currently offlineEx52tech From United States of America, joined Dec 2006, 559 posts, RR: 1
Reply 5, posted (6 years 6 months 3 weeks 3 days 3 hours ago) and read 2900 times:



Quoting 113312 (Reply 4):
The JT-3D engines operating today are "smokeless" when you compare them to the smoke they belched prior to that mod.

What mod?? The only mod I am aware of was shock mounting the fuel manifolds, which are internal, and had some problems with cracking over the years. Had an un-modded, non shock mounted, manifold fail on a B52H. The blow torch effect cut a hole in the diffuser case, burned through the main fuel line, and started a fire.

It would take a complete redesign of the combustion chamber, possibly the diffuser case, fuel manifolds, fuel nozzles, and burner cans.

Now the big question, would leaning out the mixture cause damaging temperatures to the hot section? There are five fuel nozzles in each burner can, and eight burner cans.

Maybe a can-annular burner can would do the trick.



"Saddest thing I ever witnessed....an airplane being scrapped"
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