Wright 3350

[varsity07840]

Much has been written about engine fires on B-29s powered by the Wright R3350. The B-19 and B-32 used the same engine but I've never seen anything written about engine fires on those aircraft. In particular, the B-32 cowl design was quite similar to that on the B-29. Does anyone have an explanation for that? Is it a case of little documentation, or less of an issue with those two aircraft?

 

[Shortround6]

I have no idea on the B-32 but the B-19 used a different engine?
According to one story after Wright had made a small quantity of R-3350s in 1938-42 they redesigned the whole engine (including adding a couple of inches to the crankcase/crankshaft length) and came out with new version/s.
Some of the older ones on the B-19 only ran at 2400rpm instead of 2800rpm like the engines in the B-29.

 

[wlewisiii]

According to the wiki article on the B-32, it suffered from the same oil leaks, cooling issues and engine fires as the B-29. Perhaps following up with the sources listed?

Consolidated B-32 Dominator - Wikipedia

en.wikipedia.org

 

[Howard Gibson]

Much has been written about engine fires on B-29s powered by the Wright R3350. The B-19 and B-32 used the same engine but I've never seen anything written about engine fires on those aircraft. In particular, the B-32 cowl design was quite similar to that on the B-29. Does anyone have an explanation for that? Is it a case of little documentation, or less of an issue with those two aircraft?

The Lockheed Constellation airliner was designed around the Wright R3350. It must have gotten reliable. It takes years to develop new engines. Like the Napier Sabre, it may have been pushed in to service before it was ready.

 

[Aeroweanie]

From what I've read, the details of the engine installation were the source of the problems, coupled with the relative immaturity of the engines. The B-29 had turbochargers, while the Constellation and XB-19 didn't. Turbochargers run very hot.

 

[Shortround6]

The R-3350 engines may have been right on the border of cooling regardless of the turbo installation.
The few C-69s built had cooling problems. I don't know what Wright (and Boeing and Consolidated and Lockheed) did for baffling, propeller cuffs, changing in cylinder fins, Cylinder head fins and other things. but a 1948 commercial engine was not the same as a 1944 bomber engine.

 

[FLYBOYJ]

Let's not forget the crankcase was magnesium, not a very pleasant alloy when introduced to high heat or fire.

 

[Tkdog]

I imagine the wartime bomber engines were pushed harder than airliner engines too.

 

[GregP]

I don't know about being pushed harder than airline engines.

A Douglas DC-7C made 404 mph top speed, but it cruised at 346 mph at 221,600 feet. That isn't babying the engines at all but, by then, they knew how to operate them and had a flight engineer who was very gentle on throttle changes. Of course, it didn't fly until well into the 1950s. Still, the engines were R-3350s ... later models anyway.

 

[cherry blossom]

The later Wright 3350 engines used fuel injection. Obviously that didn't directly help with cooling but it did give better fuel distribution which may have prevented some cylinders running hot.

 

[Shortround6]

The later Wright 3350 engines used fuel injection. Obviously that didn't directly help with cooling but it did give better fuel distribution which may have prevented some cylinders running hot.

Bingo!!!!!
they found that most of the troubles came from 3 cylinders (?).
Even V-12s with liquid cooling ran hot and cold cylinders due both to differences in cooling and differences in mixture distribution.

The Wright 3350 isn't as well documented as the R-2800 but the post war R-2800s had a lot of changes from even the late war C series engines used in P-47Ms and Ns.
The 3350 may have seen a lot of small changes as well in addition to the fuel injection.

 

[varsity07840]

Bingo!!!!!
they found that most of the troubles came from 3 cylinders (?).
Even V-12s with liquid cooling ran hot and cold cylinders due both to differences in cooling and differences in mixture distribution.

The Wright 3350 isn't as well documented as the R-2800 but the post war R-2800s had a lot of changes from even the late war C series engines used in P-47Ms and Ns.
The 3350 may have seen a lot of small changes as well in addition to the fuel injection.

My understanding is that there were also problems with the design of the exhaust system which had a separate forward located exhaust collector ring for the front row of cylinders, in front of the engine. That was because the cylinder exhaust ports faced forward. The rear row of cylinders had exhaust ports facing aft. This allowed extremely hot air to be blown directly on the front cylinders. In addition a cracked or damaged manifold would let flames direct hit them. The R-2800 was designed with all exhaust ports facing to the rear with pipes leading to a single collector ring behind the engine. The 3350 exhaust system was later redesigned in a similar fashion.

 

[gruad]

IIRC the ground crews used to frequently change the 3 or 4 cylinders that tended to overheat. I think these were lower but I dont know which bank

 

[daviemax]

An illuminating data snapshot from the unit histories of SB-17G SAR aircraft based at Kindley AAF, Bermuda in February 1950:

• Eight intercepts of aircraft in trouble (almost two/week).
• Seven were for feathered prop.
• Five of these were powered by R-3350s (three Connies and two B-29s).
• Other two were R-2000 (DC-4s)

While not definitive, this data does offer insight.

 

[Aeroweanie]

Let's not forget the crankcase was magnesium, not a very pleasant alloy when introduced to high heat or fire.

The R3350s that I am familiar with (used on Rare Bear) had steel crankcases.

 

[FLYBOYJ]

The R3350s that I am familiar with (used on Rare Bear) had steel crankcases.

The original ones were made of magnesium

Because of a high magnesium content in the potentially combustible crankcase alloy, the resulting engine fires — sometimes burning with a core temperature approaching 5,600 °F (3,100 °C)
From Wiki reference Dreizin, Edward L.; Berman, Charles H. & Vicenzi, Edward P. (2000). "Condensed-phase modifications in magnesium particle combustion in air". Scripta Materialia.

To save weight, the engine crankcase was made of a magnesium alloy, however, magnesium is flammable metal and can produce a fire hot enough to burn through the aircraft structure.

Wright R-3350

 

[Shortround6]

Some people confuse the steel crankcase, the power section, made in 3 pieces (?) with the compete engine.
Front reduction gear case I believe was magnesium.
Going to the back of the engine the accessories section was magnesium and the supercharger was magnesium (?).

I would note that the R-1820 went through a number of models using aluminum crankcases, and then 3 different steel crankcases.
The R-2600 started with an aluminum crankcase and went through two different steel ones.
Both engines used alloy reduction gear cases and accessory drive/supercharge cases.

I would be a little leery of that website.
Wright built a slow dribble of R-3350s during 1938-42 and according to some accounts the
Consolidated XP4Y-1 Corregidor first flew with R-3350s about 2 years before the Douglas B-19 did.

All of the smaller Wright engines went to steel crankcases not because of fires but because they found that a steel crankcase actually weighed less than an aluminum one of the same strength.

Having the rear case (all pump drives, starter motor, generator, etc ) and the supercharger housing being made of magnesium may have been more than enough set fire to things.
You can set fire to Aluminum of your source of ignition (like magnesium ) is hot enough. But Alumium tends to not burn well unless it has a high surface to volume ratio (aircraft skin is prime example).

 

[syscom3]

I don't know about being pushed harder than airline engines.

A Douglas DC-7C made 404 mph top speed, but it cruised at 346 mph at 221,600 feet. That isn't babying the engines at all but, by then, they knew how to operate them and had a flight engineer who was very gentle on throttle changes. Of course, it didn't fly until well into the 1950s. Still, the engines were R-3350s ... later models anyway.

221,000 feet? [I know its a typo]. LOL

 

[Simon Thomas]

From "Development of the Turbo Compound Engine" F. J. Wiegand and W. R. Eichberg SAE Transactions Vol. 62 (1954)

https://www.jstor.org/stable/44547322

 

[PWR4360-59B]

Let's not forget the crankcase was magnesium, not a very pleasant alloy when introduced to high heat or fire.

Pratt & Whitney, and Wright, never used magnesium for Large radial production engine crankcases. PW used forged Aluminum, and the 3350's were forged steel. Nose or gear reduction cases and accessory cases were made from Magnesium, and a very bad engineering choice for an aircraft engine. There were some cases of extreme fires while flying in rain storms, since water breaks down and feeds a magnesium fire.

The reason the B29 engines had the problems was the front cylinders exhaust outlet was towards the front, the collector ring in the front allowed all that heat to be blown back to the engine.
That is the main reason for the now flying, B29 Fifi having non standard engines. No longer a hot exhaust collector sitting in front of the engine.