Fighter Escorts of B-29's over Japan & Pacific

[Zipper730]

Throughout its service life the R-3350 ran hot on the ground and during flight. This was primarily due to its design, although the cowling was a contributing factor. In April 1942 Boeing raised questions about the cowling and also objected to the prop blades the AAF had picked for the shorter four-blade prop as they cut the flow of air to the engines during ground operations. It should have come as no surprise that the initial B-29 engines operated at or above the desired temperature limits.

What kind of propeller had Boeing proposed for the aircraft? Also, the cowling issue: Was that a USAAF demand as well?

A number of measures were taken to cool the R-3350 engines. Aluminium-finned and forged barrels were fitted to the engines [*]. Moveable cowl flaps were designed to handle this situation (devices like flower petals were installed midway on the engine nacelles), but as the cowl flaps were opened to increase cooling on takeoff and climb, drag increased, requiring more power from the engines, which further aggravated the cooling problem and contributed to shorter engine life. One modification made the top two "petals" of the cowl flaps operable, which aided cooling on the ground, but caused buffeting when when fully opened during flight.

While most all aircraft at that time seemed to have some form of cowl-flap or gill arrangement (i.e. the Fw 190) to manage varying airflow requirements through the cowling, I am surprised that the aircraft had two cowl-flaps that were inoperable early on (unless it was tested in the prototype stage, then inactivated).

I'm curious if the cowl-flaps were draggier than most airplanes, or it just had to do with the underpowered nature of the aircraft. Part of me suspects it had to do with the cowl being very tight, so the cowl-flaps had to be bigger to manage airflow at low-speed, combined with the plane being underpowered.

the cowl flaps were shortened by three inches and thus could be opened wider before buffeting occurred.

Did they reduce drag at high-speeds?

The new cowl flaps, ducted baffles (to better circulate air), and oil crossover tubes (to better circulate oil) were put into engines at the Oklahoma City Air Depot beginning in September 1944 and sent in kits to the combat forces in late 1944. In 1944 a larger cowl opening in the nacelle went into production along with the cuffs on the prop blades and a better seal on the cowl. .As a result, engine temperatures could be kept comfotably below the desired limits, and the life of the engines began to increase."

So, the cowl was loosened up a little bit by the time they arrived at the Marianas?

 

[Reluctant Poster]

What kind of propeller had Boeing proposed for the aircraft? Also, the cowling issue: Was that a USAAF demand as well?
While most all aircraft at that time seemed to have some form of cowl-flap or gill arrangement (i.e. the Fw 190) to manage varying airflow requirements through the cowling, I am surprised that the aircraft had two cowl-flaps that were inoperable early on (unless it was tested in the prototype stage, then inactivated).

I'm curious if the cowl-flaps were draggier than most airplanes, or it just had to do with the underpowered nature of the aircraft. Part of me suspects it had to do with the cowl being very tight, so the cowl-flaps had to be bigger to manage airflow at low-speed, combined with the plane being underpowered.
Did they reduce drag at high-speeds?
So, the cowl was loosened up a little bit by the time they arrived at the Marianas?

The opening increased. The sealing within the cowl was improved to direct the air over the cylinders rather than bypassing them

A discussion of the issues at the AEHS forum

enginehistory.org :: View topic - R-2600 and R-3350

This edition of the torque meter has an article on the R-3350 woes.

Torque Meter V1 N1

Another AEHS article

https://www.enginehistory.org/Piston/Wright/WrightR-3350.pdf

 

[Zipper730]

R Reluctant Poster

I found this to be of note...

Service

By cutting all possible corners in training and logistical support, accepting far less than perfect engines, and putting up with horrible weather and facilities, the first two B-29s, each with a spare R-3350 slung in its bomb bay, landed in China on April 24, 1944. Hot weather and poor runways forced use of extremely high power settings for take-off and climb. This coupled with the need to close cowl flaps (and overheat the engines) in order to fly high-altitude formations caused many engine failures and aircraft losses. B-29s were flying twelve-hour missions with six of those hours with power settings of 80% or better. Persistent efforts eventually produced acceptable fixes for the overheating in the form of revised operational techniques, tighter-fitting baffles, better front exhaust collectors, careful cylinder head temperature indicator calibration, and performance sacrifices. Perhaps the most important was a change in strategy from high-altitude formation to low altitude raids. Since the engines did not have to endure the long climb to altitude, they fared better.

I didn't know the runway conditions required overboosting to get airborne. I'm confused why the needed to close the cowl-flaps?

I'm surprised they'd need to spend half the flight at high power-settings: The B-17 took like 20-30 minutes to get to altitude right?

 

[Reluctant Poster]

R Reluctant Poster

I found this to be of note...
I didn't know the runway conditions required overboosting to get airborne. I'm confused why the needed to close the cowl-flaps?

I'm surprised they'd need to spend half the flight at high power-settings: The B-17 took like 20-30 minutes to get to altitude right?

Open cowl flaps increase cooling but induce drag. Bombers always needed maximum power to get airborne= flaps open. Conversely they needed minimum drag to maintain airspeed = flaps closed Fighters are different, maximum performance is required during combat. Although this may trigger Shortround, the British justified fixed pitch propellers for fighters with the thought that fighters have a surplus of power for take off. C
Closing the cowl flaps is a balancing act between cooling and drag. The B-29 was between a rock and a hard place in that regard. Either you fall out of the sky because you can't maintain airspeed because the cowl flaps are open or you fall out of the sky because the cowl flaps are closed and the engine fails.
In China the problem was exacerbated by the extreme ranges the missions were flown at. The bombers needed to be at maximum all up weight to carry enough fuel for the mission. Even then the bombs loads were small. Any reduction in take off weight would have made the mission even more pointless.

 

[Greyman]

Escort the B-29s with Black Lancasters.

 

[Zipper730]

What does it mean "Claims 23-16-31" mean?

 

[Reluctant Poster]

What does it mean "Claims 23-16-31" mean?

Destroyed-Probable-Damaged