Why did the propellers on the B-36 Peacemaker face backwards?

The B-36 design goes back to 1941 when the USAAC called for an intercontinental strategic bomber to strike Nazi Germany from North America. The range, cruise speed and payload specifications were too demanding to be met with current aviation knowledge. I’ve never seen it stated anywhere, but I’m guessing the pusher propeller design was chosen in an attempt to reduce overall drag and maximize range in order to meet the range specifications. If this is true, the B-36 used pusher propellers to eliminate propeller turbulence from interfering with airflow over the wing which would reduce induced drag in order to maximize range. The big tradeoffs are that:

Poor engine cooling on the ground where prop wash will not contribute to engine cooling

Turbulent air across the wings decreases propeller efficiency and performance

Loss of the propeller’s thrust effects over the wing (reduced total lift over that wind section) may require a compensatory larger wing and tail size requirements (and increasing induced drag).

The B-36 was also LARGE in order to carry lots of fuel. Here is the B-29, largest bomber of World War II, next to the B-36 for size comparison.

Here are a few photos showing the results of Convair’s drag reduction efforts.

NACA report “Full-Scale-Tunnel , Investigation of a Multiengine Pusher Propeller Installation” by Herbert A. Wilson, Jr. Issued date: NOV-42 showed improved efficiencies of the pusher configuration, but this report doesn’t explain Convair’s decision to use a pusher design in 1941.

There are advantages and disadvantages of using a pusher vs conventional tractor (puller) propeller configuration. I’ve not found a declared reason why Convair’s designers selected a pusher design, but my guess is the most likely reasons for the pusher option are:

The USAAF specification that the B-36 was designed to was very demanding for the era (high service ceiling, high max and cruise speeds, large bomb load, and very long range). The designers may have been attempting to reduce drag through streamlining the engine nacelles or reduce propeller turbulence from interfering with airflow over the wing in order to achieve the spec.

Convair wanted a “wow” design to win a contract from the USAAF.

Some replies have proposed reasons for the design (e.g., wing taper and fire suppression), but none are plausible as they don’t fit the design timeline.

Source: Alan Pietrovito (Quora)

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