You do not need an 11 volt receiver for two reasons. #1: They don't make them, and #2: (assuming this is an electric powered model) most (but not all) Electronic Speed Controllers (ESC) that drive the motors have a built in Battery Eliminator Circuit (BEC) that supplies regulated 6 volt power to the receiver via the throttle lead connection plug. All the servo connections on the receiver have the + and - leads fed from a common bus. Therefore it does not matter which of the plugs has voltage applied to the + and - terminals. If your ESC does not have a built in BEC, then you will need a voltage regulator to place in between the battery and the receiver, or you can power the receiver via a separate 6 volt flight pack. If you use a second battery, know that only the motors will be run from the 11 volt battery and the receiver and all the servos will run off of the 6 volt battery. If your airplane is an ARF (Almost Reay to Fly) with pre-installed servos and ESC, then the ESC almost certainly will have a built in BEC.

Based on your question, I gather that this is either your first electric airplane or this is your first RC airplane. If this is your first RC airplane, then please do not try to fly it until after you have received training and become proficient on a small trainer. The B-17 is not a trainer and the odds of crashing it on the first flight attempt by a first-time pilot is nearly 100%. If you are already a proficient flyer of gas or glow powered models, then there should be no major issues with flying the electric B-17.