north american known manufacturer model designation referred dragon prototype bomber aircraft developed late 1930s evaluation evaluated found considerably expensive rival aircraft despite ordering small number evaluation aircraft prototype built design development twin engined military aircraft prototype constructed north american factory california work aircraft began early mid wing metal construction powered twin radial engines fitted increased high altitude performance flown crew men featured remarkably strong defensive armament time including calibre machine guns planned fitted powered nose dorsal turrets addition manually operated weapons installed waist ventral positions pounds bombs carried internal bomb bay pounds bombs able carried range miles testing evaluation undertaking maiden flight december mines field company test flying indicated number minor problems modifications resolving resulted aircraft designated accepted aircraft assigned serial number evaluated early following year competition similar design improved version company successful course fly gun turrets proved troublesome drive motors proving issues wind blast gun slots encountered result problems nose turret dorsal turret removed proved superior performance competitor price primary factor distinguishing account modified declared winner competition douglas quoting price aircraft usd north american estimate usd aircraft order placed douglas aircraft designated despite found performance favorable order pre production aircraft designated soon contract awarded cancelled built leaving sole example type constructed operated served research aircraft retirement failed win production contract long line north american aviation medium bomber aircraft provided experience knowledge assisted development developed mitchell army standard medium bombers world war specifications data general characteristics crew length wingspan height wing area weight gross weight max takeoff weight powerplant twin radial engines propellers bladed performance maximum speed mph feet cruise speed mph range nmi pounds bombs combat range nmi pounds bombs service ceiling time altitude minutes feet armament guns calibre machine guns mounted single turrets nose dorsal positions single manually operated mounts waist ventral positions bombs pounds internal bay
North American XB-21