Such positioning limits maneuverability and increases noise. The new zeppelin's engines appear to be attached to the exterior of the envelope but are actually connected to the hidden internal framework just underneath the skin. In addition, a minimal internal structure affords less opportunity for damage in rough landings. In the LZ N07, therefore, the elaborate skeleton of ancestral craft is replaced by a simple triangular framework , consisting of three aluminum alloy longerons and only 12 sets of light, strong carbon-fiber composite girders. This arrangement gives the airship traditional zeppelin stiffness but only along its length.
Radial stiffness is maintained by the internal gas pressure.
The envelope , a multilayer laminate, attaches continuously to the three longerons and surrounds both helium gas and ballonets, compartments of adjustable volume filled with air. These ballonets can take in air from outside the ship, or release air, to maintain a constant internal pressure in the hull during ascents or descents. As in blimps, keeping the overpressure low is a safety feature. If the pressure within an envelope is significantly higher than the external pressure, a tiny puncture will lead to catastrophic failure, as when a pin explodes a balloon. The desire for unparalleled maneuverability resulted in the decision to use three engines .