Tanker follies

Previous posts showed F-35 obsolete

   The US Air Force engaged in a long, protracted and stupid tanker competition between Boeing and Airbus.  It was stupid because they assigned arbitrary rules to determine what the total life cycle costs would be.  The pretense of meaningful competition was silly, they could have just picked one, either one would have performed the job the Airbus was somewhat larger.

   They could have developed a blended wing body aircraft, where the fuselage produces lift in the amount of time they spent.  The one problem is that the body is relatively thin from top to bottom.  If only fuel was being hauled, that would not be a problem, but they are also intended to sometimes carry freight.
    A, above shows a wing-body with fairly low cargo containers being loaded or unloaded from underneath, the cargo containers would be suspended from the top and slid horizontally.
   C,D show an external fan engine which have never been fully developed because of noise problems.  The military sometimes worries about the neighbors, especially overseas, but having a more efficient engine, since the external fan moves more air at lower speed and the energy of the propulsion air goes as the velocity squared.  The other reason they have not been fully developed is a fear that if a blade breaks off, there is nothing to contain it, like the walls of the engine.  But, again, with a military aircraft margins of safety are lower.
   It never ceases to astound me, how potentially useful items do not get developed unless someone feel s like it but unnecessary impedimenta have money thrown at them almost without limit.
   The other possible development is a high-altitude engine mounted in the tail, B, to augment a twin jet.  The idea is for the engine to be set using high pressure for operation in cold temperatures at altitude and having a throttle setting that places its cruising  operating point at close to the material limit for the first row of turbine blades.  An airliner typically has 30% of its take-off weight  in static thrust of its engines.  The thrust to weight ratio of turbine engines is 6-8, larger engines having the higher ratio.  For 30%, the engines would weigh 4-5% of total aircraft weight.  Adding another engine which would produce little thrust at sea level would add maybe 4% between engine weight and additional structure needed.  In addition, it would represent an additional drag surface.  An airliner is typically 50% weight airframe and engines and the other 50% cargo and fuel.   An engine like this would be the only power at altitude, the other engines would be turned off.  For commercial profitability the plane would hav eto fly at least 3 000 miles , 5 000 kilometers.  There is also higher intial cost for the airliner and an additional maintenance line for  a different engine.  For the military, with an external fan it might be useful, since the military tends to fly long ranges.