High altitude aircraft, the Global Hawk fails

Previous posts : the F-35 is 30 years obsolete, better space launch, electric highways are a cheaper replacement for petroleum

To discuss high altitude flight we must discuss engines.

   The left curve is called the theta break, the right curve is called the throttle hook.
  On the theta break the abscissa (x axis) is the ratio, theta, of the total temperature to the design temperature of the engine, which is usually 20 Centigrade ( 68 call it 70 Fahrenheit ).  The total temperature is the addition of the atmospheric temperature plus adiabatic heating.  Adiabatic heating is one half times the mass density of air times the velocity squared ( That is the Bernoulli pressure term) divided by the specific heat at constant pressure.  The atmospheric pressure falls with altitude until about 35 000 - 40 000 feet altitude under usual circumstances and then remains constant until 60 000 feet where the temperature begins to rise under heating by sunlight. The adiabatic heating increase with velocity as the square of the velocity.
   The ordinate (y axis ) is the ratio of total pressures to the design pressure, usually sea-level  standard pressure.  The ratio is expressed as pi. The total pressure is atmospheric pressure plus the Bernoulli pressure term.
   A turbine engine is essentially a pressure device; air enters the front and is compressed and slowed by the compressor, this compression also causes adiabatic heating, after the compressor the air enters the combustion chamber where fuel is burned to provide energy for work, then the compressed, heated air passes through a turbine where it expands and cools, the turbine provides the power to run the compressor, the air then passes through a nozzle where it accelerates, the combination of the mass flow times velocity per second and the net pressure differential between inlet and engine outlet multiplied by the area of the inlet and outlet produces the forward thrust of the engine.  Both pressure and mass flow contribute to the total propulsive thrust.
   What the theta break shows is that there are two limitations to the performance of a turbine engine.  The first is pi naught, if the pressure ratio exceeds pi naught the compressor cannot contain the air mass and it will explode out the front of the engine along with the fuel in a fireball.  This happens between five and ten times a year on commercial airliners in the U.S.   If air colder than the design temperature is entering the engine the throttle must be reduced to limit fuel flow and limit eh temperature and pressure rise from the additional fuel.  This is the pressure limitation.
   The other limit is from heating. The air enters the engine and is heated by compression, when fuel is added its temperature rises additionally, if it rises too high it will overheat and cause softening and deformation of the first set of turbine blades.
  For a given engine design, there is a maximum pressure ratio which the engine can contain, if the theta falls to the left, colder, of the design point the throttle must be reduced to prevent excess pressure.  If the theta is to the right, hotter, the throttle must be reduced to prevent overheating.  The curves which descend form left to right rpresent increasing heat tolerance at the turbine blades as the successive curves rise to the right.  To the right of theta naught the thrust is reduced.  To design a turbine engine;  the material for the turbine blades is selected then a theta naught is selected, from the graph, the theta naught is traced upwards until it intercepts the appropriate heating curve, from that intercept a horizontal line is drawn until it intercepts the ordinate-pi axis which then tells the maximum design pressure ratio for the engine.
   The curve to the left, the throttle hook, is named after its fishhook shape.  What it shows is the fuel efficiency of the engine, fuel consumed per hour per pound of thrust, versus throttle position.  The key point is that the minimum fuel consumption, maximum efficiency per pound of thrust, occurs at a throttle setting of about one half.  Above one half the fuel consumption rises slowly with increasing throttle, below one half it rises rapidly.  For cruising flight, such as commercial airliners, the minimum fuel consumption point is the desired operating point, this is the theory behind cruise-climb.  In cruise-climb, the throttle is set at the most eficient point and the airliner climbs to accommodate the change in weight form fuel burn.  The point A corresponds with the theta break under sea level conditions.

   If an aircraft is lifted on a boom to 40 000 feet the carrier aircraft can provide the lift while the aircraft itself  can have an engine with theta set at a lower temperature point, to the left of sea level.  In addition, the throttle position from B to A is only used for climb, if the aircraft is carried to altitude it does not need the additional thrust for climb.  Consequently, the point A can be set at a higher heating curve than the turbine can withstand, since the additional fuel flow and additional heat will never be used, as long as point B is within the actual heating curve.  By using the combination of lower total temperature, which is achievable in relatively low-speed flight, and the heating curve for B instead of A the total pressure ratio, pi, can be increased.   Engine efficiency increases with increasing pi.
   For the Global Hawk reconnaissance drone, removing the landing gear saves weight, which can be converted into additional fuel, as well as the more efficient, higher pi, engine would increase its endurance and utility.  The Global Hawk is miss-designed.  The carrier aircraft could be either manned or unmanned, manned allows for errors in joining and recovering the two aircraft.

Big snow

Previous posts showed the F-35 is 30 years obsolete and electric  highways can be cheaper than petroleum.

Now I will give further illustration that reporters are idiots who do not know how to do their jobs or build or write stories.
   Christmas, 2010, saw 23 inches of snowfall, measured in Central Park, New York City.  How much snow is that?  Snow weight is typically taken as 10 pounds per cubic foot.  That snow was light and fluffy, so, say 15 pounds for 23 inches deep (almost 2 feet) per square foot of ground.  1 square mile equals 27 878 400 square feet, at 15 pounds per square foot the snow weighed at least 400 000 000 pounds per square mile, that is
 200 000 tons per square mile.  New York City covers over 300 square miles for a total of 60 000 000 tons.
  60 000 000 (60 million) tons of snow fell on NYC.
  Streets and sidewalks are at least 20% of the surface area, or 12 000 000 tons of snow had to be plowed and shifted.  The other question is the amount of airflow required to move that amount of water vapor before it fell as snow.
   One inch of rain on NYC would be over 20 000 000 tons.
   NYC uses under 5 000 000 tons of water per day.
   The US uses about 1 000  million tons of petroleum per year.

Space launch

Previous outstanding posts:

• The failed F-35 - The $380 billion mistake, II, III
• Costs of electric highways - Electric car: wires beat gas
• The safest nuclear reactor

  I will now further illustrate why the idiots at DARPA should not do engineering.
  The illustration shows haw a recoverable experimental launch vehicle should have been built.  DARPA and the air force got together and decided to build a reusable launch vehicle with clam-shell doors over a cargo bay.  Unfortunately, no one involved understood engineering.
   They built the thing with landing gear instead of, as illustrated, an air capture vehicle.  Slowing for landing means substantially larger wings to generate lift at low speeds; lift is proportional to the square of the speed with an additional bonus for compressibilty, landing at 200mph, 300 feet per second (fps) versus flight at 800 fps, 540 mph, is 9:64 for square of velocities, but there is a bonus of 1.5 for compressibility, Praqndtl-Glauert, so the total is 9:96.  If lift is considered at 40 000 feet air density is 1/4 so the total effect is 9:24.  The effective lifting surfaces can be under 1/2 as large, although one must make adjustments for smaller wings being less efficient.

example of boom from f-35 post

   The smaller wings mean less weight ad less surface for drag and heating on re-entry.  In addition, the higher speed may allow the elimination of the vertical stabilizer, tail, which further reduces weight and stresses; it is harder to maintain stability at lower speeds so the vertical stabilizer adds additional control forces, at higher speeds the wing devices, ailerons, can provide sufficient control.
   The vehicle should have had an attachment point ahead of the clam-shell doors for an aircraft to connect a boom to the vehicle and then lift it with a cable ( see The $380 billion mistake).   Attaching at the front means
 that the center-of-mass, c-m, is in back of the connection guaranteeing stability in flight.  Once the vehicle is placed beneath the recovery aircraft, additional supports and stabilizers can be attached at the rear sides of the vehicle to firmly secure it for landing.
   The recovery aircraft would be manned.  If the vehicle is traveling at 800 fps and has a glide ratio of 1:10, it will be descending at a rate of 80 fps.  From 40 000 feet it will have 500 seconds, 8 minutes before crashing into the ocean.  That should be enough time for recovery as long as the vehicle is fully tracked and its flight path is co-ordinated with the recovery aircraft.
   An even better result can be obtained with a reusable engine package.  The next illustration shows a package of three space shuttle main engines, SSMEs, in a winged recovery vehicle.
   For  launch, the nose cap of the vehicle would be swung away to the lower side of the vehicle with the fuel line attached to the top.  By swinging the cap out of the way, the frame of the vehicle can transmit engine thrust directly to the structure of the fuel tank.  The cap would be placed to offer minimal aerodynamic forces.  Struts from the fuel tank would attach to the lower end of the vehicle to stabilize it and allow for the engines to rotate their thrust.  For separation the struts would be bent backwards an out of the way by internal explosive charges, allowing the vehicle to separate backwards away from the fuel tank.
   For re-entry, the cap would swing closed to provide a smooth aerodynamic envelope and the vehicle would again be air-captured by a boom connected to the fuel connection on its top.  The vehicle would be landed and the engines and vehicle serviced and re-used.
   By removing landing gear and placing the fuel attachment to the upper surface, the underside would have no openings and would be easier to cover with thermal tiles.

   A further possibility  is to air launch the engines, fuel tank and payload.   In a^, is depicted a vertical ground-launched stack.  In c, d, e are depicted the assemblage attached to the top of a launch aircraft.  To launch 3 SSMEs, the rocket would way 1 500 000 lbs.  The aircraft would way a similar amount, at least, for a total of 3 000 000 lbs.  Flying at 800 fps, 540 mph, 1200 lb/  square foot of wing lift would be generated at a coefficient of lift of 1 at sea-level.  At a release altitude 0f 60 000 feet, the air density is 1/8 and the lift is 150 psf, pounds per square foot.  For an efficient coefficient of lift of .6-.7, the effective lift would be 100 psf.  For a 3 000 000 lb aircraft that would be 30 000 square feet  of wing area.  An efficient high-altitude wing of aspect ratio 10 would be 550 feet span and 55 feet mean cord.
   Their is a problem with wing weight.  If a wing is scaled up by doubling all dimensions, the wing is 2X as long, 2X cord and the center of lift is 2X from the body for a total moment of 8X.  The wing root is only 2X as deep and 2X the perimeter for 4X resisting moment unless the wing skin is thickened.  Scaling allows 2X lift and 2X area for 2X weight if skin thickness is constant.  For the higher moment, either the wing root must be greatly expanded or the skin made twice as thick.  The weight might prevent the flight of the aircraft.   I have shown it with 6 engines, with current engines it would need 10
   After take-off the aircraft would climb to perhaps 10 000 feet and the roll upside down.  The pilots, b, would be in a cockpit which would look like an old Gemini capsule.  The pilots would be seated side-by-side with the windshield opening on hinges to allow entry.  The entire cockpit capsule would be mounted on a ring mount which would allow it to rotate.   In front of the capsule would be a rocket assembly allowing the pilots to separate from the aircraft  before ascending to escape catastrophes.  After the pilots roll the aircraft 180 degrees they would rotate the capsule 180 degrees, they would be upright but the aircraft would be inverted.  They could now refuel if necessary and climb to the release altitude.   Since modern aircraft are fly-by-wire and only electronic signals are used for control inputs, rotating the cockpit only requires continuous transmission of the  control signals to maintain control of the aircraft whether upright or inverted.
   This design allows for short, heavy landing gear and easy access to the rocket before take-off, although it might require additional supports under the payload and engine modules to reduce stresses.  The release at 60 000 feet allows less drag, 7/8 of the atmosphere would have been cleared.  At release, the rocket is conveniently supported below the aircraft for easy release.
  One other possibility would be to liquify oxygen in flight, taking off with excess hydrogen to chill the oxygen. At 1 500 000 lb, oxygen is 8/9 of the fuel weight or 1 300 000 lb.  At sea level air weighs 1/14 lb/cubic foot , pcf, 20% is oxygen or oxygen is 1/70 pcf.  At 60 000 feet, oxygen is 1/560 pcf;  it would be best to climb to altitude and then liquify as this lightens the weight while climbing.  So, for 3 600 seconds per hour 800 fps, 560X1 300 000/ 800X3 600= 250..  That is 250 square feet X hours.  For a 3 hour flight = 80 square feet which is about the frontal area of the current largest jet engines.  There would also be inefficiencies, so maybe twice that area would be required.  That would still be acceptable.
   The SSMEs are designed for 60 000 feet, that is their most efficient operating point.  Releasing them at 60 000 feet allows for them to be reset for vacuum design point, and slightly better efficiency.
   The aircraft-rocket combination would take-off  from Cape Kennedy and fly south-east over the Atlantic placing itself closer to the equator for east-west launches and far enough over open water for north-south launches.  Vandenburg could then be closed.
   For high speed flight the most efficient wing profile has a flat top, called a super-critical wing.  It was developed by a guy named Whitcomb.  For take-offs, the most efficient wing shape has a flat bottom .  By rolling the aircraft while  in air, the wing at take-off would have a flat bottom and then when rolled over it would become an efficient flat top.  It would be advantageous at both ends.
   The fuel lines could be fed through the open front end of the engine vehicle with an attachment point for recovery built into the upper surface.
   Obviously, a smaller rocket and a smaller launching aircraft could be more easily built.
   I sent the idea for a launch aircraft that rolls to drop the rocket to DARPA.  They do not read their mail, but considering how bad they are at engineering, maybe they are illiterate, too.

c

The safest nuclear reactor

   The safest way to build a nuclear reactor is to float it. If the reactor and containment weigh 40 000 metric tonnes and the raft weighs another 40 000 tonnes, the total of 80 000 tonnes could be supported on a displacement of 100 meters diameter (for an area of about 7 800 square meters) with a depth of 10 meters (one tonne = 1cubic meter of water).
   An excavation, somewhat over 100 meters diameter, would be emptied to a depth of 100 meters, some of the excess space would be used for the placement of a concrete lining to retain water.  A 120 meter total diameter would have an area of 11 000 square meters, to 110 meters depth would have an excavated volume of 1 200 000 cubic meters.  At $100/ cubic meter excavation cost, the total price would be $120 000 000.
    The area of the walls would be 120 X pi X 110 = 41 000 square meters.  The area of the floor would be 11 000 square meters fora total of 52 000 square meters.  If the walls and floor are 3 meters thick, the total concrete would be 160 000 cubic meters.   Concrete would cost about $200/ cubic meter and, with labor and placement costs, maybe $2000/ cubic meter, for a total cost of $320 000 000.  Added to excavation cost the total would be $440 000 000.
   A raft of 40 000 tonnes would represent 20 000 cubic meters of concrete.  Again, at $2 000 per cubic meter total cost, it would be $80 000 000, added to the other total, the total cost would be $520 000 000.
   The cost of a nuclear reactor is $8 billion to $10 billion, so the cost would not be out of line with other expenses.  In fact, the floating of the reactor isolates it from ground motion and obviates the need for earthquake reinforcement, saving an enormous amount in construction costs; the flotation might, in fact, save money from the total cost.
   The raft and reactor would be assembled on the floor of the tank and then floated into position as the tank is filled.
   The main purpose of the design is in any event in which there is a danger of core melting.  The sea-cocks of the platform would be opened and the entire unit sun and submerged.  With passive cooling from the surrounding water, there is no danger of melting.
   In order for this to work, there needs to be a separation of the feed and exit pipes.  In b ^, an outlet pipe is shown fitted into a sleeve pipe.  The sleeve can be an active pipe for circulation or a dead-end seal, depending on need.  In the illustration the pipe continues.  Heavy support and reinforcement would be needed for high-pressure pipes for them to function properly.
   In d^, the outlet pipe, o, is shown at a higher elevation than the inlet pipe, o.  This is so that the pressure in the inlet pipe is higher form deeper submergence than the outlet driving the liquid from the inlet, through the core of the reactor and then out the outlet to maintain cooling circulation.  The heat form the reactor core will warm and expand the water further increasing circulation, as the warmed water will further drive itself through the exit pipe.
   Depicted in d, is a pressurized water reactor, the water in the reactor core is under high pressure and circulates to where it exchanges heat with a second pipe, the secondary pipe having water  then flashes into steam and drives a turbine to produce power.  The outlet pipe is connected to the top of the reactor vessel where a bubble of steam, b, is maintained.  This bubble normally prevents the reactor from going solid, being completely filled with water.  Water does not compress easily and if the vessel filled with water, the heat produced by the reactions would heat and expand the water potentially causing the water pressure to rupture welds and pipes, leading to a lack  of cooling and potential melt-down.  The bubble can compress so it can absorb changes form the heating of water or water-hammer, the sudden stopping of a flow of water.  When disconnecting the pipes, it is important to disconnect the steam outlet first, if the inlet pipe is disconnected the first, the steam bubble will expand, driving water out the inlet, and potentially uncovering the fuel rods.  By the steam pipe being disconnected first, the steam will blow out the pipe relieving the pressure and allowing the entering water to successfully cool the core.  In order to ensure the outlet opening first, it would have a shorter  sleeve so the raft will sink a shorter distance before it opens.   For the pressurized water reactor, the outlet pipe would be connected to a dead-end sleeve.
   For the inlet pipe, c, shows deep serrations in the pipe edge periphery, admitting water in a controlled manner as it descends, the systematic filling of the pipe precluding the trapping of an air bubble which could interfere with flow, the water entering in a controlled manner will systematically displace the air.  The pipe also has a longer sleeve to delay water entry until the steam has escaped.
   In a boiling water reactor, the steam pipe would be the outlet pipe.
   In a, e, shows an exhaust pipe connected to the top of he dome, there would also be an inlet pipe for the volume of the dome for additional cooling and to prevent the dome volume from acting as a flotation device.  Both pipes, inlet and outlet, would be dead-end connections.
   A ring shield, rs in a, would cover the opening between raft and water tank edge.  It would be a semi-circular metal enclosure which would ensure that the water remains clean.  In cold climates the ring shield and some residual heat from the reactor fed into the water should easily prevent any freezing.
    There will be radioactive steam and water released, but the isotopes tend to decay quickly.  Additionally, blocks of floating plastic covered by plastic tarping could be placed over the tank after the raft has submerged to further reduce any radioactive releases.
   A decision would have to be made on how much additional equipment, such as turbines and alternators, should be placed on the raft.  Once the raft sinks, the reactor would be useless.  That leaves open the danger that operators may delay submerging and consequently  allowing the core to melt.

Previous fascinating posts:

• Why the F-35 is useless - The $380 billion mistake, II, III
• Electrifying highways are comparable to buying petroleum- Electric car: wires beat gas