Flight forces : reciprocating engine take off


We consider all forces are equal  in cruise . Refered to As you can read at  Basic concepts of aerodynamics  post  , the first Newton law  in concrete. 

Power curves : Aviation Power curves

Definitions we are going to use during this post :

Fuel flow : It is the amount of fuel that goes throw the tubes.

Specific Fuel Consumption ( SFC): It is the fuel flow required for getting the unit of power. SFC=FF/Power.

The lower the SFC is the least fuel we need to get power.

Specific Range (α): It is the  distance we move per unit of power.

α=Distance in neutical miles / kilograms of fuel  or                                   α= True air speed/ Fuel flow


Maximun Range Flight

The main porpose of this flight is to move the greatest distance with  the  amount of fuel we have .

As the fuel we are burning during the flight it is proportional to the required power. To reach the maximun range flight we must get that the relation between  power required versus true air speed must be the lowest . ( Power required/True Air speed) as you can observe this relation is the lowest when power required is low ( low fuel cosumption) and the true air speed is high.

Power required ( Pr) = TAS x D, so if we devide Power required against TAS, and also this relation as we saw above should be the lowest , the result is the minimum drag. 

When do we get the minimun drag?

Don´t worry about this question it will be solved later on in the principles of flight subject. 

For the moment just know that we reach the minimun drag when the induced drag is equal to parasite drag. and they are the same when we are flying at maximum fineze angle of attack which is ( Cl/Cd)max

  • Cl : lift coeficient
  • Cd : drag coeficient

Considerations about the range 

Weight: As we know higer weight  leads on higer power required, so the higher fuel consumption is required.

Altitude: The altitude has two oposed effects. On one hand the power required increases ( high fuel consumption) and on the other the TAS increases. So our best benefit of flying high is flight time.

Wind : The wind does not affect the power required nor the true air speed . But if we have tail wind our ground speed increases leading on an increased ground distance ( range).

In some books say that when we have tail wind is recommended to reduce a bit the speed.

Maximum endurance flight

Endurance is the maximun time that an aircraft is able to be on the air.

For being the greatest time on the air we need the lowest fuel consumption, which means the lowest required power.

Consideations of maximun endurance flight

Weight: increase of weight leads in an increase of required power , which means and increase of fuel consumption, so de endurance decreases.

Altitude: An increase of altitude leads on an increase of density altitude , which means an increase of required power. The result is that endurance decreases.

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