Aero Chapter 05/06 (TS) and 05 (ADV & IUT), Thrust and Thrust Curve Review

T-45 Aerodynamics Student Workbook

Recall induced drag results from the production of lift. Induced drag dominates at low airspeeds and is

nearly negligible at high airspeeds and low angles-of-attack.

Parasite drag is drag resulting from skin friction and form (or frontal area of the aircraft). Parasite drag is

very low at low airspeeds and dominates at high airspeeds.

Total drag is the sum of parasite and

induced drag (Figure 88). The total drag

curve is frequently referred to as the thrust

required (Tr) curve because thrust is the

force acting opposite drag. Thrust required

for any airspeed may be determined from a

thrust-required curve. At the point where

total drag and thrust required are at a

minimum, the lift-to-drag ratio will be

maximum and is referred to as (L/D)max.

At (L/D)max the wing (actually the entire

airframe including the wings) is at its most

efficient operating point, producing the most

lift for the least drag. The airspeed/AOA for

maximum endurance, maximum climb

angle, and maximum power-off glide range occur at (L/D)max in turbojet or turbofan aircraft.

Maximum endurance is found at (L/D)max

because thrust required and thus fuel flow

(fuel required) are at a minimum, giving

maximum time airborne. Maximum climb

angle is also found at (L/D)max. At (L/D)max,

thrust required is at a minimum and all

excess thrust available can be converted to

climb angle which is obstacle avoidance

climb angle and not rate-of-climb. Maximum

glide range is also found at (L/D)max because

the airframe is at its most efficient operating

point and drag is at a minimum. Note it is

power-off glide range, which is at (L/D)max

and not maximum powered range. The lift -

to-drag ratio is also the glide ratio of the

aircraft. Maximum range is found on the

thrust-required curve at the point where the

ratio of airspeed to Tr is greatest (Figure 89). Maximum range may also be found by drawing a line from

the point of origin tangent to the thrust-required curve. This point defines maximum range airspeed (no-

wind).

Maximum range airspeed and AOA will vary with the aircraft’s gross weight. As the weight decreases due

to the fuel burn in the T-45, the AOA for max range increases from 12 to 13 units and the airspeed

decreases accordingly. Maximum range airspeed and AOA are drastically affected by extension of

landing gear and flaps as the T-45 bingo charts indicate.

(7-99) Original

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