Aero Engineering 315

Lesson 33

GR3 Review

General strategy Prior to class

Review reading for lessons 23 – 32 Work / review problems #26 – 42 Review handouts (turbojet performance summary

and changes to thrust & power curves) Review slides and other handouts—especially

the performance summary handout Know your memory equations (mostly GR2 and q) Be familiar with applicable supplemental data info

In class BRING calculator, straight edge, pencils

Performance SummaryRelationship Best Case Relation between

Induced and Parasite Drag for best case

Graphical relation for best case

Max Climb Angle CDo = kCL2 - Minimum from TR curve

- Tangent point on a line from origin to PR curve

Max Climb Rate No set relation - Draw a line parallel to PA curve, and move it down till it is tangent to PR curve

Breguet (5.28) or Avg Value (5.27)

Max Jet Powered Range

CDo = 3kCL2 - Tangent point on a line

from origin to TR curve

Breguet (5.26) or Avg Value (5.24)

Max Jet Powered Endurance

CDo = kCL2 - Minimum from TR curve

- Tangent point on a line from origin to PR curve

R = h (L/D)Best Glide Range (angle)

CDo = kCL2 - Minimum from TR curve

- Tangent point on a line from origin to PR curve

Best Glide Endurance (min sink)

3CDo = kCL2 - Minimum from the PR curve

)arcsin(W

DT

W

P

W

DTVCOR x

)(...

W

P

W

VDDOR R...

Climbing

Cruise

Glides

Example 5.2

An aircraft with CDo = 0.020 and k = 0.12 is flying at h = 30,000 ft and M = 0.8. If the aircraft has a wing area of 375 ft2 and it weighs 25,000 lbs, what is its drag coefficient and how much drag is it generating? If the aircraft is in steady, level, unaccelerated flight (SLUF), how much thrust is its engine producing? If its CLmax = 1.8, what is its stall speed at that altitude?

Example 5.4

A sailplane’s drag polar is CD = 0.01 + 0.02 CL

2. It has a mass of 500 kg and a wing area of 20 m2. What is its maximum glide ratio and minimum sink rate at sea level, and at what speeds are these achieved?

Example 5.6

A turbojet-powered trainer aircraft weighs 5,000 lbs and is flying at h = 25,000 ft with 1,000 lb of fuel on board. Its drag polar is CD = 0.018 + 0.095 CL

2, its wing area is 180 ft2, and the TSFC of its engines is 1.0/hr at sea level. What is its maximum range and endurance to tanks dry at this altitude, and at what speed should the pilot initially fly to achieve each?

Example 5.8

The non-afterburning turbojet engines of a Cessna T-37 jet trainer produce approximately 1700 lb of installed thrust for takeoff at sea level, and its takeoff weight is 6575 lb. Its CLmax=1.6 for takeoff and its drag polar in its takeoff configuration is CDo = 0.03 + 0.057 CL

2. Its reference planform area is 184 ft2. Normal takeoff procedure requires the pilot to rotate the aircraft to the takeoff attitude just prior to reaching takeoff velocity, so for the majority of the takeoff roll the aircraft’s CL = 0.8. What will be the aircraft’s takeoff distance at sea level with no wind?