Module 4 Jet Performance Thompson_N
- 1. Jet Performance (T-38Talon) NicholasThompson ASCI 309 – Aerodynamics Embry-Riddle Aeronautical University
- 2. T-38Talon Aircraft Fast Facts • Engines:Two General Electric J-85-GE-5A • Weight (empty): 7,165 lbs • Weight (max takeoff): 12,093 lbs • Wingspan: 25 ft 3 in • Dimensions: 46 ft 4.5 in (L) x 12 ft 10.5 in (H) • Max Speed at 36,000 ft: Mach 1.3 (858 mph) (745.6 kts) • Cruising Speed at 39,000 ft: Mach 0.9 • Max Ceiling: 53,500 ft • Range: 1,090 miles (947.2 nm) T-38 in flight. U.S.Air Force photo by Master Sgt. Lance Cheung
- 3. Understanding theT-38Talon’s Best Angle of Climb (AOC) • Best angle of climb (𝑉𝑥) is where thrust available (𝑇𝑎) compared to thrust required (𝑇𝑟) is the greatest. • Minimum drag occurs at ( 𝐿 𝐷) 𝑚𝑎𝑥, which is at the bottom of the 𝑇𝑟 curve • For turbojet powered aircraft like theT-38Talon, 𝑉𝑥 occurs at the aircraft’s ( 𝐿 𝐷) 𝑚𝑎𝑥. • For theT-38Talon, ( 𝐿 𝐷) 𝑚𝑎𝑥 is 240 kts with a drag of 830 lbs • At this airspeed (240 kts), the angle of climb can be determined by the following equation: γ = 𝑠𝑖𝑛−1 ( 𝑇𝑎−𝑇𝑟 𝑊 ) So, • γ = 𝑠𝑖𝑛−1 ( 4200−830 10000 ) = 𝑠𝑖𝑛−1 (0.337) • AOC = 19.7 degrees Curves are for aT-38 w/clean configuration Aircraft Weight (W) = 10,000 lbs Altitude: 0 ft (sea level) σ = 1.0
- 4. Understanding theT-38Talon’s Maximum Endurance Airspeed (𝑽 𝑩𝑬) • Max Endurance Airspeed (𝑉𝐵𝐸) occurs at an aircraft’s ( 𝐿 𝐷) 𝑚𝑎𝑥. • When flying at 𝑉𝐵𝐸, the aircraft thrust is assumed to be set for straight and level flight. In this scenario, the thrust required (𝑇𝑟) is equal to the thrust available (𝑇𝑎). • As previously discussed, we already know aT-38Talon with a weight of 10,000 lbs has an ( 𝐿 𝐷) 𝑚𝑎𝑥 of 830 lbs at 240 kts. • Therefore, theT-38Talon’s 𝑉𝐵𝐸 is 240 kts. T-38 in flight. Photo courtesy of www.warbirdalley.com J85-GE-5A on engine stand. Photo courtesy of www.flickr.com/photos/tom-margie/15058224043
- 5. Understanding the influence of weight on performance for aT-38Talon aircraft • If the weight of theT-38Talon is increased, so to is the amount of lift required to keep it aloft. This increase in lift also causes an increase in drag due to corresponding increase in induced drag. • With an increase in weight, the (𝐿/𝐷) 𝑚𝑎𝑥, as well as the rest of the thrust required (𝑇𝑟) curve is moved up and to the right. • This means that as weight is increased, the aircraft’s thrust and velocity must increase to maintain max endurance airspeeds and rates of climb. • In the chart to the right, you can see this relationship. • AT-38 weighing 8000 lbs has an (𝐿/𝐷) 𝑚𝑎𝑥 of ~700 lbs at 230 kts. • AT-38 weighing 12000 lbs has an (𝐿/𝐷) 𝑚𝑎𝑥 of ~1050 lbs at 260 kts. • When theT-38 weighs more, it requires more thrust at higher speeds to maintain level flight where 𝑇𝑟 = 𝑇𝑎
- 6. References Dole, C. E., Lewis, J. E., Badick, J. R., & Johnson, B. A. (2017). Flight Theory and Aerodynamics: A Practical Guide for Operational Safety. Hoboken, New Jersey: John Wiley & Sons, Inc. Margie, T. (2014, October 31). General Electric J85-GE-5. Retrieved from Flickr: https://www.flickr.com/photos/tom-margie/15058224043 Northrop T-38 Talon. (2016). Retrieved from Warbird Alley: http://www.warbirdalley.com/t38.htm U.S. Air Force. (2005, September 23). T-38 Talon. Retrieved from U.S. Air Force: https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104569/t-38-talon/