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Flight Test Engineering Course (UA)

In the Fall of 2019, I developed and taught a course in Flight Test Engineering to a select group of undergraduates in Aerospace Engineering and Physics.

Topics were divided into 1) performance, 2) stability & control, and 3) logistics, operations & hardware.

  • Performance
    • Atmosphere
    • Airspeed
    • Airspeed & Static Port calibration
    • Takeoff
    • Stall
    • Climb Theory
    • Sawtooth climbs
    • Level acceleration & Excess power
    • Level Flight Performance
  • S&C
    • S&C Theory
    • Neutral Point Estimation
    • Stick Forces, Stick force per g
    • Maneuvering Point
    • 6 DOF Aircraft Dynamics
      • Phugoid
      • Short period
      • Spiral
      • Roll substidence
      • Dutch roll
    • Flying & Handling Qualities
    • Inertial Coupling
  • Logistics, operations, & hardware
    • Data reduction
    • Flight test instrumentation
    • Telemetry
    • System identification

Lecture note samples:

The students were required to learn the theory, maneuvers, and analysis necessary to conduct flight testing. We used experimental data collected by the instructor (me) and the students.

Textbook: I assigned Kimberlin’s Flight Testing of Fixed Wing Aircraft; however, Ward’s Introduction to Flight Test Engineering was a primary resource.

Wing Vortex Question

Q: Could you explain to me why the vortex does not appear to be coming from the tip of the wing, but rather several feet closer to the fuselage on this Boeing 777?

Boeing 777 vortex – Unknown photographer

A: Good question. The answer is that the vortex is visible where the change in lift distribution -and thus, shed vorticity- is highest. The flaps are extended, which creates a sharp discontinuity in the wing geometry and lift distribution.

Here’s the physics:

  1. The extended flaps increase both the wing area and the effective angle of attack for the inboard wing. (see: Thin airfoil theory)
  2. The increased area and angle of attack increase the lift being generated on the inboard panel.
  3. Shed vorticity is proportional to the spanwise derivative of the lift distribution.
  4. The vortex rotation decreases the local air pressure and temperature below the dew point. Water vapor condenses into a fine mist. We see this fine mist.
  5. The vorticity is transported downstream (i.e. Helmholtz rule #3)

More information:

  • Notice the spanwise lift coefficient is visually displayed with a vapor cloud above the upper wing. This cloud confirms that the spanwise lift coefficient has the largest decrease at the flap tips.
  • You should remember that the entire wing is shedding vorticity. We see the vortex at the flap tip. If the humidity were higher, we might see additional vorticies.
  • Ground effect is responsible for the slight outboard track of the visible vortex. As the aircraft descends further, the shed vortex will likely be pushed further outboard; induced drag (for a given CL) will decrease.
  • It is not true that a vortex is only generated at wingtips or flap tips. Physics demands a smooth lift distribution (regardless of what we see).

The Mystery Proceedings

At the end of 8th grade, I anonymously received the 1989 Proceedings of the National Space Society’s Eighth Annual International Space Development Conference.

To this day, I have no idea who sent it.

Someone knew of my interest in aerospace. I have no idea why they picked these particular proceedings, as it was well past 1989. I still have the book. Thanks to anonymous! Sometimes the mysteries of life are never known.

Aircraft Dutch Roll with No Dihedral?

Months ago, an excellent question appeared on the Modeling Sciences sub-forum of rcgroups.com concerning an flight-dynamics aerospace engineering topic: Is dutch roll possible in an aircraft with zero effective dihedral?

The answer is yes.

Simplified Yaw-only Analysis

The dutch roll flight mode shows up in a yaw only behavior driven in frequency by the yaw stiffness Nβ and in damping by yaw damping Nr. A pilot would identify the behavior as a snake dominated dutch roll behavior. With zero effective dihedral, we could also reasonably expect only little to modest yaw-roll coupling through the rate terms, which would be primarily driven by the vertical offsets of surfaces. For the engineers, this simplified 2DOF model of dutch roll has a frequency and damping term approximated as: (derivation)

Interestingly enough, the dutch roll behavior seems to appear even if the aircraft has zero effective dihedral AND zero effective yaw stiffness, provided the product of yaw damping and sideforce derivatives are positive. Both Nr and Yβ are almost always expected to be negative.

Coupled Roll-Yaw Analysis

The dutch roll flight modes show up in higher fidelity dynamics models. The lateral 4DOF model below contains the spiral, roll, and dutch roll modes with sideslip, roll rate, yaw rate, and roll angle perturbation states:

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USS Alabama Battleship Memorial Park

The USS Alabama Battleship Memorial Park in Mobile, AL displays an interesting collection of WW2 ships and aircraft not normally seen. The collection includes several rare museum items. The park is well worth the visit. https://www.ussalabama.com/

The Battleship Memorial Park visit is contained in 3 parts:

USS Alabama (BB-60)

My visit operated under a slightly modified charter, as it was a sponsored program by the BSA and included an overnight “opportunity”. The ship is designed around three 16 inch gun turrets.

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Aircraft at Battleship Memorial Park

The aircraft collection at the USS Alabama Battleship Memorial Park (Part 1 here) is quite special. There are several gems hidden among the more ordinary museum pieces.

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USS Drum (SS-228)

The second ship at the USS Alabama museum is a WW2 submarine, the USS Drum. Part 1 (USS Alabama) is available here.

The Drum museum is a nice example of a WW2 US submarine.

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Colorado Mountains

In March 2019, I had the opportunity through my job to fly in the mountains of Colorado on a DHC-6 Twin Otter. Here are some images of the flight campaign.

TuskaUAV talk on Aerodynamics and Propulsion

As the advisor of the TuskaUAV group, I was asked to give a 30 minute chat to the student group on the topic of aerodynamics and propulsion with a special emphasis on small unmanned aerial vehicles. The four-up double sided handout is available below. The formal talk concluded with a Q/A session both during and after the meeting. Thanks for the opportunity!

Blood Moon

20 Jan 2019, 11:20 CST.