One happy son

My son’s class has a stuffed animal as a class mascot, a worm named…. Wormie. Each child takes the worm home for a few days and shows the class what adventures Wormie had at home.

We decided to take Wormie up for a flight over Tuscaloosa. And this is not just any flight, but a aerobatic flight into the sunset. The result is one very happy son (and some neat photos).

Yes, the worm increased the drag considerably.

Prandtl Lifting Line Tool

Prandtl Lifting Line theory remains an excellent tools for preliminary design and gaining intuition about the aerodynamics of unswept wings.

Implementing a PLL solver is relatively simple; I made this version in a few hours with Fortran. The solver generates SVG files displaying the wing geometry, gamma and lift distributions as well as the integrated lift and drag coefficients for arbitrary wing geometries (as approximated by linear sections). The program and input files are available at: https://charles-oneill.com/code/prandtl/prl2.zip

A flat elliptical wing demonstrates the flat sectional lift coefficient distribution resulting from an elliptical lift distribution.

pll-elliptical

The beauty of the Prandtl lifting line theory is the ability to modify the wing geometry and airfoil sections. For example, given a 20% flap deflected 20 degrees on inner wing sections, the sectional lift distribution reflects the flap deflection. Of particular interest is that the shed vorticity is proportional to the slope of the green lift distribution.

Prandtl Lifting Line

The PLL theory is also instructive for understanding control surface behaviors. In the following image, the 20% ailerons are deflected approximately +-10 degrees (Thin airfoil theory is used to determine the equivalent zero lift line.). Of particular concern is that aileron deflections at high AOA can push the local angle of attack into a stalled state.

pll-aileron

Civitan Drone Talk

Unmanned Aerial Vehicles

Thanks to the Civitan Club of Tuscaloosa and Mr. Brett Laney for the invitation to discuss unmanned vehicles and drones on the 5th of October 2016.

SlidePresentation slides: uav-civitan

Resources:

Delta Wing Demonstrator (DWD16)

Can a flyable aircraft be designed and built in 1 hour?

The Delta Wing Demonstrator is the result of this challenge in rapid aircraft design. Unfortunately, the answer was no. The aircraft actually required 1 hour and 20 minutes.

Continue reading

Low Aspect Ratio Wings

Back in 2006 as part of an independent study course, I used an inviscid CFD solver to estimate the aerodynamic performance of actual low aspect ratio wing configurations. The report (lowargeometryco2006.pdf) was written in a handbook style inspired by the classic Hoerner Lift and Drag books.¬† lowarconfigsThe configurations were: monoplane, biplane, joined-tip biplane “box”, disc, monoplane with endplates, and a shroud cowl. Biplane gap, stagger, and decalage were considered. Performance criteria such as lift slope, induced drag, lift to drag ratio (L/D) were compared for multiple configurations and aspect ratios.lowar-liftslopeThe final portion of the report provides a visual display of the pressures and flow fields near the configurations.

Wake rollup of an AR=1 wing:

lowarwakerollup

 

Wake aft of a biplane:

lowarbiplanewake

Pressure field interference with respect to biplane gap.

lowarbiplanegap

The full report from 2006 is available: LowARGeometryco2006.

The report was intended to support the OSU 2007 AIAA Design/Build/Fly teams during a competition year where the total aircraft span was severely limited:

Aircraft Systems Course

In the Spring of 2016 at the University of Alabama, I taught a brand new course titled Aircraft Systems under the course number AEM 617. Topics under consideration included:

  • Nomenclature (Sample Notes: Lesson01-Introduction)
  • Standard and Non-standard Atmospheres (e.g. Moist Air Density)
  • Airspeed (Flight Data Computer Calculations)
  • Vacuum Systems
  • v-n Diagrams including gust loading
  • Basic 4 bar mechanisms (e.g. slat & flap extensions) and Freudenstein Equations
  • FAR 23 (14CFR23)
  • FAR 25(14CFR25)
  • Cockpit Layouts
  • Flight Control Systems including equations of motion, gear ratio
  • Aircraft Hardware (e.g. AN bolts, rivets, etc.)
  • Hinge Moments (Guest Lecture)
  • Nonlinear Systems Phase Plane Analysis
  • Hydraulic Systems including Actuators, PCU (Power Control Units),
  • Fuel Systems including Inerting Systems and Refueling
  • Pressurization Systems (Guest Lecture)
  • Test Flight Systems and Instrumentation (Guest Lecture)
  • Communication and Navigation
  • Environmental Control Systems (ECS)
  • Emergency Systems
  • Survivability
  • Inertial Navigation Systems including World Reference Frames, and Strapdown Equations
  • OBOGS (Onboard Oxygen Generating System) (Guest Lecture)
  • Kalman Filters
  • Electrical Systems and Wiring¬† (Guest Lecture)
  • Morphing Wings (Guest Lecture)
  • Software Development and Modular Avionics Bus
  • A brief description of IEEE 754 floating point numbers
  • Spacecraft Attitude (Guest Lecture)
  • Propulsion (Guest Lecture)
  • Multi-Engine Vmc

The notes contain numerous hand drawn images of systems and references to many books.

Servo

Detailed Aircraft Systems of Particular Aircraft were analyzed through flight manuals, NTSB accident reports, AIAA case-studies, and expert guest lectures.

  • Cessna 170 & 310
  • Gossamer Condor
  • VTOL: VJ101 and VAK191B
  • X15
  • WW2 Dam Busters (system development case study)
  • THAAD
  • DHC-7 (aka. EO-5C / RC-7B)
  • A behind-the-scenes guided tour of the Southern Museum of Flight in Birmingham by two (2) PhDs in History and Engineering.

 

The course also included a set of lectures titled “Failure Fridays” which investigated aircraft incidents and accidents by tracking the failure points and symptoms with a special emphasis on systems. These included:

  • Cessna 182 Fuel Contamination
  • Alaska 261
  • A320 Fly By Wire
  • Boeing 737 Rudder Actuator
  • TWA 800
  • Diesel Bug
  • Advisory Circulars (AC)
  • Patriot Missile
  • Ariane 5
  • The largest non-nuclear explosion known to man. (Not aerospace, but still an impressive and covertly intentional systems failure!)

DC9JackscrewDC9jackscrew2

This course was particularly interesting; as the instructor, I learned a great deal about many topics. I had to work hard to stay ahead of the students. The students gave one of the best ratings that I have ever received. One student said:

The course was very interesting and likely one of the most valuable classes I have had in college. Rather than sticking strictly to theory as most of the Aerospace curriculum does, this class covers details about the what, why, and how for a wide range of
systems that will be particularly useful in any aerospace career.

Another student said:

This course provided me with an otherwise unobtainable insight into the real world of engineering systems, something not talked
about in other courses. This class is great for the industry engineer.

Not every comment was so positive. One student mentioned that this course required several prerequisites and that “newly transferred” students would find the course “difficult”.

More information and the full course notes are available by contacting Charles O’Neill.

SPA Prototype Aircraft

This summer, my lab in conjunction with Dr. Branam developed an aircraft for testing a prototype flight control system. The aircraft flies beautifully for a rudder-elevator control system. Low power and a large efficient wing allows for exceptional performance at the design weight. As a design decision, the rudder-dihedral roll control is sufficient for the mission purposes.

20160819_085212

SPA aircraft

The aircraft specifications are:

  • Wing span: 8 ft
  • Powerplant: OS 3815-1000 with 5000 mAh 3S LiPo
  • Airfoil: SD7062
  • Differential spoilers (marginal for roll control)
0819160854e

SPA aircraft

Thanks to the following engineers and designers:

  • Josh Richards (chief design engineer, air-to-air video pilot)
  • Christopher D. Simpson (chief systems engineer)
  • Christopher R. Simpson
  • Reid Ruggles
  • Abraham Ortiz
  • Alex West
  • Griffin Uthe
  • David Maulick
  • Liz Suttles

Counterfeit Futaba Servos

Counterfeit Futaba servos exist. My students and I managed to purchase a few for a recent aircraft project. These were purchased off of Amazon. We now call these “Faketaba” servos.

Question: How many ways can you tell that the following servo is a counterfeit Futaba S3003 servo?

IMG_2579

Answer:

  • The servo performance is significantly worse than a genuine servo. In fact, I (Charles O’Neill) initially discovered that these servos were not genuine after performing a systems check of installed servos. The return to zero had a hysteresis of about several millimeters at the servo horn, which gave a surface deflection static hysteresis “zero” of about +-10 degrees. This was completely unacceptable for our application. These were immediately removed and replaced.
  • The Futaba logo and font is not correct. As a typography enthusiast, I spotted the slight imperfections in the name sticker.
  • Gear noise is sigificantly higher for these fake servos. The gear geometry and tooth count are different from actual Futaba servos. IMG_2581
  • In addition to the gear noise, the output shaft tolerance created an issue with the bearing surfaces. Also, the spline shaft poorly fit the servo horns. The servo horns themselves were significantly thicker than genuine horns.
  • After installation, I went back and found the box that the servos were shipped in. This is obviously not a genuine Futaba box.IMG_2577IMG_2578
  • I opened one servo to investigate the counterfeit quality. The grommet was not sealed correctly, a mistake that the Japanese Futaba company would never allow. The motor is only press fit into the servo case; this is a sneaky possible failure point. The servo case is geometrically different from an actual case.

IMG_2580

  • The mounting holes are opened at the end. Actual Futaba S3003 servos are closed.

One additional point of discussion, the cost for these counterfeits was similar to actual genuine servos. My students learned a difficult lesson in trust.

Students’ Websites

My students are strongly encouraged to demonstrate their capability through a web presence.

 

Flight team at the University of Alabama.

This is an informal group of UAV and RC aircraft pilots and designers who meet each Friday at 4pm to fly and learn to evaluate aircraft.

The group is also provides UAS training for FAA certification within Part 107. Contact croneill@eng.ua.edu for details.

IMG_2352