Professional Pilot, May 2018

14 PROFESSIONAL PILOT May 2018 Skin friction coefficient 000 000090 00018 00027 00045 00036 Skin friction coefficient 000 000090 00018 00027 00045 00036 Computer Aided Design Before closing I would also like to point out the software that is operating behind the scenes before a plane becomes a reality Computer Aided Design software has been around for years but gets better it seems about every 15 minutes In the 1950s and 1960s my dad was a tool designer for GM When designing for example a press to stamp out radiator shells they would typically employ 20 25 people each designing by hand on 11x17 or larger drafting paper 1 or 2 small pieces of the press By the time this was collated and coordinated a couple of years would go by Today a couple of designers working with connected CAD software could turn out the same project in a couple of months And any changes to the design will automatically populate throughout the drawings Then the CAD software automatically generates code to run the Computer Numeric Control CNC machine that will produce the parts And the storage of the information takes a few gigs on a computer instead of a 5x5 storage closet Computational Fluid Dynamics Finally Computational Fluid Dynamics software provides the numerical and resulting graphical analysis of the way fluid flows Yep air is fluid So with respect to aircraft this software saves millions when it comes to understanding the way air flows over a surface Pro Pilot Dec 2016 page 92 Now think in terms of all the new designs that are coming about in our world of aviation We see major projects to develop supersonic planes We are delving into hypersonic 5 times the speed of sound missiles Ramjet technology is at the forefront of study To give you a better idea of what a CFD study looks like Ive included a couple of images Both relate to studies of one of many proposed eVTOL projects that are ongoing Because electric motors are so much lighter and less complicated than traditional powerplants many eVTOL projects include multiple engines to provide vertical lift with a number of them shut down when flight goes horizontal So designers are coming up with interesting ways to cage the propellers in order to reduce drag The variables are infinite and if each design had to be physically tested to determine the best solution it would take years and millions of dollars to come up with the best solution Running a design through CFD software narrows down the choices in a fraction of the time at a fraction of the cost In the top image above we see the graphical representation of the skin friction coefficient around a plain nacelle In the second image we are looking at this same nacelle but with propellers that have been caged and folded back along the sides of the nacelle It is easy to tell where drag is increased as a result of the disturbance of air flow around the folded back props It is also apparent that we could easily look at this same data for any number of different configurations within a short time at relatively little expense Its obvious I cant begin to present a comprehensive picture of what software is available to you The goal here is to remind you of the tremendous selection of products available and the areas of your life it can touch Bob Rockwood has been in the aircraft brokerage business since 1978 During his tenure at Omni Intl Jet Trading Floor he began writing The Rockwood Report which discusses the corporate aircraft market In 1986 he joined Bristol Associates as a managing partner Tool control and accountability is essential to manage costs avoid lost tool and foreign object damage to aircraft track inventories and save time One scan records who has it what job its on and whether it needs re certification recalibration or replacement Photos courtesy Snap on Image on top shows skin friction coefficient around a plain nacelle Image at bottom shows the same nacelle but with propellers that have been caged and folded back along the sides of the nacelle Drag is increased as a result of the disturbance of air flow around the folded back props