Before viewing this video be sure to download and install CutList Bridge 2.5. The previous version had a bug that could make following along with this video frustrating.

Also, you will notice that in version 2.5 you no longer have to use the Save Attributes button as was necessary in previous versions and witnessed in Part 1. All entries are now saved as you enter them.

MAC users may have had trouble using CutList Bridge because of an OS/Safari Browser bug. When you download and install CutList Bridge 2.5 you will be shown a workaround if you have this problem.

Downloading CutList Bridge

CutList Bridge can be downloaded and installed by following the highlighted link; the target post will always host the most recent version of CutList Bridge.

Overview of CutList Bridge

CutList Bridge adds two export commands to the File menu and one dialog box to the Window menu of Trimble SketchUp. The export commands are:

• Export to CutList Plus fx
• Export to Microsoft Excel or OpenOffice

The dialog box is called Extended Entity Info and as its name implies is complements and extends the Entity Info dialog box.

When CutList Bridge is installed, as indicated by the availability of these commands and dialog box, a basic cut list can be produced simply by selecting one copy of your model using the Select tool and then choosing one of the export commands from the file menu. Simple as that.

However, the Extended Entity Info dialog box can be used to assign additional attributes to your components, which will produce a richer and much more useful cut list. This first video tutorial will show you how to create a basic cut list and then embellish the cut list with material types (rough lumber, dimensioned lumber, sheet good and other items), material names (cherry, walnut etc.), sub assembly groupings and notes. Subsequent video tutorials will show you how to assign attributes helpful for cabinetry and architectural models.

Downloading the Video to Your Computer

Sometimes the performance of your internet connection, the load on it at a particular time of day, and the length of these video tutorials can all conspire to provide you a frustrating and impossible viewing experience. If this happens it may be preferable to download the entire video unto your system and view it on your local video player. The video file is an mp4. It can be viewed with most video players including QuickTime and Media Player. If you have a default, or user specified, file association for .mp4 you may have to delete it or use a download manager to download this file. Otherwise the associated application may be invoked and file streaming will prevail over downloading. There are numerous free download managers on the internet. Be careful, and do some research to locate one that is not loaded with spyware or viruses.

If you are on a PC platform running Windows OS and have Internet Explorer or Firefox you don’t have to change file association or use a downloader. Simply right click on the link(s) below and choose Save Link As. When Explorer opens choose a destination folder and select Save.

To download this video click here or paste

http://blip.tv/file/get/Chiefwoodworker-CutListBridgeTutorialPart2111.mp4

into your download manager.

Viewing in Your Browser

You may find it easier to view the video in full screen mode. Start the video before selecting this mode. To enter full screen mode click the little screen icon at the bottom of the video player. When in full screen view hold your cursor near the bottom of the screen to access the video player’s controls. Exit full screen mode with the Esc key. This part is approximately 33 minutes long. Sit back, relax and enjoy the show!

Changes In Version 2.5

Version 2.5 fixes a bug introduced in version 2.4 and is a must upgrade. This bug will cause the user to potentially loose work and attributes. In version 2.4 I changed and included code to make it unnecessary to use the Save Attributes key to save attributes. Each input change is saved as it is entered. If multiple components are selected and an attribute is entered or changed, only that attribute will be changed in all selected components. Blank fields, unless one or more became blank due to an intentional change, will not be written to all components. This eliminates the need for the Save Attributes button. The button remains but is harmless and it will be removed in version 3.0.

In the process of making this change to version 2.4 I introduced a bug that is fixed in version 2.5. Sorry folks.

Help With Installation

Download the CutList Bridge User’s Guide and locate the Installation section in the index. After reviewing this section also review Installing Ruby Plugins and follow the instructions under the heading “Older versions of SketchUp and .rb files”.

CutList Bridge Tutorial Series

I have begun a series of tutorial videos to help you learn the features of CutList Bridge. Part 1 of 3 was recently released and can be found at CutList Bridge Tutorial – Part 1. Part 2 was released today and can be found at CutList Bridge Tutorial – Part 2. Stay tuned for Part 3.

Attention MAC Users

Known Issue With Version 2.5

If you are a MAC user and have the latest Safari Version 6.0.2 but do not have the latest OSX Mountain Lion installed, you will not be able to use CutList Bridge to add component attributes. Safari 6.0.2 in older versions of the OSX make text input fields black instead of white masking the black characters entered by the user. This is a MAC problem and not a CutList Bridge 2.5 problem.

However, I have provided a work around. If, after you install CutList Bridge as instructed above, your input fields show up with black backgrounds, follow these instructions:

1. Download alternate_cutlist_bridge_css.zip by clicking on this hyperlink.
2. Extract the file cutlist_bridge.css from the ZIP folder and move it to the folder …. \Plugins\cutlist_bridge\cutlist_bridge (note the two levels of cutlist_bridge folder). This replaces the file of the same name that is already in your Plugins file under folder \cutlist_bridge\cutlist_bridge (note again the two levels of cutlist_bridge folder).
3. Close SketchUp and reopen it. You CutList Bridge input fields will still have a black background, but your entries will be red characters making them visible.

Models To Practice With

There are three models which you can download that already have attributes assigned. You can use these models to produce a cut list and experiment with changes to the attributes. The Shaker Tall Clock demonstrates most of the basic features of CutList Bridge. Base Cabinet, thanks to Matt Richardson and Greg Larson of NESAW, demonstrates most of the special Cabinet Mode features. SketchUp Home demonstrates a very large cut list whose Sub-Assembly names are automatically generated with the Sub-Assembly by Layer feature. Click the links below to download each model.

Shaker Tall Clock
Base Cabinet
SketchUp Home

Below is an image of a SketchUp cut list exported to OpenOffice. Not all lines are shown.

I am pleased to announce that American Woodworker and Chiefwoodworker have teamed to bring in-depth and quality SketchUp training to a greater audience of woodworkers. Beginning March 12, 2013 Chiefwoodworker’s Beginner’s SketchUp Tutorials and Intermediate SketchUp Tutorials will be available exclusively through AmericanWoodworkerTV.

From the day I learned of Google SketchUp (now Trimble SketchUp) I became convinced it was a tool perfectly tailored for woodworkers. I have worked hard since 2007 to provide training to fellow woodworkers in the use of this tool. I have met a lot of woodworkers over the last six years and believe I succeeded in giving them the training they needed to add Trimble SketchUp to their woodworking toolbox.

However, the reach of Chiefwoodworker’s Blog can’t compare to the audience American Woodworker enjoys. American Woodworker is dedicated to providing training to woodworkers in all areas of woodworking with quality videos hosted by knowledgeable and expert woodworkers. It is my hope and belief that reaching a much greater audience with my tutorials will provide a greater service to woodworkers everywhere. I am delighted and proud to team with American Woodworker to benefit my fellow woodworkers.

Chiefwoodworker’s Blog will continue to provide posts, newsletters and videos on woodworking and SketchUp and I will continue to support my fellow woodworkers with SketchUp assistance when asked. In addition, I will continue to develop and provide SketchUp plugins. I also expect that my relationship with American Woodworker will grow. So stay tuned to my website (srww.com, Chiefwoodworker’s Blog, Chiefwoodworker’s Newsletter and look for me on AmericanWoodworker.tv.

American Woodworker Magazine, AmericanWoodworker.com, AmericanWoodworker.TV and Woodwork Magazine are all properties of New Track Media LLC.

The Berkshire Woodworkers Guild is sponsoring a scholarship fund for students seeking a career in woodworking, architecture or related field. Applications must be in before April 1, 2013.

• Applicants should be between 16 and 25 years of age.
• Preference is given to applicants from Berkshire County (Massachusetts) and the neighboring region and who seek to make woodworking, architecture or related fields their professional goal.
• Applications should be submitted at least 30 days before course begins.
• Maximum scholarship amount is $500.
• Money is paid to applicant or to course host after successful completion of course with receipt/invoice and evidence of attendance. Payment made in advance ONLY to course host if guarantee provided for refund (less any deposit required) if student can’t attend or cancels. No payments are made directly to the student in advance of course.
• Scholarships may be used to attend schools, conferences, classes, workshops and other events that meet the approval of the scholarship review committee of the Berkshire Woodworkers Guild. In general, any program that contributes to the education of the applicant in the areas of woodworking, architecture or related fields will qualify. Preference is given for long-term continuous programs that lead to certification or a degree in the profession.
• Scholarship application guidelines and application form are available on the Berkshire Woodworkers Guild website on the SCHOLARSHIP PROGRAM page or directly from this link.
• Send completed form via email to willb@heartwoodschool.com, by regular mail to Berkshire Woodworkers Guild Scholarships, c/o Will Beemer, 148 Middlefield Rd., Washington MA 01223 or fax to 413-623-0277. Electronic submissions via email attachments (PDF or Word format) are preferred.
• APPLICATION DEADLINE FOR THE CURRENT ROUND IS APRIL 1ST.

The Heartwood School’s course list and 2013 schedule is shown below. For a complete course description go to the table below and in the second column locate the course of interest and click the link. For further information or to register contact Michele Beemer at 413/623-6677, www.heartwoodschool.com or request@heartwoodschool.com.

Date	Course
April 15-19	Fundamentals of Woodworking
April 22-26	Cabinetmaking
April 29-May3	Build Your Own: Woodworker’s Workbench
May 30-June 1	SketchUp for Timber Framers
June 1-2	Basic Concrete Countertops
June 7-9	Advanced Concrete Countertops
June 10-14	Build Your Own: Country Windsor Chair
June 13-15	Eyebrow Dormers
June 17-21	Build Your Own: Shavehorse
June 22-23	History of Timber Framing
June 24-28	Timber Framing
July 5-6	Build a Skin-on-frame Canoe
July 8-12	Converting Trees to Timber
July 15-26	Comprehensive Homebuilding
July 29-Aug. 2	Carpentry for Women
Aug. 12-16	Finish Carpentry
Aug. 19-23	Timber Framing
Aug. 26-30	Scribed Timber Framing
Sept. 5-7	Timber Frame Design & Joinery Decisions
Sept. 9-13	Compound Roof Framing
Sept. 16-20	Build Your Own: Pole Lathe
Sept. 23-27	Build Your Own: Heirloom Dovetail Toolchest
Sept. 30-Oct. 4	Stairbuilding
Oct. 7-11	Fundamentals of Woodworking
Oct. 14-18	Cabinetmaking
Oct. 21-25	Home Design for Owners & Builders

Woodworker’s Showcase is heavily weighted to the display of custom furniture, turnings, toys, guitars, chairs and all sorts of pieces made from wood. Whether you are a woodworker or someone who appreciates fine art you will enjoy this show. The is also an exhibitors floor where you can window shop for for all the latest tools and jigs and often make purchases at substantially reduced prices.

I often bring my camera to the show and capture some of the pieces on display. To see what has been showcased in the last few year follow these links:

20th Annual NWA Saratoga Woodworkers Showcase 2011
The 19th Annual NWA Woodworkers Showcase 2010

Chiefwoodworker’s Talk at Woodworker’s Showcase

This year, like I have for the last two years, I will be giving talks both days on Trimble SketchUp. The talks are introductory in nature; SketchUp can’t be taught in two hours. I demonstrate both beginner and advanced drawing techniques intended to give the interested attendee a thorough idea of the capabilities of SketchUp. My talk is centered on the free version, which is all any hobbyist woodworker needs. The Pro version has features a professional woodworker may want and I hit on some of those features in my talk too. There is an admission fee for the show, by my SketchUp talk is free, as is all the lectures at Woodworker’s Showcase. You can download the lecture schedule at http://www.nwawoodworkingshow.org/information.htm and click Demo Schedule in the menu at the bottom of the page.

I hope to see you there. Please join me in one of my talks.

In the case of exporting to the latter two applications decimal equivalents of thickness, width and length can be exported. This permits the user to add equations in the spreadsheet to calculate board feet, area, total sheets, linear feet or weight. CutList Plus fx will do all but calculate weight on its own. The Base Cabinet shown above left produces the following cut list when exported to OpenOffice. Note the organization by material type (Rough Lumber, Dimensioned Lumber etc.), Sub-Assembly and Description (component). Click on the images to see larger formats.

Downloading CutList Bridge

CutList Bridge can be downloaded and installed by following the highlighted link; the target post will always host the most recent version of CutList Bridge.

Overview of CutList Bridge

CutList Bridge adds two export commands to the File menu and one dialog box to the Window menu of Trimble SketchUp. The export commands are:

• Export to CutList Plus fx
• Export to Microsoft Excel or OpenOffice

The dialog box is called Extended Entity Info and as its name implies is complements and extends the Entity Info dialog box.

When CutList Bridge is installed, as indicated by the availability of these commands and dialog box, a basic cut list can be produced simply by selecting one copy of your model using the Select tool and then choosing one of the export commands from the file menu. Simple as that.

However, the Extended Entity Info dialog box can be used to assign additional attributes to your components, which will produce a richer and much more useful cut list. This first video tutorial will show you how to create a basic cut list and then embellish the cut list with material types (rough lumber, dimensioned lumber, sheet good and other items), material names (cherry, walnut etc.), sub assembly groupings and notes. Subsequent video tutorials will show you how to assign attributes helpful for cabinetry and architectural models.

Downloading the Video to Your Computer

Sometimes the performance of your internet connection, the load on it at a particular time of day, and the length of these video tutorials can all conspire to provide you a frustrating and impossible viewing experience. If this happens it may be preferable to download the entire video unto your system and view it on your local video player. The video file is an mp4. It can be viewed with most video players including QuickTime and Media Player. If you have a default, or user specified, file association for .mp4 you may have to delete it or use a download manager to download this file. Otherwise the associated application may be invoked and file streaming will prevail over downloading. There are numerous free download managers on the internet. Be careful, and do some research to locate one that is not loaded with spyware or viruses.

If you are on a PC platform running Windows OS and have Internet Explorer or Firefox you don’t have to change file association or use a downloader. Simply right click on the link(s) below and choose Save Link As. When Explorer opens choose a destination folder and select Save.

To download this video click here or paste

http://blip.tv/file/get/Chiefwoodworker-CutListBridgeTutorialPart1342.mp4

into your download manager.

Viewing in Your Browser

You may find it easier to view the video in full screen mode. Start the video before selecting this mode. To enter full screen mode click the little screen icon at the bottom of the video player. When in full screen view hold your cursor near the bottom of the screen to access the video player’s controls. Exit full screen mode with the Esc key. This part is approximately 33 minutes long. Sit back, relax and enjoy the show!

I am an instrument rated private pilot and the question intrigued me.  I wondered how one might go about modeling a wing. So later that day I set about to develop a proof of concept. The result is shown at right. This proof of concept, or first attempt, has a number of flaws so I decided to take it to another level. In this article I will describe in layman’s language the major design parameters and trade-offs the aeronautical engineer makes when designing a wing and then I will show you hot to model it. Let me make very clear that I am not an aeronautical engineer; the definitions and explanations I give here are my lay interpretations of things I have read over the years. If you are an aeronautical engineer and take issue with anything I say please correct me by commenting to this post. That way all readers can benefit from your feedback.

I have two simple SketchUp models the reader can download for self manipulation.

http://www.srww.com/blog/wp-content/uploads/2012/11/Wing1.skp

http://www.srww.com/blog/wp-content/uploads/2012/11/Wing 2.skp

Before proceeding some definitions are in order:

Airfoil – Airfoil is the cross section of the wing sliced by a plane parallel to the plane formed by the plane’s longitudinal and vertical axis. The airfoil generally has a positive camber on the top surface, is thicker near the front edge than back edge and the leading edge is smoothly curved approaching a semi-circle.

Ailerons

Control surfaces located at the trailing edge of the wing near the wing tips. Surfaces move in opposite direction (one up and the other down) to produce roll around the longitudinal axis of the airplane.

Airspeed

The speed of an aircraft relative to the air surrounding it.

Angle of Attack (AOA)

The angle between a wing’s chord and the direction of flight (a vector parallel to airspeed).

Chord

A straight line running from the leading most point on the leading edge to the trailing most point on the trailing edge.

Drag

Forces opposing the direction of flight. Drag has two components: parasitic drag, caused by skin friction such as ice accumulating on a wing; induced drag, caused by flight attitude such as high angles of attack.

Flaps

Control surfaces located at the trailing edge of the wing near the wing roots. Surfaces are angled down in steps. Each step produces more lift until the increased drag slows the airplane to a stall speed.

Mach

Mach 1 is the speed of sound; Mach 0.6 is sixty % of the speed of sound and so on. In dry air at 20 °C (68 °F), the speed of sound is 343.2 meters per second (1,126 ft/s).

Planform

The view of a wing looking down its vertical axis.

Stall

A point reached when the airfoil no longer produces sufficient lift to overcome weight and is produced by angles of attack greater than the stall angle. Stall can be abrupt and dangerous. Essentially the wing stops flying.

Sweep

Wing sweep is usually the counterclockwise rotation of the wing in the planform view. The major advantage is to high performance planes flying near or above Mach 1; wing sweep helps to increase the maximum airspeed of the plane.

Taper

Taper can be applied to the leading edge, trailing edge or both. Wings are generally tapered such that the chord is shorter at the tip than at the root. Taper should not be confused with Sweep. The major advantages of wing taper are: reduced weight, structural integrity (lower bending moment), reduces drag. A disadvantage of wing taper is that it reduces the AOA at which stall occurs at the tip and hence may have poorer stall characteristics.

Twist

Generally a wing has lower angle of attack (AOA) at the tip than the root. The AOA usually decreases linearly from root to tip. This type of twist is used to ensure the wing stalls first at the root and last at the tip where the control surfaces are.

Wing Setting Angle

Wings Setting Angle (also called wing incidence) is the angle between the fuselage center line and the wings chord line mapped on the y-z plane (plane of symmetry). You can think of it as a built in AOA which helps to increase lift at slow speed such as during the take-off roll and climb. Typical wing setting angles are 0° – 5°.

The Airfoil and Bernoulli’s Principle

You probably remember basic airfoil (hydrofoil in a fluid) theory from your high school physics class. Airfoils and hydrofoils operate on the Bernoulli principle which says that as a fluid increases in velocity it is accompanied with a decrease in pressure. You have seen this in action many times in your daily life. As you drive a pickup the air flows over the top at a speed roughly equal to the speed of the vehicle. The air behind the back window, in the bed of the truck, is still; not moving at all. As a result things sitting in the bed often are lifted up toward the fast moving air overhead. Indeed, the whole backend of the truck experiences some lift and makes the back of the truck a little “lighter” creating problems for the driver in wet or icy conditions.

The airfoil takes advantage of this phenomena (or more accurate one of the many laws of physics). You have probably experimented with a sheet of paper as an airfoil. If not, hold a piece of printer paper between the thumb and forefinger of your right and left hand at the end of the paper. Pull on the paper to take out the slack at the end. The rest of the paper will fall limp. Bring the paper to your lips with your lips just above the paper. Now blow steadily and easily. Notice the paper lift slightly. Now blow steadily and harder. Notice the paper lift more. The harder you blow the more the paper lifts. This is the Bernoulli principle at work. Fast moving air on the top side of the paper produces lower air pressure and results in lift being produce in the direction of high pressure (beneath the sheet) to low pressure (above the sheet).

The airfoil of an airplane wing (and many bird wings) is wider in the from with the front edge being round or curved, and tapering to a very thin edge at the back. The top surface generally has a camber and the bottom surface is generally flat. See the second image above. Oncoming air is moving at the air speed of the airplane and separated at the leading edge. As air that moves over the top must travel a longer distance to meet up with the air moving beneath the wing, it must must travel at a faster speed than the air on the bottom. Therefore the relative pressure is greater above the wing and hence lift is produced at the bottom of the wing.

In the second image above you will notice that while the distance air must travel at the bottom is less than at the top, it is still greater than the straight line distance from leading edge to back edge. Aeronautic engineers often build in a slight angle to the airfoil, called angle of attack. This has the effect of decreasing the distance that must be traveled on the bottom, and hence increases the top edge distance. This means the resulting total lift will be greater. However, if the angle is too large the face of the bottom of the wing will be presented to the oncoming air and produce excessive drag. So there is a delicate balance that must be achieved. See the third images above. Notice that the total lift is still perpendicular to the bottom surface of the plane (oversimplification) and now has components of airplane lift and drag. Airplane lift is opposite the pull of gravity while a small amount of drag tries to slow the plane and is opposite the planes travel. If the angle of attack is optimum there is sufficiently small drag such that the airplane lift is still larger than if there were no angle of attack.

This description of lift doesn’t mention downwash at the trailing edge of the wing. This downwash assists in generating lift. Lift is a complex issue when thoroughly treated and has many components. My description is admittedly simple, but still useful for basic understanding.

Modeling the Airfoil

Drawing on my early pilot training on wing design I started with an airfoil profile; essentially the cross section of a wing. Airfoils come in many shapes. In this article I am modeling a basic airfoil which only requires three steps. The picture at left shows the three perimeter portions of the airfoil. I start with a semi-circle to the left of points a and b with a radius of 12” (2 foot diameter). At the bottom of the semi-circle I extend a line 96” (8 feet) from point b to c. From a to c I use the Arc tool with a Bulge of approximately 6 5/64” (a radius of approximately 204 17/32”. The dimensions of this airfoil may not be efficient, indeed may even be a poor design. However, it does have all the characteristics necessary for flight: the front edge is smooth and curved, the trailing edge comes to a point, and the air must travel a greater distance on the top surface than it does on the bottom surface. This is a basic but not atypical airfoil. When completed I make this airfoil a component called Airfoil#0.

Modeling the Wing Setting Angle

At this point a wing setting angle can be modeled by simply rotating the airfoil around an axis perpendicular to the airfoil surface and running through the tails trailing edge (point) See the third image in this article.

General aviation airplanes have wing setting angles of 2° – 4°. Commercial airliners may have wing set between 3° – 5°. Supersonic fighters have very shallow wing set between 0° – 1°. Flying wings are considered to have no set because they have no fuselage.

The wing I modeled here has an exaggerated 8° wing set to make it more visually apparent in my images.

Tapering Wings for Stability and Structural Strength

Wings are often tapered so that they are smaller at the tip than they are at the fuselage. Lift generated at the tips of the wing have much more influence (torque – ft-lbs) on the plane around its longitudinal axis than lift near the fuselage. The ailerons are placed near the tip of the wings and to manage aileron response stability the wing tips are tapered and hence produce less total lift.

Creating the wing shape is a series of tedious steps, one which would benefit from a Ruby script, which I might write one day but not for this article. First I need to create a number of airfoils; remember an airfoil is a cross section of a wing. So I need enough cross sections, evenly spaced to give me a smooth wing shape. My wing, when finished, will be approximately 35’ in length so I arbitrarily choose to create 33 additional airfoils, spaced 1’ apart, and each one smaller by a factor of 0.98. Also, when done I want the trailing edge to be a straight line. To do this I use a combination of the Move/Copy, Scale and Make Unique tools thirty three times (this is where a Ruby script that recorded a sequence of steps and repeated them N times would help). First I use the Move/Copy tool to copy and move the previous airfoil to the left one foot. Next I use the Scale tool to uniformly scale about the opposite point a factor of 0.98. The “opposite point” is the point at the trailing edge. This will keep the trailing edges lined up along a straight line. Finally I use the Make Unique command on the Context menu to make a new component, each sequentially numbered. I now have thirty four airfoil components named Airfoil#0 through Airfoil#33.

Wing Twist to Improve Stall Characteristics

Many wing designs include wing twist; gentle continuous rotation of the wing along it length. The direction of twist has a profound effect on the planes stall characteristics. If the wing is twisted counterclockwise, when viewed from the tip and looking at the root, the wing tip will have a lower angle of attack than the wing root. Recall that wings stall – wing stops flying – when the stall angle is reached. Once the wing stops flying the pilot has little or no control of the plane.

Wings with twist don’t stall at the same time along the wings length, rather the roots stalls first because it has a larger set angle than the twisted wing’s tip. Hence stall progresses from the root outward to the tip as the AOA increases.

Ailerons, the roll control surfaces, are located near the tip of the wing. So it is desirable for the tip of the wing to remain flying (not stalled) as long as possible when the planes angle of attack reaches the stall angle. Wing twist assures this occurs.

Modeling twist is a simple matter, though a tedious one, of reducing each airfoil’s set angle a fixed amount relative to the previous one starting at the root and working toward the tip. In the case of the wing I modeled here, Airfoil#0 has a set angle of 8°. Each following Airfoil has a set angle reduced from the previous by 0.2° resulting in Airfoil#1 having a set angle of 7.8°, Airfoil#2 7.6°, Airfoil#3 7.4° down to Airfoil#33 1.4°.

In practice this can be modeled by selecting Airfoils #1 – #33 with the Select tool. Reduce their set angle by 0.2°. While all 33 airfoils are still selected use the Select tool with the Shift key to deselect Airfoil#1 leaving Airfoil#2 through Airfoil#33 still selected. Now use the Rotate tool to reduce the selected airfoils set angle by 0.2°. Now deselect Airfoil#2 leaving Airfoil#3 through Airfoil#33 still selected and reduce their set angle by 0.2°. Repeat this process for each airfoil down to and including Airfoil#33.

Airfoil#33 will have a set angle of 1.4°. Starting with Airfoil#0 with a set angle of 8° and subtracting 33 reductions of 0.2° equals 1.4°. The finish twisted will will look like the image at above left.

Modeling the Wing’s Skin

We now have the airfoil cross sections and we can use them to create the wing. I only model the skin in this article; not the internal structure called spars and ribs. Nor do I give the skin thickness. These can be modeled quite easily once the airfoils and skin have been modeled, and I will leave that exercise to the student.

Recall that the beginning airfoil was constructed with a semi-circle, straight line and an arc. SketchUp models circles and curves with line segments. Each line segment has endpoints which the inference engine will point out when you hold your cursor over it. I connected these endpoints with straight lines to produce the mesh of rectangles shown in the picture above right. Again this is tedious and repetitive but doesn’t take too long.

If wing twist is modeled the above process gets even more tedious. With wing twist no four points will form a plane – the wings twist ensures that. So the skin must be modeled with triangles; three points will always form a plane. The image at left shows the hidden geometry of a twisted wing.

Note that the wing tip is modeled using the Follow Me tool to create and one quarter sphere, then using the Push/Pull tool to extrude the one quarter sphere and finally using some hand stitching and cleanup.

Swept Wing Design for Higher Air Speed

Swept wings should not be confused with tapered wings described above. Wings are swept – angled toward the tail – on high performance planes including corporate and airliner planes. The reason is simple; swept wings allow a plane to fly faster. How a swept wing works is not simple and in-depth understanding requires a degree in aeronautical engineering. I will attempt a significantly oversimplified explanation to give you some basic understanding.

As a plane approaches the speed of sound, Mach 1, there is a speed lower than Mach 1 where, due to the complex shape of an airplane, some parts of the plane reach Mach 1. That is some areas of the plane reach Mach 1 before the plane’s airspeed is Mach 1. Shock waves appear at those points and produce drag rather abruptly and increases rapidly. These shock waves limit the speed the plane can fly. The critical Mach number (Mcr) of an aircraft is the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound. This might be a number such as Mach 0.75. To increase the speed of the aircraft the aeronautical engineer has to increase the effective Mcr. Enter the swept wing.

The Mcr of a non-swept wing is a function of the airfoil design; principally the chord line of the airfoil cross section. Before a wing is swept the chord line is parallel to the travel of the airplane and aligned with the planes airspeed. When the wing is swept the chord line is at an angle to the airspeed. The airspeed now aligned with the cord line is a fraction of the airplanes airspeed, and is proportional to a leg of the right triangle of which the chord line is the hypotenuse and the angle between the hypotenuse and leg is the sweep angle. Now the airplane can accelerate to a higher airspeed before the airspeed component parallel to the airfoil chord reaches Mcr.

As stated earlier, this is significantly oversimplified. Not all of the theoretical advantage of sweeping a wing is realized because of other effects such as skin friction and fuselage drag. In fact some supersonic aircraft do not use swept wings, such as the Lockheed F-104 Starfighter which reaches airspeeds of Mach 1.7 with straight wings.

Modeling wing sweep is a simple matter of using the Rotate tool to rotate the wing around a pivot point near or at the root. This angle is usually small but can be aggressive and deep on high performance military aircraft.

Dihedral Design for Roll Stability

Another very important design property is dihedral. Some plane wings slant up at the tip (dihedral) and some slant down (anhedral). When dihedral is designed into a plane wing it increases roll stability (stability around the longitudinal axis). Cross wind gusts tend to push one wing down (or the other up). When this happens the lower wing has a greater attack angle and presents more surface area in the direction opposite gravity. This cause the lower wing to produce more lift which opposes the rolling effect of the wind gusts. Dihedral is often used on small general aviation aircraft because this built in stability is rather inexpensive and tends to keep the inexperienced private pilot out of trouble. Anhedral is sometimes used on high performance planes for other advantages, but it is less stable. However, high performance aircraft have expensive and extensive computer sensors that can detect wind gust roll and generate computer controlled responses that can increase stability.

Modeling dihedral, like sweep, is a simple matter of using the Rotate tool to rotate the wings up around a pivot point near or at the root. The angle is usually small, maybe 5° or so.

Completed Wing Skin Model with All Major Attributes

After modeling all the major attributes of a wing skin I ended up with the image at right. I used the Eraser tool with the Ctrl key to hide most of the lines including diagonals. The remaining lines simulate the edges of the aluminum sheets a wing skin is made of.

If I were an aeronautical engineer designing a real wing I would use this skin to model the spars, ribs, aluminum sheet thickness, rivets, ailerons, flaps, fuel tanks, wing tip lighting and so on. My purpose here was to point out the type of modeling techniques one might use to model a fairly complex shape.

This modeling task included a fair number of tedious and repetitive steps that would benefit from a Ruby script to produce Macro capability (memorize a sequence of steps and repeat them 1 to N times). Writing such a Ruby script would take much longer than executing the tedious modeling, and I doubt I would find the tool useful in many of the models I tend to work on. So overall it would be a waste of time. Modeling is often like that; it often pays to do things the simple and tedious way.

I use printing to scale frequently to create shop templates. One such example is the swan neck that frames the top of a trundle bed headboard shown right. This template is much larger than one 8 ½” x 11” sheet of paper, but my printer only prints 8 ½” x 11 paper. What I did was print at a 1:1 scale in SketchUp which required about nine sheets of paper. Most of them were blank, so returned them to the printer tray. The three sheets that contained printed information I taped together connecting the line precisely. Then I backed the paper with self adhesive clear plastic, which can be purchased at any office supply store, and cut the template out with scissors. The clear plastic provided stiffening for the template and edges that will not collapse as you trace the template unto your stock.

The picture below shows the swan neck milled using the template above right. Also shown below is a template used to shape the headboard itself. Owing to symmetry I didn’t need both left and right swan neck templates, and a full headboard template; I only needed one side for the templates because they can be flipped to produce the mirror image.

I also use SketchUp to create shop drawings. Because I print off fully dimensioned drawings for all milled pieces, there is usually no need to print my drawings to a predetermined scale, I just read the dimension off the drawing. However, there are times when a scaled drawing is necessary. For example, when printing standard views of an architectural drawing a standard scale such as ¼” = 1’- 0” is needed. So let’s get into the how to of printing to scale.

Printing to scale in SketchUp is not difficult; you can print at a scale of 1:1 or any other scale you desire by following these five steps.
1.    Select Parallel Projection on the Camera menu. (Camera/Parallel Projection)
2.    Select one of the Standard Views (Camera/Standard Views/…..)
3.    Adjust the window and model size to minimize the amount of white space around the model. This is to compensate for what I consider a software bug, and is the toughest and most critical part of the process.
4.    Set your scale in the Print Preview dialog box and uncheck both “Fit to page” and “Use model extents” . (File/Print Preview)
5.    Choose print.

Steps One and Two are very important. SketchUp does not permit printing to scale using either of the other two Perspective views because it is impossible for perspective views to yield a scaled drawing.

Step three is required because there is a printing behavior that I consider a software bug when it comes to printing to scale. If you are going to print to any scale, including 1:1, first resize you drawing window so there is a minimum amount of unused drawing area on all sides of your drawing. Failing to do this will  result in multiple pages being printed when you need only one, or far too many pages when more than one is needed. The trick here is to estimate and fix in your head, the aspect ratio of the model you want to print. Next shape the window area to the same aspect ratio. Then use a zoom tool to center and enlarge the model to use all the window area available. You may have to iterate these last three steps to get the optimum setting. Try to make your window as large as possible while leaving almost no unused white space on either side, top or bottom of the window. The image on the previous page shows a case where there is too much white space on the right and left, but about just enough on the top and bottom. This is because the aspect ratio of the model is approximately 1.7:1 while the window is approximately 1:1.5, nearly the reverse.

The aspect ration of the window has been adjusted in the image at right to get a near optimum fit. Notice how little white exists around the periphery of the model. This model is correctly “cropped”.

We have completed steps 1 – 3 above. Now we have to decide what we want to do next. If this printout is to be used as a template then we need to use a scale of 1:1 scale. However, this model printout is not likely to be used as a template, but likely an elevation view of the hutch; which means it will be printed to scale on one page. The question is what scale?

The scale can be determined analytically or empirically. Analytically we start with the size of page we are going to use and then subtract the unprintable margin dimension from each edge. For example, if we are printing on 8 ½” x 11” paper with an unprintable margin of ¼” per edge, then the printable area is 8” x 10 ½”. This hutch has overall dimensions of 52” wide by 88” tall. Printing the page in portrait view is the most efficient selection for this case. This means the 88” dimension must fit in the 10 ½” height of the page. Similarly, 52” must fit in the 8” width. Use these two sets of numbers to calculate two scale  factors; 8.3:1 and 6.5:1 respectively. We must use the same scale factor for both dimensions and so we need to use the larger one. However, 8.3:1 is a difficult scale to use so we can go with 9:1 or 10:1. Either will work in this case, but 10:1 is probably more useable in terms of making measurements on the printout and calculating the actual dimension. The image at left shows the setup for this case.

In the Print Preview window above notice that “Fit to page” and “Use model extents” are both unchecked. There are four Scale inputs which the user need to fill in. In the “In the printout” input box I entered 1 and in its dropdown box chose Inches. In the “In SketchUp” input box I entered 10 (I will explain 10.000001 in a moment) and in its drop down box chose Inches. These inputs defines a scale of 1” = 10” or architecturally 1” = 0’-10”.

Here is an important little trick; after entering the four inputs in the scale area, place your cursor in the Page size “Width” and then “Height” input boxes. Don’t attempt to input anything or change what is there, simply place your cursor in each input box. This will cause SketchUp to calculate the page dimensions required to print your model. When this happens the numbers in the Scale input boxes may change slightly; in this case 10 was changed to 10.000001. It might just as well have been changed to 9.999999. This has to do with the precision the software is using to make calculations. Don’t worry about this. The important part is that when you have completed this step look at the “Tiled Sheet Print Range”. If the radio button chosen is All and the “Pages from” input boxes says 1 “to:” 1, then you are assured that you can print your model on one page with a scale of 1” = 10”. Hit OK and you should see a Print Preview shown at right. Choose Print to print the model to scale.

You can empirically determine the scale required to fit the model on one page. After completing step 3 above open the Print Preview dialog box (File/Print Preview). Place 1 in the Scale “In the printout” input and Inches in its dropdown box. These parameters are a guess based on my knowledge of the model. If I were printing an elevation view of a house I might start with ¼ in the input box. Next choose Inches for the “In SketchUp” dropdown box (if the model were a house I would probably choose Feet). Now enter pure guess in the “In SketchUp” input box. Place your cursor in both Page size input boxes to instruct SketchUp to calculate the page size. Then look at the results in the “Tiled Sheet Print Range” area. If it indicates more than one page increase your guess for the “In SketchUp” input and enter your cursor in both Page size input boxes again and check your results. If your first guess resulted in only one page try decreasing it until the number of pages is greater than one. Use this iterative process to choose a scale you are happy with.

Printing to a scale of 1:1 is the same for steps 1 – 3. After that you enter 1 and the same units for both Scale inputs. Then you print all the pages required. Put the blank sheets back in the printer tray and assemble the remaining pages as discussed earlier.

Good luck and I hope this tutorial helps.