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Wings and Empennage

 

Select "main wings" on the standard menu.

The bottom left section is blank when no wing semi-length is selected. As soon as a figure for this parameter is entered, however, it fills with 16 check boxes, most of which are not needed. With wing 1 tab selected, as above, fill in a semi-length of 15.50', and root and tip chords of 5.25'. This is for half the wing span, but Plane Maker duplicates the dimensions for the opposite wing panel. The length selected is for the straight inner section, measured from the drawing. In the lower left section, the first checkbox at left defaults to 6, which is the number of panels Plane Maker divides the wing section into for calculating aerodynamic functions. Separate degrees of incidence can be entered, if desired, but enter 1 degree for each panel at this time. Below this line check off the last 3 boxes in the aileron row. Those sections will now carry this control surface, once a few other parameters on the control geometry menu are filled in. We'll get to that shortly.

Quit out of the main wing section for a moment and select side view on the background menu. Back in the main wing window, zoom in and position the fuselage display at right so that you can see the wing section you have just created. It should be on the centerline with the leading edge poking out forward of the nose. Begin entering the long arm setting by incrementing the figure from zero. As you do so, you will see the wing move aft from the zero point until it is positioned at the measured distance determined from the drawing; this is 5.45' measured from the 25% chord position to the zero point at the nose. Now increment the vert arm until wing airfoil section is close to where you want it by comparing it to the drawing. You need to position it so that the trailing edge of the wing is exactly even with the top of the fuselage at that point. Check the leading edge also, and if it does not form a fair curve with the windshield, adjust the height of the fuselage at that point until it does.

Leave the lat arm at 0 and enter a dihedral of 2 degrees. The result should appear as in the above screen shot. Quit out of the wing window and save your work, then select "control geometry" from the standard menu. This window has a lot of settings and we'll be filling in a number of them as we go along.

For now, though, we only need concern ourselves with the top line, at right. The first two settings determine how much of the wing chord is devoted to the aileron; it's a ratio and we'll use the recommended value of 0.20 for the root and tip of the control surface. The last two values on that line set the up/down limits; choose 20 degrees. Our J3 doesn't have flaps, so leave that section blank and quit out of this window. Save your work.

To check that everything is correct, go to the "special" menu and toggle "show with still/moving controls". You should see the propeller rotating and a slow up/down movement of the ailerons. If so, let's move on to completing the main wing by adding a couple of short main wing sections to approximate the Cub's curved wing tips. I say "approximate" because there's no easy way to do curved wing sections in Plane Maker.

With difficulty, it is possible to shape a couple of the misc bodies available from the standard menu. I tried it in my Aeronca model and achieved something close to what is required; below is a screen shot of the Chief's left wingtip. As can be seen, the curved portion is a teardrop shaped misc body with an airfoil cross-section embedded in a shorter wing section so that only one side of the symmetrical body is visible. I got a fairly close approximation of an airfoil shaped body by simply starting with the correct perimeter shaped body of approximately the right thickness, then embedding it in the wing and reducing the thickness to match the wing section. It is not exact, by any means, but the result was acceptable. I read, somewhere, a short tutorial on this process by an X-plane designer whose name I can't recall. He used a similar process but had much more technical expertise than I do and was able to get an exact match of the airfoil shape with the use of spreadsheet and graphing software. I'll post the link here, if I can find it again.

For now, though, we can get a pretty good wing tip by using two additional main wing sections, stacked on the wing1 panel as seen below.

These short sections are main wing sections wing2 and wing3 with settings as seen in the table below.

   Wing 2 Wing 3
 semi-length 1.50 0.50
root chord 5.25 3.00
tip chord 3.00 0.90
 sweep 0.00 0.00
dihedral 2.00 2.00
long arm 5.45 5.45
lat arm 15.49 16.99
vert arm 2.44 2.49
incidence 1.0 1.0

If you are following along in Plane Maker your settings may differ somewhat from mine, but should be fairly close. Essentially, the only difficulty in arriving at a smoothly joined wing arises from the dihedral which means that each section will have a different vert arm setting. Zoom in very close as you line the short sections up with the main wing and with each other. Once you are satisfied with your J3's main wing, we can move on to the empennage, starting with the vertical stab.

Having to again contend with curved wing sections to get a decent approximation of the cub's vertical stab/rudder combination brings us to yet another problem: all of the sections having a movable surface ie: the rudder, as part of the panel, need to have a hinge that lines up properly with the adjacent section. The hinge line location, as you now know, is a ratio of the control surface to total surface set in the control geometry window. However, there is only one rudder setting available there for all surfaces that have a rudder; if the sections have different shapes the hinge location will vary. The j3, however, has a fairly simple shape and can be reasonably modeled in 3 sections, only 2 of which require a movable surface. We'll assemble it from vert stab 1, vert stab 2 and misc wing1. The easiest way to get it properly sized, is to import a background bitmap on the main page that includes the vertical stab, size the cub's fuselage with the +/- and direction arrows to get what appears below, displayed in wireframe ie: without textures. The background image used is here.

With this setup in place, select stabilizers on the standard menu and start with vert stab 1. And enter these settings:

 semi-length 1.84
root chord 4.60
tip chord 0.90
sweep 52.0
dihedral -90.0 
 long arm 17.61
lat arm 0.0
vert arm 1.40

In the bottom section check off all boxes on the rudder line. quitting out of the window shows the result: vert 1 should be embedded in the tail section like so:

The setting for dihedral for this stab section requires some explanation. Default for this setting is +90 degrees, or vertical as you would expect. In order to line up the hinge section with vert 2, which comes next, however, the -90 degree setting effectively turns it upside down so the root dimension of this surface will match the root dimension of the adjacent surface. Thus, the setting for root rudder ratio, when we go to the control geometry window, will place the hinge point for both vert stab 1 and vert stab 2 at the same place, making lineup much easier.

Dimension vert stab 2 as follows:

 semi length 2.85
root chord 4.30
tip chord 1.80
 sweep 21.40
 dihedral 90.0
 long arm 17.80
 lat arm 0.0
vert arm 1.40

And we now have:

Again, check off all sections on the rudder line in the bottom section of the window.

Complete the vertical stab by selecting Miscellaneous wings from the standard menu and at misc wing 1 make the following entries:

 semi-length 0.40
 root chord 1.80
tip chord 0.50
 sweep 32.00
dihedral 90.0
long arm 18.83
lat arm 0.0
vert arm 4.06

I should add that the "sweep" values entered in these tables is selected by eye, incrementing and de-incrementing them to achieve the contours that best match your background bitmap.

To complete the vertical stabilizer, select control geometry from the standard menu and set rudder chord ratio to .39/.50 at root and tip, with a 30 degree deflection. Again, the tip chord ratio (.50 in this case) is selected to get a good lineup of the hinge line, as it appears after toggling moving controls from the "special" menu.

After deleting the current texture files in your j3Cub folder, then re-outputting the texture map starting points and reloading textures, your new rudder should look like the screen shot below.

Save your work!

To complete the empennage, we need a horizontal stabilizer/elevator and the j3 has a particularly graceful one that is, unfortunately, difficult to reproduce in Plane Maker, give its curved plane limitations with which you are now familiar.

We will use 4 separate panels on each side of the stab to get fairly close to the shape we're after:

We only need to enter values for wing 2 and Horizontal stab once, since Plane Maker mirrors those elements for both right and left sides. The misc wings 2 through 5 will need entries for both sides, since they are not mirrored, but instead have a check box to specify the side to which the element belongs. In general, the procedure I use is as follows.

Display the model in wire frame (select from the Special menu) and in top view, with moving controls. Zoom in on the tail section and choose the wing 4 tab on the Main wings window. Boxes for all the values are displayed, as well as a smaller version of the tail section. You can zoom in even closer in the smaller window if necessary, using the +/- keys and positioning with the direction arrows.

The wing 4 element will be mirrored on either side of the the aircraft centerline. Referring to the sketch above, you will note that the root is smaller than the tip for this element. Enter a guess at the root length, by referring to your drawing. Similarly, enter approximations for the tip and the semi-length. Once these figures are entered, the roughly shaped element can be viewed in the right hand window, though it may not be visible until you move it into the view window by increasing the long arm setting to roughly 19'. Position the element so that the right hand end of the root is adjacent to the rudder hinge line.

You can now refine the root, tip, semi-length and sweep of the element to achieve a pleasing shape that your eye tells you is right for this section of the stabilizer. Measurements of the element also need to agree with the scale drawing and you can check this with your dividers, as well. You could, if you wish, prepare a top view that includes the stabilizer, in Photoshop, for importing as a background bitmap in the main display window, as we did with the vertical stab/rudder elements.

The same procedure is used to shape and dimension the other elements. They are moved into position by eye, using the lat arm and long arm settings, so that they line up exactly. Don't forget to check the box for misc wing 2 and 5 to specify a left hand element. Also, check off the elevator boxes for Horiz Stab. Check the aileron2 boxes for Main wing 4. *

With all elements in place, go to Control Geometry on the standard menu and enter control ratios and up/down deflection values for the stabilizer. My values were 0.40/0.46 for root/tip and 30 degrees deflection. Enter 0.04/0.46 for the aileron 2 control ration and 0/0 for throw. Confused? Here's what's happening:

We need to get the inner element, whose control surface was designated "aileron2" to move in concert with the elevator. Discovering how to do this involved some detective work: I knew it was possible, since it was working wonderfully well in the stock 172 Skyhawk updated by Anthony Booher for 7.30. By prowling through the Plane Maker menus with that aircraft loaded, I eventually discovered a setting under "Expert>special controls" in which the aileron2 control surface could be made to trim with pitch. In other words, setting the "ailerons2 trim with pitch" parameter to the same setting as the elevator up/down setting, it matches elevator movement perfectly, as long as the hinge lines up properly with that control surface. And, since the root/tip ratio is a separate parameter in the control geometry window, it can be adjusted to match the elevator even though the root/tip ratio is different. Anthony confirmed, later, on the tech list, that that is how he did it.

Here are the values I arrived at:

  Main W4  horiz stab misc w2  misc w3  misc w4 misc w5
 semi-length  1.26 2.20 0.70 0.70 0.16 0.16
root chord 2.42 3.34 1.00  1.00 0.97 0.97
tip chord 3.35  2.10 2.10 2.10 0.30 0.30
sweep 29.0 19.0 -27.0 -27.0 32.0 32.0
dihedral 0.0 0.0 0.0 0.0 0.0 0.0
long arm 17.50 18.11 19.14 19.14 19.14 19.14
lat arm 0.0 1.10 3.80 -3.80 3.80 -3.80
vert arm 1.10 1.10 1.10 1.10 1.10 1.10
check box aileron2 elevator left side    
             

You can simply use them as is, but will find it more constructive to follow the outlined procedure above and refer to my figures if you get in trouble. When you are satisfied with your work, you may wish to delete the j3Cub_paint.bmp and j3Cub_paint2.bmp files, output new texture map starting points and then reload textures to display your new empennage in all its glory. When you do this, by the way, you will no doubt be dismayed to see that some of the panels appear to be painted on one side only. You're right; Austin, for reasons best known to himself, apparently chose to output texture map points for only one side of vert stab1 and vert stab2. If you load your j3Cub_paint.bmp file into Photoshop, you will see the image below:

Note the empty space beside vert stab1 and vert stab2. Their opposite sides are supposed to be in that position, bu are not, so Plane Maker displays the right sides of those elements in the backgound colour. You can improve matters by copying the the right sides over into the empty space and then re-saving the file with the alteration. When you do, make sure you save it in Windows 24 bit bmp format. You can then re-load textures in Plane Maker to display the properly painted vertical stab, although you may wish to wait until you're ready to paint the model, as we may re-output the texture map starting points several times before painting, and each time this happens, Austin's version of the file will be output.

 

*The dihedral and positioning of W2 and W3 were originally posted here as dihedral -180 degrees, misc wing 2 on right and misc wing3 on left. This was wrong, as no elevator movement is wanted for these elements, so it is unnecessary to flip them for hinge alignment. Use the corrected dihedral of 0 degrees, misc 2 on left, misc 3 on right.

 

This completes the aircraft's main elements, so we can move on to Landing gear, struts and miscellaneous Structures.