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1/12 Gotha G IV Design, Prototype, Publish

willsonman

Builder Extraordinare
Mentor
#1
As a mild distraction from my other projects I was recently inspired by the overall shape (thanks CrashRecovery) of the Storch wing to do another WWI era plane. This will not be my typical building but more along the lines of FT building.

For those who are wondering why so small (?), a 1/12 scale Gotha comes in at a wingspan of 77.75 inches, or nearly 6.5 feet! No small plane here. I felt my approach was different enough that warranted an alternate for others who may not find playing with Sketchup a good way to go. I will go through the design, prototyping, and publishing process in detail and hope to help others out to find good ways to make their dream plane come alive.

I prefer Wings3D as my program of choice. Some may find it tedious to use multiple programs but I find Wings3D simpler to use and its a carry over from my time modeling custom planes for RealFlight. So I'll vaguely explain what I do as I go and please feel free to chime in with questions.

Program orientation: In the edit--> preferences-->camera tab I use 3ds max camera mode. The top right corner has your view buttons. I use perspective view mostly. It distorts your view when you are at angles but when on a top, side or front view its precise. Press the Y, X, or Z keys to get to your precise views. Alternately, to view from the opposite directions combine shift with that. The top middle allows you to select your verticies, edges, planes, or entire objects. Save your 3-view pictures as JPEG format and keep them in the same directory as your saved WINGS file. I generally use MS paint or GIMP to isolate each view independently. I'll explain further commands as I use them.

To start with I right-click (RC) and make a cube for a bounding box. Default dimensions are 2x2x2. RC with the cube selected (red) and I scale the x-axis to my wing length. You can use the slider or you can press tab and type in the precise percentage. 77.75 /2*100=3887.5% enlargement of that axis. Deselect the cube and RC and select image plane. Import your top-view. Select and use the rotate tool to rotate to the correct orientation. Again, use the tab button to select precise angles. Then RC scale uniform to scale until the wingspan is correct to your cube. Once it is correct deselect it and select the verticies aft. Then RC and move along the Z axis to the tail of the top view. Do the same for the front. Import your side and front views in the same way, as image planes, and size them.

Keep in mid that your views will generally NOT align well. Most 3-views are artist drawings so you have "fudge factors" to deal with. At this point I was ready to start making components. You are generally done with your bounding box. You can delete it at this point but there are some rare instances where you may need it again so I just click the eye to hide it.
 

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willsonman

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#2
Starting with the fuselage, with nothing highlighted red (selected) RC and select cube. Select the fore and aft verticies (left click and drag a box around them in your view) independently and hit X to get your side view. Right click move along Z to get the overall length. You can deselect all verticies in the Geometry graph by clicking the box that is red. Then select and adjust your top and bottom verticies the same way to get the overall dimensions you are looking for. Using the edge tool. Start looking for bend points in the side-view. You can make the box transparent by selecting the cube to the far right of the object in the geometry graph. LC and drag through your box vertically and then press your C button. This will create a new edge bisecting all selected edges. RC move--> Z to move to your hard point. From there use your vertex tool to adjust the height of each vertex to get the side profile right.

Press Y and you get the top view. Adjust your top verticies by selecting them an RC--> scale axis--> X. You can first adjust them all to the overall width if you like. Adjust to get the overall top profile.

For more detail you can select a set of edges, RC-->cut--> select a number or enter a number. This will create new verticies on each selected edge. You can connect verticies by selecting them (if not already selected) and press C. Add additional detail this way. The left right arrows in the upper left are your undo/redo buttons.

When I was done I got the attached screen shot.
 

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willsonman

Builder Extraordinare
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#3
Next I moved onto the horizontal stabilizer (H-stab) and elevators. Press Y. Click the eye of the fuselage to hide it so you are not distracted. RC--> cube, RC--> move--> Z to get into the rough position. Select the edges that pass through the Z axis. Press C. In edge tool RC--> loop cut. This effectively cuts the solid into two piece exactly along the Z axis. Delete the highlighted half by pressing delete. We are only going to create one half since they will eventually be symmetrical. No point in doing twice the work. Get your overall shape again. Again, your default dimension is 2x2x2 so we are going to set the thickness of the foam here. Select the entire object, RC-->scale axis-->Y, tab, set to (0.19685[5mm to in]/2*100)=9.8425%. Done. You have your H-stab set to the right thickness. To get curves I used the bevel tool. Select an edge, RC--> bevel, slide to get the bevel you are looking for. Add more verticies as needed for higher detail. I started by just making the H-stab. Setting the vertex for where the elevator would end on the H-stab I selected the plane, RC--> extrude-->Z. Size, add, and move verticies to shape. This creates a default hinge line that separates the elevator and the H-stab but keeps them within the same object. Once done shaping you can select the middle plane that will be for mirroring the object. RC--> mirror and you are done. You can move the object vertically to the location that you want.

I similarly made the V-stab and rudder using the above methods. Once done it looked like the attached screenshot.
 

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willsonman

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#4
The above methods were also employed to create the top wing profile along with the top aileron. The shapes of the top and bottom wings are different slightly but the top wing is larger in surface area and the aileron has a counter-balance. Since more work is yet to be done here I have not mirrored yet. This is just getting the overall to shape. The airfoil will come later.

I should also mention that the default measurement in Wings3D is in inches. This makes things very easy for export->import later.
 

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willsonman

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#7
Took the family to the fair last night. Nothing accomplished. Need to do some reading. While the scale airfoil is under cambered I will use the typical flat-bottom airfoil that FT seems to favor. It has good construction qualities and strength. With it comes an inherent change in aerodynamics. The tail incidence on the H-stab is what I am referring to. Under camber creates a tremendous amount of lift... and drag. It also creates more turbulent air that causes less effect on tail planes in its wake. Typically in WWI designs you will see quite a bit of positive incidence due to all of these factors. The positive incidence will help keep the tail level from the high lift rate of the wing and also compensate for the wash of the wing. Using a flat-bottomed airfoil will clean up that wake but still exhibit a large amount of lift, especially with a wing area so large. I may just go with a TLAR (That Looks About Right) method and tweak the plans after the prototype rather than a mathematical approach. Any aerodynamic gurus want to chime in here?
 

willsonman

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#8
Ok, so the original incidence is 4.5 degrees relative to the datum line. I'm setting mine at 2.5 degrees. With the down wash generated from the wings I think this will be a good place to start. I created a segment in the elevators to accept a BBQ skewer as a joiner. The bevel will be in the H-stab. As it pivots down there will be enough room to tuck it in. I set my angle of the H-stab and elevators by clicking on the entire object and hit the vertex tool. This gets all the verticies selected at once. Then rotate along the x axis hitting tab and typing it in. As a general rule I do it this way. If you have multiple objects grouped this way works. If you use the entire object tool it will rotate each individual object within the group. Odd, yes, but thats how Wings works. So, I cut my grove in the H-stab to accept the V-stab. Extrude down a portion of the root of the V-stab to go through the fuselage. Again, use tab to set specific distances. I created an outline in the fusealge by creating new verticies. This is for a hole to accept the V-stab and position the tail assembly.
 

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willsonman

Builder Extraordinare
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#9
This is just on one side. Some things will be just have to be explained later. Top view. Create reference lines by clicking on edge tool. Click any edge on the object. In the menu bar click tools-->connect. Then LC and hold on an edge. You will see a new vertex appear and you can slide it into position along the edge. Once you have the vertex placed let go of the LC and you will have a ray coming from your mouse pointer. Find another edge and LC and hold again, sliding this new vertex into position. You can continue this for some time but be warned its a quick way to create redundant edges. I usually do one at a time to avoid this. RC to exit the tool. Using this technique I was able to create reference lines and verticies for placement of the interplane (IP) struts. These will be for making holes for BBQ skewers as the IP struts. In the picture you can see the label on the plan and each red vertex highlighted.
 

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willsonman

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#10
With the basement now completing I'm getting back on the building, now in my new shop area! I've been working on this one on and off for awhile now. I completed the design, prototype build, and flight evaluations last fall. It flew perfectly the first time! During assembly I noted changes that needed to be made to the plans and did so. I also typed out some construction notes. I'm more of a traditionalist in this way. Build notes walk you through tricky bits that may not be implied on plans.

With the great success of Rasterize's artwork on the mini P-51 and F4U, I decided to make a final version using similar techniques. He was kind enough to provide me with printed tissue to apply onto a glassed surface but in trying this method, it did not go well. With my big printer I can print the design onto craft paper and apply it using super 77 spray glue.

Under construction... the ruler on top of the wing is 12 inches.
IMG_1867.JPG

Removable wing panels.
IMG_1965.JPG

Its big... very big.
IMG_1977.JPG

Prototype completed prior to maiden.
IMG_2036a.jpg
 

willsonman

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#11
The plans and build notes are attached here. Its a big airplane so the plans are big! The build notes has a list of materials and recommended power setup. It seems small but was more than sufficient.

I am hopeful that I can get this final version built in-time for Flite Fest 2016. Not just to show off the model but the fantastic covering technique developed by Rasterize. I am also going out on a limb here asking for folks who want to fly WITH me to please build a baby baron to accompany this airplane as a fighter escort. It is roughly the same scale size of fighter aircraft of the time and fits the theme. There is also a possibility of another escort plane in the works but its not by me so I will not say more than that.

The Gotha flies exceptionally scale-like. The wing was designed to incorporate standard FT build techniques but modified to stall more realistically without losing too much of the scale tendencies of this airplane. I would NOT recommend crazy mode on the motors but do use props that spin in opposite directions to cancel out torque. Only use rudder. If you use the rudder it will fly in a very scale way and look fantastic in the air.

Overall this is a GREAT airplane to dip your toe in the WWI era. Take-offs and landings on this are just like you should with more scale aircraft. It is a great in-between in terms of flying characteristics, teaching coordinated turns and flying the wing (not the prop) while keeping bad tendencies toned down.
 

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Rasterize

Maker of skins for foam board RC planes
Mentor
#12
Great Googly Moogly!
I really like big planes. I really like WW1 planes. I really like bi-planes. I really like this!
I hope she will be at Flite Fest. I'm with ya on the need for some scale-ish Fokkers or Albatross for top cover. :) I feel a dawn patrol forming...
 

willsonman

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#13
From here on I will be posting about the final version's construction.

These are the printouts of the lozenge pattern. I simply peel off the paper from one side of the foam, apply Super 77 spray glue to both sides, air dry for awhile, and stick them together. From there I trim the excess away.
IMG_2502.JPG

Here is a completed engine nacelle. Note the mesh at the front to let air in. This is plastic screen door material that was hot-glued in-place.
IMG_2505.JPG

I've also cut and covered the V-stab and rudder along with the H-stab and elevators. The second nacelle is waiting for assembly.
 

willsonman

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#14
Rasterize... I sure hope we can get a dawn patrol! WWI planes are a special appeal. Once you try one there is something that hooks you forever. They are challenging birds to build and fly but such exceptional flying works of art.
 

wilmracer

I build things that fly (sometimes)
Mentor
#16
Awesome! Can't wait to see this one come together. Not sure I'll have time to do a baron between now and ff but I'm sure you'll have plenty of folks eager to provide escort :)
 

willsonman

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#17
LOL, well I think my theme for FTFF this year is go big or go home. LOL. With the smaller batteries I can fly this one more and not to mention... I will not care as much if I take a hit and crash. I think I will try to incorporate a bomb drop with my FT Ordinance. And here. SHould make for some fun target practice first thing in the morning.
 

SP0NZ

FT CAD Gremlin
Staff member
Moderator
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#18
I am also going out on a limb here asking for folks who want to fly WITH me to please build a Baby Baron to accompany this airplane as a fighter escort. It is roughly the same scale size of fighter aircraft of the time and fits the theme.
Rasterize, it would be cool if you could make a custom skin for the Baby Baron escort planes for Flite Fest. Let me know and I will get you the CAD files for it.


There is also a possibility of another escort plane in the works but it's not by me so I will not say more than that.
I'm in the initial stages of designing the 1/12th scale Fokker D.VII biplane. I told willsonman that I will try to get it done for Flite Fest, but I can't make any promises. I've committed to another project with my son to develop a new BIG combat plane for Flite Fest, and that is going to be the priority. The good news is that the prototype for the combat plane is nearly complete. So, it looks like the D.VII might be a reality for FF'16.
 

AkimboGlueGuns

Biplane Guy
Mentor
#19
Not sure I'll have time to do a baron between now and ff but I'm sure you'll have plenty of folks eager to provide escort :)
If you'd like to fly in the patrol I'd be more than willing to throw an electronics ready baby baron together for you before hand. Just say the word.
 

willsonman

Builder Extraordinare
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#20
This is why I love this community. Banding together to do something really fun. You guys are awesome!

SPONZ: That is a great idea! If Rasterize can put that together it would be a hoot of a swarm!