My Method For Designing Aircraft (For Aspiring Scratch Builders)

Crawford Bros. Aeroplanes

Legendary member
Good day all,

I wanted to take time to share one of my techniques I use to build my own aircraft. Building from plans is a great way to get started in the hobby and enjoy proven and tested designs, but many of us would like to take the next step and create an aircraft that is fully our own. However, Scratch building is complicated and may leave some of us scratching our heads wondering where to start. If this is you hopefully this technique may prove useful to you.

I do not in any way claim that this method is the only method for creating a plan. I do not even claim that it is the easiest way. This is simply the method that I have created and chosen to use based on my background in carpentry, using skills that I was already comfortable using. There are many other methods of accomplishing the same thing that I am not aware of, and if anyone cares to do so please feel free to share your techniques as well.


Let's get started.

This is my technique for creating and inscribing a plan onto foamboard from a 3-view drawing. I use this technique to produce simple "FT-Style" aircraft that are based on an existing aircraft design. FT-Style aircraft are boxy aircraft with a flat sided box fuselage, but sometimes use posterboard turtledecks to create a rounded top. The simplest example of these is the Ft Simple Cub, with more elegant examples to include the FT Spitfire and Cruiser.

I will not cover the actual assembly of an aircraft in this writeup, only how to draw a template. The building techniques should be familiar to anyone who has assembled an FT speed build kit. I am writing this primarily for people who have already built working aircraft from FT kits and have a working knowledge of those techniques and the aerodynamics involved. Some of us may wish to attempt to design and scratch build our first aircraft, myself included, but do understand that much more trial and error may be involved. It does make for some good stories though!

Tools Required:

- Computer with Internet Access (or a printed 3-view drawing of an aircraft you wish to build)
- Ruler
- Pencil
- Carpenter's Square (Optional, but will result in a more accurate template)
- Cup of tea (optional?)

Selecting a Schematic

To build an accurate model of an aircraft a 3-view diagram is required. This is a schematic plan drawing of the aircraft from at least three angles- front, top, and side. As an example I am going to use a Piper PA-18 Super Cub. By searching "Piper Super Cub diagram" in my internet browser I was able to find this image:

pa18supercub.png


This image is a more detailed example than what we usually require and shows multiple views of the aircraft in different configurations, however we only need a top, side, and front view to build a model.

Calculating Scale

At this point there are two options to proceed. We can either print out our diagram, or we can simply measure it off of our computer screen. For convenience I will usually forgo printing it, however some may prefer a paper copy that may be more convenient to measure against and write on. Whichever you decide the following steps are the same.

You should already have an idea for the size of the model you are building. Usually this is the wingspan, but perhaps you have a set of wheels or a propeller you wish to use and must size the aircraft to fit those parts. Whichever the case, that is a measurement we can use to calculate our scale ratio from our diagram.

I have decided on a 40 inch wingspan for our Super Cub. With that in mind I now know that whatever the size of the wing in the drawing is, it represents a 40 inch wing on our model. Using our ruler, we measure the wingspan of the drawing (I prefer centimeters as it's more convenient on the smaller scale). The drawing measures a wingspan of 20.7 cm. To find our ratio, we divide the model wingspan by the drawing wingspan.

40 / 20.7 = 1.932

Write down this ratio! You'll notice that by working backwards, 20.7 (a measurement of the drawing) multiplied by 1.932 (our scale ratio) is 40 (a measurement of the model). We can now measure any part of the drawing (cm), multiply it by 1.932, and get the actual size of the part in inches.
(You could also just use 1.9 and achieve a good result too, I just like being picky)

Drawing the Template

With our scale ratio in hand, we can now begin drawing our template on foam board. We begin with one of the sides. I will usually tuck the template into one of the upper corners of the foam board, which allows me to use the edges of the sheet as points to measure from. If the aircraft profile has a long, flat edge, such as the top edge of the fuselage on the Cub, I will set that against the edge of the foam board to reduce the amount of cutting I need to do.

I usually begin by measuring the overall length of the fuselage and marking it on the board (remember to use our ratio to get the actual measurement!). Then I measure the deepest point of the fuselage and mark that similarly. Using these two vertices I can then create a box the length and depth of the fuselage, which gives me a useful template to draw the fuselage inside. I can then measure the length of each of the other lines and mark them to create a basic line drawing, like this:

drawn1.jpg


This profile drawing is one of four sides of the fuselage we will make. We will continue using the same technique to draw out the floor and other wall of the fuselage as one connected shape we can then cut out and fold together. I usually cut out the roof separate as I find it easier to work with that way, but that is a matter of preference. The same technique is used to make the roof. Remember to mirror the other fuselage side! When complete, the template should look like this:

IMG_20211118_152024.jpg


You'll notice the shape of the three sides, from top to bottom: fuselage left hand side, fuselage floor, fuselage right hand side. Around the edges of the floor I have marked out the score cut lines where foam will be removed to make room for the B-Folds of the fuselage sides. The vertical lines on the fuselage sides are score cut lines to allow the sides to bend inward to match the shape of the floor. The gridded lines on the floor are not to be cut, they are measurements that I marked to help me draw everything out symmetrically.

Drawing the wings

Unfortunately I do not have any pictures for the wing template, however FT wings are easy to make. If you have already built an FT kit you will be familiar with this process. Use these techniques to mark out half of the wing profile on one sheet and the other half on another. Remember to mirror each half! Add a simple rectangle off the leading edge of each wing profile, roughly 2/3 the thickness of the wing and extending from the base to within a few inches of the wingtip. This will fold under to form the bottom side of the wing. Mark a line down the wing's length about 1/3 back from the leading edge to represent the thickest part of the wing. Mark two more lines 1/2" ahead of and 1/2" behind this line. When the wing is cut out, score these lines and glue the spar between them to allow the top side to bend over and give the wing its curved airfoil shape.

Once the template is drawn, cut everything out and start building!


This ended up being a lot more information than I originally intended to write and some of it may be a bit rough around the edges, but I hope that this may be useful to some of you. I'm sure there is plenty more information on this out there, I just wanted to give my take in case it might be helpful to someone. Plus I had the afternoon free and was too tired to actually build, so I might as well make myself useful somehow.

Cheers.
 

FlamingRCAirplanes

Elite member
Good day all,

I wanted to take time to share one of my techniques I use to build my own aircraft. Building from plans is a great way to get started in the hobby and enjoy proven and tested designs, but many of us would like to take the next step and create an aircraft that is fully our own. However, Scratch building is complicated and may leave some of us scratching our heads wondering where to start. If this is you hopefully this technique may prove useful to you.

I do not in any way claim that this method is the only method for creating a plan. I do not even claim that it is the easiest way. This is simply the method that I have created and chosen to use based on my background in carpentry, using skills that I was already comfortable using. There are many other methods of accomplishing the same thing that I am not aware of, and if anyone cares to do so please feel free to share your techniques as well.


Let's get started.

This is my technique for creating and inscribing a plan onto foamboard from a 3-view drawing. I use this technique to produce simple "FT-Style" aircraft that are based on an existing aircraft design. FT-Style aircraft are boxy aircraft with a flat sided box fuselage, but sometimes use posterboard turtledecks to create a rounded top. The simplest example of these is the Ft Simple Cub, with more elegant examples to include the FT Spitfire and Cruiser.

I will not cover the actual assembly of an aircraft in this writeup, only how to draw a template. The building techniques should be familiar to anyone who has assembled an FT speed build kit. I am writing this primarily for people who have already built working aircraft from FT kits and have a working knowledge of those techniques and the aerodynamics involved. Some of us may wish to attempt to design and scratch build our first aircraft, myself included, but do understand that much more trial and error may be involved. It does make for some good stories though!

Tools Required:

- Computer with Internet Access (or a printed 3-view drawing of an aircraft you wish to build)
- Ruler
- Pencil
- Carpenter's Square (Optional, but will result in a more accurate template)
- Cup of tea (optional?)

Selecting a Schematic

To build an accurate model of an aircraft a 3-view diagram is required. This is a schematic plan drawing of the aircraft from at least three angles- front, top, and side. As an example I am going to use a Piper PA-18 Super Cub. By searching "Piper Super Cub diagram" in my internet browser I was able to find this image:

View attachment 211964

This image is a more detailed example than what we usually require and shows multiple views of the aircraft in different configurations, however we only need a top, side, and front view to build a model.

Calculating Scale

At this point there are two options to proceed. We can either print out our diagram, or we can simply measure it off of our computer screen. For convenience I will usually forgo printing it, however some may prefer a paper copy that may be more convenient to measure against and write on. Whichever you decide the following steps are the same.

You should already have an idea for the size of the model you are building. Usually this is the wingspan, but perhaps you have a set of wheels or a propeller you wish to use and must size the aircraft to fit those parts. Whichever the case, that is a measurement we can use to calculate our scale ratio from our diagram.

I have decided on a 40 inch wingspan for our Super Cub. With that in mind I now know that whatever the size of the wing in the drawing is, it represents a 40 inch wing on our model. Using our ruler, we measure the wingspan of the drawing (I prefer centimeters as it's more convenient on the smaller scale). The drawing measures a wingspan of 20.7 cm. To find our ratio, we divide the model wingspan by the drawing wingspan.

40 / 20.7 = 1.932

Write down this ratio! You'll notice that by working backwards, 20.7 (a measurement of the drawing) multiplied by 1.932 (our scale ratio) is 40 (a measurement of the model). We can now measure any part of the drawing (cm), multiply it by 1.932, and get the actual size of the part in inches.
(You could also just use 1.9 and achieve a good result too, I just like being picky)

Drawing the Template

With our scale ratio in hand, we can now begin drawing our template on foam board. We begin with one of the sides. I will usually tuck the template into one of the upper corners of the foam board, which allows me to use the edges of the sheet as points to measure from. If the aircraft profile has a long, flat edge, such as the top edge of the fuselage on the Cub, I will set that against the edge of the foam board to reduce the amount of cutting I need to do.

I usually begin by measuring the overall length of the fuselage and marking it on the board (remember to use our ratio to get the actual measurement!). Then I measure the deepest point of the fuselage and mark that similarly. Using these two vertices I can then create a box the length and depth of the fuselage, which gives me a useful template to draw the fuselage inside. I can then measure the length of each of the other lines and mark them to create a basic line drawing, like this:

View attachment 211973

This profile drawing is one of four sides of the fuselage we will make. We will continue using the same technique to draw out the floor and other wall of the fuselage as one connected shape we can then cut out and fold together. I usually cut out the roof separate as I find it easier to work with that way, but that is a matter of preference. The same technique is used to make the roof. Remember to mirror the other fuselage side! When complete, the template should look like this:

View attachment 211974

You'll notice the shape of the three sides, from top to bottom: fuselage left hand side, fuselage floor, fuselage right hand side. Around the edges of the floor I have marked out the score cut lines where foam will be removed to make room for the B-Folds of the fuselage sides. The vertical lines on the fuselage sides are score cut lines to allow the sides to bend inward to match the shape of the floor. The gridded lines on the floor are not to be cut, they are measurements that I marked to help me draw everything out symmetrically.

Drawing the wings

Unfortunately I do not have any pictures for the wing template, however FT wings are easy to make. If you have already built an FT kit you will be familiar with this process. Use these techniques to mark out half of the wing profile on one sheet and the other half on another. Remember to mirror each half! Add a simple rectangle off the leading edge of each wing profile, roughly 2/3 the thickness of the wing and extending from the base to within a few inches of the wingtip. This will fold under to form the bottom side of the wing. Mark a line down the wing's length about 1/3 back from the leading edge to represent the thickest part of the wing. Mark two more lines 1/2" ahead of and 1/2" behind this line. When the wing is cut out, score these lines and glue the spar between them to allow the top side to bend over and give the wing its curved airfoil shape.

Once the template is drawn, cut everything out and start building!


This ended up being a lot more information than I originally intended to write and some of it may be a bit rough around the edges, but I hope that this may be useful to some of you. I'm sure there is plenty more information on this out there, I just wanted to give my take in case it might be helpful to someone. Plus I had the afternoon free and was too tired to actually build, so I might as well make myself useful somehow.

Cheers.
Thanks man!!!
 

Hondo76251

Legendary member
Thats pretty much how I've always done it as well. Pencil, ruler and some old school drafting! Lol

Only thing i might add is, depending on the scale i want to build at, I find that altering some of proportions slightly can help with flight characteristics. IE: I've found that the smaller you go the larger the control surfaces need to be in proportion to the size, especially the tail feathers. On a model thats say 30" wingspan, i might have the tail proportions as much as 150% or more in relation depending on how the original was proprtioned. Its actuall kind of neat how much you can alter the proportions and still maintain the "look" of the original plane.
 

Crawford Bros. Aeroplanes

Legendary member
Thats pretty much how I've always done it as well. Pencil, ruler and some old school drafting! Lol

Only thing i might add is, depending on the scale i want to build at, I find that altering some of proportions slightly can help with flight characteristics. IE: I've found that the smaller you go the larger the control surfaces need to be in proportion to the size, especially the tail feathers. On a model thats say 30" wingspan, i might have the tail proportions as much as 150% or more in relation depending on how the original was proprtioned. Its actuall kind of neat how much you can alter the proportions and still maintain the "look" of the original plane.
I agree, I just thought that seemed like something for a different article if you know what I mean. I find that sometimes I have to alter proportions for aesthetic reasons too, sometimes more rounded planes need a bit of work to look good in FT style.
 

Crawford Bros. Aeroplanes

Legendary member
Have you finished the plane yet, and can you post some pictures of it? I use similar methods in CAD and I'd like to see how your plane turns out.
I haven't gotten further than what I've shown here yet, I drew up the template a few days ago but then got busy so I haven't had a chance to work on it. Probably going to get more done tomorrow though. This is my entry for the Piper Cub Building Challenge if you want to head over there to keep up with it.