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Drawing Your Own Model Aircraft Plans

Issue No 30, 29 May 2023

By: Anthony O. Ives

Drawing plans for a small, lightweight model aircraft is fairly straightforward especially if its based on an existing full scale aircraft. However, the bigger, heavier your aircraft design becomes then the more the drawings plans for your aircraft becomes more complex requiring more detailed design analysis. Heavier aircraft also come with additional legal requirements, there are usually different legal requirements for different weights of aircraft, generally the heavier the aircraft the more legal requirements that are required. However, with the increase in popularity of drones (quadcopters) most aviation authorities have introduced some legal requirements even for the lightest of radio controlled aircraft so it is important that you always check the requirements of the aviation authority for the country you live in. A future article will discuss airworthiness requirements in more detail. Its a good idea to get some experence building model aircraft from plans before attempting to draw your own plans which will help you with some of the practical aspects of building model aircraft. A previous article [1] discussed how to build a model aircraft from plans which may help you understand the practical issues you have to consider when building model aircraft.

Before starting to draw your plans you have to decide what your aircraft dimensions need to be, things such as wing area, etc. If you are building a model aircraft that is a replica aircraft of a full size aircraft then deciding your dimensions is going to be more straightforward. For replica aircraft you can find the dimensions of the aircraft you want to build in a typical aircraft directory such as reference [9] all you have to do is scale down the dimensions to size of the aircraft you want. Most aircraft directories have a 3 view drawings of the aircraft, which will make the task easier, some aircraft directories even gave all the dimensions but with 3 view drawing and a wing span or wing area you can roughly estimate all the other dimensions. If the aircraft you want to create is replica that is rare you may need to estimate everything from photos, etc or use an aircraft which is similar looking. However, even with model aircraft that are replicas some things may need to change for example you may need to use larger areas for your tailplane and tailfin, this is due to the fact that model aircraft need to be more stable [2] than a full size aircraft with a pilot in the cockpit.

Using references [2] to [8] you can work out the dimensions of an aircraft you want to build if it is your own unique design or if it is for a specific purpose. References [2] to [8] also come useful even for replica aircraft as they allow you to work what size of engine you need, what fuel tank size you need, etc.

Once you know all the dimensions of the aircraft you want to draw plans for, there is a number of ways to create your plans. The most modern method is to use CAD (Computer Aided Design) software on a computer. Most CAD software allows you to build a 3D (Three dimension) digital model, known as a DMU (Digital Mock Up) which you can exam almost like the actual aircraft and decide if components can fit, etc. Once you are satisfied that the aircraft is the way you want it to look, you can use the software to produce a set plans for printing. CAD packages is the way modern commerical aircraft are designed, typical packages used in the commerical world is CATIA, Solid Works, etc. However free CAD packages are also available such as FreeCAD [12].

The alternative way to draw plans is the old fashion way using pencil and paper which for small aircraft this is the way I prefer to draw my plans I also find it more therapeutic as you do not have the stress of trying to get a computer do what you want. While a computer method always seem faster, more convenient and easier in the real world they usually have all sort of problems that you never thought about. Using a CAD package can take longer if do not have a lot of experience using them, computers in general always take longer than you think and if hit the wrong button you can lose a lot work you have done. However, CAD packages do have their advantages particularly if you are designing something large and complex, but even in the commerical industry world drawings need printed on paper for people to make parts that need to be made manually. To draw your plans manually you can will need a pencil, paper of course, but a drawing board can come helpful, as well as can drawing compass and other drawing tools such as rulers, squares, etc. In reality you can draw your plans using the simplest of drawing equipment.

After you have decided whether to draw your plans manually or use CAD software you would first draw the outline of the design based on the dimensions. If you are drawing your plans manually it should look something like the one below:

Aircraft Outline for Design Plans

The wing, tail surfaces, control surfaces, etc are sized using references [2] to [8] if its a not replica aircraft however, the fuselage size you will need would be based on what you want to carry in the fuselage as well as the size of engine and fuel you need. Deciding the size of structural components such as wing skins, wing spars, wing ribs, fuselage skins, fuselage stringers and fuselage frames/formers can be done in a numbers of ways. If you are designing an aircraft that is similar to one that you have built before then you can assume the structural components will be similar in size. For smaller model aircraft you can visually check and generally feel if it strong enough however, it is a good idea to do some basic structural calculations. Some future articles will give an overview of some of the simple structural analysis that can be done for small aircraft. For larger aircraft you will need to do structural calcuations, depending on your aircraft weight there may airworthiness requirements that specify strength requirements. Commerical aircraft can require testing as well to be certified by an aviation authority.

In most cases in terms of flight stability and aircraft structure the intial design is based on what previous experience the designer has on similar aircraft. Then usually some analysis is done to see if the aircraft design meet all requirements in terms of weight, strength, flight stability, etc. The design is then modified and then analysis repeated to see if all requirements are met if not then the process is repeated. Hence why the design process is often considered an iterative process. Structural and flight stability analysis are advanced topics that I will discuss in future articles.

Once you have decided and drawn the outline of your wing, fuselage and tail surfaces, you would decide where you put all structural components such as ribs, fuselage frames/former, etc as well fuel tanks, radio equipment, etc. In addition you want to plan a build process, and of course you will have to decide which airfoils you want to use, as well as other aerodynamic profiles which I will discuss in future articles. Drawing your plans is essential combining a lot of the topics that I discuss in all my articles especially those related to aircraft design analysis and performance.

Please leave a comment on my facebook page or via email and let me know if you found this blog article useful and if you would like to see more on this topic. Most of my blog articles are on:

Mathematics
Helicopters
VTOL UAVs (RC Helicopters)
Sailing and Sailboat Design

If there is one or more of these topics that you are specifically interested in please also let me know in your comments this will help me to write blog articles that are more helpful.

References:

[1] http://www.eiteog.com/EiteogBLOG/No27EiteogBlogPlans.html

[2] http://www.eiteog.com/EiteogBLOG/No5EiteogBlogStability.html

[3] http://www.eiteog.com/EiteogBLOG/No1EiteogBlogLiftCL.html

[4] http://www.eiteog.com/EiteogBLOG/No2EiteogBlogDragCD.html

[5] http://www.eiteog.com/EiteogBLOG/No3EiteogBlogMass.html

[6] http://www.eiteog.com/EiteogBLOG/No4EiteogBlogThrust.html

[7] http://www.eiteog.com/EiteogBLOG/No6EiteogBlogRange.html

[8] http://www.eiteog.com/EiteogBLOG/No7EiteogBlogEndurance.html

[9] The Great Book of Modern Warplanes, Mike Spick, 2003, Greenwich Editions

[10] Civil Jet Aircraft Design, Lloyd R. Jenkinson, Paul Simpkin, Darren Rhodes, 1999, Butterworth Heinemann

[11] Aircraft Performance & Design, John D. Anderson Jr., 1999, McGraw Hill

[12] https://www.freecad.org

Disclaimer: Eiteog makes every effort to provide information which is as accurate as possible. Eiteog will not be responsible for any liability, loss or risk incurred as a result of the use and application of information on its website or in its products. None of the information on Eiteog's website or in its products supersedes any information contained in documents or procedures issued by relevant aviation authorities, manufacturers, flight schools or the operators of aircraft, UAVs.