Designing a Model Aircraft: Calculating Thrust and Lift for an Efficient Flight

[TheArrow]

TL;DR

Planning to build a model aircraft, looking for feedback

Hello Everyone,

I'm planning on designing a model aircraft that would be powered by an Arduino and electric motor. I'm interested in pursuing an aerospace degree and I figured the best way to get a headstart would be be to dive right into a project. This is also probably overthinking/overdoing it, but I want to get in the mindset of "thinking" like an engineer.

Thinking aloud, if anyone actually knows what they're doing, by all means correct me or give ideas:

1. Since I have a payload in mind (i.e. the Arduino board, the power supply, servos, etc.), I have to ballpark how much thrust the prop will need to generate to move the aircraft. From playing around with the industry standard design simulator, Kerbal Space Program, I'm looking at this similarly to Delta-V. A rocket needs to provide sufficient Delta-V to lift the payload and the mass of the rocket to fulfill whatever mission objectives are laid out for the payload.
2. Design an airframe around the motor and other components with sufficient lift to make the plane do plane things.
3. Design a controller to do pilot things.

So for Step 1, I was wondering how I would go about computing how much thrust would be required so I can select an appropriate prop/motor combination.

For Step 2, a question that comes to mind off the top of my head would be whether the bottom of the fuselage counts as a lift surface when doing calculations pertaining to surface area (assuming this will be a cantilever wing monoplane design). So the bottom of the wing will be flush with the bottom of the fuselage.

Anyways, that's all I have for now. I'll update this thread with progress as I go along.

 

[russ_watters]

You're talking about a fixed-wing airplane, right? Have you looked into what hobby kits are available, and how they are designed? For your first, maybe it would be better to build an already designed airplane and learn from its design? Making an autonomous airplane is not a small task.

 

[TheArrow]

You're talking about a fixed-wing airplane, right? Have you looked into what hobby kits are available, and how they are designed? For your first, maybe it would be better to build an already designed airplane and learn from its design? Making an autonomous airplane is not a small task.

I've built static model airplanes before. But I haven't ventured into the RC field. The kits that I've seen are a bit out of my price range (being unable to work at my usual job because of the Rona) at the moment. For the most part this was lending itself more towards a FreeCAD design exercise that could eventually lead to putting together a physical model in the future. And yes, a fixed wing design.

 

[jrmichler]

I want to get in the mindset of "thinking" like an engineer.

An engineer starts by doing some research on the scope of the project. The suggestions by @russ_watters are an excellent place to start. Have you considered getting a model glider (3' to 4' wingspan) and adding the Arduino? Less cost than a powered model, and the control challenges would be the same. An RC model will have power supply, servos, servo wiring, and servo linkages all properly sized, connected, and working. You could replace the controller with your Arduino.

If you really want to design your own model airplane, get a book such as Aerodynamics, Aeronautics, and Flight Mechanics by McCormick. That's not the only book out there, but the first edition has 652 pages of everything you need to know about lift, drag, power, and controllability. Especially controllability.

For structural design, Aircraft Structures by Peery covers aluminum construction very well. I do not have a good recommendation for the wood and/or fiber reinforced composite construction used by model airplanes.

I once had the idea of designing and building my own real airplane, so I bought and read the above books. And I bought a 1946 Taylorcraft BC-12D for a rebuild project to learn the practical aspects. All of that convinced me to do something else.

 

[TheArrow]

If you really want to design your own model airplane, get a book such as Aerodynamics, Aeronautics, and Flight Mechanics by McCormick. That's not the only book out there, but the first edition has 652 pages of everything you need to know about lift, drag, power, and controllability. Especially controllability.

For structural design, Aircraft Structures by Peery covers aluminum construction very well. I do not have a good recommendation for the wood and/or fiber reinforced composite construction used by model airplanes.

Thank you for the book suggestions, I'll give those a look over. I don't want it to come across as me underestimating the scope of the project or anything like that (nobody should underestimate the challenging job engineers have). For me, it's more about stumbling into problems naturally and then looking for solutions for those problems. It's not entirely about completing the project and having a physical little plane zooming around. It's more so exploring and stumbling on purpose. But I will look into a little glider model in addition to your book suggestions. Thank you so much for your informative reply!

 

[Baluncore]

It's not entirely about completing the project and having a physical little plane zooming around.

Any experimental electric powered model will benefit from good glide characteristics. Buy a kit or a set of plans, then build an RC model glider. That way you get the quick reward and some experience soaring.
Then fit the battery, control system and motor once you know what your powered launch requirements are. Consider a pusher prop that will be less susceptible to damage when landing.
With GPS on a glider, it should be possible to autonomously map the rising air as it flows over a hill, or in a thermal.
Glider pilots are aware of the ground conditions and the flow of air around them, so they can avoid getting into trouble in the first place. They understand the range of forces on the aircraft.

 

[TheArrow]

Any experimental electric powered model will benefit from good glide characteristics. Buy a kit or a set of plans, then build an RC model glider. That way you get the quick reward and some experience soaring.
Then fit the battery, control system and motor once you know what your powered launch requirements are. Consider a pusher prop that will be less susceptible to damage when landing.
With GPS on a glider, it should be possible to autonomously map the rising air as it flows over a hill, or in a thermal.
Glider pilots are aware of the ground conditions and the flow of air around them, so they can avoid getting into trouble in the first place. They understand the range of forces on the aircraft.

After all these replies, I'm definitely going to find to a cheap glider model and play around with it while I work through the books that were suggested to better understand what's going on. I've flown myself for hundreds of hours in flight simulators but also in real life as a student pilot in powered aircraft. So I have an intuitive understanding of how forces of flight work, but not necessarily a quantitative or analytical sense for the exact relationship those forces have with each other. But the book by McCormick is exactly what I'm looking for with that.

 

[Borek]

Google Ardupilot. Starting from scratch if you have no experience and financial means sounds to me like a way to fail.

There are several RC DIY model/plane/whatever forums, where you will easily get help from people doing these things (designing models, tinkering with autopilots) and having a lot of experience. They will probably guide you to some sets of approximate rules they use for any more or less typical model, I remember reading them collected somewhere on a web.

 

[Lnewqban]

My recommendations:
* Regarding books:
https://www.amazon.com/dp/1854861905/?tag=pfamazon01-20

https://www.amazon.com/dp/0938716786/?tag=pfamazon01-20

https://www.amazon.com/dp/0830639012/?tag=pfamazon01-20

* Regarding websites:
https://www.av8n.com/how/

https://cmsw.mit.edu/angles/2019/mark-drela-the-airplane-whisperer/

http://www.charlesriverrc.org/articles.htm

https://www.modelaircraft.org/

* Web forums:
https://www.rcuniverse.com/forum/

http://www.rcgroups.com/forums/index.php

 

[TheArrow]

Google Ardupilot. Starting from scratch if you have no experience and financial means sounds to me like a way to fail.

Thanks I'll take a look into Ardupilot.

My recommendations:

Thank you for the resources!