MachUp - Free Online Aircraft Design Program

Have you ever wanted to design your own aircraft? Or built a canard and then spent hours trying to figure out where the center of gravity should be? Or wondered about how stabilizer placement will affect the stability of your aircraft? If you can answer yes to any of these questions (or yes to any questions regarding aircraft design) then MachUp is for you!

MachUp is a free, online aerodynamic analysis tool used for aircraft design, analysis, and optimization. This tool was developed by graduate students under the leadership of Dr. Doug Hunsaker at Utah State University. I myself have been working on the development of MachUp for over a year now. My work specifically has related to calculating the aerodynamics of the propellers and modeling how prop-wash can affect the aerodynamics of lifting surfaces, like wings. Using this tool, aspiring aircraft designers with little to no knowledge of aerodynamics or aeronautical engineering can design their own aircraft. From a simple flying wing to a canard with distributed electronic propulsion, MachUp allows users to design their own aircraft and easily analyze its aerodynamics.

The purpose of this article is not to be a users manual for MachUp. Rather, my goal is to introduce you to its potential and give you an idea of where you can find the tools you need to get started.

So lets get started!

MachUp is available as an online tool that is free and open for anyone to use. You can access several different versions of MachUp by going to the USU Aerolab website. Once you are there, click on the 'Log In' button in the top right corner and either log in or register, depending on if this is your first time. Registration is super quick, easy, and free! Its just to help us keep track of our user base and keep our users informed about important future updates (They only happen once or twice a year, so we won't be blowing up your email inbox). 

Once you are registered and logged in, you can choose to access two different versions of MachUp: MachUp 4 and MachUp 5. They are basically the same with a couple of key differences, namely that MachUp4 was designed with engineers in mind and MachUp5 was designed for everyone else. So I'll be focusing on MachUp5 in this article, but if you have a sound understanding of aerodynamics and non-dimensional coefficients then go ahead and dive into MachUp4!

Once you get into MachUp, you'll see a window that looks like this:

To give you a brief overview, there are basically three steps to using MachUp:

1. Build the airplane
2. Set the flight conditions
3. Run an analysis

Now lets dive a bit into each of those steps. Just an FYI: This is not meant to be a tutorial. I'll be creating a few of those later. My goal right now is just to give you an overview of how MachUp works so that you can get in and start playing with it yourself.

So, first step: Build the airplane. 

This is done by adding wings and/or propellers to the 3D design space. To add a wing, click on 'Add' in the top toolbar and then click 'Wing'. Once a wing has been added, various characteristics about it can be modified using the 'Object', 'Geometry', and 'Material' tabs on the right side. These characteristics include the root and tip chord lengths, sweep angle, dihedral angle, airfoil characteristics and much, much more. You can even add control surfaces to your wings and set the mixing for those control surfaces, enabling you to do complex control mixes like elevons, V-tail's, etc.

The same goes for propellers. Click on 'Add' and then select 'Propeller'. Now, with the propeller selected, you can modify elements of it's geometry, including the number of blades, the pitch , diameter, and airfoil characteristics. You can even specify the characteristics of your power system including the motor, esc, and battery. MachUp will then use this information to give you an estimate of how the propeller will operate at a given flight condition and throttle setting.

By combining a bunch of wings and propellers, you'll be able to design an entire aircraft! For example, here is a DEP (Distributed Electric Propulsion) Aircraft that I designed based on a VTOL aircraft created by NASA. Its important to note that although I created a fuselage and nacelles using a couple of the other objects available in the 'Add' menu, the only objects that are currently used in the aerodynamic analysis are the wings and propellers. So any other objects you add are purely for visual appeal and don't actually affect the aerodynamics. We'd like to add the functionality in the future to analyze other objects, like fuselages, we just haven't gotten around to it yet. 

Once you have an aircraft built, we're on to the second step: Set the Flight Condition.

To do this, click on the 'Condition' tab on the top-right side. In this tab you get to set various aspects of the flight condition including the velocity, angle of attack, and any control surface deflections. You'll also be able to set the rpm's or throttle setting (if you specified a motor for all your propellers) of the propellers. 

Now take a second to note the 'Units' selector at the top. MachUp5 is currently set up to use two different systems of measurement: English and Metric. If you select 'English', the aircraft dimensions that you specified while you were building your aircraft will be in feet, the velocity of the aircraft will be measured in feet per second, and the forces on the aircraft will be measured in pounds. If you select 'SI', the aircraft dimensions will be in meters, the velocity of the aircraft will be measured in meters per second, and the forces on the aircraft will be measured in Newtons.

Once you've specified the flight condition, you're ready for step three: Run an Analysis.

On the 'Analysis' tab, take a look at the 'Run' drop-down menu. This menu contains all of the different analyses that MachUp can do on your aircraft. To run an analysis, simply select the analysis you want and click 'Update Results'. Note that depending on the analysis you want to run, it may take anywhere from 1-30 seconds, so you may have to learn a bit of patience. If you get frustrated, just think about how much faster this is than doing all of these extremely complex calculations using a slide rule. Now, here is a brief description of all the analyses you can run.

• Forces and Moments: Analyzes the forces and moments on the aircraft for the given flight condition. The results are first split into the forces created by the lifting surfaces (wings) and the props and then they are combined to give the total forces at the bottom. FL is the lift force. FD is the drag force. FS is the side force. MX, MY, and MZ are the moments about the x, y, and z axes respectively.
• Performance Derivatives: Analyzes how the aerodynamics of the aircraft change with small changes in the flight condition, specifically the angle of attack and sideslip angle. I'll write another article explaining more about this later, but the important bit is this: For an aircraft to be considered stable, Cm,alpha < 0, Cl,beta<0, and Cn,beta>0. If your analysis shows these results, small disturbances to the flight condition will not cause your aircraft to flip over. Also, you want to get the Static Margin as close to 0.05 as possible. This is a measure of the stability and maneuverability of the aircraft and should be used to find the correct placement for the center of gravity (CG).
• Aerodynamic Center: Calculates the aerodynamic center of the aircraft. The aerodynamic center is the point about which changes in the angle of attack do not affect the pitching moment. It is pretty important and used in more advanced aerodynamic calculations, but may not be necessary for what you want to do.
• Stall Onset: This analysis takes airspeed that you specified in the flight condition and then increases the angle of attack until any part of the aircraft stalls. It then tells you the stall angle of attack, the amount of lift you can produce at that angle of attack and the specified airspeed (right before stalling) and the location of the stall. Arguably, the next analysis is probably more useful to you if this sounds interesting.
• Stall Airspeed: Calculates the minimum airspeed that you need to fly based on a specified aircraft weight. This is one of the slowest analyses to run, but also one of the most useful. Essentially, once you have designed your aircraft, you set anticipated weight of your aircraft, and this analysis will tell you how fast you need to be going before you can get off the ground. Also gives the same information as the Stall Onset analysis.
• Target Lift: Calculates the angle of attack necessary to produce a specified amount of lift at the given airspeed.
• Pitch Trim: Calculates the angle of attack and elevator deflection necessary to trim the aircraft for a target lift and moment at the given airspeed. To run this analysis, your aircraft must have an elevator and you must have designed it well enough that it is possible to trim it in pitch.
• Distributions: Saves a text file describing the distribution of the forces and moments on the wings and propellers.

Now, as a final word about running an analysis I will say this: MachUp has limits. MachUp is designed to analyze aircraft within the realm of linear aerodynamics. This basically means below stall. So, if you put in an angle of attack of 50 degrees and produce 1,000 lbs of lift on your 2-foot RC aircraft, you have not broken physics. You simply went beyond the range that MachUp can accurately predict. The same applies to things like propellers. You can't swing a 3-foot prop on an FT Power Pack C, so don't try. It won't give you accurate results. 

With that said, if you design an aircraft and set the flight conditions within reasonable operating limits, MachUp will give very accurate results. We've compared the results produced by MachUp to both CFD and wind-tunnel tests and MachUp provides very accurate results in a fraction of the time that either CFD or wind tunnel testing would require. It has been used in a multitude of projects, including designing several advanced UAS systems employed by AggieAir for long-range, remote sensing missions.

So, there you have it. Thats your introduction to MachUp. I hope you enjoyed it and that you will stay tuned for more articles about how to use MachUp. Throughout the whole process of creating MachUp, our goal here at the USU Aerolab has been to put aircraft design into your hands. Now you don't need a PhD to get your hands dirty designing an aircraft. So get out there and make something awesome!

And from all of us in the USU Aerolab, 

Happy Flying!