I just released the first major update of the interactive tutorials since they were originally released four months ago. As I reworked and added to the tutorials, I carefully thought about what I could do to make the calculator easier to use. All of the calculator changes that I’ve released in the last couple of weeks have been as a result of this process.

There are changes in every slide, with two major additions. First, I added a quiz to test your knowledge of the calculator and website. After the quiz is over, you can go back and learn the correct answer to any questions you may have gotten wrong. Right now the quiz is just for fun.

But by far the biggest new feature is a brand new step-by-step example of optimizing a power system. This tutorial is almost as long as all the other tutorials combined, and it doubled the size of the tutorial flash file to 2MB. My goal was to answer every question that might come up during the optimization process.

The propeller calculator uses the behavior of an airfoil to help predict the behavior of the propeller as a whole. Gas propellers use the Clark Y 15%, the other propeller types use MH 116. That is the reason why those two airfoils are preloaded and available with Mach data.
All of the airfoil performance data has been calculated using XFoil. XFoil is a great program, but learning to use it is not easy and learning how to get good results from it is much harder still. The results that I had gotten from XFoil for these two airfoils were not very smooth, and in turn it made the power system graphs not very smooth, either. I had accepted it as a fact of life.
I recently went back and revisited my approach for calculating the airfoil data. After carefully thinking about the problem, I came up with an improved method to get results from XFoil. I just released a new version of the calculator with the improved airfoil polars. I find them much improved.

The Data Server setting controls which Content Distribution Network (CDN) is used in connection with your account. A CDN is a network of servers that behave as one very fast server. When a data transfer request is made, the server that is physically closest to you is automatically chosen. Data updates are transparently mirrored throughout the rest of the CDN.

RCadvisor uses two CDNs behind the scenes to speed-up file transfers. One CDN is in the United States and the other in Europe. Large files such as the calculator, tutorials and airfoils database are downloaded from the chosen CDN. Your user data is also stored in the CDN that you selected.

The features available to you are identical regardless of which CDN is selected. This setting is totally unrelated to the Imperial/Metric unit setting. You can also change this selection at anytime through your account settings. But keep in mind that your saved data is not mirrored across networks. Data that was saved in the United States CDN will not be visible if you change the setting to use the Europe CDN.

Picking the ‘wrong’ location will probably make large file downloads (such as running the calculator) go at less than half the speed. If you live outside these two locations, such as Australia or New Zealand, I suspect that the United States CDN will work better for you.

After much work, feedback from the beta testers, and endless revisions, the tutorials are finally ready. To get to them, click the menu item above. They are designed to quickly and easily answer all of the common questions that arise while using the calculator. The feedback so far has been very positive - the reviewers found them very easy to follow and understand.

I’m replacing the Survey with the Tutorials. Several of you took the time to fill out the Survey and I got some very good feedback. Thanks! From now on, please feel free to use the Contact Form to get in touch with me and share your opinion.

Of all the power system components, the propeller has the most potential for creating a disastrous situation. For example, it is almost impossible to run a motor at only 5% efficiency, but it is not too hard to do the same with a propeller.
Here are some quick guidelines for helping you avoid such disasters:

• Maximize the diameter of the propeller. The larger the diameter, the more efficiently the propeller will operate. Think helicopter (large propeller). For an airplane with a landing gear, this diameter will be limited by the clearance required.
• Match the propeller maximum efficiency to the desired flying speed. The propeller pitch and RPMRevolutions per minute. determine the airspeed where maximum efficiency is reached.
• Make sure the propeller is a good match for the motor. This means not overloading the motor and running the motor at an RPM where is it efficient.

Meeting all of these constraints while maximizing the efficiency of the propeller is hard. That is where software like the calculator can really help. There is no excuse for the cruise speed to have a propeller efficiency less than 50%.

Each tab in the calculator is a separate editor (with the exception of the last tab, Account). Each editor is independent from every other editor. For example, the motor editor analyzes the motor by itself. In other words, there is no propeller attached and a constant voltage/current is simulated. What is the value of analyzing a motor by itself? It lets you isolate the performance characteristics of that motor. It is then much easier to compare two motors and to easily see how the motor behaves across its entire operating envelope.

ToolTips are your friend. Hovering your mouse over the fields will display help about it. When a field glows red, hovering your mouse will display the error message. The propeller editor will glow the propeller name field when there are concerns that relate to the entire component. This will be expanded shortly to include the other editors.

The charts are updated in real time. If the selected chart is for a power system and the data for the propeller in that power system is edited, the chart will update to reflect the new data. The charts also update in real time as the Knobs are moved. It is amazing what one learns by doing this. Give it a try!

The power system efficiency is the product of the efficiencies of every power-related component. If the battery is operating at 75% efficiency and the motor is operating at 75% efficiency, I can guarantee you that the overall power system is operating at no more than 56.25% (0.75*0.75) efficiency. I can also guarantee you that it will be less than that! That is why it is so important for every component to pull its own weight, so to speak. If a single power system component is at 50% efficiency, it’s going cut in half the overall power system efficiency.

By definition, the efficiency of a propeller is zero when the forward speed is zero. It’s a little hard to understand why it has to be this way. Let me try and explain.

Imagine a 1,000 pound cement block that is bolted down to the floor. You push and push on it with all your force. If you’re built anything like me, the block will not budge. Despite all the energy you’ve expended in trying to move it, you have nothing to show for your efforts. You’ve accomplished no useful work.

A propeller works the same way. It can turn as fast as it wants and cause a great deal of air to move, but if there is no forward movement, there is no ‘useful’ work accomplished. The goal of an airplane propeller is to pull the airplane forward – not to cause a pleasant breeze or a lot of noise.

The efficiency of a system is measured by its ability to convert energy into useful work. That is the key to understanding this. Since without forward motion there is no useful work being accomplished, by definition, the efficiency of the propeller has to be zero. In turn, since the overall power system efficiency is the product of the efficiency of every power-related component, it too has to be equal to zero.