Capable Computing Inc.: MotoCalc

Model Airplane News, Oct 2002 by Gimlick, Greg

MODEL AIRPLANE NEWS

PRODUCT REVIEW

Removing the guesswork from electric flight setups

Modelers know that they need tools to practice their craft. This Includes the usual selection of hand tools that has been around for decades, but electric fliers should also learn the value of a good performance simulator. Simulators for electric-flight equipment have really come Into their own in the last few years. One such program Is Capable Computing Inc.'s MotoCalc. It Is one of the more detailed of these programs, and with the right input, It can really save you time, money and frustration as you select the perfect combination of model and equipment to produce the flight characteristics you're looking for. Sure, you can do the same task with a calculator and a lot of formulas, but MotoCalc makes it much easier and will translate the results into simple language, if you wish.

This is a full-featured performance simulator, and as such, it has a slightly steeper learning curve than some, but I find the additional features to be well worth the effort to master the program. A particularly nice feature of MotoCalc is that a fully functional trial version can be downloaded from www.motocalc.com. If you decide you like it, you can register and pay for it online. It will run for about 30 days before you must decide whether to buy it, but considering the time, money and aggravation it saves you, you'll wonder why you didn't buy it sooner.

WHERE DO I START?

If you are brand new to electrics, it can be intimidating to look at a screen full of unfamiliar inputs. MotoCalc has a "MotoWizard" help feature that guides you through it all, and I suggest you use it to help familiarize yourself with the program, even if you have used another program, such as ElectriCalc. When you start MotoCalc with the Wizard activated, it brings up the screen shown in Figure 1. I'm going to use my Cavazos Vortex SP airplane as the subject in this simulation. I enter the name of the model and select "1 Motor." Pretty easy so far, right? If you want to use a plane that's already in the database, you can hit the button that says, "Copy Plane from MotoCalc Window." Hit "Next," and the performance window pops up and asks what your performance and duration expectations are for the plane. Hit "Next," and the third screen (Figure 2) appears. Enter the wingspan, area and approximate weight without the motor, battery pack and speed control. This confuses a lot of folks, but it makes sense if you want to change setups in the program. The airframe's weight always remains the same, but the weight of equipment varies. By entering the weight of airframe and radio only at this stage, the final flying weight is adjusted automatically when you change power systems in the simulation. The next two screens concern the airfoil type and thickness, but don't let that intimidate you. The Wizard just wants you to select the style (under-cambered, for example) and the relative thickness (Figures 3 and 4). I'll discuss this more later, but for now, just choose what looks like your wing's cross-section.

The screen labeled "Field" gives the program some environmental data to adjust its calculations. If you live near an airport, you can easily check out the elevation of your area by calling the fixed-base operator; otherwise, you can check a map or just guess. This data helps the program adjust for atmospheric influences on performance.

The "Options" window lets you specify some motor parameters or let the program select them. Since I know I'm going to use an Aveox 1406-2Y direct drive in my Vortex, I selected "direct drive only," "brushless only," "Aveox" and "at most 8 cells." I like this window because it allows you to plug in a system that you have on the shelf and see how it will work.

"BUT IT'S THE WRONG MOTOR!"

The program recommended an Aveox 1015/1.5Y motor on 7 cells to swing a 7.5x5 prop. I'm using a 1406/2Y motor, so what do we do now? Don't panic; you don't have to buy a new motor just yet! Of course, if you haven't bought a drive system, this will give you a good recommendation about which one to buy. But to specify the motor I want to use, I hit the "Copy Result to MotoCalc Window." The main screen pops up with all the data the program selected. Since I know I want the 1406 motor, I just go to the motor section and choose "Open." The pop-up window (Figure 5) shows a list of motors; I highlight the 1406. Click "OK," and the info will replace the old info in the main window. Figure 6 shows the main screen with all the changes made to reflect the equipment I have for the Vortex. The battery, prop and speed control changes are done the same way as the motor. I have some old 1400SCR cells and a folding 6x6 prop, so I simply selected them from their respective lists.

ACCURACY MATTERS

Before I hit the "Compute" button, I want to make everything as accurate as possible. In the information that comes with the Vortex SP, it says that it uses a thinned RG-14 airfoil. I may not know what that means for my performance, but I do know that it will make the projection more accurate if I can enter the information. It's specific and will replace the estimations I made previously in the airfoil windows. At the top of the main menu line is a button for "Airframe," and under that pull-down menu is a selection for "Coefficient Calculator." Selecting that brings me to the window seen in the Figure 7 screen.