A farewell to James Linder
Greg Gimlick | [email protected]
It's hard to think of Christmas when it's the end of August and the temps here in North Carolina have been hovering in the high 90s or at 100° for the last couple weeks. Then again, it's refreshing to think that it will be much cooler by the time you read this.
I hope everyone has a great holiday season and that the new year brings you all the toys that make life so much fun. Thanks for your support this year; I hope we have another great one.
Farewell to a Friend
A while back I mentioned working on an Approach Engineering Cobra conversion kit for my Swift helicopter. James Linder founded Approach Engineering in Utah, and I'm extremely sad to report that he was killed in August in an Apache crash.
James was a full-time instructor pilot for the Utah National Guard and, more importantly, a loving husband, father, and good friend to many people. He and I were collaborating on adapting his new Apache kit to fit the Quick QJ-10 airframe I had just sent him. He was a talented designer and an incredibly smart engineer by trade. I'm at a loss for how to express my feelings to his family and the rest of his friends. I hope someone will buy his kit line and continue it, but there is no way to make up for the loss of James and his friendship.
On the Soapbox
I want to remind everyone about the purpose of the last few "Electrics" columns and the lessons within. They were intended to be guidelines showing how to plan a power system.
I've taken some heat for the August issue, in which I showed how to figure out amp minutes and divide by current, etc., to make decisions regarding duration. Some readers took me to task for planning on discharging Li-Poly batteries to their full capacity. Those were exercises to show you how to do the calculations without regard to efficiency, battery type, etc. I thought I made that clear, but apparently not. I am not advocating complete discharge. It's all relative in planning, though; if you get more duration from one setup than another, it will still be so when you figure in efficiency or reduce the discharge to 70% of capacity. The purpose is to understand the steps involved.
Electric Airplane Performance-Simulation Programs
One thing is without question in my mind: owning one of the simulation programs will save you more money than it costs in the long run and teach you more than you will learn in hours surfing the Internet. Are they perfect? No, but they are a lot more accurate than you will be with your pencil, paper, and calculator. These programs contain databases and algorithms to consider all the parameters and can be updated with ease. I believe that the top two programs are ElectriCalc and MotoCalc. I'm going to touch on each of them briefly this month and next, but I won't pretend to do them justice since that would require a full feature article for each.
MotoCalc (Mcalc)
MotoCalc is the brainchild of Stefan Vorkoetter of Capable Computing, Inc. He has been around the electric-flight world for a long time and can be found on many RCGroups forums.
Right off the bat you'll appreciate the web support the company provides for this simulation. You can download a full-featured version for a trial period before you buy it, so there's no risk.
MotoCalc has often been described as difficult to learn, and it probably does have a slightly steeper learning curve than ElectriCalc for a beginner. Don't let that influence your decision, though, until you've gone through the tutorials, both online and off.
The tutorials will carry you step by step through the whole planning process. Most questions I've gotten about MotoCalc through the years could have been answered had the user taken some time to read the manual or try the tutorials. They will teach you more than any book on the market.
When you open the program you're greeted with a "tip window"; it's wise to keep that activated while you learn your way. The MotoWizard window is the place to start if you're learning MotoCalc. It will take you through the setup step by step.
I plugged in a Sig LT-25 and made choices along the way as it worked across the screen. Following are the steps and selections I entered:
- Performance: Sport
- Model: Wingspan, area, and weight without motor, battery, and ESC
- Airfoil type: Basic info such as flat-bottomed, semi-symmetrical, etc.
- Thickness: You are given diagrams and you pick thin, fat, etc.
- Field: Elevation; I left it at sea level.
- Motor: Your choice; brushless, brushed, either. I chose brushless.
- Gear & Prop: I chose direct or geared and a maximum propeller size of 14 x 10.
- Battery: You can choose "any" and let it pick, but I selected A123 cells in a six-cell pack.
- Results: You will be given a list of motors to select from with ratings to let you know MotoCalc’s best choice. I chose the recommendation of a Neu 2215/1.5Y.
When you complete these steps and hit "Accept," the program will take you to the main window. From there you can select "Compute Report" and you’ll be presented with a window full of information.
This is where many people get confused and discouraged, but there is a not-so-hidden gem you’ll learn to love: the "Opinion" button. When you hit this you’ll be presented with an easy-to-read opinion of your setup. Following was my result.
MotoOpinion — Sig LT-25
Sea Level, 29.92 inHg, 59°F
Motor: Neu 2215/1.5Y BAM; 1020 rpm/V; 6.1 A no-load; 0.004 Ohms. Battery: A123 ANR26650 M1 (30C); 6 cells; 2300 mAh @ 3.3V; 0.01 Ohms/cell. Speed Control: Castle Creations Phoenix 60; 0.0012 Ohms; High rate. Drive System: Generic 14x9 in Prop w/2.5:1 Gearbox; 14x9 (Pconst=1.17; Tconst=1) geared 2.5:1 (Ieff=92%). Airframe: Sig LT-25; 724 sq. in.; 104.8 oz RTF; 20.8 oz/sq. ft; Cld=0.059; Clmax=1.06; Cl2=-0.07; Cdo=0.027; Cl/CDmax=1.24. Stats: 83 W/lb in ???; 21 mph stall; 29 mph opt @ 57% ... (full numeric display shown in program).
Possible Power System Problems:
- The full-throttle motor current at the best lift-to-drag ratio airspeed (31.6 A) is lower than the motor’s maximum efficiency current (81.8 A). A higher current level would improve system efficiency.
- Current can be increased by using more cells, a larger diameter or higher pitched propeller, a lower gear ratio, or some combination of these methods.
Power System Notes:
- The voltage (16.6 V) exceeds 12 V. Be sure the speed control is rated for at least the number of cells specified above.
Aerodynamic Notes:
- The static pitch speed (57 mph) is within the range of approximately 2.5 to 3 times the model’s stall speed (21 mph), which is considered ideal for good performance.
- With a wing loading of 20.8 oz/sq. ft, a model of this size will have trainer-like flying characteristics. It would make an ideal trainer, for use in calm to light wind conditions.
- The static thrust (94.7 oz) to weight (104.8 oz) ratio is 0.9:1, which will result in very short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and steep climb-outs.
At the best lift-to-drag ratio airspeed, the excess-thrust (58.6 oz) to weight (104.8 oz) ratio is 0.56:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver.
General Notes:
- This analysis is based on calculations that take motor heating effects into account.
- These calculations are based on mathematical models that may not account for all limitations of the components used. Always consult the power system component manufacturers to ensure that no limits (current, rpm, etc.) are being exceeded.
This should be enough to get you over the initial hump of looking at the opening screens and wondering what to do next. From this point you can tweak the setups by changing all of the parameters you see across the display. You can set up filters to assess only propellers within a certain range or gear ratios, etc. It’s extremely versatile.
You can hit the "Opinion" button anytime you don’t fully understand the results, and it will spit out a report, as shown, along with recommendations.
I’ve mentioned before that data-gathering tools are essential if you want to get into tweaking and experimenting with electrics. I’ve been using the Micro Power from Eagle Tree Systems, and it does everything most modelers will want to do.
I recently obtained the Seagull system from Eagle Tree complete with wireless data transfer. This is the pro-level unit, and now I can monitor the two motors I have ganged to an Inner Demon gearbox in my giant-scale Pitts. A full article about this incredible system is to come!
I hate that space has run out. Next time I will look at ElectriCalc and how to get going with it. Again, all electric-power fliers should own at least one of these programs, especially as they’re learning. If you don’t want to play engineer, you don’t have to — just copy someone else and have fun at the field.
MA
Sources
- MotoCalc
(519) 638-5470 www.motocalc.com
Transcribed from original scans by AI. Minor OCR errors may remain.
