Quick reminder. Check your user data location setting! It’s found under
My Account -> Edit -> User Information -> User Data Location

I came across a member whose e-mail address was something like joe@ohioelectricpower.com and was using a user data location of Europe. Not good! Not only is the user data stored there, but the calculator and tutorials are downloaded from that location, too. You make a wrong choice, and the load speed for the calculator and tutorials is cut in half. Ouch!

I had lunch with a friend about a month ago. Having some opinions on the subject, he asked me what software bug tracking application I was using. I said that I wasn’t using any. Surprised, he then asked me how I was keeping track of the bugs I hadn’t fixed yet. I said that I didn’t have any.

Since the day I launched the website, I’ve had a strict ‘zero bug tolerance’ policy. The minute I learn that the software is not working as I intended, I drop everything I’m doing and don’t rest until the problem is resolved.

‘Resolved’ can mean many different things. It usually means that the bug is fixed and gone forever. But it can also mean that I’ve done everything that I can and it’s not fixable because I either don’t have enough information or it’s totally out of my control. These cases are rare and my policy is to document everything that I know about the problem in an FAQ right away. That is why it is so important to check the FAQs when you are having a problem.

Note that about 95% of these bugs I find myself before a software release. I use my calculator regularly to answer questions about my model airplanes. (I started writing the software in the first place when I discovered that there were no model airplane calculators available that could even begin to do the computations that I wanted to do.) I also regularly test it under Windows, Linux, Internet Explorer, Mozilla Firefox, Opera and Safari.

A much better question from my friend would have been to ask what I use to keep track of my to-do list. Well, I don’t really keep track of small changes that I want to make. You see, I take care of those right away, too.

I’m constantly making changes to the software and testing them. I’m never more than an hour or two away from having a version of the calculator that I could release. If the change is important enough, I do. It is not unusual for me to make 3 or more releases in one week.

I do have a notebook by my computer that I’m constantly writing into. This is where I write down ideas, figure out how I want something to look or work, and generally take notes as I work.

Why am I telling you all of this? Because if you think that something is not quite right, I want to hear about it. Don’t assume that it’s a bug that I haven’t gotten around to fixing yet. It’s not!

The case may be that my intention is not clear enough. That happens a lot - this is a global product with a global audience. I have many registered users from Australia and Europe, for example. In these cases I do my best to explain it to you and then I make changes to the calculator to help the next user.

But it could also be that either you are doing something with the calculator that I didn’t anticipate or you’ve discovered a real problem that I didn’t run into in my testing. Thankfully, these cases have been pretty rare so far. Either way, I want to hear from you. I’m bound to run into the same problem myself eventually, but it’ll get fixed or changed much sooner if you take a couple of minutes to tell me about it.

One of the units in the calculator is not, shall we say, kosher. You won’t find it mentioned in any serious engineering textbooks. I did not make it up, and the conversion factor is accurate. But let’s just say that it is of limited practical value.

Have you found it?

To add a new component, just edit the name and press the Enter key. There is ToolTipA ToolTip is a small text box that appears when the mouse pointer is hovered over a screen object. The box disappears when the mouse pointer is moved away from the object or after a specified period of time, usually a few seconds. help for this, but if an error message is being displayed then you won’t see the ToolTip. The help ToolTip is always available while you are typing in the new name.

I’m working on a very nice 5 minute quick introductory tutorial that will cover this. The tutorial will be online (using Flash, of course!) and interactive.

As a side note, the calculator and website are being continuously updated. I may send out the newsletter only once a month, but I’ve already had a couple of updates of the calculator in the last week. There is also a very nice new banner at the top of the web pages, in case anybody hadn’t noticed.

Suppose you are looking for a good airfoil for an indoor tailless model. Go to the airfoil calculator, set the Reynolds number to 20k, set the angle of attack to 5 degrees, and make sure the chart is not going to be updating with every edit. A good choice would be one of the Scale charts.

Now, click and select the first airfoil that you want to examine. You’ll see the Cl, Cd and Cm values for it quickly updated. Press the down arrow on the keyboard. The next airfoil will be selected, and since the chart does not need to update, it happens almost instantly.

Using this technique, you can iterate through all the components very quickly, easily identifying candidates worthy of further study.

Analyzing the performance characteristics of an airfoil, specially at very low Reynolds or high Mach numbers, is hard. It is computationally expensive and requires an expert analyst to review the results to make sure the computations are valid. For the airfoil computations, I use the well-respected XFoil software. Analyzing one airfoil and compressing down the data takes my dual core workstation hours. At the present time, it is simply not practical to include these computations in the calculator. I’m in the process of building a library of airfoils to include in the calculator. Do you have a favorite? Let me know!

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%.