Summer Lows

One of the problems that I have with learning (as opposed to just memorizing) weather is that it can sometimes be difficult to pick out the principles when looking at the real-world complexity of it all. Take today for example. On the SFC Prog Chart, I see a pretty strong region of lows over the Great Lakes, one off the East Coast, and a couple of weaker systems over the Midwest and West Coast. What’s the first thing we learn about lows? That they draw surrounding air into them, and that the inflow is deflected to the right because of Coriolis effect, causing counter-clockwise circulation around the system. Now take a look at the Visible Satellite loop. The system over the Great Lakes is a decent illustration of what happens around an area of low pressure. But from the perspective of a student just learning, how strong an impression would that low off of the East Coast make?

8-29 SFC Analysis

2 Animation Vis_Satellite_GLAnimation Vis_Satellite_NJ

That’s where I got to thinking about how I’d teach this. Why not pick out an extreme example rather than trying to pick out something lame from the day-to-day weather? Take the weather picture from 4 years ago today–right about the time Hurricane Katrina was making landfall near New Orleans. A hurricane (aka, cyclone) is basically just a low pressure system taken to an extreme. They dominate the weather around them, and it’s easy to see what all a low does by looking at a hurricane. The pressure at the center of a hurricane (usually in the 800-1000 mB range) is well below any of the examples on today’s weather map. The first thing you’ll notice from the Visible Satellite image is the circulation around Katrina: air moves in along the isobars and breaks to the right to create the counter-clockwise swirl. This wind flow pattern is driven by warm, humid air rising from the surface at the center of the low.

From what I hear, stuck-wing drivers like departing out of a low since the rising air improves their climb performance…whether this is relevant for those of us who never climb above 1500 AGL, I couldn’t say. This rising air around a low also drives cloud formation as the moist air is pulled aloft and cools. Once again, Katrina illustrates this to the extreme: the spiraling bands moving toward the eye are lines of cumulus and cumulonimbus clouds. This is where the rule of thumb that bad weather is usually associated with low pressure systems comes from. (Although I’d call bullshit that the opposite is true–that highs mean good weather. I’ll post more on that this winter when there’s a high sitting over the Columbia River Basin, locking us into low IFR and icing conditions.)

So what happens to all the air that is pulled into the low? The rising air erupts out of the top of the low and spreads out from there. Apparently, with a hurricane, how the rising air is drawn away is an important factor in how powerful the storm will be–if the rising air isn’t being drawn off, it acts as a cap on the column of air at the center of the low, weakening the storm. In the upper atmosphere above the low, there is actually a reversal in the circulation. If you look on the northwest corner of the Katrina image, you can actually see this: there are high clouds that are spiralling clockwise. These are cirrus clouds that are formed from from moist air lofted into the upper atmosphere.

Hurricane schematic

Any other thoughts or learning points for teaching about low pressure systems? Add them to the comments–I’ll be setting this up as my first community ground lesson soon.

Third World Helicopters

Remember the Nigerian Helicopter built from old car parts? I recently saw 2 new entries to aviation industry from the developing world. The first is from a Chinese farmer who built his helicopter from wood, a steel frame, and a motorcycle engine. Apparently, the homemade aviation industry is ripping along in China. The Zimbabwian machine looks pretty ambitious. What really struck me about this one was the dual tail rotor assembly. Both of them claim to be flyable, and both make the Mini-500 that I saw a couple of weekends back (with 20-lbs of dumbbells for ballast, sitting on the floor in front of the pedals) look almost airworthy.


I’m not making fun of either of these attempts. I think it speaks to the universal thrill humans get at the idea of leaving the ground behind and seeing the world from above. Would be interesting to see if either of these home-made helicopters are really capable of flight, and whether the designers were able to overcome the many engineering challenges associated with rotary-wing aircraft. The low power-to-weight ratio of piston-driven engines was one of the challenges that kept early helicopters from even getting off the ground, where they would be subject to the aerodynamic challenges of spinning airfoils. Seeing as though these attempts all start with heavy components–like the junked car the Nigerian “inventor” used, or steel and wood blades and structures, it’s hard to believe these could really be getting too high up. Nevertheless, this last one, also from China, not only gets off the ground. If you believe the comments, he’s had it up above ETL. Unlike the first Chinese example, this farmer had help from detailed plans he obtained online.

Part 61 Changes

Wouldn’t you know it, I just found out about several changes to the FARs that might affect the endorsements, and will definitely affect the requirements for the PPLH and CPLH certificates. That’s supposed to be part of the power of a wiki though–that user communities keep the content evergreen. The rules go into effect late in October, and are summarized here [FAR Changes] and in an AOPA article. The duration of student pilot certificate pilot certificates is now the same as a 3rd-class medical. There’s also a change in the definition of cross-country time, although it’s hard to tell from the AOPA write-up how it applies to helicopters. Looks like I’ll have to dig into the regs some to figure that out.

One thing that didn’t change was the requirement for maintaining instrument currency. The FAA had proposed adding a cross-country flight and specific procedures and approaches.

Quick Weight and Balance Calculator Beta Release

Don’t want to read about it? Download the calculator now!

Note: These instructions refer to an older version of this calculator. You can still download it from the above link, and view version 3’s features on the Weight and Balance Calculator B3 release page.

Do you run a weight and balance before every flight? Or do you just guesstimate how much fuel you can carry and assume you’ll be close enough to being in CG? I know guys who don’t do a W&B except for check rides. Not good enough for me. Limitations are limitations, and early in my training I developed worksheets for each helicopter so that I had the baseline CG values for every flight. From there it was easy to add a weather check, and HIGE/HOGE calculations into my pre-flight routine.

Now, there are plenty of these already out there. Maybe your flight school has one. I put some real thought into this though to make it user-friendly and packed with features. First, on the Conditions page, you fill in the red boxes with the basic empty weight and arm data. Password protect the worksheet and nobody can inadvertently alter those values. Next, enter all the variable data into the green boxes: pilot and passenger weight, baggage weight, optional equipment (default is installed), and fuel. After the passengers and baggage weights are entered, the Calculator displays the maximum allowable fuel weight (which may be greater than the fuel capacity). The CG graph is updated automatically with the take-off (solid green) and zero-fuel (open white) conditions. Endurance is based on a an editable burn rate (usually 8-10 gph). This is a quick and clean way for students to see how CoG shifts and changes during flight. By unlocking the red cells, they can develop a better understanding of how weight and arm are related to payload capacity.

Quick Weight and Balance Beta Screen shot

I thought about hiding the calculations page altogether, but as a learning tool it’s great. Your students can complete calculations by hand and then check their calculations there. For a beta version, this is also a good troubleshooting tool.

The student worksheet is meant to be used day-to-day for manual calculations. The graphs, arms, weights, capacities, and limitations are reproduced from my POH, but you must confirm that they are consistent with your aircraft’s POH. All cells are unlocked and the sheet is unprotected so you can enter the data for your aircraft. The rest of it is simply an intuitive template for doing W&B calculations and gathering pre-flight data. It should also print out very nicely.

A few disclaimers. I have tried it with several helicopters and it works fine. They are all Beta IIs though. I also run Windows Vista and Microsoft Office 2007, so I have no idea how the Calculator will work with your system. I do know–and this one’s important kiddies–that you must enable active content and macros. The ultra-histrionic Office 2007 automatically disables these features unless you tell it to enable them. I also locked the worksheet so that you’d have to read the instructions. Getting the unlock is easy, but it does require an active internet connection.

I’d like to see some ideas for practice problems that force students to develop a working knowledge of CG. The calculations themselves are only tedious, but applying them to real-world scenarios is what I’d like to get at. In the screen shot, for example, I have to take 240-lb Bubba on a 1.25-hour flight. Can I do it without him having to leave his boots behind?

Anyway, you can download the Quick Weight and Balance Calculator Beta right here or from the Extras! page. This post, however, is where comments, criticsims, corrections, and suggestions belong.


I want people to be able to come here and comment freely. But, in the beginning anyway, I’m requiring that all comments be approved before posting. If your comment doesn’t show up right away, patience. I’ll get to it.

Wiki Rotorcraft Flight Manual: Ground Zero

I’m sitting around, trying to figure out how I’m going to get from 246 hours of helicopter time to 1000 hours. Networking has never been my strong suite, and I don’t have anybody who’s willing to mentor me through this phase. That means I need to be a flight instructor. For me, personally, this is no problem. Flying is a second career for me, I’ve taught before, and I think it’s great fun and rewarding. Right now though there are 13.2 million CFIs out there, some of who just finished their CFI yesterday. I need a way to stay sharp, and if I’m not working or working on a rating, I just can’t keep up.

I thought I would expand on my otherwise basic lesson plans, and in doing so I came up with an idea. Since I’m on VerticalReference every day, and there are many knowledgeable pilots there, why not draw them in? So I put this post up: Teaching Techniques: Hovering. I thought this could evolve into a great series–the “Teaching Techniques” tag could be a search term that anybody could go back and look at in the future. I thought there’d be enough idle CFIs that it’d get a lot of comments. I even committed to updating the first post based on the comments.

By the time the topic was dead, it got a disappointing 14 comments (3 of them were mine). Hopefully that isn’t foreshadowing…. But it has over 1800 views, which is 2-6 times the views that other posts in the Flight Training forum get. I thought the outcome was pretty useful, although it took me processing people’s experiences and drawing a lot from conversations I had. In the end, I didn’t think it was successful enough to warrant a follow-up.

Well, I came back to the idea after looking into a WordPress blog for another project. Since that project didn’t pan out, I now have time to work on this one. Anyway, check out About Wiki RFM if you want to know why I think this is a good idea and how it works. If you agree that it’s worth it, contribute once I start adding content! Otherwise I’ll just let it join the rest of the electronic jetsam that’s drifting out there. If it takes off, even a little bit, I’ll figure more out about how it should work.