Homebuilders Workshop: Brave New World
Thursday, July 13, 2017 at 5:58PM
Ed Wischmeyer in RV-10, RV-9A, avionics, crosswind components, crosswinds, database cards, glass cockpits, homebuilts

By Ed Wischmeyer

Oh, brave new world… with all the glass cockpits available for homebuilts, these days you can spend hours working on your airplane with only a laptop and high speed Internet, no screwdriver or wrench required. And with the cost of database updates, you can have the $100 hamburger without even having to drive to the airport. Keeping the database cards in a pill bottle makes them harder to lose, at least until that pill bottle plays hide and seek under the car seat.

Yes, I’ve been doing a lot of software update thrashing, hampered by instructions filled with mostly accurate statements and software that can often run correctly. That is, it can run correctly. And yes, I screwed up a bit too by not reading the screens carefully enough. My error, but as often happens with pilot error, I had help with inconsistent screen layouts.

One potential problem is that if you use an SD card that’s too big, it can cause problems, so I went and bought a pair of eight GB cards. At least I’m not working with early glass that can’t recognize an SD card bigger than two GB.

• • • • •

Best answer of the year: somebody asked an Air Force fighter pilot if he’d been to Iraq. “Not on the ground,” he said.

• • • • •

This past week has had unusual weather in coastal Georgia. It has been cooler and drier than seasonal (yea!) and really windy (boo!). We had another day with winds from the southeast at 20G30, which is to say, 45 degrees to both runways at my airport. If that same wind was from the southwest, I could align with a taxiway and land across one of the runways, but from the southeast…

Here’s a cute rule of thumb for figuring out crosswind components. In my youth, trig tables and I were great friends, and I’d do the calculations in my head, but now that I’m old and gray… or is it’s old and grey…

Take the angle of the wind to the runway and divide by 10. Then multiply that times the wind speed and divide by six. To make it a little more visual:

Approximation  Formula                       Error

10 degrees -> 1 -> 1/6 * wind speed     0

20 degrees -> 2 -> 2/6 * wind speed   -1%

30 degrees -> 3 -> 3/6 * wind speed    0

40 degrees -> 4 -> 4/6 * wind speed    2%

50 degrees -> 5 -> 5/6 * wind speed    7%

60 degrees -> 6 -> 6/6 * wind speed   13%

70 degrees, use full wind speed     6%

80 degrees, use full wind speed     2%

90 degrees, use full wind speed     0

No, I didn’t think this one up, but it’s pretty cute, and surprisingly accurate, probably as accurate as the reported winds. For you spam-can drivers, remember that the published crosswind is the maximum demonstrated crosswind component, most often 17 knots (20 mph). For you homebuilders, there is no crosswind limitation; it’s whatever you think you can do, depending upon skill, landing gear alignment, and who knows whether you got your databases to download correctly. 

Another neat rule of thumb is for converting temperatures from Fahrenheit to Celsius. The real formula is Degrees C = (degrees F – 32) * 5/9. The easy way is Degrees C = (degrees F – 30) * 1/2. The reverse is Degrees F = (2 * Degrees C) + 30. This is close enough for room temperatures. And just remember that -40 is the same in both.

Nope, I didn’t think that one up either, but it is slick.

• • • • •

Two weeks before my 50th high school reunion, the weather risk was high of not being able to fly myself there, and driving was not a feasible option – too far. So I made a reservation on the airlines. While there, I talked with a buddy who used to fly and loved it but gave it up because he wasn’t using the airplane enough. I chided him gently that he was limiting his Cessna 210 to transportation and not thinking of it as entertainment.

Those thoughts came roaring back when I was pondering the recent, occasionally IFR, trip to Virginia in the RV-9A. With a surgically stiffened back, it’s a pain to unload the baggage area, and the RV-9A pitches and rolls in turbulence, likely a combination of only moderate-wing loading and an airfoil that changes lift significantly with only modest changes in angle of attack. An RV-10 would, I’m told, not be much better, although it would be easier to load and to climb in and out of.

However, a well-equipped four-seat RV-10 can easily cost $200K, lots more than an old retractable gear airplane. The spam-can and would cost more to insure and maintain and would not be able to carry some of the neat experimental avionics (which I’ve mostly mastered, but which still drive me nuts sometimes), and when time came to sell, both would have held their value. Translation: the spam-can costs lots more to operate, and you won’t get those operating costs back.

But I still think of the RV-9A as transportation…



Article originally appeared on In Flight USA (http://www.inflightusa.com/).
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