AIR WAVES

Model Airplane News, May 2004

SOARING WITH GAS EAGLES

I was very impressed by your April 2004 issue with the Great Planes Christen Eagle II biplane on the cover. My wife gave me one for Christmas, and I'm thinking about using a gasoline engine for power. The author, John Reid, made it sound as though the Fuji 50cc engine is a good choice. Is there anything else you can add to what he has already said about this engine? I have only basic experience with gas engines and need all the help I can get. Thanks.

Bill Paez,

Detroit, MI

Bill, the Fuji 50 engine is a good match for the new Christen Eagle, and it fits nicely in that big cowl. The main thing about gas engines is that you must securely attach them to the firewall and use good-quality hardware. Use ¼-20 stainless-steel bolts and plenty of thread-locking compound. Gas engines tend to produce more vibration than glow engines, so it is important that they're securely attached. Also, make sure you properly balance the prop. Install a kill-switch to positively shut off your engine so it can't be started accidentally. After every flight, thoroughly inspect your engine as well as the rest of the model. Have fun with your new gas-powered Christen Eagle! GY

TWO BATTERIES BETTER THAN ONE?

I would like to use two receiver battery packs (and two switches) in my plane for a redundant setup. I have 9 servos, but I am not sure which battery capacity to use. Also, should I use 4- or 5-cell battery packs? I have heard all the pro's and cons from several of my club members. What do you suggest?

Alfred Johnson,

MSgt. USAF (Ret.) [email]

Alfred, for most of my models, I simply use a 4-cell, high-capacity battery (1800 to 2000mAh), and I use a heavy-duty switch harness from JR. I have a field charger and I top off my packs before every flight. With some of my big stuff, I have used two 5-cell, 1200mAh Ni-Cd battery packs (with two separate switches), and this setup has performed well. Running 6V battery packs does give more servo speed, but the packs will also be drained a bit faster than 4-cell packs because of the increased voltage. When you connect two complete battery systems to a receiver (one in the battery port and the other in an auxiliary channel), you basically connect the two in parallel and combine their capacities, while the voltage remains the same. As a rule, use only battery packs of the same voltage and capacity when you install a redundant system. For insurance, it is important to properly maintain your equipment and cycle your packs on a regular basis. Don't gamble: one well-maintained pack is better than two old or questionable ones. GY

HEAVY METAL?

Looking through the latest issue, I found this glaring mistake. On page 112, in the article "Scale Techniques: Working with Aluminum" by Dick van Mourik, the material-about 0.256 and 0.128 inch thick, as quoted in the text-seems a bit on the thick side! I think the decimal is in the wrong place. It should probably be 0.0128 and 0.0256. Other than that, I enjoyed the column.

Jerry Smith,

Acworth, GA

Jerry, yes, you are correct! Those darn decimal points jumped over one too many places; ¼-to 1/8-inch aluminum would indeed be too thick for forming cowls-unless, of course, we're talking about full-size aircraft! Thanks for pointing out the error! GY

HOVER STICK

I read with interest your GWS Slow Stick hop-up article in the March issue. It shows a picture of a gearbox for the Mega brushless motor you used that looks very light. Where did you get that gearbox? I need a gearbox with a 2:1 or 2.5:1 ratio for a Mega 16/15/5 brushless motor that I plan to install in a scale FW-190 that will weigh around 25 ounces. Because it's a warbird, I am trying to keep it as light as I can for a great performance. Thanks for your help.

Moses Huang

[email]

Moses, the gearbox I used is actually two parts: the gearbox itself and a mount for the motor. I obtained the gearbox from Mega Motor USA (megamotorusa.com), and it's screwed directly to the motor. Its gear ratio is 2.8:1, which is very close to the 2.5:1 ratio that you're looking for. The motor mount is a GWS item (no. EMM400T) from e-flightline.com. It is made to slide onto a stick, and a rubber band holds it in place. Good luck with your Focke-Wulf, and send us a picture or two for "Pilot Projects" when you've completed it.