Airwaves

CHOPPER CONTROL

Great timing on your July 2002 "Almost-Ready-toFly Heli Guide"! I've been thinking about getting into helicopters, and the article provided a lot of useful information. I noticed in the chart that it says the Century Helicopter Raven uses CCPM for the control system. What is CCPM in a helicopter? [email]

DAVID NEFF

David, glad to hear you enjoyed the article; thanks for the feedback. CCPM stands for cyclic/collective pitch mixing, and it offers a control system that is more precise, has more power and is less complex than a standard oneservo control system. Just like the one-servo system, CCPM uses three servos for the three main controls: roll, elevator and collective. The lower swashplate on a standard system has four balls that are set 90 degrees apart, and most CCPM systems use three balls set 120 degrees apart.

The difference between standard and CCPM systems is in the way the servos work the swashplate. In a standard system, one servo works one control input; in CCPM, all three servos work together to achieve the same results. For example, if an elevator input is given, all three servos work together to move the swashplate fore and aft. In a standard system, only one servo moves the swashplate fore and aft. With two or more servos working together, servo torque is maximized. CCPM also eliminates the need for complex mechanical mixing, which requires many more parts.

CCPM mixing is achieved through the programming that's in many of today's helicopter radio systems. Though it sounds complex, CCPM is pretty simple to set up. In fact, because CCPM uses so few parts, building and maintaining a CCPM heli has become very easy. Take the heli plunge, David, and have fun!

FUELIN' AROUND

I don't know whether you can help, but I am just getting back into the RC hobby and would like to make some fuel. My problem is finding the nitromethane. I used to get it from a speed shop in New Jersey, but I can't seem to find any in the Pennsylvania mountains where I live now. I would like to get at least one gallon, just to add to fuel and test small amounts of home brew. Any information you might have would be great.

Another question: I picked up a case of K&B 100 in gallon cans that still look good.

Do you think the fuel is still usable? Anything I should look for? Thanks! [email]

DON

These days, I get my nitromethane from Klotz Special Formula Products, (800) 242-0489. The Klotz folks sell nitro and other common fuel components via mail order.

If the K&B 100 cans have been tightly sealed, the fuel should be OK. To check it, pour some into a clear glass jar and look at it; it should be a light amber color with no solid flakes in the mix (nothing that looks like crumbled white crackers!). Flakes such as these are castor-oil lubricant that has precipitated from the suspension with the other fuel components. Although not usually a good sign for the fuel's viability (castor often becomes rancid), some experts claim that the flakes will dissolve if you allow the fuel container to sit in the sun for a while.

If the fuel has turned dark brown or viscous (thick), one or more of the ingredients has deteriorated, and the mixture is useless.

DAVE GIERKE

BALANCING ACT

The letter from Bill Trueblood about Gerry Yarrish's "Thinking Big" column on biplanes in the June 2002 "Airwaves" prompted me to send this letter.

About four years ago, I built a WACO model E biplane from an old Sterling kit and installed the recommended engine-a .40 K&B. The kit was originally designed for U-control, but I installed RC instead. The airplane flew very poorly; it was very erratic, and no amount of trimming made it fly with any stability. After three engines and all kinds of changes, I gave up and stowed it in the garage.

After reading the article specially the reference to determining the CG-I dragged the WACO out and checked its CG in accordance with the article computations and compared it with the plan. I found a difference of 1 1/4 inches, in a tailheavy direction! I checked the results a couple of times and found that this new CG was accurate, according to the article.

I installed my O.S. .70S 4-stroke and 3 1/2 ounces of lead in the nose to match the CG computed in the article. The results were spectacular! It flew hands-off on the test flight and has become a totally enjoyable airplane to fly. Thanks for the good information.

RICHARD EIMERT

Monsey, NY

Glad to be of help, Richard. CG is something that has always mystified modelers, and you can't always trust what's listed on the plan or in the kit. Having a good formula that you know will work is the best way to make sure that your model is properly balanced. A balanced airplane will fly just great.

Copyright Air Age Publishing Aug 2002
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