Air Waves

* ARE ½A ENGINES HISTORY?

I was an avid RC modeler and Model Airplane News reader about 10 years ago. Recently, I decided to get back into the hobby by building a backyard flyer, maybe a .020- or .049-size model. Cox ½A glow engines were always popular, but I can't seem to find them anymore. The hobby shops in my area don't have them, and my Web search was unsuccessful. I purchased Model Airplane News and Backyard Flyer and couldn't find any ads for ½A engines. I'm finding a lot of useful information, but Backyard Flyer seems to cover mostly electrics. Did something happen in the last 10 years to make small glow engines history?

BRIAN MONGOLD [EMAIL]

Welcome back, Brian! Yes, a lot has changed in the last 10 years (mostly for the better) in the RC hobby. Fortunately, the Cox brand is alive and well. Cox still produces its line of glow engines, from the tiny Tee Dee .010 to the Tee Dee .09 and a variety of others. Check the company's website: coxmodels.com. Cox has also branched out Into glow and electric RC planes and, in fact, we reviewed its Micro Warbird series in our March issue; take a look!

New battery technology, more efficient motors and extremely small, light servos and receivers have given electric-powered models incredible performance that equals or surpasses that of glow-powered models. This segment of the hobby has grown enormously in the past few years. Backyard Flyer is your best source for the latest in electric-flight technology. The choice is yours-glow or electric. - KR

* WHAT'S A TIP-STALL?

Whenever I read Model Airplane News, I notice that several of your writers refer to "tip-stalls" in their articles. What exactly is a tip-stall? I also fly full-scale aircraft, and I never heard this term until I got into RC flying. Most aircraft wings are designed to stall from the wing root out to maintain aileron control. Thanks for helping me to understand this term.

MARVIN LUEBBERT [EMAIL]

Marvin, you are on the right track. I am also a full-scale pilot and instructor, and I believe that the term "tip-stall" is rarefy heard because most commercial aircraft are designed to avoid this condition. The wing design affects its lift, drag and stall characteristics. A rectangular wing stalls at the root first; thus, the ailerons are effective at high angles of attack. An elliptical or moderately tapered wing's stall progression is distributed evenly throughout the length of the wing. This type of wing will lose aileron effectiveness during a stall. Highly tapered wings will stall near the tip first, thereby resulting in loss of aileron effectiveness and a tendency to drop a wing. This is a tip-stall, and it can lead to a spin or a snap roll. Unfortunately, the rectangular wing's lift and drag distribution makes it suitable only for slow-flying aircraft (such as the Piper Cherokee with the "Hershey's bar" wing). Elliptical and tapered wings provide good high-speed flight and rolling characteristics, and designers use various means to reduce the tendency for tipstalling. For acrobatic aircraft, the tapered wing provides a higher roll rate and more axial roll than that of a rectangular wing. Also, many acrobatic maneuvers make use of the stall characteristics of the tapered wing. Snap rolls and spins are easily started and stopped at the desired point. An airplane with a rectangular wing will not enter a snap roll cleanly, if at all, and the recovery occurs some time after the controls are released; this makes precision aerobatic flight more difficult. When model airplane reviewers refer to an aircraft's tendency to "tip-stall," they mean that the aircraft inadvertently enters a spin or snap roll, such as when performing a tight turn or pulling up-elevator to enter a loop. A plane with a severe tendency to tip-stall is not fun to fly because any slight misapplication of elevator or rudder can result in a snap roll. An unexpected snap roll during your takeoff or landing approach will certainly get your attention! -KR

* ELECTRIC VS. GLOW HELIS

I am contemplating getting into RC helicopters, so your review of the Megatech Horse-Fly was timely for me. I've been flying fixed-wing planes for about 15 years, mostly .40 to .90 sizes. My question is: is it better to start with a glow-powered heli or the HorseFly? There aren't many heli fliers in my club, and those I've asked have no experience with small electric helis. Thanks for your help.

HENRY DUNBAR [EMAIL]

Henry, we're glad to see that you're interested in joining the ranks of heli fliers. Learning to fly a helicopter is a challenge, but it will also give you a sense of accomplishment. If you just want to get your feet wet and are not certain that helis are for you, the Horse-Fly is the way to go. A .30-size glow heli will cost at least three times more. The Horse-fly requires no setup, and the inherent stability of its coaxial dual rotors will greatly reduce your learning curve. It will also tolerate minor tip-overs, whereas a glow heli will require repairs. Furthermore, a nitro heli is significantly more expensive to operate, mainly because of the cost of fuel and replacement parts.