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So What's So "Different" About the Delta Vortex?

by Bruce Tharpe

Modelers have had a long love affair with delta-winged aircraft. Deltas really came into their own during the early days of R/C pylon racing, when there was an open class for any type of design. Because deltas are a naturally "clean" configuration, they enjoyed a lot of success in the speed-driven world of pylon racing. Since then, it seems, delta wing designs have been reserved for the simple pursuit of speed. Many of them have been published in magazines over the years, as well as a number of kits. The common thread with most of them has been "Look how fast this bugger can go!"

Not that there's anything wrong with that! Speed is cool. I enjoy watching fast models make low flybys, and I've flown a lot of fast models. The adrenaline rush is great, but it does wear off. Like most experienced pilots, I can handle fast planes but ultimately return to slower, aerobatic models that are easier to see and enjoy in a more relaxed frame of mind.

That's where the Delta Vortex comes in. I've always loved the shape of the delta wing, but have also wondered why it's been restricted to small, fast, speed demons. Why not big and aerobatic? Why not make a delta that would fit into the mainstream of the sport modeling spectrum? My basic design goals were to create a delta with lots of wing area, keep it very light, and make it fully aerobatic without any concern for top speed. That's the basic difference between the Delta Vortex and all of the other deltas available now.

You can take your Delta Vortex to the field and fly it just like any other sport model you've flown lately. Fire up the front-mounted engine, taxi out, fly through all of your aerobatics, shoot a few touch-and-goes, land, and taxi back. The neatest part is watching a big triangular-shaped object do all those things!

Touch-and-go lovers will really love the Delta Vortex. Since deltas, by nature, can fly at very high angles of attack without stalling, they tend to land with the nose way up in the air (think Space Shuttle). The main gear struts on the Delta Vortex prototype had to lengthened after the first flights because the rudders scraped the ground on each landing. The main wheels are positioned so that after touchdown, you can rollout with the nose held high until the last bit of forward motion bleeds away.

For some reason, one feature that is typically omitted from deltas is rudder control. Well, if you like aerobatics, you need a rudder - and the Delta Vortex has two! They're great for doing big, graceful stall turns. Knife edge is trickier, but possible. Deltas don't like to stall, so snaps and spins with a delta are different, but spectacular, in their own way. This thing does a beautiful flat "spin" with full throttle. It's hard to describe, because I don't believe it's a true spin; it actually seems to be flying in tiny circles around one wingtip. Chalk up another pleasant difference for this delta.

One last word on speed. Even though it wasn't designed for speed (the airfoil is four inches thick at the root, the tricycle gear and engine hang in the breeze, and the servos and control linkages are all exposed on the bottom side of the wing for simplicity), the Delta Vortex still scoots right along. With a .90 in the nose, it probably does 80 m.p.h. or so, I'd guess over 100 in a dive. That's pretty fast for a sport model, but much slower than a Quickee racer. And since it's so large, it doesn't disappear in the blink of an eye.

If you've read my other articles, you know I'm not a big fan of overpowered models. Still, some models deserve more power than others, and this is one of them. In addition to being clean, deltas are inherently strong, due to their low aspect ratio and truss-shaped structure. And since it looks something like a jet, it would be disappointing to have anything less than jet-like performance. A good .60 two-stroke will fly it with authority, but won't give the out-of-sight vertical performance of a .90. I've found it easier to land with a .60 because it slows down better with a smaller prop.

Normally, you would need at least a 1.20 four-stroke to equal the power of a .90-size two-stroke engine, but you may have noticed that I only recommend up to a .91 four-stroke. There are three simple reasons for this: weight, prop clearance, and vibration. The Delta Vortex builds nose-heavy, so it's important to choose an engine with a good power-to-weight ratio. Some designs are perfect for four-strokes, but the Delta Vortex is more suited to the smooth power of a two-stroke engine.

Besides an engine, you will need an engine mount, 16 oz. fuel tank, fuel line, radio, three 3" wheels, and three to four rolls of covering material to complete this kit. Elevon mixing is required; most radios these days have this feature. If yours doesn't, you can use a simple aftermarket electronic mixer. Standard servos are okay for the rudders, but heavy-duty, ball-bearing servos are strongly recommended for the elevons. You'll need five or six servos, depending on whether you use a single servo to drive the rudders or duals. With dual servos and the right computer radio, you can program the rudders to both move outward, using the flap control on the transmitter, to serve as airbrakes. It works!

At first, many modelers think the Delta Vortex utilizes a foam wing, but it doesn't. It's a traditional design with ribs and spars, sheeting and capstrips. The kit features balsa and ply-wood parts that are machine-cut and sanded to their final shape using templates for accuracy. There are no die-cut (die-crunched) parts in BTE kits. The greatest thing about this kit is that once the wing is built, you're practically done! The fins and rudders are solid sheet balsa, and there are separate hatches for the fuel tank and radio, so installation, inspection, and maintenance are no problem.

Thanks to hundreds of satisfied customers, the word is spreading fast about the quality of our kits. At BTE, our sole guiding philosophy since the very beginning has been this: Building a model airplane should be as enjoyable as flying it. That means top-quality materials and hardware, parts that fit without fudging, nicely drawn plans, and thorough instructions that are easy to understand.

In the Greek alphabet, the capital letter D is named delta. In the engineering world, the term "delta" is used to signify a difference. In the model airplane world, most sport modelers that I know enjoy bringing something "different" to the field. Well... here's your chance!

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