Radio Control: Soaring
Daryl Perkins, 940 Baird Rd., Santa Rosa, CA 95409
Gliding in Australia
Gliding in Australia (I was there for the Electric World Championships) is incredible. And yes, the water really does go down the drain backwards. The thermals and dust devils (Willy-Willies, as they call them) behave differently. As a joke: you have to stand on your head and thermal inverted just to make the airplane go up.
We took some hand-launch gliders with us, and I can testify the thermals are big and meaty. In fact, while Larry Jolly was flying a seven-cell duration at the World Games, I almost hand-launched his plane out, and he required only seven seconds of motor blast to make his five minutes.
Reader mail: What is a zoom launch?
I get letters. Lots and lots of letters. I love it. It keeps me in touch with what you want to read about. Please keep them coming. I apologize if I don't respond to all of them, but I don't correspond well.
John T. Deden of Missouri City, Texas writes: "I enjoy your RC Soaring column very much, and pardon my stupidity, but I have an important question... What the heck is a zoom launch?"
John then explains he uses a hi-start: 100 feet of rubber and 440 feet of braided line.
John, there are numerous fliers all over the country who, like you, don't have the opportunity to interact with other fliers or clubs due to geography. So: the zoom launch is tricky when using a hi-start. The term usually refers to launching with a winch, although it is possible to zoom using a hi-start. Even when using a winch, very few fliers approach the launch correctly.
The importance of the launch
This letter gives me the opportunity to discuss something I've been meaning to address for quite some time now: the launch. Too many fliers don't take the launch seriously enough — they see it as just a way to get the plane into the air. Approach the launch differently. It is the most important part of the flight.
When I read ads, they often tout how a glider flies in a simulator. I don't fly in a computer; I fly in the real world, where 5–10 percent extra launch altitude will almost always beat an extra percent or two of max L/D or minimum sink. At a contest, assuming no lift, the longest times will almost always be achieved by the flier who launches the highest.
Assumptions for this discussion
- Standard club winch with a retriever.
- Braided nylon line with virtually no stretch.
- An airplane that can take the rigors of a hard launch with minimal wing flex (excessive wing flex costs energy). Most contest models will do.
Preparing the sailplane for an aggressive launch
Set the sailplane to pull as hard as possible without tip-stalling. This takes a few launches to get right, but once correct the airplane will rotate immediately out of your hand and appear to go almost vertical.
My launch setup is aggressive:
- Droop the whole trailing edge (flaps and ailerons) about 1/4 inch measured from the trailing edge.
- Add up elevator until the model begins to be unstable, then back it off a couple of percent and call it good.
Once the model is stable on tow, maintain good line tension. Line tension is energy. You don't necessarily need to stand on the pedal to do this. Any line you don't unnecessarily let out can be added to your launch height. Learn to use rudder to steer your model up on tow — it will handle much better with minimal control input.
The zoom (winch)
I see more people lose altitude during the zoom than you could possibly believe. To zoom, use the winch to accelerate the model to maximum speed, and then use that speed to gain altitude.
- I typically initiate the zoom when the model has practically stalled the winch, or when the line is approximately 70° to the turnaround (not straight over it).
- At that point, take out the launch camber and nose the model over, directly at the turnaround.
- Too much nose-over and you will hook your line.
- Not enough, and you won't gain maximum acceleration from the winch.
How long you should dive depends on winch power and aircraft weight. The lighter the model, the quicker it will accelerate, so the optimum time "in the bucket" will be shorter. Heavier models accelerate more slowly and require a longer dive toward the turnaround. I can't give a precise number; going directly toward the stake takes practice. With practice you can obtain slightly higher launches using this technique.
Now, pull up. Aerodynamicists might tell you to pull hard and go straight vertical, but verticality is hard to get consistently. I most often climb out directly into the wind at approximately a 75° angle. It's easier to read the energy in the airplane and nose over at the appropriate time without stalling.
With a little practice you should be able to out-launch the competition. And what do you do with that extra altitude? Work on your aerobatics.
Zooming with a hi-start
Yes, you can zoom with a hi-start, and you can get slightly — but not significantly — higher by doing so. A little wind helps because the hi-start is limited in power.
- Do virtually the same thing as with a winch, but initiate the zoom when the line is about 45° to the stake.
- Line tension is your only source of power, so use it when you have it.
- Don't zoom vertically or you will most certainly hook your line.
Thank you, John, for the question.
Video note
I recently reviewed a video related to the sport: 1994 International Slope Race. Tallant Productions did a fantastic job bringing high-speed action slope racing into the living room. I love racing, although I haven't had much time lately.
Transcribed from original scans by AI. Minor OCR errors may remain.
