RADIO CONTROL SCALE AEROBATICS
Eric Hawkinson
319 Yellowstone Ave., Billings, MT 59101
Introduction
The first order of business is to beg for input—especially photographs of your scale aerobatic machines. Readers like to see what others are flying, and you can enjoy seeing your favorite airplane in print. Written input is also appreciated; tell me what you are flying, what you need help with, your latest discoveries, or secret tricks.
Living in the outback as I do, I can't personally provide all of the information that readers desire and deserve.
To continue discussing scale aerobatic maneuvers, I'll look at a couple of basic autorotative events. No, I'm not getting mixed up from flying helicopters; they are more commonly associated with the term "autorotation"—the energy-management task of touching down without power applied to the rotor blades. I'm referring to the spin–snap–and–tumble family of maneuvers that fixed-wing aircraft perform.
What is a spin?
The most basic autorotative maneuver is the simple upright (or inside) spin. Not many maneuvers in competition events generate as much controversy as spins. Whether or not the aircraft stalled upon entry and remained fully stalled, what control inputs are appropriate, and similar issues provide hours of hangar talk and heated debate in scale and precision aerobatics circles. I won't try to solve those debates here; I'll just give you my "spin" on the subject.
A spin is an asymmetrical stall condition. The inside wing is stalled while the outside wing generally is not. That's why the aircraft descends with a more nose-high attitude than in a spiral dive or a downward vertical roll.
To define a spin precisely in print is mostly folly, because the requisite control inputs and spin characteristics vary greatly between aircraft. As my scale combat pals can tell you, a small airplane and/or one with high wing loading or small tail surfaces can be easily "snapped" into a spin with the application of elevator and nothing else. On the other hand, a lightly loaded trainer with relatively forward CG (center of gravity) and small rudder can be virtually impossible to spin.
To simplify the discussion, I'll refer to the "typical" scale aerobatics model.
Entering a spin
If you are new to spins, or about to spin a new model for the first time, remember that the altitude above the model is not nearly as helpful as the altitude below the model.
- Reduce power to idle.
- Maintain altitude with increasing amounts of up elevator; the airplane will eventually stall.
- As it stalls, input full rudder in the desired direction of the spin and hold it.
- Hold rudder and up elevator throughout the maneuver.
In most cases, that's all your model needs to initiate and continue a spin. Release rudder and up elevator after a few rotations, and the airplane should stop spinning fairly quickly and recover in a dive.
Some airplanes will enter and maintain a spin only with the application of aileron along with elevator and rudder. This aileron application will be in the same direction as the rudder for an upright spin (for example, right rudder and right aileron for a spin to the right). The added drag of the upward-deflecting aileron on the inboard wing and the added lift of the downward-deflecting aileron contribute to the asymmetrical stall condition that makes a spin.
Some people believe that using aileron somehow makes a spin impossible. That's incorrect. However, very few airplanes will maintain a spin with aileron and elevator only.
Recognizing a spin versus a spiral dive
How do you know your model is spinning and not just doing a vertical barrel roll or a spiral dive? Experienced pilots often recognize it instantly by the stall "break," the aircraft attitude, and the exit/recovery behavior. It's harder to explain than to demonstrate and harder for a judge or spectator to ascertain than for the pilot.
The best signs of a true spin are the descent path and recovery:
- In a spin, the aircraft descends on a vertical path that nearly intersects the aircraft's CG.
- In a spiral dive, the CG describes a much larger-diameter corkscrew path.
- In a spiral dive, recovery will be instant when the controls are released because there was never a stall condition present.
- Upon release of the controls from a spin, there will normally be a slight lag before full control is regained because the inner wing needs a moment to recover flying speed.
With some airplanes, it may take a full turn or more after controls are released from a spin before rotation stops. Most scale aerobatic airplanes will recover in about 1/4 to 1/2 turn after the controls are released.
Recovery can sometimes be accelerated by applying opposite rudder, but that might result in just changing the direction of the spin. Experiment at altitude until you are comfortable.
Troubleshooting: airplane won't spin
If you are not able to get your airplane to spin, the most common culprits are:
- Forward CG
- Not enough elevator or rudder travel
- Tail surfaces that are too small (rare in scale aerobatic airplanes, since full-scale prototypes are generally designed to spin readily)
Make any CG adjustments in small increments so you don't get a nasty surprise.
Inverted spins
I had a discussion with a pilot who couldn't get his airplane to spin inverted, even though it spun up easily upright. After reviewing setup parameters, it turned out he had followed some good advice the wrong way. He had watched a video in which an aerobatics expert said to never cross the aileron and rudder controls in a spin. The segment involved upright spins only, and the advice was correct for those maneuvers.
However, for inverted spins (and for flat spins), the controls must be crossed. For an inverted spin to the right, the airplane is stalled with down elevator and the rudder is applied to the left. Aileron, if needed, is applied to the right.
Recovery is the same for inverted spins as for upright spins: release the controls and recover the model smoothly from the ensuing dive.
Flat spins
When you are comfortable entering and recovering from normal spins, try flat spins. Be warned that some airplanes absolutely refuse to recover directly from a flat spin. I continued several flat spins all the way to the ground many years ago while learning to do them.
There is a great deal of conventional advice regarding flat-spin recovery that isn't reliable. Adding or flipping power, reversing elevator or other controls—many methods work on some airplanes, but I've only found one method that has worked on every airplane.
You need to enter a flat spin before recovery is an issue. Flat spins are most often entered from a normal spin. Start at a higher altitude than normal until you are familiar with your airplane's recovery habits.
To enter a flat spin:
- Enter the spin as usual.
- After the spin is stabilized, slowly apply opposite aileron input to the direction of the rudder.
For an upright flat spin to the right: enter with up elevator, right rudder, and ailerons. Then slowly "cross" the ailerons to the left while holding full right rudder and full up elevator. The nose should raise slightly and a flat spin should develop.
Some airplanes will flat-spin with extremely shallow nose-down attitudes; at any rate, the fuselage will be much flatter than in a normal spin. The descent rate will be noticeably less in a flat spin than in a normal spin. With certain aircraft, the flat spin can be made even flatter by releasing or possibly reversing elevator, and/or by adding a bit of throttle. Others may recover or fall back into a normal spin with these control changes. Only flight testing will tell you what your airplane will do.
On your first attempts at the flat spin, don't wait too long to initiate recovery. It's easy to get mesmerized by the maneuver and not allow room for recovery. After a few turns in the flat spin, initiate the universal flat-spin recovery method.
Universal flat-spin recovery method
This is the method I've found works on every airplane: return to a normal spin by "uncrossing" the aileron.
- Example: if you have an upright flat spin to the right where the ailerons were crossed to the left, recover to a normal spin by changing the ailerons back to the right. The nose will drop and the airplane will be in a regular upright spin to the right, from which you can perform the standard recovery.
- For an inverted flat spin, the aileron and rudder controls will initially be crossed; then change the aileron slowly to the same direction as the rudder to transition to a flat inverted spin. Recover to a normal spin by recrossing the controls to be opposite, then release.
There are other recovery techniques that work some of the time or for some designs. One is to release the controls and wait for the airplane to recover. Another is to release the controls and add a burst of power to break the stall. I have flown airplanes that will recover using either technique, and I have flown airplanes that will not recover using any technique other than a return to a normal spin and then a standard recovery.
Learn the universal method first, then try other options at a safe altitude to see if they work for your airplane.
Closing
I'm out of room. Until next time, have fun and fly safely!
Transcribed from original scans by AI. Minor OCR errors may remain.
