Of all 3D maneuvers, it’s possible that none represent 3D flying more than hovering. While learning to hover can be extremely challenging, you can make it easier for yourself by knowing the primary forces involved. Control while hovering is maintained solely by the propeller thrust or “prop-wash” over the tail surfaces and the inboard portions of the ailerons. It typically takes approximately half throttle to maintain a stationary hover but that usually provides only marginal control. Therefore, you need to continually pump the throttle higher while hovering in order to generate more propwash over the surfaces without holding the higher throttle positions long enough to cause the airplane to climb.
Next, understand that the “propwash,” generated by the turning propeller, spirals around the fuselage and strikes the left side of the vertical tail, thus producing a strong left yaw tendency during hover. Consequently, you’ll need constant right rudder inputs to keep the fuselage vertical. (Note: Building in a couple degrees of right thrust lessens the effect of the propwash while hovering, but it does not eliminate it.)
A great deal of the propwash also strikes the underside of the left stab, causing the plane to pitch forward during hover. Therefore, barring any wind, you can expect to regularly need up-elevator along with right rudder to keep the fuselage vertical while hovering.
There is also considerable left rotational torque while hovering, so you’ll need to hold in large amounts of right aileron to keep the wings stationary. If the plane continues to torque to the left despite holding in full right aileron, you may have to increase the right aileron travel. If you can’t keep the plane from torquing even with full aileron, you’ll have to boost the throttle higher each time the plane starts to torque to further increase the effectiveness of the ailerons.
The standard entry into a hover starts by slowing the airplane and then abruptly pulling to vertical, causing the airplane to suddenly stop all forward movement. Be aware that you most likely will need to input some right rudder and aileron to counter the propeller forces while pulling up to vertical. Then immediately start pumping the throttle to maintain the same height as well as control.
A hover will quickly unravel if you are late correcting a deviation, so keep your fingers moving at all times, even when the airplane appears momentarily stable. This will make sure that you’re always ready to respond to deviations the instant they occur.
As a rule, if the tail swings more than five degrees from vertical while hanging on the prop, it will be very hard to stop the deviation due to the pendulum effect. To minimize over-controlling, you must try to limit your rudder and elevator corrections during hover to small brief bumps or jabs.
If a deviation is larger than five degrees and requires a larger correction, any large correction will have to be immediately followed by a quick opposite jab to keep the response from escalating.
Try to limit over-controlling by keeping your inputs tiny and brief, and if you must input a larger bump, immediately input an opposite bump to limit the response.
ADVANCED HOVER TIPS
Since a sustained hover demands immediate corrections, use of too much expo will delay the control response and thus hinder hover success. If you feel that the plane is lagging behind your control inputs, reducing the expo settings will likely improve your ability to hover.
It has long been said that an aft CG makes an airplane easier to hover. While a tail-heavy condition helps flat spins and tumbling maneuvers, after years of 3D flying and testing, neither an aft nor forward CG has proven to have much impact on hovering flight. In fact, more and more professional 3D pilots set up their planes these days slightly nose-heavy to make them more predictable and less erratic. All things considered, most pilots are best served to go with a “neutral” CG (near the wing’s thickest point or approximately one third of the wing chord) to achieve the best overall performance.
Although it’s rarely possible to achieve a perfectly vertically balanced airplane, i.e., with the tail hanging straight down, getting it as close as possible can make the airplane lock into a much easier hover. If you can, try to position the batteries and other items as high as possible in the fuselage to offset the weight of the landing gear, etc.
On the other hand, if over-controlling seems to be a persistent problem, i.e., the corrections you make typically end up causing more deviations. To solve this, in addition to practicing smaller control inputs, try increasing your expo percentages.
If your airplane exhibits an especially strong tendency to pitch forward while hovering, putting in additional up-elevator trim will certainly help. But the trick that works best is to aim to hover with the fuselage tilted a couple degrees toward the canopy.
Some 3D pilots like to determine the exact power setting that their airplane hovers at and then they flatten the throttle curve a bit around that setting to make the throttle less sensitive. On a similar note, using a lower pitch propeller affords a larger power sweet spot during hover in which the throttle is less sensitive and therefore less prone to over-controlling.
To avoid over-controlling, try to limit your rudder and elevator corrections to small, brief bumps or jabs when working to keep the fuselage vertical during hover.
While there will always be pilots who try to impress others by throwing the sticks into the corners until altitude forces them to recover, they don’t come close to knowing the satisfaction that comes from learning to hover. It may be challenging, but you can take confidence from knowing that you’re now armed with the knowledge to learn at a rate much faster than most! Good luck.