Thursday, August 10, 2017
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Transitioning to Inverted Flight

Tranitioning to Inverted Flight
Don’t let this happen to you; make sure all components are secure before flying.

By Tony Yap

If you’ve been to a helicopter fun-fly recently, you’ve probably noticed that most of the top pilots spend more time inverted than upright! Being comfortable flying inverted is the first big step most pilots take toward mastering helicopter 3D flight. With a little practice, you, too, can add inverted flight to your repertoire.

PREPPING FOR INVERTED

You should check a few things before you flip your heli upside-down for the first time. You’ll need a helicopter with a collective-pitch head. Unless you can find a way to make gravity work in the opposite direction, your fixedpitch heli isn’t going to cut it! Most collectivepitch heads and idle-up flight-mode setups provide roughly +10 to -10 degrees of blade pitch on the main rotor while maintaining a constant head speed throughout. This setup allows you to pull back on the collective stick to create lift while your heli is upside-down.

A last item on the radio front is a heading-hold gyro. Although it isn’t absolutely necessary, a heading-hold gyro will make flying inverted much easier. When flying inverted, 3 of the 4 controls—collective, cyclic pitch and yaw—will be “mentally” reversed. Only cyclic roll inputs (aileron) seem to stay the same. Not having to make constant yaw corrections on the tail will greatly reduce the pucker factor the first time you flip your helicopter.

If you have a nitro- or gas-powered heli, make sure that your engine is in top running condition. There is nothing worse than being upside-down without engine power! Along those lines, make sure your clunk line moves freely in the tank to ensure the engine can draw fuel while inverted. For both gas and electric helis, be sure that the removable components—primarily flight and receiver packs—are securely strapped down. Up to this point, your helicopter has probably never experienced negative G, and you definitely don’t want parts to fall or get thrown off! A few years back, I was test-flying a friend’s brand-new Raptor 90 without the canopy. When I went inverted, the loosely mounted battery pack fell off, contacted the main blades and launched itself and the blades into the sunset. The resulting imbalance tore the entire rotor head off the main frames, leaving the fuselage carcass to fall straight down from about 100 feet, smack dab in the middle of our runway. Reminiscent of a Wile E. Coyote cartoon, it was the most spectacular helicopter crash I’ve ever witnessed. Trust me. You don’t want this to happen to you.

Transitioning to Inverted Flight

In terms of flying skills, you should already be comfortable hovering in all attitudes and with upright forward flight. You also need to be confident flying the heli upright using the idle-up, or stunt, mode, as you’ll need that negative collective-pitch range for level inverted flight. You should also be reasonably comfortable flying loops and rolls before you attempt sustained inverted flight.

TAKING THE LEAP 

There are a number of ways to get your helicopter upside-down for the first time. Some pilots prefer a half roll to inverted during forward flight, and others like a half flip from a hover to an inverted hover. I find that a half loop from forward flight is easiest for a number of reasons: first, the half loop will increase your altitude, and that gives you extra time to recover if things go wrong. Second, it will also reduce your airspeed, so the heli won’t be moving quite as fast when it transitions to inverted flight for the first time. Finally, the recovery is as easy as completing the half loop back to level flight.

OK; enough preparations. Let’s do it! First, get your helicopter into forward flight in the idle-up mode. Depending on how your pitch and throttle curves are set up, you may hear an increase in engine rpm and head speed compared with normal mode. This is generally a good thing, as it will increase the responsiveness of your collective and cyclic controls. When you’re confident that you’re ready, make a pass over the field at a moderate forward flight speed. As you pass over the center of the runway, gently pull back on the cyclic to initiate the half loop. As you approach the inverted position, smoothly pull back on the collective stick while easing off of the nose-up cyclic. The goal is to be at about a quarter stick on the collective and neutral on the pitch cyclic when the helicopter reaches a slightly nosedown, inverted, forward-flight position. It will take a few tries to get the timing just right. The key is to remember the bailout routine: pull back on pitch cyclic again to complete the loop, feeding in positive collective as you fly out of the maneuver and back into upright forward flight.

Transitioning to Inverted Flight

PRACTICE, PRACTICE, PRACTICE

As you practice, gradually extend the inverted part of this maneuver before you need to start the recovery. Once you’re proficient with upside-down, straight and level flight, it’s time to start turns. Practice your first turns away from yourself so that the helicopter is never pointing directly at the pits. Since roll is the only function that is not reversed, I start my turns with roll cyclic and follow with opposite rudder and nose-down pitch-cyclic inputs to make a coordinated turn. Again, if you get disoriented, complete the half loop back into forward upright flight.

When flying inverted is almost second nature to you, experiment with various ways of entering and exiting inverted flight, such as with a half roll or a half flip. You should also practice at various flight speeds. While flying at moderate to fast speeds, you won’t need to play with the collective much, as you can maintain altitude with pitch cyclic alone. As you transition to slower hovering speeds, you’ll likely find that your left thumb will need to be a lot more active on the collective to maintain a constant height.

Keep practicing and good luck!

 

 

Edited for the web by Jon Hull

 

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