Educational by Chapter of the Powered Paragliding Bible

I: First Flight

01 Training Process

02 Gearing Up

03 Handling the Wing

04 Prep For 1st Flight

05 The Flight

06 Flying With Wheels 

II: Spreading Wings

07 Weather Basics

08 The Law

09 Airspace   

10 Flying Anywhere

11 Controlled Airports

12 Setup & Mx

13 Flying Cross Country

14 Flying With Others

III: Mastery

15 Adv Ground Handling

16 Precision Flying

17 Challenging Sites

18 Advanced Maneuvers

19 Risk Management

20 Competition

21 Free Flight Transition

IV: Theory

22 Aerodynamics

23 Motor & Propeller

24 Weather & Wind

25 Roots: Our History

V: Choosing Gear

26 The Wing

27 The Motor Unit

28 Accessories

29 Home Building

VI: Getting the Most

30 Other Uses

31 Traveling With Gear

32 Photography


--- Not in book ---

33 Organizing Fly-Ins

34 Places To Fly

35 Preserving the Sport

36 Tandem

Understanding Paramotor Torque & Twist

Mar 18, 2013 | Section IV Theory & Understanding | Chapter 23 Motor & Propeller

See also Paramotor Torque Twist and Crash,   Fixing Torque By Hand

This is one of the most confusing aspects of understanding paramotor dynamics. The basics are like this (we'll assume a belt-drive machine): The various torque effects conspire to twist your body left, the resulting redirected thrust now pushes your body left, which causes the wing to bank right. So although you're body is being twisted left you're going into a right bank. That's why right banks are easier on belt drive machines. But people get confused by the fact that their body is twisting (yawing, really) toward the left.

Basics on a belt drive machine:
  1. body twists (yaws) left,
  2. thrust pushes body left
  3. causing wing to go into a right bank.

Master PPG 2 has a great animation on all the factors that go into making torque effects so dangerous and how to counter them.

Torque and its related minions have contributed to a number of crashes. The pilot starts twisting under the risers, usually to the left which pushes him left and decreases forward thrust. The wing goes right in an unwanted right turn. At this point, the pilot is confused—he's pointed left, the wing is right, he's slowing down and not climbing. The lack of climb makes him stay on the throttle—exactly the wrong reaction. In extreme cases, the pilot pulls so much left brake to stop the turn that he spins the wing. Ouch.

Why? There are two powerful forces and a bunch of nearly irrelevant ones. It's not terribly important to know what they are but it is important to 1) recognize when it's happening and react accordingly, and 2) set up your machine to minimize the effect.

We'll assume your prop spins counter-clockwise as viewed from the rear. Nearly all belt driven machines, which is nearly all of the large ones, spin this way.

Quick overview

Torque is what happens when you spin a prop in the air. The engine/pilot tries to spin opposite. Just like when drilling into a chunk of wood and your hand wants to twist opposite the drill bit. In this analogy, the wood is air, the drill bit is your prop and the drill is you.

Note that the closer the ropes (risers) are together, the less force it takes to twist up in them.

The PPG Bible covers this topic thoroughly but here's a summary. Torque acts in two planes, around the vertical axis (but only if the motor is tilted back) and around the propeller axis.

Lay a paramotor flat on its back, hanging by ropes attached to the carabiners, so the propeller plane is horizontal with the floor. Now throttle up. You'll spin like a twister. Angle the motor up a bit. You'll still spin, just not quite as much. Angle it up further, you'll still spin, just not quite as much. You get the idea. That's the effect of a motor hanging back and its called the Horizontal Component of Torque (HCoT).

Now hang from bungee chords with the propeller plane vertical. Throttle up. It wants to tilt you right. That's the riser shift or weight shift component of torque (WSCoT). HCoT is twisting your body left while WSCoT is tilting you right. Both are causing a right turn, though.

The real villain of twist is that thrust gets redirected, causing a bank and not propelling forward any more. Otherwise the wing wouldn't really care all that much.

What Matters

Here are the forces that matter in order of importance.

1. The most powerful twisting force for most pilots is the Horizontal Component of Torque (HCoT). It's only present on machines that tilt back, though. It's easy to minimize by decreasing the tilt back. On low hook-in machines, move the hang points aft. On others, make whatever adjustments are necessary to get the prop plane more vertical.

2. Offset thrust (OTh) is where the thrust line pushes on one shoulder or another. This may be caused by torque if it twists the thrust line over to one shoulder. What matters is where the thrust line is relative to the center of the risers. That's why numerous manufacturers of low hook-in machines move one riser out using a metal piece on their right swing arm.

The significance of this force is that it matters less how much power you have. If the thrust line is too far off, you'll twist wildly. Solve it by making sure that, even at full power, your thrust line stays centered.

The above forces account for nearly all torque related accidents, usually in combination with a harness setup that doesn't resist the twist.

3. Weight shift component of torque (WSCoT) has limited effect based on how much riser shift happens. Go up and do a maximum weight shift without brake input. How much turn do you get? On everything I've flown its easy to counter with brakes. 

4. Gyroscopic Precession is barely relevant, mostly because it's so fleeting. Gyroscopic action will make you twist left as you tilt back. It only happens during the tilting. So as the wing lifts and tilts you back (if your motor is normally tilted back in flight), it will cause a brief twist to the left. But once you're leaned back, the effect goes completely away.

5. P-Factor, or Asymmetric Blade Thrust is essentially irrelevant. Not only is the force small for our craft, but it's actually trying to counter the other forces that cause problems.

P-Factor is where the descending blade enjoys greater relative wind which gives it more pull. The effect is made smaller by our slow speed. On airplanes with high horsepower, it's a big deal, for us, it's not. Imagine the prop disk angled not just 10 or 20° but 90°. Now the into-the-wind blade gets lots more lift. This is the same reason why helicopters want to bank more as they speed up without pilot input.

6. Rotational Mass Acceleration is present during throttle up only. It's the least relevant of all forces since it's only present during that brief time that the prop is accelerating.

Its the force touted by geared redrive users who claim that torque is countered by having the motor's rotating mass run opposite to the prop's—a partially true statement that's nonsense since the force is fleeting and small. Plus, the prop has far more rotational inertia than do the motor's spinning parts so the pilot still feels a twisting during prop acceleration.

Another Effect: Loaded Riser Twist

This one isn't related to torque directly but it powerfully contributes to most torque-related crashes. It is that, when the wing goes right, the motor wants to yaw left and vice versa. It aggravates the normal problems since, if during liftoff the motor yaws you left, thrust will then push you left relative to the wing which goes to the right. As the wing goes right, the left riser stays loaded while the right riser unloads and your body twists around the loaded left riser, causing even more left yaw.

You can see this clearly in Master PPG 2 (it's explained through both animation and live action). Here's another video where you can see these effects. In each case the wing goes one way, aggravating the pilot's twist the other way. This is why, on belt driven machines that you're not completely familiar with, you should:

  1. Takeoff with partial power (as your situation allows) then ease into full power once up 25 feet),
  2. Get the wing slightly left before lifting off (to the right for geared machines).
  3. If you feel excessive twisting ease back on the power.
  4. Once at a safe altitude, go to idle then ease into full power while looking up at the wing to see how much twist the machine has normally.
What to Do In All Torque Twists

First and foremost practice what to do if it starts: Reduce power, reduce brakes. It's better to land straight ahead or with minor turns than it is to crash on your side at full power. That's expensive at best. Don't just let off the gas completely, back off to about half of what you have now then adjust.

Second is to make sure your machine is adjusted to minimize all twisting effects. Find an instructor or experienced pilot who understands these concepts and implement the suggestions.

Good luck and don't become a twisted sister.

Thanks to Lance Marczak for pointing out the video.

A well adjusted machine lets the pilot relax with minimal turn tendencies.


© 2016 Jeff Goin & Tim Kaiser   Remember: If there's air there, it should be flown in!