Category Archives: Aerodynamics

Discussions primarily focusing on helicopter aerodynamics – particularly aerodynamics relating to the Robinson R22 and R44 helicopters.

In a flare, why does manifold pressure decrease?

We recently received this question: “In a flare, why does manifold pressure decrease?”

When you make a flare or a steep turn in forward flight, the momentum of the aircraft trying to stay on it’s original course adds ‘load factor’ to the helicopter’s weight, which causes the blades to cone upward. As the blades cone their center of mass moves inward toward to hub. This causes the rotor RPM to increase (like an ice skater in a spin bringing their arms inward – ‘coriolis effect’ or ‘conservation of momentum’ in effect).

If the helicopter did not have a governor (or in governor-off training), the engine and rotor RPM would increase unchecked – you would need to manually roll the throttle down to avoid an engine overspeed. But because the governor is on and working, it senses an engine RPM increase and the governor backs off the throttle to avoid an engine overspeed- showing a manifold pressure decrease.

But be careful – abrupt maneuvers, especially at max gross, high density altitudes and/or in turbulence will reduce the chance that the governor will respond in time.

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Near OGE hover limits with a tailwind

Out of ground effect (OGE) hover charts are based on zero wind conditions. What happens if you are near OGE limits with a tailwind? See NTSB report here.

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Helicopter Airfoils

How many different airfoils are there on a helicopter? Do they all just produce lift?

What is the difference between a symmetrical and asymmetrical airfoil? Which one is better for helicopters?

What is the difference between Chord Line and Chord? What about Blade Span?

Answer these questions and learn more about Helicopter Airfoils by watching this video:

Click to watch a video on Helicopter Airfoils

Helicopter Airfoils Video

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Torque Reaction in Helicopters

  • Why do helicopters have tail rotors?
  • Why do some helicopters not have tail rotors?
  • Why do many helicopters spin out of control if they lose their tail rotor?

Watch the following video to learn how about torque reaction in helicopters.

Click to watch Helicopter Torque video

Helicopter Torque video preview

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Three Axes of Rotation

  • What are the three axes of rotation in flight?
  • How does the helicopter move around the axes?
  • Where do the three axes converge?

Watch the following video to learn how to about the three axes of flight, as demonstrated in a Robinson R22 helicopter.

Click to watch Three Axes of Flight video

Three Axes of Flight video preview

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