Simple ground effect question

Just bought the huey and flying around is hella fun. I was wondering if i fly fast like above 100 knots but still very low do i still get a lift advantage from the ground effect?

An airliner landing at 140+ knots still experiences ground effect... so I imagine the effect would still be experienced by a helicopter flying at a slower airspeed.

To piggyback on what TOTEN said, yes, at lower speed there is a bit of ground effect, but a helicopter's ground effect can be very different from that of a fixed-wing aircraft. A fixed-wing creates its ground effect as it displaces a large amount of air from in front of it. A helicopter (UH-1 in this case) doesn't have the same kind of speed necessary to generate the same amount of ground effect proportional to its volume and mass. It's still there, but very minimal by comparison. Which is why ground effect is more applicable to hovering and low-speed flight.

thanks both of u

Just bought the huey and flying around is hella fun. I was wondering if i fly fast like above 100 knots but still very low do i still get a lift advantage from the ground effect?

No Ground effect in a helicopter at 100 knots for sure :smartass:

You have ground effect in a hover, building up an air cushion below the aircraft. When you start moving two things happen.

1. Your rotor disk is slightly tilted forward, pushing the air in a way backword correlating with the degree of rotor tilt and parts of the downwash don't stay below the rotor disk.

If you make a hard emergency takeoff, by applying full collective and as much forward cyclic as possible to accelerate, you lose ground-effect immediate.

2. When accelerating, as airspeed increases more and more of the downwash reflected by the ground is behind the aircraft and no longer between the ground and the rotor disc.

As a reference, you may refer to the transverse flow effect.

At 0 airspeed the helicopter operates in air disturbed by himself with his rotor, close to the ground this builds up also ground effect.

When accelerating and moving forward more and more of the Rotordisc starts operating in clean undisturbed air because the downwash and vorticity stay behind. And because the aircraft stays not longer at that point where the downwash is reflected by the ground there is no way to build-up an air cushion anymore.

But at the same time, you losing Ground effect your rotor system gets more and more effective because of the transverse flow and operating in clean air. And luckily This effect combined with the translational lift provides your helicopter with more lift than you loose with the absence of a Ground effect.

Its pretty complex but I hope I was able to explain that in an understandable way.

In the end, when flying a helicopter it is not important to understand the theoretics behind his behavior. It is important to know about and use its behavior and characteristics in the right way :smilewink:

Haha thanks friend, good explanation, i understand.

Most of what was said above is true, but the Huey can and does fly in ground effect at speeds up to max Vne. Ground effect is typically 1 1/2 times the diameter of the main rotor disk. You can see this as you fly high speed over the ground - the closer you get, the slower your descent rate is going to be. Your heli will want to roll into the direction of the retreating blade as you will have asymmetrical lift being generated but its almost not noticeable. And AFAIK, asymmetrical lift isnt even really modeled well in the sim even if at all. Thats a phenomenon you would experience while transitioning from level flight to a hover over a buildings edge or a cliff where half of the rotor disk downwash is directed straight down and the other half is billowing up underneath your aircraft due to the building. Essentially half of your helicopter is in ground effect while the other half of your helicopter isnt generating nearly as much lift and you risk a dynamic rollover if you arent careful.

Oh, interesting. Thx for the info

Most of what was said above is true, but the Huey can and does fly in ground effect at speeds up to max Vne. Ground effect is typically 1 1/2 times the diameter of the main rotor disk. You can see this as you fly high speed over the ground - the closer you get, the slower your descent rate is going to be. Your heli will want to roll into the direction of the retreating blade as you will have asymmetrical lift being generated but its almost not noticeable. And AFAIK, asymmetrical lift isnt even really modeled well in the sim even if at all. Thats a phenomenon you would experience while transitioning from level flight to a hover over a buildings edge or a cliff where half of the rotor disk downwash is directed straight down, and the other half is billowing up underneath your aircraft due to the building. Essentially half of your helicopter is in ground effect while the other half of your helicopter isnt generating nearly as much lift and you risk a dynamic rollover if you arent careful.

@BranchPrediction

I am sure you did it unintentionally, but you open pandora's box when asking questions about helicopter physics.:music_whistling:

Ther is no roll tendency because of the dissymmetry of lift ( forward-moving / against backward moving rotor blade and the resultant airspeed difference).

While the difference in airspeed is a fact, the lift generated by the rotor blades (with the same pitch angle) is, in general, the same, regardless of it's forward or backward moving.

The reason is blade flapping. The forward moving blade moves (flaps) also upwards reducing the Angle of Attack and thereby the lift produced. While the backward moving blade flaps down increasing the Angle of Attack and thereby the amount of lift. So the system tries to equalize itself.

In a semirigid (2 Blade) Rotorsytem this flapping is supported by the tethering Hinch and works like an analog balance. When on side moves up because of more lift created, the other side automatically moves down.

In a fully articulated rotor system, any rotor blade is supported by a flapping hinge that allows him to flap independently.

In a rigid rotor system, flapping is supported due to bending in the rotor head structure and or the Rotorblade itself. Which requires a material that absorbs this bending without breaking. (

Be aware: Flapping leads to dislocation of the center of gravity in the rotor blade with respect to the rotor disc, and thereby to acceleration and deceleration of the rotor blades called; lead and lag.

But this is another story. :smilewink:

The sideward moving tendency in a helicopter when accelerating belongs mainly to the transverse flow effect.

The push by the tail rotor is mostly counteracted by construction. In most cases due to a tilted main rotor drive shaft.

Because this is highly complex and dynamic, the pilot has to level any of this tendency in a small amount.

:book::doh::cry:

Helicopter flight, in general, is a miracle. And good must be a helicopter pilot because for any problem in physics there is a solution to make helicopters possible anyway. This can't be a coincidence.:angel:

Damn, i can learn so much here on the forums. Yeah helicopters are trully impressive and require so much skill from the pilot.

No, you wont notice any ground effect at 100knots.

I dont have the time right now to go into the Deep parts, or even readning the other posts carefully. Anyway, I got some 4K of low level flights(< 100 feet) and I never noticed ground effect at speed. Nap of the Earth flying at 0-3 feet and below 60knots, yes then it is noticable.

@Hammer 1-1: Ground effect is commonly described as up to 1 rotor diameter. Thats also about the height you can notice it. The nature of the ground makes small differences in ground effect but anyway, at around 1 rotordiameter its not noticable.

[Edit]

Took a picture from one of R.W Proutys helo aerodynamics books:

Easy to see that above one rotor diameter there isn't much ground effect left.