Features and FAQ

Fan Efficiency. The Frost Boss C49-4 blade fan provides the greatest coverage for the lowest fuel consumption of any frost fan on the market. In a continental climate, like Australia, with large temperature inversions and low katabatic wind speeds, the C49 can achieve coverage of approximately 10ha. The same fan in an island climate, like New Zealand, in a cold valley with a strong katabatic drift and a small temperature inversion will achieve coverage of approximately 6 – 7 ha.

The noise signature from the C49 is smooth, and at a low level, without the distinctive “Iroquois” chopping sound of the 2-bladed fans. The 4 blade fan, by virtue of its greater blade area, allows a higher blade pitch to be used without running the risk of the blades stalling. This allows the fan to run at a slower speed, thus making less noise, while still doing the same work.

It also converts more of your fuel into useful wind and less into turbulence and noise. Evidence from actual frost events shows that 4 blade fans have a greater penetration capability than 2 blade fans, thus giving them greater coverage.

Due to the katabatic drift, frost fans cover an elliptical shape rather than a circle. The FrostBoss C49 (4-blade) fan rotates around the tower every 6 minutes, 40 seconds and for the FrostBoss C59 (5-blade) fan every 7 minutes.

It is important for us to understand the direction of the katabatic drift before we can recommend correct positioning of proposed frost fans. It is always helpful when growers have already studied this in advance. Download the Fact Sheet here to learn more about katabatic drift and how to determine its direction.

The C49 fan blade is twisted from the tip to the root in a progressive manner, whereas all other frost fans are twisted linearly. The progressive pitch of the blade gives it a distinctive 3 dimensional shape, especially towards the blade root. This combined with the progressive increase in blade width, and the rounded blade tips, gives improved performance and an aesthetically pleasing blade shape.

Thrust is used to measure the performance of a propeller on an aircraft, and is not a good measure of the penetration capability of a frost fan. The parameter best used to measure a frost fan performance is the wind momentum, and in particular the uniformity of the wind momentum.

A uniform wind momentum is best achieved with a blade design that has the blade angle pitched progressively from the tip to the root. In this way, the air flows uniformly across the fan diameter, and creates a uniform blast of wind. The C49 fan has over 20 degrees of progressive pitch in the blade.

On the other hand, some 2 blade fans have only 5 degrees of pitch between the tip and the root of the blade. This is nowhere near enough pitch variation (called twist) to achieve a uniform wind momentum. Instead, the blade tips end up creating all the wind momentum, which mixes with the slower air in the middle of the fan blast, introducing unnecessary mixing, which absorbs energy from the wind stream. This in turn dilutes the momentum of the wind stream, before it even gets a chance to drive out into the orchard or vineyard.

Thrust is a useful indication of how much power the engine is putting into the fan, but it gives no indication about the uniformity and penetration capability of the wind stream. This is a bit like a car wheel-spinning … the power is going into the wheels (thrust) but the wheels are making a lot of noise and turbulence.

C49 fans spin very easily when an ambient wind hits them, from any direction other than edge-on to the fan plane. This quickly turns the fan out of the wind thus avoiding shock loading. Two blade fans, on the other hand, tend to rock on the teeter assembly for a bit, before spinning in the wind. Even if spinning slowly, a two blade fan will continue to rock on its teeter assembly. In areas that experience strong winds, large diameter, two blade fans can be subjected to considerable shock loading in changeable wind conditions, resulting in damage to the blade attachment assembly.

Neither - the most important aerodynamic property of a frost fan is the momentum of the wind stream it generates. This 'wind momentum' is the product of the wind flow rate, the wind speed and the air density. The more momentum the wind stream has, the further it penetrates into the orchard or vineyard.

Yes it does. The more thrust the helicopter can produce, the more wind momentum it will generate, and so the greater the amount of warmer inversion air it can blow down into the orchard. With a helicopter, the thrust developed by the rotor equals the weight of the helicopter, so the heavier the helicopter can be made, the more effective it will be at frost fighting. Thus any helicopter used for frost fighting, should be operating at its maximum safe operating weight, by carrying additional dead weight, in order to maximize the amount of wind momentum it can produce.

The main source of noise from a frost fan comes from the high tip speed of the fan, so the longer the blades are and the higher the fan speed, the more noise it makes.

NZ Frost Fans designed the 4 blade fan to be quieter without losing performance. The blades were designed and pitched, to match the maximum torque of the engine. Because of this, the engine and fan can operate at a lower speed (1700-1900rpm) and achieve better coverage and fuel economy with less noise.

NZ Frost Fans also manufacture a conventional 2 blade fan for use where noise is not a major issue. The FrostBoss C29 fan achieves its maximum output at a relatively low speed (2100rpm) compared to other 2 blade fans due to the design and pitch of its blades.

Yes they are. Not only is the fan running much slower, but the engine is running slower as well, so both the aerodynamic and the mechanical noise is reduced.

Further, the low frequency chopping sound is not present with a C49 fan. It is this sound that is most annoying on still nights, because it is low frequency sound, and carries much farther than high frequency sounds. This is like your neighbour playing music really loud, and all you can hear is the bass beating and no music to go with it.

The C59 has 5 blades and operates at lower rpm, whilst covering the same area as the C49 with even lower noise levels.

FrostSmart® remote monitoring provides access to real-time monitoring of fans via the internet, together with text alarms and historical data and graphs on temperature, run-hours and machine performance.

Together with its sister business, Australian Frost Fans, New Zealand Frost Fans regularly services more than 2000 machines across New Zealand and Australia using specialist equipment and custom-built bucket trucks. They are specialists - frost fans is all they do. You’ll be dealing with people who understand the industry having spent most if not all their working lives around frost fans.

New Zealand Frost Fans are happy to provide advice including suggested fan layouts for your orchard or vineyard. They handle the whole process from consent application (where required) to site preparation and foundations, installation and servicing.