Dendronautics - A bird's eye view

Towering over 30 metres above the forest floor, the treetops which make up the rainforest canopy are said to contain half of the world's plant species. Described almost a century ago by naturalist William Beebe as ‘another continent of life’ waiting to be discovered, the canopy has yet to give up many of its secrets.

Aeronautical engineer Dr Graham Dorrington believes that the best way of visiting this incredible habitat is from the air, flying on board purpose-built airships. In order to promote this method of research, he has even coined a term to describe it: dendronautics.

‘It’s a whole new landscape out there that hasn’t been explored. We can walk below it, but I think flying above it is going to change people’s appreciation of it,’ enthuses Dorrington.

Having already designed and tested two prototype airships in Borneo and Guyana, Dorrington is well aware of the huge technical challenges his project entails. ‘They’re not insurmountable, but they’re very tricky,’ he admits.

The potential rewards for such exploration are however immense. Rainforests worldwide are a haven of biodiversity, with expeditions to remote areas routinely uncovering tens of new species. And with an estimated 70% of existing cancer drugs derived from rainforest plants, we clearly have much to gain from studying these pristine forests.

Lighter than air

Dorrington’s airship is basically an oversized helium balloon, carrying researchers suspended below it in a gondola as they skim over the treetops, propelled by electric motors.

Helium is the second lightest gas after hydrogen (a no-no for modern airships because of its high flammability). By displacing the much denser air around it, the helium-filled envelope makes the airship buoyant. Every kilo of load the ship needs to carry requires a cubic metre of helium to keep it up in the air.

‘It’s a constant battle against weight. Making very small airships is very difficult: you put something on board to make the airship better, but that makes it heavier,’ explains Dorrington, ‘you have to question every gram.’

Dorrington’s latest airship was held aloft by a sizeable 500 cubic metres of helium, making it somewhat awkward to manoeuvre. ‘When flying a rainforest airship, the key thing is not flying quickly, but flying with control so you can take samples,’ he says. The aerodynamics of the ship therefore need to be closely scrutinised.

Airship aerodynamics

'As air flows over a spherical balloon, it separates at the rear into what we call a wake. The pressure in the wake is low and that’s what’s causing most of the drag,’ explains Dorrington. In order to minimise drag, his design has a pointed tail to prevent separation of the air flow as much as possible.

The airship’s size also leaves it at the mercy of gusts of wind, which can sweep it dangerously off course. ‘You’ve always got some movement of air and you need very clever monitoring systems,’ comments Dorrington. In the future, these systems could allow the airship to counteract wind automatically by activating motorised propellers thrusting against the wind as soon as a gust is detected.

Another alternative would be to build a ship with pneumatic legs that could anchor it to trees, emulating a giant crane fly bobbing above the treetops. ‘My dream is to have an airship that will move forward grabbing onto trees,’ envisions Dorrington.

Further challenges include maintaining the ship at the desired height despite fluctuations in temperature (which affect the helium’s density and therefore the airship’s buoyancy). Dorrington has also put significant effort into testing different electric motor and propeller combinations. ‘The reason I’ve gone for electrical propulsion is I want to minimise noise,’ he explains, ‘I don’t want loud engines because I don’t want to cause disturbance.'

Although much work is still required to overcome these hurdles, Dorrington firmly believes that the unparalleled view of the rainforest his airship could offer scientists would make it all worthwhile.

The bulk of canopy research is currently carried out using cranes erected on the forest floor. The crane’s arm swivels around its base,  granting researchers access to a circular area of rainforest. Dorrington believes that his airship could complement this type of work with much wider ranging studies.

‘The cranes tend to cause disturbance, and they may not have a representative patch of forest – the rainforest is very heterogeneous, very variable in its content,’ he explains. From its unique vantage point, the airship could undertake biodiversity studies on a vast scale, possibly using software capable of recognising leaf shapes to measure biodiversity. ‘You could catalogue how many species are down there and so you could calculate the biodiversity index and prioritise conservation areas.’

The airship could allow scientists to observe mass flowering events and other phenomena which are only visible from above the canopy, and also to get up close to its numerous inhabitants.

Dorrington is itching to build a new airship and put his latest ideas to the test, but so far lacks sufficient funding. ‘If we’re prepared to spend billions sending probes to Mars to search for life, then we should get our own inventory in order’ he argues. ‘If you have a goldmine nearby, you want to find out what’s in it. Europe has a goldmine: it’s called French Guyana. So why don’t we go out and explore it?’

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     All images courtesy of dendronautics.org

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