Hi John, It is actually a quite difficult thing to specify because the performance of helicopters varies dramatically.
To explain .. Temperature and altitude play a very large role, basically the higer you are, the thinner the air, the less bite on the rotors. There is a measure called density altitude, which is where the temperature comes in, the hotter it is, the thinner the air = same issue as above The combination of the two is one of the most important things a pilot looks at There are very few helicopters that routinely take off vertically, generally they will rise to a hover then move forward in ground effect (which is like a cushion of air between the rotors and the ground). This actually allows heavier helicopters to take off without needing so much power for a vertical climb out, and which many cannot do for performance reasons and options if they have an engine failure. Weight is another very critical factor, but that is an operational matter we will never know anything about and is often driven by temperature and altitude issues as well. So the bottom line is not so much the actual space, it is the approach and departure paths that are the most critical. Some choppers can come right in and drop and depart vertically, say into a foot ball field surrounded by a stadium. However, I know the pilots would much prefer to have options for approach and departure that gives them a way in and out without having to climb vertically, and probably means that they can carry more in terms of payload, people, etc. Again, this is all very much dependent on the type of helicopter, some can do it, others not depending on their performance envelopes. If we map the buildings around any marked landing areas, then any pilot will know immediately he is dealing with obstacles and can plan his flight accordingly. Height of those building is a VERY useful piece of information, but one we are unlikely to be able to provide from Sat images The other thing we can do is map power lines, other buildings, and groups of trees around the LZ's to show possible approach and departure paths, this would be very useful information for mission planners and pilots Hope that helps Regards Mark Cupitt "If we change the world, let it bear the mark of our intelligence" See me on Open StreetMap <https://www.openstreetmap.org/user/Mark_Cupitt> On Thu, Feb 19, 2015 at 7:31 PM, john whelan <jwhelan0...@gmail.com> wrote: > Project 892 task 23 is an example. The following question got sent to me > probably because I've been validating merrily away. > > >What is the minimum diameter for a Helipad (leisure=common)? > > Based on my own experience of visiting a remote Scottish Island the local > football pitch, being smooth, level and firm enough was the designated > helicopter landing place. > > I'm not sure that you can tell enough from satellite imagery that a > certain bit of ground is smooth, level and firm enough to take the weight > of a helicopter. However we seem to have a fair number of circular > leisure=common areas tagged near fairly small villages. > > So can we flesh out a bit more of the requirements please and better > identify what we should be looking for and mapping. > > Thanks John > > _______________________________________________ > HOT mailing list > HOT@openstreetmap.org > https://lists.openstreetmap.org/listinfo/hot > >
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