I was just checking out Portoviejo on Google Earth. There is a decent sized field at the end of Avenida Recaurte that would be decent for the Bixler, if you are allowed to fly there.
I also found this picture from Reales Tamarindos airport! Maybe you can get in with this group of RC fliers?
http://www.panoramio.com/photo/37261203
Whoa! I didn't know they flew RC at the airport! (even though planes rarely come down there)
The field you mention is called Parque La Rotonda, it would really be a good place, but you have to fly tight, so you don't lose your plane.
There is another place about the same size at the other end of Avenida Ricaurte, but there are more "bad guys" around there.
The military have an airstrip and a big field, but it's a restricted area.
Big place behind Velboni, but between buildings.
If you search for Colegio Cristo Rey, it's a high school, and they have a nice soccer field, but there are trees around too. I live two blocks away.
Going out of the city towards the suburbs, there might be places to fly as big as the stadium, with permission from the owners. Just so far away. Problem too is they're real hilly.
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Well I can probably do a couple of trips for my first flights. There are enough big places if I get permission and if I can get there.