In reference to a recent crash of a full-scale SE5a replica, it was suggested that a high "density altitude" may have been a factor. This was a new term for me so I looked it up on wikipedia:

http://en.wikipedia.org/wiki/Density_altitude

I'm wondering if this explains why it seems harder to fly my Puppeteer lately in the hot summer temps. The engine is running just as it always has but I get the feeling that the model is having to labor a bit more (as compared with crisp winter days) to get into and then stay in the air.