You can look it up in the CFR part 95 and 97 regs. (the Radio Control section of the FCC rules) The maximum allowed is essentially right where the manufacturers all shoot for.

http://frwebgate3.access.gpo.gov/cgi...ction=retrieve

Too much legaleese for me to want to dig through it right now...

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Well... OK I dug was easy to find using search on the section number from the table of contents.

Sec. 95.210 (R/C Rule 10) How much power may I use?

(a) Your R/C station transmitter power output must not exceed the
following value under any conditions:

------------------------------------------------------------------------
Transmitter
power
Channel (carrier
power)
(watts)
------------------------------------------------------------------------
27.255 MHz............................................... .. 25
26.995-27.195 MHz.......................................... 4
72-76 MHz............................................... ... 0.75
------------------------------------------------------------------------

(b) Use of a transmitter which has power output in excess of that
authorized voids your authority to operate the station.

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Not sure why the formatting is maintained in the edit message box and not in the posted message. somethings goofy. (must be "tabs" in the text I copied... and the system is deleting them.)