As you have probably heard, the world speed record for RC jets was officially set on January 26, 2010 in the Dominican Republic. The new world record of 337 MPH was set by David Shulman and Axel Hache flying a JMP Firebird. Here is another way of looking at this speed record.
Firebird flew an average of 337.18 MPH......but what was the Firebird's "scale speed"? Scale speed is figured as 'fuselage lengths per second'.
The Firebird's scale speed was approximately 2,788 MPH That is Mach 3.6
Here's the math:
Firebird length = 92.5 inches
5,280 feet per mile
63,360 inches in a mile
X 237.18 mph
21,363,724 inches per hour Divided by 92.5 = 230,959 (fuselage lengths per hour)
230,959 (fuselage lengths per hour) divided by 60 = 3,849.3 (fuselage lengths per minute)
3,849.3 (fuselage lengths per minute) divided by 60 = 64.15 (fuselage lengths per second)
F-15 Eagle length = 63ft 9in = 765 inches X 64.15 (fuselage lengths per second) = 49074.75 inches per second X 60 = 2,944,485 inches per minute X 60 minutes per hour = 176,669,100 inches per hour.
176,669,100 inches per hour divided by 63,360 inches in a mile = 2,788 MPH
At 337.18 MPH the Firebird is flying at 64.15 fuselage lengths per second
IF the Firebird were the same size as the USAF F-15 Eagle, the fuselage length would be 63ft 9in = 765 inches
IF the F-15 Eagle flew 64.15 fuselage lengths per second that would be 2,788 MPH = Mach 3.6 (at sea level 70 degrees F)
Here's a crosscheck on the calculations:
The F-15 Eagle is 8.27 times the fuselage length of the RC Firebird
337.18 MPH X 8.27 = 2,788.5 MPH
PS: See the video of the speed record flight on YouTube http://www.youtube.com/watch?v=7cOIg-YIj7Q