Citation V/Ultra/Encore (C560)
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types
Air Traffic Control Issued New Clearance
Procedure
I was working West departure R-Side. Atlanta was on an East operation; and TRACON was sending departures out on the North side. At ZELAN fix; they turn for their departure routes. The first one out was Aircraft X; and the second one was Aircraft Y flight. As they checked on frequency; I climbed them to FL230. About the time they got to ZELAN; I noticed a substantial overtake. My airspace starts at 15;000 FT; and below is Atlanta Approach. The aircraft were inside my airspace; same altitudes when I noticed; and asked the front aircraft to state his airspeed; he replied 250 KTS. I asked for faster; 280 KTS or greater; he agreed. I told Aircraft Y maintain 270 KTS or less. At ZELAN; Aircraft X turned south for the Jogar departure; about a 45 degree turn to the left. I told Aircraft Y to fly present heading; so he doesn't turn south; and create a faster divergence and separation. There rates of climb were the same; so I was trying to work the speeds out. It was about 4 minutes later I resumed Aircraft Y speed to normal when I had lateral separation. I had noticed there was still a 50 KTS overtake between the two of them. Altitudes were within 1;500 FT; and Aircraft Y had the head winds. It is not required for a pilot on climb out to fly a filed true airspeed. It is a recommended climb profile. It has happened several times that jets; including air carriers; will fly at 250 KTS on climb out to cruising altitudes. That's fine; but when I get 5 miles between airplanes climbing out of the TRACON; and they are running a departure rush; we don't have time to ask everybody airspeeds. The next best thing is to just issue everybody speeds. But if we do that that will back up approach when the smaller jets will do 280 KTS; and the bigger jets like to climb out at 330 KTS. The simplest thing is on any departure procedure coming out of Atlanta be it the ATL6 non RNAV or any RNAV; departures; 'If any turbojets climbing out above 10;000 FT; will be slower than 280 KTS; advise ATC'; it's not instructing the pilots to fly faster; it won't force pilots to fly faster by us; it will how ever let us know so we can plan accordingly.
ZTL Controller experienced a conflict with two successive departure aircraft; the reporter suggested that more detailed speed information is provided by the aircraft to permit improved controller planning.