Re: PW JT-8D Cruise Parameters for MD88 and B-727

From:         UserID@gwis.com
Organization: Gateway to Internet Services
Date:         21 Nov 95 01:20:32 
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Hi Shane:

The B-727 cruise numbers need some clarification:

1990 = 1.99 EPR, etc.

It's been ten years since I've flow the 727, but cruise fuel flows at
average gross weights of approx 150,000 lbs, M.82, FL350 are about
3,500#/hr/eng.

I've never flown the DC-9/MD-80, but I would guess that the cruise fuel flows
are proportionately less due to the incresed efficiency (higher bypass
ratios) of the P&W JT-8D-209 engines.

EPR is only 1.00 with throttle at idle, on the ground or in flight.
Take-off EPR on the JT-8D-15 engine at my airline runs about 2.05 to 2.12
depending upon density altitude, air conditioning pack on/off
and engine anti-ice on/off!

Also, EPR is a dimensionless number (i.e., no units) that is the ratio of
PT7 divided by PT2. PT7 is the total pressure (statis + dynamic) at
engine station 7 divided by station 2. This means, in layman's terms, total
turbine/exhaust pressure divided by engine inlet/compressor pressure. It's a
measure of engine "work" produced, very roughly equivalent to BMEP on
a reciprocating engine. (i.e. EPR is measures as, for example, 1.84. That's
it. It's not 1.84 yards, or 1.84 degrees, or 1.84 anything. It's 1.84. That's
it !!!!!!)

Thanks for the opportunity to provide some info.

Regards, George