Douglas Skyray

In article ,
Andy Dingley writes:
On Thu, 26 Aug 2004 20:54:01 +1000, "The Raven"
wrote:

Just to add another question, how did it compare to the EE Lightning which
was known as a pretty good interceptor performance wise?

No comparison. Their engines are a generation apart.

Yeah - the Skyray used a Pratt & Whitney JT3B (J57) 2-spool high
pressure turbojet with reliable variable-area nozzles and a reliably
lighting afterburner.
The Lightning used a single-spool, low pressure ratio Rolls Avon, and
whenever one would take off or climb, there were always bets on wheter
both, one, or no afterburners (reheat, it's a Brit after all) would
light.
The J57 provided much better fuel economy, and it, and the JT3D
turbofan flavor that followed it, are still pushing airplanes around
all over the world.

(Now, if you were to talk about the XF4D prototype's original
Westinghouse J40 - well, an engine design might be screwed up if it
were a GE, but you can be sure if it's a Westinghouse.)

Aircraft of the Skyray's period, if not the Lightning, were airframes
way ahead of engine technology. Although some did have quite high
performance, they couldn't maintain it owing to their high fuel
consumption. Engines had to become more powerful and more fuel
efficient (and better reliability helped too) before they stopped
being by far the weakest link.

Uhm, if you look at the consumption numbers for more modern engines,
you'll see that they are only more efficient when they aren't using
reheat. The greater ram drag of a turbofan means that they don't
deliver the non-afterburning thrust at high speeds that a straight
turbojet does. The extra unburned mass flow from the fan section
allow for higher afterburning thrust, but at a serious cost in fuel
flow. Consider, if you will, the example of the TOrnado, which can be
routinely outrun by a Tu-95 when it's not using reheat.

The solution to long supersonic endurance has been to make it
big enough and clean enough to fly supersonically on a relatively
small ampunt of thrust while carrying a lot of gas (SR-71, B-58,
F-111, A-5, Mirage IV), or make it able to cruise without
reheat. (Concorde, F-22 - although the Concorde needs reheat for
acceleration and climb)


--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster