Avon engines

[Caravellarella]

Dear Boys & Girls, please, can any of you tell me, definitively, the intake diameter of the Avon Mk.520 series (as fitted to the De Havilland Comet 4 series)? All my research only tells me the width/girth and length of the engine.

Terry (Caravellarella)

 

[galgot]

Regarding if modified intakes more suited to the Avon would have made the "City of Hobart" have better performances than a ATAR powered IIIE, it is perfectly possible. But then one have to keep in mind all the modifications to the airframe that would imply, big redesign of the whole air intake and air duct (expensive... the Australian evaluation called for an alternative engine, not an alternative airframe) , and if these intakes are increased in size, bigger frontal area which could have cancelled the benefit.

Of note, the J-79 as a mass flow even bigger than the Avon, and the intakes are indeed enlarged on the Kfir compared to ATAR powered MIIIs. But I believe the even bigger thrust made if worthy (though the integration due to heat was quite some work, with rear fuselage being cooled via multiples air inlets AND being isolated on the inside from the engine by a titanium "blanket", otherwise the J-79 would burn the rear fuselage).

 

[galgot]

I'm aware that the Kfir suffered from stability (aft CG) issues due to the J79 being shorter and heavier (more weight positioned further aft in the fuselage) and the additional cooling equipment required for it ate into the performance advantages the J79 offered. At this point I just want to know if there's anything SNECMA could have done to improve the ATAR's thrust output without increasing its weight, I want to know if they could have done anything to improve the Mirage III/F1's thrust to weight ratio.

No, it's the contrary. The J-79 had to be mounted at the same approx position as the ATAR to keep a correct CG and because the frames carrying the engine are where they are, but even though heavier, it was also shorter, which created a forward CG shift making the plane more stable and not very "fighter like".
So the Israelis went from the Mirage IIIC perfectly balanced with his ATAR9B/C, to the Mirage 5J/Nesher with a longer fuselage forward of the CG, which made it more stable, and then to the early Kfir sans canards, which was very powerful for sure, but was stable as a brick, and they did not liked it.
Hence the canards on the Kfir C2, and the retrofitting of small flats surfaces on the early Kfirs (because the intakes structure weren't reinforced on these to carry full size canards, the US leased F-21s were these btw), which kind of rebalanced the airframe and added benefits.
Sorry for OT.