Topic For Discussion

[Lawman]

I suspect the figures are correct, they are certainly from a reliable source!

I strongly suspect that the Spey could be made to fit the same envelope as the TF30, probably by virtue of a larger fan. A larger fan may even give the Spey the boost it needs to trump the TF30, and deliver a better Tomcat engine than anything until the F110 engined ones became available. I would guess (don't shoot me when I'm wrong!) the larger Spey would probably be close to 16,000 dry, and 24,000 augmented. This would certainly be a major improvement!

[jcf]

Jane's ATWA 1968-69 lists diameters in the range of 37 to 37.5 inches for the Civil Spey(the original Spey), the Military Spey, the Spey Junior and the RR/Allison Spey TF-41, the TF-41 having the largest diameter.

As to why RR didn't create a larger fan version of the Spey, especially as they realized right away that the bypass-ratio was too low, is anybody's guess.

Cheers, Jon

[Zen]

RR and the UK had settled on the 'optimum' (their thinking) bypass ratio of less than 1, because they thought embedding the engines in the wings was the way to go, even though previously in the mid 40's Whittle Turbofan designs where much more 'modern' as was Griffiths monsterous Confrafan designs.

So thats why they had low bypass ratio's.

Medway and its junior the Spey I seem to reccal had a lot of compressor stages, which rather precluded a high bypass ratio anyway.

A better turbofan was the Bristol Pegasus, and I think they did offer it at one point as a 'straight through' turbofan. In fact its quite modern in concept (three shaft I think), though the step from that to the RB.211 was much more fraught that they'd expected.

However by the 70's a rather different version of the Spey for civil applications was built, with a much higher bypass ratio. Was'nt it called the Tay or somesuch?

[jcf]

Hi Zen,
I'm familiar with the thinking behind the original BPR decision (which BTW, according to Gunston, was also based on a faulty evaluation of the best ratio for a podded engine which, because of incorrect assumptions about nacelle drag, also came out at around 1), the puzzle is why they waited so long to address the issue. The Tay didn't arrive until the early '80s.

Pegasus is basically an Orpheus with a new front end and it is not a three-shaft engine, which I believe is still unique to RR and related designs, with the exception of the Kuznetsov NK-321

Jon

[Daryl J.]

So we'd have to have a:

Tomcat I
Tomcat II
Tomcat III
Tomcat IIIa


or would that actually be a Spey'd Cat?  Hmmmm....not a slogan I see the Brits falling over themselves for:  Love your Cat, have it Speyed!



Daryl J., unable to resist

[Radish]

I like that idea...Spey'd 'Cat.
Brilliant.