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Propulsion / Re: EJ200 unbuilt variants
« Last post by Hobbes on April 15, 2017, 10:53:18 am »
RR sees no need to offer another marine gas turbine (which are sold in tiny numbers) in addition to WR-21 (25 MW) and MT30 (40 MW)?
Here is the problem:   Your scenario envisions the RN needing a large carrier rather quickly, and the UK somehow convinces the US to sell them one.  This is at the height of the Cold War and the VietNam War.  The supercarriers have a long build time, and the UK would be doing good to get one in 4-5 years.  This, plus the lack of suitable facilities to handle it, as mentioned above.  The US Oriskany class was still in service, but as I understand it they could not handle Phantoms, which nixes them for the UK.  However, three Midways are still around.   They could handle Phantoms, but not the new F-14s and S-3s.   They were old, but still had plenty of life in them.  In fact, the Midway and Coral Sea remained in service until the 90s.   I thin they would be the only choice assuming short notice.  Perhaps a deal to sell one to the UK for a token sum in return for buying American aircraft and doing as much refit as was reasonably possible in the US.

The time line I was looking at was several years after the cancellation of CVA01, i.e. the late 60s or very early 70s, when Eagle, Ark Royal, Hermes and possibly Victorious were still in service, none of which were expected to be able to see out the 70s, but there was no new carrier building and the existing CVA01 design had been recognised as flawed and compromised (mostly by political limitations), meaning a new design would be needed to keep the RN in the carrier game after the late 70s.  This means there is enough time to build an existing design and upgrade infrastructure to support a new ship of Forrestal size, but not enough time to design, then build a new ship.

Assuming the baseline capability was three carriers able to operate Phantoms and Buccaneers then, irrespective of whether Victorious and Hermes were still available or not, the RN would still need one new carrier by the early 70s and another by the late 70s and a third by the early 80s.  Acquiring FDR and upgrading her to the same standard as Midway and Coral Sea, to replace Vic and Hermes would mean a new build carrier wouldn't be needed until the late 70s, still too soon for a new design to be ready.  So the solution buy FDR and upgrade her in the US, upgrade Ark, then Eagle in the UK, retire / sell Vic and Hermes as CTOL carriers, while ordering a Nimitz in 1970 for delivery in 1979 to replace Ark.  A second one could be ordered in the mid 70s for delivery in the mid 80s to replace Eagle and a third in the mid 80s to replace FDR in the mid 90s. 

Initially I was thinking along the lines of an Anglo French CVN, or even a modernised CVA01 but the timing just didn't work out and the costs likely would have exceeded those of a US build at Newport News, slotting in between the builds for the USN.  Besides, the 53,000 ton limit was a political one, the RN always wanted a Forrestal sized ship to its growth potential and ability to operate and USN carrier aircraft type, it would also make it easier to design, or adapt UK aircraft designs for carrier operations. 

Maybe a way to get the RAF on board would be to literally get them on board with their Phantoms retaining carrier compatibility to provide a surge capability when required. there could possibly be a (highly inefficient) political compromise where the FAA has Fleet air defence, maritime strike and ASW, while all land attack and interdiction missions are the domain of the RAF flying their own Buccaneers, then Tornados, Jaguars and Harriers from the carriers as required by operational deployments.  Maybe the RN could even magnanimously allow their own Buccaneers to be transferred to the new RAF maritime command and look after the maritime strike role as well.
Alternative History and Future Speculation / Re: Q-band Tartar for the RN
« Last post by r3mu511 on April 15, 2017, 08:02:06 am »
re. higher frequencies and precision:

yes, the shorter wavelength of higher frequencies would, for a given antenna aperture size, give a narrower beamwidth (ie. being proportional to wavelength divided by aperture diameter) which would thus give better angular resolution, hence the advantages for resolving finer/more precise details...

thus it's a tradeoff in accepting a possibly larger surface clutter return in exchange for the better precision afforded by the higher frequency...

a narrower beamwidth also gives the possibility for better inter-clutter visibility: ie. one might receive more clutter return from the higher frequency if the EM energy falls upon a clutter cell, but the smaller surface patch could allow one to irradiate a cell containing a target which lies between clutter patches...
Propulsion / Re: EJ200 unbuilt variants
« Last post by zen on April 15, 2017, 06:27:05 am »
What I don't understand is the absence of maritime GT options for this engine to succeed the Spey.
Had the USN had the CVV type then this being produce able in other yards would permit the possible sale of one to the RN.
Alternative History and Future Speculation / Re: Q-band Tartar for the RN
« Last post by zen on April 15, 2017, 06:19:16 am »
For a SAM I'd imagine replacing the rocket with something more suited to the mission. Opting for a higher acceleration at the cost of endurance.

The use of Q-band is highly suited to precision in built up areas. There where civilian maritime radars for use in harbours and rivers based on this concept by the late 60's.

UK had worked a lot on this type and at least two working seeker designs were produced for Red Dean.
The RN felt that Q-band was the best option for their studies into a self defence SAMs for ships.
Popsy A
Popsy B using Red Hawk as the upper stage.
Mopsy using the US Meteor AAM with a UK Q-band seeker.
And then Orange Nell also using a Q-band seeker.
They would be very familiar with the issues that this band has.
I was thinking more of replacing the radar /missile combination to field something like AIM-47 or Eagle instead.
Alternative History and Future Speculation / Re: Q-band Tartar for the RN
« Last post by pathology_doc on April 15, 2017, 04:22:28 am »
A booster would take care of most of your problems.   The guidance system is a bit more difficult but would be fixable with sufficient time and resources behind it.

All well and good, assuming politics don't get in the way, but then there are the inter-service rivalries. Add on top of that the costs of redesigning the structure to deal with sea conditions (saltwater corrosion etc). Booster addition is going to be difficult, because the British tended to go for wrap-arounds (which means at least two) and that brings the requirement to get separation right. If you put a useful second-stage tandem booster on it, you get a missile that probably isn't much smaller than Terrier anyway.

The ground interference problem is interesting. Red Dean should arguably have been continued as a research programme in order to sort that issue out, even if it never went into full service, with a parallel programme to transistorise follow-on models and get at least the guidance-system weight and eventually the size down.

Red Hebe, of course, was never going to be small - probably because the ultimate driver of the size was the desire to fit a tactical nuclear warhead in it. Nuclear Falcon was a small nuke, but that presumes willingness of the Americans to supply the British with the warhead.
Alternative History and Future Speculation / Re: Q-band Tartar for the RN
« Last post by r3mu511 on April 15, 2017, 03:25:34 am »
... Q-band (Ka-band and Ku-band) avoids the issues of clutter over water, since the frequency is absorbed by water, obviating the issues of confusing reflections...

there appears to be some confusion here between: (1) the atmospheric attenuation of EM radiation due to oxygen and water vapor in the atmosphere, with it's marked attenuation increase in the higher frequency ranges, (2) the large attenuation of EM energy when propagating in sea water, due to the decrease in skin depth with increasing frequency leading to greater EM losses, and (3) sea surface clutter backscatter and it's relationship to the incident frequency...

the first one applies when the EM wave is propagating in the atmosphere, where higher frequencies such as K-band will experience greater attenuation losses due to the water vapor in the atmosphere... the second applies when the EM wave is propagating in sea water where the skin depth of K-band and higher frequencies is very small leading to a large loss in signal strength as it propagates through the sea water... but neither of these two determine the reflection losses as applied to the case of sea surface backscattering (ie. sea clutter) at the interface between the atmosphere and the sea surface...

in this third case, it is the reflection coefficient of sea water which determines the portion of the incident EM energy which is scattered, and in conjunction with the surface contour determines the clutter echo received...

what empirical studies/models show is that the backscatter normalized cross section of the illuminated sea surface patch is larger for higher frequencies (hence greater clutter return), for reference, this can be seen in the empirical model derived in "An Improved Empirical Model for Radar Sea Clutter Reflectivity", Hansen/Mital, Naval Reseach Lab, 2012, where a log (base-10) relationship to frequency was found for the sea surface clutter... this model was based on experimental data collected for various incident frequencies (including K-band), polarizations, grazing angles, and sea states, as presented in ch.7 "Sea and Land Backscatter" from "Radar Design Principles", Nathanson/Reilly/Cohen, 1991...
Propulsion / EJ200 unbuilt variants
« Last post by JFC Fuller on April 15, 2017, 03:06:29 am »
The attached document has, toward its end, reference to potential versions of the EJ200 and its growth curve. Also reproduced here is the text from a 1996 Flight International Article talking about thrust vectoring and potential growth paths entitled ITP draws up thrust-vector plan for EJ 200.

Eurojet partner ITP of Spain is planning to run vectored-thrust nozzle tests on an EJ200 engine developed for the Eurofighter EF2000 in early 1998. A first flight test could take place as early as 2000. ITP is already responsible for the nozzle on the basic EJ2000.

A thrust-vectoring EJ200 variant is one of several growth options being examined by Eurojet for the future. ITP is working with DASA, particularly because of its X-31 (thrust-vectoring, post-stall manoeuvring demonstrator) connection, says Rolls-Royce Military Aero Engines chief of advanced propulsion systems design, Stephen Morgan.

ITP, in which R-R has a 45% share, has set up a full-scale technology-demonstration programme for an axisymmetric thrust-vectoring nozzle for the engine. The nozzle is controlled by a novel arrangement of three concentric rings and the four standard EJ200 nozzle actuators.

The system fits within the current installation envelope and the nozzle provides the required pitch and vector control "as well as independent divergent petal exit area control", says Eurojet. The nozzle, is expected to be offered for the EF2000, as well as other airframes, such as the Saab JAS39 Gripen.

Retrofitting the engine to the EF2000 would present no problems, according to Morgan. The aft bulkheads of the production aircraft have been strengthened in anticipation of higher loads, and "-within the engine architecture, we're well placed to take care of it".

The vectoring nozzle would operate initially at the baseline EJ200 power levels of 60kN (13,500lb) maximum dry thrust, and 90kN with reheat. Optional growth plans cover taking power much higher by around 2010.

Eurojet's first growth step would raise normal power to about 72kN and combat power to above 103kN. Eurojet believes that this is feasible in 2000-7 by incorporating an updated low-pressure (LP) compressor, improved turbine cooling and materials.

The updated compressor would have a pressure ratio of 4.6 and a 10% increase in fan flow. "We're currently at [89kN] and, with Eurofighter in mind, the contract calls for a 15% increase in power. It's a straightforward step to 15% in the first phase," says Morgan, who adds that the fan change would be mainly a R-R responsibility, while MTU would upgrade the compressor.

The second phase of growth would follow in about 2010, taking dry thrust to around 78kN and combat power to nearly 120kN. This bigger step, would require a new LP system with a high-flow fan, a higher pressure ratio and a revised LP turbine. The core would also require "up-flowing".

The third EJ200-powered EF2000, the DA5, is due to be flown for the first time at Manching, Germany, in November, with the DA4 (the first UK-based EJ200-powered airframe) to fly in December. The DA1 and DA2 will have EJ200s in 1997.

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