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Subject: CVF propulsion question
EssexBoy    6/29/2008 5:53:12 AM
Hello, can anyone help a non-engineer understand something? On the CVF propulsion page on the Navy-Matters website it states that modern steam propulsion never seemed to be a likely option for CVF. Yet on the PA2 page of the same website it states: "however DCN had done a considerable amount of work investigating propulsion options, and despite a close association with Rolls-Royce, for an aircraft carrier of this size equipped with steam catapults it favoured using a modern steam (boilers and turbine) propulsion system with conventional shafts. As DCN was leading the ship platform design and build aspects of the Romeo Project/Juliete, it's ideas would have predominated if that Project had continued." Does anybody know why the UK weren't interested in steam propulsion? Was it simply that they were initially only interested in a STOVL carrier and therefore didn't need the steam for catapults? The reason I ask is that from my limited knowledge it appears that using steam propulsion the UK could have built a smaller, cheaper CATOBAR carrier and avoided a lot of the problems involving manufacturing and basing the CVFs. Do you think this would have been possible? Thanks Essex
 
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Herald12345       6/29/2008 9:06:53 AM
Yes. Its also true to say that the RN was interested in fuel economy and compact well-distributed power-plant footprint in its carrier. Its kind of hard to do that with steam turbines-much easier to do with gas turbines and diesel-electrics.
 
Herald.

 
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ArtyEngineer       7/2/2008 3:55:52 PM
I believe that if the carrier is retrofiited to a CATOBAR configuration the Catapult will be of the electro magnetic type, hence no need for steam.
 
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EssexBoy       7/3/2008 3:21:51 PM

Yes. Its also true to say that the RN was interested in fuel economy and compact well-distributed power-plant footprint in its carrier. Its kind of hard to do that with steam turbines-much easier to do with gas turbines and diesel-electrics.

 

Herald.





Odd that DCN came to a different conclusion. I wonder why?
 
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flamingknives       7/3/2008 3:42:33 PM
I suspect that DCN was looking at the fact that the Marine Nationale need catapults, and are unable to function without them. Since EM catapults are a little way away at the moment, going down that route isn't an option if you want carrier capability before 2025. The French are stuck with steam catapults, hence steam propulsion makes more sense.
 
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LB    CVF size   7/4/2008 10:40:52 AM
Actually the CVF seems very large for the intended size of the air wing and one would assume that doing without cats and arrester gear would allow a smaller carrier.    Consider that the Charles DeGaulle is about 45,000 tons and operates around 40 aircraft while CVF is about 65,000 tons and operates the same number of aircraft.   The 25,000 ton HMS Hermes could operate almost 30 Harriers.  Given Rafale the French were always going to go CATOBAR.
 
It almost seems that the RN is losing many advantages of going V/STOL.  Operationally it's better to have 3 carriers and 2 wings so 2 wings are normally available than 2 + 2 where 1 carrier down for service means the air wing is grounded.  So it would seem a better trade to go for the most cost effective carrier instead of building one too big and putting extra capability into it.  Then again it's not as if the RN will have enough escorts to support 3 carriers so maybe 2 is better...

 
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interestedamateur       7/4/2008 12:40:06 PM

Actually the CVF seems very large for the intended size of the air wing and one would assume that doing without cats and arrester gear would allow a smaller carrier.    Consider that the Charles DeGaulle is about 45,000 tons and operates around 40 aircraft while CVF is about 65,000 tons and operates the same number of aircraft.   The 25,000 ton HMS Hermes could operate almost 30 Harriers.  Given Rafale the French were always going to go CATOBAR.

 

It almost seems that the RN is losing many advantages of going V/STOL.  Operationally it's better to have 3 carriers and 2 wings so 2 wings are normally available than 2 + 2 where 1 carrier down for service means the air wing is grounded.  So it would seem a better trade to go for the most cost effective carrier instead of building one too big and putting extra capability into it.  Then again it's not as if the RN will have enough escorts to support 3 carriers so maybe 2 is better...




 
Have a look at the very long VT/BaE carrier thread. Herald explained this during a rather amusing (to an outsider!) 242 post argument between himself and Neutraliser which incidentally included whether the Falklands was like the Battle of Iwo Jima or Mauritius amongst other things! As I understand it, the reasons for the small number of aircraft are due to the two Islands and the fact that the RN has significantly increased bunkerage.
 
No doubt Herald will correct me if I've got it wrong.
 
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neutralizer       7/5/2008 6:33:17 AM
IIRC, way back when CVF was being first mooted there was a statement from someone that a rule of thumb was athat each aircraft needed 1000 tons displacement.  Clearly this approximation doesn't seem to be holding.  It also seems common sense that greater displacement needs greater propulsive power so there is a cost involved.  It also seems that the crew is small compared to US CVNs.  Of course there are many possible reasons for this including less crew needed for 'housekeeping', different tradestructures that mean RN has fewer but more widely qualified maintainers for ship and aircraft (in the past this has been a clear differentiator between UK, etc forces and the US, don't know if it still is).  Of course smaller crews would suggest a smaller ship!  Improved accommodation can't be the whole answer.
Another of my inspired guesses, all pics of USN carriers always show aircraft parked on the flight deck.  Reading the RN's desciption of CVF dimensions suggests it has 2 hangar decks, and it may be that 40 aircaft is the maximum capacity of these with aircraft manouvring space and RN has decided they want to be able to keep all aircraft below (for whatever reason, including deception).  Another possiblility is connected with CVF being a 'multi-mission' ship, not just a carrier.  25,000 tons displacement seems a hell of price to pay, even if it is partially for a greater fuel load for ship and aircraft.  However, they obviously think the price is worth it, whatever 'it' is.
 
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stephen    cvf size etc    7/5/2008 2:32:16 PM
I have heard the 1000 tons carrier per plane ratio before, and have been wondering why the CVF is approaching 2000 tons of ship to support one aircraft. There was an article in the press which suggested that the capacity of the hangar was only for 14 aircraft! I cannot believe that is correct so perhaps there are two hangar decks or the statement was simply wrong.
 
One aspect of the CVF design was the the bow was narrowed to improve performance in line with French expectations of ship speed. This would limit the ability to stow as many aircraft below decks but not by 20-30 units.
 
So I suspect one of the earlier contibutors to the thread was correct, the RN have probably increased the supply capacity of the ship and/or not fully exploited the capacity for flight group planning. It will be unlikely the UK will field two full naval air groups for these ships, especially given there are barely 30 harriers operational at any one time.
 
Stephen
 
 
 
 
 
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flamingknives       7/5/2008 3:35:07 PM
It's quite possible that 40 aircraft is the standard airwing, and there is capacity above and beyond this for surge operations.
 
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gb-rate       7/5/2008 8:01:21 PM
    The airwing is definately undersized for the carrier. It wouldn't be a great leap of imagination to come to the conclution that the RN was behind this undervalueing since they cared more about the short term goal of getting the hulls in the water. A smaller airwing makes the whole project cost much reduced when politicians look at the bill besides the RN knows that the aircraft would be wholely owned by the RAF so consequently placed less importance on there being enough planes for the decks.
    On the issue of the F 35s we need at least 150 to be able to even fill the undervalued decks which will probably will not happen, it is my opinion that the 3rd tranche Typhoon should be sacrificed to ensure a full order.

 
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