The Ship Model Forum

Just to clarify, I didn't write that top speed; Seasick did and stripped out the quote tags.

Strange. Most published sources give a maximum speed of mach 1.95.

Seasick wrote:Tracy White wrote:


Before the F/A-18 was adapted to carrier operations it was the YF-17 Cobra. The Cobra was much lighter and easily capable of mach 2.

Colored pencils are hard wax, an insulator

Tracy White wrote:
Additionally, the Typhoon's square intakes will focus the stresses on the corners whereas the ovoid structures on the Vought birds spread it out.



One might gather from a simple census of the intake design choice made by modern fighter designers that square intake has strengths that far outweigh the issue raised above.

In reality, a fighter's intake is never a load carrying structural member. So resistence against stress concentration would have only a modest impact on its weight. The design of intake on a supersonic aircraft is largely dictated by the fact that jet engines can not operate unless the air it is sucking in hits its compressor face at subsonic speeds. This applies even to engines in highly supersonic aircrafts. What square intake allows one to do is to set up multiple intake shock ramps to reduce supersonic intake air to subsonic velocities before it hit the fan and compressor faces of the engine. This allows turbojet and turbofan engines to function efficiently at Mach 2+. While in theory this can also be done with a central shock cone in a round or semi-circular intake as was done in the SR-71, Mig-21, Mirage III, V and 2000, the shock cone in a round intake can not disappear while the shock ramps in a square intake can retract completely. Consequently a square intake with ramps is adaptable to efficient engine operation over a wider range of speeds than with a Mig-21 like round intake with a central shock cone. Fighters with round engine intakes and no shock cone, such as F-16, can not efficiently slow the supersonic intake air to sonic speeds before it hits engine face. Consequently they are limited mostly to below Mach 1.8.

The square intake is good for a fighter jet, but the square intakes on the Typhoon diminish further its ability to be adapted to carrier operations.

Before the F/A-18 was adapted to carrier operations it was the YF-17 Cobra. The Cobra was much lighter and easily capable of mach 2.

Tracy White wrote:Additionally, the Typhoon's square intakes will focus the stresses on the corners whereas the ovoid structures on the Vought birds spread it out.

One might gather from a simple census of the intake design choice made by modern fighter designers that square intake has strengths that far outweigh the issue raised above.

In reality, a fighter's intake is never a load carrying structural member. So resistence against stress concentration would have only a modest impact on its weight. The design of intake on a supersonic aircraft is largely dictated by the fact that jet engines can not operate unless the air it is sucking in hits its compressor face at subsonic speeds. This applies even to engines in highly supersonic aircrafts. What square intake allows one to do is to set up multiple intake shock ramps to reduce supersonic intake air to subsonic velocities before it hit the fan and compressor faces of the engine. This allows turbojet and turbofan engines to function efficiently at Mach 2+. While in theory this can also be done with a central shock cone in a round or semi-circular intake as was done in the SR-71, Mig-21, Mirage III, V and 2000, the shock cone in a round intake can not disappear while the shock ramps in a square intake can retract completely. Consequently a square intake with ramps is adaptable to efficient engine operation over a wider range of speeds than with a Mig-21 like round intake with a central shock cone. Fighters with round engine intakes and no shock cone, such as F-16, can not efficiently slow the supersonic intake air to sonic speeds before it hits engine face. Consequently they are limited mostly to below Mach 1.8.

I am no engineer; I will have to plead ignorance, but these problems sound like their very bread and butter. These things do not spring fully formed from the forehead of Zeus, but are the result of asking the very questions we are discussing here. What we lack is the impetus of danger to make the impossible, possible. Indeed, the zero risk path has proven itself to build unworthy aircraft in the past, and perhaps now with the F-35.

I believe the argument against low intakes is that they may ingest steam and warm air from the catapult track; with the CV 21's electric catapult this would not be an issue. Presumably, a British carrier's ski lift or catapult could avoid this issue.

Additionally, the Typhoon's square intakes will focus the stresses on the corners whereas the ovoid structures on the Vought birds spread it out.

The F-8 and A-7 had the intake infront of the cockpit. The F-16 and Typhoon both have at behind the cockpit.

Werner:
Once again, modern computer methods will fix many of the ills you describe.

The methods you mention prevent the problem in the initial design process. The computer can't change the laws of physics. The carrier modifications for the F-16 would raise the takeoff weight of the aircraft, and the location of the landing gear made it vulnerable to dammage. The F-8 and A-7 are similar looking to the F-16 at first glance but are very different. The Typhoon has the same problems.

What about the F-8 and A-7? Their inlets were certainly in the same class. Pilots who flew the F-8 had a high regard for it....

Werner wrote:Once again, modern computer methods will fix many of the ills you describe. They won't fix the intake location, but the Russians have shown ingenuity in this area by creating auxiliary inputs over the top of the wing, which open for take off and landing.

They will make it quicker to rework things, but they cannot overcome fundemental design elements that make an airframe unsuitable for carrier ops. The Typhoon's inlet makes it completely unsuitable for carrier ops and it's fuselage and wing design preclude relocating the inlet without a near-total redesign.

It would have been interesting to see how the Boeing design would have fared; other than the STOVL problems I think it was a much better program.

Tracy White wrote:It can if you suddenly bulk up the forward fuselage it'll throw your weight & balance off, which *may* result in weight being added aft to balance out, if things can't be shifted around. Lower air scoops such as that found on the Typhoon and F-16 very bad for carrier-bound aircraft, especially with the landing gear forces being transmitted through such a structure.

Once again, modern computer methods will fix many of the ills you describe. They won't fix the intake location, but the Russians have shown ingenuity in this area by creating auxiliary inputs over the top of the wing, which open for take off and landing.

We live in a new era, when an airplane like the 777 can take to the skies years before the first aluminum panel is cut, or a Tyrannosaur can run again, 75 million years after her death.

The governing laws of physics are immutable; modern computers give us opportunities to succeed or fail without risk. It is a "brave new world".

It can if you suddenly bulk up the forward fuselage it'll throw your weight & balance off, which *may* result in weight being added aft to balance out, if things can't be shifted around. Lower air scoops such as that found on the Typhoon and F-16 very bad for carrier-bound aircraft, especially with the landing gear forces being transmitted through such a structure.

Seasick wrote: Modifying an aircraft for carrier operations is a very complex process. It makes aircraft put on weight and cost more. A fighter making a carrier landing puts far more stress on the aircraft than a land based aircraft may take in years of operation.

The F-35 process teaches us that modern finite-element analysis will tell the manufacturer exactly what parts need strengthening to make a land-based aircraft suitable for a carrier. Clearly, based on the F-35 the number of changes amount to less than 35% of the structure of a modern combat plane. Most of these changes consist of slightly thicker structures or bulkheads and do not influence the design or manufacturing process in any meaningful way.

In the long term the Rafael suffers from the fact that there will be a much smaller number of aircraft produced than for other types. This results in higher operating cost as the aircraft ages. The Eurofighter would need some serious redesign to be made acceptable for naval service. The air intakes are in a bad location and the forward landing gear would need to be redesigned completely. The airframe and landing gear strengthening needed for arrested landings would require a near total redesign.

The only options to replace the F-35K are an RN F-35C variant, a RN F/A-18F variant, or a newer version of the Harrier.

Mofifying an aircraft for carrier operations is a very complex process. It makes aircraft put on weight and cost more. A fighter making a carrier landing puts far more stress on the aircraft than a land based aircraft may take in years of operation.

Laurence Batchelor wrote:Only the USN and not the RN needs carriers of 80,000tons, largely because it has the defence expenditure to operate them and also as its % of GDP spent on defence is much much higher than the UK's.

An unfortunate turn of phrase. The USN is the only service which can afford large flight decks based on the necessity of politics. Obviously, nearly every maritime service covets large flight decks; only Russia, France and now Britain have had the political will to even try for a minimal CTOL carrier.

Europe seems to have turned it's back to the regional conflicts that were spawned by centuries of European colonialism, relying on "Uncle Sam" to sort it out. Poor Australia, on the fringe of several future conflicts is seen as America's "lap dog", when in fact they are all too aware of the global "realpolitik".

If the USA would give up it's self-determined role as global peacemaker, we could cut our expenditures accordingly. Of course, there would be a sudden spike in wars abroad, but that's your lookout.

By the way, the worldwide GDP dedicated to the military is at a historical low, (US included), as it should be.

The CVF's were never designed around the F-35 or any other aircraft for that matter.
They were designed around tthe 1998 Defence Review White Paper which stated the need for a certain sized airwing; which could deliver a set figure in payload terms; in the number of sorties so desired; in either surge or sustained operations.
The RN could potentially put any one of 10 aircraft either in service or not on the present 65,000ton sized ships.
Only the USN and not the RN needs carriers of 80,000tons, largely because it has the defence expenditure to operate them and also as its % of GDP spent on defence is much much higher than the UK's.

I have always said they need to design ships to be ships and not for the purpose of carrying a specific battery of weapons. If you build the ship you can more quickly provide it with useful weapons. Designing a carrier around a plane which has not yet flown is a bureaucrat's folly.

Werner wrote:This is the moment when an extra 50 or 100 feet of flight deck is worth it's weight in gold bullion.

The three main UK Royal Naval bases need major modifications just to support the present 65,000ton ships.
Only one will actually have them and be used to support these carriers which will be Portsmouth I believe.
Thus any bigger and even more infrastructure costs would have to be incurred into the project.
Also the 1998 Defence Review worked out what our ideal sized carrier and airwing should be.
The CVF design as is currently meets those requirements.
It's just the airwing composition which is open to debate not the size of the ships anymore.
I think also the idea of Merlins or Sea Kings for AEW to be another poor mans folly!
Why does the RAF get AWACS and the FAA gets something inadequate?

This is the moment when an extra 50 or 100 feet of flight deck is worth it's weight in gold bullion.

Werner wrote:I think the best thing would be to navalize the F-22, taking advantage of twenty years of the Air Force's investment.

The same would apply to the Typhoon also which I think has consumed around �5billion for RnD and been in the pipeline since the 1970s.

Here are some of the novel design concepts the RN & BAE have considered if we are forced to ditch the F-35 and go for a navalised Typhoon, undoubtively ramping up the costs of operating such better twin engined aircraft:

The second application, FJCA was a more promising project. The biggest issues in this case are strengthening the landing gear and fuselage to allow arrested recovery of the aircraft and the marinisation of certain potential areas of corrosion. In the case of the former BAE Systems devised some novel solutions. For take-off the Typhoon's excellent short field performance combined with a ski jump ramp should allow for relatively short deck take-offs, removing the need for catapults. For recovery a number of studies were carried out, for example one looked at the use of fans to blow air across the deck while the aircraft lands. This would decrease the required landing velocity and therefore reduce the forces on the aircraft fuselage upon arrest. Other investigations examined linking the Typhoon's FCS to the pitch and roll of the carrier. This would allow automated flared landings to be carried out again reducing stresses on the aircraft.