It’s amusing that you get so hung up on Delta experience, as though it were an entirely new discipline of aerodynamics.

Newsflash. The Fairey Delta 2’s ‘FCS’ was cables and hydraulic boosters. It was of no relevance to the Tornado, nor to the Typhoon. Nor are the Mirage III and Milan of much relevance to the Rafale.

Despite its conventional tailed configuration, the highly unstable Jaguar ACT was of direct relevance to both, however.

Because the fundamental problem isn’t how to control a canard Delta aircraft, but how to prevent a highly unstable aircraft from diverging in pitch so quickly that it breaks up. It’s about detecting variations and making thousands of tiny corrections to keep the aircraft going nose-first and in the desired direction.

The usual offensive nationalistic guff.

“France is better than any partnership of aeronautical nothings like the UK, Germany, Italy and Spain. France alone has relevant experience. The usual empty, half-witted and tedious boasting. Dassault is Ferrari and EF GmbH is Toyota (why not Skoda, or Citroen?)….”

So let’s look at the facts.

The Mirage 2000’s instability should more properly be regarded as relaxed stability, and the aircraft remains controllable even without FBW. It uses what is in essence an analogue FBW system for what might properly be regarded as stability augmentation.

But we’re talking about the level of instability that is only possible with a fully Control Configured Vehicle, using full authority Active Control Technology.

With the F-104CCV, the FBW/ACT Jaguar and EAP, the EF partners had MUCH more experience in this field than Dassault, not less.

“The Rafale A, which first flew in July 1986, was a technology demonstrator with the additional task of optimizing the aerodynamic configuration for the full Rafale development program. It was the first French aircraft with full authority digital FCS.”

Five years earlier…..

“The first U.K. aircraft with a full authority digital FCS was the FBW Jaguar demonstrator aircraft. (Note: Programme 1977-84, first flight 1981.) The aim of this national research program was the design, development, and flight demonstration of a safe, practical, full-time digital FCS for a combat aircraft. The prime objective was the identification of the design methodology and airworthiness criteria necessary for flight certification and throughout the program the FCS was to be treated in all aspects as though it were intended for production. Although it was not intended to demonstrate the aerodynamic benefits of ACT, the program included flight demonstration of the aircraft in a configuration that was aerodynamically unstable in the longitudinal (pitch) axis, and demonstration of a stall departure and spin prevention system. These aspects were considered crucial to the practical realization of ACT. It was also decided that the FBW Jaguar digital FCS would have no backup flight control system of any kind from the outset of the program.”

Both from:

“Les Essais en vol des performances des systémes de
commande de vol numeriques”, published by NATO’s RESEARCH AND TECHNOLOGY ORGANISATION at BP 25, 7 RUE ANCELLE, F-92201 NEUILLY-SUR-SEINE CEDEX, FRANCE.

Note that the FBW Jaguar had no back-up for the digital FBW FCS, whereas Rafale has an analogue back-up.

“It was also decided that the FBW Jaguar digital FCS would have no backup flight control system of any kind from the outset of the program. The reason for this was twofold. Firstly, a mechanical system could not control an unstable configuration. Secondly, an independent electrical backup, whether analogue or digital, would introduce so much additional complexity, both in the design of the system (hardware and software) and in the flight clearance processes, that it would be counter productive. From the flight test point of view any such backup system would almost certainly have to be tested in flight with all the associated hazards that this would involve. In the event, the decision to have no back up system was fully justified since other demonstrator programs (e.g., the U.S. (AFTI) F-16) had significant problems with their backup systems.”

Someone had better tell NASA that their first unstable FBW aircraft in 1977 was pre-dated by the YF-16 and by the YF-16CCV, let alone by the FBW F-8 (1972) which was claimed to be the first aircraft with a Digital Fly-By-Wire (DFBW) FCS.

TMor,

EAP -Encore Au Parking- Hangar Queen, etc.

Are those nicknames that make you chaps feel better, because they’re unknown over here, where the EAP is remembered fondly, not least for its serviceability and availability. It might be interesting to compare the flying rate achieved in the same period by Rafale A and EAP…..

They have had troubles in developping FCS. It wasn’t easy at all, while Dassault had not such troubles.

There were troubles, of course, not least because the decision was taken to re-invent the wheel. With a well regarded, very effective UK-led FBW FCS developed and flying on EAP, the Germans were given design leadership of the FCS. This naturally imposed a delay between EAP and the DAs, though in the event, it seems that the final solution was closely based on that of EAP. But you infer technical troubles that needed to be ‘put right’ when what there were were challenges that were successfully met.

If you think that Dassault didn’t face and overcome similar challenges, you’re deranged!

The Flight article which you liked so much demonstrated the contribution of instability to agility (always disputed by some of your compatriots) and gave useful evidence as to why the long-coupled canard is an advantage (again, something that is always disputed by some of your compatriots).

I was pleased to see an article from 1999 again.

It did not support your contention of “Widely varying CofG positions” except with external stores – which you blokes were heralding as being something unique to Rafale a page ago.

It did not support your contention of a “nightmare to fix the FCS”.

Do you think that (even with their less ambitious targets on instability) Dassault’s FCS people didn’t find that:

“A lot of aerodynamic studies and windtunnel testing were required to understand the complex flow mechanism and to maximise the benefits while keeping detrimental effects as low as possible”

and that they didn’t have to

overcome “very significant challenges”?

You clearly don’t really understand what you read. Transonic pitch up is inevitable in an aircraft of Typhoon’s configuration and instability, and obviously needs to be mitigated. The paper you linked to contains nothing to support your contention that this was a “Max G load overshoot experienced at transsonic speed” nor that it was a major or unusual problem, nor that it “led QinetiQ et al. to be more cautious.”

I hope that you did understand this extract from your linked Flight piece. (You may recall how many French posters have disputed the correlation between instability and agility).

In a longitudinally stable configuration, the centre of pressure is behind the centre of gravity (cg). As the aircraft pitches up, lift increases and acts to push the nose back down. In manoeuvres, the trailing-edge control surfaces must be deflected upward, reducing lift, to trim the aircraft.

In an unstable configuration, lift acts forward of the cg and therefore amplifies any pitch excursions – intentional or unintentional.

(This gives a hint as to why pitch up needs to be mitigated)

Instability reduces the trim drag of a delta because, in manoeuvres, the trailing-edge surfaces are deflected downward, towards the optimum wing camber. Leading-edge devices, when deflected downward, further optimise camber and allow the delta wing to generate high lift with less drag.

An unstable aircraft is also more responsive in pitch, increasing its agility. Although the Euro-fighter becomes stable supersonically, when the centre of pressure moves aft, it is still less stable than a conventional configuration and therefore retains the advantages of reduced trim drag and better turn performance.

A delta alone does not provide the required agility, however. Adding a foreplane generates lift ahead of the cg, helping destabilise the aircraft, and do you think that a longer coupled canard destabilises the aircraft (thereby making it more agile) more or less than a short-coupled canard? and the interaction of the foreplane vortex with the wing flow increases total lift to more than the sum of both surfaces. The same vortex interaction shifts the wing aerodynamic load distribution inboard, reducing bending moment and structural weight.

Eurofighter says the delta/canard configuration results in a shorter, lighter aircraft, but admits it has less attractive features. The foreplane, for example, can amplify the already non-linear aerodynamic characteristics of the delta. Another hint, for you, as to the true significance of the AIAA paper to which you linked. Full-authority fly-by-wire is required to handle the aerodynamic non-linearities and to artificially stabilise the aircraft.

Experience with highly unstable configurations, provided by the German F-104 Control Configured Vehicle and UK Active Control Technology Jaguar research aircraft, was fed into the Experimental Aircraft Programme (EAP). First flown in 1986, the EAP demonstrator incorporated many of the design features of what was to become the Eurofighter, and made “an extremely valuable contribution” to the programme, says Friemer.

Eurofighter designers wanted as much instability as possible, for minimum drag and maximum agility. “We aimed for 15% early on, but settled for 8%,” says Friemer.

The maximum pitch instability possible was determined by the capability of the flight controls. “We needed highly dynamic actuators, which drove the level of instability we could achieve,” he says.

“Widely varying CofG positions”, eh?

Not true. The C of G range would fit within a box whose cross section is “the size of a sheet of A4 paper”, according to a senior EF GmbH design engineer.

A “nightmare to fix the FCS”?

Not true again, according to the Typhoon project pilot at QinetiQ at the time – oh yes, and not according to Messrs Penrice, Turner, Bowman et al either.

You imply that there was a serious problem with “Max G load overshoot experienced at transsonic speed”

Not true again.

If you’re going to resort to made up nonsense, then any further argument is pointless. You show your prejudices with the imbecilic accusation that Typhoon is “a less than perfect design”. No aircraft is perfect, but you infer that Typhoon is further from perfection than Rafale, which is predictable nonsense.

Farnborough 98 and Farnborough 2000 – though the displays were alternated – Hartley one day, Worning the next.

The absolute ultimate, jaw-droppingly brilliant display was apparently the one at Warton when the Singapore evaluation team were there……

😉

:diablo:

😀

TMor,

Moussez toes the party line. All the time. CP may have done when he was a Typhoon TP (though I doubt it), but is very balanced and critical now. He also has extensive experience of a very, very wide range of aircraft (including F-35 cockpit) and is widely respected amongst his peers as having one of the sharpest and most analytical pilot minds out there.

Some of you French blokes will argue about anything, even when Rafale is being given the benefit of the doubt and credited with an advantage.

if the RAF wants to put a higher G limit than, say the german air force, then surely they can decide the G limit they want as long as it stays within the manufacturer limits.

No they can’t, because the lowest limit is the one incorporated in the software release, and everyone has the same software. Thus German Typhoons (for example) will have austere air-to-ground, even though they don’t want or need it.

caution isn’t the only driving factor when it comes to setting up limits on the plane’s manoeuvrability. For instance they say in the article about the Rafale that the FCS protects the flight envelope, but also the airframe so it can reach its 7000 hour potential!

Dassault would also want their aircraft to meet the contractually agreed airframe life, and so would EF GmbH. I suspect that the difference is that

1) both manufacturers say the same thing:

“Here’s our aircraft. Extensive testing and simulation leads us to conclude that g should be limited to X, alpha to Y, etc. in order to meet the required safety and airframe life requirements.”

2a) Then the CEV take a long hard look at the aircraft and say:

“Y’know, Dassault got this absolutely right. If we do what they say, then the aircraft will meet the requirements.”

3a) And the MN and AdlA get their jets, observe the manufacturer’s limits (as validated by the airworthiness and test folk) and are happy.

but

2b) WTD61 take a look at their aircraft, and say:

“This is all a bit close to the limits, to be safe, to fulfill our duty of care, and to fulfil European H&S legislation, perhaps we should reduce the g limits a tad.”

and

2c) QinetiQ take a look at their aircraft and say:

“If we just validate EF GmbH’s recommendations, people might ask what value we add to the process – we’re privatised now, so we need to do something to justify why we’re here. You might say that the Alpha limits are a bit generous, so lets fly a series of trials and recommend a slight reduction…..”

etc.

and as a result

3b) The RAF, Luftwaffe, AMI and EdA get their jets, with limits tinkered with by the airworthiness and test folk) and are just slightly puzzled that the jet isn’t quite as impressive as the DAs were…..

You suspect, but in fact, you don’t know anything.

Yeah, yeah. I made it all up, Kovy. The over-caution of QinetiQ isn’t a regular topic of conversation at OEU level……. and WTD61 are regarded as glass chewing warriors who go the extra mile to get the most capable possible aircraft to the frontline.

Both the armée de l’air and the MN put safety, service life and and costs of use as priorities.

They do indeed, but they do so without unnecessarily and over-cautiously restricting the jet.

That would be silly.

But I wouldn’t mind betting that the current in service airspeed limit is lower than the limit cleared by industry.