Typhoon v Rafale Question
 

Good afternoon all …

OK … so my somewhat battered edition of Kermode (1972) isn’t too helpful on the topic of canards/foreplanes (no duck jokes please), so I thought some of you aerodynamicists might be able to help.

I came across a couple of cross sections recently of the Typhoon and Rafale which sparked my curiosity. Broadly speaking both aircraft are similar high performance, inherently unstable, designs benefiting enormously from the magic of FBW to achieve phenomenal maneuverability. In fact there is a degree of striking physical similarity in design other than the obvious use of canards/ foreplanes.

http://i1004.photobucket.com/albums/...psa878bf2d.jpg

Typhoon Cross Section

http://i1004.photobucket.com/albums/...ps99800669.jpg

Rafale Cross Section

I was, however, surprised to see that the Rafale has a marked Dihedral of the canard/foreplane as opposed the Anhedral of the Tyhoon. I understand that pitch control is provided by symmetric operation of canard/foreplanes and wing flaperons, while roll control is primarily achieved through differential operation of wing flaperons.

So my question … Why the need for either Anhedral or Dihedral on the respective canards/foreplanes ? What is the aerodynamic advantage ?

As I say just curious ...

Best ...

Coff.

I am no aerodynamicists.
But a guess.
Maybe this is to do with what the canard vortices are used for.

I'm not 100% about canards but from what I know about wings.
Dihedral (upward angled) wings contribute to stability. Often found on passenger a/c.
Anhedral (downwards angled) wings have more maneuverability. Found in museums on the Harrier.

Maybe with the Rafale, they wanted the back end to be manoeuvrable and the nose to be stable?

The physics are explained here http://en.wikipedia.org/wiki/Dihedral_(aircraft)

I don't think you will ever get an "exact" answer to your question, as aerodynamic design has so many trade-offs and compromises, and even more so in supersonic aircraft that have static instability controlled by FBW such as Rafale and Typhoon.

As you probably already know, more dihedral gives strong spiral stability which is generally desirable in transport aircraft. Anhedral gives manoeuvrability in subsonic aircraft - one of the reasons the SHAR had massive anhedral.

In the case of two supersonic fly-by-wire aircraft, I suspect you would have to go deep into the original design objectives of the aircraft, and then interview at depth the engineers who set out to meet those objectives. The fact that the Rafale and Typhoon have (apparently) similar flight characteristics shows that there are several ways of reaching the same end result, depending on which compromises the designers choose. I wouldn't believe any "simple" answer to your question!

Thanks Trim :ok:

Yes ... I understand the basic physics behind conventional wing anhedral and dihedral along with the need to trade off/compromise in order to optimise design/performance goals. It's just that such a marked anhedral on the Tyhoon canard/foreplane is perhaps easier to understand given the marked anhedral on the aft pitch control surfaces of such legacy mil FJ' like the Phantom, Harrier etc. against the complete reverse on the Rafale.

It's an interesting question ... Let's see what others come up with ...

Thanks again ...

Coff.

That's a fairly unique and interesting concept...

Like a bendy bus!

Those French...

Nose stable for not spilling of wine from lunchbox
Tail unstable for rapid surrendering and running away while waving white scarf???

Bonjourrrrrrrrr yer cheese eating surrender monkeys - said groundskeeper willie.
And yes, I do acknowledge the bravery of our chums across the water.

Foreplanes...not canards!

If my (failing nowadays) memory serves weren't the foreplanes on SaaB's mighty Viggen level?

RedhillPhil ...

Yep ... Viggen foreplanes appear to be level

http://upload.wikimedia.org/wikipedi...GGEN_AJ-37.png

LAL ... Stood corrected ... Foreplanes not Canards :ok:

I too would suspect that the vortex pattern is significant; re differences in fuselage cross section.
Rafale has some main-plane anhedral, so perhaps there is no need for it on the fore-planes.
Is there any difference in the fundamental control laws – aircraft axis reference vs fight path vector reference. IIRC Typhoon is the latter.

I would also think the proximity of the intakes would also come into play, as they actually are beneath the Foreplanes, unlike the Tiffie where they are below the fuselage. The cross section view does no show that well.


Photos: Dassault Rafale M Aircraft Pictures | Airliners.net

Canard foreplanes... :ok:

-RP

Coff,
Rafale's anhedral wing is good when you wanna play dead (or surrender :}), quickly.
Ducklings take dihedral to blow where they are supposed to, that is, whenever they don't blow under the wings.
Typhoon is a completely different design and just because they both have tails on the wrong side of the aircraft, they are nothing alike really.

Maybe someone can correct me if I am wrong. Memory says the reason for the Harrier anhedral was the Pegasus required a shoulder mounted wing and the max length of the outriggers decided the final angle.

I suspect the Harrier's anhedral may have also assisted with that aircraft's ground-effect hovering ability. John Farley?

Somewhere in the mists of time and Merlot, I seem to remember that the Phantom's tail was originally designed flat and was ineffective, it wasn't until the anhedral was added that the tail worked properly. Maybe something along similar lines ?

First you decide where you want the canards to be, in the vertical and longitudinal axes, which is a complicated ballet of size, moment arm, area ruling and visibility, even before you get to canard/wing interactions.

Anhedral and dihedral may have something to do with the interaction bit, but more importantly, you don't want large gaps opening up at small deflection angles. I talked to one of the lead designers on Gripen last year, and he said that he caught a lot of flak for making the inlets square (versus oval on Viggen) but it was for exactly that reason.

Also, the "dihedral" on Rafale's canards is sometimes a factor of viewing angle:

http://kovy.free.fr/temp/rafale/rafale_show9.jpg

The Toom's tail anhedral IIRC was to get it out of a bad vertical location relative to the wing (pitch up issues) and I believe the Harrier's anhedral had too do with avoiding excess roll stability, although JF may correct me.