PDA

View Full Version : When Was Close-Coupled Canards First Possible?


Jane-DoH
21st Aug 2011, 00:30
While I know a delta-winged aircraft's takeoff and landing performance can be improved by using a canard to shift the C/L forward allowing the elevons to be drooped; some aircraft use close-coupled canards to further improve low speed performance by using the vortices generated off the tips of the canard to amplify the vortices off the delta-wing.

When did the knowledge first exist to produce a canarded delta whereby the vortex off the canard could be used to amplify the vortex off the wing's leading-edge?

Lyman
21st Aug 2011, 02:24
Needn't be canards per se, either. Hard chine, a la F-18, F-16. Brian Abraham, ask him, he knows.

Brian Abraham
21st Aug 2011, 05:57
The SAAB Viggen was the first to use the close coupled canard delta configuration, and the reason given for choosing this layout was, The canard arrangement has notable advantages in achieving a good field performance and weight-lifting abilities without resort to complex highlift "flappery." Lift/drag ratios are better by virtue of the fact that the foreplane, with drooped elevators to raise the nose on take-off, is providing positive lift, rather than lift being partially killed by the raised elevators or elevons of conventional wing-before-tailplane or tailless delta aircraft. There are much reduced interference effects between the mainplane and the smaller surface with a canard than with a conventional configuration.The Swedes disperse their aircraft and use motorways, hence the interest was primarily in STOL performance.

This paper by U. Claréus, Project Manager, JAS 39 Aerodynamics, Saab Aerospace, may be what you are after.

MACH Aviation Magazine - på webben (http://www.mach-flyg.com/utg80/80jas_uc.html)

Brian Abraham, ask him, he knows.
The flattery is misdirected Lyman. I do enjoy digging for the info in hope of guiding some one to a possible answer though. :)

Graybeard
21st Aug 2011, 12:10
When they stretched the DC-9 to make the 80 series, they had to make the tail larger. I thought at the time that would have been the perfect opportunity to add a canard instead, a la Piaggio.

Lyman
21st Aug 2011, 15:33
A Piggio operates out of SFO near hear. I think it is a charter.

IMO. canard, VT, Blown wing, etc. are creatures of Mil flight. On the other hand, if an airframe (commercial) needs tweaking with these things, then it perhaps should not be built, as a new airframe will design benefit the improvement out of its necessity.

IE Vortex generators, belly strakes, even NOTAR.

Maybe not NOTAR, the Tail Rotor is an evil to be wary of.

Managing airstream is a complexity. The last basic improvement that has my endorsement is the Wright's relocation of the Tail to the Tail.

Isn't NASA trying to develop fast jet "Wing Warping"?

There's the Ticket :ok:

Jane-DoH
21st Aug 2011, 21:09
Brian Abraham

The SAAB Viggen was the first to use the close coupled canard delta configuration

I'm not disputing that. I'm wondering when it was first possible to produce such a design that would work.

the reason given for choosing this layout was,
The canard arrangement has notable advantages in achieving a good field performance and weight-lifting abilities without resort to complex highlift "flappery."

What kind of "high-lift flappery" could have provided the desired performance for a delta-winged fighter design? As I understand the Viggen had a fairly low AoA on takeoff and landing.

Lift/drag ratios are better by virtue of the fact that the foreplane, with drooped elevators to raise the nose on take-off, is providing positive lift, rather than lift being partially killed by the raised elevators or elevons of conventional wing-before-tailplane or tailless delta aircraft.

I always thought that would always result in an unstable design?

There are much reduced interference effects between the mainplane and the smaller surface with a canard than with a conventional configuration.

Unless you're talking about downwash off the tail, I'm not sure I understand.

ChristiaanJ
23rd Aug 2011, 17:00
....using the vortices generated off the tips of the canard to amplify the vortices off the delta-wing.My guess is, that there you're confusing 'wing tip vortices' (from the canard in this case) with the 'vortex sheet' behind the canard,
Which acts (as suggested) not totally unlike a 'chine', while having advantages as a control surface at the same time.
As to your "when?" question, I have no idea, and I'll leave that to the historians here on PPRuNe....

FlightPathOBN
25th Aug 2011, 01:07
Speaking of 'wingtip vorticies', does anyone else consider the 'winglets' on the Airbus variants to be virtually worthless?

Lyman
28th Aug 2011, 17:09
That leaves, "Close-Couple".

Jane, can you enlarge on the coupled (arm?) bit?

flight.....define "virtually"?

barit1
28th Aug 2011, 17:12
When they stretched the DC-9 to make the 80 series, they had to make the tail larger...

Earlier than that, the DC-9-50 introduced fixed chines (aspect ratio << 1.0) on the fwd fuselage at floor level.

ChristiaanJ
28th Aug 2011, 17:42
Speaking of 'wingtip vorticies', does anyone else consider the 'winglets' on the Airbus variants to be virtually worthless?I doubt that.
It's added 'hardware', hence weight. so if the idea was 'virtually worthless' it wouldn't be there.... engineers are not as stupid as you seem to think.
Never mind that a lot of not-Airbus aircraft now also feature winglets.

CJ