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Canards And Airliners  
User currently offlinePPVRA From Brazil, joined Nov 2004, 8875 posts, RR: 40
Posted (4 years 6 days 10 hours ago) and read 3177 times:

We've seen pretty much all major commercial aircraft manufacturers crunch engineering formulas to stretch out some of their products, at times to what look like extremes. And sometimes, with brand new wings. But why not simply add canards? Stretch the fuselage in front of the wings, add a pair of canards like the Sonic Cruiser, and end of story. Sure you probably need some structural re-enforcements for the canard, but are they that difficult? I feel like I am missing something. Will flight control software need to be changed significantly from standard, non-canard aircraft, thus making it uneconomical?


"If goods do not cross borders, soldiers will" - Frederic Bastiat
14 replies: All unread, jump to last
 
User currently offlineGolfOscarDelta From India, joined Feb 2008, 169 posts, RR: 0
Reply 1, posted (4 years 6 days 9 hours ago) and read 3152 times:

You mean like this:


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Photo © Oleg V. Belyakov



From what i've read, Canards seem to have the following drawbacks
1. No Clean stall break (=> FAA won't certify) (Starship)
2. Very limited CG range (Starship and Avanti)
3. Complex flaps on the canard (Avanti) / movable canards (Starship) required to match moment/lift from deploying flaps on wings
4. From an operational perspective it may interfere with gate operation.

The main reason to use a canard would be to
1. Stall Proof the aircraft: i.e. prevent unintentional stalling by large AoA's, i think most of the new FBW aircraft have enough flight envelope protection that having a canard to do that is unnecessary, also, a canard by stall proofing the aircraft doesn't allow the wing to reach its maximum Cl.
2. Eliminate down force and make wing smaller by creating a lift based trimming forces: Nowadays in most cases airliners are pretty well trimmed with load and fuel and the tail produces little down force in cruise and i'm not sure that the advantages offered by a canard outweigh the drawbacks they impose.

I'm sure the more experienced folks around here will add a whole buncha more reasons to this and correct any fallacies i may have made.

[Edited 2010-04-12 20:43:25]

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 2, posted (4 years 6 days 7 hours ago) and read 3106 times:

Quoting PPVRA (Thread starter):
But why not simply add canards?

As a retrofit option, you're talking about running primary lift structure though one of the most densely packed portions of the airplane...you're going to have to do massive modification to the flight deck, EE bay, crew rest, or the premium cabin. None of those are particularly appealing options.

Quoting PPVRA (Thread starter):
Will flight control software need to be changed significantly from standard, non-canard aircraft, thus making it uneconomical?

It would need changing, but the change wouldn't be that much worse than what you have to do with a big stretch anyway, so I can't see that being the major obstacle.

Quoting GolfOscarDelta (Reply 1):
From what i've read, Canards seem to have the following drawbacks
1. No Clean stall break (=> FAA won't certify) (Starship)
2. Very limited CG range (Starship and Avanti)
3. Complex flaps on the canard (Avanti) / movable canards (Starship) required to match moment/lift from deploying flaps on wings
4. From an operational perspective it may interfere with gate operation.

As a retrofit, you'd avoid a lot of these issues because you'd still have the tail (fixes the stall and CG issues). The problem, I suspect, is that the extra work of a whole new lifting surface doesn't come close to passing up a simple tweak to the existing stuff.

Tom.


User currently offlinerwessel From United States of America, joined Jan 2007, 2238 posts, RR: 2
Reply 3, posted (4 years 6 days 6 hours ago) and read 3096 times:
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I think you're talking about a three-surface arrangement like on the Piaggio Avanti. In that case the forward wing isn't really a canard, rather it's actually a forward wing. Call it a biplane with a ridiculous amount of stagger.

In the case of the Avanti, you also get all three surfaces lifting, and the forward wing has no control surfaces, which keeps it simple. Conceptually, this might make a decent airliner design (it certainly works well for Piaggo!), but as a retrofit it would be fairly radical.

For a stretch, if you can find a place to mount the forward wing that doesn't generate a host of secondary problems (how's this thing going to fit into a typical gate?), it wouldn't be impossible. You would end up redoing the horizontal stabilizer and elevators, and the exact places you'd stretch to fuselage is an interesting question. You'd probably have to increase the size of the vertical stab as well, particularly if you now grew the forward fueselage more than you would in a more convention stretch.

The question is how much less work this would be than a wing extension.

But the Avanti had somewhat different goals and problems to solve - most notably the normal position for a wing on a bizjet is in a darn inconvenient spot - just look at the massive fuselage fairings around most bizjet wings. By going to a three surface arrangement Piaggo was able to mount the wing in a fairly ideal "mid" position while doing a good job area-ruling the interface, and still provide a larger than normal cabin. An airliner stretch is not going to be able to make use of any of those (and in fact, the forward wing will almost certainly get in the way of something).


User currently offlineswiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 4, posted (4 years 5 days 21 hours ago) and read 2939 times:

Quoting GolfOscarDelta (Reply 1):
1. Stall Proof the aircraft: i.e. prevent unintentional stalling by large AoA's, i think most of the new FBW aircraft have enough flight envelope protection that having a canard to do that is unnecessary, also, a canard by stall proofing the aircraft doesn't allow the wing to reach its maximum Cl.

Stall proof in a way, yes. But consider pulling out of a dive - high speed stalling. Canard will stall first, forcing nose down again.


User currently offlinePPVRA From Brazil, joined Nov 2004, 8875 posts, RR: 40
Reply 5, posted (4 years 5 days 21 hours ago) and read 2914 times:

Thanks for the responses everyone!

I guess if (and that's a big if) one wants to go in this direction, it's best to plan it out starting at the clean sheet stage. As for the gate space problem, could a moving system be implemented to resolve this without adding much weight? Folding, contracting, spinning (in case it is located above the fuselage). . ?

Quoting rwessel (Reply 3):
I think you're talking about a three-surface arrangement like on the Piaggio Avanti. In that case the forward wing isn't really a canard, rather it's actually a forward wing.

Either one, really. Just thinking of simplifying stretches or possibly taking stretches even further than what is done today.



"If goods do not cross borders, soldiers will" - Frederic Bastiat
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (4 years 5 days 20 hours ago) and read 2902 times:

Quoting PPVRA (Reply 5):
I guess if (and that's a big if) one wants to go in this direction, it's best to plan it out starting at the clean sheet stage.

Agreed.

Quoting PPVRA (Reply 5):
As for the gate space problem, could a moving system be implemented to resolve this without adding much weight? Folding, contracting, spinning (in case it is located above the fuselage). . ?

Technically, yes. This is exactly the situation that initially came up with the 777 regarding the wing tips. The fact that nobody took the folding option and elected to deal with it at the airport infrastructure end is probably very telling for the canard situation as well.

Quoting PPVRA (Reply 5):
Just thinking of simplifying stretches or possibly taking stretches even further than what is done today.

I think the problem is that, if it's a simple stretch, it's a lot easier to just tweak the existing surfaces than add a new one. And, if you're going for an even farther stretch (beyond what you can do today), you're committed to redesigning the fuselage structure anyway, so there's nothing really driving you towards a canard.

Tom.


User currently offlinerwessel From United States of America, joined Jan 2007, 2238 posts, RR: 2
Reply 7, posted (4 years 5 days 16 hours ago) and read 2759 times:
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Quoting swiftski (Reply 4):
Stall proof in a way, yes. But consider pulling out of a dive - high speed stalling. Canard will stall first, forcing nose down again.

That's only a matter of degree - yes, the canard design will likely stall the front wing with the main wing at a slightly lower alpha than a conventional design. That just means you have a bit less alpha to pull at any time, not just when pulling out of a dive. Conversely, the increased lift from the canard design will help you pull out of the dive, so frankly, it could probably go either way, depending on the exact design.

Nor is the net effect any different than stalling a conventional design in the pullout from a dive - in either case, once you exceed the alpha limit, you're going to stall, and the nose will drop.

And this is only really an issue for fairly low speed dive recoveries - once you actually get to high speeds, you're going to hit your G limits long before you hit your alpha limits.

And just for the record, I detest the whole "accelerated stall" concept. IMO there are many pilots (and passengers) who have ended up dead because we teach this idiotic notion that stalling is principally related to airspeed (unless it’s, *gasp*, an *accelerated* stall!). Of course we do that because the vast majority of airplanes don't have AoA indicators (and frankly those should be an equal, or maybe even higher, priority than airspeed indicators). But that's a personal hobbyhorse, and not really relevant to the thread...


User currently offlinePPVRA From Brazil, joined Nov 2004, 8875 posts, RR: 40
Reply 8, posted (4 years 5 days 14 hours ago) and read 2705 times:

I just noticed that the Tu-144 pictured above does have a folding canard. Didn't realize that at first.

Quoting tdscanuck (Reply 6):
Technically, yes. This is exactly the situation that initially came up with the 777 regarding the wing tips. The fact that nobody took the folding option and elected to deal with it at the airport infrastructure end is probably very telling for the canard situation as well.

Good point. On the other hand, the new A/B short/medium haul products appear to be growing in size, which could pose a bigger challenge to airport gate space than the 777 did just based on the number of 737 movements they see everyday, and into smaller gate spaces. Also, the 777's wingspan seems to be just slightly longer than the 747, which would make the airlines' choice of not going with the folding wingtips make a lot of sense. Move things around a bit and you can squeeze in an extra 40cm of wing.

With that said, folding wingtips sounds more complicated than shorter wings + a folding canard (or small forward wing as stated above) near the fuselage. I'm thinking of fitting all that heavy mechanic stuff all the way down the wing. . .eek.

[Edited 2010-04-13 15:44:16]


"If goods do not cross borders, soldiers will" - Frederic Bastiat
User currently offlinePPVRA From Brazil, joined Nov 2004, 8875 posts, RR: 40
Reply 9, posted (4 years 5 days 12 hours ago) and read 2674 times:

Quoting PPVRA (Reply 8):
On the other hand, the new A/B short/medium haul products appear to be growing in size

With that, of course, I assume so will wingspans. There have even been hints at twin-aisles, so space is tightening up   



"If goods do not cross borders, soldiers will" - Frederic Bastiat
User currently offlinePPVRA From Brazil, joined Nov 2004, 8875 posts, RR: 40
Reply 10, posted (4 years 4 days 18 hours ago) and read 2521 times:

This is probably even more far fetched, but is there any chance of we seeing morphing materials in civil aircraft any time soon? i.e., less than 20 years? I'd imagine that applying it for things like winglets and such would be fairly conservative and safe?


"If goods do not cross borders, soldiers will" - Frederic Bastiat
User currently offlineavt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 11, posted (4 years 4 days 17 hours ago) and read 2497 times:

As mentioned above, you'd have to enlarge the vertical stab, or add strakes, and pretty soon, you're flying a Beech 1900D.  

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 12, posted (4 years 4 days 5 hours ago) and read 2416 times:

Quoting PPVRA (Reply 10):
This is probably even more far fetched, but is there any chance of we seeing morphing materials in civil aircraft any time soon?

I'm pretty sure that the temperature sensitive nacelle chevrons are close to production...so yes.

Tom.


User currently offlinecobra27 From Slovenia, joined May 2001, 1003 posts, RR: 0
Reply 13, posted (4 years 3 days 13 hours ago) and read 2257 times:

Avanti doesn't have a reasuring look for me. It seems it to be harder to fly, but am sure its not true.
But is the most economical bussines plane out there, with 700 km/h speed and about half of fuel consumption of kingair.


User currently offlinerwessel From United States of America, joined Jan 2007, 2238 posts, RR: 2
Reply 14, posted (4 years 3 days 10 hours ago) and read 2221 times:
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Quoting cobra27 (Reply 13):
Avanti doesn't have a reasuring look for me. It seems it to be harder to fly, but am sure its not true.

FWIW, I've never heard a negative comment about the Avanti's handling...


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