KELPkid
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Why Are The Vast Majority Of Canards Pushers?

Wed Jun 12, 2013 8:21 pm

Just curious.

The classic modern canard right here (Rutan Long-EZ):


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In another tech/ops thread I'm involved in, another poster mentioned that the canard mounting point is a "busy" area of the plane's structure. I could see how putting an engine in there would just make things a mess.

It seems in the case of the Beech Starship, they *could* have used a tractor configuration, although the engine nacelles would have to have been longer to keep the props from hitting the swept leading edge of the wing. Then the aircraft would have benefitted from induced lift due to the prop wash. Then again, it is a product of Burt Rutan's mind.


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I'd bring up the Piaggio Advanti, but there seems to be considerable debate as to whether or not it's really a canard  
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oly720man
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RE: Why Are The Vast Majority Of Canards Pushers?

Wed Jun 12, 2013 8:39 pm

You'd also have the canards sitting in a rotating prop wash which would do no favours (favors) to the aerodynamics.
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rfields5421
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RE: Why Are The Vast Majority Of Canards Pushers?

Wed Jun 12, 2013 10:56 pm

I'd think a canard needs clean airflow to the canard and to the wing leading edge to be most efficient.

Which more or less requires canard prop aircraft to be pushers.

Even the jets with canards would be considered pushers.
 
prebennorholm
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RE: Why Are The Vast Majority Of Canards Pushers?

Thu Jun 13, 2013 12:12 am

It's mostly a center of gravity issue.

A canard must have its center of gravity much further back than an ordinary plane. That would be hard with a heavy engine up front.

Quoting oly720man (Reply 1):
You'd also have the canards sitting in a rotating prop wash which would do no favours (favors) to the aerodynamics.

Prop wash doesn't do any favor to ordinary planes either. But for center of gravity reasons it is on even bigger disadvantage to have the weight of the engine in the tail.
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KELPkid
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RE: Why Are The Vast Majority Of Canards Pushers?

Thu Jun 13, 2013 6:16 am

Quoting prebennorholm (Reply 3):
Prop wash doesn't do any favor to ordinary planes either

Accelerated airflow due to propeller slipstreams creates extra lift over certain sections of airfoils    And most prop airframes take advantage of this in some form or another...
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Scooter01
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RE: Why Are The Vast Majority Of Canards Pushers?

Thu Jun 13, 2013 10:06 am

There are conversion kits available for the specially interested group of pilots that needs STOL capabilities on their Cessnas. WREN, Robertson, etc.

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Here's also a video that explains a lot of the issue:
http://www.youtube.com/watch?feature=player_embedded&v=5eSFqGyKgsw

Hope this clears up something....


Scooter01
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KELPkid
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RE: Why Are The Vast Majority Of Canards Pushers?

Thu Jun 13, 2013 3:36 pm

Quoting Scooter01 (Reply 5):

Interesting. That one's new to me. Having intimate knowledge of the Cessna 182 nose area, I'm wondering how the canard interfaces structurally with the airframe. The only relatively beefy part up there is the engine mount  
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mrocktor
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RE: Why Are The Vast Majority Of Canards Pushers?

Thu Jun 13, 2013 8:42 pm

Quoting prebennorholm (Reply 3):
A canard must have its center of gravity much further back than an ordinary plane. That would be hard with a heavy engine up front.

This is the answer. The more forward the CG, the higher the share of the lift being carried by the canard. Since the canard is generally already the limiting surface (since it rarely has high lift devices), you really want your CG as far back as you can get it.
 
KPWMSpotter
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RE: Why Are The Vast Majority Of Canards Pushers?

Fri Jun 14, 2013 1:10 pm

In the designs you reference, the aircraft aren't pusher-configuration to fascilitate canard installation, the canard design was actually driven by the desire for a pusher engine configuration.

When you're powering an aircraft with a propeller, it is desirable to install the propeller in a pusher configuration. Tractor propellers are inherently destabilizing, and forward mounted engines are much harder to fair for aerodynamic efficiency. Pusher propellers are stabilizing, and allow a much more streamlined nose.

The Long-EZ configuration is just one which "works". It's aerodynamically efficient and all of the pieces are in the right place. If you shuffled the flying surfaces around to a conventional configuration (wing forward), the CG would be way too far aft. With the Starship, sure you could mount the engines the other way around, but then you would lose the stabilizing and aerodynamic benefits of a pusher propeller.

The only tractor canard aircraft I'm aware of are STOL conversions (like the Robertson STOL C182 posted above). In this case, the canards aren't true lifting surfaces, they are installed to supplement the elevators and allow more control authority at low airspeeds. In this case it's a good thing to have the canards in the prop wash, giving more control effectiveness.
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nomadd22
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RE: Why Are The Vast Majority Of Canards Pushers?

Fri Jun 14, 2013 7:58 pm

A lot of people don't care for the thought of debris off the wheels getting kicked up into their $3,000 props. But canards are almost stall proof. If you read the final version of the John Denver report, he had to work pretty hard at crashing his Long-Ez.
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dlednicer
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RE: Why Are The Vast Majority Of Canards Pushers?

Sat Jun 15, 2013 6:20 am

There are plenty of tractor propeller canard aircraft:

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KPWMSpotter
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RE: Why Are The Vast Majority Of Canards Pushers?

Sun Jun 16, 2013 5:59 pm

Quoting dlednicer (Reply 10):
There are plenty of tractor propeller canard aircraft:

Not to get bogged down in semantics, but the Quickie series and the Grizzly aren't truly canard aircraft, they are tandem wing aircraft (since the forward surface contributes a significant percentage of the total lift).

There's nothing *wrong* with installing a tractor propeller on a canard aircraft, but the configuration certainly does make it easy to install a pusher propeller (and why not install the pusher propeller when you can, it being aerodynamically superior).
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dlednicer
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RE: Why Are The Vast Majority Of Canards Pushers?

Tue Jun 18, 2013 3:54 am

I forgot three:

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