What stalls first?

[emteeoh]

As I understood it, canard planes are usually designed so that the canard stalls at a higher airspeed than the main wing so that the nose will drop before the main wing stalls, making a stall "resistant" plane. The alternative is a canard that is still flying when the main wing stalls, which would aggravate the stall and be hard to recover from... I think.

 

 

However, I was reading about retractable gear on infinity's website, and saw this in the FAQ:

Someone (we'll call "A") relayed a friend's personal belief (we'll call "B") 'that during take off, if the main wing begins to fly before the canard and unloads the main gear, the oleo struts begin to extend, raising the aircraft's aft section and effectively decreasing AOA'. ANSWER: NO! -- if so, someone better warn Beech Craft, AV Tec 400, Jet Cruiser, etc. In reality ("A" figured), 'the nose lifts off before the main wing begins to fly (carrying load off the main gear)'. ANSWER: YES!! -- the canard begins to fly first and the plane rotates. If the wing begins to fly before the canard, then the canard is stalled -- a plane that really does this has some serious canard problems whether the mains are our main retract oleos, fixed main gear oleos, fixed fiberglass hoop main gear, retract fiberglass main gear, or retract fiberglass hoop main gear. "A" reasoned, "I hadn't thought about this before and now wonder if the main wing does start lifting at this time, wouldn't the hoop style fixed gear also stand up creating a negative AOA too?" ANSWER: CORRECT!!! -- logic prevails when one thinks this through :-) ;

 

I don't think this FAQ point is terribly well written, but it seems to say the opposite: that the canard stalls at lower speeds than the main wing, because, during takeoff, the nose lifts off first.

 

Now I'm not so sure what's really going on! What am I misunderstanding/overlooking here?

 

Is it possible that the canard stalls at a different AOA but the same speed?

[Phil Kriley]

You're really confusing yourslf here. The FAQ is correct. When the plane is sitting on all three gear, the wing's AoA is such that it cannot fly until the canard lifts the nose and creates a positive AoA on the wing.

 

Once both the canard and wing are providing lift, you want the canard to stall first - if the wing were to stall first it would likely be unrecoverable.

 

One other point - airfoils do not stall due to airspeed - they stall when they exceed their critical angle of attack (AoA). And airfoil can stall at ANY speed...

 

Hope that helps!

[emteeoh]

yes, that helps a lot. I *was* confusing myself quite a bit. Thanks

[Phil Kriley]

My favorite book to help understand why a plane does what it does is "Stick and Rudder" by Langewisch (sp?). It was first written back in the 1940's, but is as true today as it was then. Give it a read - I learned a LOT from it!

[TMann]

The whole Idea is to drop the nose so you can create some airspeed to get the canard flying again. Dropping the main wing first would cause the plane to try flying backwards. Never a good situation.

 

Even Bi-planes have a different angle of attack (Top wing vs. Bottom wing) in an effort to reduce the dramatic effect of the stall.

[argoldman]

The whole Idea is to drop the nose so you can create some airspeed to get the canard flying again. Dropping the main wing first would cause the plane to try flying backwards. Never a good situation.

 

Even Bi-planes have a different angle of attack (Top wing vs. Bottom wing) in an effort to reduce the dramatic effect of the stall.

Almost right, My Mann,

 

The idea is to keep the wing and it's ailerons flying and acting properly in all conditions and never achieve the angle of attack at which it would stall. As was mentioned before it is the angle of attack, not the airspeed that controls stall. The canard is scheduled to stall at a lesser angle of attack than does it's attached wing. In the typical canard "stall" there is really not much of an airspeed increase, if any, however the canard, when reaching its stall angle of attack will stall, the plane, rotating around the C/L of the still flying wing will decrease the angle of the canard, to the air stream (relative wind) bringing it back to the realm of the flying.

[Waiter]

Is it possible that the canard stalls at a different AOA but the same speed?

Deja-Vu:

 

1) For a particular weight/CG, (for us subsonic folks) the airfoil will always stall at exactly the same AOA, regardless of speed. Speed has nothing to do with a stall, AOA has everything to do with stall.

 

2) The Canard is supposed to stall at less AOA then the main wing.

 

3) I think the item you are refering to (from the Infinity Web Site) is trying to get to this point: With the plane sitting on all three, regardless of the airframe speed, there isn't sufficient AOA for the main wing to produce lift.

 

I can see what your saying, so let me try it this way:

 

With the plane sitting on all three gear, its AOA would be ZERO, regardless of speed.

 

(Note: The following AOA are estimated)

At 200kias, to maintain level flight , the AOA is about 1.5 degrees

At 150kias, to maintain level flight , the AOA is about 2.5 degrees

At 100kias, to maintain level flight , the AOA is about 10.0 degrees

At 60kias, to maintain level flight , the AOA is about 20.0 degrees

 

As you can see, If I was going to attempt to hold an AOA of ZERO, I would be in a descent, regardless of my speed. \

 

Waiter

[Phil Kriley]

Almost right, My Mann,

 

The canard is scheduled to stall at a lesser angle of attack than does it's attached wing.

Question: Are the chord lines of the wing and the canard parallel? To be clear - the plane is designed so that the canard will stall before the main wing. If the AoA is identical for the canard and the wing, then your statement above is correct. But I thought the canard had a higher incidence than the main wing - right?

 

So if I'm correct, then the canard stalls first, but not necessarily at a lower AoA. IOW - the main wing may be at 20 degrees, but the canard may at 25 degrees. Or am I wrong? Do the wing and canard have the same incidence relative to the fuselage?

[Waiter]

Are the chord lines of the wing and the canard parallel?

I seem to recall the wing and canard were "leveled" with the templates while the longerons were level. However, as you point out, this doesn't necessarly mean that the "Chord" is level, only that the top of the template was level. The "level" templates could have held the wing in any AOA desired.

 

Anyway, to remove AOA from the discussion, I'll try again:

 

I can see what your saying, so let me try it this way: It may be a better visualization anyway:

 

*****************************************************

With the plane sitting on all three gear, its Deck Angle (waterline) would be ZERO, regardless of speed.

 

However, while airborne,

 

(Note: The following Deck Angles are estimated)

At 200kias, to maintain level flight , the Deck Angle is about 1.5 degrees

At 150kias, to maintain level flight , the Deck Angle is about 2.5 degrees

At 100kias, to maintain level flight , the Deck Angle is about 10.0 degrees

At 60kias, to maintain level flight , the Deck Angle is about 20.0 degrees

 

As you can see, it requires a positive deck angle in order to produce lift. If I was going to attempt to hold an Deck Angle of ZERO, I would be in a descent, regardless of my speed.

 

Waiter

[Phil Kriley]

Thanks Waiter! Here's a follow-on question: Do you know at approx. what deck angle the canard will stall? JOOC - I'm bored today!

[Waiter]

Straight and level about 20 degrees. (SEEMS LIKE 90 when your doing it) This will happen at about 55KIAS and depends greatly on CG. (I operate at the aft limit)

 

Sometime at flyins, everyone else does a high speed pass. I find low speed passes equally impressive. I'll do a slow pass and just "hang" there at about 55 - 60 KIAS, gear down, speed brake down. SSSLLLOOOWWW

 

 

 

Waiter