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Higher CLmax?


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One issue with canards is that you can never reach maximum lift coefficient (CLmax) of the wing. One result of this is a a faster touchdown speed. Flaps/slats are not possible because of the risk of stalling the wing before the canard.

 

How could a greater CLmax be reached for takeoff/landing?

 

Please note: this topic is THEORETICAL ONLY. I am not suggesting modifying the aerodynamics of a canard aircraft in any way without thorough stability and control analysis and *extensive* wind-tunnel / flight testing, all of which performed by someone smarter and braver than me...

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Here's my first thought: add flaps and/or slats to the main wing, mechanically coupled to a device that reduces the pitch of the canard or canard elevator.

 

I envision two separate settings: "cruise" with flaps up and "Landing" with flaps down. Coupling the two would prevent the two surfaces from ever being in a "mixed" state (not sure how to do said coupling, pushrod?). Adding high-lift devices to the wing would increase CLmax and the stall AOA, while lowering the AOA of the canard would delay stalling the canard so you can use more of that higher CL of the wing.

 

Of course what happens in flight when you shift to landing mode? A quick decrease in lift of the canard, increase in lift of the wing... what happens to pitching moment when you add flaps? I'll go look it up...

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How could a greater CLmax be reached for takeoff/landing?

See what the Starship did. Flaps extend, and the sweep of the canard decreased, as the sweep was coupled to the flaps. In fact, the canard would have a slight forward sweep with full deflection of the flaps.

 

Here's my first thought: add flaps and/or slats to the main wing, mechanically coupled to a device that reduces the pitch of the canard or canard elevator.

Whoa - backwards. See above. When the flaps extend, the pitching moment increases a lot - you then need MORE lift from the canard, not less. Reducing the lift of the canard as the flaps extend is guaranteed to drop the nose and require more elevator, which you will soon run out of as your speed decreases.

 

The Starship moved the canard center of lift forward by decreasing the sweep in order to counteract the added pitching moment from the flaps on the main wing.

 

You could also add flaps to the canard, but with full width elevators, where would you put them? The canard could slide forward/backward, but the sweep change was apparently deemed simpler, mechanically.

 

You also have to be careful, as the canard center of lift (and therefore the aircraft center of lift) moves forward, by whatever means, that you don't move the center of lift forward of the aircraft CG, at which point the aircraft would become unstable in pitch.

 

Of course what happens in flight when you shift to landing mode? A quick decrease in lift of the canard, increase in lift of the wing... what happens to pitching moment when you add flaps? I'll go look it up...

See above.
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So I think there's two separate troublespots to consider when lowering the wing flaps:

 

1) Changing the canard by reducing the AOA or increasing the stall angle. Otherwise you can't take advantage of the increased stall angle of the main wing (canard will still stall before the "clean wing" stall angle).

This is why I suggested reducing AOA of the canard, but doing so contributes the other problem:

 

2) Control issues caused by a big pitch-down moment from the increase in wing lif, "negative" increase in wing pitch moment.

You're right, you'd need to increase the lift of the canard in order to maintain control. So you'd have to ease in a bunch of aft-stick to compensate for the flaps? Or Vortal's suggestion of separate flap / pitch controls.

 

See what the Starship did. Flaps extend, and the sweep of the canard decreased, as the sweep was coupled to the flaps. In fact, the canard would have a slight forward sweep with full deflection of the flaps.

 

Didn't know that about the Starship! Did the canard unsweep to change location of the aerodynamic center or to delay onset of stall? I would guess both, as it helps with both problems above.

 

 

 

 

Interesting to scratch the surface of some of the big design decisions: makes you appreciate how hard the original designers had it.

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it would be a nice thing to find a way of installing a high lift device (not necessarily flaps) on these canards because this is the main show stopper to have bigger canard aircrafts. you don't want to land at 150kts or faster, because all the runways aren't 6000ft long, and landing of runway at that speed is a problem.

in the other end, you don't want to much wing surface to land slow and have to much induced drag at high speed... (trade offs!!!)

we have the example of the starship, with a heavy high lift system, that brought the stall speed something like 5kts down, and was not worth the weight added (you'll find these comments in other threads in this forum)

 

what is acceptable on a LEZ or a COZY IV is not accepetable on a 6 seater or a twin... or even bigger

and forget Fly by wire also!

 

that's a problem I'm working on right now, this one and others...

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So I think there's two separate troublespots to consider when lowering the wing flaps:

You need to study some aero texts, with respect to CG/Aerodynamic center relationships, as well as pitching moments. Also, you don't increase "Lift" by adding flaps, you increase maximum lift coefficients. It doesn't do any good to increase the lift on the main wing if you don't do the same on the canard, since the canard MUST stall first. You can't go slower (which is the whole purpose of putting the flaps on) if the canard is stalled. It doesn't do any good to LOWER the incidence angle of the canard, because it doesn't change the max Cl of the canard, which is what determines the stall speed.

 

Didn't know that about the Starship! Did the canard unsweep to change location of the aerodynamic center or to delay onset of stall? I would guess both, as it helps with both problems above.

Just to change the aerodynamic center - it wouldn't have any effect (or at least not much of one) on the stall onset. Don't know why you'd think it would...

 

Interesting to scratch the surface of some of the big design decisions: makes you appreciate how hard the original designers had it.

Yeah, which is why I'm always amazed when non-aircraft designers think that they can just change things willy-nilly. There's a lot going on here, in many different regimes. The first thing is to understand the balance of forces on the aircraft when in a static situation - once you do that, you can understand what the issues are with lift augmentation devices on canard aircraft.
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it would be a nice thing to find a way of installing a high lift device (not necessarily flaps) on these canards because this is the main show stopper to have bigger canard aircrafts.

Actually, the main show stopper to having bigger canard aircraft is that they're not as efficient as conventional or 3-surface aircraft. I know that canard aficionado's don't like to hear that, but it's a fact. While canard aircraft do have some advantages (stall resistance), there's nothing that a canard aircraft can do that a non-canard can't do if the engineering is applied to it, and although all else being equal, the canard is more efficient, all else is never equal, and in reality the 3-surface aircraft is the most efficient, and the conventional layout is not less efficient than the canard.

 

in the other end, you don't want to much wing surface to land slow and have to much induced drag at high speed... (trade offs!!!)

Induced drag is a maximum when at low speeds and high AOA's. It's at a minimum at high speeds. Adding wing area to land more slowly does not add to induced drag at high speeds - it actually lowers the AOA required, lowers the Lift Coefficient, and increases profile drag (more skin friction due to more skin).
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Actually, the main show stopper to having bigger canard aircraft is that they're not as efficient as conventional or 3-surface aircraft. I know that canard aficionado's don't like to hear that, but it's a fact. While canard aircraft do have some advantages (stall resistance), there's nothing that a canard aircraft can do that a non-canard can't do if the engineering is applied to it

Agree 100% with you, canard aren't as efficient as conventional or 3-surface aircraft. Just have a look at what's flying over your head and 99% of the time it's a conventional aircraft. The 1% left is maybe canard or a 3 surface (when you get to see an avanti)

 

But are we in the canard business for efficiency? i'm not, if i was i would go for a lancair or something like that... Canard business is about the looks, if you see a king air pass by, you will hardly notice it, if a starship passes by, every one will have there eyes wide open on it.

People say that a canard is safer because it's unstallable. Seriously, are you trying to stall you aircraft at each flight?

 

People (private) buy things on the looks before buying on efficiency, (i'm working on business aircraft, and customers want the thing to look good, and to be cheep, then later on to be efficient (at lease not to inefficient)...they prefer 300lb wood than 50lb laminate for there interiors, 150lbs of flashy paint than a 50lbs of plain white...)

 

Canard aficionado's just wont admit that they have/want a canard because it looks cool, not because it's "more efficient"...

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But are we in the canard business for efficiency?

Yes - that and stall resistance. The fact that in theory, conventional aircraft and 3-surface aircraft are more efficient doesn't mean that in the particular use-model of aircraft that I'm looking for (which for me is a high-speed cross country cruiser) that a more efficient conventional or 3-surface aircraft actually exists. It does not.

 

i'm not, if i was i would go for a lancair or something like that...

Would you? Why would you want to get about 1/2 of the fuel efficiency of a COZY MKIV? Your basic premise is flawed. The other 4-seat aircraft (Cirrus, Cessna 400, Lancair IV/P, etc.) get about 10-12 NMPG. I get anywhere from 17 - 25 NMPG - better than my Subaru Outback, at about 2.5 times the speed.

 

Canard business is about the looks...

That's absurd on the face of it. Picking an aircraft because of it's looks is brain damaged. If you like the looks, that's great, but the functionality has to be there. VE's get 35 - 60 NMPG, LE's get 25-40 NMPG, and COZY's 15-25 NMPG. Looks are one thing, but efficiency is a large part of the appeal. Find other 2 seaters or 4-seaters that get that type of efficiency.

 

People say that a canard is safer because it's unstallable. Seriously, are you trying to stall you aircraft at each flight?

First of all, no one claims they're "unstallable", what's claimed is that they're stall resistant, which they are.

 

And claiming that stall resistance in an aircraft is unimportant because you don't TRY to stall your airplane regularly shows a lack of understanding of flying fundamentals. I have had the stall resistant nature of my airplane save my ass at least once, when I had a bit of ice on the canard and stalled it on downwind-base turn at 800 ft. AGL. No issue - go around, let the ice melt for 5 minutes, back in business. Conventional aircraft - very exciting at the best, assuming I could recover from the stall / incipient spin in 800 ft.

 

There is no question that the stall resistance is a safety feature of the aircraft. It's hardly the only important characteristic of the type, but don't minimize it - it IS important.

 

Canard aficionado's just wont admit that they have/want a canard because it looks cool, not because it's "more efficient"...

Speak for yourself, will you please? Especially when you don't know what you're talking about. I got my plane because it was the only four seater that I could afford that could do what I wanted vis-a-vis speed, efficiency, carrying capacity, and safety. While I like the looks, it was item #4 or 5 on the importance scale.

 

So then, stall characteristics aside, what conventional design meets or beats a Cozy, performance, cost, community support, material, plans built, engine?

None. Exactly zero. Even in kit form - don't restrict it to plans.
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You need to study some aero texts, with respect to CG/Aerodynamic center relationships, as well as pitching moments. Also, you don't increase "Lift" by adding flaps, you increase maximum lift coefficients.

I mean by dropping flaps, you increase the lift coefficient (both maximum and current), resulting in an increase in lift.

 

 

It doesn't do any good to LOWER the incidence angle of the canard, because it doesn't change the max Cl of the canard, which is what determines the stall speed.

 

My thought was that lowering the incidence angle of the canard would reduce the AOA the canard sees, allowing you to pitch the wing closer to its maximum AOA before the canard stalls. You don't need the CLmax of the canard to change, just the total angle that the canard stalls at.

 

As to whether there would be enough elevator authority to pitch far enough....?

 

 

Just to change the aerodynamic center - it wouldn't have any effect (or at least not much of one) on the stall onset. Don't know why you'd think it would...

 

All things being equal: a swept wing will stall before an unswept (starting at at the tips for aft swept). That's why they thought putting heavy wingsweep mechanisms on F-14's were such a great idea. But it's certainly true that I don't know how much of an effect it would be.

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First of all, don't make me say what i didn't, i have said that it was PRIMARILY for the looks, a assume that people are not stupid enough to build/buy an aircraft that just looks good, and flies bad!

 

The other 4-seat aircraft (Cirrus, Cessna 400, Lancair IV/P, etc.) get about 10-12 NMPG. I get anywhere from 17 - 25 NMPG - better than my Subaru Outback

go on lancair's website, you will see 15mpg (22gph)@330mph, i think you can reach your 17gph if you slow down at 200mph... far from your 10-12gph...

then again i didn't tested it my self

 

Speak for yourself, will you please? Especially when you don't know what you're talking about. I got my plane because it was the only four seater that I could afford that could do what I wanted vis-a-vis speed, efficiency, carrying capacity, and safety. While I like the looks, it was item #4 or 5 on the importance scale.

so explain to me why people are not massively buying Cozys? i mean if it's the best 4 seater, cheapest, most efficient, heavier caring aircraft, people would just buy this aircraft and leave the others aside! yes there is a community of cozy builders, i do respect them, but still canards are marginal

 

it doesn't mean that you don't agree with me that everyone has your vision, nor do i assume that everyone agrees with me. check this http://www.canardzone.com/forum/showpost.php?p=3541&postcount=2

think most people that decide on the Cozy just fall in love with the shape of it.

(i didn't go far to find that!)

 

Still, go around these thread and look how people reacts regarding the style of a starship or any other canards, and after don't tel me that people chose there aircraft without thinking about the looks in the top 3 position.

 

For advantages of stall resistance, it is an advantage, don't get me wrong (by the way, 800ft to recover from a stall? WOW!! need a BRS?) but there is some disadvantages in a day to day use of the aircraft (unless you get iced every time you fly) like prop strikes on take-off and/or landing, you can't land on grass or not prepared surface without damaging the prop (or at least risking to damage it).

 

I still love these aircraft because of their spec, speed, range, loading capabilities, but i did came here first because of the looks, i do admit, and thanks I'm not brain damaged, at least not to my knowledge... (maybe my witting is bad, but English is not my native language, i please ask your tolerance)

 

and that's how a "Higher CLmax?" thread became a "why canard are better than conventional" thread

 

is someone working on that issue (CLMax) in there mods?

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My thought was that lowering the incidence angle of the canard would reduce the AOA the canard sees, allowing you to pitch the wing closer to its maximum AOA before the canard stalls. You don't need the CLmax of the canard to change, just the total angle that the canard stalls at.

At any given speed, the canard (and main wing, for that matter) need to produce a given amount of lift, determined by the CG/AC relative positions, and the pitching moments of each. The maximum lift that can be produced is determined by the Max Cl of the airfoil, which occurs at a fixed AOA. If you want to go slower (that's the point of the flaps, right?) you MUST be able to generate a higher Cl. Lowering the incidence angle of the canard only forces you to have a larger elevator deflection to achieve the necessary Cl at a particular IAS - it doesn't change the AOA at which the canard airfoil will stall one whit. Since it's the canard that determines the stall of the aircraft as a whole, you haven't changed anything in the right direction. In fact, because adding flaps ADDS to the nose-down pitching moment, and requires MORE lift from the canard, you'll run out of elevator sooner, and in fact stall the canard at a HIGHER IAS than you otherwise would. The fact that the main wing has a larger theoretical maximum Cl is meaningless, because the canard won't let you get there using your methodology. For the canard to go more slowly, you either need to add area, move the canard forward, or add high lift devices (flaps, slats, etc.).

 

Do a force/moment balance, please, while looking at the lift equation - you'll see what needs to happen.

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The Tomcat had swept wings to go real fast---fastest plane ever in the Navy. Unfortunately, the swept wings did not lend itself real well to getting aboard the boat---hence the mechanism to swing them forward. There were many "optimization" features on the Turkey such as a variable engine inlet, variable engine nozzle, and glove vanes. You will see that the Navy's latest operational fighter (F-18E/F) has fixed wings and a fixed inlet. It is a slower plane----but the reduction in complexity and weight can emphasize other attributes.

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First of all, don't make me say what i didn't, i have said that it was PRIMARILY for the looks

Read your own quote:

 

"Canard aficionado's just wont admit that they have/want a canard because it looks cool..."

 

go on lancair's website, you will see 15mpg (22gph)@330mph, i think you can reach your 17gph if you slow down at 200mph...

In which case you've now spent three times as much money to reach the lower end of the COZY efficiency range.

 

so explain to me why people are not massively buying Cozys? ... yes there is a community of cozy builders, i do respect them, but still canards are marginal

There are ~300 flying COZY's, about the same # of Velocities, and almost 2000 VE/LE's. Except for the RV-10, which will soon surpass all other 4-seaters combined, the COZY/Velocity is by far the most popular 4-seat homebuilt out there, and the COZY is by far the most popular 4-seat plans built aircraft - heck, except for the VE/LE, it might very well be the most popular plans built aircraft of any size. About 1600 sets of plans have been sold. I'd call that extremely successful - hardly marginal.

 

All that said, I hardly expect canards to take over the market for many reasons, not the least of which is the construction technique, which many don't like. Also, like ANY high wing loading aircraft (Lancair, Glasair, etc.), they need more runway (far more a function of the wing loading than the canard configuration) and cannot tolerate very rough fields. Go land a Glasair on a sandbar - see how long the gear lasts and try to get back out. No different than a COZY.

 

For advantages of stall resistance, it is an advantage, don't get me wrong (by the way, 800ft to recover from a stall? WOW!! need a BRS?)

The issue isn't the stall, in the turn, it's the spin that results from the stall. A low altitude spin is a BIG issue. Have you ever unintentionally spun an aircraft? Think you can recover in less than 800 ft.?

 

but there is some disadvantages in a day to day use of the aircraft (unless you get iced every time you fly) like prop strikes on take-off and/or landing...

Google Cessna prop strike - see what you get. ANY plane can have a prop strike in a poor landing.

 

(maybe my witting is bad, but English is not my native language, i please ask your tolerance)

Your English is far better than my <whatever> - that's not the issue. The issue was the claim that was made about looks being the deciding factor. And the fact that John Slade made an offhand comment about it hardly makes it definitive.

 

and that's how a "Higher CLmax?" thread became a "why canard are better than conventional" thread

No one said they were better, or the be-all and end-all of flying machines. In fact, I was the one that pointed out that theoretically, they're not. All planes have their pros and cons. Look at my OSHKOSH forum presentation to see what I have to say on the matter.

 

is someone working on that issue (CLMax) in there mods?

Other than adding VG's to the canard and main wing, which a few people have done (and which has been talked about numerous times on the COZY and canard-aviators mailing lists), if they are, they're hiding it well.

 

The VG's is the best solution. No moving parts, 5 - 10 kt decrease in approach speed, low cost, low weight, minimal top speed loss (2 kts, max). See:

 

http://www.cozybuilders.org/cad_files/

 

for info on Mark Beduhn's VG installation.

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Read your own quote:

"Canard aficionado's just wont admit that they have/want a canard because it looks cool..."

i still don't see the word "only" in my quote...

 

Have you ever unintentionally spun an aircraft? Think you can recover in less than 800 ft.?

i once did it in 500ft, but usually around 1000ft... BRS! or just don't fly in icing! if you do ice, don't wait to have a critical ice thickness to make you aircraft stall (thats what i have been tought in my private pilot licence)... cozys aren't equipt with de-ice and therefor shouldnt go flying in icing condition... still stall resistance is a good thing in that case..

 

ANY plane can have a prop strike in a poor landing.

can you break a prop on a cessna by just pulling a bit to mutch on take off and landing? and is that "poor take-off and landing condition"?? the only way i see you can strike a prop is by not rounding on landing, but in this case you forward landing gear will collapse just like any aircraft...

 

arf, what ever (the argument)

 

 

thanks for you link, and for the notice on the oshkosh presentations, i have seen them a couple of times. it give basics on what has been done and what not to do... can't wait for the 2008 presentation (if there is some)

 

concerning high lift, i am working on that right now, (see the my heavy mod thread). i am comparing strait canard and slightly swept canard with roncz profil and what is the differences. one this is done i'll try to see if the moving flaped canard- wing slat flap combination can ad something, i'll let you know...

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Marc,

 

Oh, I follow you on the free body diagram (I've got a BS/MS in AE, but I've never used it directly to make a living).

 

It seems to me that we need to increase the stall angle of the canard (what I was saying) while at the same time increasing the lift of the canard (what I believe you were saying). Tricky, no wonder they went with a sweeping canard on the Starship.

 

Lowering the incidence angle of the canard only forces you to have a larger elevator deflection to achieve the necessary Cl at a particular IAS - it doesn't change the AOA at which the canard airfoil will stall one whit.

 

I agree it doesn't change the stall AOA of the airfoil itself, but does in relation to the wing.

 

Follow me for a second: Say a canard airfoil stalls at 30 deg at 0 incidence. The wing at 0 incidence stalls at 32 deg (you're safe, the canard stalls before the wing). Lower the canard incidence by 5 degrees. Now say you actually have enough elevator authority to pitch until the wing "sees" 35 degrees, the canard sees: (32 - 5 = 27). Wing stalls before canard: screwed! So I think the incidence angle *does* change the stall condition of the canard. (Note: ignores downwash or any other coupling effects.)

 

Which is why I mentioned lowering the incidence of the canard before: to delay canard stall until the wing gets closer to its max lift. And as I said before, I don't know if you'd have enough elevator authority to pitch up (lift of the canard) to actually reach said max lift coefficient.

 

Of course, the elevators already act like flaps on the canard. Crap, this is a complex thing...

 

PS ... and I hope I didn't come across as a Tomcat basher... that's the last crowd I want to incite a flame-war with :scared:

I don't care, I'm still free.

You can't take the sky from me.

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Well, rather than changing the canard's angle or airfoil, you could slide it forward. As long as you have enough control authority, I think that'll do it. (I'll sit silent on the cons to this. I know I've seen a dissertation on it written by Marc somewhere in these forums, but I'm too lazy to look for it right now.)

 

However, you might want to read http://www.ezchronicles.com/?p=33:

But several years ago an actual event established the truth. You have all read about the incident right? If I remember correctly, a North Carolina VariEze was making a 200 mph-ish low pass, felt a jolt and power loss, and landed on a parallel runway.

Wondering what the heck, the pilot got out and saw dangling wires in back and fluid on the ground. He put the nose on the ground and walked back and was astonished to find that there was no lower cowl - and no engine. A crash crew pickup pulled up with the engine in the bed. I remember him attributing the engine being pulled off by a failed male inlet and lower cowl. Must have been especially interesting for the first time flyer in the back seat.

 

Interestingly, he stated that control response during the landing gave little or no indication that the engine had departed the aircraft. Others claiming experience in this arena seem to agree. So what about the unrecoverable nose down dive? Obviously the nose is being held up by trading off speed. There are evidently some areas of GU canard operation that haven’t been fully documented. And the area of interest here looks like one of them.

 

Losing your *ENTIRE* engine is not the same as adding flaps to your main wing, but it does suggest that the canard might have a little more control authority than we intuitively expect. I should emphasize "might" because you need to remember that the plural of "anecdote" is not "fact", and that's what this story is: a bunch of anecdotes. Also, its about VE's, not cozy's. That means its different but the same, probably.

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Follow me for a second: Say a canard airfoil stalls at 30 deg at 0 incidence. The wing at 0 incidence stalls at 32 deg

32deg relatively to? air? let say air... (sorry i dont have the english technical words)

(you're safe, the canard stalls before the wing). Lower the canard incidence by 5 degrees.

5 deg compared to the fuselage?

the canard will still stall at 32 deg, and by lowering the canard by 5 deg you have reduce de lift force from the canard, and your aircraft won't be balanced for level flight any more, it will pitch down...

to be able to lower your canard, you'll need to change the airfoil (to have a higher lift coef, and eventually have a bigger canard (you know? ½.rho.S.V².Cl?)

and this comes back to marc's demo

 

one of the ways to do this, have your canard and wing settled up for cruise.

put flaps on your wing to get a higher Clmax , and flaps on the canard to have a higher CLmax, if you have say 10% more CL on the wing you must add an large amout (taking the force/moment balance in account)to on the canard (to keep the same stall margin between the wing and the canard) then you realize that the pitching moment of the wing is bigger, so your canard has to carry even more... so you try to keep the flaps generating less pitching moment by reducing the down angle of the flaps (look at the starship, the flaps doesn't drop down like say commercial aircraft) or add slats...(to be confirmed for the slats)... it is mind blowing!

 

edit :

loosing your engine does pitch your nose down... if you don't take in acount your CG moving aft super quick (loosing your engine) giving your canard more arm lift (is that correct?) and so more authority to balance your aircraft and less arm lift to your wing, and with luck (like this guy) your aircraft finaly balances out

but you agree with me that moving around the CG in flight is MUCH more complicated (in calculations, you can still move your fuel around like in the concorde)...

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Let me try again with pictures (increased the incidence angle for better visuals):

 

First drawing shows canard & wing at 0 incidence and 30 AOA.

Second shows the aircraft pitched at the same attitude, but with -10 deg incidence on the canard. The AOA the canard sees is reduced by 10 degrees, so the canard will no longer stall before the wing.

 

... by lowering the canard by 5 deg you have reduce de lift force from the canard, and your aircraft won't be balanced for level flight any more, it will pitch down...

 

Yeah... like I said you have to 1) prevent the canard from stalling at the same angle to take advantage of the increased stall AOA of the wing, and 2) Have enough pitch/lift from the canard to balance the wing.

 

They seem to be mutually exclusive... but I'm not sure jettisoning the engine is the answer.:P

 

A fore-and-aft sliding or variable sweep canard? Uh, this is a lot of work to save a couple of knots on landing speed.

post-6142-141090164092_thumb.jpg

post-6142-141090164094_thumb.jpg

I don't care, I'm still free.

You can't take the sky from me.

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Yeah... like I said you have to 1) prevent the canard from stalling at the same angle to take advantage of the increased stall AOA of the wing, and 2) Have enough pitch/lift from the canard to balance the wing.

 

When you extend a flap on the wing, it does not allow the wing to go to a higher AOA. Contrary to popular belief, it usually reduces the maximum AOA that is possible without stalling. However, you do get a much higher CL for the SAME AOA with flaps vs. without flaps.

 

It isn't the best reference, but see the plot of CL vs AOA here:

 

http://www.simhq.com/_air/air_002a.html

 

So, does this finally explain why decreasing the canard incidence is bad if you deploy flaps on the wing?

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First drawing shows canard & wing at 0 incidence and 30 AOA. Second shows the aircraft pitched at the same attitude, but with -10 deg incidence on the canard. The AOA the canard sees is reduced by 10 degrees, so the canard will no longer stall before the wing.

Yeah, and it will also not produce as much lift as it needs to per the force and moment balance, which WAS in balance in the first drawing. You seem to be having a hard time understanding the force and moment balance issue here...

 

If you lower the canard incidence, you lower the AOA, you lower the Cl, and you lower the lift produced. You can't do that and still have the plane fly, at least not level - you will accelerate downward. You will need to pull back on the elevator to get the effective AOA, Cl, and lift back. You will hit Max Cl at essentially the same point that you would have previously, if not earlier. You have achieved nothing, except for making the plane unstable and running out of elevator earlier than previously.

 

Please - stop proposing stuff that violates force and moment balances.

 

Over and out.

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