New canard designs?

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ultralajt

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I do see two other issues that must be studied. The “one side” canard will load the boom in torsion. That may or may not be an issue. Second, with a “split” canard the aspect ratio get lower that something that maybe bring an aerodynamic efficiency penalty and “interesting” behavior at the extreme of the operation envelope.
I agree!
 

autoreply

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Canards need a larger AR as the wings. A structurally divergent wing loading in torsion might be problematic too (same problem as fwd swept wings). To me, this configuration with booms and a conventional tail makes more sense.
 

Himat

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Canards need a larger AR as the wings. A structurally divergent wing loading in torsion might be problematic too (same problem as fwd swept wings). To me, this configuration with booms and a conventional tail makes more sense.
"The Canard wing need a larger AR than the main wing", is that the correct interpretation of your statement? I would rather say that the common way to arrange a Canard layout airplane is to give the front wing a larger AR than the main wing. This is done to achieve the wanted stability with a safe “stall”. If the wanted “stall” behavior can be met otherwise, it’s not a requirement.

Structural the load is divergent until the canard reaches “stall” AOA but I am not sure if that poses a problem beyond a possible weight penalty. My guess is that it’s down to the detail design if an airplane like this is “better” or “worse” than an orthodox design. And what is good and bad do depend on the design priority.
 

ultralajt

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"The Canard wing need a larger AR than the main wing", is that the correct interpretation of your statement? I would rather say that the common way to arrange a Canard layout airplane is to give the front wing a larger AR than the main wing. This is done to achieve the wanted stability with a safe “stall”. If the wanted “stall” behavior can be met otherwise, it’s not a requirement.

Structural the load is divergent until the canard reaches “stall” AOA but I am not sure if that poses a problem beyond a possible weight penalty. My guess is that it’s down to the detail design if an airplane like this is “better” or “worse” than an orthodox design. And what is good and bad do depend on the design priority.
Yes, in order to canard stall before the main wing, one option beside giving it larger angle of attack than main wing is to make it with larger aspect ratio. As it is common knowledge a high aspect ratio wing came earlier to stall, than low aspect ratio wing. This is an efect of the planform. Of course, designer should evaluate and take compromise between angles of attack and also of aspect ratio....knowing that high aspect ratio lead to short chord and low Re numbers..that again can affect the canard aerodynamic behaviour. It is not an easy job I suppose... so, I am rather fan of clasicc aeroplane layout ..somehow affraiding the invisible or unpredictable problems at canards..even by a fact that they seems to be very simple.

Regards!

Mitja
 

Jay Kempf

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Alright then gentlemens, I give you new canard design! :)

I use a coffe break to make this sketch. I dont want to design something real like that as I am not fan of the canards, but I want to sketch something new..I think I managed.
Dont bother wit cooling air intake location... was just my instant vision....could be different.
Dont bother also with obvious tail heavy apearance. Wing can be moved to match with proper CG.. or wing tips can be sweept backwards a bit...

But it is really new? Did you see anything similar with "split" canards alerady?


View attachment 22188

I see some benefits from that layout:
- better view forward
- when aproaching to the stall of canards, downwash will hit outer wing panels and lowering their AoA, so ailerons will work good and wingtips will not stall instantly due aileron acutating.
- main landing gear could be installed inside canard booms in the main wing.
- Canards could be mounted with negative dihedral, in line of pilot sight, so minimal area will obstruct pilots view..actually no canard area will be visible from the cockpit...


What do you think?
Go! Dont be affraid to express your opinions!

Aerodynamic thoughts, structural thougts..

I wonder what surprises I am waiting... :)

Mitja
Interesting. The logic is good. I see no reason why it couldn't work if you managed the weight and boom structure and fairings. Not sure of the anhedral logic. Lifting surfaces are stable with dihedral.

Another thought along that line of thinking is to have the booms coming off the top of the rudder portion so they are way up in height if your goal is to get them out of sight and out of interference with the main wing. There was a guy selling a composite BD5 fuselage. You could prototype right off of that pretty easily. Be prepared to defend yourself for ever on your unjoined stabilizers :)
 

ultralajt

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... There was a guy selling a composite BD5 fuselage. You could prototype right off of that pretty easily...
... I dont want to design something real like that as I am not fan of the canards, but I wanted to sketch something new..I think I managed..
Mitja ;)

EDIT: just see now.. I just modify your own design. It was probably burned in to my memory. I like your design!
 

bmcj

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I give you new canard design! :)

22188d1359365985-new-canard-designs-new-canard-001.jpg

What do you think?

Mitja
Based on aesthetics alone, I LIKE IT!!!

On looks alone, the only change I would make is to eliminate the inclination of the booms and have the canard at the same elevation as the wing. I would also opt for a little dihedral in the canard (perhaps to match the dihedral angle of the outer wing panels).

Again, this opinion is strictly appearance driven, with no aerodynamic evaluation.

Bruce :)
 

PaulS

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It certainly looks like it has potential but...
What I see in the drawings is high wing loading which is good for speed but I also see high drag which makes speed very expensive.
There will of course be some turbulence between the booms and the wing where they merge - by necessity.
Considering the 10 -20% load on the canard "rule" the load on the forward booms will be very high and the canard(s) will have to be larger.

This is without anything but the drawing to look at and no specific information, so take it for what it is worth.
 

Aircar

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This thread belongs in "new technology etc" -- the discussion is all based on fixed geometry aircraft also. The usual argument that a canard must, almost by definition, be of lower net Cl (based on wing area), than an aft tail is all based on passive stability calculation and unchanging aircraft configuration between the landing condition and the high speed cruise --it can be that the lifting forewing layout actually allows for an increase in lift coefficient or wing area or some other factor to multiply lift that can be deleted for high speed.

Look at the conventional aircraft (aft tail ) layout and see how much you can extend the wing trailing edge for example BEFORE the aircraft becomes untrimmable --very little . Fowler flaps are the most usual method of getting more lift out of a conventional configuration and require a large tail and place limits on the forward Cg plus a large download ( I recall a figure of 5 tons on the 747 to trim with flaps out --could be quite inaccurate but makes the point )

A longitudinally moving canard is the most obvious way to increase the pitch authority of a canard with mainwing flaps --Kelly Johnston took out a patent on this in the 40s and Burt Rutan revived it with the forward sweeping Starship canard --a Swiss motorglider (Kolibri) did it too and for small aircraft it need not be terribly complex (the unique French long eze with a parasol canard a la Mignet could for example simply parallelogram fore and aft as one option -sliding forward in a slot is not that much of an issue and probably easier than the F111 system as on the Starship . Even more than playing with the canard position the main wing on a 'tandem' can be increased in area without upsetting the longitudinal trim in certain geometries (added area being at the aircraft aerodynamic centre is sometimes possible more easily than in aft tail designs -- the B52 is an example of a conventional design which allows big flaps and little trim problem and forward sweeping wings with flaps could also work but get into significant structural issues -birds do this to increase area and Cl for landing and end up with lifting tails at the same time .
Mitja's 'split canard' proposal is interesting and is anticipated actually (can't recall the design offhand but it was published ) - I studied the Zimmerman 'flapjack' designs for some time and came up with a configuration having canards mounted on the forward projecting prop shaft housings and only on the outboard side so acting as Spillman tip sails and elevons -- a related layout .

As has been noted, it is sometimes not possible to satisfy a design requirement and still be conventional and I would include the roadable aircraft as a prime candidate in this category --the bulk and difficulty of 'doing something' with the large tailcone and remote control surfaces is a real issue with configuring for the road (and when you HAVE to have 'variable geometry' anyway it may only be a small step to make it able to operate in flight to some extent and optimize performance or 'solve' low speed issues. Or you could 'fudge' the intention of specifying a low STALL speed and deliberately design your aircraft for a HIGH take off and landing speed by being unable to rotate until doing high speed (eg Terrafugia) --meets the LSA provision but not the spirit --a perverse intention in my view.

PS ALWAYS join aft tails --or else be prepared to defend not doing so FOREVER :devious: !
 

autoreply

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Structural the load is divergent until the canard reaches “stall” AOA but I am not sure if that poses a problem beyond a possible weight penalty.
I do think so. Unlike a fwd swept wing (change fiber direction), you can't "un-diverge" it. Unless it can flex up and down enough without breaking (then it's certainly going to flutter before stall), it'll break before stall.

With such a rear C of G (of the boom, relative to the canard), flutter is a certainty and making it stiff enough... I'm not sure you can get it stiff enough in the real world.
Didn't the Rutan Voyager also had considerable problems here?
 

bmcj

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Didn't the Rutan Voyager also had considerable problems here?
Yes, the canard was stiffer than the wing and flexed less, causing a divergent pitching mode due to the boom tie in between the wing and canard. Burt commented that he wish he had known that earlier so that he could have designed a LIGHTER, more flexible canard.
 

Himat

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I do think so. Unlike a fwd swept wing (change fiber direction), you can't "un-diverge" it. Unless it can flex up and down enough without breaking (then it's certainly going to flutter before stall), it'll break before stall.

With such a rear C of G (of the boom, relative to the canard), flutter is a certainty and making it stiff enough... I'm not sure you can get it stiff enough in the real world.
Didn't the Rutan Voyager also had considerable problems here?
This is two important remarks about the feasibility of the design. I do think these problems could be engineered out. I do see two possibilities to do this.

One is “fly by wire”. Have the control surface on the canard operated by an actuator controlled by a fly by wire system. Add sensors and have the computer keep the canard from fluttering by feedback control. The booms can then be made compliant enough that they don’t break and the fly by wire system prevents flutter.

The other option is to arrange the stiffness in the booms and canard in such a way that if the boom flex up, the canard flex to a lower AoA. That way the driving force is moved out of phase with the vibration in such a way that the boom and canard do not flutter. The one side of the boom canard surface might make this possible.
 

rtfm

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Hi,
I seem often to discover old threads which, IMO are still relevant today, so instead of starting a new, parallel thread, I'll just continue with this one, if that's OK?

While I wait for epoxy to cure (currently busy bonding the fin and rudder for the Fleabike), I've been looking into the possibility of a new small canard. I like small planes, not only because my router is limited to a sheet of ply, but also because small planes are lighter, cheaper to build, and easier to store/transport.

I'd borrow the folding wing concept of the Fleabike (two hinges - the inner hinge folds upwards against the rudder, the outer hinge folds down). No wing strakes (like the Apollo design). Also borrowing from the Apollo, different airfoil sections for the root (higher Re numbers) and the tip (lower Re).

While I have yet to spend a lot of time thinking about the placement of dual fins/rudders as indicated in the sketch below (a-la-Revelaero), it does allow the outer panels to fold, reducing the 8.7m span to 3.6m when folded. The folding points could bear with a bit of tweaking to get the folded span down more.

I'd be looking to use a small motor (no money for the bigger ones) - in the region of 50hp


1627869247739.png

When it comes to wing placement, I have three options.
Option 1: pretty standard placement, which results in significant downwash from the canard onto the main wing.
1627869687356.png
Option 2: high canard, and low main wing (like the Flea). The advantages of this arrangement is that because it is very much like the traditional Flea, I'm pretty familiar with airflows, and it gets the canard up high, out of ground effect.
1627869760801.png
Option 3: high main wing. This is interesting, and though I haven't pondered this too much, it is the configuration favoured by Hugh Lorrimer's Iolaire. Certainly this reduces the downwash issue significantly. Both option 2 and option 3 seem better than the "standard" configuration.
1627869821541.png
As always, open to comments, criticisms and suggestions.

Duncan
 
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rtfm

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2 and 3 would probably have higher drag, though?
I don't see why?

From your avatar, I assume you are a canard person? If that's the case, perhaps you could offer an opinion about whether my proposed design would have a relatively slow stall? I'm not that interested in a high cruise speed (although that would be nice) - I'm more interested in a relatively slow (ie short) landing and take-off. I would expect the plane to have a MAUW of around 300kg
 

rtfm

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Hey Voidhawk9 - I've just visited your X-Plane site - very nice! Perhaps we might talk about modelling whatever I settle on for this design. My experience with X-Plane is that it is a pretty **** good modeler of actual designs.

Duncan
PS The link to your building site doesn't work for me...
 

Voidhawk9

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Sorry, my builder site is down, and I haven't taken the time to rebuild it yet. Must get to that... a bit like the project itself!

For your proposed alterations, you need pylons, which adds intersections.
The low-wing one would be difficult to get clean flow off the trailing edge at the root, with no space for a trailing fillet. A mid-wing is usually better, but if the fuselage is tapering you can still get separation at the root.

I understand speed isn't the end goal, but less drag is always more efficient!
 
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