Performance of canard gliders
Alfonso Gonzalez
over a clasical shaped glider.
On a normal glider the tail plane must generate negative lift to prevent
the glider entering in a unrecoverable
dive. The faster you go the further foward you have to push the stick,
and I believe, it will generate greater
- lift and with it induced drag.
On a canard glider in order to lower the nose to gain speed the canards
only need to produce less lift,
which will reduce drag. (Similar behaviour to the negative flap
positions?)
Any opinions?
Daniel
performance is similar to a 25m Nimbus, but with much smaller wingspan (the
fact tthat the canard creates lift allows you to make them bigger). This
means it should be possible to have good efficiency AND good agility !
I just started a smal study on it and would highly appreciate to know if
sombody has some experience or idea.
P.S. : what about a small gasturbine instead of a piston engine for self
starting motorgliders?
Robert Nase Johnson
I searched on "rutan solitaire" and came up with the following:
http://www.cyberspace.co.nz/~rajiv/ras-archive/pre-191995/0105.html
You could prob do better --
Bob Johnson
Tom Seim
the stab is always creating negative lift: this occurs in only certain slow
speed flight regimes. I have been told that the stab can very from negative
to positive to neutral lift, depending upon the position of the center of
lift and the center of gravity. At out best L/D I suspect that the stab is
neutral.
The canard is always lift producing (about 1/3 of total lift) and is set at
a considerably higher angle of attack than the main wing. This higher angle
of attack is also higher drag. When the canard is approaching stall speed
the main wing is well above its stall speed. Therefore you can't get the
main wing to the verge of stall. This is required for good thermalling
performance (slower speed translates to tighter circles) and is IMHO the
principal reason why you don't see any canard configuration sailplanes.
I am not an aerodynamic engineer; therefore everything said here may be
totally wrong, in which case I apologize in advance.
Alfonso Gonzalez wrote in message <37E14BAB...@sarenet.es>...
Greig Glover
the tail in the back, the center of gravity has to be
ahead of the center of lift, which, at low speeds, is
usually about the 1/4 cord location. The rear stab may be
producing minimal lift, but not positive lift, at least
not for a very long time(certain situations may produce
momentary times of positive lift when pushing stick forward
very rapidly, but this is a rare case.) If the center of
gravity is behind the center of lift, then the aircraft is
dynamically unstable. This is true of some new aircraft,
like the F-16, which has the CG at about neutral or
slightly aft of the center of lift, but it also has a
sophisticated computer system to fly it and keep it
stable. Humans could not do it.
The biggest draw back of canards is that your angle of
attack is limited. As mentioned above, you can not allow
the rear wing to stall, or else you will tumble out of
control, so you have to allow the front wing to stall
first. This never allows you to drive the main wing to
it's maximum lift coefficient(Clmax). In conventional
gliders, pilots thermal around all day at the peak of the
lift curve, and don't get too worried if they approach the
stall.
Food for thought: has anyone ever thought up or designed a
sailplane that is fly-by-wire it could fly with an unstable
CG?
Greig Glover
Morris, MN
USAFA '83
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Wayne Paul
Tom Seim wrote in message ...
>This is an interesting question, but first we must correct your error that
>the stab is always creating negative lift: this occurs in only certain slow
>speed flight regimes. I have been told that the stab can very from negative
>to positive to neutral lift, depending upon the position of the center of
>lift and the center of gravity. At out best L/D I suspect that the stab is
>neutral.
>
>The canard is always lift producing (about 1/3 of total lift) and is set at
>a considerably higher angle of attack than the main wing. This higher angle
>of attack is also higher drag. When the canard is approaching stall speed
>the main wing is well above its stall speed. Therefore you can't get the
>main wing to the verge of stall. This is required for good thermalling
>performance (slower speed translates to tighter circles) and is IMHO the
>principal reason why you don't see any canard configuration sailplanes.
>
>I am not an aerodynamic engineer; therefore everything said here may be
>totally wrong, in which case I apologize in advance.
>
Sounds good to me!
Wayne
http://stimpy.acofi.edu/~wpaul
Ian Molesworth
theory behind why canards did NOT make good thermalling aircraft.
Perhaps some of the aerodynamicists can restate the case.
Ian
Bruce Hoult
<alfg...@sarenet.es> wrote:
> I wonder if a canard shaped glider could have some performance advantage
> over a clasical shaped glider.
What you say is true in high speed flight.
I think the problem is with low speed flight. Canards *must* be designed
so that the canard stalls before the main wing does. If that's true in
level flight then it means that you can't even get the main wing *near* to
the stall in tight turns. Which would not do good things for your
thermalling ability.
-- Bruce
Mike Brook
Bruce Hoult wrote in message ...
>
>What you say is true in high speed flight.
>
>I think the problem is with low speed flight. Canards *must* be designed
>so that the canard stalls before the main wing does. If that's true in
>level flight then it means that you can't even get the main wing *near* to
>the stall in tight turns. Which would not do good things for your
>thermalling ability.
>
...And also it means that you cannot operate the wing at anything like its
max coeff of lift for takeoff or landing. Therefore to achieve the same
thermalling, takeoff, and landing performance as a "proper" glider you need
more wing area or lower wing loading, and the increased drag from this at
high speeds more than negates the advantage (if any) you might have gained.
To quote from someone who I cannot remember, "there isn't much wrong with
canards that can't be cured by revising the position of the stabiliser"
Guido Frey
They are acutually building a canard glider called fva 27. To my great
concern the page is in German only:
Ausführliche
Beschreibung der FVA27
But try to contact these guys via mail, they are normally very nice and willing to help.
You van also download a model of the fva27 at:
Hope this might help.
Best regards,
Guido Frey
Alfonso Gonzalez schrieb:
I wonder if a canard shaped glider could have some performance advantage
over a clasical shaped glider.
Ola Rřer Thorsen
I'm a member of the FVA and worked on the FVA27 a year ago. I since then
I've moved so I don't know the most recent news about the plane. When I left
it looked like the plane would have it's maiden flight in a couple of years.
The FVA27-project was started in the mid-eighties, a lot of things have been
discovered on the way.
You have mentioned a lot of advantages/disadvantages with a canard sailplane
already, so I'll just add something about the problems I've seen with a
canard:
As you have said the Canard profile has to produce a lot of lift. Due to the
profile used on the FVA27's canard (FX-63-137, a very cambered airfoil) you
get a contious negative elevator rudder moment, which is difficult to trim
(a trim spring must be so stiff that normal thermal flying will be more like
an arm workout). There is no neutral stick position, the rudder will be
sucked upwards all the time, the faster you fly the stronger. We found a
solution to this, however, but it makes the whole control system more
complex.
Also, the high lift (CL) produced by the canard leads to a large induced
drag of the canard. And, the tip vortices from the canard may hit the main
wing and thereby disturb the laminar flow on the main wing and increase the
total drag further.(this has not been investigated, I'm only guessing here).
So it remains to see if the advantages of the canard still beats the
disadvantages. It will be very exciting to see how the FVA27 flies in the
end. Anyway it will be a very exotic sailplane! :-)
Regards,
Ola Rřer Thorsen
(to translate german to english it's possible to use the
http://babelfish.altavista.com translator. It doesn't translate 100% right
but it's not bad either).
Ricardas Rusteika
Tom Seim wrote:
>
> The canard is always lift producing (about 1/3 of total lift) and is set at
> a considerably higher angle of attack than the main wing. This higher angle
> of attack is also higher drag. When the canard is approaching stall speed
> the main wing is well above its stall speed. Therefore you can't get the
> main wing to the verge of stall. This is required for good thermalling
> performance (slower speed translates to tighter circles) and is IMHO the
> principal reason why you don't see any canard configuration sailplanes.
As I know, Genesis 2 stab does not produce a lift but it circles without
problems.
Is it different thing?
Ric
John H. Campbell
published an article in SOARING (TECHNICAL SOARING, too, I think) detailing
flight tests on the Rutan "Solitaire". Check it out (a Solitaire has also
appeared on the cover of SOARING more than once). Despite the fact that
this elegant and certainly unique ship was the winner of an SSA design
contest (that favored innovation and motorglider issues), they concluded
that the canard configuration was a loser for sailplane operations.
Comparison graphs showed that the "Solitaire" was less capable than a
Schweizer 1-36 "Sprite", as I recall. Apparently, the sink rate and
stall speed would go up dramatically in circling flight, and the straight
flight polar fell away beyond the low speed "design point". It seems that
getting 2 wings to interact properly can be worked out OK for one angle of
attack but that operation at other angles of attack is compromised--not good
for dolphin-style soaring or just alternating between climb and cruise.
Mind you, lots of people would get enough of a thrill out of flying a
Rutan-inspired design or a kit-built motorglider even if it doesn't stay up
that well.
--JHC
Eric Greenwell
= I wonder if a canard shaped glider could have some performance advantage
= over a clasical shaped glider.
= On a normal glider the tail plane must generate negative lift to prevent
= the glider entering in a unrecoverable
= dive. The faster you go the further foward you have to push the stick,
= and I believe, it will generate greater
= - lift and with it induced drag.
= On a canard glider in order to lower the nose to gain speed the canards
= only need to produce less lift,
= which will reduce drag. (Similar behaviour to the negative flap
= positions?)
This has been thoroughly discussed before in many articles. Perhaps you
can find some in Technical Soaring or other publications. The two
greatest problems with the canard (as I recall previous articles) are:
1) the inability to operate the main wing at it's peak lift, which means
it doesn't thermal as well as possible
2) the wake from the canard disturbs the air flow over the main wing,
which means it can be optimized only over a small speed range - not good
for a glider that must fly slowly to thermal and go fast to cruise
And a third reason that affects both canard and conventional gliders:
3) it is the main wing that is the most efficient due to its span (tip
losses) and larger chord (Reynolds effects). By using the canard to
produce some of the lift, it means the glider is less efficient overall.
This is also true of conventional gliders, but because the horizontal
stabilizer is much smaller, it contributes less drag.
Bug and rain contamination of the canard can make aircraft control a
real problem. This and other problems all lead to the conclusion it is
much easier to design a conventional glider than a canard. And finally,
the canard configuration appears to have no benifit whatsoever for a
glider! Its much-touted "stall resistance" in airplanes is what makes it
unsuitable for thermalling, and even in airplanes, leads to higher
landing speeds than a conventional airplane with the same size wing.
--
>>Delete the "REMOVE" from my e-mail address to reply by e-mail<<
Eric Greenwell
Richard Kiray
placed in front of the pilot. There have been too many accidents due to
failure to "see and avoid".
> I wonder if a canard shaped glider could have some performance advantage
> over a clasical shaped glider.
> On a normal glider the tail plane must generate negative lift to prevent
> the glider entering in a unrecoverable
> dive. The faster you go the further foward you have to push the stick,
> and I believe, it will generate greater
> - lift and with it induced drag.
> On a canard glider in order to lower the nose to gain speed the canards
> only need to produce less lift,
> which will reduce drag. (Similar behaviour to the negative flap
> positions?)
>
> Any opinions?
Doug B. Hoffman
canard design for gliding. As I recall, from reading about it, in
addition to the visibility problems there were thermaling performance
issues. I think the issue was drag in turns. Any one else have better
recollection?
-Doug
Bill Daniels
into the issues. As I recall it, the low speed performance was lacking.
Rutan makes a point of the canard's stall and spin resistance. To achieve
this, the CG must be very far forward. If the CG is placed for best L/D,
the stall/spin characteristics are unacceptable. If the CG is moved far
enough forward to make a glider docile, the canard will then carry a
disproportionate load, making the induced drag for the canard surface very
high at low speeds.
The Rutan homebuilt canards and their derivatives perform very well at high
speeds where induced drag is negligible, but are not known for their slow
speed performance as shown by short field performance.
Bill Daniels
Doug B. Hoffman <dhof...@oakland-info.com> wrote in message
news:dhoffman-190...@annex-1-2-port-39.dialup.coast.net...
Charles Crosby
>Back in the 60's, I was interested in canard designs until I really looked
>into the issues. As I recall it, the low speed performance was lacking.
>
>speeds where induced drag is negligible, but are not known for their slow
>speed performance as shown by short field performance.
I think Bill has pretty much summed it up. There is also a misconception
about what the tail on a normal glider is normally doing. Generally, with
the static margins and amount of camber used on most conventional
sailplanes, you have to be flying quite fast before the tailplane actually
starts pulling down. At lower speeds (when induced drag matters) it lifts
.... Further problem with the canard is the non-uniform downwash (inboard
of the canard tip) and and upwash (outboard ...) on the main wing. This
affects the main wing load distribution, which is pretty critical for
getting low induced drag.
Charles
Peter A Hearne
Back in the early 1960s we schemed up a FBW idea for a man powered
aircraft which seemed to have distinct "theoretical " advantages but was
generally thought by the more high-minded to be cheating.
Peter Hearne
In article <02ef1022...@usw-ex0102-015.remarq.com>, Greig Glover
<gloverN...@runestone.net> writes
Luc Bernard
> > I wonder if a canard shaped glider could have some performance advantage
> > over a clasical shaped glider.
> > Any opinions?
I don't know about performance, but I have seen one such canard glider
hanging from a hangar ceilling at the EAA Oshkosh Airventure Convention 6
weeks ago. If you're interested, I can send you a digitalized picture of
it via e-mail.
Luc Bernard
nospamlu...@videotron.ca
remove "nospam" to reply
Bert Willing
Richard Kiray wrote:
> I'd be concerned about a reduction in visibility due to the canard surfaces
> placed in front of the pilot. There have been too many accidents due to
> failure to "see and avoid".
Yep. In the region I fly, I would take the purchase of a canard glider as a
very effectice attempt to commit suicide.
--
Bert Willing
-----------
Caproni Calif A21S D-6600
Come fly at La Motte du Caire in the French Alps:
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