Canard Design - Unrecoverable Stall?
Matt
However, I recently read somewhere about how this type of aircraft,
which is supposedly immune from stalling, can instead succumb to an
unrecoverable stall condition. The article I read did not explain how
this happens, but it suggested that the main wing stalled before the
canard making recovery impossible. This aparently occured in an early
generation canard design.
Is this correct?
If so, are all canard designs susceptible of this condition?
Or, has this problem been properly addressed in current designs?
Any thoughts would be appreciated.
Matt
George R. Patterson III
>
> I am intrigued by the canard wing design (Long EZ, Velocity, etc).
> However, I recently read somewhere about how this type of aircraft,
> which is supposedly immune from stalling, can instead succumb to an
> unrecoverable stall condition. The article I read did not explain how
> this happens, but it suggested that the main wing stalled before the
> canard making recovery impossible. This aparently occured in an early
> generation canard design.
First off, canards are not immune from stalling, or even particularly
resistant to stalling. The difference is in the recovery. The front
wing on canards is deliberately set at a higher angle of incidence than
the main wing, so it stalls earlier. That makes the nose drop. If the
pilot takes no action, recovery is automatic until the nose comes back
up and the aircraft stalls again. If the pilot is unused to the aircraft
and attempts to pull the nose back up, the second stall will be more
severe and result in the loss of lots of altitude. A friend of mine was
killed this way. If the pilot takes appropriate action, stall recovery
is easier than in conventional aircraft.
Now to the main point. The phenomenom to which you refer is called a
"deep stall" condition. It occurs when both wings on the canard stall
with the aircraft in a nose-high condition. It is usually unrecoverable
unless turbulence causes a change in position.
> If so, are all canard designs susceptible of this condition?
> Or, has this problem been properly addressed in current designs?
From what I've read, it's very difficult to duplicate, so nobody can be
sure that a particular aircraft won't deep stall. Some designs are known
to be susceptible. Last I heard, nobody knew the exact cause, so they
can't fix it. Research was continuing as of last year.
George Patterson, N3162Q.
Ron Natalie
>
> I am intrigued by the canard wing design (Long EZ, Velocity, etc).
> However, I recently read somewhere about how this type of aircraft,
> which is supposedly immune from stalling, can instead succumb to an
> unrecoverable stall condition.
The canard in normal flight regimes doesn't stall because the
canard (the short wings in the front) stall first and that lowers
the AOA before the main wing ever gets to stall. Hold the stick
in your lap in a canard and the nose just goes up and down as the
canard stalls and flies and stalls...
However, if you manage to get the main wing to stall, then
it may be very difficult to get the nose down to lower the
AOA. How does this happen? In one case, a plane was flipped
by wake turbulance, in another the aircraft was grossly
out of aft CG. It's not a very common occurance.
If you want a whole lot more details, ask the question again
over in rec.aviation.homebuilt.
Ian Marks
kboat...@aol.com (KBoatri144) wrote:
>
>
>>> I am intrigued by the canard wing design (Long EZ, Velocity, etc).
>>> However, I recently read somewhere about how this type of aircraft,
>>> which is supposedly immune from stalling, can instead succumb to an
>>> unrecoverable stall condition.
>
This is also the reason canard planes can only do 'military' type
aerobatics. The main wing is diffucult to stall and when it does you are in
deep doo-dah (pardon my french)
KBoatri144
>> I am intrigued by the canard wing design (Long EZ, Velocity, etc).
>> However, I recently read somewhere about how this type of aircraft,
>> which is supposedly immune from stalling, can instead succumb to an
>> unrecoverable stall condition.
The Velocity is a 4 place canard which experienced deep stall in certain
situations (particularly aft CG). They added cuffs to the wings, and, in
conjunction with flying the aircraft in the approved CG envelope, this solved
the problem.
EZ's have also been lost to deep stall. The ones I am aware of were aft cg
related.
If you want more information on deep stalls in canard aircraft, go to:
http://cozy.canard.com/ There is plenty of information on this subject in the
old newsletters.
KB
Daryl1953M
Hans-Georg Michna
>Now to the main point. The phenomenom to which you refer is called a
>"deep stall" condition. It occurs when both wings on the canard stall
>with the aircraft in a nose-high condition. It is usually unrecoverable
>unless turbulence causes a change in position.
George,
this doesn't sound very credible. Since conventional aeroplanes
are nose-heavy, wouldn't the nose drop eventually anyway?
Sure, you'd lose lots of altitude.
Hans-Georg
[No mail please]
George R. Patterson III
>
> "George R. Patterson III" <grpp...@earthlink.net> wrote:
>
> >Now to the main point. The phenomenom to which you refer is called a
> >"deep stall" condition.
> this doesn't sound very credible. Since conventional aeroplanes
> are nose-heavy, wouldn't the nose drop eventually anyway?
Someone more knowledgible on canards will have to tackle the "whys" of
this, but the two or three articles I've read which discussed it say
no. The aircraft is stable, nose high, uncontrollable, and falling
rapidly. Occupants may or may not survive contact with the surface.
> Sure, you'd lose lots of altitude.
How about from 8,000 ASL to sea level with no change in attitude? That
was the experience of the first person to survive a deep stall incident.
George Patterson, N3162Q.
FD
Hans-Georg Michna wrote:
> "George R. Patterson III" <grpp...@earthlink.net> wrote:
>
> >Now to the main point. The phenomenom to which you refer is called a
> >"deep stall" condition. It occurs when both wings on the canard stall
> >with the aircraft in a nose-high condition. It is usually unrecoverable
> >unless turbulence causes a change in position.
>
> George,
>
> this doesn't sound very credible. Since conventional aeroplanes
> are nose-heavy, wouldn't the nose drop eventually anyway?
yeah, conventional aeroplanes, but canard homebuilt airplanes are usually
tail heavy!
fra
>
>
> Sure, you'd lose lots of altitude.
>
> Hans-Georg
>
> [No mail please]
Hans-Georg Michna
>Hans-Georg Michna wrote:
>>
>> "George R. Patterson III" <grpp...@earthlink.net> wrote:
>>
>> >Now to the main point. The phenomenom to which you refer is called a
>> >"deep stall" condition.
>
>> this doesn't sound very credible. Since conventional aeroplanes
>> are nose-heavy, wouldn't the nose drop eventually anyway?
>
>Someone more knowledgible on canards will have to tackle the "whys" of
>this, but the two or three articles I've read which discussed it say
>no. The aircraft is stable, nose high, uncontrollable, and falling
>rapidly. Occupants may or may not survive contact with the surface.
>
>> Sure, you'd lose lots of altitude.
>
>How about from 8,000 ASL to sea level with no change in attitude? That
>was the experience of the first person to survive a deep stall incident.
George,
guess I'll have to believe this. Aerodynamics can be more
complex than one first thinks.
Well ... perhaps the plane wasn't properly loaded and had the
center of gravity too far aft ...
Hans-Georg
[No mail please]
Charles K. Scott
Matt <r...@nospam.com> writes:
> I am intrigued by the canard wing design (Long EZ, Velocity, etc).
> However, I recently read somewhere about how this type of aircraft,
> which is supposedly immune from stalling, can instead succumb to an
> unrecoverable stall condition. The article I read did not explain how
> this happens, but it suggested that the main wing stalled before the
> canard making recovery impossible. This aparently occured in an early
> generation canard design.
>
> Is this correct?
> If so, are all canard designs susceptible of this condition?
> Or, has this problem been properly addressed in current designs?
>
> Any thoughts would be appreciated.
>
> Matt
First let me premise my information by saying that while I am building
a homebuilt airplane, it isn't a canard. I've read with interest
everything I could find regarding the situation in question but have
not flown one myself.
The problem with the canard type homebuilt is that the canard angle of
incidence is critical to safe operation. The canard MUST stall first
in order to lower the nose before the main wing stalls. If the angle
of incidence for the canard is correct then it will always stall first
and since the main wing never stops flying, the problem of "deep stall"
is, or should be a non issue.
How then did some of the aircraft get into this position? In the case
of the Velocity, apparently an owner was testing high angles of attack
and managed to get high enough for the main wing to stall. This turned
into a stable, albiet fast, descent. The airplane pancaked onto the
ground with no fatal injuries to the pilot.
The factory tried to duplicate the condition by applied sealing tape to
the gap of the canard to increase the force it was capable of
imparting. The test pilot took the airplane out over the Atlantic a
little ways and at around 8,000 feet, tried to yank into a high AOA.
He was successfull, the airplane's main wing stalled and it began a
stable descent of around 500 to 800 fps, I think, not sure about the
rate of descent. The pilot attempted to power up and fly out of the
vertical motion but gave up after a while. He opened the canopy and
attempted to get the nose down by leaning way out over the nose. No
joy.
He was wearing a parachute and thought about going over the side but
decided that he might as well stay with the plane and ride it in. It
pancaked into the ocean not far from shore with no injury to the pilot
or plane. Helpful observers who witnessed the impact towed him to
shore where the only damage to the airframe occured from over
enthusiastic helpers, as they tried to push it onto the shore. The
airplane is made of foam covered fiberglass, it floated fine, not that
they wanted to test it this way.
At that point a LOT of testing was done on the main wing and some fixes
were devised which prevented the main wing from stalling. These
included cuffs for those already flying and a revised strake for the
plans from then on.
So does proper adherence to the plans guarrantee you a stall free main
wing? Yes if you do not exceed the aft center of gravity. But even
conventional airplanes will stall and be unrecoverable if the aft
center of gravity margin is exceeded by too great a weight.
There was a fatal deep stall incident that involved an ATC vector into
a wingip vortex.
In this situation the owner chose to depart from the plans and add
additional area to the fuel tanks in the wing. The only place where
this could occur was aft of the tanks. This was recommended against by
the factory and knowledgeable builders in the strongest possible terms
but the owner persisted anyway. In addition there was apparently
little baffling to limit the gas from immediately surging aft.
Now to the incident. The airplane was successfully flown and one day
was inadvertantly vectored behind one of the heavies that produces an
extremely powerful wingtip vortex. This flipped the airplane over on
it's back. Almost immediately several things happened: in the nose up
position, the gas surged to the rear, the engine quit and the main wing
stalled. The pilot was on the radio constantly explaining what was
happening.
He did not survive the impact with the ground.
In this type of airplane, the canard absolutely should not be built
larger than specs and it must be set with the proper angle of
incidence. If this is done, the airplane can be flown without fear of
main wing stall. You cannot stall the main wing under any
circumstances no matter how long you pull the stick back. What happens
is that the canard stalls and the nose pitches down. The canard
unstalls, the nose comes back up and the canard stalls again. This is
a stable condition and is only dangerous if you let the canard stall
too close to the ground. I watched a canard perform the "pitch buck"
all the way down the runway at Oshkosh without loosing altitude. It
simply flew along pitching gently up and down as the canard stalled and
unstalled.
The only problem with this type of aircraft is that because the main
wing never stalls, it lands pretty fast. This is OK if you don't mind
needing long, paved runways. It also means that engine failure will
result in a pretty high touchdown speed, over 70 mph and more like 80.
Corky Scott
Hans-Georg Michna
>yeah, conventional aeroplanes, but canard homebuilt airplanes are usually
>tail heavy!
You mean the forward canard wings have a lower angle of attack
than the main wings, such that they push the nose downward?
Well that is one interesting design. Certainly unconventional.
Probably needs artificial stability through fly-by-wire.
Hans-Georg
[No mail please]
Marc J. Zeitlin
A lot of stuff which is basically correct, but I'd like to expound on
it a bit.
> ...... If the angle
> of incidence for the canard is correct then it will always stall first
> and since the main wing never stops flying, the problem of "deep stall"
> is, or should be a non issue.
With the caveat (as Corky mentioned later in his post) that the C.G.
MUST be in the recommended range, and NOT too far aft. Also, the
vortex generators on the main wing are very important to prevent
spanwise flow at high AOA's, as are the lower winglets.
> He was successfull, the airplane's main wing stalled and it began a
> stable descent of around 500 to 800 fps, I think, not sure about the
> rate of descent.
Deep stalls in these canard aircraft (COZY's, Velocity's, etc.)
generally develop steady state vertical speeds of ~4000 ft./min, or
close to 50 mph. Survivable, but not pleasant. 500 to 800 ft./min
would be wonderful, if true, but sadly is not. In a L.E., with the
stick full aft in a pitch buck (canard stalled, main wing flying) and
engine idling, we were decending at about 600 ft./min. At full
throttle (same stalled condition) we were CLIMBING at about 600
ft./min. Do THAT in a Cessna :-).
> At that point a LOT of testing was done on the main wing and some fixes
> were devised which prevented the main wing from stalling. These
> included cuffs for those already flying and a revised strake for the
> plans from then on.
This is all for the Velocity aircraft.
Nat Puffer did some extensive testing of the COZY MKIV deep stall
characteristics. He was only able to get the plane to deep stall if
the C.G. was ~ 2" BEHIND the rearmost recommended position. He was
able to get the plane to recover by moving a 135 lb. weight
approximately 6 feet forward within the fuselage, to position the C.G.
forward. A COZY will not deep stall if built to plans (with lower
winglets, vortex generators, correct canard incidence, and proper C.G.
position).
> ...... You cannot stall the main wing under any
> circumstances no matter how long you pull the stick back.
Not completely correct. As mentioned before by George Patterson, I
believe, it is always possible to get the main wing to stall by
PIO's. If you dynamically work the aircraft into successively higher
and higher AOA's by pushing and pulling on the stick, you will
eventually stall the main wing. In a STATIC one G situation, however,
you are correct.
>.... The only problem with this type of aircraft is that because the main
> wing never stalls, it lands pretty fast.
Actually, it's more because there are no flaps than that the main wing
doesn't stall. Most people don't do full stall landings in high
performance cruiser type aircraft, I don't think.
> ..... This is OK if you don't mind
> needing long, paved runways. It also means that engine failure will
> result in a pretty high touchdown speed, over 70 mph and more like 80.
Engine failure or not, the speed is the same. It's not substantially
different than other high speed aircraft such as Glasairs and
Lancairs, BTW, and is sometimes even slower, even though those
aircraft DO have flaps.
Good post, though, Corky - thanks.
--
Marc J. Zeitlin email: marc_z...@bose.com
Noise Reduction Technology Group phone: 508-766-4226
Bose Corporation fax: 508-879-3049
The Mountain web: http://www.bose.com
Framingham, MA 01701-9168
rokhed
> yeah, conventional aeroplanes, but canard homebuilt airplanes are usually
> tail heavy!
This statement is rather misleading. Canards DO typically have a
farther aft CG than conventional aircraft, however the CG range remains
forward of the Center of Lift, just as it is in conventional designs.
The CG must be forward of the Center of Lift, to produce a nose down
moment after stall, enabling the wing to start "flying" again.
Of course, most canard designs don't rally have a "tail" at all, and
hence can't very well be "tail heavy"
--
"How sweet is mortal sovranty!" - think some:
Others - "How blest the Paradise to come!"
Ah, take the Cash in hand and waive the Rest;
Oh, the brave Music of a Distant Drum!
-- Omar Khayyam
Charles K. Scott
Charles.K.Scott@**NOSPAM**.dartmouth.edu (Charles K. Scott) writes:
> I watched a canard perform the "pitch buck"
> all the way down the runway at Oshkosh without loosing altitude. It
> simply flew along pitching gently up and down as the canard stalled and
> unstalled.
I should have been more clear about this. The airplane was in the air,
over the runway, demonstrating the pitch buck to the audience.
Corky Scott
George R. Patterson III
>
> This statement is rather misleading. Canards DO typically have a
> farther aft CG than conventional aircraft, however the CG range remains
> forward of the Center of Lift, just as it is in conventional designs.
Not true. The center of lift matches the center of gravity. You could
also argue that a canard has two centers of lift; one behind the center
of gravity and one in front.
> The CG must be forward of the Center of Lift, to produce a nose down
> moment after stall, enabling the wing to start "flying" again.
That's not the way a canard works. Stall recovery in a canard is begun
when the front wing stalls. That eliminates the lift at the front of
the aircraft, and the nose drops. Unless the pilot mishandles it very
badly, the rear wing never stalls.
Even with more conventional aircraft, it is not a given that the COG
must be forward of the COL. Several aircraft have been made at one time
or another in which that was not true. These aircraft have lifting tails
and take a bit of getting used to. As far as I know, nobody has marketed
one since about 1920, but they fly. The principle is much the same as
the canard wing, except that the rear wing is smaller than the front.
George Patterson, N3162Q.
rokhed
>
> rokhed wrote:
> >
> > This statement is rather misleading. Canards DO typically have a
> > farther aft CG than conventional aircraft, however the CG range remains
> > forward of the Center of Lift, just as it is in conventional designs.
>
> Not true. The center of lift matches the center of gravity. You could
> also argue that a canard has two centers of lift; one behind the center
> of gravity and one in front.
Agreed. I was speaking only of the primary wings center of lift, and
not of the aircraft as a whole. It is true that the overall center of
lift of a canard in normal (read "not stalled") flight matches the CG.
It may be worth pointing out that the Center of lift in a conventional
aircraft does not match the CG, but is in fact aft of the CG. A
negative lift force produced by the horizontal stab keeps the nose up in
level flight. (mathematically this does, in practice, equate to the
center of lift location matching the CG)
>
> > The CG must be forward of the Center of Lift, to produce a nose down
> > moment after stall, enabling the wing to start "flying" again.
>
> That's not the way a canard works. Stall recovery in a canard is begun
> when the front wing stalls. That eliminates the lift at the front of
> the aircraft, and the nose drops. Unless the pilot mishandles it very
> badly, the rear wing never stalls.
Again, I agree that the rear wing in a canard does not stall (except in
very unusuasl circumstances), but my point was that the CG in a canard
MUST be forward of the center of lift of the rear wing, to enable the
nose to drop. The original posters claim that canards were "tail heavy"
seemed to imply otherwise. It is unfortunate that I may have only
further confused the issue. Perhaps I should stick to turning wrenches,
I obviously don't turn phrases too well. 8^)
>
> Even with more conventional aircraft, it is not a given that the COG
> must be forward of the COL. Several aircraft have been made at one time
> or another in which that was not true. These aircraft have lifting tails
> and take a bit of getting used to. As far as I know, nobody has marketed
> one since about 1920, but they fly. The principle is much the same as
> the canard wing, except that the rear wing is smaller than the front.
>
> George Patterson, N3162Q.
Well a "conventional" aircraft with a lifting tail isn't really
conventional. This configuration could be made to work safely (I think)
if the horizontal tail was designed to stall at higher angle of attack
than the forward "wing", in which case what you really have is canard
where the primary lifting surface is the canard itself rather than the
rear "wing". I suspect, however, that you'd tend to lose altitude
rather quickly while in the stall. If the tail stalls before the wing
stall recovery will be impossible, resulting in either a flat spin, or a
tail first fall from the sky. I'd not want to fly such a craft. 8^)
Thanks for the corrections
- The Rokhed
--
pizza, ANSI standard: /an'see stan'd*rd peet'z*/ [CMU] Pepperoni
and mushroom pizza. Coined allegedly because most pizzas ordered
by CMU hackers during some period leading up to mid-1990 were of
that flavor.
-- The Jargon File
Alex Yeilding
>"Charles K. Scott" wrote:
>
>
>> ...... You cannot stall the main wing under any
>> circumstances no matter how long you pull the stick back.
>
>Not completely correct. As mentioned before by George Patterson, I
>believe, it is always possible to get the main wing to stall by
>PIO's. If you dynamically work the aircraft into successively higher
>and higher AOA's by pushing and pulling on the stick, you will
>eventually stall the main wing. In a STATIC one G situation, however,
>you are correct.
Marc:
Can you elaborate? I was under the same impression as Corky. Even if
the pilot is doing a 6-g pull-up, wouldn't the canard stall first,
lessening the pullup and avoiding a stall of the main wing?
Is it that the actual pitching moment results in different relative
wind to the canard from the main wing. I guess I can see that, but
would think it would be insignificant.
What can cause the main wing to stall in a properly designed, built,
and loaded canard craft?
--
Alex
Transpose first two letters of return address to reply by email.
J P Rourke
>Matt wrote:
>>
>> I am intrigued by the canard wing design (Long EZ, Velocity, etc).
>> However, I recently read somewhere about how this type of aircraft,
>> which is supposedly immune from stalling, can instead succumb to an
>> unrecoverable stall condition. The article I read did not explain how
>> this happens, but it suggested that the main wing stalled before the
>> canard making recovery impossible. This aparently occured in an early
>> generation canard design.
>First off, canards are not immune from stalling, or even particularly
>resistant to stalling. The difference is in the recovery. The front
>wing on canards is deliberately set at a higher angle of incidence than
>the main wing, so it stalls earlier. That makes the nose drop. If the
>pilot takes no action, recovery is automatic until the nose comes back
>up and the aircraft stalls again. If the pilot is unused to the aircraft
>and attempts to pull the nose back up, the second stall will be more
>severe and result in the loss of lots of altitude. A friend of mine was
>killed this way.
I'm sorry to hear that, but from everything I've read, heard and experienced
(not much experience yet) on the Velocity, this is not true on most canards,
certainly not for the Velocity. You can hold the stick all the way back the
whole time and still keep flying (if with power it will actually climb),
although the nose will bob up and down some.
A few modified Velocity a/c did deep stall, but only after mods specifically
recommended *against* that moved the cg aft of the kit manufacturer's
recommendation. This is the way a deep stall occurs in ANY aircraft, even a
Cessna. (by definition, a "deep stall" is one that is unrecoverable)
I think it may be possible to deep stall a Velocity (or other canard) with rapid
pitch up towards vertical at high speeds, but I'm not sure if even that will
cause one. It was also reported by a couple of test pilots that entered deep
stalls during aft-cg testing, that the descent rate (in the deep stall) was low
enough that they decided to "ride it in" unharmed (both into water), but I
wouldn't count on it.
One other deep stall resulted in a fatality, but mostly because he went inverted
after encountering wake turbulence from a 727 due partially to ATC error. (he's
also the one who modified the fuel tanks to allow a cg too far aft in some
cases). It was also suggested that the wake turbulence probably would have
caused structural failure of your average 152 or 172, but the Velocity stayed
intact (until hitting the ground inverted)
> If the pilot takes appropriate action, stall recovery
>is easier than in conventional aircraft.
>Now to the main point. The phenomenom to which you refer is called a
>"deep stall" condition. It occurs when both wings on the canard stall
>with the aircraft in a nose-high condition. It is usually unrecoverable
>unless turbulence causes a change in position.
>> If so, are all canard designs susceptible of this condition?
>> Or, has this problem been properly addressed in current designs?
>From what I've read, it's very difficult to duplicate, so nobody can be
>sure that a particular aircraft won't deep stall. Some designs are known
>to be susceptible. Last I heard, nobody knew the exact cause, so they
>can't fix it. Research was continuing as of last year.
???
The cause is well-known, and well-researched. Mostly it's operation of the
aircraft with cg aft of the allowable "box".
john rourke
Ron Natalie
>
> Not true. The center of lift matches the center of gravity. You could
> also argue that a canard has two centers of lift; one behind the center
> of gravity and one in front.
You've lost me on that one. There is one center of gravity
and one center of lift. I suspect that it even doesn't change
that much as the canard stalls.
Marc J. Zeitlin
> Can you elaborate? I was under the same impression as Corky. Even if
> the pilot is doing a 6-g pull-up, wouldn't the canard stall first,
> lessening the pullup and avoiding a stall of the main wing?
Yes, the canard will stall first, but I believe there are still two
ways to get the main wing to stall. First, if there is a significant
nose up dynamic rotation, the AOA of the main wing may get too high
and it may stall. This can occur during the PIO's mentioned above.
Think of the plane as having a "natural frequency" of oscillation
(nose up and nose down) - if you drive the nose up and down with the
stick at that frequency, the magnitude of the oscillations will
continuously increase. Eventually, the nose will get so high (due to
rotational momentum) that both wings will stall. This, however, does
NOT imply a "deep stall".
The second way to stall the main wing is to do an accellerated stall
by means of a high G pullup. At high speeds, the canard can generate
more than enough lift to get the nose high enough to stall the main
wing (just like the tail can generate enough downforce to cause an
accellerated stall in a conventional configuration). Again, this does
NOT imply a "deep stall".
> Is it that the actual pitching moment results in different relative
> wind to the canard from the main wing. I guess I can see that, but
> would think it would be insignificant.
Probably right (about the insignificance) - it's not the different
relative winds caused by the pitching movement, but the final AOA
caused by the pitching movement that will cause the main wing to
stall.
> What can cause the main wing to stall in a properly designed, built,
> and loaded canard craft?
The two situations mentioned above (and major wind shear, of course,
or major wake turbulence).
Remember, however, that just because the main wing stalls does not
mean that the aircraft has entered a "deep stall", and is in an
unrecoverable situation. Most of the time (unless the CG is too far
back) the nose will drop, airspeed will pick up, and both wings will
start flying again.
Canards are not "stall proof", just "stall resistant". Given that the
base-to-final stall/spin turn is a major contributor to accidents, and
that this happens in essentially level, low speed, one G flight, these
are the stalls that the canard configuration protects against. You
can pull the stick back all the way, descend at ~600 fpm, be pitch
bobbing with the canard stalling and unstalling, and have complete
roll control of the plane. No stall/spin accident. This is NOT,
obviously, the recommended landing configuration :-).
George R. Patterson III
Ok, we'll stick to proper terminology.
The canard aircraft has two lift points, since both wings provide lift.
If you don't want to call these "centers of lift", then you have one
COL, which is a function of the two lift points. Similarly, a
conventional aircraft has two lift points, one of which is negative. In
level flight, the COL always matches the COG. It moves aft when the
front wing stalls in either type of plane.
George Patterson, N3162Q.
Alex Yeilding
>continuously increase. Eventually, the nose will get so high (due to
>rotational momentum) that both wings will stall.
Ah, that is what I was missing. Thanks.
>
>The second way to stall the main wing is to do an accellerated stall
>by means of a high G pullup. At high speeds, the canard can generate
>more than enough lift to get the nose high enough to stall the main
>wing
Still don't understand this. As long as the wing in front has a
higher angle of incidence, seems it would stall first, whatever the
speed or g loading. Once it does, it will lessen the g loading,
preventing the main from stalling. (Same as it would do in level
flight over a planet 3 or four times the mass of the Earth, or as it
does with slow level flight on Earth)
>(just like the tail can generate enough downforce to cause an
>accellerated stall in a conventional configuration)
That seems very different. The tail is not approaching stall in a
high-g situation, so retains effectiveness and the ability to push the
main into a stall situation. Again, this does
>Canards are not "stall proof", just "stall resistant". Given that the
>base-to-final stall/spin turn is a major contributor to accidents, and
>that this happens in essentially level, low speed, one G flight, these
>are the stalls that the canard configuration protects against.
I thought it also protected against a too-tight (e.g. 60-degree 2-g)
too slow turn.
Marc J. Zeitlin
> Still don't understand this. As long as the wing in front has a
> higher angle of incidence, seems it would stall first, whatever the
> speed or g loading. Once it does, it will lessen the g loading,
> preventing the main from stalling. (Same as it would do in level
> flight over a planet 3 or four times the mass of the Earth, or as it
> does with slow level flight on Earth)
OK, after a little more research, I think I can explain this better
(obviously didn't do so well before :-) ). From AC 61-67C (
http://www.bts.gov/ntl/DOCS/bak/Ac61-67b.html ) :
c. Accelerated stalls can occur at higher-than-normal
airspeeds due to abrupt and/or excessive control
applications.
These stalls may occur in steep turns, pullups, or other
abrupt
changes in flightpath. Accelerated stalls usually are more
severe than unaccelerated stalls and are often expected
because
they occur at higher-than-normal airspeeds.
I think what I was trying to get at was that due to the higher
airspeed, it is possible to create a large rotational velocity in
pitch angle that will cause a higher than critical AOA on the main
wing. Similar to the PIO cause, but not related to oscillations, just
to the dynamics of the pitch angle.
Boy, it's been a long time since I've done aerodynamics :-). Thanks
for poking me.
FD
Hans-Georg Michna wrote:
> FD <fra...@ix.netcom.com> wrote:
>
> >yeah, conventional aeroplanes, but canard homebuilt airplanes are usually
> >tail heavy!
>
> You mean the forward canard wings have a lower angle of attack
> than the main wings, such that they push the nose downward?
>
have I ever mentioned angle of incidence?
highflyer
>
> "George R. Patterson III" <grpp...@earthlink.net> wrote:
>
> >Now to the main point. The phenomenom to which you refer is called a
> >"deep stall" condition. It occurs when both wings on the canard stall
> >with the aircraft in a nose-high condition. It is usually unrecoverable
> >unless turbulence causes a change in position.
>
>
> this doesn't sound very credible. Since conventional aeroplanes
> are nose-heavy, wouldn't the nose drop eventually anyway?
>
>
>
> [No mail please]
Canards are not conventional airplanes. If the aft wing is stalled,
it cannot rise above the flying one in front.
HF
highflyer
>
> FD <fra...@ix.netcom.com> wrote:
>
> >yeah, conventional aeroplanes, but canard homebuilt airplanes are usually
> >tail heavy!
>
> You mean the forward canard wings have a lower angle of attack
> than the main wings, such that they push the nose downward?
>
> Probably needs artificial stability through fly-by-wire.
>
> Hans-Georg
>
> [No mail please]
No, of course not. The aft wing is at the aft end of the airplane.
Both wings are lifting and the CG is in the usual location on the
MAC. However, if the aft wing is allowed to stall, all relationships
are void and the result is a "conventional" aircraft that is seriously
tail heavy.
HF
highflyer
>
> >
> > This statement is rather misleading. Canards DO typically have a
> > farther aft CG than conventional aircraft, however the CG range remains
> > forward of the Center of Lift, just as it is in conventional designs.
>
> also argue that a canard has two centers of lift; one behind the center
> of gravity and one in front.
If y ou accept that argument you could just as easily argue that the
canard has two hundred centers of lift. There is only one center of
lift, and it is the summation of all the incremental lifts from all
of the surfaces of the aircraft that can produce lift and these are
NOT restricted only to WINGS.
>
> > The CG must be forward of the Center of Lift, to produce a nose down
> > moment after stall, enabling the wing to start "flying" again.
>
> That's not the way a canard works. Stall recovery in a canard is begun
> when the front wing stalls. That eliminates the lift at the front of
> the aircraft, and the nose drops. Unless the pilot mishandles it very
> badly, the rear wing never stalls.
>
That is pretty much the way the canard works. However, you want to be
sure the aft wing NEVER stalls. Therefore it is set up so that the
forward wing will stall first, moving the Center of LIft AFT and
creating the nose down moment to unstall the aircraft. If the rear
most wing stalls the center of lift moves forward and it may not be
possible to reduce the angle of attack with the CG aft of the
center of Lift.
highflyer
>
> George R. Patterson III wrote:
>
> >
> > Not true. The center of lift matches the center of gravity. You could
> > also argue that a canard has two centers of lift; one behind the center
> > of gravity and one in front.
>
> and one center of lift. I suspect that it even doesn't change
> that much as the canard stalls.
George,
I believe that approximately 15% of the total lift on a LongEze
comes from the canard. Of course, when it stalls, its lift
coefficient merely stops increasing and starts decreasing slowly
with increasing AOA, so the lift does not leap suddenly aft, but
it does commence a definate movement in the aft direction that
changes the relationship to make the CG more forward than normal
compared to the CL, resulting in a definate nose down moment and
prompt stall recovery. Normally and hopefully, the rear wing
remains well below its stall AOA throughout.
HF
highflyer
> >
>
> >
> >> ...... You cannot stall the main wing under any
> >> circumstances no matter how long you pull the stick back.
> >
> >believe, it is always possible to get the main wing to stall by
> >PIO's. If you dynamically work the aircraft into successively higher
> >and higher AOA's by pushing and pulling on the stick, you will
> >eventually stall the main wing. In a STATIC one G situation, however,
> >you are correct.
>
> Marc:
>
> the pilot is doing a 6-g pull-up, wouldn't the canard stall first,
> lessening the pullup and avoiding a stall of the main wing?
>
> wind to the canard from the main wing. I guess I can see that, but
> would think it would be insignificant.
>
> and loaded canard craft?
The "rate of change" of pitch can be critical. A high RATE of pitchup
can allow the airplane to continue to pitch up after the canard stalls
from inertia, perhaps reaching a pitch where the main wing is ALSO in
a stall condition. In that case, the behavior is more problematical.
However, it is my understanding that every case recorded of deep
stall had an aft CG condition, including the one that killed Pug Piper.
HF
Marc J. Zeitlin
> The "rate of change" of pitch can be critical. A high RATE of pitchup
> can allow the airplane to continue to pitch up after the canard stalls
> from inertia, perhaps reaching a pitch where the main wing is ALSO in
> a stall condition. In that case, the behavior is more problematical.
Thank you. This is what I had been trying to say.
> However, it is my understanding that every case recorded of deep
> stall had an aft CG condition, including the one that killed Pug Piper.
This is certainly the case for the Velocity's and Cozy's/AeroCanard's
that have deep stalled.
Hans-Georg Michna
>Still don't understand this. As long as the wing in front has a
>higher angle of incidence, seems it would stall first, whatever the
>speed or g loading.
Alex,
true, but the main wing can stall a split second later.
One very simple example is that you point your aircraft's nose
vertically into the sky. After a short time your plane will have
zero speed and everything will be stalled.
However, as long as the plane is nose-heavy, as all planes are
except those with artificial, fly-by-wire stability, the nose
will eventually drop and the plane will eventually become
flyable again, albeit after losing lots of height.
Hans-Georg
[No mail please]
Charles K. Scott
"Marc J. Zeitlin" <marc_z...@bose.com> writes:
> I think what I was trying to get at was that due to the higher
> airspeed, it is possible to create a large rotational velocity in
> pitch angle that will cause a higher than critical AOA on the main
> wing. Similar to the PIO cause, but not related to oscillations, just
> to the dynamics of the pitch angle.
Marc, so far all this discussion about possible high speed main wing
stalls has been theoretical, right? Have you any information of such a
main wing stall occuring in the real world?
Thanks, Corky Scott
Marc J. Zeitlin
> Marc, so far all this discussion about possible high speed main wing
> stalls has been theoretical, right? Have you any information of such a
> main wing stall occuring in the real world?
AFAIK, no. The only main wing stalls I've heard of have been the
Velocity ones, the ones Nat's COZY MKIV did during Deep Stall testing
(with Jim Patton as pilot, I believe) and Pat Young's COZY MKIV deep
stall/crash. All of these were in steady state 1G flight.
Just so you know, Jim Patton did numerous main wing stalls and was
able to recover from them all, even with the CG slightly rearward.
Only after the CG was moved 2" beyond the rearmost position was he
unable to recover (entering a stable Deep Stall) until he moved the
135 lb. weight 6 ft. forward.
KBoatri144
>> main wing stall occuring in the real world?
In addition to the Velocity accidents and the Cozy tests, EZ's have also
experienced this problem due to aft CG.
There is a thumbnail report on testing Burt Rutan did on this phenomenon in an
archaic issue of Sport Aviation. IIRC, he had a friend who experienced the
problem. For his tests, he took a non-flyer EZ and attached it to the top of an
automobile to create an inexpensive wind tunnel. Again, IIRC, he found that
the EZ could experience this problem at aft CG.
KB
highflyer
> <snip>
> Just so you know, Jim Patton did numerous main wing stalls and was
> able to recover from them all, even with the CG slightly rearward.
> Only after the CG was moved 2" beyond the rearmost position was he
> unable to recover (entering a stable Deep Stall) until he moved the
> 135 lb. weight 6 ft. forward.
>
I don't have the numbers to actually calculate the shift in the
CG caused by moving the 135 pound weight forward six FEET. That
is a shift of 810 foot pounds. To move the CG only back to the
approved envelope, which would be a shift of 1/6 of a foot, the
airplane weight as tested must have been 4860 pounds. I rather
suspect it was about half that, or less, indicating that, while
the deep stall may only occur with an aft CG condition, recovery
from it may require a shift forward to well within the CG limits.
That tells me it is, indeed, a pretty stable condition once it is
allowed to develop.
It never fails to amaze me how many little situations in aviation
are best dealt with by avoidance and finesse rather than by plain
old brute force! <g>
HF
highflyer
In aerobatic circles we usually refer to that effect as
"The heavy end eventually comes down first!"
The only significant difference between a "canard" and a "conventional"
aircraft is the relative distribution of lift between the two "wings."
Most "conventional" aircraft actually use a negative lift on the
aftermost "wing" to ensure that the Center of Lift will move AFT
as the speed decreases. It is a desireable feature of aircraft
designs that the CL remains at or behind the CG for all modes of
flight. If you allow the Center of Lift ahead of the Center of
Gravity you will likely encounter an situation where the stall
becomes unrecoverable. This is extremely unlikely if the Center
of Lift remains behind the Center of Gravity.
Remember, it may be common practice to make the aftermost "wing"
a negative lift airfoil for longitudinal stability purposes as
detailed in the previous paragraph, but it is by NO means necessary.
Burt Rutan reasoned that if he could make both required "wings"
provide positive life at all times in normal flight, it would
reduce the total lift required, thereby reducing the total drag
and increasing performance on any given amount of power.
I think most of you will agree with me, that Burt has rather
conclusively proven the validity of that. The KIS is a really
clean little airplane, but this year at Sun-N-Fun, in the low
power homebuilt race, every single tandem wing aircraft entered
did better than the KIS, and a number of them even PASSED him
during the race.
Burt also reasoned, that with the tandem surfaces arranged to
provide positive lift, with significant lift contributions from
each wing, he could position the fuselage to separate the wings
and make it a box large enough to hold the people. This concept
eliminated a lot of the parasitic weight in a conventional fuselage
design.
By putting the major lifting surface right at the engine, and moving
it to the rear of the airplane, he could move the bulk of the
airplane into air that is undisturbed by the slipstream, reducing
the overall drag. This is at the cost of a slight reduction in
propellor efficiency, much of which can be regained by slightly
increasing the propellor diameter. If the inflow area to the
propellor is kept clean and the prop is positioned so that the
inflow to the prop does not disrupt the airflow over the wing
and around the wing fuselage junction this configuration can
be more efficient in terms of airspeed per horsepower. Proper
design of the aft end of the aircraft can actually reduce the
overall drag because the prop inflow can be used to clean out
the relatively dead air in the boundary layer, that increases
in thickness toward the aft end of the aircraft.
The result is a very clean and efficient aircraft at cruise
speeds and better.
However, in aviation, nothing is ever free. There is a price to
pay for this configuration. In ANY configuration where both of the
"tandem wings" are generating positive lift, to maintain the pitch
stability at low speeds required, it has to be arranged to that the
Center of LIft NEVER gets ahead of the CG. This is normally done
by arranging for the aftermost wing to remain away from the stall
Angle of Attack well past the condition where the forward wing is
stalled. That means that the aftermost wing can never quite get
up to its greatest possible lift coefficient, so you are always
speed limited to a speed slightly above stall speed.
Much has been made about this "fast" landing characteristic because
it is a canard. In actual practice very very few airplanes ever
get any closer to a stall in normal operation than the canard does.
A normal landing is ten to fifteen percent of Vso above actual
stall. Even the landing we refer to as a FULL STALL landing is
NOT actually a FULL stall. Generally making a touchdown at ten
percent of Vso or better above the actual FULL stall condition.
A typical factory built taildragger with its original tailwheel will
be in the three point attitude at a speed in level flight of ten to
fifteen percent of Vso above the stall. That is why you can just
fly a taildragger off the ground without ever picking up the tail.
Just let it fly off and hold the attitude and you will climb out
very close to your best angle of climb speed. Lower the nose slightly
to let the speed increase to your best RATE of climb speed, which
is about thirty percent above Vs.
The biggest change in the landing of a typical canard homebuilt is
due instead to the difficulty of adding flaps and the very clean
and low drag nature of the design. These combine to make it
difficult to descend and decrease airspeed at the same time!
Many clean homebuilts have this problem. I have encountered it
in Vari-Eze's, Long-Eze's, Quickie's, Pulsars, RV's, and many
other small and efficient airplanes.
You cannot make a steep approach without some way to increase the
drag. Many canards use some type of speed brake to increase the
drag and allow a steeper approach. The flat nature of these
approaches, and the slippery nature of the airplanes, combine
to make approaches SEEM faster than they are. With the difficulty
of slowing the airplane down while descending, they often ARE
faster than they need to be.
HF
Marc J. Zeitlin
> ........ To move the CG only back to the
> approved envelope, which would be a shift of 1/6 of a foot, the
> airplane weight as tested must have been 4860 pounds. I rather
> suspect it was about half that, or less,........
Probably closer to 1700 lb. or so.
> .... indicating that, while
> the deep stall may only occur with an aft CG condition, recovery
> from it may require a shift forward to well within the CG limits.
I don't know how much the weight would HAVE to have shifted - maybe
shifting it 3 feet forward would have been enough. However, IIRC, Nat
stated that the weight was moved completely forward to ENSURE that the
plane would "un-deep stall" :-). It would not surprise me at all if
the CG would have to move forward substantially to get out of the deep
stall condition, considering it's stability.
> That tells me it is, indeed, a pretty stable condition once it is
> allowed to develop.
This is certainly the case from reading all the accounts of people
that have been in this situation and have tried to get out. Once
stable, nothing works except a major CG shift.
> It never fails to amaze me how many little situations in aviation
> are best dealt with by avoidance and finesse rather than by plain
> old brute force! <g>
You bet.
Hans-Georg Michna
I enjoyed reading your article. Not only do you know what you're
talking about, you also say it very well and understandable.
Thanks!
While we're talking about various canard designs, does anybody
know how well the Beech Starship sells? Is it a commercial as
well as an aerodynamic success?
Hans-Georg
[No mail please]
rokhed
> While we're talking about various canard designs, does anybody
> know how well the Beech Starship sells? Is it a commercial as
> well as an aerodynamic success?
>
> Hans-Georg
I think one can safely say the starship was (sadly) NOT a commercial
success. The Starship is no longer in production, therefore I doubt it
could be considered to be selling well. 8^) www.raytheon.com/rac
(Raytheon owns Beech) does not list the Starship in their product line.
--
Blue Room, the: n. The extremely large room with the blue ceiling
and intensely bright light found outside all computer installations.
Hans-Georg Michna
>I think one can safely say the starship was (sadly) NOT a commercial
>success. The Starship is no longer in production, therefore I doubt it
>could be considered to be selling well. 8^) www.raytheon.com/rac
>(Raytheon owns Beech) does not list the Starship in their product line.
Why? Does anyone know?
Hans-Georg
[No mail please]
Alex Yeilding
>The only significant difference between a "canard" and a "conventional"
>aircraft is the relative distribution of lift between the two "wings."
>
>snip lots of good stuff about design advantages of canard pusher design
>
>However, in aviation, nothing is ever free.
I've been meaning to ask about the inevitable trade-offs. You mention
the well-known one about landing speeds, and point out that it is
likely not a very big deal. Surely there are other trade-offs, or the
few new GA plane designs would be canards. Looking "weird" or jokes
about knowing that the feathers go on the back of an arrow are not
enough to drive design based on the trade-offs you mentioned. After
all, tri-gear planes have become de rigueur for new designs, despite
the fact that to a non-flying layman, a taildragger looks more stable
(because of the wide spread of wheels under the VISUAL center of
gravity).
So, what are the other trade-offs? Do they have a narrower CG loading
range? What about flight characteristics?
And while I'm picking your brain, most canards have laminar flow
wings. I don't think the two design features are tied inexorably
together, but what trade-offs are involved there? If the only issue is
keeping the wing clean, why don't all planes have laminar flow wings
(or at least all planes not designed to be flown in icing conditions)?
Michael
> >(Raytheon owns Beech) does not list the Starship in their product line.
>
> Why? Does anyone know?
Because they didn't sell. Only about 50 were ever made. The
aircraft looks cool, but the fact is that it is a turboprop that was
priced like a jet.
Meanwhile, Cessna was selling simple little jets that were
cheaper and faster.
You just don't get very far on looks in the multimillion dollar
aircraft game.
Michael
Charles K. Scott
la...@mindspring.com (Alex Yeilding) writes:
> And while I'm picking your brain, most canards have laminar flow
> wings. I don't think the two design features are tied inexorably
> together, but what trade-offs are involved there? If the only issue is
> keeping the wing clean, why don't all planes have laminar flow wings
> (or at least all planes not designed to be flown in icing conditions)?
That most canards utilize laminar flow is a result of the kind of
construction used to fabricate them which allows the designer to use
laminar airfoils and shapes, not because they are canards. They are
almost exclusively composite constructed which usually means some type
of fiberglass over foam or a composite shell that is bonded together
over foam ribs. Builders spend many months sanding and filling in
pinholes. It's this finishing process, plus the original shape which
is designed to promote laminar flow.
When the first Vari EZ flew, some aerdynamicists claimed that it was
the first real world aircraft to have laminar flow. Again, this is due
to the seamless construction. No bumps, rivets or butt joints to trip
the flow to turbulence.
Since the advent of the canards, other efficient designs have appeared.
The Glassair, Lancair, KIS, Pulsar, Stallion, Europa and several
others. All these airplanes are tractor configured but all take
advantage of laminar flow and not uncoincidentally, all are made from
composite materials.
The P-51 Mustang had a wing that was designed for laminar flow but many
aerodynamicists have speculated that it's highly unlikely that real
laminar flow occured with this wing due to the inherent problems of
keeping the airfoil perfectly smooth, what with mechanics standing on
it, the ammo bay doors, the landing gear doors and all the rivets and
butt jointed metalwork. By the way, laminar flow wings can be nasty
stallers, with very abrupt breaks and little warning. The Mustang was
no exception. In combat and also demonstrated nicely during a fly-off
conducted by EAA around 8 years ago, the Mustang stalled completely
without warning during gradually increased G forces in turns and
snapped and gyrated wildly out of the turn, tumbling crazily for a few
moments until the pilot was able to get things back under control. The
Mustang was the only fighter to demonstrate this characteristic amonst
the group which consisted of an F6F Hellcat, a Spitfire and a P-47
Thunderbolt, along with the Mustang. Wait, there may have been an F4U
Corsair as well. Not sure.
Corky Scott
George R. Patterson III
> rokhed <rok...@freestone.boulder.co.us> wrote:
> >I think one can safely say the starship was (sadly) NOT a commercial
> >success.
> Why? Does anyone know?
The starship was unconventional in both design and the extensive use of
composite materials. As a result, the FAA refused to certify the design
without a lot of beefing up of the structure. That made it heavier and
more expensive to manufacture, which priced it out of the market.
At least, that's the gist of an article in Flying magazine a year or two
back.
George Patterson, N3162Q.
Hans-Georg Michna
Michael,
so, in short, the Starship was too expensive for its class. Too
bad, it was such a good-looking aircraft!
Hans-Georg
[No mail please]
Hans-Georg Michna
>The starship was unconventional in both design and the extensive use of
>composite materials. As a result, the FAA refused to certify the design
>without a lot of beefing up of the structure. That made it heavier and
>more expensive to manufacture, which priced it out of the market.
>
>At least, that's the gist of an article in Flying magazine a year or two
>back.
George,
hmmm, interesting twist. I wonder if it's true and, if it is, I
wonder whether the FAA was right. We'll never know.
Hans-Georg
[No mail please]
Robert VanHorn
range, payload, etc., made it a poor buy. Wing got
so heavy because FAA kept on Beech's case to add more and more composite
material until the weight just got obscene.
That's why the Jet Cruiser (single engine turboprop pusher being built in
Long Beach California) has a metal wing with
a composite fuselage.
rjvh
Michael wrote in message <01be9c88$f154bba0$8301010a@mike-s-desktop>...