Canards

[Tom-D]

Can you spin a Canard aircraft, such as the Long EZ?

 

[Sac Arrow]

For that matter, what happens when those things stall?

 

[flyingmoose]

Can you spin a Canard aircraft, such as the Long EZ?

In theory no, because the canard stalls first you can never stall the wings.

 

[N801BH]

Where the heck is Captian when we need him..

 

[Captain]

Somebody call?

 

[N801BH]

Somebody call?

yuppers...

you are a Sierra Lima guy ain't ya ?

 

[Captain]

A Piaggio doesn't technically have a canard as it doesn't conntrol pitch. They call it a forward wing instead.

But yes, typically the forward wing is designed to stall first. An exception would be if the main with anti-ice fails. In that situation they tell you to turn off the forward wing too and get the heck OUT of icing conditions as they don't want a dirty main wing to stall before the clean forward wing.

 

[redtail]

A Piaggio doesn't technically have a canard as it doesn't conntrol pitch. They call it a forward wing instead.

But yes, typically the forward wing is designed to stall first. An exception would be if the main with anti-ice fails. In that situation they tell you to turn off the forward wing too and get the heck OUT of icing conditions as they don't want a dirty main wing to stall before the clean forward wing.

Does the forward wing change pitch automatically based on airspeed? Just curious. I played with the Piaggio in X-Plane a little. Must be awesome to fly the real deal!

 

[Velocity173]

No you can't spin a Long Eze. Only canards I've even heard of stalling are some of the early Velocitys. A wing change solved that problem. I've got the old style wing with the vortilons and I have no problems. I don't have the VGs so she'll just pitch buck with a 500 fpm decent rate. I can apply full pedal left and right and it'll just Dutch roll bank and forth.

 

[Sac Arrow]

Yeah but if you stall in a canard, how can you control the pitch? (The canard is the pitch control surface right?) Or do you just have to live with whatever loss of altitude you get before the canard regains flying speed?

 

[Velocity173]

Yeah but if you stall in a canard, how can you control the pitch? (The canard is the pitch control surface right?) Or do you just have to live with whatever loss of altitude you get before the canard regains flying speed?

It all depends on the particular canard. Mine doesn't have VGs. If I stall it (58 kts) by holding the stick all the way back to the stop, it'll pitch buck. That is it'll bob up and down and descend at 500 fpm. During this whole stalled descent I can roll either with stick or rudder. If I let go of the stick it will immediately recover and start flying again. Other Velocitys with VGs on the canard will stayed stalled with the stick full aft with no pitch buck. If they release the stick it will recover easily as well. But like I said during this stall the main wing is still flying and you can apply full pedal left and right. It'll do this kind of slow Dutch roll thing. I've even stalled my canard with my CG aft of the limit and she still recovers fine.

 

[Doggtyred]

Can you spin a Canard aircraft, such as the Long EZ?

If it was built properly and flown within demonstrated envelope, you wont stall it and therefore it wont spin.

Key caveats.... built properly.. flown within demonstrated envelope...

The canard's critical angle of attack is exceeded before the main wing's critical angle of attack. The canard provides a fraction of the lift - 20% or so. The main wing provides the rest. Losing the canard lift lowers the AOA on the main wing when the nose pitches down.

When you stall the canard, the nose pitches down and the canard begins flying again. A canard aircraft being flown on the edge of stall (stall, unstall, stall, unstall) will bob...

remember you control airspeed with pitch, and altitude with power.. so you can descend, maintain altitude or even climb, while bobbing the nose.. if you've got the power the plane will perform.

 

[Captain]

Does the forward wing change pitch automatically based on airspeed? Just curious. I played with the Piaggio in X-Plane a little. Must be awesome to fly the real deal!

No, it's fixed. It does have a flap on it that is automatically deployed with the main wing flaps in a two step process (up - mid - down).

What does change with speed is the horizontal stabilizer. In a conventional plane the elevator provides a down force to balance the plane. In a Piaggio the elevato provides neutral to up force to balance the plane. That elimination of the elevator down force equates into a big savings of drag. The only time a Piaggio elevator pushes down is to rotate taking off and to flare when landing.

 

[redtail]

No, it's fixed. It does have a flap on it that is automatically deployed with the main wing flaps in a two step process (up - mid - down).

What does change with speed is the horizontal stabilizer. In a conventional plane the elevator provides a down force to balance the plane. In a Piaggio the elevato provides neutral to up force to balance the plane. That elimination of the elevator down force equates into a big savings of drag. The only time a Piaggio elevator pushes down is to rotate taking off and to flare when landing.

Yes, I remember now. Haven't messed with x-plane in awhile.(gotta make time to get back into it)

That's pretty interesting about the horizontal stabilizer! I didn't know that.
Thanks.

I see them fly over my house from time to time while landing at JFK, I live about
4 miles away, right in the approach path of 22L/R. They have such a unique sound, you can't miss it.

 

[Captain]

Too bad you don't live near Teterboro. I go there about 50 times for every 1 time I go to JFK!

 

[dmspilot]

What are the disadvantages of a canard versus a conventional design?

 

[zaitcev]

Can you spin a Canard aircraft, such as the Long EZ?

You can spin Saab Grippen, although not most of canard aircraft. It requires the canard surface being fully moving like stabilator on Cherokee.

Note, however, that you can easily kill yourself in LongEZ if you stall while uncoordinated. See the N555JD crash. So although canard design provides a degree of protection, it is not magic.

 

[denverpilot]

Aircraft can still be made that can fall from the sky. Story at ten, film at eleven.

 

[Velocity173]

What are the disadvantages of a canard versus a conventional design?

Noise. Reason why Burt Rutan won't do canards anymore that have a prop in the back. Airflow from the fuse/exhaust get cut by the prop. Every time I would fly into my home airport my mech would comment on how loud it was coming in. Inside the cabin it isn't bad though. FOD. Anything coming off the airframe or nose wheel is going through the prop. Happens more often than people think. High stall speed. Sure the main wing won't stall but with and engine out you'll still have to maintain around 60 kts for touchdown because of the canard's stall speed. CG. Most canards are parked nose down because of the aft CG. Unless you're a fatso you'll need ballast up front. Generally not true (ballast) with Velocitys though. Cooling. Some (not mine) have cooling problems in the climb. Luggage space. Depends on the design but most don't have much room for luggage compared to a typical tractor configuration. Composite. Almost all (not talking Piaggios) are composite. Some people are die hard metal freaks that would never fly a plastic plane.

 

[Sac Arrow]

Okay, stupid question - so, both the canard and the main wing provide lift (as opposed to a conventional elevator which is subject to a down force). How does it fly stable? Wouldn't that be like flying a conventional plane with an aft CG loading?

 

[redtail]

Too bad you don't live near Teterboro. I go there about 50 times for every 1 time I go to JFK!

Hey you fly over my house!

Yeah I learn to fly at TEB in 1998 when they had two or three flight schools. Now they have none and last time I checked, ramp and Port Authority landing fees were around 90 bucks total for a skyhawk

I miss the airport but it's just not worth it. MMU & CDW are just a short hop away. I even inquired about a Port Authority employee discount and was denied! Oh well

 

[Tom-D]

What IF::::

you zoom it up to vertical, pull power, allow it to stop and fall backwards, will it spin?

 

[docmirror]

Yes, I've spun a Vari-Eze. It's very hard to do, but through a series of cross-coordination with rudder-lettes and bank angles, the main wing will exceed critical AOA.

Mine was the equivalent of a lazy whip stall at about 60deg left bank with power off.

 

[N801BH]

......I even inquired about a Port Authority employee discount and was denied! Oh well

.

Man.... Tough deal when they won't cut any slack to fellow employees... Must be too many $100,000+ salaries to be paid to give the milk away.

 

[Capt. Geoffrey Thorpe]

Duck.

 

[redtail]

.

Man.... Tough deal when they won't cut any slack to fellow employees... Must be too many $100,000+ salaries to be paid to give the milk away.

Must be.

Back to canards, I was wondering why it is that the concept was basically abandoned after the Wright Bros?

Why no Cessna, Piper, etc canards

 

[Velocity173]

What IF::::

you zoom it up to vertical, pull power, allow it to stop and fall backwards, will it spin?

I suppose if you had enough rudder authority, yes. I don't think it would produce enough yaw to spin it though. These rudders actually produce more roll than yaw. I can bank my aircraft by applying full pedal as fast as most typical GA aircraft with a yoke. Canards are very responsive in roll with the pedals but very little yaw. You have to do some serious cross controlling in a crosswind landing. a lot of guys do turns just with rudder alone.

 

[Doggtyred]

Okay, stupid question - so, both the canard and the main wing provide lift (as opposed to a conventional elevator which is subject to a down force). How does it fly stable? Wouldn't that be like flying a conventional plane with an aft CG loading?

It flies very stable... The CG is BETWEEN the canard spar and main wing spar..

About 20-30% lift provided in front of CG.. remainder provided behind it.

In a conventional winged/tailed plane, the CG is VERY CLOSE to of the center of lift, and the tail acts as a trim device...

edit.. If you want to go fast, minimize trim drag by loading aft CG in a canard... This means minimal deflection of the elevators on the canard, and less drag.

Less twitchy/more stable loading is incurred by forward CG, resulting in greater lift required by canard, but resulting in more drag from elevator deflection.

 

[zaitcev]

How does it fly stable? Wouldn't that be like flying a conventional plane with an aft CG loading?

There's a fairly extensive discussion in Denker 6.1 (6.1.7 in particular deals with canard design), but the basic principle of stability is simple: the rear flying surface needs to have a smaller angle of attack than the forward one. That is all. Note that in case of a conventional airplane, it is not required for the tail to fly at a negative angle of attack for stability, just for it to be smaller. The collorary in case of a canard airplane is that the canard flies at a greater angle of attack, so it has a greater area loading, if the airplane needs static stability (some military canard airplanes rely on flight to computers for stability, so they have negative static stability).

 

[kyleb]

High stall speed. Sure the main wing won't stall but with and engine out you'll still have to maintain around 60 kts for touchdown because of the canard's stall speed. CG.

Doesn't the high stall speed really come down to compromises most canard designers have made to bias the design towards efficient cross country performance? When Velocity created the 173, they upsized the lifting surfaces and signifcantly decreased stall speed at the loss of some cruise performance.

 

[Velocity173]

Doesn't the high stall speed really come down to compromises most canard designers have made to bias the design towards efficient cross country performance? When Velocity created the 173, they upsized the lifting surfaces and signifcantly decreased stall speed at the loss of some cruise performance.

Dan Maher created the 173 to compete with a C-172. Hence the 173 designation. It was suppose to be a good handling stable trainer like the C-172 but yet a faster cruise. I think they're completely different handling machines. Even with the increased wingspan and bigger canard my 173 is much more responsive and lighter on the controls than a C-172. It's also way more more pitch sensitive as all canards are. I've been to Velocity twice and each time they had an aircraft there getting its landing gear replaced because the pilot got into PIO and crushed the gear. They are also beefing up the gear on a lot of RGs but that's a whole separate issue.

Anyway you really can't compare a 173 with a C-172. My canard stalls right at the factory demo speed just under 60 kts. That's pretty high when you compare it to other tractor configurations. The 173 is a decent trainer but it's a better cross country aircraft. I cruise at 165 KTAS running 2500 rpm. While I don't sit up right in a large cabin the reclined seating with the throttle quadrant on the left and stick on the right is the most comfortable seating in any plane I've flown. In cruise the aircraft is as stable as any production I know of. I can take my hands off the controls and she'll track straight as an arrow. Landing just requires a lot of attention. Very sensitive. There is no big flare like a C-172. Slight nose up like a jet and she'll touch down nice and smooth. Get into PIO and you better do a go around.

Oh I will note that I have landed with the canard in the air at 55 kts without it stalling. I'm guessing that is due to the benefits of IGE? So I suppose you could get into a slower canard stalling speed in a forced landing than one out of IGE.

 

[Velocity173]

From the VariEze manual:
"intentional spins have been attempted by holding full aft stick and using full rudder, with all combinations of aileron control, and at all cg positions. These controls were held through 360 degrees of rotation . Full aft stick and full rudder results in a lazy spiral which results in a steep rolling dive at 3 + g and 100 knots. At any time, the spiral can be immediately stopped by removing rudder control and a completely straight forward recovery can be made. That maneuver is not a spin, since at no time is the aircraft departed from controlled flight. If the above maneuver is done at aft cg, the rotation rate is higher so the lazy spiral is more of a slow snap roll. However, even at aft cg the recovery is immediate when controls are neutralized."

You'd have to do some pretty violent maneuvers to spin one of these things.:wink2:

 

[Captain]

What IF::::

you zoom it up to vertical, pull power, allow it to stop and fall backwards, will it spin?

I did that in the sim last recurrent. I too was interested to see what would happen.

The setup: I'm PNF and the other guy goes heads down while the instructor set the plane up. The goal was to pitch straight up in a zoom climb and give the controls over to the PF as a tail slide was beginning.

The result: We broke the sim. We came off motion and the sim fell with a hard THUD! I was bummed as I really did want to see it. Took around an hour to get the sim running again after that,

 

[N801BH]

I did that in the sim last recurrent. I too was interested to see what would happen.

The setup: I'm PNF and the other guy goes heads down while the instructor set the plane up. The goal was to pitch straight up in a zoom climb and give the controls over to the PF as a tail slide was beginning.

The result: We broke the sim. We came off motion and the sim fell with a hard THUD! I was bummed as I really did want to see it. Took around an hour to get the sim running again after that,

I am a cheap bastard,, but... I would have paid 5 bucks to watch that,

 

[Tom-D]

The result: We broke the sim. We came off motion and the sim fell with a hard THUD! I was bummed as I really did want to see it. Took around an hour to get the sim running again after that,

If you broke the sim, are you dead?

 

[wabower]

No but when they fall off motion it can be a major jolt to whatever hits first. I whacked an elbow on the IOS table that took a month to heal up.

If you broke the sim, are you dead?

 

[docmirror]

I didn't have time earlier to expand on the spin characteristics of a canard, but I want to give some more data points because I think some are getting into an area of complacency about a canard and not being able to spin it. I assure you they will spin.

I'm not an aero eng, just an EE so please forgive me if I mangle some of the details. My only experience is with VariEze sn78-2, which was an early model, plans built VariEze. It was one of three produced under plans SN 78 (we were cheap bastards).

First, the VariEze was generally a delight to fly. My prev experience was in a Citabria, and some in a Pitts S2. Of course, being an acro dude I wanted to explore the limits of the EZ, and put some of the details to my own test envelope. One could find the early copies of The Canard Pusher somewhere online and verify that even Burt himself never said the plane was 'spin proof'. The best we could get is that it was 'highly resistant to a departure of lift from the main wing'(mid 70s, I don't know the issue).

Anyway, the first set of EZ plans out had a fairly long canard. After a time, there were three important changes made to the plans, and a suggested retrofit for planes already flying. The first thing they recommended was to cut of about 5-6" from the tips of the canard. This reduced elevator authority with a shorter span, but made the landing profile a bit flatter and faster. I can't recall if we lopped off the canard or not but I know we built to to the long plan to start with, and we had lots of elevator authority which I preferred.

Next, and I think directly as a result of a visit from several pilots to the Rutan factory, the plans were modified and included a set of leading edge cuffs. The reasoning as I came to understand it is that builders/owners were doing what they normally do, and increasing the weight of the engine, prop, accessories. I know my plane had a starter, alt, and a vac pump which Burt always recommended against. He didn't mind those little 12 amp pancake alternators, and a small motorcycle batt up in the nose, but a starter, bigger batt, and a vac system were beyond the design goals of the VariEze(were later incorporated in the LongEZ). Anyway, the cuffs were intended to partially offset the rear CG situation that was developing with bigger engines/acc and heavy rear seat pax with full fuel. This would put the plane at or above gross weight, right at the absolute back of the CG envelope. The cuffs provided some much needed lift to the double tapered and well swept back wing of the VariEze. Later LongEZ had a smaller chord taper ratio, and also quite a bit less sweep, and a bit less anhedral(on the ground anyway). Finally, the last major change was the big P-51 like air scoop on the bottom of the fuselage, to a NACA type duct for cooling. It wasn't that the big scoop was inefficient in bringing in air to the engine, it's that the big scoop was blanking part of the intake air for the lower section of the prop, thus producing a lopsided thrust plane with more thrust being produced during the top revolution of the arc than the bottom. This was not as pronounced at low speeds and power settings because of the higher AOA tended to equal things out. But, at higher speeds and higher power settings the thrust line difference was notable with the big scoop on the plane. It would be like a change in pitch with a pylon mounted engine of an amphib.

So, there we were, with a plane with the long canard, and nearly full span elevator, no leading edge cuffs, the big air scoop underneath, and full rudder travel which was later reduced because pilots were over-controlling the planes with the rudders. I put two 90Lb sacks of dry sand in the back seat, sealed in garbage bags, added full 24 gal of fuel, and I was about 160Lbs back then up front. Fully within the weight and CG envelope, I could take off on a warm day, climb to about 6-7000' and reproduce a nice little whip stall/spin with high bank angles, full aft stick, hard left rudder, and feed in some throttle. It would not burble like a normal GA high lift type wing found on a Cherokee, but it would depart from lifting moment rather quickly. The left wing would generally tuck under, and aileron had no effect. Depending on the deck angle of entry, it would take about 3/4 of a turn for the nose to pitch down at least 60deg, and more likely ~75deg down. If you didn't reduce power and rudder quickly, the plane would pick up speed so fast it would exceed Vne, which I did once by a few MPH.

I guess you could argue that it was more accurately a 'death spiral' but it was a very tight, and very fast rotating spiral, and the ailerons still had no effect, so I go ahead and call it a spin. Once the power and elevator were reduced, the plane would fly right out, and recovery was a normal mode ~3.5G pull out to level flight.

Later mods also offered a big belly plate that would come out and down at about 40deg angle and provide some descent control. I never fitted it to my plane, and I sold the plane after about a year flying it around San Diego and SoCal.

Bottom line, through a series of pilot actions, within the parameters of the original envelope of the designer, the VariEze could be made to spin repeatably. The mods including the NACA inlet, cuffs, and smaller canard probably took much of the authority needed to get into this realm, but it also reduced the pilot input as well. The LongEZ was a much more stable plane to fly, although I have only about 45 minutes in the back seat of one and it was long ago. The wing taper was less, the sweep was less, and the anhedral was less, and I believe they increased the winglets quite a bit as well.

 

[David]

It sounds like you were in a spiral dive not a spin as you suggested. I don't understand why you feel it was a spin. In a spin, the airspeed doesn't increase. Would that be different for a canard?

http://www.richstowell.com/documents/12StallSpinMyths.pdf

I didn't have time earlier to expand on the spin characteristics of a canard, but I want to give some more data points because I think some are getting into an area of complacency about a canard and not being able to spin it. I assure you they will spin.

I'm not an aero eng, just an EE so please forgive me if I mangle some of the details. My only experience is with VariEze sn78-2, which was an early model, plans built VariEze. It was one of three produced under plans SN 78 (we were cheap bastards).

First, the VariEze was generally a delight to fly. My prev experience was in a Citabria, and some in a Pitts S2. Of course, being an acro dude I wanted to explore the limits of the EZ, and put some of the details to my own test envelope. One could find the early copies of The Canard Pusher somewhere online and verify that even Burt himself never said the plane was 'spin proof'. The best we could get is that it was 'highly resistant to a departure of lift from the main wing'(mid 70s, I don't know the issue).

Anyway, the first set of EZ plans out had a fairly long canard. After a time, there were three important changes made to the plans, and a suggested retrofit for planes already flying. The first thing they recommended was to cut of about 5-6" from the tips of the canard. This reduced elevator authority with a shorter span, but made the landing profile a bit flatter and faster. I can't recall if we lopped off the canard or not but I know we built to to the long plan to start with, and we had lots of elevator authority which I preferred.

Next, and I think directly as a result of a visit from several pilots to the Rutan factory, the plans were modified and included a set of leading edge cuffs. The reasoning as I came to understand it is that builders/owners were doing what they normally do, and increasing the weight of the engine, prop, accessories. I know my plane had a starter, alt, and a vac pump which Burt always recommended against. He didn't mind those little 12 amp pancake alternators, and a small motorcycle batt up in the nose, but a starter, bigger batt, and a vac system were beyond the design goals of the VariEze(were later incorporated in the LongEZ). Anyway, the cuffs were intended to partially offset the rear CG situation that was developing with bigger engines/acc and heavy rear seat pax with full fuel. This would put the plane at or above gross weight, right at the absolute back of the CG envelope. The cuffs provided some much needed lift to the double tapered and well swept back wing of the VariEze. Later LongEZ had a smaller chord taper ratio, and also quite a bit less sweep, and a bit less anhedral(on the ground anyway). Finally, the last major change was the big P-51 like air scoop on the bottom of the fuselage, to a NACA type duct for cooling. It wasn't that the big scoop was inefficient in bringing in air to the engine, it's that the big scoop was blanking part of the intake air for the lower section of the prop, thus producing a lopsided thrust plane with more thrust being produced during the top revolution of the arc than the bottom. This was not as pronounced at low speeds and power settings because of the higher AOA tended to equal things out. But, at higher speeds and higher power settings the thrust line difference was notable with the big scoop on the plane. It would be like a change in pitch with a pylon mounted engine of an amphib.

So, there we were, with a plane with the long canard, and nearly full span elevator, no leading edge cuffs, the big air scoop underneath, and full rudder travel which was later reduced because pilots were over-controlling the planes with the rudders. I put two 90Lb sacks of dry sand in the back seat, sealed in garbage bags, added full 24 gal of fuel, and I was about 160Lbs back then up front. Fully within the weight and CG envelope, I could take off on a warm day, climb to about 6-7000' and reproduce a nice little whip stall/spin with high bank angles, full aft stick, hard left rudder, and feed in some throttle. It would not burble like a normal GA high lift type wing found on a Cherokee, but it would depart from lifting moment rather quickly. The left wing would generally tuck under, and aileron had no effect. Depending on the deck angle of entry, it would take about 3/4 of a turn for the nose to pitch down at least 60deg, and more likely ~75deg down. If you didn't reduce power and rudder quickly, the plane would pick up speed so fast it would exceed Vne, which I did once by a few MPH.

I guess you could argue that it was more accurately a 'death spiral' but it was a very tight, and very fast rotating spiral, and the ailerons still had no effect, so I go ahead and call it a spin. Once the power and elevator were reduced, the plane would fly right out, and recovery was a normal mode ~3.5G pull out to level flight.

Later mods also offered a big belly plate that would come out and down at about 40deg angle and provide some descent control. I never fitted it to my plane, and I sold the plane after about a year flying it around San Diego and SoCal.

Bottom line, through a series of pilot actions, within the parameters of the original envelope of the designer, the VariEze could be made to spin repeatably. The mods including the NACA inlet, cuffs, and smaller canard probably took much of the authority needed to get into this realm, but it also reduced the pilot input as well. The LongEZ was a much more stable plane to fly, although I have only about 45 minutes in the back seat of one and it was long ago. The wing taper was less, the sweep was less, and the anhedral was less, and I believe they increased the winglets quite a bit as well.

 

[docmirror]

I'm not going to go much further than I have already. The differences between a tight spiral and a spin are for the NTSB to sort out from the wreckage. At the break on entry, there was a definite spinning tendency. I think the canard may have evolved the spin after a full rotation or so to the death spiral as has been mentioned. However, the first 3/4 or 1 full rotation would be characteristic of a spin. I didn't have the balls to keep it in that attitude for more than about 1-1/2 rotations, so there is a significant difference in the canard actions once the spin has begun with a tractor engine conventional wing plane.

Bottom line for me was, the typical scenario of increasing bank angle, pitch, and rudder around to get lined up on base or final for landing. This is the exact profile I was trying to recreate which causes so many fatal spins, thinking that the VariEze would just mush along and bob the nose as it does in level unaccel flight. If you add a bit of power to that mix with aft CG, the wing will tuck, the planet will turn upside down, and you will impact the dirt in a very ungraceful way. Call it what you will.