Canard Stalls
 2005.11.11
 


This is the sixth try to come up with something useful on EZ stalls, something I can live with. Pun left in.

Bottom line is I really flinch when that word stall is used. It’s useless to resist because Burt uses the term stalls in his early Canard Pusher comments. I think everyone miss-uses the word stall, but evidently I’m the only one that feels a dink on the noggin when it happens.

Lately, the least-worst is Adam Smith’s comment in the November Sport Aviation, on page 3 of the Tailwinds insert, which should be about page 99.
Anyway, Adam says Rutan designed “airplanes that a pilot could not stall so aggressively as to lose control of the aircraft.” OK, count me in. I actually like that.

I think a more useful mental rabbit to chase is low speed sink, especially in a turn. My stall hang-up is a detail, but I can’t get away from it. Bottom line, a plane should fly as described in the Owners Handbook. Mine does. It doesn’t stall in the classic sense. If a guy is forced to be extremely aggressive during a landing, he should be able to be deliberate, forceful, and confident.

Gritting my teeth is caused from hearing stalls referred to as some nebulous, teetering condition. To me there is no comparison or relationship between stalling my old Cessna 120, or a T-28, versus when I’m sitting solid in the VariEze with 1500 rpm and full aft stick. That canard ain’t mushing or dropping. Loss of lift in a turn gets away from our pure point here. Wing rock can be addressed with CG. Back to the canard stall…

The nod is a specific result of the canard being at good old maximum lift point. It’s not hanging on the edge. Any reduction in angle of attack and the canard is still flying, with a huge weather vane behind to help it behave. The airframe as a whole is fine. Add power and it climbs. Reduce power and it descends.

OK, there can be a merging of landing stomach-tightening goofs in both planes that I could make if I really tried. There was one time in the C-120 over the numbers where I got slow and was hoping to just settle in. It was on the verge of stalling, wallowing, and I went around. I guess if I did that in the EZ it would also be slow to respond and if no power was added, it would sink bad. I don’t want to be there in either one, so I adjust. That’s kinda where the 22 mph buffer comes in.

But if I thought that the EZ’s nose was going to fall through like the Cessna would have, or that the main wings weren’t perfectly happy, I would have a totally different approach to flying the plane than I do now. I wouldn’t do some of the things I do now, that are well within the scope of the Owner’s Handbook.

One of the benefits I see is when deciding to depart the pattern because someone calls in and I don’t see them. Several times on downwind or base I have pulled out into areas I know are clear to let the intruder show himself. I know he doesn’t see me.
Starting at around 110 mph and slowing, in a 30 to 45 degree turn, there has occasionally been a gentle nodding in the turn. My plane only “nods” with aft CG so I don’t always feel it. I’m appropriately confident there. The Cessna would have required a lot more of that pilot stuff to stay above the stall speed to keep from creating a crop circle below.

Let’s talk about the canard a minute.
Why was the elevator cord lengthened?
Answer, pitch sensitivity. This was a big problem until the cord change. This particular plans change was one of the first things that shook any supposed intuitive understanding I may have had of how this canard plane worked.

On my own, my first knee jerk reaction would have been exactly wrong. Why would you add area to a pitch surface that was already causing over-controlling?
Because, with the air pressure on it, the surface was harder to move. Less sensitive. You could push a little harder on the stick and it wouldn’t react as much. It was pointed out how important it is to have your arm resting on the side console. Thanks for letting me over-anal-ize that.

Number two, why were the canard tips cut off four inches on each end?
The problem was the heavier engines. Roughly, for every four pound increase in the engine area, one pound must be added in the nose. Burt had already said that if your VariEze weighed more than 620 lbs, to chop it up and start over.

Remember talking about being over the numbers and being slow and mushing and wallowing around? That’s one of the potential problems here, the airframe stalling overall. To get the limited stall, besides the airfoil, the canard was designed to be limited in size; width and length, in order to only lift the nose of the airframe so high.
The key was to determine that desired max airframe angle, then size the canard to that point of maximum lift, and then keep working backwards, including installing the main wings at a lower angle than the canard. That would limit the angle that the “airframe” could be lifted to by the canard and allow the wings to stay happy. The original canard and airframe design did just that, based on the 175 lb C-75 engine.

With the heavier engines, the nose would come up higher. Duh.
An immediate fix was to add ballast to the nose; 12 lbs in one well documented case.
Burt pulled off a miracle weight savings idea, to just reduce the “size” of the canard so everything would go back to where the canard would only lift the airframe angle “so high”. Thus the four inches were cut off the ends of the canard. It was nice that the ends had that space and elevators weren’t affected. There is a raw, well-aged canard in our hangar that you can see went through that exact building and update evolution.

So, the canard will only lift the nose so high. That’s not a stall. To me.
Someone recently mentioned the delicious in-flight experience of seeing water from rain moving forward on the elevators, or canard; I don’t remember which. That is spectacular.

Gary Hunter also mentions seeing an oil track coming out, or forward, in the corner of the NACA inlet on Pushy Galore, which he remedied by bringing the sidewalls within the 7 degrees of the relative wind. Air flow is crazy.

A lady passing through our hangar mentioned that she just couldn’t believe that that little wing would even lift the nose at all. I tried to suggest that if I was making a 200 mph low pass down 17L and pulled back on the stick, don’t get in the way.

Going a little further to really expose myself to error, I think that at cruise the canard is already really heavily loaded, maybe 95%. It was mentioned in one of the early VariEze articles that it provides about 30% of the total lift.

There were three canard fighters in the WW II era, from Japan, the US and Germany, I think. The US model was the Ascender, which came to be un-affectionately known as the Ass-ender. None of them worked because the front surface was treated like a horizontal stabilizer, unloaded. The Ascender was extremely unstable in pitch. Burt’s canards work because of the heavy loading.

So, say the canard is loaded to maybe 95% in cruise, then you pull the stick back to the stop and reduce the power a little and it lifts up maybe a foot or so, and then just sits there at 100%. The canard angle of maximum lift. That’s amazing to me. I wanna try that in a Cessna 120!

And it may explain why those that claim the rain/pitch trim problem is reduced or eliminated with the addition of wheel pants, might just be right. Those tires are on a long moment arm opposing the canard. So maybe the canard goes from 95% to something like 92% lift effort in cruise and has more lift left when it gets wet.

Point is, the canard is a spectacular piece of work. Burt brainstormed past his initial design to allow us to throw in a heavier engine without adding ballast. We should also not accept anything that contaminates that canard/main wing relationship, especially the canard max lift angle.

Or suggest that it might/should consistently have different/worse flight characteristics than as advertised. We should know the slow flight personality of the plane and address errors, per the Owners Handbook. We should visually imprint the max attitude where we are comfortable maneuvering, and keep it there or better. (The airfoil always stalls at the same angle).
If it’s not right, we can add nose ballast to get the CG forward a little if needed. Taping or sealing the elevator gaps would put our freedom, and the max airframe angle, way over the line, as would being sloppy about the canard contour or having the elevator/canard gap more than one-tenth inch.

But there we’re moving into attitude control issues in the flare. That’s far enough for this time.
Concerning the landing slow flight stuff, my main thought here when saddling up leans toward having the 22 mph buffer if I do have to do any of that fancy pilot stuff to get the tires to spin-up evenly.
Thanks for your cool notes and suggestions.
Bill James, Fort Worth VariEze.

Official technical data disclaimer:
It is always a significant event around the family dinner table when the author is right about something. After confirmation from the wife, the kids usually take a moment to appropriately commemorate the occasion. Hopefully he is close here.


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