from EZChronicles by Bill James
1. Why were the canard tips shortened?
2. Why was the elevator cord lengthened?
3. Why did the VariEze have anhedral?
4. Why is canard lift affected by moisture?
5. Does the Canard stall?
6. Sink, Vortelons, Wing Cuffs, Trailing edge fences
7. Is Density Altitude accurate?
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1. Why were the Canard tips shortened four inches?
The way I heard it, early-early on, Shirl Dickey, (Sponsor of historic RACE events) found that his VEze was squirrel-ly on landing. Burt determined that the nose was rising the too high. They put about 12 lbs ballast in the nose and with that slightly decreased AOA it flew correctly. Burt made a Plans Change to cut four inches off each canard tip to get the same beneficial reduction in AOA but without the added ballast. It was a simple, perfect fix. All good.
Obviously, changes to the canard are significant. The EZ design has a critical AOA relationship between the canard and wings where the wings still have a certain stall margin when the canard is at max AOA. On Shirl Dickey’s VariEze that was re-established with the canard tip reduction. The nose wheel lift-off speed provides a critical indication of whether the aircraft is at proper CG. Or not. Using information in the operator’s handbook and plans and CPs, and knowledgable people, it’s up to each of us individually to confirm that the critical canard/wing relationship is correct – when building, confirmed during the restricted period, and retained thereafter.
The same GU canard worked successfully on the VEZ, LEZ, Cozy, and even the Berkut according to Dave Ronneberg’s comments in my hangar, from min speed and high speed. As designed, it is predictable at slow speed and the faster you go the more it lifts.
There is an excellent read on this masterful and critical evolution in CP 14 p4-6. It starts with the loss of efficiency that was creeping into the fleet because of excessive weight, and the how-to and why of reducing the canard span. It’s a fascinating progression of Burt’s gifted aerodynamic thought.
An aside. You’ve probably heard the story where an EZ Driver bet that on takeoff he could rotate his LEZ, pull the engine to idle, and fly around the pattern. And he won the bet. The catch was, he rotated at 130 kts.
2. Why was the Elevator cord lengthened?
On early VariEzes, pitch sensitivity was an issue. A plans change lengthened the elevator cord from front to rear. To some, making the elevators larger initially seemed counter-intuitive. But the larger surface required slightly more force to move the elevator making pitch response less sensitive. Some builders had already adjusted to the sensitivity and didn’t need to make the plans change. The CPs provide a short and interesting progression of Burt helping us work through those mental gymnastics.
Ref CPs 17-5, 18-5, 20-3.
3. Why did the VariEze have anhedral?
The first two RAF VariEzes, the 399 lb N7EZ and the 585 lb N4EZ used “elevons” for roll input and control. At that time the elevons (now elevators) on the canard moved in opposite directions for roll, and in the same direction for pitch, at the same time. Ailerons were not introduced until CP 13. For that short time the pitch and roll linkage was combined and mixed, with two 12-inch pushrods connected from the elevons down to the sidestick in a small space between your right knee and the fuselage wall. Beautifully simple.
A great design, only it didn’t work as well as intended. The elevons were small, barely adequate. Unfortunately, while less stability was needed, wing sweep in-and-of-itself adds stability to the mix. To add instability, the main wings were installed with anhedral, an 10.9 inch main wing droop. Adding anhedral reminds me of Klaus’s admonition to add lightness.
However, also lurking in the mix was an additional unnoticed, unintentional, crazy result. The way I heard it, Peter Lert was doing the aft CG testing and discovered that the roll control seemed to be reversed, especially at low speeds. When flying the airplane with no rudder input, applying “left stick” resulted in a right turn, and “right stick” resulted in a left turn. A lot of flying and record setting had already been accomplished in those first two VariEzes. I guess with everyone having so much fun, no one noticed that they were actually turning with rudder. But they were. Spoilers were designed and then ailerons became standard.
Why the crazy turns? Turns out that the airflow from the deflected elevon changed the wing AOA which produced an opposite roll. The wing’s being bigger, their opposite roll won out. The fix was ailerons. The elevons became elevators. The anhedral was no longer needed and wasn’t used on the Long EZ.
In my opinion, there is not much difference in flying a stock VEze with anhedral compared to my VEze with level wings. Of course I am required to claim the 2 kt benefit.
4. Why is canard lift affected by moisture?
I don’t know but I’ll mention some non-technical observations.
In a LEZ with the GU canard in light mist or rain, I have seen a thin string-like gathering of water dancing along the top of the full width of the canard, like a transparent strand of yarn. One would assume that ridge of water acts like a spoiler tripping the airflow over the top of the canard.
Maybe, a slick surface allows the low pressure to raise more water higher than on a dull surface such as primer, and with more surface tension the water is pulled up less. I flew my VEze several years in white primer and noted little rain effect. Now with shiny paint I notice loss of lift. Some folks report their canard rises in rain. It could be that variances in curvature result in a more fore or aft location of the water “spoiler”, producing different results. One of the CPs state that the fix is to sand the top canard surface fore and aft with 600 grit sandpaper.
Evidently wheel pants may reduce the rain effect. It makes sense that with the gear on a long moment arm working opposite the canard, pulling the nose down, maybe less drag pulling the nose down reduces the load on the canard, and it just works better.
5. Does the canard stall?
I would like to just say no the canard doesn’t stall, but I would be in a minority. In my training a stall includes disruption of lift and control, and specific steps are necessary to recover. However, folks do refer to the canard sitting at max lift as stalled. To me, the word stall is skewed here, as if the canard has “stalled right there at that condition”. The way I see it, when the canard lifts to max AOA and stays up there, there is pretty healthy lift, not stall.
The important thing is, what should an EZ Driver expect at minimum speed with full aft stick? Paraphrased from the Long EZ Owner’s Manual: “Any Power setting may be used at full aft stick without changing the way the airplane handles. You can climb, descend, or maintain level flight. The “stall” may consist of stabilized flight, a mild bucking oscillation, or an uncommanded Dutch roll, relieved by relaxing back stick slightly. Inaccurate airfoil shapes, incidence errors, or errors in weight and balance can result in degradation of the normal safe stall characteristics.” Unquote from the Long EZ Owner’s Manual. Stall is also discussed in CP 20-3.
The last thing a canard driver in extremis should experience is concern or confusion over what he has heard about what the aircraft will or might or won’t do at minimum speed with full aft stick. Stall resistance is designed in, confirmed during the restricted period, and must be confirmed and retained thereafter. Per the owner’s manual.
An example, a canard driver on downwind heard another aircraft call entering but couldn’t locate it. He became distracted and turned out of the pattern. He located the other aircraft and orbited a couple of times for spacing. In a forty-five degree bank looking back over his shoulder, the nose began a gentle “nod”. No problem. Normal. There was no hint of loss of control or canard drop-through. The airplane held max AOA and handling per the Owner’s Manual. Because of the bank in the turn, the max lift “nod” would occur at a higher speed than if the wings were level.
A word of caution during the min-speed confirmation test flights. Yes, minimum speed needs to be confirmed. But flying at minimum speed is natural but not normal. The early CPs recommended extreme caution and a parachute. Spur-of-the-moment formation flight at minimum speed would be injudicious.
In a side-by-side canard plane, after a single pilot min-speed test flight has been carefully and successfully conducted, then if adding a second front-seater for another min speed test, the airplane is a different animal and could/should require a ballast change.
Thoughts on Sink and Stall
Sink is normal. Sink develops and may increase with continued aft stick and low power. Accelerated sink on landing can damage the gear attachments or worse. Acceptable weight loading is not just what can lugged into the air, weight may matter more on landing. An extreme example, some aircraft can’t land without damage to the landing gear, etc. without reducing the load they just took off with. Weight increases momentum and min-speed. In one EZ, in level flight with the pilot and 8 gallons the full aft stick min speed is 62 mph. More heavily loaded, the full aft stick min speed for the same plane is 85 mph. Heavier, the min-speed AOA is the same but it takes more power and higher speed to maintain level flight. ask a bush pilot. With no power, the descent rate and momentum is higher. Not a good combination for an unplanned landing.
The terms “Stall” and “Sink” can be erroneously intermixed. You can hear comments about an EZ that stalled and the nose fell through like a lawn dart. This is not an acceptable canard installation. The question is, did the canard actually become completely devoid of lift and stall, or was the aircraft actually entering normal, stabilized-if-brisk descending flight, or sink, as described in the owner’s manual? It could be hard to tell if the landing was botched close to the ground. If an aircraft is suspected of this nose drop-through it should be cautiously confirmed at altitude. If that canard aircraft in fact turns into a lawn dart, that is not normal or acceptable. The aircraft should be grounded and corrected.
One more little thing on min speed, in an engine out landing, an EZ needs a 22 mph buffer above min speed to reduce the sink rate.
Bottom line, when a Canard Driver actually has a problem and has to do some of that pilot stuff, there should be confidence, not hesitation, that the aircraft is going to operate as designed.
Vortelons improve stability, (as do the leading edge cuffs, if so-installed). I don’t fly the VariEze without vortelons. I did once right after painting. Vortelon evolution is an interesting story.
Trailing edge fences. I agree that they improve stability and reduce takeoff and landing distance. Klaus has excellent info on his site.
7. Bonus for summer flyers. Is Density Altitude accurate?
Is this true? The Density Altitude broadcast for the local airport is correct – except on a hot day, on the runway.
Here in N TX on a 104 F degree day the local airports reported the DA at 4200 ft. However, the temperature measured in the broiling heat at four feet above the runway was 139 F where the wings, prop, carb and pistons live during ground roll and liftoff, with a DA there over 8000 ft. Any guess on how large that super-heated runway air mass would be? Surely it affects the length of the runway up to maybe 20 feet high. Then above 20 ft the DA may actually be 4200 ft as reported. On a hot day even at sea level, leaning before takeoff is advisable. I have been told that all takeoffs must be made at full rich. Check with your instructor. You are the pilot, it’s your call. As my mother and her friend Shakespeare used to say, discretion is the better part of valor.
A note on the Canard Pusher Index available now. Way back when the boxes of VariEze parts appeared in my garage, even though I had read everything that had been written or published on the EZs, I had no real idea what I was doing or what I had in the boxes. I spent the next three months re-reading the CPs, updating my plans and inventorying the parts. Time well spent but the CP Index would have made it much easier. It’s quick and the CP info is great fun.
In the 1990s the EZ tide was shifting from mostly builders to mosty buyers. This is where the CSA, now COBA network stepped up providing their important service. Thanks guys.
Bill James
VEze N95BJ
Built 5 yrs. Flying 25 yrs. Avid student 47 years.
OKAY.