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Old 07-11-2005, 08:35 PM
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Default Acrobatics

Via Wayne

Introduction from Tom Staggs:

Over the past few weeks (Hicks: This email was written several years ago), there have been a series of posts about Canard aircraft and aerobatics, inverted flight, deep stall, parachutes, and bailing out. As I have a fair amount of experience in 4 of the 5 topics (never left the plane), I thought I'd pass along some experiences and observations on the different topics.

To allow the follow-on conversations to address the individual topics, I'll separate my comments into separate posts. I'd appreciate it if anyone who has any ideas or opinions PLEASE post them. If we don't share our thoughts, we run the risk of repeating the mistakes of those who have already learned the lesson.

For those of you who didn't see the message by John Bullens the other day mentioning that I flew aerobatics in my EZ, let me explain. I am a professional airshow performer flying low-altitude aerobatics in my Long-EZ throughout North America. I hold an unrestricted low-altitude waiver from the FAA and Transport Canada, although I have higher personal limits for all my maneuvers. I have flown at 56 show sites in 17 American states and 5 Canadian Provinces.

I have managed to log over 1,000 hours in the EZ, including over 300 either practicing or performing aerobatics. My Long-EZ is basically a per-plans plane, with a few noteable exceptions: I have an 160-HP O-320-E2D, beefed up the engine mount extrusions for the torque imposed by aerobatics, installed a NACA inlet on the belly, and extended my aileron span (absolutely no effect on roll rate, by the way!!!!).

I look forward to hearing everyone's comments and suggestions.

Fly safely,

Tom Staggs
Long-EZ N13YV
Arlington, WA


Aerobatics in an EZ

There is a big difference between "capable" and "suited" when it comes to aerobatics. Someone pointed out in an earlier posting that Tex Johnston managed to roll the prototype 707 in front of a crowd, but that didn't mean that all 707's should be rolled, or that it was a bright idea.

The Long-EZ and Veri-EZE are both capable of simple aerobatics, but neither is well-suited to aerobatics. Why? Their roll rates are slow (approximately 50-degrees for a Long-EZ using coordinated controls compared to 180+ degrees per second in most aerobatic planes), they lack the ability to hold the nose up during knife-edge flight, they lack the ability to use prop blast over the tail to provide control authority at low speeds, and the planes' stability in true out-of-control flight is not predictable.

The bottom line: if you want to fly aerobatics, you should have built an RV or Pitts. Our planes are great for cross-country, but they just aren't good aerobatic planes.

Another thing to consider is how the planes' efficiency is a detriment to its ability to fly aerobatics. Given the clean lines, an EZ will easily out-accelerate most any other prop plane in their horsepower class, assuming the planes aren't climbing. When maneuvering with RV-4's with constant-speed props and 20 more horsepower, I can easily pull well out in front, all because of our wonderful aerodynamic efficiency. When flying aerobatics, should you accidentally allow the nose to get too low or stay down for too long, you can find yourself shooting through red line faster than you could ever imagine.

The elasticity of our fiberglass wings makes them poorly suited to safely flying aerobatics. When flying at maneuvering speed, if you rapidly apply full stick, your ailerons function more like large trim tabs, twisting the wing opposite the deflection of the control surface. I have been able to document this through videotape by recording the fore & aft motion of the winglet during aileron inputs. This twisting of the wing result in decreased roll authority during the first 30-degrees of a roll, a fact that is evident when reviewing my boresight videotape shot with "schnoz cam", a video camera mounted in the nose of my EZ.

It's worth noting that when Rick Fessenden was flying the Berkut in airshows, the stiffer Berkut wings with its Kevlar and Carbon fiber construction allowed him to achieve a faster and more responsive roll rate and a stronger ultimate load.

In swept wing airplanes, applying full rudder into the direction of roll increases the roll rate. The advancing wing's centroid of lift swings farther outboard from the center of mass, providing it with an increased moment arm, while the retarded wing has its centroid move inboard. This lift asymmetry results in a rolling moment around the center of mass. What it means to you is that your roll rate increases by using excessive rudder when compared to conventional "balanced" flight.

Just because a maneuver can be flown in an EZ, is it safe to fly it in an EZ? If you haven't been trained to fly aerobatics in a conventional aircraft designed for acro, then I'd recommend you not fly them in your EZ. Even with the training, beware of our planes' weaknesses. Remember, the nose of canard planes "fall through" most maneuvers, and once pointed down, speed will build up faster than you could ever imagine. I would recommend that you limit yourself to steep turns or wingovers. If you have to try something inverted, do so knowing that the plane might not forgive you your mistakes.

So what maneuvers can be flown in an EZ? Loops and rolls, as well as variations on the theme such as barrel rolls, wingovers, half-cubans.

Which can't be flown: spins, snaps, hammerheads, and tail slides. The first two can't be accomplished because of the inability to stall the main wing while simultaneously yawing the plane, the third because we lack air flow over the rudders as we approach zero airspeed, and the last because of the terrible post-stall gyrations encountered as the plane weathervanes after swapping ends (see the article in the CSA Newsletter last year).

As for the wide-body family of canard planes (Cozy, Velocity, AeroCanard, etc.), I would not recommend any types of aerobatics in these aircraft. Their widened fuselages result in more lifting area forward of the center of mass, decreasing the dynamic and static stability of the canard design. In cruising flight, they're very safe, but they should not be used for aerobatics. While flight testing one of these designs, I found out that rapid application of aft stick could actually result in an uncommanded increase in angle of attack, despite being countered by full forward stick. This was likely the result of the increased lifting area incorporated in these designs. Such a phenomena could easily result in overstressing the wings to the point of failure.

For those of you who have read this far, yes, I have scared the daylights out of myself flying aerobatics in the EZ. When I perform in a show, it's a routine that I have flown literally hundreds of times, always developing maneuvers above 5,000' AGL before moving them slowly downward. There are some maneuvers that although I can do, I have chosen not to include in my routine because they lack enough margin for error or ability to be reproduced consistently.

If you're still insistent on flying aerobatics in your EZ, please get together with a local pilot who has already mastered the maneuvers. Make sure that they really know what they're talking about; don't fly with someone who accomplish the maneuver by luck instead of skill. Above all, don't try to perform a maneuver based on advice or technique you read about on the internet....

Fly Safely,

Tom Staggs
Long-EZ N13YV
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Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

maker of wood, fiberglass, foam dust, metal bits and one day a Cozy will pop out and swiftly whisk me from meeting old friends and family to adventures throughout the world
  #2  
Old 07-11-2005, 08:37 PM
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(Hicks: WARNING: DO NOT TRY THIS AT HOME!!!!!)


Inverted flight in a canard

Over the past few weeks, there was a string of messages about whether or not our canard aircraft are capable of sustained inverted flight. I found the messages that assured us such a maneuver would be "impossible" to be rather humorous: as an airshow performer, one of the maneuvers in my routine is to fly my Long-EZ down the showline inverted.

Having said this, it's time for my "don't try this at home disclaimer". I'm sharing my thoughts and observations here because I feel that the better we understand our aircraft, the safer we can be.

As many contributors to this news group pointed out, an airfoil couldn't care less about "up" and "down"; airfoils only care about the relative wind. In the case of the Long-EZ I fly, I have the GU25 airfoil on the canard (the original design), and the modified Eppler 1230 on the main wing. They're both flat bottomed, which implies very poor negative angle of attack characteristics.

With a flat-bottom airfoil the maximum coefficient of lift is typically substantially less than what it is for positive angles of attack. In other words, the maximum G's generated in inverted flight would be less than what they are for conventional, right-side-up flight.

In the POH for the Long-EZ, the performance envelope shows G limitations of +5, -2. I don't know whether the negative-G capability was ever proven in flight test, but I would suppose, knowing Burt's thoroughness, it most likely was. I know that my experience in a stock O-235 Long-EZ showed that these parameters were achievable, both at positive and negative G.

The inverted characteristics of my Long are quite reasonable, although they require a fair amount of forward stick force with a very steep force gradient. Coordinated turns are possible and actually easier to attain inverted than upright (I believe this might stem from the fact that my knees are braced during inverted flight, allowing for greater precision applying rudder inputs).

When I make an inverted pass, I always start it with at least 5 degrees nose above the horizon, and I never let the nose fall below the horizon. Just before I roll back upright, I push to about 20 degrees nose up before commencing my roll.

Now for the bad news: although the EZ should exhibit tame stall characteristics inverted (mine does), it is also significantly easier to enter a deep stall. I have twice encountered this phenomena, but have been able to recover from it by rocking the wings with the rudders, my guess is that they are not blanked when inverted like they are in an upright deep stall. In both cases, my CG was within the 103" limitation although towards the aft portion of the range (102.1" with an O-235, 103.0 with an O-320) and I was at very low airspeed "floating" over the top of the loop in mist or light rain. In the O-235 case, my engine was not producing power, but with the O-320, I was at full throttle.

Both times, I was applying more forward stick to hold my nose up, then applied even more forward stick. The nose seemed to hang above the horizon as I suddenly felt my shoulders dig into my straps. The stick then seemed to go lifeless in my hand; I could cycle the pitch with no apparent effect, nor did the ailerons seem to be capable of rolling the plane. In the first incident, I noticed my airspeed was still on the peg after approximately 2-3 seconds of "falling". In the second incident, I saw about 40 kts of airspeed and about -3,000 fpm on the VSI after a similar period of time.

In both cases, application of full rudder resulted in a simultaneous yaw and wing rock. After one or two more applications (too scared to remember exactly how many times I cycled the rudders), the plane sliced nose-low while rolling upright. As the nose feel through, airspeed picked up and I was able to fly away.

Lesson learned: Avoid large control inputs at negative G in an EZ, realize that moisture can impact the aerodynamic characteristics of the airfoils, and be ready to use the rudders to recover.

By the way, eliminate the inverted pass portion of my airshow routine when there's any kind of visible moisture.


Fly Safely,

Tom Staggs
Long-EZ N13YV

Aerobatics in the Cozy
From Tom Staggs:

The worst characteristic of the Cozy when doing aerobatics is that a sudden onset of positive G's can cause the plane to pitch up uncontrollably, easily overstressing the plane. This is the result of a Cozy having more projected area (when viewed from above) forward of the center of mass than the Long-EZ.

Another thing is the Hammerhead. Without propwash across the rudders, you can't kick the nose around at zero airspeed. The result is a tail slide, and I have never been half as scared as I was during my two unintentional tailslides when the nose oscillated +/- 135 degrees and then didn't dampen out until right as I approached redline airspeed going straight down.


Oddly enough, I just found the rough drafts of the messages I posted nearly 6 years ago. Here is the file containing them - please feel free to pass them along. (Hicks: These are the previous posts provided above.)

You might want to include a little post script:

I retired from flying airshows at the end of the 1999 airshow season after 8 years on the circuit. During that time, I had two close calls with the ground, both cases where my nose got buried and I didn't have the pitch authority to change my flight path. Since that time, I have become a visiting instructor at the USAF Test Pilot School at Edwards AFB. I have instructed 5 of the last 7 classes of seniors in the flying characteristics of the canard configuration, including limited aerobatics. All of the pilots love the way the plane handles but agrees that it is not a good aerobatic platform.


Fly safely,

Tom Staggs
Long-EZ N13YV
EAA Flight Advisor
__________________
Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

maker of wood, fiberglass, foam dust, metal bits and one day a Cozy will pop out and swiftly whisk me from meeting old friends and family to adventures throughout the world
 


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