Dubai - WAG - Gyro down 9.12.15

Thank you for posting that link Abid.

It gives me a place to direct clients when they inquire about why "helmet secure?" is on the pre-takeoff checklist for The Predator.

This is not the only mishap involving a helmet not being secure; it is the most recent and best reported that I am aware of.

I feel there is a lot of good information available in the report.
 
I found it interesting that the last paragraph in Section 1.17.1 states that the normal takeoff airspeed of a gyrocopter at Maximum Take Off Mass is 30 km per hour.
​​
Maybe the FAI supplied that figure for this accident report, but I seriously doubt anyone flying gyros can lift off @ under 19 mph.

My experience is I was lifting off around 32-33 mph when I was powered by a Rotax 503 in a single place gyro. As my personal weight got heavier and additionally, when I switched to a four stroke engine that added about an additional 65# to the gyro's weight, that my lift off speed is around 46-48 mph.

Another gyro pilot I know flying a single place Rotax 912 states he lifts off also in that upper 40's mph range. A two place machine likely lifts of @ an even higher airspeed, especially when two people are on board.

I was struck how this accident had such a continuous stream of mistakes on the part of the pilot to make it a chain made up of several links. It does appear that his cyclic movements did cause the rotors to slow too much, and seems to indicate a severe flapping to have caused one rotor blade to break off. It also appears to have been a torque roll situation.

Also, striking is the lack of oversight of the race officials, such as allowing a pilot w/ only 20 some hrs. of PIC (way below their 45 hrs. of PIC time minimum).
 
We had a scary loss-of-helmet incident at a flyin in New Hampshire some years ago. A passenger taking a ride in a SxS Air Command lost a helmet on takeoff. It hit the prop and the rotor on the way out. The pilot, just climbing out with a wooded swamp ahead, managed to turn off track and squeeze the gyro into a backyard. No injuries.

When hopping students I took to pulling on the passenger's chin strap myself (and to hell with personal space) before taking off.

But here the aircraft design is not off the hook. An aircraft is safer it if does not execute an uncommanded snap roll if/when the pilot is distracted. Sure, a good pilot won't allow himself/herself to BECOME distracted (first rule: fly the aircraft). In the real world, however, fallible human beings are a part of the aircraft-pilot system. Recreational gyros should not be all-out widowmaker racers like the Gee Bee.

The system should be designed to employ available. cost-effective fail-safe measures. Torque compensation in gyros has been around since the Cierva era. IMHO, every designer should design for torque- and slip-roll compensation, and then test to verify it.
 
Torque roll it seems to me was later. He made plenty of errors including going to low G with his cyclic actions. He was toast right there flying so low. Wish they would consider safety as the #1 priority at such events and only allow experienced pilots to do this type of event. 45 hours for a pylon race is also a joke
 
Our long custom in the gyro world (dating back to Igor Bensen) is to blame every crash in which low G may have been involved on the low G itself. If low G is usually or always lethal, then the autogyro itself is a fatally flawed design concept, and has been so from Cierva's time. This is exactly what a great many non-gyro fliers have believed all along.

The plain fact is that low G is inevitable in an aircraft, thanks to thermal and mechanical turbulence. These natural, normal atmospheric disturbances simply cannot be avoided. IOW, you are going to encounter low G most times you fly a gyro. If, every time you do, you are dancing on the edge of a fatal crash, then the critics are right -- you (we) are idiotic.

Fortunately, things aren't (or don't have to be) that dire. When a gyro goes haywire in a short-duration low G event, it's not the low G, but fuselage instability in the face of loss off rotor thrust, that usually causes the splat. The airframe must be designed to track straight, and not execute uncommanded aerobatics, when rotor thrust gets low. This requirement means that the frame must not have uncompensated HTL, divergent slip-roll coupling or uncompensated torque roll.

Cierva and his immediate successors worried about all these low-G stability problems, and designed to prevent them. They used CLT engine placement, large H-stabs, differential stab incidence, wings with tremendous dihedral and large dorsal fins (and/or mast fairings). We should do at least as well.

Yes, there's obviously pilot error involved in this crash. In fact, never mind the helmet, it's pilot error to fly that fast and aggressively with such low hours in the aircraft in question.

Still, the behavior of the gyro once things began going south also reveals some needless crashiness, traceable to slip-roll and/or torque roll. These problems can be eliminated by design.
 
Doug Riley;n1141310 said:
Our long custom in the gyro world (dating back to Igor Bensen) is to blame every crash in which low G may have been involved on the low G itself. If low G is usually or always lethal, then the autogyro itself is a fatally flawed design concept, and has been so from Cierva's time. This is exactly what a great many non-gyro fliers have believed all along.

The plain fact is that low G is inevitable in an aircraft, thanks to thermal and mechanical turbulence. These natural, normal atmospheric disturbances simply cannot be avoided. IOW, you are going to encounter low G most times you fly a gyro. If, every time you do, you are dancing on the edge of a fatal crash, then the critics are right -- you (we) are idiotic.

Fortunately, things aren't (or don't have to be) that dire. When a gyro goes haywire in a short-duration low G event, it's not the low G, but fuselage instability in the face of loss off rotor thrust, that usually causes the splat. The airframe must be designed to track straight, and not execute uncommanded aerobatics, when rotor thrust gets low. This requirement means that the frame must not have uncompensated HTL, divergent slip-roll coupling or uncompensated torque roll.

Cierva and his immediate successors worried about all these low-G stability problems, and designed to prevent them. They used CLT engine placement, large H-stabs, differential stab incidence, wings with tremendous dihedral and large dorsal fins (and/or mast fairings). We should do at least as well.

Yes, there's obviously pilot error involved in this crash. In fact, never mind the helmet, it's pilot error to fly that fast and aggressively with such low hours in the aircraft in question.

Still, the behavior of the gyro once things began going south also reveals some needless crashiness, traceable to slip-roll and/or torque roll. These problems can be eliminated by design.


An airframe to track straight with no wing on, with thermals, gusts, thrust of varying degree that is still in pilot's control, rudder input still effective and a pilot flailing the stick to its very stops trying to catch his flying helmet behind him? Show me a gyro that will handle that please.
His accident started when he decided he could with 20 hours PIC go to World Air Games and do gyroplane pylon racing. It came much closer when he started flying with unbuckled helmet chin strap, his fast un-coordinated turns to one side inched him closer, his helmet flying off his head and his reaction to it, sealed his fate. Unfortunately, no amount of money or any other thing comes in between Mr. Darwin and aviation. Aviation applies Darwin's theory to all of us really quickly.
 
My point, Abid, was not that no crash would have occurred in this case with better frame stability. I don't know that.

The Dubai accident, however, turned out to be an unintended test of the aircraft's frame stability. Frame stability might make a difference in other cases. We have had crashes in which frame stability WAS the culprit. We've had lots and lots of PPO's traceable to HTL, for one thing. There also have been crashes in which divergent slip-roll coupling was pretty clearly at fault. Torque roll contributes to many low-G crashes,as various photos and videos attest.

A gyro must respond to the pilot's control inputs, obviously. If the pilot's control inputs are wrong but the craft responds faithfully, that's pilot error, not a design problem.

Pushing the stick forward should reduce the rotor disk's angle of attack, and can be expected to cause the nose to drop to some extent. Nose drop is NOT necessary with forward stick in a direct-control rotor, and it's better if the drop is quite limited and is aerodynamically "snubbed" (as it will be if the craft has an adequate HS). What should NOT happen when the stick is pushed forward, no matter how fast, hard or far, is a roll. This is an uncommanded maneuver.

Ditto divergent slip-roll coupling. Uncoordinated flight in a gyro is mostly a novelty; we can steepen our glide as much as we want without slipping, by simply slowing down. Still, there is no reason why, if the craft enters a slip, the slip ought to grow and grow UNCOMMANDED until the gyro rolls over in the air. We all know that FW planes are designed with the opposite trait -- they exhibit dihedral effect. When slipped, the FW plane tries to level itself and point in the direction it's travelling.

A gyro can and should be designed with the same healthy behavior.

The Dubai accident report suggest that the aircraft in question had one or more of these issues. The issues came to the fore when the pilot committed his control errors.

We should press our designers to do better.
 
Doug Riley;n1141333 said:
My
We should press our designers to do better.
The problem Doug, is that they don’t know how since most designers of modern hobbycopters aren’t engineers and are simply following the Bensen pattern. The originator of the Eurotub, Vittorio Magni, was a helicopter mechanic who learned how to “design” gyros by having built a Bensen from plans.

The shame of it all is that Cierva had solved most of the stability problems of gyroplanes in the 1930s, resulting in a machine that had a safety record far better than contemporary FW aircraft.
 
jm-urbani;n1141336 said:
chuck let natural sellection do it's work
JM, I don’t mean to disparage Italian products or Italian designs.

My favorite wife was an Italian design, having been born in Italy and brought to the US at age 6 when her parents emigrated.

My favorite automobile was a 1959 Alfa Romeo Giulietta Sprint Veloce. My Italian wife was ticked; she said: “$4300 and it doesn’t even have a cigarette lighter!”

Unfortunately, both had flaws.
 
The angle of attack stability of the Magni results from the over balanced (nose heavy) rotor blades. An upward gust causes the rotor to pitch in a nose down direction, keeping the machine headed into the relative wind.

The downside of an over balanced rotor is a heavy stick.
 
Good old British poet John Donne wrote that no man is an island. Donne died 200 years before the theory of natural selection, but he was correct as a practical matter.

When poorly-designed machines, and pilots with bad judgment, cause fatal gyro crashes, the rest of us get punished. I wish I had a dollar for every time I showed up at an airport with a gyro, only to be kicked out for "safety" reasons, or to receive a torrent of abuse about "them things killed three of my friends...."

An FAA inspector told me, with a straight face, that the pilot of a tilt-spindle gyro "really has no control." I guess he didn't realize that a rotorhead employing a tilting spindle with flap hinges is the EXACT mechanical equivalent of a swashplate cyclic.

Our reputation hurts all of us.

Awhile ago, we tried to get the FAA to allow factory-built Light Sport Aircraft. The FAA refused. The basis for their denial (I am paraphrasing here) was that the gyro community didn't have its s**t together regarding stability and design standards.

It's interesting that the Magni derives from Jukka Tervamaki's ATE-3 and ATE-5. Jukka is a real engineer. In fact, he's the first person that I can recall writing up a narrative of PPO, around 1973-4, in a letter to the PRA magazine. He prescribed a large H-stab as the solution to what he called the "residual moment about the autogyro CG" during low-G maneuvers. He was speaking of pitching moments, but rolling moments can be just as deadly.

The FAA was only partly correct about us. There are plenty of people in our community who do understand airframe stability. The knowledge isn't universal, though, and so we still have $100,000 "sophisticated" gyro designs with various "residual moments about the CG." These can kill even pilots who don't make stupid mistakes. But it's all avoidable.
 
In addition to torque roll elimination via tailplane differential, Cierva eliminated throttle-yaw coupling by carefully balancing dorsal fin area vs belly fin area.

I well remember the rudder pedal toe dance during takeoffs and landings in my Bensen B-8. A Dominator tall tail accomplishes the same thing as Cierva’s dorsal-belly fin balance. cierva_c-30.jpg
 
In my experience with both 1- and 2-place Dominators, Chuck, you're right. There' s not much rudder work to do in these gyros, except for intentional slips and twirls.

Some ultralight gyros, notably the Gyrobee, have smaller vertical fin areas than the Bensen (the 'Bee had 4 or so sq. ft. instead of Bensen's six). I used to get leg cramps mashing my 'Bee's left pedal against the stop doing 18 mph takeoffs. Things got more reasonable as you picked up airspeed.

Dr. Bensen was exquisitely calibrated as to what informalities he could get away with in a small, light, low-powered gyro (his original engine was the 40 hp. direct-drive Nelson). The list of shortcuts includes minimal accommodation of 2/rev mast shake, no pre-coning angle in the metal blades, no roll-torque compensation (well, if the side-mounted gas tank was empty), torque-yaw effect, the infamous scrub brake, rigid axle, and on and on. These little shortcuts have not worked out as well in heavier/enclosed gyros, hence some of the problems we're talking about.

Interestingly, though,one thing that a stock Bensen doesn't have much is slip-roll coupling. There's not enough side area below the CG to create it. The Umbaugh/Air&Space, inspired by Bensen but a radically different design, has it, however.
 
Bensen came up with a design that any teenager with a paper route could afford and was able to build with a minimum of tools; mainly an eggbeater drill, a file and a hacksaw.

The B-7 had a horizontal tail which was dropped on the B-8 for reasons I don’t understand. Perhaps the offset gimbal rotor head along with over reflexed and over balanced wood blades provided what Bensen believed was adequate stability. The over reflexed, torsionaly flexible rotor blades limited top speed to ~60 mph. Also, a direct drive Mac engine didn’t apply gobs of torque to the prop.

But times have certainly changed in the internet age; no more teenagers with paper routes, disappearing newspapers and $100K Bensen derivatives.
 
Here's what Cierva said about torque compensation:

US patent 2098320 Juan de la Cierva
Filed March 6, 1934 (UK patent application filed March 13, 1932)

http://www.google.com/patents/US2098230?printsec=abstract#v=onepage&q&f=false

…The problem of torque reaction correction therefore assumes great importance. In fact, it has been found (in machines employing tilting of the rotor for control purposes) that a greater amplitude of lateral control movement of the rotor is required to compensate the torque reaction in all conditions of flight from engine-off to full throttle than is required for the purpose of lateral control. Further, if the torque reaction is compensated by displacement of the rotor, or by an equivalent (such as modification of the periodic pitch variations of the blades thereof) a continual adjustment is necessary during flight, since, while at a constant throttle setting the reaction torque is substantially invariable, the couple opposing it is the resultant of aerodynamic forces (for which the rotor is principally responsible), inertia forces and gravity; the aerodynamic forces being subject to fluctuations on account of wind gusts and changes of attitude of the aircraft while the inertia forces vary with the accelerations to which the aircraft is subjected. The couple opposing the airscrew reaction torque thus depends on the momentary values of the aerodynamic forces and of the accelerations….
 
Bingo! Translation from techno-speak: Using the rotor to stabilize the airframe against torque is a bad idea -- because the rotor's thrust varies constantly with gusts and maneuvers.

Using the rotor to stabilize against PPO moments is equally a bad idea, and for the exactly the same reason. Either get rid of the moment by design, or neutralize it with fins.
 
JM -- I hope that, if we keep the pressure up, the promoters of these new gyros (whether $15,000 gyros or $100,000 gyros) will design out any slip-roll and torque-roll characteristics.

It's perfectly possible. Such design improvements do not necessarily make the aircraft either ugly or unstable on the ground.

Look at corporate jets. They all have fairly high cockpits and nose-gear legs. They are designed to look sexy and fast, the better to sell to their rich customers -- and they succeed.
 
No Title

Beauty is in the eye of the beholder.

Having flown two seat Dominators I find them beautiful just as I find a woman with curves beautiful when some prefer thin and scrawny.

You may have noticed that most of my pictures are taking while flying because that is how I spend most of my time in a gyroplane despite the mile taxi to the run-up area for runway three zero at KSMX.

I think this picture of The Predator is beautiful despite her high stance and lack of retractable landing gear. I have a client in the back seat with vast aviation experience that loves the way she flies without power-pitch-yaw coupling.

I don’t see the value in retractable landing gear on a ninety knot aircraft and I see weight, complexity and having to remember to put the landing gear down as serious negatives.
 

Attachments

  • photo131396.jpg
    photo131396.jpg
    94.4 KB · Views: 1
Vance beat me to it. The Predator seems to me to have nearly an ideal layout for a semi-enclosed tandem gyro. And CLT tandem is the way to go for (relative) efficiency, especially in a pusher gyro.

Note that Ernie Boyette knows perfectly well how to build a CLT, full enclosed, side-by-side pusher gyro. His LFINO was just such a craft.

I read that the Eiffel Tower was controversial when proposed and built. Some thought it an ugly celebration of soulless iron industrialism. Many more, however, thought (and think) that it is an elegant giant sculpture.

Now, the George Washington Bridge in NYC is seriously industrial-functional, lacking the grace of, say the Golden Gate Bridge, built in the same era. I read also that the GW's criss-cross girder structure was supposed to be covered, but it was left exposed to save money. IOW, it's the Dominator of suspension bridges. Or the Dom. is the George Washington Bridge of gyros.
 
Top