MTOSport accident factual report

[PTKay]

The German Accident Investigation Office released the factual report
on the MTOSport fatal accident from July 16th, 2011.

http://www.bfu-web.de/cln_030/nn_223968/DE/Publikationen/Bulletins/2011/Bulletin2011-07,templateId=raw,property=publicationFile.pdf/Bulletin2011-07.pdf

Go to page 39. (in German, some photos)

[Master Roda]

Translated:

Day of the accident, the pilot completed a total of five half-hour sightseeing flights with guests having a support MTOsport at the airfield Breitscheid. Witnesses saw at 15:06 hrs1 how the gyroplane with the last flight in to land, about 200 meters before the runway 25 at about 60 m high with aligned fuselage nose in the direction of slope, suddenly in flight direction to the right tilted around the longitudinal axis. Then he performed about half a turn to the right around the vertical axis and thereby fell from nearly vertical. In the fall of the autogyro both persons were fatally injured and destroyed the autogyro.

The trim system of pneumatic tubes were connected throughout. The two upper control rods in the direction of rotor head were separated. The lower control rods were connected between the base joint and lever. The control rods on the base tube fuselage were also connected to the base joint, but pinched in the front seat. All pins of the control were available. In part, the ball bearings of the control rods were broken out of the brackets. A dual control was not installed, the front control handle was broken off. The rudder control cable was generally available, including the turnbuckles and was led inside the pulleys. The rudder control rods were broken off between the pedals in the front ball joints. The engine was torn from the fuselage to the left. The two plastic tanks were repeatedly torn or broken. It smelled of fuel at the accident site, individual fuel puddles were still present. The fuel lines to the engine was filled with fuel. The nose section was destroyed by the instrument panel. The nose gear was broken. The main gear beam was not damaged.

The accident site was located about 220 m before the start of the operating runway runway 25 at the edge of a meadow on a green stripe with a flat scrub and heath vegetation. The autogyro was lying on his left side of the fuselage in the direction of about 110 °. The two occupants were trapped in the wreckage. Rescue tube through the hull in the area of ​​the front control stick and the rotor mast and Prerotatorstange including a control rod was pinched off. The tail boom was at the transition from double to single tube carrier pipe carriers canceled, but still connected to the rudder control cables to the hull. All components of the autogyro were in the area of ​​the impact site. The blades were connected to the rotor head. Both blades were bent up and had to part bends or folds on the bottom. The trim weights were present in the leaves. The rotor head bearings and Teeterbolzen were free to rotate. The Prerotatorritzel on the rotor head as well as the brake rotor showed no damage. The Rotorhub was bent on one side down (Journal 240) and on the other side (sheet No. 259) and upwards in the direction of rotation of the rotor.

[Gyro_Kai]

Good translation. It should be noted that the pilot had more than 9000 hours on various fixed wing planes, having flow transport planes at the military and on humanitarian missions.
In his 26 hours transitional training he had performed 86 landings with instructor, in the following 22 hours 55 landings. Although the ratio for me as a neebie was much higher in terms of landings per hour, I see this not as a problem, because I guess when the landings were ok, you could focus on doing things where the gyro is really different, like vertical descents.

We had a long discussion not only on the forum but also between instructors, but there is not even a hint of a theory, what may have gone wrong. The wreckage did not indicate any machine failure.

Kai.

[Master Roda]

Kai,

Our gyroplanes don't simply fall from the sky, we know this.
From the flight pattern, it can be seen that there was a control failure. Either by the pilot or the mechanics.

Very sad indeed, and my condolences.

Jon

[rfsolutions]

I have a question about the MTO sport and other AutoGyro gyroplanes. They are restricted by placard & POH from aerobatic flight. The POH considers bank angles greater than 60 degrees aerobatic flight?

Question :
Without an attitude gyro (I haven't seen one equipped with one), how would a pilot know when they are approaching or exceeding the aerobatic restriction of 60 degree bank angle?

Maybe a CFI familiar with the aircraft can answer?? I'm not sure what the manufacturer expects to happen at 60 degree bank angle? Stress on the rotor system...?

[WaspAir]

Reliance on a gyroscopic instrument is a bad habit from the airplane world. Gyroplane and glider pilots are expected to be able to tell their bank angle without any such instruments.

It should be pretty obvious by looking out the window. A 60 degree bank is far more than necessary for normal maneuvers, and if flown level in a coordinated fashion, will pull 2g, and that's enough to get most people's attention. The horizon is pretty easy to use without any instruments.

The U.S. Private Pilot Practical Test Standards (Gyroplane) are based on the assumption that you can tell your bank angle from the horizon, i.e.:

1. Exhibits knowledge of the elements related to steep turns.
2. Selects a safe altitude.
3. Establishes the manufacturer’s recommended airspeed or if one is
not stated, a safe airspeed not to exceed VA.
4. Smoothly enters a coordinated steep 360° turn with a 40° bank.
5. Performs the task in the opposite direction, as specified by the
examiner.
6. Divides attention between gyroplane control and orientation.
7. Maintains the entry altitude, ±100 feet, airspeed, ±10 knots, bank,
±5°; and rolls out on the entry heading, ±10°.


Where it's critical, the manufacturers sometimes provide an aid. The 18A has a 45 degree limit, it's marked on the windshield with a V of red tape (put one side of the V on the horizon, and you're at 45).

[Gyro_Kai]

In the German regulations you are to stay below 60 degrees bank angle. How to measure it, is not mentioned.

Kai.

[Vance]

Reliance on a gyro instrument is a bad habit from the airplane world. Gyro and glider pilots are expected to be able to tell their bank angle without any such instruments.

It should be pretty obvious by looking out the window. A 60 degree bank is far more than necessary for normal maneuvers, and if flown level in a coordinated fashion, will pull 2g, and that's enough to get most people's attention. The horizon is pretty easy to use without any instruments.

The U.S. Private Pilot Practical Test Standards are based on the assumption that you can tell your bank angle from the horizon, i.e.:

1. Exhibits knowledge of the elements related to steep turns.
2. Selects a safe altitude.
3. Establishes the manufacturer’s recommended airspeed or if one is
not stated, a safe airspeed not to exceed VA.
4. Smoothly enters a coordinated steep 360° turn with a 40° bank.
5. Performs the task in the opposite direction, as specified by the
examiner.
6. Divides attention between gyroplane control and orientation.
7. Maintains the entry altitude, ±100 feet, airspeed, ±10 knots, bank,
±5°; and rolls out on the entry heading, ±10°.


Where it's critical, the manufacturers sometimes provide an aid. The 18A has a 45 degree limit, it's marked on the windshield with a V of red tape (put one side of the V on the horizon, and you're at 45).

Hello J.R.,

I am not able to accurately judge angle of bank visually.

On a motorcycle it was about leaning it over until she started sliding around.

I am going to have two inclinometers on Mariah Gale so that I can begin to calibrate my perspective of bank and pitch.

I have had more than one knowledgeable pilot say that I don’t have my bank angles right.

I pay more attention to the yaw string and the feel of the controls and have somehow failed to calibrate my angle of bank.

I imagined that I could not exceed 60 degrees of bank in a rotorcraft but I have seen pictures that Ed took where The Predator is close to 90 degrees of bank at the air show.

Do you have some tips for me on how to judge angle of bank and pitch more accurately?

I need help with my attitude recognition.

I had trouble in a helicopter too and liked having an attitude indicator.

At this point I don’t have any vacuum instruments on Mariah Gale, do you feel I would find them useful?

I am planning on a Garmin 695 so that will give me some sense of things.

Thank you, Vance

[StanFoster]

Vance- I don't know if this will help you or not, but a 45 degree bank is of course halfway from level to vertical. A 60 degree bank is when your whole rotors diameter is only taking a horizontal distance bite that is equal to its radius. That's why if course it takes 2g to sustain altitude because you only have half your rotor. Stan

[WaspAir]

I am going to have two inclinometers on Mariah Gale so that I can begin to calibrate my perspective of bank and pitch.

* * *

I pay more attention to the yaw string and the feel of the controls and have somehow failed to calibrate my angle of bank.

I imagined that I could not exceed 60 degrees of bank in a rotorcraft but I have seen pictures that Ed took where The Predator is close to 90 degrees of bank at the air show.

Do you have some tips for me on how to judge angle of bank and pitch more accurately?


At this point I don’t have any vacuum instruments on Mariah Gale, do you feel I would find them useful?

Well, here are a few thoughts to start things off.

1, if you intend to continue airshow performances, we need to get your ability to recognize bank angles polished up really well for safety.

2, if by inclinometer you mean a "slip-skid ball" (a common use of that term), it won't show you the bank if you stay coordinated; it will be centered when your yaw string is centered.

3, if you are used to paying attention to the yaw string, you might already be halfway there. I don't remember where it is on your Predator, but if the yaw string lies against your windshield (as usually done on helicopters and gliders with yaw strings), you have a useful indicator already, but you just haven't been extracting all the information it is offering. Keeping the string straight with respect to a plane running through your mast and the center line of the aircraft shows that you're coordinated. But if you do a good job of keeping the string straight that way, comparing the string position to the horizon is a good indicator of your bank angle. When the string is straight up with respect to the horizon, you have no bank; when the string is parallel to the horizon, you're at 90 degrees of bank. A 60 degree bank will put the yaw string at thirty degrees to the horizon, and sixty degrees away from a true vertical line. I suppose you might have a string mounted off the windshield somewhere that streams back at you more horizontally, in which case this won't help that much; which is it for you?

4, If you have any intention of putting in a gyroscopic instrument, I suggest you consider an electric one so that you don't have to mess with vacuum pumps, lines, and such. There are some nice ones available. We have an electric attitude indicator in one of our 18As just as a back-up in the highly unlikely case of getting caught in or above some quickly forming cloud layer. The challenge for you would be to check it often enough to confirm your belief as to bank and pitch and "calibrate" your senses, but not to spend much of your time looking at the panel. A turn coordinator instrument would not be my first choice, because it's good for yaw rate information but doesn't show bank angle as directly. Personally, I think you can hone your senses without the expense of a gyroscopic instrument, through some combination of yaw string and windshield markings.

[JEFF TIPTON]

Vance; in your case might I suggest using 1/8 inch trim striping added to the windshield. With some trial and error, you can set to line up with the horizon at 45 or 60 degrees your choice. This would be similar to using the cabane struts in older tube and fabric aircraft.

[rfsolutions]

Reliance on a gyroscopic instrument is a bad habit from the airplane world. Gyroplane and glider pilots are expected to be able to tell their bank angle without any such instruments.

It should be pretty obvious by looking out the window. A 60 degree bank is far more than necessary for normal maneuvers, and if flown level in a coordinated fashion, will pull 2g, and that's enough to get most people's attention. The horizon is pretty easy to use without any instruments.

The U.S. Private Pilot Practical Test Standards (Gyroplane) are based on the assumption that you can tell your bank angle from the horizon, i.e.:

1. Exhibits knowledge of the elements related to steep turns.
2. Selects a safe altitude.
3. Establishes the manufacturer’s recommended airspeed or if one is
not stated, a safe airspeed not to exceed VA.
4. Smoothly enters a coordinated steep 360° turn with a 40° bank.
5. Performs the task in the opposite direction, as specified by the
examiner.
6. Divides attention between gyroplane control and orientation.
7. Maintains the entry altitude, ±100 feet, airspeed, ±10 knots, bank,
±5°; and rolls out on the entry heading, ±10°.


Where it's critical, the manufacturers sometimes provide an aid. The 18A has a 45 degree limit, it's marked on the windshield with a V of red tape (put one side of the V on the horizon, and you're at 45).

I don't have problems determining bank angle. Some people do though (as illustrated by Vance). The test standards allow you to go to 45 degrees (40 + 5) which is only 15 degrees from the critical limits established by AutoGyro. The 18-A has a visual attitude indicator on the wind screen as you described to keep it within it's placarded limits. The FARs do not define aerobatic flight as a 60 degree bank angle. All of my gyros have exceeded 60 degrees of bank angle plenty of times and probably will a few more times. The MTO Sport is placarded against aerobatic flight but you have to read the AutoGyro definition in the POH to understand that a 60 degree bank is considered aerobatic flight (not the FAR definition). If an experienced fixed wing pilot transitions into one of these aircraft (used to looking at an attitude indicator) and gets comfortable yanking and banking one of these maneuverable little machines around, how do they ensure they avoid the 60 degree restriction?

With the availability of solid state attitude indicators I agree that anything vacuum operated would be a waste money.

I was wondering how the MTO instructors ensure students & new rotor craft pilots don't hit the 60 degree mark while practicing the required steep turns? A 5000 hour fixed winger may consider a 60 bank angle fun?

[Vance]

Thank you Stan,

That is a thoughtful response.

I have tried several ways to imagine it, all with limited success.

I get too caught up in the entrance and making a coordinated turn and don’t seem to know when to stop the roll.

Thank you J.R. I agree completely with 1, I want to be safe.

The inclinometer is the simple ball in a curved tube. I realize that it won’t give me angle of bank but I hope it will give me a better sense of things. I am particularly interested in pitch. I find my perception is often at odds with what I measure with my smart level.

What I was asking about is an attitude indicator AKA artificial horizon.

I feel the challenge is in my sense of lean is not well calibrated and based on the wrong inputs.

My yaw string is on a stick in front of the windshield because I found it would stick to the windshield and not work well. Now that it is free I find it more useful. I might try one of each.

I am grateful for your input.

Thank you Jeff, I am familiar with that from my flight time in a Stearman.

I will give it a try.

Thank you, Vance

[Vance]

Hello Marv,

When I flew the Calidus Michael felt we were close to 60 degrees when I was aiming for less and I had adverse yaw as well. I can see how someone could get into trouble with the lack of wind as an indicator of adverse yaw.

The Predator seems happy at bank angles well in excess of 60 degrees and generally has very little adverse yaw even when I don’t stay on top of the pedals.

Thank you, Vance

[WaspAir]

If an experienced fixed wing pilot transitions into one of these aircraft (used to looking at an attitude indicator) and gets comfortable yanking and banking one of these maneuverable little machines around, how do they ensure they avoid the 60 degree restriction?

I was wondering how the MTO instructors ensure students & new rotor craft pilots don't hit the 60 degree mark while practicing the required steep turns? A 5000 hour fixed winger may consider a 60 bank angle fun?

I am finding it extremely hard to imagine a 5000 hour fixed winger who is comfortable at 60 degrees but doesn't know it's 60 degrees from the combination of looking outside and the seat of his pants, or who routinely flies his fun steep banks solely by reference to his instruments. I have never met such a pilot.

[PW_Plack]

...A 60 degree bank is far more than necessary for normal maneuvers, and if flown level in a coordinated fashion, will pull 2g, and that's enough to get most people's attention...

Isn't this a flawed assumption from the fixed-wing paradigm? I doubt you'll pull 2G in a gyroplane at 60 degrees of bank.

[Passin' Thru]

Isn't this a flawed assumption from the fixed-wing paradigm? I doubt you'll pull 2G in a gyroplane at 60 degrees of bank.

Paul, I agree completely, but I must add you'll NOT maintain altitude in a gyro at 60° bank ... :peace:

[WaspAir]

A steady, level, coordinated 60 degree bank in any wing-borne (rotary or fixed) aircraft is a 2g maneuver, with radius determined by airspeed. I'm not suggesting MTO gyros (or even all airplanes) have the grunt to sustain airspeed, altitude, and turn radius for long in such a turn. That's not the point. My opinion is:

1) If you're yanking and banking to 60 degrees however briefly and you don't feel the g load, find a new hobby before you get hurt.

2) If you want to fly steep but don't know what 60 degrees looks like, keep your turns shallow until the day you can put on a 'chute and take an hour of dual in a Citabria.

[ckurz7000]

Hi Vance, you wrote:

My yaw string is on a stick in front of the windshield because I found it would stick to the windshield and not work well.

This happened to me, too, until I realized that there is a right and wrong way to tape the yaw string to the windshield. Here is an illustration:

86072

The wrong way is to tape the yaw string on its bottom end. The correct way is to tape the yaw string on its top end so that it is blown back over the point you taped it. This will prevent sticking to the windshield in most cases.

-- Chris.

[ckurz7000]

Just a remark: the limit of 60% bank and 30° pitch is not anything due to the MTO. It is the legal definition of aerobatics in Germany. Since autogyros are not legal to fly aerobatic manoevers, these limits apply. This may (and will) be different in other countries.

-- Chris.

[Doug Riley]

The discussion has branched a bit.

Regarding the crash, I assume that no one is suggesting that the MTO pilot suddenly commanded a 60-degree plus bank while on final? Unless we know that he was a wild man, prone to such stunts, that seems incredibly unlikely.

Do we know that the breakage of the upper pushrods occurred in the crash? How about the partial separation of the rod-end bearings mentioned in the factual report? Sometimes you can separate crash damage from pre-crash failure by looking for signs of fatigue.

Close examination of an identical, intact aircraft would be a useful investigative tool. One could make a list of components that might shift and pin the controls.

A Rotax 900-series engine, as a pusher, induces right roll -- the direction this gyro rolled.

[ckurz7000]

The original report also contains GPS traces of the flight track. It is apparent that the final approach on the fatal flight was made significantly higher than on the other flights. It is possible that the pilot wanted to demonstrate a vertical descent. Given the gusty wind conditions and little rudder authority with the engine idling, it could be a compound problem instigated by the vertical descent, gusty winds, no rudder, overcontrolling with the stick, maybe unrecognized tail sliding, etc.

-- Chris.

[Gyro_Kai]

Another possibility would be that he wanted to slip and overdid it in the wrong (torque) direction, played the throttle, a little push here a gust there and you may instigate a roll over.

Kai.

[GyroCFI]

Isn't this a flawed assumption from the fixed-wing paradigm? I doubt you'll pull 2G in a gyroplane at 60 degrees of bank.

If it's done correctly you'll pull 2 G's. I've taught this maneuver hundreds of times.

[Lee Scatt]

If it's done correctly you'll pull 2 G's. I've taught this maneuver hundreds of times.
Don, did you actually have a g-meter installed?
I can't recall having the 2g feeling in a gyro, yanking as hard as I dared.
I flew aerobatics in a Decathlon and I am accustomed to the sensation.

[MichaelBurton]

A steady, level, coordinated 60 degree bank in any wing-borne (rotary or fixed) aircraft is a 2g maneuver, with radius determined by airspeed. I'm not suggesting MTO gyros (or even all airplanes) have the grunt to sustain airspeed, altitude, and turn radius for long in such a turn. That's not the point. My opinion is:

1) If you're yanking and banking to 60 degrees however briefly and you don't feel the g load, find a new hobby before you get hurt.

2) If you want to fly steep but don't know what 60 degrees looks like, keep your turns shallow until the day you can put on a 'chute and take an hour of dual in a Citabria.

That is just the trick steady level and coordinated. The 60 degree turn could be a much lower or higher g force depending on the pilot inputs. A 60 degree turn with a hard pull might be in excess of 4 gs. In a descent it could be near 1 g. In either case I don't find it hard to determine the approximate angle.

I did not intend to suggest that I would do a hi g maneuver in a gyro. I would not. Nor would I do a low g maneuver.

Steady level and coordinated all at the same time? How much fun is that.

[ckurz7000]

I saw traces of a recording g-meter in a gyro test flight situation in which the pilot tried to get the highest possible g loading. He wasn't able to exceed 2.5 g, no matter how hard he pulled. And I'm not even talking steady state here, just transient spikes didn't go above 2.5 g.

-- Chris.

[Passin' Thru]

Chris, you are correct. An autorotating rotor has some self-limiting factors that are often not well understood.
We all know that the rotor's rotational speed (RRPM) increases with load up to the point that blade drag equals autorotative driving force, then it won't turn any faster to produce the required additional lift and it just "mushes" thru.
I know what 2 g's feels like, (and 3 or 4) and from subjective, non- instrumented experience, that a reasonably vigorous roll in to a 60° bank and progressive back pressure attempting to hold altitude, will not reach 2 G's before it mushes thru. As you stated, really severe full jerk backs may produce very brief "spikes" up to about 2.5 G's just before it mushes thru.

This is flying regular 2 blade teetering rotors most familiar to most of us. Three blade articulated rotors with pitch- cone coupling may behave slightely different. I never tried it with one of those. ;)

[C. Beaty]

A rotor tach is a fair “G” meter within the normal working range of a rotor. Rotor RPM varies as the square root of “G” load.

At 2 “Gs”, rotor RPM will increase by a factor of 1.414 over straight and level.

The “wall” that Pete suggests occurs when the flow over the rotor approaches mach1; that’s a sort of speed brake that inhibits further RPM increase. An airfoil can reach drag divergence well below freestream mach1, depending on angle of attack.

[Master Roda]

We have a G meter around here somewhere. I'll see if I can get Jim to go out pull some turns with it.

[Doug Riley]

Seems as if I remember that Jim reported momentary recorded G's at/near 4.0 in the entry of a loop...?

RRPM drastically limits steady-state G's, but rotor lift can be juiced momentarily by increased disc AOA alone. This increases coning angle and stresses the blades. I also recall that Jim ran into cracking on the bottom of his Skywheels hub back in the day, from this very effect.

[Master Roda]

You are correct Doug.

The hubs cracking is why Jim ventured into making rotors. We even still have a few of those cracked hubs.

[PTKay]

Final report has been published:

http://www.bfu-web.de/cln_030/nn_223970/DE/Publikationen/Untersuchungsberichte/2011/Bericht__11__3X104__Gyrocopter__Breitscheid,templa teId=raw,property=publicationFile.pdf/Bericht_11_3X104_Gyrocopter_Breitscheid.pdf

Generally, the conclusions are:

dynamic roll over due to slip and turbulence,
experienced FW pilot reflexes contributing by low time on gyroplanes.

[Gyro_Kai]

Thanks for posting, Paul.

It should be mentioned, that the handbooks of all models have been amended by 2 additional warnings, quoted in this report. The first is about avoidance of low and negative G.
The second one explicitly prohibits strong slip-maneauvers, which have been identified as probable cause for this accident and is also assumed to be the cause of the recent accident of Andi Tille on Mallorca.

Kai.

[Resasi]

And we all continue learning.

[thomasant]

Generally, the conclusions are:

dynamic roll over due to slip and turbulence,
experienced FW pilot reflexes contributing by low time on gyroplanes.

Can dynamic rollover occur in a gyroplane while airborne? I believe there has to be contact with one wheel or skid with the ground for dynamic rollover to occur. Can anyone please help clarify this? Thank you.

[WaspAir]

Perhaps this is intended to describe adverse roll coupling with yaw (e.g., left yaw generates right roll), when the side of the craft is exposed to the airflow during an uncoordinated maneuver.

[Gyro_Kai]

Yes, slip-roll coupling is the word. Most of the cabin is below the CG so in a side slip this causes a roll moment on the entires structure. If done in the same direction as the propeller torque, it can go South very quickly.

Kai.

[PTKay]

Can dynamic rollover occur in a gyroplane while airborne? I believe there has to be contact with one wheel or skid with the ground for dynamic rollover to occur. Can anyone please help clarify this? Thank you.

You are right.

I should have used the term dynamic "torque-over".

[thomasant]

Thank you all for clarifying.

[Doug Riley]

Kai, do we really know that the aerodynamic center of the cabin surface is below the CG? This can be a tricky determination with high-thrustline (low CG) gyros.

The fact that the CG is low means that the center of pressure of the fusleage (when slipping) may also be relatively low without creating a rolling moment about the CG. That is, CG and center of pressure of the fuselage tend to travel together.

[Gyro_Kai]

Doug,

you are probably right. Eyeball-gauge is not correct.

The tricky thing about a fast slip is any additional sudden influence. This may be a sudden added throttle, generating a torque-roll-over. Or you get a gust from behind, which causes the induced drag of the rotor to suddenly drop, again resulting in a roll-over.
In a slip there is no mitigating H-stab.
Once the roll starts, it controls the rotor down into the roll, similar to a dynamic roll-over, regardless what you do with the stick.

Kai.

[Doug Riley]

It's relatively easy to test for this problem, once you know where the CG is. Make an accurate 3-D model of the gyro, without a rotor. Suspend it on a half-gimbal (with the gimbal yoke below) so that the model pivots around the roll axis. Place weights as needed to put the model's CG right on the pivot. Hold it out the window of a moving car. The speed of the car is not important.

If model banks its top toward the wind, it lacks roll stability. If it banks its bottom toward the wind, it has "dihedral stability" and will be stable in roll.

This does not account for prop torque, only for the torque caused by body drag during a slip.

Prop torque can be compensated for using differential H-stab incidence and/or tall vertical surfaces, as Chuck Beaty has described here many times. It is important, though, to place the compensating tail surfaces close enough to the prop, or make them wide enough, that the propwash does not "miss" them in slipping flight.

One of the early Cierva machines with a fixed rotorhead, IIR, used a fin mounted above the rotorhead to provide stable slip-roll coupling. This isn't practical with a tiltable rotorhead, though. A wide-chord mast enclosure would do almost the same thing.

[Resasi]

Side-slipping on an open frame machine (Bensen) can be done reasonably aggressively,(This has been worked up to gradually).

The aerodynamic side loads in a cabin machine would add a whole new dimension. As a 'low time' gyro pilot he may not have worked up to what was manageable in that particular type..

I speak simply as one who gradually explores the boundaries of whatever type is being flown, and today was doing some of the most extreme sideslipping done to date in the Besen, with low medium and high power settings.

It surprised me what was possible. I feel sure that a cabin/structure would induce a roll moment that would be limiting.

[Doug Riley]

I discovered roughly the same thing in a tandem Dominator with small nose pod. I asked a student (who was already a pilot of Cub-type planes) to slip it a bit in cruising flight.

He immediately stomped rudder and pushed the stick WAY into cross-control. We went into a powered right slip that just about relocated one of my eyeballs, all at about 75 mph. I could feel the wind blowing across my face, from right to left, instead of into my face.

However, the Dominator showed no sign of rolling into the slip at all. A right slip on a Rotax 912 machine is the direction that can be amplified by engine torque.

We weren't at full throttle, only cruise power, and we didn't hit any downdrafts. So the test wasn't the most extreme one possible. It only felt that way at the time.

I normally do radical "showoff" slips in vertical descent, with zero airspeed and idle power.

[ferranrosello]

There is no adverse coupling between yaw and roll axis. In fact there is a positive coupling because of rotor flapping.

But here is a huge difference in roll behaviour between fixed wing aircraft and rotorcraft. There is only one reason for that: regular fixed wing aircraft exhibit a strong damping effect in roll. A rotary wing does not exhibit any damping effect in roll. They exhibit a damping effect in pitch axis provided that they have an effective horizontal stabilizer.

This means that when you try to perform an aggressive and quick roll in a plane you will find nearly impossible to do it very fast. But this is not true in a gyro. Usually we are moving the stick very little for banking the rotorcraft. Why? The stick in roll is a banking regime control. It controls the speed of banking. If you get a bank with a big lateral travel of the stick the rolling motion will happen at very high speed, so fast that probably you will end in and inverted position with the nose pointing at the ground...

Anyway, this accident is very similar to Andy’s accident in Palma de Mallorca. First of all you enter a slip. If the slip is aggressive you will need to put the stick much more far away of its neutral position than in a regular turn. But we aware that this roll is not generating a turn: it is preventing the pedal input in yaw of generating a turn to the side of the pedal input. But what happens when if you want to stop the slip and release the pedal input too early? You will roll over in one second...

I think that this is the problem in those accidents.

Ferran

[ckurz7000]

There is no adverse coupling between yaw and roll axis. In fact there is a positive coupling because of rotor flapping.

Ferrán, only if you just consider the rotorsystem is there no yaw-roll coupling in a gyro (and that's true only if you neglect coning). You need to take into account the vertical shift in the center of pressure as the yaw angle increases. This is due to the shape of the fuselage and very pronounced in semi-enclosed gyros such as Magni, ELA and MTOSport. In those, and similar, gyros the center of pressure shifts downward below the CG with increasing yaw angle. This induces a roll moment.

I agree with you that uncoordinated rudder and stick movements, as may happen when you get out of a side slip, can lead to an increase in bank angle. In general, there are a number of things that all work against the pilot in the three accidents of that kind that I'm aware of:

1) Downward shift of the center of pressure with increasing yaw angle will induce a roll moment.
2) Engine torque induces a roll moment to the right (all three accidents torqued over to the right).
3) In at least two cases there was some partial unloading of the rotor, which reduces the moment counteracting roll.
4) Uncoordinated control inputs can lead to a preponderance of lateral cyclic input resulting in an unintentional roll.
5) Flight in gusty conditions, where gusts from the right increase the rolling tendency in that direction.

Greetings, -- Chris.

[dinoa]

Many design programs will calculate the area centroid fo a view in profile like Rhino for instance. The point will be a rough approximation of the center of pressure of the object when flow is sideways like in an extreme 90 degree slip.

Dino

[Doug Riley]

The centroid is a good start. Paul Abbott's simple method of balancing a cardboard cutout on a pencil works just as well as a computer program.

However, the centroid analysis is only approximate. The aerodynamic behavior of the object depends on its shape in all three dimensions. For a more accurate analysis, you need to use a 3-dimensional model. A wind tunnel is nice, but "flying" a model outside the window of a moving car will get you there, too.