Another sad event

[AerBabe]

I just heard on the news (http://news.bbc.co.uk/1/hi/england/cornwall/5037072.stm) that there has been a fatal gyropcopter crash in Cornwall. Not much detail has been released yet. My sympathies to family and friends.

[Keygrip]

It always saddens me to hear of pilots losing all during the pursuit of their pleasures.

Saddens me to think of the families reaction when the police car pulls up at the front door to explain that Dad (or whoever) is not going to be coming back again.

I often wonder what actually goes through the pilots minds when they finally realise that it's "Game Over". No chance to say "Goodbye".

I hate this part of our industry.

[QDMQDMQDM]

Pretty gusty here this afternoon, especially over the moors. Not ideal gyroplane conditions.

QDM

[QDMQDMQDM]

Isn't the big danger negative G on the rotors?

[englishal]

Sad news, and my condolences.

I watch them practicing up and down the runway at my home airfield on the weekends, with the instructor chasing them down the runway in his / her car. They look fantastic fun, but the negative G thing puts me off....but this is the same with helicopters like the R22 as well, so I don't know how much of an issue it really is.

I *believe* that 2 seater variants are pretty dangerous, something to do with the rotorheads??? (which is why when they are learning the instructor chases them down the runway in the car).

Fate is the hunter, for what it is worth, at least the person in this sad event died doing something they enjoyed, rather than of terminal cancer or some other pointless way......

[bladewashout]

...the negative G thing puts me off....but this is the same with helicopters like the R22 as well, so I don't know how much of an issue it really is.
I *believe* that 2 seater variants are pretty dangerous, something to do with the rotorheads???

All twin-bladed helicopters with teetering rotor heads have the same negative-G issue, including the Hueys, Jet-Rangers, R22, R44. In simple terms under low G there is a lack of upward main rotor thrust. This situation generates a roll to one side caused, amongst other things, by the tail rotor because the main rotor is no longer producing a lifting moment on the helicopter. If the instinctive reaction to push the cyclic left is followed, the unloaded rotor flaps excessively to the left but without load it doesn't move the aircraft. The blades can flap over 40 degrees over and the massive aerodynamic forces of the blades tilting the rotor mast bangs it against its 'bump stops' and will literally break the rotor right off the machine, and can chop off the front canopy or the tailboom as it does so.

The only way to survive the situation (which is outside the normal flight envelope) is to apply rear cyclic and raise collective to load the disc, *before* trying to correct the roll, which can be violent.

The 2 seater variants are not inherently dangerous, and (as far as I am aware) the Bell Jetranger, with the same rotorhead design, is one of the safest aircraft flying today.

There will be no way to determine what happened until an accident report comes out. My sympathies are with the families.

BW

[Stafford]

Thanks Bladewashout,

Even I understood your clear, concise description of the situation. I understand that the Pilot intervention time is also an issue on the R22/44 in particular ? Very sad news since they do look like fun.

[bladewashout]

Intervention time for low-g is going to be important, but so long as you re-load the rotor as soon as you start to feel light in the seat, you are probably doing as much as you can, and although it is generally too dangerous to actually train for, it is rammed home as a killer under the topic of 'mast bumping' and even the slightest feeling of low G is enough to start alarm bells ringing in a teetering-rotor-helicopter-pilot's head. I have no direct knowledge but would guess the intervention time is not very different in different types.

However low rotor RPM in low-inertia rotors (like the R22) does have very short intervention time, as little as 2 seconds in certain flight regimes, but the only required action is to push the collective down, rolling on throttle and maybe a flare. The R44 has a much longer intervention time (10 secs? (guess)) and the Jet-Rangers/Hueys longer still. It is mainly a function of rotor mass - the heavier the blades the higher their momentum and the longer they take to slow down. R22s have light blades, and a very loud horn goes off if rotor RPM gets down to 97% of normal.

If the blade pitch is not reduced to reduce drag and allow the engine torque to increase rotor RPM (or use the upward airflow to start autorotation if the drive has failed) then once the rotor RPM reduces below about 75-80% of normal RPM, the upward airflow as the helicopter starts to fall increases the aerodynamic angle of attack on the blades. They can stall and the increased drag acts as a massive rotor brake which exceeds the engine torque, so you can't speed them up even on full throttle. In a low-RPM accident, it is not unknown for the blades to have stopped, or almost stopped, rotating by the time the aircraft reaches the ground. All rotary-wing-pilots know this stuff.

None of the above is speculation on this incident, which (as is often the case) may turn out to be another series of unfortunate minor causes with a very sad outcome.

BW

[Fergus Kavanagh]

Gyroplanes equipped with a properly proportioned horizontal stabiliser are
quite resistant to Pilot-induced-oscillations (PIO) and consequent
Power-pushover (PPO).
PIO is avoidable. PPO is unrecoverable.
Most BRITISH gyroplanes do not have adequate horizontal stabilisers fitted.
The rest of the world has moved on, and these type of accidents are declining
as a result.
In the UK, gyro pilots cannot install a horizontal stabiliser unless it has passed
BCAR Section T requirements.
The stringency of these requirements, and the cost of meeting them, for what
is essentially a hobby activity, has resulted in the continued flying of unsafe
and unstabilised designs.
I have a term for this. I call them Administration-induced accidents.

Recent Mandatory Permit Directives in this area demonstrate an apparent
refusal to recognise the Catch 22 which is at work here.
It is, apparently, far more important to cover administrative @rses, than to
allow the adoption of devices that have demonstrably reduced the accident
rate elsewhere.

Simple question; How many PIO/PPO accidents have occurred in properly
stabilised machines.
Answer: Possibly 1.

It may well be that I am wrong in this instance, but the general point is
correct.

The eye-witness account quoted in the BBC yesterday had all the hall-marks
of a PIO/PPO accident, and someone here has said conditions were gusty.

If anyone can let me know the name of the unfortunate victim, please e-mail
me at [email protected],as I know some gyro-heads over there.

A properly stabilised gyroplane has broadly the same weather limitations as
a helicopter, and for similar reasons.

Low-G is a potential killer on ANY teetering rotor system, gyro or helicopter.

Regards

Fergus Kavanagh

[englishal]

Thanks Bladewashout for that excellent technical description.

[The Nr Fairy]

Fergus:

While you're evidently knowledgeable about the stability aspects of gyroplanes, I would suggest based on the one line description in the news article that PIO/PPO is stretching it a bit, unless "the rotor folding in on itself" is a symptom of PIO/PPO. Can you expand ?

[Fergus Kavanagh]

Firstly, Thanks to the gentleman who e-mailed me the details. Took a load off my mind. However, I remain sad and angry in equal measure.

Thanks indeed to Bladewashout for the detailed description of low-G as applies
to helicopters.

There are some differences where gyros are concerned, however.

The primary difference is that the forward propulsive force( the pusher propeller)
remains active during the Low-G event.

The result is that the propulsive force is active, but the control, and drag of the
rotor are temporarily lost.

Given that in most current gyros, and almost ALL UK-operated gyros, there
is a vertical offset between the propellor thrustline and the vertical location
of the CG, the resultant combination of forces during the low-G event serve
to tumble the machine rapidly forward.

This rotation can be very rapid, in the order of 100+ degrees/second.
The rotor could not follow such a rate of change even if it were properly
loaded.

The result is a massive destructive mast-bump, which destroys the rotors,
usually resulting in the rotor hitting the propellor and tail fin/rudder.

The machine then tumbles vertically to the ground.

The normal eye-witness description is of a loud bang, followed by pieces
departing the aircraft, as it falls. The rotors are frequently described as
stopped and folded back on themselves.

The likelihood of this type of event occurring is dependent on the degree
of vertical offset between the thrustline and the centre of mass.

Whatever the offset, the undesirable effects can be reduced by a large amount, by the use of a horizontal stabiliser.

This (a) stabilises the pitch attitude in normal flight, reducing the potential
for PIO, and (b) slows the rate of rotation in the event of PPO, which may give the pilot some time to throttle back and save the situation.

The dynamics of PIO/PPO are fairly well understood at this stage.
These accidents SHOULD NOT be happening.

I am not aware of any accident or problem caused by the use of the currently
available crop of stabilisers.

If the above is not as clear as it should be, its because I'm knackered tired
just now. Sorry.

I have no technical qualifications, but I read any and all available accident
reports, and I also avail of the expertise available from the Rotary Forum in
the U.S. and elsewhere.

I have built, and am learning to fly, my own gyro, which now has a generous
horizontal stabiliser, and even I can see the difference.

On a positive note, I believe the CAA now has someone on board who has
actually had a flight in a gyro, so maybe things will improve in time.

Hope this helps, Nr Fairy.
I appreciate the verdict is brief and premature, but I've come across too many of these reports not to see the signs.
There will be assertions re weather decisions, pilot experience etc., but the
underlying issue is stability in pitch.

[Chuck Ellsworth]

Fergus has done a very good job of explaining the stability issue ( or lack thereof ) regarding gyroplanes.

What I would like to read is an explination from the British CAA as to why they can not grasp basic physics such as those involved in poorly designed gyroplanes with an excessive vertical C of G offset that will guarantee a power pushover if PIOéd or upset by turbulence which is unrecoverable and almost always results in the death of the people in the gyroplane.

As Fergus explained the addition of a functional, effective horizontal stabalizer will greatly add to the stability of a gyroplane with a high thrustline offset such as in the RAF 2000, a very popular kit gyro that has a horrendous record of killing its occupants in bunt over accidents due to PIO and or turbulence induced pitch excursions resulting in the unloading of the rotor disk and a power pushover bunt caused by simple physics.

I seldom post here anymore, however I do fly in Europe and know several British CAA inspectors in the fixed wing arena of aviation and found them to be great where safety considerations enter the operation of aircraft.

So to the individuals who make decisions regarding aircraft safety in Britian could you please explain to me why you are unable to grasp basic physics and refuse to allow the gyroplane group to improve the stability issues with reference to high thrustline gyros such as the RAF 2000. Or if you finally grasp this simple law of physics and are to inflexible to allow changes such as the addition of a H.S. why don't you ground all gyroplanes that have excessive thrustline offsets?

P.S.:

Helicopters and gyroplanes are very different breeds of flying machines and comparisons between the two can cause confusion in understanding their respective stability issues.

Chuck Ellsworth

[Zulu Alpha]

I am a fixed wing pilot so apologies in advance for asking a simple question..

Would you mind explaining what a teetering rotor head is (I know what a rotor head is, but what makes it teetering).

Many thanks

[Fergus Kavanagh]

ZA,

Very briefly, a teetering rotor system has two, and only two, blades attached
to a rigid hub bar, which 'teeters' back and forth on a pivot bolt.
It is much simpler than a fully articulated rotor head.
This is as applied to gyros only, which have fixed pitch blades.
Helicopters incorporate collective pitch into a similar arrangement, but I'm not
up to speed on the detail.

The FAA has a downloadable Rotorcraft Handbook which explains it in reasonable
detail, and is quite readable.

Cheers.

[Zulu Alpha]

Fergus, thanks...I hadn't appreciated that a Gyrocopter had fixed pitch blades, obvious when you point it out but I'll take a look when I'm near one.

[VP959]

Fergus has summed up the situation admirably well. We do indeed, it seems, suffer from administratively induced accidents in the UK.

The key thing is giving the pilot time to respond, so reducing the probability of a serious PIO. It's blindingly obvious that a horizontal stabiliser in the right place and of the right area can slow the pitch response, so doing just this.

Despite this, our CAA refuse to accept that horizontal stabilisers work, based on some very limited research done at Glasgow University. They have, instead, effectively banned (by gross restriction) all non-centreline thrust gyros in the UK instead.

The recent gyro MPD will tend to reduce the overall skill level of pilots in the longer term, so will, I am sure, exacerbate the problem and cause more deaths.

I do wish we could get rid of the "Nanny culture" that seems to prevail in this country. Surely to goodness we should be allowed the feedom to make our own assessment of what is safe or unsafe?

VP

[Fergus Kavanagh]

Just for the benefit of fixed-wing pilots reading this thread;

The PIO/PPO issue in gyroplanes is somewhat analogous to the
stall/spin issue for fixed-wing aircraft.

The difference is that a properly-configured gyroplane can be rendered
almost immune to the problem, or at least radically improved.

The problem is that in the U.K., the changes required are not
being facilitated by the authorities.

['India-Mike]

Fergus, you're wrong - fundamentally, absolutely wrong. There is no analogy, equivalence or any such like between FW stall/spin and gyro ppo/pio.
FW types can be certified for stall and/or spinning. These then become defined limits of the flight envelope (in the case of stall), or approved manoeuvres (in the case of the spin, where approved). Such types can legally be operated in these regimes, and safely be operated in these regimes (admittedly with a greater degree of risk than straight and level).
There is NO gyro certified for ppo/pio. It is not a flight envelope boundary. Gyro ppo/pio is not necessarily fatal, but evidence says that it generally is - but no gyro pilot deliberately goes there. However, a lot of FW guys (myself included) go into stall and/or spin, where approved.
I would strongly encourage FW bretheren NOT to think of ppo/pio as analagous to FW stall/spin. Jeeze......

[Chuck Ellsworth]

India_Mike, you are correct that the stall/spin departure from controlled flight in a fixed wing and a power pushover bunt event in a gyroplane are two distinct and different issues.

However in defense of Fergus I do believe that he was trying to find an analogy that fixed wing pilots could relate to.

Obviously you understand the physics and aerodynamics involved in a unloading of the rotor disk resulting in a PPO bunt, can you give me any reason why the British CAA resist pilots adding a stabalizing device to gyros such as the RAF 2000 that will improve their propensity to kill their occupants due to the flawed design ( high thrustline and no H.S.) of the machine?

Chuck Ellsworth

['India-Mike]

Chuck

No, I can't. Sorry. But.....

CAA will probably quote the philosophy of 'equivalent safety' with regards the RAF 2000. But I can't answer your question on their behalf.

[Chuck Ellsworth]

India_Mike:

Yeh, I guess none of us can really fathom the inner workings of Government bureaucracies and as time marches on they get ever more cluster.ucked with evasive myopic policies and rules that is churned out of the innards of the ever expanding legions of deep thinkers that they employ.

I am just starting my retirement from a lifetime of aviation and this is my first summer off in over fifty years, the adjstment from working in aviation to retirement took about two heart beats.

One of the most enjoyable flights of my career was April 29/06 when I boarded a KLM MD11 in Amsterdam for my flight home to Vancouver after finishing my last commitment in the flying business...

....anyhow I will of course ocassionally surf these boards to see what is happening in the flying arena just for something to do. :ugh:

Chuck E.

[Fergus Kavanagh]

IM,

You are of course, technically correct.

I was, as Chuck said, trying to give fixed-wing folk a sort of 'handle' to relate
to.

The reason I put anything on this forum at all relating to this event, is
because it is the 'Private Flying' forum, presumably mostly frequented
by fixed-wingers.

The gyro fraternity are already painfully aware of these issues.

Apologies if I have confused or misled anyone.

['India-Mike]

Fergus

Yes, I understand - perhaps I was a bit harsh in my response. But proportionately few fw guys die from stall/spin (other than at low level, or if untrained). How many gyro people recover from a fully-developed ppo?

Chuck

The current CAA guys at a working level are great. Without them (2, and now 3 thankfully including a tp) my own personal view is that the suits in the uk would have stopped most if not all gyro flying here. Hats off to these 3 gents, if not their bosses! As for 50 years' of flying - phew. I haven't yet experienced 50 years' of life never mind flying!

[Chuck Ellsworth]

Yeh I_M I mentioned in a previous post here thatI found the CAA front line grunts to be great to work with, it is the entrenched bureaucracy that is the wall to be penetrated, changes within are slow or non existant...

Actually I willl be starting year 54 on the 23rd of this month in my flying career, but that has no real meaning anyhow except that I'm getting older.

May I say one more thing on this subject of flying?

Having spent all my life in aviation and watched the progress of aircraft and worked as a professional pilot up until this past month and I am truly happy to be out of it.

I understand aircraft and their systems including the new computer driven variety, however the mindboggling paper work, rules, regulations, policies and the moronic enforcement of these issues that are chocking the industry finally over whelemed me and I am happy to get out.

An example is one day a couple of years ago I had landed and parked my airplane after flying an airdisplay in an airshow and I was refused passage across a ramp because I did not have a green safety vest on...I was wearing a blaze orange flight suit that was ten times more visiable than the vest...but that did not meet the rules...

...fu.kin morons.

You guys have a good flying career and stay alive...that is what really counts.

Chuck E.

[The Nr Fairy]

I found this (http://www.thisiscornwall.co.uk/displayNode.jsp?nodeId=144143&command=displayContent&sourceNode=144131&contentPK=14580026&moduleName=InternalSearch&formname=sidebarsearch) update, posted on Saturday.

[Fergus Kavanagh]

As there has been a substantial number of viewers on this thread,
I'm posting a link to further discussion of the stability issues involved
on the Rotary Forum in case anyone wishes to know more about it all.

Thank you.

http://www.rotaryforum.com/forum/showthread.php?t=8684

[The Nr Fairy]

The AAIB have issued a special bulletin - available here (http://www.aaib.dft.gov.uk/publications/special_bulletins/s6_2006___raf_2000_gtx_se__g_reba.cfm) - I found the other thread first, that's all.