Gyro accident at Springs

[MICHIEL]

Gyro accident at Springs on 9Feb according to posting on avcom today.Pilot/student with broken shoulder.

[saraf]

Does anybody know what happened here??????

Glad to see the guys are ok.

Speedy recovery.

Regards

SARAF

[Gyronaut]

Damn! Sorry to hear about this.
Glad the pilot is ok.
I have not heard anything but would hazard a guess that it was caused by either blade-flap or gyroscopic precession.
Catches the unwary all the time.
I look forward to hearing conclusively so we can all learn from it.

Len

[grostek]

Damn! Sorry to hear about this.
Glad the pilot is ok.
I have not heard anything but would hazard a guess that it was caused by either blade-flap or gyroscopic precession.
Catches the unwary all the time.
I look forward to hearing conclusively so we can all learn from it.

Len

Hi Len,

Maybe you can start the ball rolling by explaining to a gyro pampoen like me what causes blade flap and gyrosopic precession. Also seems to happen during takeoff???

Then a possible explanation how to prevent the two from happening.

Kind regards,

Gunter Rostek

[Gyronaut]

... gyro pampoen ...

I think we all are to varying degrees, so dont put yourself down!

Blade flapping is a complex theory that Juan de la Cierva grasped when he invented the autogyro in 1919. The short answer (if there is one) to Grostek's question is: There isn't a short answer.

To understand High Speed Blade Flap we have to understand dysimmetry of lift and gyroscopic precession. Disymmetry of lift first: As the advancing rotor blade increases in forward velocity, (advancing/leading blade) The retreating blade decreases its forward velocity. (Retreating/Lagging blade). So the advancing blade speeds up and the retreating blade slows down relative to the wind. As the advancing blade rises due to lift (and forward airspeed across the leading edge)then Ciervas theory was that the weight of the blade moves inwards towards the centre of the disc thus further increasing blade speed (just like an ice skater speeds up her spinning action as she/he moves her arms or legs inwards). This is known as the Coriolis Effect. The coning angle is thus also obviously affected. The retreating blade slows down due to a number of reasons but one of the reasons would be forward airspeed now acting from the trailing edge to the leading edge. As lift decreases on the retreating blade, the blade drops slightly and as it drops the weight moves away from the disc further slowing the blade. This is usually balanced out by the movement of the blades on the teetering hinge. Lift between the advancing and retreating blades reaches an equality via the amount of lift being produced at different rotor blade airspeeds and relative angles of attack. Once this equality is reached, safe flight can take place. Heavier rotors require less speed before they reach this equality. So, if the rotor RPM is inadequate for the forward speed and the angle of attack of the advancing blade is increased (for a given rotor) it will "fly" while the retreating blade "stalls". Gyroscopic precession causes the blade to flap up 90degrees later (in front) forcing the retreating blade down (taking the tail with it).

These forces are so violent that the controls reach the stops making it impossible to counter them and things go belly-up from there.

I fear I have waffled on trying to explain my understanding of it without planning my answer too carefully but I am not an engineer, just a humble pilot.
I hope it makes some sense. We have also discussed it in another thread which may help. See viewtopic.php?f=16&t=7884

I therefore contend that on takeoff 2 things must be in place to avoid blade flap. 1) Adequate rotor RPM for the given rotor system to ensure coning on the advancing AND the retreating blades, and 2) Stick full back against the stops to maximize the angle of attack leaving no leeway for possible additional violent reactions. Once the load is taken up by the rotor in flight, violent blade flapping cannot and will not happen.

I know this method of takeoff I describe may result in take-off behind the power curve but at 2 feet above the ground, building forward speed, flying behind the power curve is less of a danger than thundering down the runway on the ground, stick slightly forward, rotor rpm bleeds off and when the angle of attack is slightly increased for takeoff all the above happen in and instant and BANG. its over.

I hope this makes some sense

Len

[Gyronaut]

FO Gyro wrote a very lucid explanation of Blade Flap on Avcom; see http://www.avcom.co.za/phpBB3/viewtopic ... 91#p526997

[grostek]

Thank you Len ,

For a very clear description of what is happening during blade flap and why it is happening.

Have also read the description given by FO Gyro on Avcom.

Am now slowly begining to see how a Gyro operated within required parameters is inherently safer with superior short field performance,than a fixed wing,

Bottom line seems to be "do what you have been trained to do".

Now can someone please tell me if a tractor (motor in front) Gyro has different operating procedures or safety concerns.

Kind regards,

Gunter Rostek

[Gyronaut]

Thanks Gunter

I have never flown a tractor gyro. My logic tells me that it will be subject to the same forces with regard to blade-flap.

On a really positive note though, a tractor gyro will NOT be subject to the other killer known to us and that is Power Push Over. (PPO)

A whole new subject and I am not sure if you really want to go there.

Its got to do with the thrust line being above the CofG and a strong nose-down attitude or unloading the rotor while adding power WILL spoil your day.

Will only ellaborate if you are really interested.

Kind regards

Len

[grostek]

Hi Len,

Internet has been down for more than 12 hours here, so I applogise for not answering sooner.

Once again thank you for taking the time to answer my questions.

From your answer it seems as if the tractor gyros have more benign ground handling .

Can also not find any specific advise on the net, so will have to wait until the first one in SA is completed and flown, for feedback.

As for PPO,I assume this varies from type to type and is heavily dependand on the effort and testing put into the design by the designers.

My overall impression is that tractor Gyros may be more forgiving.
but only time will tell if this is true.

Once again thank you for your input

Kind regards,

Gunter Rostek.

[weedy]

Talk to Johan aka Wagtail about tracktor gyros, he has built and flown a few.