ROTORS

[fransstrydom]

Anyone ever experienced a rotor flap while flying straight and level?
SCARY PILOT

[greg vos]

In flight the rotor is loaded, the blades will be at speed say 380rpm or higher depending on your DA and load, this means they have centrifugal outward force.
Are you sure you had rotor flap ? Or could it have been a patch of severe turbulence? Turbulence coupled with a low friction head set up could give you misleading feedback?
All manufacturers have set up friction guidelines and if this is out of specification it adds to the various possibilities

I'm keen to learn every day so I hope more expierienced pilots will chirp

[Induna]

Hi,

I support Greg's explanation. The higher the DA the faster the rotor will spin. The faster the rotor spin the higher the centrifugal force, hence less chance of rotor flap, as the blades becomes even more rigid.

At sea level my gyro has a rotor RPM of 350-353RPM. at higher DA it can go up to 380RPM, which means a 8% increase in speed, so unlikely to be rotor flap.

regards

Jacques

[fransstrydom]

Anyone ever experienced a rotor flap while flying straight and level?
SCARY PILOT

Hi,

I support Greg's explanation. The higher the DA the faster the rotor will spin. The faster the rotor spin the higher the centrifugal force, hence less chance of rotor flap, as the blades becomes even more rigid.

At sea level my gyro has a rotor RPM of 350-353RPM. at higher DA it can go up to 380RPM, which means a 8% increase in speed, so unlikely to be rotor flap.

regards

Jacques
[/quote

Your replies are quite wellcome gentlemen.Let me firstly supply some inputs.These rotors are composite 33footers.I regret i cannot furnish rotor rpm for both occasions.Both times in the afternoon and in summer.Extremely violent vertical up and down movement,i think it can be between 50mm peak to peak,stick shake violent, with loud rotor flapping,so much so that the air vent bubbles popped out the windows.This continued for several seconds.Both times i managed to survive.This does not happen with 30 foot rotors.I suspect that if it is turbulence it would be much more of a common occurance.Teeterbolt tightened very lightly.
Scary Pilot

[Induna]

Wow, that sounds scary indeed. what gyro type is it if i may ask?

I suspect that 33ft rotors will turn slower than 30ft. observe what your rotor rpm is on both occasions when flying again. in the afternoon and in hot weather the rotor will spin faster, as the air is less dense. that should make your blades more rigid.

Is the teeter bolt not too tight? (like in excessively tight? ) In the Magni maintenance manual it states that if this bolt is too tight it put a lot of stress on the bearings and can result in vibration in the stick in both axis.

[FO Gyro]

Yes, in the cruise, I've had the violent forward and aft what felt like rotor flap before. Very scary when it happens. Goes away if you reduce power immediately. My previous VPM M16 we converted to a Rotax 914 did it. Horrible.

[fransstrydom]

Yes, in the cruise, I've had the violent forward and aft what felt like rotor flap before. Very scary when it happens. Goes away if you reduce power immediately. My previous VPM M16 we converted to a Rotax 914 did it. Horrible.

Glen,do you think it is power problem?Did it ever happen again?
Did you change something to make it go away.

After the first time we stripped the rotor head for inspection.Could not find a problem.Inspected the whole aircraft and found nothing wrong.
Scary pilot.

[FO Gyro]

Not a power problem, as I've had it in the cruise, at a pretty normal cruise setting of around 5 000 rpm. I'm not too sure what the fix is unfortunately, but know it seemed to occur on the older models. Maybe Eric Torr can provide more info. I think I heard someone say it's to do with the Centre of Pressure moving too much in one direction, causing a pronounced assymetric lift whereby the rotor starts to flap at a high speed. The teeter bolt might be too tight or loose, not sure which.

[fransstrydom]

I agree,centre of pressure is detemined by airframe attitude and speed,not power.Control stick friction can inhibit coupling between airframe and rotor motions in an airframe,destabilising the whole gyro .The gyro should self stabilise.Interesting that you also experienced this in straight and level flight.I was settling the aircraft,cutting back throttle after climb and settling nicely when this happened.
Scary Pilot

[greg vos]

I am battling with the concept of high speed blade flap?
Remember when we were kids we had a dunlop swing ball? a tennis ball on a small rope and it was attached to a pole, the idea was to hit the ball around and then the other payer hits it back? now the ball in flight with velocity would need serious turbulence or a serious force for it to move off its given trajectory?
So my thinking is a blade at rotational speed (say a Rpm of above 350rpm) will have a huge amount of outward force or Centrifugal force, with this in mind I am battling to grasp high speed blade flap? In helicopters with say a Rrpm of say 504 Rrpm the force on the rotor hub is some 14 Ton for a Robbie IIRC? I was also tought that a small increase in head overspeed would double that force on the head components and for this reason rotor speed management in helicopters is rather important, so I went on a google search with a 11 hour flight returning to SA I used the time to attempt to gain some insight.

I came up with nothing, no evidence that High speed blade flap happens? now Im the first to admit my google skills and PC skills are not great, I did come up with this old thread on the forum its littered with comments from many seasoned Gyro Pilots, but all seem to happen at low speed during take off) or during low rotor speed ops...but nothing on high speed flap? flap at low Rrpm is understandable but at High speed is where I am stuck??

viewtopic.php?t=15604

Would the highly experienced guys please explain in detail if possible how this happens? Im battling with it?

[John Boucher]

https://en.wikipedia.org/wiki/Dissymmetry_of_lift

[greg vos]

https://en.wikipedia.org/wiki/Dissymmetry_of_lift

Thanks John familiar with this being a Heli pilot myself, however a gyro does not have the pitch change during rotation, as you are aware the pitch on a Heli blade through 360' changes for every degree of rotation. A gyro the pitch is static through the full 360 rotation

There are videos on you tube demonstrating this in flight with helicopters, however i have been unsuccessful in finding a video clip of a gyro blade doing this ...the blade flap once the gyro has exceeded manufacturers quoted Vne is quite possible but one would really need to exceed the aircrafts operation limits and reading what the Op has posted it's not clear if this flap is accuring at high speed and beyond the safe operation limits only? Or speeds beyond the manufacturer stated safety operational speed. A modern day gyro should not suffer these problems while operating within its flight envelope.

Now we refer to page 64 of Phil Harwoods book wherein he states CLEARLY Blade Flapp cannot occur in the air, as the rotors are spinning to fast!
Phil Harwood is an instructor Pilot and possible the worlds authority on gyro copter flight.

Not sure many of us instructors want to be giving this man lessons ?

The book I'm referring to is "flying a new generation Gyrocopter" written by Phil Harwood.

So ?..