rotor flap

[Resasi]

Having done the last half of my training on a Bensen without a prerotator, which I considered was invaluable for the appreciation of rotor handling, it was an education for me to experience the onset of blade flap/sailing on a windy day before I even started taxiing.

When thought about, the reason was quite clear, it is the movement of air through the disc and angle of attack of the disc that influence flap/sail and the gyro does not have to be moving forward for that to occur.

 

[Vance]

It is my understanding that the disk doesn’t stall Leigh; the blade stalls because the critical angle of attack has been exceeded.

I feel the spinning of the blade changes the relative wind the blade sees and more RPM allows a greater disk angle of attack before a blade stalls.

I feel it is angle of attack of the blade and not the disk angle that flaps a blade.

In my opinion that is why more rotor rpm allows a greater disk angle before flap occurs.

The fog is lifting, I am off to fly.

Regards, Vance

 

[captgyro]

Wow

Wow

Really appreciate all the input, although the first time I read all the responses I was a little confused, but, after reading them several times I feel like I understand a lot better. On the MTO , at least, prerotating to 200 rpm before coming back with the stick should prevent the problem. Also, after landing coming all the way forward with the stick should prevent it from happening. I was also taught to keep the stick toward the wind to prevent flipping it over. Any comments on that? Thanks again for all the good input. Stephen

 

[Resasi]

Correct Vance, but in explaining blade sail/flap I felt it might be useful for the student to consider the disc as a whole above his head rather like a flat plate, in addition to considering each individual rotor blade, though I can see how that can be misinterpreted and possibly confusing

My statement actually was ...angle of attack of the disc that influences blade sailing.

As should be known, though the stick is going straight back back, the advancing and retreating blades to the pilots right and left, are rising and descending. Right advancing with too great an angle of attack causing it to stall.

Hope it's a great flight

 

[MadMuz]

Speaking from my stick frame gyros, as opposed to factory machines, on landing into the wind at less than walking pace, the stick is held back until the nosewheel settles on the ground and the rotors have thrown off their lift and begin slowing down.... once the rotors have slowed down sufficiently (unless I am taking off again) I taxy with the stick back enough to keep the rotors turning at around 100 rpm (in Australia, taxying is recommended with rotors turning over about 80rpm to prevent hub bar damage) and upon having to turn a corner, if there is little or no wind, I just make the turn as long as the ground speed is only about walking pace.... if it is windy as you are making the same slow turn, the rotors are at least flat with the stick forward and if gusting, yes, tilt the disk towards the wind.... show the wind the top of the rotors, not the bottom.....

The thing you have to be careful with taxying with rotors turning, especially if they are turning more than about 100rpm, is that if you taxy too fast, turn and move the stick to the right quickly or hard, there is a risk that the right hand main wheel will lift.... and same to the left in left turns..... so if the rotors are still going hard, don't try to make a quick turn off the runway.... I have found, the faster the rotors are turning (taxying) the slower the taxy speed has to be in a turn and the slower the movements of the joystick..... as well as the opposite, the slower the rotors are turning (taxying) you can taxy a bit faster around corners/exit runway etc and be a bit faster with the stick.... Finesse is everything with gyros

This is how it works for me, not everyone might agree.... something to think about :yo:

 

[bosca]

Very well put Muzz.
Kym.

 

[Texasautogyro]

Really appreciate all the input, although the first time I read all the responses I was a little confused, but, after reading them several times I feel like I understand a lot better. On the MTO , at least, prerotating to 200 rpm before coming back with the stick should prevent the problem. Also, after landing coming all the way forward with the stick should prevent it from happening. I was also taught to keep the stick toward the wind to prevent flipping it over. Any comments on that? Thanks again for all the good input. Stephen

Muzz is correct the only thing I would add is that rotor speed to clear the tail in some gyros is higher then 100 rpm
I also train to hold stick back on landing so the nose wheel comes down close to no ground roll. It's all about rotor management. Knowing this also prevents flap.

Just so you know you can have stick full back at 140 rpm and still have over 6 inches of clearance above the tail in an MTO. There is a very specific reason to train with them spinning while on the ground. Many accidents happen because students do not get that training properly. On an MTO there is a green arc and yellow on the rotor RPM. I hope you get the right training what and why they are important and what the safe zones mean.

 

[birdy]

My impression is; when a blade hits something it is because one blade is flying producing lift and the other is stalled because the critical angle of attack of the airfoil has been exceeded.
True, but as i said before, the retreating blade dosent have to be stalled.
Any teetering rotor has exactly equal lift, no matter how many degrees they may be teetering, rite up until they start hitn the stops.
When the bar hits the stops, its actualy unloading the retreating blade, decreasing its AOA, while at the same time increasing the load on the advancing blade, increasing its AOA.
Neither blade is stalled, they are both still flying.
The destructive part comes next, if the AOAs arnt bort back closer together, ( pilot reducing the disc AOA, AS).
If allowed to worsen, they will try to teeter more to equalise lift, but they are be,n restricted by the stops.
Obviously no rotorhead is strong enuf the resist this intense leaverage, so sumthns gota give.
Still, both are still flyn, only with increasingly divergent AOAs. ( iv used your faverot word Vance, is it in context?)
Any rotorhead/ gyro is destroyed long before retreating blade stall can rip it off.

 

[cfibob]

Capt. .....get with Craig...he is a good instructor. Follow the instructions. You will have many years of safe flying fun. Remember....instructor...yes. Forum....not so much.

 

[C. Beaty]

Airfoils stall at angles from 8° to 15º depending on airfoil and Reynolds number. –Reynolds number depends on the product of chord and airspeed. Higher airspeed = higher Reynolds = higher angle of attack at stall.

It is possible in theory to tick the teeter stops of a Bensen rotorhead without stalling the retreating blade at normal flight speeds but not during rotor startup when Reynolds number is low.

Tilting the rotorhead of a Bensen type gyro does exactly the same thing as tilting the swashplate of a helicopter.

 

[Piot135pd]

Wow

Really appreciate all the input, although the first time I read all the responses I was a little confused, but, after reading them several times I feel like I understand a lot better. On the MTO , at least, prerotating to 200 rpm before coming back with the stick should prevent the problem. Also, after landing coming all the way forward with the stick should prevent it from happening. I was also taught to keep the stick toward the wind to prevent flipping it over. Any comments on that? Thanks again for all the good input. Stephen

How far you've come !!! I'm very happy with the way you trained me and from your post just 3 years ago now you're a gyro DPE with a thriving gyro business !! Congrats Steve !!!

 

[Vance]

Stephen Rastanis is an inspiration to us all. I am proud to know him and call him a friend.

 

[jhpdoc1]

on a gyroplane with a semi-rigid, teeter-head rotor system, blade flap may develop if too much airflow passes through the rotor system while it is operating at low r.p.m. This is most often the result of taxiing too fast for a given rotor speed. Unequal lift acting on the advancing and retreating blades can cause the blades to teeter to the maximum allowed by the rotor head design. The blades then hit the teeter stops, creating a vibration that may be felt in the cyclic control. The frequency of the vibration corresponds to the speed of the rotor, with the blades hitting the stops twice during each revolution. If the flapping is not controlled, the situation can grow worse as the blades begin to flex and bend. Because the system is operating at low r.p.m., there is not enough centrifugal force acting on the blades to keep them rigid. The shock of hitting the teeter stops combined with uneven lift along the length of the blade causes an undulation to begin, which can increase in severity if allowed to progress. In extreme cases, a rotor blade may strike the ground or propeller. [Figure 20-2]

To avoid the onset of blade flap, always taxi the gyroplane at slow speeds when the rotor system is at low r.p.m. Consideration must also be given to wind speed and direction. If taxiing into a 10-knot headwind, for example, the airflow through the rotor will be 10 knots faster than the forward speed of the gyroplane, so the taxi speed should be adjusted accordingly. When prerotating the rotor by taxiing with the rotor disc tilted aft, allow the rotor to accelerate slowly and smoothly. In the event blade flap is encountered, apply forward cyclic to reduce the rotor disc angle and slow the gyroplane by reducing throttle and applying the brakes, if needed. [Figure 20-3]

this may help till you get back to the states. there is no bad question but there are some bad responses. come on guys.

Excellent explanation. Clear and direct.