Blade Flap

Once 200 plus is on the clock, we can go to WOT.
But can it go streight to max erpm [ belt slip] or dose it have to take the rotors with it?
If it cant, i wouldnt be tryn to lift off with it still engauged.
 
Michael good clarification. I think that is why we refer to it is 'sailing' or a runaway blade that is going out of control.

Having clarified that we can experience this in flight,If you continue until you feel it in the stick as a bump or a big stirring motion then you need to take corrective action immediately or risk loosing your blades and possibly your life. Cut the power, push the blades forward to dump the lift, steer, and break. Good luck
What is your recommended immediate action to be taken for blade sail in flight?
 
Resasi
This is Blade sail on the ground. You wont get blade sail in flight. (If you manage to lose RRPM in flight enough to cause blade sail you will have more to worry about.)
 
Paddy my point is that there appears to be a phenomenon that has been experienced in flight by two people on DW's. They described it to me as a form of blade sail in flight. Certainly something that was observed by some very experienced gyro people, and in two out of the three observed events did not end in a crash. The last did but was survived.

I would concur with you that loss of rrpm below a certain point in flight is generally fatal. I have been trying to discover more about this seemingly little known, little talked about rare occurrence, that may be recoverable from, by throwing it out to a wider group on the forum
 
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I should mention that the one flap-after-liftoff incident I experienced was with Rotordynes, not DWs. They were on my very light Gyrobee, which does not have a prerotator.

The rotor diameter is over 24 feet; the machine weighs 251 lb. empty and I weigh about 175. Draw your own conclusions.
 
I am guessing a blade loading of around 31.54, disc loading of around 0.94 approx, which I think means slow turning blades and below optimum figures for both.

Would they be harder to get up to speed?
Quicker to slow down and unload?

Working on trying to understand all the connections which will help me better understand rotor management on the ground and air, as well as select the right blades for the right combination of weights and operating altitude.
 
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There is nothing strange or mysterious about blade stall. All rotor airfoils will stall when the angle of attack reaches 12º or so. Calling stall flapping, sailing or skiing only serves to obfuscate the stall issue.

In forward flight, the inboard portion of the retreating blade is always stalled because the local angle of attack exceeds 12º and as airspeed increases, the stalled region spreads outward. But I doubt if any gyro has sufficient power in level flight to reach a forward speed that results in total stall.

But rotors can and do stall in flight, normally chopping off the tail of the gyro. This happens in gyros with offset propeller thrust lines and/or uncompensated propeller torque when the balancing force of rotor thrust is removed, allowing the airframe to pitch or roll so violently that the rotor can’t follow and stalls. I’m not certain whether the pilot can bang the stick around rapidly enough to completely stall the rotor.

Aggressive maneuvering in flight can result in the rotor contacting the flap stops but even so, it’s not completely stalled; otherwise, the practitioner would be pushing up daisies. But still, it’s dancing with the devil.

Contacting the flap stops during rotor startup is precisely the same phenomenon as discussed above. Too much of the retreating blade exceeds an angle of attack of 12º. The remedy is to slow down and flatten the rotor disc before it stalls completely and begins chopping up the airframe.

Highly cambered rotor blades begin stalling at the trailing edge first which produces a gradual rather than abrupt stall and are easier to start than symmetrical or mildly cambered blades that exhibit leading edge stall.

A gyro can be forced into the air before the rotor blades are ready to fly, something that I do most of the time in order to clear a bumpy runway. The machine judders and wallows for a few seconds until the rotor comes up to flying speed. Normally performed at nowhere near full power and just enough airspeed to remain airborne.
 
Leigh, your numbers are about right.

How a given airfoil behaves (how much lift and drag and whether it stalls or not) is a function of only three things: airspeed, air density and angle of attack.

Note that "load" isn't one of them. We often talk about our rotors being "loaded" or "unloaded" at so many G's -- but that is a metaphor. Airfoils don't sense loads, they sense those three parameters, period.

A slight complication with rotary airfoils is that their AOA and airspeed are functions of BOTH RRPM and the aircraft's own airspeed. In particular, at a given RRPM, the retreating blade's airspeed goes DOWN as forward airspeed goes up, and its angle of attack goes UP as forward airspeed goes up.

If my Gyrobee rotor ran into retreating-blade stall on takoff, it was probably because I levelled the rotor to gain airspeed a bit early -- before RRPM was all the way up. This increased forward airspeed but decreased the autorational drive that brings up RRPM. I probably then hauled the rotor back to "pop" off (increasing both blades' AOA suddenly). This direct increase in AOA combined with the AOA increase caused by the relatively high airspeed was enough to make one Gyrobee's worth of lift, but put the retreating blade right at stalling AOA.

The disc loading had no direct effect on this process, except that it allowed the machine to get off the ground while flapping, instead of doing its flapping while still stuck on the deck. As Chuck points out, a retreating-blade stall is a retreating-blade stall, on the ground or in the air.
 
As a relative novice, I don't understand how high speed blade flap can happen once you are off the ground... please explain? Surely if there is enough lift being generated by the rotor to get you airborne (even behind the power curve) blade flap is impossible??

Maybe I am missing something here?
 
I have the retreating blade stall bit and it results. If I understand correctly Doug, pushing the stick forward too soon on a take-off roll, before the blades got up enough rrpm, allowed acceleration forward. When the stick was bought back (perhaps a bit too briskly) lift off then took place with flapping occurring because of too high a forward airspeed with regard to the retreating blade. Rotor width and AUW having the effect that even at the low speed what lift was produced allowed lift off.

Can you then say that having too large a rotor diameter for the weight of gyro and pilot increases the risk of this occurring both on take off and with aggressive maneuvering in the air?
What are the results of having a very large diameter rotor. Lifts off sooner, climbs better, is a 'floater' lands slower, all of which I would expect of a lightly loaded fixed wing, and...? What is the downside gyro-wise?
 
...What are the results of having a very large diameter rotor. Lifts off sooner, climbs better, is a 'floater' lands slower, all of which I would expect of a lightly loaded fixed wing, and...? What is the downside gyro-wise?

Your blades turn slower and therefore you'll have a lower top speed and greater danger of blade flapping on take off(just like Doug described). Your disk loading is lower, too, so you'll feel the bumps in the sky more pronouncedly. And if you like to yank and bank a lot, your maneuverability will be impaired a bit (greater rotor inertia).

-- Chris.
 
Thank you Chris that confirms my thoughts, Doug and Chuck for helping me clear it up in my mind.
 
This happens in gyros with offset propeller thrust lines and/or uncompensated propeller torque when the balancing force of rotor thrust is removed, allowing the airframe to pitch or roll so violently that the rotor can’t follow and stalls.
I think that could be in a different catagory CB.
Its more like cyclic pitch stall, as opposed to wot this thread is talkn bout.
Same result tho. :(

Note that "load" isn't one of them. We often talk about our rotors being "loaded" or "unloaded" at so many G's -- but that is a metaphor.
It may be un 'aviational' or incorrect terminoligy Doug, but its a word we all know, coz we can all feel it.
We cant see AOA, only feel its changes, in Gs.

Maybe I am missing something here?
As stated above, its all to do with the AOA of [mainly] the retreating blade.
It make no difference wether your on the ground [ low/no load] or in the air [ loaded].
If the AS differential is high enuf [ or the teetering limits too small] youll contact the stops.

Iv flown sum pretty sooty gyros with low loaded rotors [ low rrpms with high power/ASs available] and iv never experianced too much teetering.
 
A friend of mine, Lloyd “Depity Dawg” Poston had a Lycoming powered gyro with Hughes rotor blades. We were flying off a grass strip and his prerotator broke. (The “Depity Dawg” nickname came from the appearance of his gyro; a pod made from a surplus drop tank with a big white star painted on the side.)

Hughes blades are barely hand startable when conditions are right. With a 20 mph wind, conditions weren’t right. Stand on the seat, huff and puff to hand spin the blades, put some air through the rotor and start tapping the flap stops. After several tries, the futility became obvious.

We swung the gyro around so the tail was facing the wind with air blowing on the top of the rotor. The equilibrium speed of the rotor as a windmill isn’t very high but it was high enough that when I swung the gyro around to face the wind, the blades “caught” and came up to speed normally.

Hughes blades are symmetrical and work as well upside down as right side up.
 
Michael good clarification. I think that is why we refer to it is 'sailing' or a runaway blade that is going out of control.

Having clarified that we can experience this in flight,If you continue until you feel it in the stick as a bump or a big stirring motion then you need to take corrective action immediately or risk loosing your blades and possibly your life. Cut the power, push the blades forward to dump the lift, steer, and break. Good luck
What is your recommended immediate action to be taken for blade sail in flight?

In flight the problem is worse. Cut the power and bring the stick back. The problem here is that by bringing the stick back you will increase lift. This is not your friend at this point and may increase the affect. If you don't lift the nose you will most likley enter a dynamic roll over. The best defense for this problem is not to exceed the Vne of your design.
 
In flight the problem is worse. Cut the power and bring the stick back. The problem here is that by bringing the stick back you will increase lift. This is not your friend at this point and may increase the affect. If you don't lift the nose you will most likley enter a dynamic roll over. The best defense for this problem is not to exceed the Vne of your design.

Hello Michael,

Is in flight blade flap caused by high indicated air speed?

How does in flight blade flap lead to a dynamic rollover?

Why wouldn’t slowing down be good if high airspeed is the problem?

Thank you, Vance
 
Hello Michael,

Is in flight blade flap caused by high indicated air speed?

How does in flight blade flap lead to a dynamic rollover?

Why wouldn’t slowing down be good if high airspeed is the problem?

Thank you, Vance

In flight blade flap is caused by the same thing that causes it on the ground unequal lift. The greater your speed the greater the differential in lift. At some point you will exceed the ability of your rotor head to compensate. At this point lift will be equalized by the rotor rolling toward the direction of lower lift. Slowing down is the right thing. The problem is that in order to do this you may need to add lift. Adding lift would increase the force that is trying to roll the gyro over. I am assuming that in order to get to this point the gyro is in a descent. I do not know of a gyro that can get going this fast and not be pointed down hill.

The speed that this will happen is dependent on the rotor speed of the gyro.
 
Although the blade flap in flight is possible (at least in theory), our gyros are not capable to reach airspeeds fast enough. So it is impossible to reach that condition because of airspeed.

But it is possible if we experience a great loss of rotor rpm in flight because of a very low g manoeuvre. In the recovery we could find blade flap (or retreating blade stall).

Ferràn
 
Although the blade flap in flight is possible (at least in theory), our gyros are not capable to reach airspeeds fast enough. So it is impossible to reach that condition because of airspeed.

But it is possible if we experience a great loss of rotor rpm in flight because of a very low g manoeuvre. In the recovery we could find blade flap (or retreating blade stall).

Ferràn

It is possible for any gyro even a gyro without an engine to get going fast. Just pitch the nose down. Excess speed can cause the retreating blade to have insufficient lift and initiate a dynamic rollover due to excess blade flap.
 
Do you have any idea of what forward AS could induce retreating blade stall in your gyro?

It is impossible to get that AS in a normal gyro. Our gyros Vne is not because of retreating blade stall.

What is for you a dynamic rollover? Anyway the consequence of insufficient lift in the retreating blade in a teetering rotor is blade flapping, not a rollover.

Ferràn
 
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