Blade Flap

Also interested in that post Birdy. Agreed that any set of blades will flap if too much air is passed through them at to low a rotor speed.

I like the advice given to hold the stick just off the backstop when building up rrpm because this gives you teetering room and therefore time to react when the stick begins to signal.

But does not the RRPM range for blade flap in a given wind speed through rotors of a particular diameter vary with rotor inertia/weight and profile?
 
I fly off grass strips. Sometimes I do a soft/rough field takeoff by holding the cyclic full aft until the gyro lifts off and then leveling off into ground effect to build up airspeed. Is this a risky move that could lead to a blade flap? The rotors seem to build up RRPMs very quickly and the forward speed is not very fast when I get off the ground.
 
I don't think that's the same thing as horsing it into the air. When I do a takeoff like that I don't balance on the mains at all. I rock back and stay rocked back until the rotors come up to speed and it comes off the ground.
 
Im going to defer to others who are more technically saavy but it seems to me that if you dont feather your rotor forward you either cant lift or if you do you stay behind the power curve when you do. It strikes me that in that situation your rotor has to be revved high enough to get you lifted off but if you dont speed it up fast by lowering the aoa you could maybe flap.

When I go from full back to the mains she wants to rock back and give me more drag, I keep it flat which speeds the rotor and up Igo (and by by blade flap) If you are just flying up and not gaining rotor speed seems like you could be at risk. This make sense to anyone or am I off base?
 
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Once again:

Given th following configurations:

UL-Single seater with 60-70 HP
UL-Dual Seater with 100 - 130 HP

most rotors (8,0 - 8,6m) are flap-proof on a regular T/O at full throttle/stick fully back once the rotor has reached min. 200 rpm.

In strong headwinds (> 20kts) prerotation should be done with stick fully forward right to min. 120 rrpm. Then You can decide to proceed with prerot to >200rpm or disengage the prerot, SLOWLY pull the stick back and make the headwind speed up the rotor whilst the throttle is continoulsy engaged to keep the gyro at stand still (preventing rolling back). When rotor-rpm is >200 the rotor is "full-throttle-flap-proof".

Flap-prevention after Landing/braking the the rotor in strong headwinds: place the gyro against the headwind, stick fully fwd right until rotor-stops.

Angelo
 
Your rite Mark and Resasi, there is a difference between blade lengths, profiles, weights ....., but to the average beginer, not sumthn you could distinguish easily.

Is this a risky move that could lead to a blade flap?
Only if you give it too much power too early Tim.
The geaster risk would be getn too high and caugh behind the curve.

This make sense to anyone or am I off base?
Your rite on the money. ;)
 
Nice to get the real scoop right from the moo's mouth, so to speak Birdy. You being our man in the air all the time.

Love building up all the theory, and this has been a great place to get it, but no substitute for hands on day in and day out for what really works.

It was slight sobering to be told that one could still get blade flap in the air unusual as that might be. But I guess under certain circumstances such as a low RRPM lift off from a rough field TO as Tim was describing, with a then too rapid acceleration in ground effect with light blades might just produce it.

One more tick in the box for having an efficient prerotator to shorten the roll and get those blades up to a good speed prior to brake release.
 
Resasi said:
...One more tick in the box for having an efficient prerotator to shorten the roll and get those blades up to a good speed prior to brake release.
Click to expand...

And one more tick in the box for having an effective rotor brake, too.

-- Chris.
 
Will have a good rotor brake Chris, but have to say forward stick does have a dramatic effect to the point never considered having to apply braking.
 
I should've added to my earlier description of my soft/rough field takeoff that I prerotate to 200 RRPMs before I start my forward roll. Once in the air I level off and build up airspeed in ground effect. My rotor RPMs are up there at that point so it sounds like I should be OK taking off like that.
 
Tim, while it dose work, its not the shortest way to get off and definatly not the safest.
Safty first;
If this is how you take off short, your leaving yourself open for bent alu if sumthn simple, like a loss of power or sinking air should turn up and catch you on 2 control limits.[ WOT and full aft stick]
Not a happy place to be, even if your still in GE.
Just try chopn the power just after you break ground and see how uncomfortable it is.
 
Timchick said:
I should've added to my earlier description of my soft/rough field takeoff that I prerotate to 200 RRPMs before I start my forward roll. Once in the air I level off and build up airspeed in ground effect. My rotor RPMs are up there at that point so it sounds like I should be OK taking off like that.
Click to expand...

Tim, that pretty well discribes my rough field tale offs. When she rocks back and you feel the rotor drag, that's when the blades really accelerate and when I start advancing the power. I picture it as my lift behind me, and easing off the back pressure brings the generated lift over and she lifts off in ground effect and accelerates quickly to Vx or Vy with my wheels only a couple of feet off the surface. When prioperly executed, it's kinda like water sking when you come up on the step.
A power out at 2-3 feet never bothered me too much. Back when I was teaching myself to fly AND maintain the old Mac, the dang thing would often seize right about there!;)
 
Birdy,
I don't give it full throttle until I'm off the ground. What would be the shortest way to get off a rough field?

Pete,
That's exactly how it feels. And I no longer have to worry about the Mac.
 
Yes, but still I prefer to taxi with the rotor stopped, particularly when the wind's strong.

-- Chris.
 
What would be the shortest way to get off a rough field?
Click to expand...

Given You have a sufficient prerotator: speed up to 250-260 rrpm, stick fully back and full throttle to get off the ground as soon as possible, then gather fwd-speed by pressing the stick slightly fwd to keep the gyro at 3-6 ft AGL and start Your climb at 50-70 mph fwd speed (depending on the gyro-model).

This gives sufficient safety if the motor dies down during T/O for a soft em-landing.

Angelo
 
I don't give it full throttle until I'm off the ground. What would be the shortest way to get off a rough field?
Sorry Tim, i missread your picture.
I read it as, full backstick and full power [ once the rotors were up] and just hold it there till it staggered into the air.
Mind you, theres not many gyros that have the power to weigh to do that.

Now im understandn you proper, i wont be loosen any sleep over your TOs. ;)

But, if you want to know my way, here goes.
[ firstly you need a prespinner that gets your blades to min flight rpm, and be able to hold it on till you break ground.]
Prespin to max capability,[ in my case, bout 250 rpm], with full backstick to hold machine from creepn forwards.
Once max rrpm is gained, simultainiously push stick to near full forward and got to WOT, while maintaining prespinner engaugement.
In bout 2 secs, or 30 paces youll reach low flight AS with rotors at TO rpm.
Ease back on the stick and ascend near virtical. Hold prespinner engauged till clear of trees, machanical turbulance or wotever it is. :)

Yes, there is greater risk should the noise stop compared to a normal TO, but with the full flight rrpm, and sufficiant AS, the risk is pretty low. ;) [ and sure beets walkn home]
 
I guess that's where your double pull prerotator is coming in handy Birdy. My guess is not too many get to 250.

Since the blades when airborne are now probably going faster than the prerotator is capable of, surely the 'prespin' now has no input to the blades?

In the event of an engine failure the prespin loses power too so the 'prespin' won't be any help. I however can see that in the event of blade slowdown you can still input energy to the blades but at the cost of torque which I am presuming you accept at that stage and presumably will have some degree of control over with rudder.
 
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