Air speed v Rotor speed

Just wondering if anyone has ever noticed what the indicated airspeed is in an MTO with the stick fully back and showing 200 rotor rpm.
My standard take-off procedure is to pre-rotate to 200 rrpm and then move off, build up rotor rpm with a gradual increase in power.
I have never noticed myself but was wondering what airspeed do I need to get up to before my airspeed catches up with the rotor. I have always done it by feel but was thinking that there maybe some mathematical formula to work it out.
There seems to be some pretty clever people on this forum so what better place to ask the question.

At 200 rotor rpm I always go to full power instantly not gradually,the rotor will not flap,

at least its never flapped on me.


Regards,

eddie said:

At 200 rotor rpm I always go to full power instantly not gradually,the rotor will not flap,

at least its never flapped on me.


Regards,

Click to expand...

I agree, at 200 RRPM, I'm now looking for some air speed. The rotor will take care of itself at this point.

Rick,
That's a good question. There are many variables to consider in this equation. I'm not aware of any formula however.
No two gyros are identical in this light (close maybe, but not identical).
Machine weight, rotor disc size (blade length), type of rotor, headwind speed, etc. all play a contributing part.
The above comments are correct as to most rotors, regardless of size as they reach their maximum stiffness
w/o coning around 200 rrpm. That is a 'rule of thumb' safe speed to start a full power forward roll. My Sportcopter ( a heavier machine w/27' blades) and calm air
brings the nose up at 285 rrpm's and lifts off at 315 - 325. Normal ground speed at that point (if I understand your initial question correctly) is about 35 - 40 MPH when "air speed catches up with the rotor" (transitional lift takes place).
S/L flight rrpm is 365. All rotors are 'self-governing' to about ± 10% of their S/L speed in most maneuvers. I, just like you, like to 'ease' in steady power above that point (although full power addition is safe now)
because I have lots of runway to play with and I feel it's less taxing on the overall machine. It's just the way I learned and I am more comfortable allowing the rotors to 'do their own thing' rather than slamming the power to them as in a short field take off.

Here in Oz there are two schools of thought when it comes to prerotation and takeoff, there are some that prerotate to 200 and then go to WOT and there are others that add the power slowly to build up rotor rpm.
As an instructor we are told to teach the latter method in an effort to get the student to have an understanding of rotor management and get them to match the airspeed with rotor rpm during the takeoff roll, hence the original question.
Anyone that goes to WOT at 200rrpm will want to be careful how much rotor rpm they lose when transitioning from prerotation/ stick forward to stick fully back. I generally lose about 20rrpm, if however you happen to lose 40 or 50 rpm due to circumstances, going to WOT could be dangerous.
One of the exercises I use when training is to only prerotate to 100rrpm and with stick fully back gently add power to build up rotor speed, WOT at that rotor speed will be a disaster.......

Rick E said:

Anyone that goes to WOT at 200rrpm will want to be careful how much rotor rpm they lose when transitioning from prerotation/ stick forward to stick fully back. I generally lose about 20rrpm, if however you happen to lose 40 or 50 rpm due to circumstances, going to WOT could be dangerous.
One of the exercises I use when training is to only prerotate to 100rrpm and with stick fully back gently add power to build up rotor speed, WOT at that rotor speed will be a disaster.......

Click to expand...

I pre-rotate to 100 RRPM and build to 200 by slowly adding throttle while on my take-off run. At 200 RRPM I go to full throttle. I pay special attention to staying lined up with the runway and correcting for any drift or cross wind. At rotation I put the nose down to stay in ground effect until I see 60+ mph.
Going to full throttle at 200 RRPM has not been an issue for me. Using this method, I don't lose any RRPM, I am actually building it. My machine's pre-rotor won't take me to 200. The euro gyros that have pre-rotors that go to 200+, may have an issue going to full throttle from a stand-still. Like has been said, different machines may require different techniques.

Our field is 450 mtrs with 10 mtr trees either end, i pre rotate to 220 rpm, stick then full back and full beans, once the nose is up and getting light on the wheels i kick the turbo in. With 2 up in the cavalon we use 200 mtrs, a little more while waiting to hit 55 mph then away. We have just put the ivo prop on at 30 hrs, but not seen a notable difference in performance on take off

Rick E said:

Just wondering if anyone has ever noticed what the indicated airspeed is in an MTO with the stick fully back and showing 200 rotor rpm.
My standard take-off procedure is to pre-rotate to 200 rrpm and then move off, build up rotor rpm with a gradual increase in power.
I have never noticed myself but was wondering what airspeed do I need to get up to before my airspeed catches up with the rotor. I have always done it by feel but was thinking that there maybe some mathematical formula to work it out.
There seems to be some pretty clever people on this forum so what better place to ask the question.

Click to expand...

Not sure if this answers your question, but one of the exercises I was taught in training was taxiing on the ground and playing with the stick to get the feel for how the aircraft speeds up with forward stick as one loses rotor RPM, and visa versa. If I recall correctly about 25-28knots would maintain 200RRPM in the MTO.
I will do this exercise again next time I am out and confirm.