#### Abid

##### AR-1 gyro manufacturer

- Joined
- Oct 31, 2011

- Messages
- 6,464

- Location
- Tampa, FL

- Aircraft
- AR-1

- Total Flight Time
- 4000+ 560 gyroplanes. Sport CFI Gyro and Trikes. Pilot Airplane

People seem to lack details of why Blade Sailing happens and what is the math and measurement behind it. Its not mythology or magic.

I am taking the liberty of copying and posting a post by Mike Goodrich from an unrelated thread which is all about measurements of just this phenomenon. The context was a discussion with Jean Claude who uses Discrete Math he has programmed in Excel sheet but also Kolibiri has done some calculations programmed in some software with logic coming from papers from NASA research. These things are complex in details and not in the span of flight instructors or pilots but we should definitely understand as to where these POH recommendations, numbers, logic come from and also mainly why. Here is the quote or post from Mike while he was developing GWS (Gyroplane Warning System) which simplifies the algorithm with approximations and uses the main factors to predict different flapping and bad behavior. I hope Mike will answer people's questions here.

My intention is not to dig down and explain what goes into everything that happens and then what factors are so minute that they can be ignored to simplify and come up with a simple formula for a given type of rotor based simply on rotational speed, forward airspeed and radius or diameter of the rotor and static pressure and outside air temp. I think that is beyond the scope of operations persons. Intention is simply to give you an idea that its not magic and in fact a firmed up mathematical relationship between the listed factors and that drives the recommendations in a POH.

Note the RV curve in the bottom graph starting at 150 RRPM pre-rotation and then full throttle movement forward with a 912 powered 2 seater gyroplane (ELA). (R = Rotor RPM, V = Velocity in KPH). Even at 150 Rotor RPM it shows the amber alarm was set off which means you are 4 seconds away from blade sailing or flapping and it got close to red alarm which means in GWS that you are 2 seconds away from actual blade sailing/flapping and the solid black line is you flapping or sailing the blade. So starting at 150 RRPM with a 2 seat modern gyroplane with 912ULS power, you are basically 3 seconds away from disaster. This was for a 8.7 meter rotor.

AR-1 uses as standard 8.6 meter rotor. AR-1 POH recommendation that you don't do takeoff roll till you go at least 160 RRPM. Its pretty right on. Actually the recommended RRPM is 180-200 but you'd be safe at 160 RRPM with little care. Below that you better have experience nursing the blades up slowly watching RRPM trend.

If any gyroplane rated pilot or CFI cannot make sense of these graphs, its best to discuss and understand. This is where these recommended POH pre-rotation RPM come from. They don't come from someone pulling them out of their ears. Since many gyroplanes use same airfoil and similar engines, this will be very similar for Magni, AutoGyro, ELA, SilverLight and so on.

"

If (as I suspect) JC's calculations are somewhat based on the results of my testing, don't forget that I go to WOT as soon as I release the pre-rotator and bring the stick back.

If John's TO procedure is "

Also JC's calculations are based on 2200N (500 lbf) thrust, you'd better make sure that you really have that. One of the discrepancies we found with my measurements was that I obviously wasn’t getting the thrust out of my old 1,000 hour 912S that JC assumed I was.

Plus check the stick position (into/outof wind) discussions for cross wind take offs. This will have an impact on your take off run and flapping risk.

As I said before JC's calculations are remarkably accurate but, I've learned the hard way, that if you want to fly to his limits you'd better fly to the same degree of accuracy.

Here is a graph I'm preparing for the presentation of my GWS to explain the flapping alarm to the uninitiated. I’ve modified it for your 8.5 m rotor.

For the stick back (@20°) acceleration, It translates to

Rrpm<2.5 x TAS (kph) = danger,

Rrpm>2.5 x TAS (kph) = safe

Here is the same graph with the basic alarm limits for the GWS. The actual alarms lines are not simply straight lines and are more complicated but it gives you an idea.

Here is an actual recording of a 150 Rrpm pre rotator take off with an 8.7 M rotor overlayed on the graph for that rotor. You can see that it flirted with the red alarm. You can also see that I needed to be at about 40 kph before I recovered my initial pre rotation Rrpm and about 60 kph before the rotor really started to accelerate. If this had been a downhill or a stick into Xwind TO the flat part of the curve would have been much longer and the risk of flapping much greater.

Mike G

I am taking the liberty of copying and posting a post by Mike Goodrich from an unrelated thread which is all about measurements of just this phenomenon. The context was a discussion with Jean Claude who uses Discrete Math he has programmed in Excel sheet but also Kolibiri has done some calculations programmed in some software with logic coming from papers from NASA research. These things are complex in details and not in the span of flight instructors or pilots but we should definitely understand as to where these POH recommendations, numbers, logic come from and also mainly why. Here is the quote or post from Mike while he was developing GWS (Gyroplane Warning System) which simplifies the algorithm with approximations and uses the main factors to predict different flapping and bad behavior. I hope Mike will answer people's questions here.

My intention is not to dig down and explain what goes into everything that happens and then what factors are so minute that they can be ignored to simplify and come up with a simple formula for a given type of rotor based simply on rotational speed, forward airspeed and radius or diameter of the rotor and static pressure and outside air temp. I think that is beyond the scope of operations persons. Intention is simply to give you an idea that its not magic and in fact a firmed up mathematical relationship between the listed factors and that drives the recommendations in a POH.

Note the RV curve in the bottom graph starting at 150 RRPM pre-rotation and then full throttle movement forward with a 912 powered 2 seater gyroplane (ELA). (R = Rotor RPM, V = Velocity in KPH). Even at 150 Rotor RPM it shows the amber alarm was set off which means you are 4 seconds away from blade sailing or flapping and it got close to red alarm which means in GWS that you are 2 seconds away from actual blade sailing/flapping and the solid black line is you flapping or sailing the blade. So starting at 150 RRPM with a 2 seat modern gyroplane with 912ULS power, you are basically 3 seconds away from disaster. This was for a 8.7 meter rotor.

AR-1 uses as standard 8.6 meter rotor. AR-1 POH recommendation that you don't do takeoff roll till you go at least 160 RRPM. Its pretty right on. Actually the recommended RRPM is 180-200 but you'd be safe at 160 RRPM with little care. Below that you better have experience nursing the blades up slowly watching RRPM trend.

If any gyroplane rated pilot or CFI cannot make sense of these graphs, its best to discuss and understand. This is where these recommended POH pre-rotation RPM come from. They don't come from someone pulling them out of their ears. Since many gyroplanes use same airfoil and similar engines, this will be very similar for Magni, AutoGyro, ELA, SilverLight and so on.

"

If (as I suspect) JC's calculations are somewhat based on the results of my testing, don't forget that I go to WOT as soon as I release the pre-rotator and bring the stick back.

If John's TO procedure is "

*I often advance the throttle to WOT within 25m of the start of the takeoff roll*" that's half of his TO roll before he's at full throttle. This will help avoid blade flap or sailing but will extend his TO run to beyond the calculation.Also JC's calculations are based on 2200N (500 lbf) thrust, you'd better make sure that you really have that. One of the discrepancies we found with my measurements was that I obviously wasn’t getting the thrust out of my old 1,000 hour 912S that JC assumed I was.

Plus check the stick position (into/outof wind) discussions for cross wind take offs. This will have an impact on your take off run and flapping risk.

As I said before JC's calculations are remarkably accurate but, I've learned the hard way, that if you want to fly to his limits you'd better fly to the same degree of accuracy.

Here is a graph I'm preparing for the presentation of my GWS to explain the flapping alarm to the uninitiated. I’ve modified it for your 8.5 m rotor.

For the stick back (@20°) acceleration, It translates to

Rrpm<2.5 x TAS (kph) = danger,

Rrpm>2.5 x TAS (kph) = safe

Here is the same graph with the basic alarm limits for the GWS. The actual alarms lines are not simply straight lines and are more complicated but it gives you an idea.

Here is an actual recording of a 150 Rrpm pre rotator take off with an 8.7 M rotor overlayed on the graph for that rotor. You can see that it flirted with the red alarm. You can also see that I needed to be at about 40 kph before I recovered my initial pre rotation Rrpm and about 60 kph before the rotor really started to accelerate. If this had been a downhill or a stick into Xwind TO the flat part of the curve would have been much longer and the risk of flapping much greater.

Mike G

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