0 G flight condition

C. Beaty

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The so-called power pushover is the result of a design flaw; engine thrustline above the CG where rotor thrustline must pass forward of the CG to offset the forward tumbling moment. Remove rotor thrust and over it goes.
A Dominator with engine thrustline below the CG “tumbles” in a noseup direction if rotor thrust is removed.
 

Tyger

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The zero g in the illustration is shown as beginning before the curve and ending well after the curve.

In my opinion what is shown in the illustration is incorrect.
I agree... that is a simplified diagram and very specific to the aircraft in this program, which have achieved a high enough velocity for the plane to continue upward for a significant period after most of the thrust has been removed. This is when it becomes "ballistic". This is borne out in the text of the article:
"At approximately 360 KT TAS (185 m/s, Mach 0.61), when the aircraft is pitched nose-up 45°, the pilots commence the 0 g parabola. They push forward on the control yoke ("push over") to lower the angle of attack of the wings, which reduces wing lift, and simultaneously reduce power to a level just sufficient to overcome drag. At this point the aircraft's movement approximates that of a ballistic mass rather than that of an aerodynamic craft."
 
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wolfy

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Well also at least offset flapping hinge reduces 2 per rev compared to teetering one.
I saw in person Chuck Aaron's Oshkosh 2015 aerobatic show. His rotor head and rotor blades were changed and made with Titanium and had many differences from regular helicopters.
He is only one in four helicopter pilots in the world to have an official license to do aerobatics in helis. We all are just mere mortals
Full credit to Chuck Aaron no doubt, but I am always amazed that every time I have seen him mentioned he is thought of as the god of helicopter acro.
No one ever seems to mention his instructors and mentors Karl Zimmerman and Rainer wilke who taught him how to do these stunts and are who I think the true helicopter legends when it comes to the MBB Bo 105.

wolfy
 

hillberg

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Full credit to Chuck Aaron no doubt, but I am always amazed that every time I have seen him mentioned he is thought of as the god of helicopter acro.
No one ever seems to mention his instructors and mentors Karl Zimmerman and Rainer wilke who taught him how to do these stunts and are who I think the true helicopter legends when it comes to the MBB Bo 105.

wolfy
Ole Chuck had to pretty much learn on his own - His many trips to the aerobatic box was known as the locals would call about a helicopter tumbling out of control near the red school house. (Launch Copter eight... Off we'd go...) Funny he never mentioned the legends in our talks -

IMG_0004.JPG
copter 9
 

fara

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The zero g in the illustration is shown as beginning before the curve and ending well after the curve.

In my opinion what is shown in the illustration is incorrect.
Vance:
I am sorry. Did you then try and go through the whole article and the equations shown. The article also contains actual measurements from two aircraft doing the maneuvers and of course not to mention it is an article sponsored by government research scientists who are also Ph.Ds and qualified enough to be deemed capable of studying the problem
 

fara

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I agree... that is a simplified diagram and very specific to the aircraft in this program, which have achieved a high enough velocity for the plane to continue upward for a significant period after most of the thrust has been removed. This is when it becomes "ballistic". This is borne out in the text of the article:
"At approximately 360 KT TAS (185 m/s, Mach 0.61), when the aircraft is pitched nose-up 45°, the pilots commence the 0 g parabola. They push forward on the control yoke ("push over") to lower the angle of attack of the wings, which reduces wing lift, and simultaneously reduce power to a level just sufficient to overcome drag. At this point the aircraft's movement approximates that of a ballistic mass rather than that of an aerodynamic craft."

That is not correct. That is a deep misunderstanding and completely and utterly makes exactly the point I have been trying to make.

Whether you are at 350 knots or 75 knots the Physics does not change. The duration of acceleration does. For their test aircraft the duration of complete freefall (0 g) is about 25 seconds whereas for lower momentum aircraft it will simply be a couple of seconds. Why do you think the actual Physics would change? Can you show me how it would? And remember we are not talking about being at 0 g to get in trouble. You get below 0.5 g and you are already getting in trouble in a 2 bladed rotor or a weight shift trike
 
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fara

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The so-called power pushover is the result of a design flaw; engine thrustline above the CG where rotor thrustline must pass forward of the CG to offset the forward tumbling moment. Remove rotor thrust and over it goes.
A Dominator with engine thrustline below the CG “tumbles” in a noseup direction if rotor thrust is removed.

And a Dominator has never had a PIO accident?
 
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Vance

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Vance:
I am sorry. Did you then try and go through the whole article and the equations shown. The article also contains actual measurements from two aircraft doing the maneuvers and of course not to mention it is an article sponsored by government research scientists who are also Ph.Ds and qualified enough to be deemed capable of studying the problem
Yes, I read the article Abid.

I wasn’t writing about the article, I was commenting on the illustration you posted.

In my opinion it is wrong in an important way.

This is not a difficult concept.

For a low g event you need acceleration.

One way to accelerate is a curve.

In my opinion you cannot approach weightlessness in un-accelerated flight in a gyroplane.

In other words the beginning and end points for 0 g in the illustration are incorrect.

Pitching nose up at 45 degrees in a gyroplane won’t get you to 0 g.
 

fara

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Yes, I read the article Abid.

I wasn’t writing about the article, I was commenting on the illustration you posted.

In my opinion it is wrong in an important way.

This is not a difficult concept.

For a low g event you need acceleration.

One way to accelerate is a curve.

In my opinion you cannot approach weightlessness in un-accelerated flight in a gyroplane.

In other words the beginning and end points for 0 g in the illustration are incorrect.

Pitching nose up at 45 degrees in a gyroplane won’t get you to 0 g.

Ok. The illustration is from the article but you are not talking about the article. The article is the one that claims exactly that people have this popular belief where 0 G starts in a parabola and the correct thing is it starts while the climb is still going on. So if the illustration they showed is wrong then the article or paper is wrong. I get your position. Thanks for it.
 

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The so-called power pushover is the result of a design flaw; engine thrustline above the CG where rotor thrustline must pass forward of the CG to offset the forward tumbling moment. Remove rotor thrust and over it goes.
A Dominator with engine thrustline below the CG “tumbles” in a noseup direction if rotor thrust is removed.
And a Dominator has never had a PIO accident?
Chuck is writing about a power push over.
Pilot induced oscillation is very different than a power push over.
As far as I know a Dominator has never had a power push over.
 

fara

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Chuck is writing about a power push over.
Pilot induced oscillation is very different than a power push over.
As far as I know a Dominator has never had a power push over.
Got it because there definitely are accidents with PIO in Dominators and it can definitely PIO from my own personal experience
 

Tyger

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That is not correct. Whether you are at 350 knots or 75 knots the Physics does not change. The duration of acceleration does. For their test aircraft the duration of freefall is about 25 seconds whereas for lower momentum aircraft it will simply be a few seconds. Why do you think the actual Physics would change. Can you show me how it would?
You misunderstood me. I didn't say the physics changed, I agreed with Vance that the diagram was inaccurate, as 0 g begins when they cut the power. They chose to do that at 45º, to make the best parabola, just like the angle you choose when you want to shoot a cannon the greatest distance (and get the largest area under the parabola). I think you are misreading the article a bit. Please reread the part I quoted: "when the aircraft is pitched nose-up 45°, the pilots commence the 0 g parabola. They push forward on the control yoke ("push over") to lower the angle of attack of the wings, which reduces wing lift, and simultaneously reduce power to a level just sufficient to overcome drag"
When only the acceleration of gravity (net) is acting on it (and only then), can you get the 0g, at which point it starts to curve in a parabola (which the diagram does not show occuring till much later). That's why their diagram is so misleading.
I am not sure what you mean by the "duration of the acceleration", though. Do you mean the time before the plane gets to zero vertical velocity? In their example, I figure it's less than 13 seconds, if one starts decelerating from 360 kts at a 45º angle). At 75 kts it's just a few seconds.
 
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Vance

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Ok. The illustration is from the article but you are not talking about the article. The article is the one that claims exactly that people have this popular belief where 0 G starts in a parabola and the correct thing is it starts while the climb is still going on. So if the illustration they showed is wrong then the article or paper is wrong. I get your position. Thanks for it.
"Although space flight is the only way to provide long periods of true freefall, a much cheaper and more accessible method is available in an aircraft flying a parabolic trajectory. During such parabolic flight an aircraft flies a trajectory that provides freefall for up to 40 seconds. Parabolic flight generates freefall by following a trajectory wherein the acceleration of the aircraft cancels the acceleration due to gravity (Figure 1), along the aircraft vertical (z) axis. Essentially, if the aircraft and its occupants "fall" together at 9.81 m/s2, "0 g" is achieved, where there is no reaction force on the occupants by the aircraft. Such a flight typically consists of 30 to 60 parabolas, each providing about 25 seconds of freefall. Between parabolas, the aircraft must climb to regain altitude, and during this 40 second interval when downward velocity is reduced and eventually becomes upward velocity, g levels reach 1.8 g. (Contrary to popular misconception, the 0 g freefall phase of flight begins as the aircraft climbs, and does not occur solely as the aircraft descends. Although the aircraft has upward velocity during the initial 0 g phase, its acceleration is downward: the upward velocity is decreasing.)"

Maybe if you read it slowly Abid you will recognize that it reads that the weightlessness begins when the plane is still going up as it begins its parabolic curve.

I can pitch nose up in The Predator and my G meter will read one G until I start rounding out at the top. I have never seen less than .6 g.
 

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Vance

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Got it because there definitely are accidents with PIO in Dominators and it can definitely PIO from my own personal experience
Chuck did not write that a Dominator would not PIO.
I have not experienced PIO in a Dominator.
Perhaps with a little practice you could learn to fly a Dominator.
 

fara

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You misunderstood me. I didn't say the physics changed, I agreed with Vance that the diagram was inaccurate, as 0 g begins when they cut the power. They chose to do that at 45º, to make the best parabola, just like the angle you choose when you want to shoot a cannon the greatest distance (and get the largest area under the parabola).
When only the acceleration of gravity (net) is acting on it (and only then), can you get the 0g, at which point it starts to curve in a parabola (which the diagram does not show occuring till much later).
I am not sure what you mean by the "duration of the acceleration", though. Do you mean the time before the plane stops ascending? In their example, I figure it's less than 13 seconds, if one starts decelerating from 360 kts at a 45º angle). At 75 kts it's just a few seconds.

To be more precise they reduced the power to a certain level because to get the deceleration they want.
Acceleration is positive and negative as we know. You want low G your speed needs to change (acceleration). It reduces as you up it has a negative sign of course and the quicker the speed changes, the more the negative acceleration. So if our speed decreases from 75 knots to say 30 knots (30 - 75 = -45 knots or - 23.15 meters/sec) in 3 seconds that is approximately - 23 (m/sec)/3 (sec) = -7.6 m/sec^2 That is pretty low g and is fairly good representation of a zoom climb in a gyro actually if you left it there it gets worse and you get to true 0 g which could last a couple of seconds but you were already getting in trouble in the 3 seconds before getting to 0.2 g.
Basically instead of dealing with a parabola of 60 seconds with 25 seconds of pure 0 g and more of low g, we would experience things in much shorter periods but it would still be the same thing
 

fara

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Chuck did not write that a Dominator would not PIO.
I have not experienced PIO in a Dominator.
Perhaps with a little practice you could learn to fly a Dominator.
I did. I have 8 hours in it. I did not care for it much. Its just not my personal preference. I landed it plenty of times.
 

fara

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"Although space flight is the only way to provide long periods of true freefall, a much cheaper and more accessible method is available in an aircraft flying a parabolic trajectory. During such parabolic flight an aircraft flies a trajectory that provides freefall for up to 40 seconds. Parabolic flight generates freefall by following a trajectory wherein the acceleration of the aircraft cancels the acceleration due to gravity (Figure 1), along the aircraft vertical (z) axis. Essentially, if the aircraft and its occupants "fall" together at 9.81 m/s2, "0 g" is achieved, where there is no reaction force on the occupants by the aircraft. Such a flight typically consists of 30 to 60 parabolas, each providing about 25 seconds of freefall. Between parabolas, the aircraft must climb to regain altitude, and during this 40 second interval when downward velocity is reduced and eventually becomes upward velocity, g levels reach 1.8 g. (Contrary to popular misconception, the 0 g freefall phase of flight begins as the aircraft climbs, and does not occur solely as the aircraft descends. Although the aircraft has upward velocity during the initial 0 g phase, its acceleration is downward: the upward velocity is decreasing.)"

Maybe if you read it slowly Abid you will recognize that it reads that the weightlessness begins when the plane is still going up as it begins its parabolic curve.

I can pitch nose up in The Predator and my G meter will read one G until I start rounding out at the top. I have never seen less than .6 g.

Vance I don't understand your point. You are saying their figure is wrong because it shows zero G before the direction change happens while the aircraft may still be climbing upwards though decelerating. Then you quote their own statement that is contradicting what you are saying:

"Contrary to popular misconception, the 0 g freefall phase of flight begins as the aircraft climbs, and does not occur solely as the aircraft descends. Although the aircraft has upward velocity during the initial 0 g phase, its acceleration is downward: the upward velocity is decreasing."

May be its semantics that are getting lost. I am sure your G meter reads what it reads. I am not doubting that. I am glad you have never seen lower than 0.6 g in it. That is why you are here.
 

Tyger

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Yes, obviously the paper is about how to get as close to exactly "0 g" as possible, for the longest amount of time.
 

Vance

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I did. I have 8 hours in it. I did not care for it much. Its just not my personal preference. I landed it plenty of times.
Some people learn slower than others Abid.

I did not experience PIO in a Dominator after my first flight.

I don’t fly a Dominator because I prefer near center line thrust to a low thrust line.

I prefer a separate vertical stabilizer and ruder to a full flying tail.

I also prefer more horizontal stabilizer volume and out of the propeller slipstream.

I prefer a Lycoming for power.

An American Ranger is still my personal favorite production gyroplane.

I suspect I will like the balance on the rudder a lot.
 

Tyger

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To be more precise they reduced the power to a certain level because to get the deceleration they want.
Acceleration is positive and negative as we know. You want low G your speed needs to change (acceleration). It reduces as you up it has a negative sign of course and the quicker the speed changes, the more the negative acceleration. So if our speed decreases from 75 knots to say 30 knots (30 - 75 = -45 knots or - 23.15 meters/sec) in 3 seconds that is approximately - 23 (m/sec)/3 (sec) = -7.6 m/sec^2 That is pretty low g and is fairly good representation of a zoom climb in a gyro actually if you left it there it gets worse and you get to true 0 g which could last a couple of seconds but you were already getting in trouble in the 3 seconds before getting to 0.2 g.
Basically instead of dealing with a parabola of 60 seconds with 25 seconds of pure 0 g and more of low g, we would experience things in much shorter periods but it would still be the same thing
You seem to be talking about a change in vertical velocity from 75 to 30 kts... I'd like to see a gyro with that kind of vertical velocity. That would be some zoom.
 
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