0 G flight condition

fara

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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.

Yeah I did not care for the close tail and full moving tail or the low thrust line. I was new to gyroplanes at the time. I should try it again now when I get a chance. I had flown it in 2005 also. Remember getting out and telling myself what in the world and going back to trikes and airplanes for almost the next whole decade. It just wasn't my cup of tea.
 

Vance

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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.
I don’t disagree with the article although is appears I disagree with your interpretation of the article Abid.

Peace out.
 

fara

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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.

Vertical velocity? No just velocity with a vertical component.
Oh I see what you mean. Ok but still the point of the article still applies. The low g happens well before the change of direction does and most pilots don't think so. Most think I push the nose over and that's when 0 g or very low g occurs. That is not quite how it can happen. Zoom climbs are different than steady climb rate climbs
In a zoom climb in an AR-1 with 915 you would go over 2500 FPM one up but you would also slow down quickly or decelerate quickly. In a gyroplane in a zoom climb the additional danger is of prop thrust helping to unload rotors as well. In a steady climb where the rate of climb is constant there is no such thing happening.
 
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C. Beaty

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A “G” meter typically measures acceleration rather than load about the vertical axis and therefore rotor load. If there was sufficient propeller thrust to do a vertical climb, the “G” meter would still read 1 G even though the rotor was completely unloaded and if the vertical climb could be maintained long enough, the rotor would come to a complete stop. “G” load is not a good measure of rotor load.
 

C. Beaty

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The bottom line to all of this is that the power pushover in the case of the high thrustline gyros or the power pushup in the case of the Dominator is the result of a design flaw.
How about correct design where the propeller thrust line is centered on the CG and there is no push over or push up? Cierva accomplished this in the 1930s but he was a real engineer rather than a make believe one.
 

anthom

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I feel there are a couple of issues where there seems to be some misunderstanding. Here are my thoughts:

1. Parabolic trajectory perfectly describes projectile motion, say, something like a bullet from a gun, or a shell from an artillery gun. That is because these projectiles do not have a separate propulsion system once they are ejected from the barrel.

2. It is true that there are no straight lines in a parabola. However, as the angle is increased to say vertical, hypothetically it is a straight line up because there is no more parabola. To experience low to zero G, an object does not have to follow a parabolic trajectory.

The part where the G effect begins to decrease is when the vertical component of velocity begins to decrease and get to zero. After that the object begins it's downward path and increases its vertical component of velocity due to acceleration due to gravity and then comes back to the surface.

As far as powered aircraft are concerned, normally they have a set optimum angle of climb depending on the power curve that determines the Vx. In this case the aircraft climbs in a straight path. Similarly in the descent and normal approach for landing.

In a Zoom climb, there is increased acceleration in the climb with a steep angle of climb due to the high power/thrust being used. The problem begins if a rapid nose push is done with cyclic without power reduction, causing a sudden decrease in the vertical component of the climb thus reducing the G. It can go negative when the apex is crossed and goes downward, Now all that remains is the horizontal component of thrust, which begins to cause a rapid loss of lift due to the decreased AOA, and depending on the high thrust line offset of the gyro, the tumble begins.

The way to avoid the loss of G at the top of the zoom is to either do a high banked turn at the top or simply reduce throttle without pushing the nose.

 
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fara

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I feel there are a couple of issues where there seems to be some misunderstanding. Here are my thoughts:

1. Parabolic trajectory perfectly describes projectile motion, say, something like a bullet from a gun, or a shell from an artillery gun. That is because these projectiles do not have a separate propulsion system once they are ejected from the barrel.

2. It is true that there are no straight lines in a parabola. However, as the angle is increased to say vertical, hypothetically it is a straight line up because there is no more parabola. To experience low to zero G, an object does not have to follow a parabolic trajectory.

The part where the G effect begins to decrease is when the vertical component of velocity begins to decrease and get to zero. After that the object begins it's downward path and increases its vertical component of velocity due to acceleration due to gravity and then comes back to the surface.

As far as powered aircraft are concerned, normally they have a set optimum angle of climb depending on the power curve that determines the Vx. In this case the aircraft climbs in a straight path. Similarly in the descent and normal approach for landing.

In a Zoom climb, there is increased acceleration in the climb with a steep angle of climb due to the high power/thrust being used. The problem begins if a rapid nose push is done with cyclic without power reduction, causing a sudden decrease in the vertical component of the climb thus reducing the G. It can go negative when the apex is crossed and goes downward, Now all that remains is the horizontal component of thrust, which begins to cause a rapid loss of lift due to the decreased AOA, and depending on the high thrust line offset of the gyro, the tumble begins.

The way to avoid the loss of G at the top of the zoom is to either do a high banked turn at the top or simply reduce throttle without pushing the nose.


hi Tony
I think I get everything you are saying. Certainly parabolic flight is just one classic way of certainly producing low G. The zoom climb is another possibility. As I mentioned before and Chuck has also mentioned if the thrust is enough it’s actually possible to unload the rotor while in cockpit G seems normal because the thrust has started carrying significant portion the weight of the gyro against gravity. In a zoom climb this is also possible. You are flying a 915 now on your AR-1. Even though you are using a warp drive, I can tell you the static thrust is going to be close to 580 pounds which applies almost fully as the speed slows down. So be careful.

Greg and Chris built their new AR-1 with an Edge Performance 155 hp modified 912 engine. It’s even higher performance because it’s also 30 pounds lighter than 915 and has 15 more HP. He sees sustained 2000 fpm climb rates one up at sea level
 
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anthom

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Yes Abid, I agree. I have since stopped doing such aggressive maneuvers, nor do I teach them. I only use enough power as required to establish a sustained climb.
 

Philbennett

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Yep and I think this is the very point Tony, in the end flight instructors are teaching a pilot course not theorising about aerodynamics. I went to bed last night and wake up to 3 pages arguing the nuances.

It is important to give the student the correct information and be able to explain things accurately but fundamentally as far as low g and LOC is concerned I can think of few recent accidents where a "zoom climb" was reported as causal. However for those that were [usually in the past and usually connected to impromptu "displays"] the very thing to remember is that a gyroplane doesn't get shot out of a cannon it was flown there with suitable inputs of the controls - in which case if you continue to put in suitable inputs of control you don't get into a problem. One of the controls available is throttle and whilst we dance around the problem I don't know of a single flight instructor who doesn't know / understand or teach the need to close the throttle as a default in response to an inadvertent nose high situation.
 

Doug Riley

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A Dominator can be PIO'ed by a newbie. However, in scores of demo lessons that I've given in one at flyins, I've never had even a complete non-pilot porpoise the Dom WHILE POWER IS UP. The immersed H-stab simply damps out any pitch oscillations.

The time when the student can get behind the machine is when the throttle is closed -- say, on an idle-power approach. The short-span H-stab loses its effectiveness when the throttle is closed. Then the Dom reverts to flying more like a Bensen. That means more lag and a "rubbery" control response. PIO in these circumstances is not ideal, but it also is not likely to be lethal. The remedy is simply to hold the stick still.

We seem persistently to confuse the two issues associated with low G flight in gyros:

1. If the airframe is laid out in such a way that it departs from straight-line flight once rotor thrust is reduced, then we can get drag-over, PPO, torque-over and/or divergent slip-roll coupling (sideways drag-over). No designer should tolerate ANY of these behaviors, in my opinion. They are all preventable. They all make low-G flight more hazardous than need be. Rotor thrust should not be used to stabilize an otherwise unstable airframe in any axis.

2. Even if the airframe itself does track straight in low G, sustained low G results in a loss of RRPM. Losing a little RRPM is OK, losing a lot, in a teetering-rotor craft, results in a self-propagating retreating-blade stall. This, in turn, causes the familiar blade-tail and blade-prop collisions.

Starting with Bensen, the promoters of many gyro designs that have unstable airframes have managed to deflect blame. They've done so by focusing only on #2. I suspect (though our data are lousy) that many low-G-PPO/rollover crashes would not have happened if only some low-G RRPM loss, and not the airframe going berserk, had been involved. IOW, some would have flown out of it if not for poor airframe configuration.
 

hillberg

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Nose high - cruise - Something happens boom muscle memory kicks in . . . My two brother are fix wingers with a helicopter add on - They pause a moment the do whats needed. Fix wing issues? ADD POWER - GET NOSE DOWN!

They pause - others don't - and do the wrong thing

I don't pause I add a little aft cyclic and then lower collective as needed if any at all.

I don't like to fly fixed wing but when I do I pause.
 

Jean Claude

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A “G” meter typically measures acceleration rather than load about the vertical axis and therefore rotor load. If there was sufficient propeller thrust to do a vertical climb, the “G” meter would still read 1 G even though the rotor was completely unloaded and if the vertical climb could be maintained long enough, the rotor would come to a complete stop. “G” load is not a good measure of rotor load.
I don't think so, Chuck.
The G-meter of an aircraft is an indicator of the load factor of the wing: The measured G's are the component perpendicular to the orientation of the instrument.
Thus, when the aircraft is climbing vertically (i.e the instrument vertically oriented) then the indication is 0. While in inverted level flight, it indicates -1
To experience low to zero G, an object does not have to follow a parabolic trajectory.
I disagree.
A 0 g experiment in a uniform gravitational acceleration field always requires a parabolic trajectory.
This parabola is the consequence of a uniformly accelerated vertical velocity (-1G) necessary to follow the gravitation, and a constant horizontal velocity.
Give Vh and Vv any initial value, and the resulting trajectory will always be a parabola.

In an airplane, the engine thrust is adjusted to compensate exactly for aerodynamic drag, and everything happens as if it were a stone thrown into the void.
So just like it, the speed on this trajectory is not constant. It is uniformly accelerated downwards and only constant horizontally.
And G =0, even during the ascending part of the obtained path
Sans titre.png
 
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fara

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I don't think so, Chuck.
The G-meter of an aircraft is an indicator of the load factor of the wing: The measured G's are the component perpendicular to the orientation of the instrument.
Thus, when the aircraft is climbing vertically (i.e the instrument vertically oriented) then the indication is 0. While in inverted level flight, it indicates -1

I disagree.
A 0 g experiment in a uniform gravitational acceleration field always requires a parabolic trajectory.
This parabola is the consequence of a uniformly accelerated vertical velocity (-1G) necessary to follow the gravitation, and a constant horizontal velocity.
Give Vh and Vv any initial value, and the resulting trajectory will always be a parabola.

In an airplane, the engine thrust is adjusted to compensate exactly for aerodynamic drag, and everything happens as if it were a stone thrown into the void.
So just like it, the speed on this trajectory is not constant. It is uniformly accelerated downwards and only constant horizontally.
And G =0, even during the ascending part of the obtained path

Jean:
I think I understand your points. G definitely goes low and can even reach 0 depending on what happens and what pilot inputs are in a zoom climb and levelling from a zoom climb. Are you saying that even though zoom climb is not a complete parabola it still follows a parabolic trajectory. Could you clarify if that is what you are meaning to say partly here
 
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fara

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Jean:
I think I understand your points. G definitely goes low and can even reach 0 depending on what happens and what pilot inputs are in a zoom climb and levelling from a zoom climb. Are you saying that even though zoom climb is not a complete parabola it still follows a parabolic trajectory. Could you clarify if that is what you are meaning to say partly here

Jean. Never mind you added or edited to your initial comment and that clarifies it.
 

Vance

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This is the G meter in The Predator after an air show including a zoom climb and steep turns.

The tell tails indicates a maximum of 2.1 Gs and a minimum of .6 G.

Anytime I am flying a straight line at a constant speed it will show 1 G.

A curved path in any direction is acceleration and will affect the G meter.

Simply slowing down barely moves the needle.

The maximum rotor speed I saw was 450 rotor rpm and the minimum was 275 rotor rpm.

In my opinion if I had continued in a parabolic curve over the top I would have seen less rotor rpm. The rotor on The Predator does not respond instantly to a change in Gs.
 

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GyroPaul

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So an aircraft would need multiple G meters to capture additional data? Imagine a jet going strait up with the pilot experiencing 2 G but the lift component of the wing could be 0 G. Same pilot doing a tight turn might experience 3 G that could match the wing load, right? Different way to measure G forces?
 

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The measurement could be on different axes. If you picture a Formula 1 race driver, stomping on the gas or the brake will push the driver into the seatback or against the belts, while hard cornering produces lateral g-force that shoves your head and helmet side-to-side.
 

Jean Claude

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Jean:
I think I understand your points. G definitely goes low and can even reach 0 depending on what happens and what pilot inputs are in a zoom climb and levelling from a zoom climb. Are you saying that even though zoom climb is not a complete parabola it still follows a parabolic trajectory. Could you clarify if that is what you are meaning to say partly here
Sorry, my translator knows not "zoom clim". Can you explain to me ? Thank you
 

XXavier

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Sorry, my translator knows not "zoom clim". Can you explain to me ? Thank you

I'm a bit surprised with this discussion... An object in free fall (zero g) does always follow a parabolic trajectory. That, in the absence of air resistance and if the gravitational field is uniform and parallel... In the real world, it's always an approximation to a parabola, but a good one, provided the airspeed is not too high...
 
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