Negative Gs?

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
15,593
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2200+ in rotorcraft
I read in many threads on the Rotary Wing Forum that negative Gs should be avoided in a gyroplane.

It is my understanding that Gs (gravity) is about acceleration.

I find it easy to see how a fixed wing can achieve negative Gs because its wing will work in either direction and the aircraft can be accelerated down ward. I have been in a fixed wing in turbulence and had to tighten my seat belt to keep from hitting the roof with my head.

It is hard for me to understand how a gyroplane can accelerate downward faster than gravity (thirty two feet per second per second).

I had a G meter on both The Predator and Puff and I was not able to get much below .6 Gs or much above two Gs even in what I felt were very aggressive maneuvers in either aircraft. The results were surprisingly (to me) similar for such different gyroplanes.

I would like to understand what sequence of control inputs would cause a gyroplane to fly to negative Gs.

I agree that negative Gs should be avoided and it would help me to understand what to avoid.
 

Attachments

Texasautogyro

Gyro Master Instructor
Joined
Aug 23, 2011
Messages
1,751
Location
Tomball Texas
Aircraft
AutoGyro MTO Sport/Cessna 172
Total Flight Time
3800 with over 1900 in gyro
Vance I totally agree with you. In my MTO the most aggressive turn only put out about 2.6 on my G meter. This was a full deflection turn at 90 knots. I do see how you can go negative on a very abrupt zoom climb with full stick forward push. This could certainly go negative. This happens because the gyro will continue on it's path upward while you are trying to deflect the disk to a nose over or downward motion. This reverses airflow and is commonly referred to as a bunt over.
 
Last edited:

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
15,593
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2200+ in rotorcraft
I do see how you can go negative on a very abrupt zoom climb with full stick forward push. This could certainly go negative. This happens because the gyro will continue on it's path upward while you are trying to deflect the disk to a nose over or downward motion. This reverses airflow and is commonly referred to as a bunt over.
Thank you Desmon.

I am trying to follow along and don’t understand how the rotor can provide negative lift long enough to accelerate the gyroplane downward.

I would like to understand how that works.
 

XXavier

Member
Joined
Nov 13, 2006
Messages
863
Location
Madrid, Spain
Aircraft
FW Savannah XL + ELA R-100 and Magni M24 autogyros
Total Flight Time
1391 FW + 497 gyro (Aug. 2019)
I read in many threads on the Rotary Wing Forum that negative Gs should be avoided in a gyroplane.

It is my understanding that Gs (gravity) is about acceleration.

I find it easy to see how a fixed wing can achieve negative Gs because its wing will work in either direction and the aircraft can be accelerated down ward. I have been in a fixed wing in turbulence and had to tighten my seat belt to keep from hitting the roof with my head.

It is hard for me to understand how a gyroplane can accelerate downward faster than gravity (thirty two feet per second per second).

I had a G meter on both The Predator and Puff and I was not able to get much below .6 Gs or much above two Gs even in what I felt were very aggressive maneuvers in either aircraft. The results were surprisingly (to me) similar for such different gyroplanes.

I would like to understand what sequence of control inputs would cause a gyroplane to fly to negative Gs.

I agree that negative Gs should be avoided and it would help me to understand what to avoid.
Imagine that you are in an ascending lift moving at a constant velocity, and that, at a given moment, the lift stops. It does it by reducing its velocity to zero within a given timespan. If that reduction of velocity takes place at a rate of less than 9,8 m/s every second, you would feel a reduction of your own weight, and if the lift brakes at a rate of more than 9,8 m/s every second, you will feel a 'negative weight', since the mass of your body would be subjected to a negative acceleration of a value higher than the acceleration of gravity. Hence, the net acceleration acting on your body is negative, and you are in 'negative g's'.

A similar thing would happen in the case of an aircraft moving upwards that slows down, reducing its vertical velocity...
 
Last edited:

XXavier

Member
Joined
Nov 13, 2006
Messages
863
Location
Madrid, Spain
Aircraft
FW Savannah XL + ELA R-100 and Magni M24 autogyros
Total Flight Time
1391 FW + 497 gyro (Aug. 2019)
Thank you Desmon.

I am trying to follow along and don’t understand how the rotor can provide negative lift long enough to accelerate the gyroplane downward.

I would like to understand how that works.
No need to have negative lift. You are moving upwards at a given velocity thanks to the 'pull' of the rotor. If that pull slackens, the vertical velocity will decrease, and a -negative- acceleration appears.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
15,593
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2200+ in rotorcraft
Imagine that you are in an ascending lift moving at a constant velocity, and that, at a given moment, the lift stops. It does it by reducing its velocity to zero within a given timespan. If that reduction of velocity takes place at a rate of less than 9,8 m/s every second, you would feel a reduction of your own weight, and if the lift brakes at a rate of more than 9,8 m/s every second, you will feel a 'negative weight', since the mass of your body would be subjected to a negative acceleration of a value higher than the acceleration of gravity. Hence, the net acceleration acting on your body is negative, and you are in 'negative g's'.

A similar thing would happen in the case of an aircraft moving upwards that slows down, reducing its vertical velocity...
It appears to me you are using a different definition of negative G then I am.

Please help me understand what your definition of a negative is Javier.

In my definition of negative Gs the aircraft needs to accelerate downward faster than if I fell out (thirty two feet per second per second). I feel this would require negative lift.

Put another way; at one G I weigh 240 pounds, at .6 Gs I weigh 144 pounds and at zero Gs I weigh nothing.

At negative Gs I would accelerate out of the aircraft unless I was restrained.
 

XXavier

Member
Joined
Nov 13, 2006
Messages
863
Location
Madrid, Spain
Aircraft
FW Savannah XL + ELA R-100 and Magni M24 autogyros
Total Flight Time
1391 FW + 497 gyro (Aug. 2019)
It appears to me you are using a different definition of negative G then I am.

Please help me understand what your definition of a negative is Javier.

In my definition of negative Gs the aircraft needs to accelerate downward faster than if I fell out (thirty two feet per second per second). I feel this would require negative lift.

Put another way; at one G I weigh 240 pounds, at .6 Gs I weigh 144 pounds and at zero Gs I weigh nothing.

At negative Gs I would accelerate out of the aircraft unless I was restrained.
You have 'negative Gs' when the balance [gravitational acceleration/negative acceleration caused by change in velocity] is negative.

Imagine you are moving upwards in a rocket, within the atmosphere, and that the rocket engine suddenly stops. The air drag will slow down the rocket, inducing a negative acceleration in your body. If that negative acceleration has a higher value than 9,8 m/s2, then you'll hit the roof... (If unrestrained...).

In the case of a gyro, suppose you are flying in ascending flight, that is, with a given vertical component, and if you reduce the vertical velocity (by closing the throttle, or by easing the stick forward) a negative acceleration will appear, because you are moving within the atmosphere, and forces (vertical lift - vertical drag) cease to be balanced. While they were, during the ascending flight at constant velocity, no acceleration existed, either positive or negative, but if you reduce the lift, drag does -momentarily- prevail, the ascending velocity decreases, and a negative acceleration will appear...
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
15,593
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2200+ in rotorcraft
The source of the divergence of opinion?

The source of the divergence of opinion?

You have 'negative Gs' when the balance [gravitational acceleration/negative acceleration caused by change in velocity] is negative.

Imagine you are moving upwards in a rocket, within the atmosphere, and that the rocket engine suddenly stops. The air drag will slow down the rocket, inducing a negative acceleration in your body. If that negative acceleration has a higher value than 9,8 m/s2, then you'll hit the roof... (If unrestrained...).

In the case of a gyro, suppose you are flying in ascending flight, that is, with a given vertical component, and if you reduce the vertical velocity (by closing the throttle, or by easing the stick forward) a negative acceleration will appear, because you are moving within the atmosphere, and forces (vertical lift - vertical drag) cease to be balanced. While they were, during the ascending flight at constant velocity, no acceleration existed, either positive or negative, but if you reduce the lift, drag does -momentarily- prevail, the ascending velocity decreases, and a negative acceleration will appear...
I would define what you are describing as less than one G rather than negative Gs Javier.

On the G meter pictured they have a scale for negative Gs. It goes to -.75Gs where I would be pulling on my seat belt 180 pounds because the aircraft would be accelerating downward faster than I would accelerate in free fall.

I wonder if people who say to avoid negative Gs in a gyroplane are using your definition of a negative G (anything less than one G).
 

Attachments

XXavier

Member
Joined
Nov 13, 2006
Messages
863
Location
Madrid, Spain
Aircraft
FW Savannah XL + ELA R-100 and Magni M24 autogyros
Total Flight Time
1391 FW + 497 gyro (Aug. 2019)
No... If you are in ascending flight and slow it down, (the vertical component of) drag may prevail momentarily over (the vertical component of) lift. If that is the case, and for a few moments, until forces get equalized again, the balance of forces vertical drag/vertical lift will point downwards, and you'll have negative acceleration.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
15,593
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2200+ in rotorcraft
No... If you are in ascending flight and slow it down, (the vertical component of) drag may prevail momentarily over (the vertical component of) lift. If that is the case, and for a few moments, until forces get equalized again, the balance of forces vertical drag/vertical lift will point downwards, and you'll have negative acceleration.
In my opinion what you describe would not fit my definition of a negative G; even temporarily Javier.

Negative acceleration yes but not strong enough acceleration to achieve negative Gs.
 

XXavier

Member
Joined
Nov 13, 2006
Messages
863
Location
Madrid, Spain
Aircraft
FW Savannah XL + ELA R-100 and Magni M24 autogyros
Total Flight Time
1391 FW + 497 gyro (Aug. 2019)
A good way of visualizing all this is the example of the slowing-down lift. We may add air drag to see how a negative acceleration can be measured inside the lift.

Imagine that the lift moves upwards and slows down suddenly because the motor stops hauling it upwards. In the absence of air drag, or of any other braking force, such as mechanical friction of the lift with the rails, deceleration due to that slowdown can't exceed 9,8 m/s2, because if it did, the lift box, and all things inside it will start moving in 'free fall' (upwards, but free fall anyway).

But let's add a braking force, such as air drag. In that case, (upwards) free fall won't take place because that braking force will act downwards. As a result, anyone measuring acceleration inside the lift (duly fastened to it to impede another free fall...) will see a negative acceleration. Everyone inside will feel a 'negative weight' pulling him towards the roof...
 

XXavier

Member
Joined
Nov 13, 2006
Messages
863
Location
Madrid, Spain
Aircraft
FW Savannah XL + ELA R-100 and Magni M24 autogyros
Total Flight Time
1391 FW + 497 gyro (Aug. 2019)
In my opinion what you describe would not fit my definition of a negative G; even temporarily Javier.

Negative acceleration yes but not strong enough acceleration to achieve negative Gs.
That depend on the balance of forces [vertical component of lift/vertical component of drag] If the forces are balanced, there is no acceleration, and you are subjected to the Earth's gravitational field. The weight felt by your seat will be constant.

Now, let's suppose that lift increases suddenly. Drag will grow, and the forces will become balanced again. But, for the brief moment that [the vertical component of] lift prevails over [the vertical component of] drag, an upward acceleration will appear, and your seat will feel a higher weight. The excess will be exactly the mass of your body times the upward acceleration.

In the case that it is [the vertical component of] drag that prevails, things will be the other way round, and your seat will feel a smaller weight. But if the imbalance of forces is strong enough, if the [the vertical component of] drag overcomes [the vertical component of]lift, your seat will fell a 'negative weight', because the acceleration balance (gravitational/deceleration due to motion) will be negative...
 

eddie

RAF, turbo subaru 230hp
Joined
Jan 19, 2011
Messages
1,683
Location
Polvadera,nm 87828
Aircraft
230 HP turbocharged RAF
Total Flight Time
8,000 plus
I have a question concerning negative G force,the NASA jet is making a nose over

descending flight, the people in back are floating in air,is it a true negative act or just less

than 1 G. Its something I have always wondered about.



Best regards,
 

Stan V

Newbie
Joined
Jan 23, 2011
Messages
1,271
Location
Monticello, GA
Aircraft
Piper Arrow/RAF2000
Total Flight Time
450
I have a question concerning negative G force,the NASA jet is making a nose over

descending flight, the people in back are floating in air,is it a true negative act or just less

than 1 G. Its something I have always wondered about.



Best regards,
Not negitive, but 0 G
 

XXavier

Member
Joined
Nov 13, 2006
Messages
863
Location
Madrid, Spain
Aircraft
FW Savannah XL + ELA R-100 and Magni M24 autogyros
Total Flight Time
1391 FW + 497 gyro (Aug. 2019)
I have a question concerning negative G force,the NASA jet is making a nose over

descending flight, the people in back are floating in air,is it a true negative act or just less

than 1 G. Its something I have always wondered about.



Best regards,
The 'vomit comet' follows a carefully planned trajectory so that every object inside the plane behaves as in free fall. It is an (approximately) parabolic trajectory. Zero Gs.

Were it not for the air drag, if we shoot a shell, it will follow an (approximately) parabolic trajectory, and anyone inside the shell will experiment zero weight during that trajectory, as they will be in free fall...

The pilots of the 'vomit comet' try to duplicate the flight of that shell, using engine thrust to compensate for the deceleration induced by air drag.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
15,593
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2200+ in rotorcraft
I have a question concerning negative G force,the NASA jet is making a nose over

descending flight, the people in back are floating in air,is it a true negative act or just less

than 1 G. Its something I have always wondered about.



Best regards,
In my opinion that is zero Gs Eddie.

Negative Gs would have them run into the ceiling unless they were restrained.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
15,593
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2200+ in rotorcraft
That depend on the balance of forces [vertical component of lift/vertical component of drag] If the forces are balanced, there is no acceleration, and you are subjected to the Earth's gravitational field. The weight felt by your seat will be constant.

Now, let's suppose that lift increases suddenly. Drag will grow, and the forces will become balanced again. But, for the brief moment that [the vertical component of] lift prevails over [the vertical component of] drag, an upward acceleration will appear, and your seat will feel a higher weight. The excess will be exactly the mass of your body times the upward acceleration.

In the case that it is [the vertical component of] drag that prevails, things will be the other way round, and your seat will feel a smaller weight. But if the imbalance of forces is strong enough, if the [the vertical component of] drag overcomes [the vertical component of]lift, your seat will fell a 'negative weight', because the acceleration balance (gravitational/deceleration due to motion) will be negative...
I have felt lighter in the seat flying a gyroplane.

I have not needed to be restrained to keep from leaving the seat.

The G meter at .6 Gs indicates to me I felt 144 pounds in the seat of my pants.

I was at the top of a zoom climb.

I feel this is a long way from negative Gs and I don't know what control inputs would produce negative Gs in a gyroplane.
 

phantom

Newbie
Joined
Apr 1, 2009
Messages
1,417
Location
Eagle River
I have been caught in very rough air three times in a gyro and the only thing that kept me in the seat was the seatbelt , I know this because one of the machines had a full cabin that was framed with angle aluminum , one of the angles was right over my head and about eight inches above and my seatbelt was loose enough for me to be able to turn in my seat to operate the clutch for the prerotator in the top of the cabin behind me, when it got rough I didn't tighten the seat belt and I wacked my head on the angle hard enough to raise a bump but it didn't cut me, after that flight I glued some split rubber water hose over the angle.
Norm
 

dabkb2

Dave Bacon
Joined
Sep 26, 2005
Messages
2,188
Location
Vista, Ca
Aircraft
2 KB2 90Mac KB3 582
Total Flight Time
289 hours
Vance, I do not think this will answer your question about what control inputs will cause a negative G, but I think the danger in a gyro comes if you reverse the airflow through the blade.
 
Top