0 G flight condition

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
It is obvious on this forum from comments etc. that many gyroplane pilots as well as CFIs don't talk about or even possibly fully understand the low to 0 G flight conditions that are without a doubt death sentence in a 2 bladed rotor system or even in weight shift trikes. Both these categories of aircraft have had their share of low G bunts, tumbles etc. Both suffered from gaining pilot population from airplane pilots who had the wrong response at the wrong time built into their muscle memory. Trikes have improved their record slowly with increasing training and specific training subjects around different ways that can get the pilot into trouble. Hopefully gyroplanes will catch up in reducing this kind of accident.

I wanted to simply start this specific discussion with parabolic flight which we all know is the classic example or way of creating freefall or sensation of 0 G.
First some facts.
You do not have to go to negative G to lose control
You don't even have to get to full 0 G to lose control.
You only need to get to low enough G to start to lose control and any sustained period of low G will create problems that are unrecoverable.

However, these just don't happen without pilot input unless you are flying in some severe turbulence like in a thunderstorm etc.

The biggest misconception among many pilots and even CFIs is that to create zero G you have to push the nose down from a steep climb up and then you get to zero G.
WRONG!

You get to zero G on your steep climb up, remain in zero G in the pushover phase and continue in zero G into the initial sharp descent.
The very beginning of the sharp climb up is where you can experience high G (1.5 to 1.8 Gs) and while you are still going upwards you begin to go towards low G and get to zero G while still heading up.

"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"

0-G-Path.jpg

Unless this simple fact is understood by all pilots and CFIs and actually conveyed to the students during training, the zoom climb showoff maneuvers that you see are not understood to have the danger that puts you right on the edge. The perceptive pilots know how to do the zoom climb without getting themselves in danger. Some of them (including me) also did not or do not know this fact but we are quick to perceive in our seats that things are starting to go the other way and do something to load the aircraft (which usually means make a banked coordinated turn). I certainly was not taught any of this in trike ground school by my BFI/AFI because he had no clue either but I did intuitively understand and feel that this was wrong and always either stopped the zoom climb smoothly or converted it to a sort of wing over keeping G forces. God knows I must have done 100's of zoom climbs smoothly and safely before I ever understood this and knew where I was going when doing these zoom climbs. Being a high time trike pilot/CFI and test pilot and a curious person I then had to find stuff to study what is actually happening in this parabolic flight and thankfully there are many things available to read about it. The math is there but that is not we as pilots have to really care about. We just have to conceptually understand where we get to 0 G because the popular belief is its on the down low.

This is why you will see comments from experienced gyroplane CFIs on some bunt over accident videos saying something to the effect of, well the pushover is not so drastic but he definitely lost control. Its simply because he was at zero G before he ever pushed over. There is a famous video from Japan of a bunt over where this probably applies in spades.

Here is the link to an article from where I have captured this picture. Hope this will help CFIs and pilots alike in discussing this subject during ground briefings. Again the understanding of the math is less important than understanding of the concept and what is generally happening.

 
Last edited:

anthom

Member
Joined
Mar 20, 2011
Messages
1,081
Location
Texas
Aircraft
AR1, Aviomania Genesis Sport
Total Flight Time
3500
Good article.
One can experience it in severe turbulence and sudden sustained downdrafts. Flying in the vicinity of large cumiliform clouds, mountain flying and abrupt maneuvers are hidden gremlins waiting to get the unwary. Quick throttle and speed reduction when encountering such situations help. Good sizable horizontal stabilizers with good tail volume help. Rotor loading with back cyclic or banking is recommended. The importance of Ground instruction is a must.
 

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
Good article.
One can experience it in severe turbulence and sudden sustained downdrafts. Flying in the vicinity of large cumiliform clouds, mountain flying and abrupt maneuvers are hidden gremlins waiting to get the unwary. Quick throttle and speed reduction when encountering such situations help. Good sizable horizontal stabilizers with good tail volume help. Rotor loading with back cyclic or banking is recommended. The importance of Ground instruction is a must.

Yes exactly. I am certainly not teaching my primary student to do zoom climbs and finish it with a levelling out coordinating throttle and pitch rotation such that you don't go below 0.7 G or finish it with a wing over. That isn't happening. But I can certainly teach him the importance of flying an attitude in pitch and keeping it steady or discuss with him in ground discussion what the dangers are building excessive speed horizontally and just letting it go to do a zoom climb without care for what it may bring when it accelerates down quickly to the top.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,570
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
It is obvious on this forum from comments etc. that many gyroplane pilots as well as CFIs don't talk about or even possibly fully understand the low to 0 G flight conditions that are without a doubt death sentence in a 2 bladed rotor system or even in weight shift trikes. Both these categories of aircraft have had their share of low G bunts, tumbles etc. Both suffered from gaining pilot population from airplane pilots who had the wrong response at the wrong time built into their muscle memory. Trikes have improved their record slowly with increasing training and specific training subjects around different ways that can get the pilot into trouble. Hpefully gyroplanes will catch up in reducing this kind of accident.

I wanted to simply start this specific discussion with parabolic flight which we all know is the classic example or way of creating freefall or sensation of 0 G.
First some facts.
You do not have to go to negative G to lose control
You don't even have to get to full 0 G to lose control.
You only need to get to low enough G to start to lose control and any sustained period of low G will create problems that are unrecoverable.

However, these just don't happen without pilot input unless you are flying in some severe turbulence like in a thunderstorm etc.

The biggest misconception among many pilots and even CFIs is that to create zero G you have to push the nose down from a steep climb up and then you get to zero G.
WRONG!

You get to zero G on your steep climb up, remain in zero G in the pushover phase and continue in zero G into the initial sharp descent.
The very beginning of the sharp climb up is where you can experience high G (1.5 to 1.8 Gs) and while you are still going upwards you begin to go towards low G and get to zero G while still heading up.

"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"

View attachment 1150821

Unless this simple fact is understood by all pilots and CFIs and actually conveyed to the students during training, the zoom climb showoff maneuvers that you see are not understood to have the danger that puts you right on the edge. The perceptive pilots know how to do the zoom climb without getting themselves in danger. Some of them (including me) also did not or do not know this fact but we are quick to perceive in our seats that things are starting to go the other way and do something to load the aircraft (which usually means make a banked coordinated turn). I certainly was not taught any of this is in trike ground school by my BFI/AFI because he had no clue either but I did intuitively understand and feel that this was wrong and always either stopped the zoom climb smoothly or converted it to a sort of wing over keeping G forces. God knows I must have done 100's of zoom climbs smoothly and safely before I ever understood this and knew where I was going when doing these zoom climbs. Being a high time trike pilot/CFI and test pilot and a curious person I then had to find stuff to study what is actually happening in this parabolic flight and thankfully there are many things available to read about it. The math is there but that is not we as pilots have to really care about. We just have to conceptually understand where we get to 0 G because the popular belief is its on the down low.

This is why you will see comments from experienced gyroplane CFIs on some bunt over accident videos saying something to the effect of, well the pushover is not so drastic but he definitely lost control. Its simply because he was at zero G before he ever pushed over. There is a famous video from Japan of a bunt over where this probably applies in spades.

Here is the link to an article from where I have captured this picture. Hope this will help CFIs and pilots alike in discussing this subject during ground briefings. Again the understanding of the math is less important than understanding of the concept and what is generally happening.

A zoom climb is a well-known coffin corner of gyroplane flight and all of the CFIs I know explain its effects early in their training syllabus and return to it several times during the training.

I feel that a zoom climb can more accurately be portrayed as projectile motion https://en.wikipedia.org/wiki/Projectile_motion.

The thrust of the engine serves to unload the rotor further.

The top of a pilot induced oscillation has the same effect.

In my opinion your illustration would be more accurate if the reduced G was shown as beginning when the curve starts.

Parabola:
Noun
A symmetrical open plane curve formed by the intersection of a cone with a plane parallel to its side. The path of a projectile under the influence of gravity ideally follows a curve of this shape.

In my opinion there are no straight lines in a parabolic curve.
 

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
A zoom climb is a well-known coffin corner of gyroplane flight and all of the CFIs I know explain its effects early in their training syllabus and return to it several times during the training.

I feel that a zoom climb can more accurately be portrayed as projectile motion https://en.wikipedia.org/wiki/Projectile_motion.

The thrust of the engine serves to unload the rotor further.

The top of a pilot induced oscillation has the same effect.

In my opinion your illustration would be more accurate if the reduced G was shown as beginning when the curve starts.

Parabola:
Noun
A symmetrical open plane curve formed by the intersection of a cone with a plane parallel to its side. The path of a projectile under the influence of gravity ideally follows a curve of this shape.

In my opinion there are no straight lines in a parabolic curve.

That illustration is actually from that article I cited
 

hillberg

Super Member
Joined
May 24, 2010
Messages
2,732
Location
Low Earth Orbit
In a MD 500 Sikorsky S 58 or a Bell 407types you can do [not legally]- low Gs loops rolls and push overs. Just not too much to avoid droop stop pounding.

Bell Hueys Hillers Robinsons and Jet Rangers it's a fast way to die when the rotors are unloaded.

Offset flapping hinges force a mast moment into the fuselage directing the helicopter to go... teetering hubs do not.

Under slung two bladed heads have the machine hanging the mass follows the rotors thrust as it hangs below.
in low G the rotors can't force the mast moment to the machine below - the controls aim the rotors the machines mass doesn't follow, inertia continues to influence the fuselage. Mast bump happens and the head leaves for its own adventure - In all the helicopter I've flown it's a no brainer to keep things loaded. and the aft pressure to remove that light feeling to come.
In the OH 58 we used to go NOE and instead of forward cyclic to follow the ground we'd roll in a turn "diving" into the contour of the slope.
No low G's allowed.

I'm amazed at the Sport Copter test pilot doing loops and rolls all positive Gs.

I'm a fan of Helicopter aerobatics - Chuck Arron finishing his act at 200 feet was breath taking. And the all big manufactures test flight footage too.
 

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
In a MD 500 Sikorsky S 58 or a Bell 407types you can do [not legally]- low Gs loops rolls and push overs. Just not too much to avoid droop stop pounding.

Bell Hueys Hillers Robinsons and Jet Rangers it's a fast way to die when the rotors are unloaded.

Offset flapping hinges force a mast moment into the fuselage directing the helicopter to go... teetering hubs do not.

Under slung two bladed heads have the machine hanging the mass follows the rotors thrust as it hangs below.
in low G the rotors can't force the mast moment to the machine below - the controls aim the rotors the machines mass doesn't follow, inertia continues to influence the fuselage. Mast bump happens and the head leaves for its own adventure - In all the helicopter I've flown it's a no brainer to keep things loaded. and the aft pressure to remove that light feeling to come.
In the OH 58 we used to go NOE and instead of forward cyclic to follow the ground we'd roll in a turn "diving" into the contour of the slope.
No low G's allowed.

I'm amazed at the Sport Copter test pilot doing loops and rolls all positive Gs.

I'm a fan of Helicopter aerobatics - Chuck Arron finishing his act at 200 feet was breath taking. And the all big manufactures test flight footage too.

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
 
Last edited:

Philbennett

Junior Member
Joined
Aug 17, 2014
Messages
477
Location
London
There is a small but important caveat to that diagram and that is stick position- to fly that profile the pilot has to have either trimmed for zero g or actively moved the stick. You don’t fly that profile by accident is my point.
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
4,916
Location
Colorado front range
Aircraft
Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
Total Flight Time
stopped caring at 1000
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
In the US there is no such thing as an acro license for any category/class. What is available is just a low altitude waiver from the normal FAR location/alt limits. If you have the urge you can try it yourself above 1500, off airways, and away from crowds, in VMC.
Somewhere I have an old videotape (converted PAL to NTSC) of a military helo acro competition, held in Italy as I recall. Lots of Bo-105 action and some Augusta Westland.
 

hillberg

Super Member
Joined
May 24, 2010
Messages
2,732
Location
Low Earth Orbit
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
Wrong I've been with Chuck at Camarillo
It's a stock MBB 105 airframe and the removal of excess weight and a battery move is all is has. You are wrong on all counts
 

Philbennett

Junior Member
Joined
Aug 17, 2014
Messages
477
Location
London
To add the comments on the Japanese pilot low g are to highlight exactly the point that you don’t need aggressive manoeuvres to create an issue - almost all people do not enjoy zero g flight and so are unlikely to fly the upward part of the curve. The more likely scenario that catches fixed wing pilots is the climb, high nose attitude and lowering airspeed causing a sudden forward stick response. It is likely in the climb that the stick is held at 1g for most. In the Japanese accident and his “display” the dive for spee and zoom climb didn’t cause the issue - it would be the progressive and steady forward stick to create a push off the top or intension to level out that is more likely the cause of his low g.
 

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
Wrong I've been with Chuck at Camarillo
It's a stock MBB 105 airframe and the removal of excess weight and a battery move is all is has. You are wrong on all counts

So his is a complete stock helicopter? That is strange. The Oshkosh announcers must have been smoking JBird's product then. But then again he points to modifications as well


Anyway, you were with him so you must know better. I certainly have not talked to him personally about it and this is a tangent to this thread.
 

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
In the US there is no such thing as an acro license for any category/class. What is available is just a low altitude waiver from the normal FAR location/alt limits. If you have the urge you can try it yourself above 1500, off airways, and away from crowds, in VMC.
Somewhere I have an old videotape (converted PAL to NTSC) of a military helo acro competition, held in Italy as I recall. Lots of Bo-105 action and some Augusta Westland.

You are correct. Wrong word to use. Its not a license but he was indeed was evaluated on behalf of FAA by Rich Lee (Boeing) in the modified helicopter to get his "all-attitude" SAC stunt performance clearance in the US back then
 
Last edited:

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
To add the comments on the Japanese pilot low g are to highlight exactly the point that you don’t need aggressive manoeuvres to create an issue - almost all people do not enjoy zero g flight and so are unlikely to fly the upward part of the curve. The more likely scenario that catches fixed wing pilots is the climb, high nose attitude and lowering airspeed causing a sudden forward stick response. It is likely in the climb that the stick is held at 1g for most. In the Japanese accident and his “display” the dive for spee and zoom climb didn’t cause the issue - it would be the progressive and steady forward stick to create a push off the top or intension to level out that is more likely the cause of his low g.

Its hard to say with certainty but in a pitch up at some point the deceleration is happening and it is taking us down towards low G.
The main point or push is that its not negative G and its not always the pushover that creates the problem. The problem starts ahead of that at the last stages of climb out. Even if its reaching 0 G, low G is sustained from that point forward, continuing during pushover and descent. That is a few seconds. Plenty of time for rotors to get in danger zone
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,570
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
That illustration is actually from that article I cited
I knew that.

It doesn't matter where it is from, in my opinion it is wrong.

In my opinion there are no straight lines in a parabolic curve.
 

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,660
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
I knew that.

It doesn't matter where it is from, in my opinion it is wrong.

In my opinion there are no straight lines in a parabolic curve.

Ok. No one in that article suggested there are straight lines in a parabola but obviously the start of the maneuvering is via gaining horizontal speed first. Why exactly do you opine that its wrong. What specifically did they show in the article that is wrong?
 

hillberg

Super Member
Joined
May 24, 2010
Messages
2,732
Location
Low Earth Orbit
So his is a complete stock helicopter? That is strange. The Oshkosh announcers must have been smoking JBird's product then. But then again he points to modifications as well


Anyway, you were with him so you must know better. I certainly have not talked to him personally about it and this is a tangent to this thread.
Chuck was based at Camarillo Airport That helicopter is stock - Battery moved for C/G , Aux fuel tank and the interior removed, Chuck would visit the Air Unit and drop off flats of Red Bull, He's a number one showman and we'd watch him over at the Little Red School house near Santa Paula.

His hangar was on the East end next to Steves Turbine Exec project and we would often shoot the breeze. When I asked about the mods he'd smile a funny grin and say "We moved the battery" It adds to the show. His toughest part was getting the FAA to accept the TCDS as it was authorized for the Aerobatic flight in the MBB 105 and his first complete loop.

No flapping or drag hinges on the MBB

That helicopter was as clean as the Air Units - A great example to taking care of business. A shame he retired to Florida after family issues.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,570
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
Ok. No one in that article suggested there are straight lines in a parabola but obviously the start of the maneuvering is via gaining horizontal speed first. Why exactly do you opine that its wrong. What specifically did they show in the article that is wrong?
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

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,570
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
To add the comments on the Japanese pilot low g are to highlight exactly the point that you don’t need aggressive manoeuvres to create an issue - almost all people do not enjoy zero g flight and so are unlikely to fly the upward part of the curve. The more likely scenario that catches fixed wing pilots is the climb, high nose attitude and lowering airspeed causing a sudden forward stick response. It is likely in the climb that the stick is held at 1g for most. In the Japanese accident and his “display” the dive for spee and zoom climb didn’t cause the issue - it would be the progressive and steady forward stick to create a push off the top or intension to level out that is more likely the cause of his low g.
In my opinion based on my observations a typical gyroplane in a zoom climb will level off on its own as the gyroplane runs out of energy and indicated air speed.

The gyroplane in the video had a high thrust line in relation to the center of gravity so at wide open throttle as rotor thrust is lost it wants to bunt over on its own.

I feel it is important to understand that the problem is unloading the rotor rather than specific cyclic inputs.
 

Resasi

Gold Supporter
Joined
Jul 2, 2007
Messages
8,023
Location
London/ Kilifi Kenya
Aircraft
Gyrs, RAF 2000/Mgni/Bnsn/Hrnet/Mrlin/Crckt/MT-03/Lyzlle AV18-A/Prdtor. Pax ArrowCopter
Total Flight Time
100+ gyro, 16,000+ other
Quibbling aside, it is my perception the Fara’s initial post highlights a hugely important point, that has until recently been tragically misunderstood, or indeed never perceived as a huge danger zone by a large percentage of gyro pilots.
 
Top