Negative Gs?

C. Beaty

Gold Supporter
As a guestimate, I expect that a typical tandem EuroBensen has a pitch axis moment of inertia (MOI) of about double its roll axis MOI.

The pitch axis tumbling moment, propeller thrust x CG offset, is probably in the range of 150 ft-lb. (300 lb. thrust x 6” offset). And of course, a horizontal stab can resist that as long as there’s sufficient airspeed for it to do so.

The roll axis torque is perhaps 200 ft-lb. so that torqueover rate of acceleration is 2.67 times as great as pitchover rate of acceleration with a non-flying horizontal stab.

It can roll over in a heartbeat as many have done so.

No one is arguing against horizontal stabilizers; a horizontal stabilizer can provide angle of attack stability even with thrustline offset. To do so, the resultant of incremental lift change, rotor plus stab, must trail the CG. An upward gust must pitch the machine nose down, keeping it headed into the relative wind.

But it is far better to avoid the offsets.
 

fara

AR-1 gyro manufacturer
I'm posting an excerpt from the summary posted by Raghu in the thread referenced. It is the essence, and seems to be eluding you.

"11. It is important to do what ever to stay away from low g conditions. Irrespective of stability characteristics all teetering rotor gyros need to stay away from sustained low g conditions. Any more than a fraction of a second of neg G can be very detrimental."

If I inadvertently get into a situation of low G, all that it takes is a fraction of a second for getting into a bad situation. If I'm at WOT and experience a downdraft, my reaction is to reduce power first, which itself takes a couple of seconds. ( I do have the helicopter hours for this action to be drilled into me). So I have already lost a couple of seconds, and I realize that I am starting to get inverted. It then sinks home that my throttle is stuck. I'm inverted by now. I do not need to go on with the sequence of events....

How hard is it to include this feature in the manufacturing process for a machine that prevents this "roll over"?

IMHO, I just find it mind boggling that you as a manufacturer are trying to sabotage your own business.


Thomas:
First no you are not rolling over in any transient low G.
2 seconds is a hell of a time and is considered sustained. In turbulent situation even in mountain flying you will hardly come across downdrafts that big unless you deliberately fly into situations where it is expected to be very very nasty. Airplanes who can handle negative Gs don't even fly

Please read these. You are not remembering the whole thread by Raghu
http://vps.zoniehosting.com/~rotary/forum/showpost.php?p=561596&postcount=128

http://vps.zoniehosting.com/~rotary/forum/showpost.php?p=564388&postcount=320

Raghu's question to Birdy:
"So tell me birdy, you are flying straight and level at 30 mph in a gyro and suddenly you hit a perfectly calibrated downdraft and end up exactly in 0g. Your gyro is perfectly CLT, and you have no tail or pod so the airframe has no pitching tendencies with respect to AOA.

What happens next? More specifically what happens a second late"

Your own calculation on how much AoA will increase on the disc in just one second starting to reload this rotor and this is just CLT and without a tail from 0 G
http://vps.zoniehosting.com/~rotary/forum/showpost.php?p=562860&postcount=227

http://vps.zoniehosting.com/~rotary/forum/showpost.php?p=562064&postcount=167

I did not say anything about I am not providing "any" solution to torque rolling moment. I am just not giving the solution Chuck Beaty prescribes. He is a bit closed minded or ego controlled and sometimes well not so right. His idea of over indulgence on CLT as the pillar of static stability is not correct for instance. Raghu even proved that in that thread over low speed range calculations. There is nothing wrong with CLT and CLT, LTL and HTL machines can all have stability.

Chuck Beaty's question to Raghu:
"What happens, Raghu, in the lower airspeed range where the rotor is still flying but the horizontal stabilizer is not?

Do we still have AOA stability?"

Raghu's answer here:
http://vps.zoniehosting.com/~rotary/forum/showpost.php?p=561986&postcount=141
 

fara

AR-1 gyro manufacturer
No one is arguing against horizontal stabilizers; a horizontal stabilizer can provide angle of attack stability even with thrustline offset. To do so, the resultant of incremental lift change, rotor plus stab, must trail the CG. An upward gust must pitch the machine nose down, keeping it headed into the relative wind.

But it is far better to avoid the offsets.

Really Chuck:
Now this different because in thread to Raghu and many threads before that also you were questioning that at slow speeds HS will be ineffective in providing AoA stability for the fuselage.

http://vps.zoniehosting.com/~rotary/forum/showpost.php?p=561981&postcount=140

http://vps.zoniehosting.com/~rotary/forum/showpost.php?p=561986&postcount=141
Glad to see you have actually changed that position. Welcome to the club of how HTL can provide pretty good and effective pitch stability over a wide speed range, slow and fast.
 
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thomasant

Member
I'm done with this thread.

I'm reminded of some lines from Shakespeare's "Macbeth" that I had studied way back:

Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more. It is a tale
Told by an idiot, full of sound and fury
Signifying nothing.


;)
 

C. Beaty

Gold Supporter
This is silly, Fara.

You’re saying that a stalled stab can provide angle of attack stability?

Or even if not stalled but developing insufficient lift to keep incremental lift resultant behind the CG can provide angle of attack stability?

But propeller torque compensation is at least as important as pitchover resistance.

This is all about the promotion on your copy of a Magni copy.

Perhaps if Cierva had had you to advise him, he wouldn’t have wasted so much time designing a stable Autogiro.
 
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fara

AR-1 gyro manufacturer
This is silly, Fara.

You’re saying that a stalled stab can provide angle of attack stability?

Or even if not stalled but developing insufficient lift to keep incremental lift resultant behind the CG can provide angle of attack stability?

But propeller torque compensation is at least as important as pitchover resistance.

This is all about the promotion on your copy of a Magni copy.

Perhaps if Cierva had had you to advise him, he wouldn’t have wasted so much time designing a stable Autogiro.
Promotion of my gyro. Did you even see me post here much in the last 3 or 4 months before you started attacking a manufacturer before you even knew the sequence of events of a fatal accident?
I can't believe I am the one defending a German gyro. Does that sound like promotion of my Gyroplane?

So it's back to the stab is stalled. So Raghu wasted his time answering you, explaining why that works or the graph he posted. You never really cared for what he said there. You ignore factors that come into play, just look at airspeed and thus the stab must be stalled because there is nothing else like a rotor or anything else going on.
Yup. I am done too.
Someone like Raghu can spend his energy showing you the reason why field experience shows hardly any PPOs in Magni etc. and that doesn't make sense to you though multiple wind tunnel models point the same direction. I had told Raghu why he is bothering and his effort will go over some people and people like you and Birdy will never change their minds. I guess I was right about that.

You claim so many torque over accidents in Euro Bensens but you include Andy's accident which had the engine at idle and no torque. I have heard of one other accident in an MTO that was due to slip roll coupling but in the 4 years I have been here I have not heard of any others of either Magni or AG or even ELA.

Chuck this is about you and your beliefs regardless of studies, research scientists or statistics. You have in fact hijacked the issue for years and have a core following. Actual statistics, studies and the rest be damned. It has to match your thoughts or its not valid.
Have a happy holiday.
 
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hillberg

Newbie
How can anyone know if nobodies seen the whole video leading up to the crash?
(heard that the machine rolled right pitched forward then rolled left with left rudder)

Sounds like Hillarys take on Benghazi. . .
 

birdy

Newbie
"So how many engineering degrees do you hold my friend?"
Well well well, now thats music to my ears. :)
Yeh Muz, wot would you know, you dont have that pice o paper.
 

Murray Barker

Junior Member
You dont need a degree to understand basic physics.

Im sure if you put 5 AG1's and 5 Dominators together for sale to gyro newbies the AG1's would out sell the Dominators by a mile.
 
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eddie

RAF, turbo subaru 230hp
Murray your absolutely right the new modern gyro not only looks right, but it flys right,
contary to what all of the egocentric naysayers think or say, the new gyro has taken over
the market and will continue to do so.



Best regards,and happy new year,
 

Vance

Gyroplane CFI
I talked to a student pilot yesterday who has read this thread and he misunderstood the point I was trying to make completely so I felt I should give it another try.

The intent was twofold.

1) I feel that imagining that all I have to do is avoid negative gs to be safe in a gyroplane is a mistake leading to the impression that unless you are pulled down by the seat belt everything is fine.

It is my observation that a gyroplane in controlled flight won’t reach negative gs and imagining that was not debatable; I used it as a lead into describing what I perceive are the dangers of imagining negative gs are the problem. .

2) The understanding I was trying to address is I feel a low g event is to be avoided and tried to explain the dangers of a sustained .6 g condition; low rotor rpm and limited rotor authority. It appears I didn’t do it well.

I feel torque roll can also be a challenge in a low g event and I reduce power in The Predator in a low g event for that reason. I don’t know what there is to debate about that even though I see a lot of pages of words in this thread.

The student pilot asked me if smoothly pulling the cyclic back was the right thing to do. I feel it depends on how the low g event was achieved and I am more inclined to leave the cyclic neutral because of the reduced authority over the rotor I have in a low g event. If feel this is one of the challenges of a short answer.

The reason for the question mark at the end of the title was to find out if I had a solid foundation to build on. It appears to me I did not.

It appears based on the student’s response I need to rethink my approach to sharing the things I feel are important to safe gyroplane flight.
 
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bryancobb

Junior Member
Vance,

Try to stay in the simple realm when it comes to the physics of flying and it will serve you and your students well.
Simple ideas like ...
* Throw away the phrase "Negative-G's." A gyro will never go there.
* Replace it with "Low-G condition." A gyro will go there, and very quickly.
* There are many things that can occur in flight are a threat to a pilot's life, not just low-G condition.
* A gyroplane in controlled flight can & will get into a low-G condition
* A low-G condition does not have to be "sustained" to be dangerous
* Low rotor RPM is not the most significant thing to fear in a low-G condition. Teeter Stop Hitting IS! Torque rolling IS!
* In a low-G condition, re-loading the rotor SHOULD always be your goal. In almost all low-G events, gentle application of aft cyclic will do that.
* It is my opinion that you do not have a soild foundation upon which to build. It is my opinion that your understanding of rotary wing aerodynamics is flawed in a handful of key areas and until you open your mind and stop having the attitude that your understanding is already 100% correct, you may be teaching your students wrong information, and may not be be giving them the tools they need to safely react when something out of the ordinary happens in the air.
 

birdy

Newbie
Yeh Vance, keep it simple, to hell with reality.

* Throw away the phrase "Negative-G's." A gyro will never go there.
False.

* Replace it with "Low-G condition." A gyro will go there, and very quickly.
False

* There are many things that can occur in flight are a threat to a pilot's life, not just low-G condition.
Like, an ignorant pilot.

* A low-G condition does not have to be "sustained" to be dangerous
Depending on duation, how low, machine configuration and wot the pilot dose.

* Low rotor RPM is not the most significant thing to fear in a low-G condition. Teeter Stop Hitting IS! Torque rolling IS!
But it is the one efferct that can send sh1t to the fan.

* In a low-G condition, re-loading the rotor SHOULD always be your goal. In almost all low-G events, gentle application of aft cyclic will do that.
............ Ah, correct.

(Rain has set in ere, so expect more of my dribblen. ;) )
 

Vance

Gyroplane CFI
Vance,

* In a low-G condition, re-loading the rotor SHOULD always be your goal. In almost all low-G events, gentle application of aft cyclic will do that.
Thank you David, I finished writing a response and saw you had already responded.

I will post it any way. I feel it is a different way of saying the same thing.

We seem at odds about moving the cyclic back in a low g event so I would appreciate your thoughts on my response to specific low g situations.

Thank you for your help!
 

Vance

Gyroplane CFI
Vance,

Try to stay in the simple realm when it comes to the physics of flying and it will serve you and your students well.
Simple ideas like ...
* Throw away the phrase "Negative-G's." A gyro will never go there.
* Replace it with "Low-G condition." A gyro will go there, and very quickly.
* There are many things that can occur in flight are a threat to a pilot's life, not just low-G condition.
* A gyroplane in controlled flight can & will get into a low-G condition
* A low-G condition does not have to be "sustained" to be dangerous
* Low rotor RPM is not the most significant thing to fear in a low-G condition. Teeter Stop Hitting IS! Torque rolling IS!
* In a low-G condition, re-loading the rotor SHOULD always be your goal. In almost all low-G events, gentle application of aft cyclic will do that.
* It is my opinion that you do not have a soild foundation upon which to build. It is my opinion that your understanding of rotary wing aerodynamics is flawed in a handful of key areas and until you open your mind and stop having the attitude that your understanding is already 100% correct, you may be teaching your students wrong information, and may not be be giving them the tools they need to safely react when something out of the ordinary happens in the air.

I can’t throw away something that I don’t have. People on this forum are often suggesting that negative gs are dangerous.

One of the points of the thread is that low g events are dangerous.

In is my observation that a gyroplane does not reach low gs quickly unless it is a weather event.

Flying experimental gyroplanes is dangerous, I explain that every way I can to student pilots and try to find teachable moments in every flight lesson to explain what could have gone wrong and what we would do to manage it or avoid it. I am a ground school enthusiast and carefully explain many of the ways to get hurt or killed in a gyroplane. Part of the student pilots homework is reading and analyzing accident reports.

In my opinion the danger is a combination of how low for how long.

Low rotor rpm is a symptom of low gs. Low rotor rpm leads to flapping the blades and hitting the teeter stops and parts of the aircraft. It is not something to fear but rather something to avoid.

Fear takes the fun out of things for me and I have a low fear threshold.

I feel aft cyclic is not the always the way to reload the blades.
Because rotor thrust is reduced by the low g event and I have less cyclic control it may be a bad thing to move the cyclic in any direction. It depends on how the low g condition was reached.
If it was wind shear I would reduce power and wouldn’t move the cyclic back.
If I was the top of a zoom climb I would reduce power and wouldn’t move the cyclic back because moving the cyclic back is what precipitated the low g event.
If I was slow I would reduce power wouldn’t move the cyclic back.
If I had a lot of airspeed I would reduce power and I might pull the cyclic smoothly back.
Gravity will take care of things in a short term uncommanded low g event soon after I smoothly pull the power back.

I don’t pretend to understand gyroplane rotors Bryan and I am careful to explain that to students.

My mind is open Bryan and that is why I ask questions and carefully read the answers trying to relate it to my observations.

Thank you for your thoughtful advice Bryan. I am grateful you left helicopters out of this post.

I was explaining to my student yesterday that people like you help me to express things I might not otherwise have the opportunity or inclination to express. For example I probably would not have explained in such detail why moving the cyclic smoothly aft in a low g event may not be the best choice and there is probably value in the explanation.
 
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birdy

Newbie
We seem at odds about moving the cyclic back in a low g event so I would appreciate your thoughts on my response to specific low g situations.
To reload an unloaded rotor, you need to get the disc AOA back to a more faverable angle.
There are 3 things that will do it.
1, the pitch offset is the first thing to react, and its automatice, and very presice.
But it cant work if the pilot restricts its movement.
2, gravity will soon have you fall into a more faverable disc AOA, but theres a time lag.
3, pilot input, if correct will regain poistive disc AOA, but humans are unreliable, and can over/ under correct in amplitude and rate.

Let the offset do its thing, thats wot its there for.

The offset, for its simplicity, is remarkably accurate in rate and amplitude of correction, is not prone to over correction, and is always active.

Holding the stick neutral is ok, to a point, in a pitch stable machine.
 

Vance

Gyroplane CFI
Thank you David.

Letting the rotor do what it wants in my approach because of the reduced rotor authority. I have not tried to hold the stick still.

It doesn’t read like we are too divergent in our approach to a negative g event.

Thank you.
 

WaspAir

Supreme Allied Gyro CFI
If I was the top of a zoom climb I would reduce power and wouldn’t move the cyclic back because moving the cyclic back is what precipitated the low g event.
I'm not following here, Vance. As I envision the typical dangerous zoom climb, one pulls back, loads up the rotor a bit, and eventually runs out of energy/power to maintain the climb. Pushing forward at that moment (a common fixed-wing pilot stall recovery reflex to regain airspeed) unloads the rotor and that's what awakens the low-g demon. Merely commanding high-g in the climb will not by itself lead to low-g in the aftermath, and doesn't precipitate the problem any more than the take-off did.

Are we talking about a different scenario?
 
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