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Vance;n1125767 said:
In my opinion aerodynamic force is related to the square of the velocity of the air passing over the control surface.

Brilliant! One must never let scientific fact interfere with opinion.

But Friedrich Nietzsche, a well known 19[SUP]th[/SUP] century German philosopher said; “There are no facts, only interpretations.”

I suppose you’re a Nietzscheite, Vance.
 
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jm-urbani;n1125765 said:
what is a slow bunt over please ?

It was written , Slow speed bunt over.
This can happen at SLOW SPEEDS, when the pilot puts on a lot of power and forward stick, or in a zoom climb, when you reach the top and stick forward with power on to increase speed.
Both of these maneuvers can cause your gyro to tumble with total loss of control.
ALL pusher type gyros are able to accomplish this no matter what the thrust line is or tail configuration.
H-stab in the prop wash is a bit more forgiving but not enough to save your life.
H-stab below the prop wash is not as efficient and has a smaller envelope of safety.
A high thrust line is more sensitive to a bunt over because the nose lowers with power.
CLT is more forgiving, but can still do it.
LTL raises the nose with power and an unskilled pilot will compensate by pushing the stick forward while under full power and tumble the machine.
So, again, every machine has a definite and unique envelope of safety that should be known by the pilot.
I guess my post does not address how tall the tail should be, but any tail designed properly would work.
 
C. Beaty;n1125807 said:
Brilliant! One must never let scientific fact interfere with opinion.

But Friedrich Nietzsche, a well known 19[SUP]th[/SUP] century German philosopher said; “There are no facts, only interpretations.”

I suppose you’re a Nietzscheite, Vance.

He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.

Chuck for many years I've learned from you , mostly from your mistakes and mine as well.
You are a brilliant man that technology and real life situations have passed by.
Not all things are written in stone and some of the most rediculas and obscure engineering approaches work as well or better than proven methods.
Just because it's not your way or your slide rule says different, that doesn't mean it won't work.
Physicist and engineers deal with the most rational way to come to a means and at times depend on the obscure irrational approach to get the job done because it works.
Without thinking outside of the box, we would never have anything new and would still be hammering with chicken bones.
 
gyrojake;n1125830[I said:
Without thinking outside of the box, we would never have anything new and would still be hammering with chicken bones. [/I]
You’re right, Jake. Cierva set out to solve the stall problem of FW aircraft and in the process, solved the problem of rotors moving edgewise by the invention of flap hinges and thus paved the way for the helicopter. The helicopter proved to be nearly indispensable but the Autogiro was a dead end, going the way of the dirigible.

A gyroplane in the most inefficient means of aerial navigation ever conceived; with rotor blades going 500 mph while the rest of the machine goes 50 mph.

Bensen resurrected a dodo bird by combining Arthur Young’s underslung, teetering rotor with Cierva’s tilt head cyclic control system, utilizing a simple, bolt together airframe of square aluminum tubing that any teenager with a paper route could afford to build; a perfect hobbycopter.

Bensen chose square tubing because the airframe could be bolted together without using internal spacers by placing bolts tangent to walls. The downside was that bolt holes at the tubing corners was structurally, the worst possible location. A square tubing mast also exacerbates two/rev vibration problems of seesaw rotors.

So now, 60 years after Bensen, people are still building Bensen clones but hiding the airframe behind Flash Gordon style fiberglass panels and bolting on $30,000 engines.

The only genuine innovations in gyros have been the designs of Dick DeGraw. Dick has no interest in the retail gyro business so has no need to dress his machines in Flash Gordonesque fiberglass panels, instead using simple panels without compound curves.
 
The gyroplanes I have flown let me know when I have diminished control.

I try to approach the edges of the flight envelope progressively.

With almost all of the gyroplanes I have flown the envelope is so big there is no reason to get near the edges even if with very aggressive flying.

I stay away from low rotor rpm and abrupt aggressive forward cyclic movements just because I have a low fear threshold.
 
jm-urbani;n1125877 said:
So it is impossible to find out the secure envelope of a given gyro ...

You are, of course, in a strict sense you are correct. But this is not a very useful statement. During flight testing you approach the boundary of the safe envelope very slowly and carefully. For example, during a very gentle push-over you record the g-force, reduction in rotor rpm and (ideally) also flapping angle. Then you very gradually become more aggressive during the push-over until you reach a predetermined safe limit. This is then published as the boundary of the safe envelope. One doesn't have to kill a pilot and destroy a gyro just to determine when it becomes unsafe.

That's the difference between the "safe envelope" and the "deadly envelope". All I care is to stay safe.

-- Chris.
 
A competently designed gyro with correctly located propeller thrust line and torque balance will tolerate zero G for a short time.

From the book, Cierva Autogiros by Brooks about the first fatal Autogiro accident:

“This was the first Autogiro fatality. Up to this time, more than 120 Autogiros had been built (including more than 30 prototypes), 30 to 40 pilots had been trained on them, and well over 100 pilots had flown Autogiros in the United States alone. About 35,000 hours had been flown over a total distance of about 2½ million miles. This represented a remarkable safety record. For comparison, General Aviation in the United States had an accident rate of about one fatal accident every 5,000 hours in 1939. This had improved to about one every 40,000 hours by 1969—a rate not attained by General Aviation in the United Kingdom until 1974. Autogiros were therefore remarkably safe during this early period, even while engaged in experimental and development flying, their safety record being comparable to General Aviation 40 years later.“
 
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jm-urbani;n1125887 said:
Chris,

I honestly don't understand the necessity of making gentle push-overs when we never need to do this ?
I am not saying you are wrong and that I am true, and just trying to understand

regards

jean michel

It is my observation that a common way for people to damage a gyroplane is to unintentionally let the airspeed get low and try to arrest the unintended descent by pulling back on the cyclic.

Perhaps because of this "recognition and recovery from low airspeed and high rate of descent" is part of the FAA Practical test standards for a rotorcraft, gyroplane rating.

Depending on the examiner it involves slowing the gyroplane either at full power or cruise power until 500 feet per minute descent is achieved and then recovering by lowering the nose to pick up airspeed and raising the nose before adding power.

I feel knowing how aggressively you can lower the nose is an important part of learning to manage this maneuver.

Slow flight is also a part of the practical test and it involves level flight, climbs, and descents and turns to specific headings at an airspeed slightly above the airspeed requiring maximum power for level flight.
 

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jm-urbani;n1125893 said:
Chuck,
please can you tell us more about torque balancing in the real world ?
can we do this with our amateur gear ?
I remember you explained that the guy in Dubai had rolled over because of engine torque at zero G

JM, anything that removes the rotation from the propeller slipstream will eliminate torque.

First of course is contra rotation of propellers; the slipstream does not rotate if the pitch of the propellers is adjusted for equal and opposite torque. Powered parachutes use contra rotating propellers to eliminate gyroscopic effects.

Pitcairn tried vanes just aft of the tractor propeller that removed slipstream rotation at the suggestion of NACA. That was the AC-35 that I’ve previously posted pictures of.

But the most practical solution is tail surfaces located in the center of the propeller slipstream with differential incidence. Nearly all Autogiros used this principle.

Torque.JPG
 
JM, you might obtain torque balance with your all flying vertical tail by the use of large, full length trim tabs. The upper ½ set in the opposite direction from the lower ½.

Tie your gyro to a tree, place main wheels on bathroom scales and adjust tabs for equal readings while engine power is being run up and down.
 
jm-urbani;n1125887 said:
Chris,

I honestly don't understand the necessity of making gentle push-overs when we never need to do this ?
I am not saying you are wrong and that I am true, and just trying to understand

regards

jean michel

My reply was to give an example that it is quite possible to establish a safe envelope for a gyro. When undergoing certification that is indeed an important part to demonstrate

-- Chris.
 
Just to state the obvious: you can't simply add trim tabs with opposite deflection to the hstab of, e.g., an MTOSport. You would first need to get rid of the lateral offset of the rotor head.

-- Chris.
 
ckurz7000;n1125901 said:
Just to state the obvious: you can't simply add trim tabs with opposite deflection to the hstab of, e.g., an MTOSport. You would first need to get rid of the lateral offset of the rotor head.

-- Chris.

You’re right, Chris; providing torque balance without removing the offset of the rotorhead would spoil the aesthetics. But I don’t think it would affect the flying qualities.
 
Just adding trim tabs with an off-center rotorhead will only compensate a small fraction of the prop torque aerodynamically. This would still only give you a perfect balance at a certain weight/power combination. To do it properly, all the torque needs to be balanced aerodynamically.

I find it ludicrous that some gyro manufacturers offer LATERAL trim to give the illusion of a well balanced gyro. Adding lateral trim can't be technically easier or cheaper than to make a differential hstab. So I am led to conclude that they really don't understand the problem.

-- Chris.
 
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ckurz7000;n1125905 said:
I find it ludicrous that some gyro manufacturers offer LATERAL trim to give the illusion of a well balanced gyro. Adding lateral trim can't be technically easier or cheaper than to make a differential hstab. So I am led to conclude that they really don't understand the problem.

-- Chris.
Sad but true. Most “"designers"” of "“modern"” gyros simply copy a design that’ has proven successful in the marketplace and add their own decorations.

Lateral trim is required to reduce stick pressure resulting from coning angle. A coned rotor tilts sideways during translation because the blade in front operates at a higher angle of attack than the rear blade.

A better way is to use a small offset of the roll pivot in the rotorhead gimbal assembly.
 
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C. Beaty;n1125911 said:
Lateral trim is required to reduce stick pressure resulting from coning angle. A coned rotor tilts sideways during translation because the blade in front operates at a higher angle of attack than the rear blade.

A better way is to use a small offset of the roll pivot in the rotorhead gimbal assembly.

True, Chuck, but that's a much smaller "first order" effect compared to prop torque. One would expect that they at least get the "zeroth order" effect right.

-- Chris.
 
ckurz7000;n1125938 said:
True, Chuck, but that's a much smaller "first order" effect compared to prop torque. One would expect that they at least get the "zeroth order" effect right.

-- Chris.

The Zeroth Order would only be good for approximating One style of machine..
Even then, the approximation is not close enough to be efficient.
When I offset my head I use a set of roll blocks that I could shim till I get the desired effect.
Then I machine the blocks off center for that one machine.
 
gyrojake;n1125830 said:
He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.

Chuck for many years I've learned from you , mostly from your mistakes and mine as well.
You are a brilliant man that technology and real life situations have passed by.
Not all things are written in stone and some of the most rediculas and obscure engineering approaches work as well or better than proven methods.
Just because it's not your way or your slide rule says different, that doesn't mean it won't work.
Physicist and engineers deal with the most rational way to come to a means and at times depend on the obscure irrational approach to get the job done because it works.
Without thinking outside of the box, we would never have anything new and would still be hammering with chicken bones.
Jake, you are a gentleman and a scholar, even though you don't like to take credit for it. :)
 
Offsetting the rotorhead to one side and offsetting the roll pivot to one side are two different, unrelated effects.

Offsetting the rotorhead to one side of the airframe is for purely aesthetic effect; it makes the airframe fly level but does not compensate for propeller torque. Unload the rotor in cases where there is no aerodynamic compensation for propeller torque and torqueover is likely regardless of rotorhead offset.

Offsetting the roll pivot of the rotorhead gimbal assembly eliminates sideways stick force that results from coning angle. The required roll pivot offset is purely a function of coning angle,

Chris understands this but others obviously don’t.
 
Perhaps the attached sketch will eliminate some of the confusion about offsets. Angles and offsets are exaggerated for the sake of illustration. offsets.JPG
 
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