Gyroplane Thrustlines vs. Center of Gravity

[eddie]

Excellent answer stewart.

Best regards,eddie.....

 

[birdy]

Bloodyell Stew, why complicate a simple, very capable machine with all that lectric automation dead weight?
Just do it.

The only thing id like to try out that would increase rates, simply, is a teetering prop.

 

[Murray Barker]

Firstly "Mad Muz", the plus or minus 2 inches is a strong recommendation, not a "you will do this or else". Please read the appropriate regs.

Also it is a strong recommendation that a horizontal stabilizer be fitted. A small flat piece of plywood isn't a HS.

This seems to be one of the things the Euro gyro manufacturers have got right.Some would say the only thing..

Unfortunately we have had our fair share of buntovers ,with obvious results, in Australia
None of these as far as records indicate, have involved a CLT gyro with a decent HS.

Some however involved pilots who thought they could fly anything,unstable or not, until the right set of circumstances during flight comes along.

 

[SIIaCanuck]

Bloodyell Stew, why complicate a simple, very capable machine with all that lectric automation dead weight?
Just do it.

The only thing id like to try out that would increase rates, simply, is a teetering prop.

Vectored thrust?

Genius.

With the way things are going, all that 'lectric stuff will weigh about as much as a pocket calculator.

Perhaps you're right though, best to keep it simple.

 

[MadMuz]

Firstly "Mad Muz", the plus or minus 2 inches is a strong recommendation, not a "you will do this or else". Please read the appropriate regs.

Also it is a strong recommendation that a horizontal stabilizer be fitted. A small flat piece of plywood isn't a HS.
.

My bad Murray, I must have missread the regs, I thought that it read 'had to'

I personally wouldn't like to fly a machine without an appropriate HS, I went for a fly (as a passenger only) in an early RAF that cured me of that completely.... butt puckering stuff..... and a guy I built side by side 2 seater for in the late 90's wanted a tall tail with no HS..... that confirmed it..... unquestionably

 

[Doug Riley]

Stew, as an engineer you'll recognize that agility in a rotorcraft has as much to do with the behavior of the rotor as it does with the behavior of the fuselage. PPO, torque-over and yaw-induced precessional stalls are all cases of the rotor's being unable to get out of the way of a fuselage that can accelerate (angularly) faster than the rotor can.

There's nothing to be gained from making the gyro's fuselage statically unstable while using the same old rotor that can only precess so fast without diverging or beating itself to pieces.

The trend (generally a healthy one IMHO) since the Bensen era has been toward larger, lower-RPM and more massive rotors. This does not make for ideal cattle-mustering machines, but otherwise has saved lives and enhanced the ability of sport gyros to fly decently on smallish engines.

 

[Resasi]

Might be splitting hairs here, and no wish to look for conflict. Given and accepting that the stability/agility ratio between fixed wing and gyro flying machines are not related, together with Doug's observation above, I remain just slight puzzled by this

Agility is in no way related to stability.
You can be stable or unstable but still have the same level of agility.
The down side to the big HS asa fix for instability, is it costs energy, and the damping effect slows the rate.
rate

.
I am guessing the second 'rate' was finger trouble, and that an HS slows the rate...I am assuming of pitch. It has made for a safer machine and at albeit a small cost in rate of pitch, and of available power. But surely a decrease in agility, if agility in a flying machine is measured in roll, pitch rates, and available surplus power.

I am simply guessing and happy to be enlightened but if I add an HS to the Bensen, I am expecting to have a safer machine but at a small cost in agility. Of course hoping so small as to be unnoticeable.

 

[C. Beaty]

A horizontal stabilizer causes the airframe to more quickly align itself with the flightpath of the rotor.

This does not equate to a reduction of agility; conversely, airframe lag and overshoot resulting from inadequate or no horizontal stabilizer is hardly an indication of agility.

 

[birdy]

A down loaded HS ( needed to counter the rotating force of a HTL ) costs energy in any high rate pitching or acceleration. Pretty simple.
A highly damped machine, wether its through a slug of an airframe or nose heavy blades has, as intended by the engineer, a slow rate of responce.

If your normaly opperateing in confined areas in unpredictable conditions, you need energy efficiancy and high responce rates.
Most people dont, so its not so critical.

 

[C. Beaty]

Move the stick and the rotor settles into its new orientation and assumes a new flight path within 2 or 3 revolutions.

A stabless airframe doesn’t do anything right away. The new thrust vector orientation, displaced relative to the CG, begins an acceleration of the airframe in pitch or roll, whatever the case may be. As the airframe accelerates, it eventually overshoots the commanded position, where unlike a FW, the rotor provides very little damping.

The reaction of most individuals accustomed to flying without a horizontal stabilizer in a feeling of increased crispness.

Professionals like Birdy can utilize lag and overshoot to play toss and catch.

With a Bensen type airframe, always use a “T” tail as keel mounted horizontal stabs don’t do much. With ‘T” tails, differential incidence can be used to cancel torque roll although torque isn’t a big issue with 4’ props turning 4.000 rpm. Torque = (HP x 5252)/rpm

 

[birdy]

The reaction of most individuals accustomed to flying without a horizontal stabilizer in a feeling of increased crispness
If undamped efficiancy and lighter stick pressures means crispness CB, then your onto it.

 

[birdy]

Oh, i forgot, it can also be pitch and power stable too, if its built proper.

 

[C. Beaty]

Crispness means tighter coupling of rotor and airframe, with minimum lag and overshoot, Birdy. Loosely coupled airframe and rotor makes flying such a gyro feel like stirring a tub of oatmeal.

Stick force in a gyro depends upon rotor and control system characteristics alone. Generally, heavy rotor = heavy stick. Noseheavy rotor = heavy stick. Tailheavy rotor = light stick.

A Bensen with seat tank and light wheels is almost exactly CLT so a stab doesn’t detract from efficiency.

Angle of attack stability means that a flying machine always heads into the relative wind. An upward gust requires that a gyro pitch noseup; a downward gust requires that a gyro pitch nosedown. More throttle and the gyro should go noseup, keeping airspeed constant.

 

[birdy]

A Bensen with seat tank and light wheels is almost exactly CLT so a stab doesn’t detract from efficiency.
Zactly.
And i think you got your gust/pitch bit assup.

 

[C. Beaty]

How embarrassing! You’re right- I was bass ackwards in response to gusts. Thanks for catching it.

In an upgust, the resultant wind is rising, so an aircraft must pitch nosedown to maintain constant angle of attack.

 

[birdy]

I had to read it a few times to be sure, but figured you were just baitn me.

 

[Jean Claude]

In my opinion, the rate of roll (or pitch) primarily depends of the angular clearance given to the hub. Damping of the tail is negligible. Example:

 

[birdy]

Bout the only thing that governs roll rate, below the teeter bolt, is the length of the mast, or more accurately, the distance between the teeter bolt and the COM.
Greater the seperation, slower the rate.

Pitch is a compleatly different chook.

Damping in pitch, by design, is sposed to tame pitch rates.
Highly damped frames wont fly into their rotors, but their undamped ( not nose heavy) rotors could fly into the frame, usualy the teeter stoppers.
If the pilot ignors the hammering stick warning, his tail is next in line.
A miss match of damping magnitudes between frame and rotor could see a ham fisted opperater do damage.

 

[Jean Claude]

Birdy, To apply a continuous rate of roll (or pitch), RTV must pass through the mass center. So, the rate not decreases. In this case, my sketch shows the mast height is irrelevant. The mast height is involved only in the change of roll rate when the stick is fix (this is called damping)

 

[MadMuz]

Doesn't lengthening the mast lower the center of mass, which slows the roll rate (of the entire machine) therefore what Birdy said is pretty well bang on? That's how I see it?


You cant really achieve a continuous roll rate (like an aerobatic FW) because we can only roll as far as to not unload the rotor? From my experience, a short mast makes for a very quick to respond machine (less stable) and a long mast machine more 'damped' (more stable) so I find it hard to disagree with Birdy?