THE MAGNI DIFFERENCE : By Greg Gremminger

 

THE MAGNI DIFFERENCE  : By Greg Gremminger

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We are proud that Magni gyros have been a primary influence on the improved safety of our sport over

the last couple decades. The safest and most popular gyroplanes around the world are either Magni

gyros, or the number of aerodynamic clones of Magni gyros, that have essentially eliminated the

traditional safety issues of Buntovers and Pilot Induced Oscillations. However, there are other less

obvious, but still important, safety and reliability issues ‐ other than simply the Magni “Big Tail Way

Back” aerodynamic solution adopted by the Magni “clones.”

Although the Magni “Big Tail Way Back” configuration is now popularly

emulated by numbers of Magni “clones,” some explanation of more hidden

attributes of this configuration are worth discussing. The large horizontal

stabilizer, mounted far back on the tail keel is an excellent way to afford

“Dynamic Pitch Damping” to any aircraft. The big secret with the big tail is

that the further aft it is mounted the much, much more effective it is as a

DYNAMIC pitch damper. It turns out in gyros, as in all aircraft, the secret to

positive, precise and stabile control is the DYNAMIC damping afforded to the

airframe by the horizontal stabilizer. This is the feature many gyro designers

are now adopting – but there appears to be little appreciation or

understanding of just how this is an advantage over just a purely large tail.

A large tail is a STATIC stability advantage certainly – most people understand

this as a “balance beam” of the horizontal stabilizer statically balancing the

destabilizing surfaces forward of the CG. This is all true in the simple

determination of STATIC stability. But, as it turns out, strong DYNAMIC pitch

damping is what even more so effects precise handling while also

complementing or enhancing the aircraft’s STATIC stability. In fact, strong DYNAMIC pitch damping can

actually make a presumed statically unstable aircraft fly with strong static stability. This may seem

implausible, and the technical reasons are difficult to understand, but there are numbers of examples

that show this to be true.

A simple static analysis of the sum of moments is a very incomplete analysis of the stability and control

performance of an aircraft. For instance, many designers, considering STATIC analysis only, strive for

Centerline Propeller Thrustline (CLT), or Low Propeller ThrustLine (LTL) to achieve flight static pitch

stability as determined by the sum of static forces acting about the Center of gravity (CG). Actually, a

purely CLT gyro, or any aircraft, might not be statically stable anyway. A LTL configuration would

actually be statically stable in a paper sum of moments static analysis – the CG would be forward of the

Rotor Lift Vector (RTV) – but this would only be when the propeller is developing thrust to hold the CG

forward of the RTV in flight. (When power/thrust is minimal, this LTL “Thrust Enhancement” of static

stability is non‐existent. When static flight stability depends on propeller thrust, the gyro is not

necessarily statically stable or as statically stable, and the control handling may require more pilot

proficiency in the less stable aircraft with power reduced.

True static flight pitch stability, independent of propeller thrust or even airspeed, can be provided by the

horizontal stabilizer. The horizontal stabilizer can be mounted at a negative incidence angle to force the

CG into its statically stable location forward of the RTV. This is one way to balance other static

destabilizing airframe moments, such as a high Propeller Thrustline (HTL). But, the down‐loaded

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horizontal stabilizer requires more rotor (or wing) lift to compensate – requiring more power for flight

with the down‐loaded horizontal stabilizer – less efficient flight. This effect is minimized when the

horizontal stabilizer is mounted on a long tail boom – more nose‐up airframe moment with less download

from the stabilizer.

The Magni secret, and the one copied by the Magni “clones,” is that the horizontal stabilizer is not

counted on to provide a static stabilizing nose‐up moment on the airframe. The horizontal stabilizer on

the Magni, and on its “clones,” is absolutely level to the airstream (when properly loaded). This does

not provide even enough nose‐up moment to balance the HTL statically destabilizing moment from the

high mounted engine on this configuration. The large horizontal stabilizer, mounted far aft of the CG,

provides very strong DYNAMIC pitch damping to the airframe that effectively provides the necessary

and strong static flight stability of this configuration. The Magni (and “clones”) “Big Tail Way Back”

provides the DYNAMIC pitch damping that makes the gyro fly STATICALLY pitch stable – even though a

simple Sum of Static Moments analysis would suggest otherwise. As it turns out, the “Way Back” part

of “Big Tail Way Back” is the most important part towards the desirable strong DYNAMIC pitch damping.

Numerous examples of HTL gyroplanes, that some would suggest are susceptible to buntovers and pilot

induced oscillations, are the new generation of gyroplanes that incorporate the “Big Tail Way Back”

configuration. Magni gyros and its “clones” are perfect examples of this. This configuration is very

certainly significantly HTL. Conventional “wisdom,” predominate in the gyro culture, suggests that these

would be an accident waiting to happen – that they would be STATICALLY unstable and would therefore

be very difficult to fly safely. However, these “Big Tail Way Back” configurations are shown by standard

accepted static stability flight testing methods to be strongly statically pitch stable. Upon a disturbance

from pitch attitude or airspeed, the aircraft inherently quickly returns to the original trimmed condition

without oscillation or over‐shoot, and without pilot input (both with the stick free and the stick fixed).

This is STATIC flight pitch stability. The strong DYNAMIC pitch damping causes this aircraft to return to

its initial static trimmed condition with minimal oscillations – actually no oscillations – that might induce

pilot over control (Pilot Induced Oscillations).

Besides professional British Section T and other flight tests demonstrating the static pitch stability of this

configuration, deployed experience with large numbers of Magni gyros and its “clones” demonstrate no

tendencies toward buntovers and Pilot Induced Oscillations – the characteristics a purely but incomplete

static sum of moments analysis might suggest. There are no reported incidences of Pilot Induced

Oscillations or Power Push‐Overs or buntovers in these “Big Tail Way Back” gyroplane configurations.

Even more anecdotal evidence of the stable and precise control afforded by the strong DYNAMIC

damping is the turbulence penetration and apparent safety of this configuration reported by

experienced and less experienced gyro pilots in strong winds. More anecdotal evidence of these

benefits come from the ease of learning to fly such configuration gyroplanes. There is none of the

traditional “jab and counter jab” technique required on the traditional unstable gyrocopters of the past

– control is precise and accurate – move the cyclic stick and the gyro obediently flies to that attitude

with no oscillations or over‐shoot that less stable gyrocopters might require. The aircraft controls

exactly like all airplanes are intended to – except that it is much less susceptible to turbulence

disturbances and still has all the beneficial attributes of a gyroplane (no stall, slow and fast flight, short

and slow landings, etc.)

One last point before moving on to some real Magni Differences: This “Big Tail Way Back” dynamic

damping benefit is not confined to only the low seater Magni and “clone” configuration. That applies to

almost any configuration gyro that has a “Big Tail Way Back”. The point is though, with the

incorporation of a strong dynamic damping “Big Tail Way Back”, it is no longer necessary to try to

provide static stability with a cabin mounted very high above the ground to achieve CLT or LTL. Gyro

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configurations that depend on propeller thrust to enhance static stability do not assure static stability

and familiar/safe handling in all flight situations. When power is reduced or quits, the stability

enhancement disappears. But, more importantly at higher airspeeds where gyros without good

dynamic damping surfaces become less stable, the prop thrust reduces naturally at higher airspeeds –

just where the enhanced static stability is most necessary! Using a “Big Tail Way Back” for strong

dynamic pitch damping, that effect and Static stability actually improves at higher airspeeds.

We are certainly very proud that several decades of Magni safe operation has influenced the gyroplane

community and designers to incorporate such an important technology as a “Big Tail Way Back.”

Actually, that has never been a secret that Magni demonstrates. The Autogyros of the 20’s and 30’s did

the same thing with their tractor configurations and long tails. And, almost all airplanes, from Curtiss

and Bleriot, to today, employ the “Tail Way Back” configuration to achieve the control characteristics

that have proven to be so desirable and safe.

Having said all of the above, I now want to expose to you some Magni differences that the “clones” have

not fully appreciated or successfully emulated.

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The Magni Rotor:

Precision, composite rotor blades:

The Magni rotor and rotor system is very unique. It is

fabricated under precise procedures and autoclave

processes from high‐tech composite materials –

carbon fiber and fiberglass. The precision of this

process controls very exacting geometric and mass

distribution consistency for superior balance. The

“balance” of any rotor system requires the

aerodynamic axis of lift to be coincident with the mass

axis and the exact spinning axis of the rotor. Most

rotor systems using extruded and/or fabricated

components have difficulty in exactly matching these

two centers exactly, with rotor balance being a

compromise between the two. The precise control of

the fabrication of each Magni rotor blade, where each

station of the rotor from root to tip is an exact

reflection of that station on the opposite rotor,

precisely aligns all three axes for unsurpassed rotor

smoothness. Unlike other composite gyroplane rotor

blades, Magni does not mix an aluminum spar with

composite materials – the process of curing the

composite materials in an autoclave causes geometric

distortions and a minimum, due to the mismatched

coefficients of expansion of the two materials under

heat. By using a carbon fiber spar the full length of the

rotor blade, the autoclave process yields precise

geometry and mass distribution on each rotor blade.

Magni gyros have been renowned for the smoothness

of their rotor system.

High inertia rotor:

Magni’s composite rotor blades are indeed heavy –

about twice as heavy as most other blades of similar

size. Some would tout this as a disadvantage to high

maneuverability, but the high inertia of a heavy rotor

provides very forgiving flight and significant control

and stability advantages. Traditional gyrocopters had

very light stick forces – could hardly feel when you

were moving the stick. Many in the gyro community

consider this light stick characteristic to be a sporty

advantage and why gyros are so highly maneuverable.

What is not so popularly admitted is that this lack of

sensation of stick pressure and stick movement has

actually contributed to the traditional buntover and/or

Pilot Induced Oscillations that are so famously

attributed to traditional gyros! Because of the

sensitive nature of cyclic rotorcraft control, very slight

unfelt movements of the stick can result in rapid and

surprising maneuvering – often inadvertent and

unintentional from startled novice pilot reactions.

Pilots of all aircraft fly by the feel of stick or yoke

pressure in their hand and arm, not by the less

precisely sensed actual movement of their hand or

arm. When stick feedback pressures cannot be readily

felt by the pilot’s hand or arm, the tendency for overcontrol

is possible because, without this stick feel, the

pilot needs to wait for a reaction in the attitude of the

airframe or a corresponding feel of G‐Load in their

“seat of the pants”. In fact, proficient pilots

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subconsciously learn to gage their proper and precise

control input with the consistency of the feel of the

stick and the corresponding seat of the pants G‐Load

sensations in their seat, back, shoulders and neck. It is

this consistency between the feel of the stick and the

feel of their “seat” that makes proficient pilots able to

fly with precision, and/or to recognize a mismatch in

these two sensations. A subconsciously detected

mismatch would indicate entering into an

uncomfortable realm of instability where stick

pressures are not timed with or proportional to the

pilot’s “seat of the pants” G‐meter. For this reason,

Magni gyros intentionally provide strong stick

“feedback” feel to help especially new pilots avoid any

tendencies to over control and possibly initiate Pilot

Induced Oscillations. When a pilot has little feel of the

resistant pressure in the cyclic stick, as seems to be

desired by many for “light touch” maneuverability,

there is also the tendency for less proficient pilots to

over control. Lately, there seems to be recognition

among more in the gyro community that higher inertia

blades actually provide this safety advantage. The

option of tip weights in some of the lighter aluminum

rotor blades is becoming more popular. Most

describe this as “more forgiving”. As far as a

maneuverability disadvantage of a heavier rotor and

stronger stick forces, the rotor still responds to

commanded cyclic displacement inputs and will still

maneuver just as much and quickly as any similar

weight gyro – just need to use a little muscle to make

more severe maneuvers while the heavier stick

reminds you that you are making them.

Magni’s higher inertia rotor presents another stability

advantage. As discussed above, DYNAMIC pitch

damping is an advantage to stability, avoiding buntover

and Pilot Induced Oscillations, turbulence reaction, etc.

Above we were talking about AIRFRAME dynamic pitch

damping. But the spinning ROTOR also has its own

independent DYNAMIC pitch (and roll) damping

properties. These properties are a function of the

rotor RPM, and of the inertia of the rotor. Now, the

airframe and the rotor are independent inertial

DYNAMIC systems. But, they are both interacting with

each other – the rotor interacts with the airframe pitch

through the Rotor Lift Vector lifting or lowering the

nose, and the airframe interacts with the rotor through

cyclic inputs of the rotor spindle which tilts with the

airframe whenever the airframe pitches or rolls. Any

two dynamic inertial systems that can mutually affect

each other can either excite or dampen harmonic

reactions in the whole system. When the two natural

response rates or natural oscillation frequencies

interact they can create desirable or undesirable

harmonies as a total system. Picture a child swinging

their legs on a long swing. When his legs are swinging

in phase and synchrony with the swings of the swing,

the swing oscillations grow. When their legs are

swinging in the opposing phase with the swing, the

oscillations dampen – can be slowed down to a stop.

When the child swings their legs out of synchrony with

the natural swinging oscillations of the swing, very

erratic movements of the swinging swing are

generated. Now picture this whole swing system with

a child on a very short swing. More difficult to

harmonize leg swings with swing swings! This is

analogous to a rotor system that either matches or

harmonizes with the natural rates and frequency of the

airframe, or not. The heavier Magni rotor is designed

to match or harmonize with the airframe dynamic

reactions to produce a total harmonized response to

pilot input and/or turbulence disturbances. A heavier

rotor already has an inherent advantage in damping

turbulence disturbances simply because of its higher

inertia. But, a rotor system that is dynamically

harmonized properly with the airframe, as the heavier

Magni rotor is, makes the whole aircraft control and

responses much more desirable and intuitive. This is

often recognized by pilots who fly various brands and

models of gyros – the Magni is more comfortable flying

in heavy turbulence. The higher inertia rotor matched

dynamically with the airframe is the reason. In short,

there are other issues to consider when choosing a

rotor to install on a gyroplane, or any rotorcraft, other

than it is simply light or cheap. Magni has done the

development work to evolve this desirable harmony

between the two systems.

Rotorhead configuration:

The Magni rotor system as a whole is very unique in

the gyro world. Examine the pictures below. There

are no similar rotorhead configurations to the Magni

configuration. Most rotorhead configurations are

variations on the Bensen rotorhead. The Magni

rotorhead does not use the rather thin “teeter towers”

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that can flex sideways with loads on the rotor. Magni

uses a solid “teeter block” that includes the internal

large main double ball bearings. The block cannot flex

in any direction. Flexure of “teeter towers”, especially

on heavier 2‐place gyros where taller “towers” are

necessary, creates 2‐per‐rev rotor shake.

The Magni hubbar uses two thick welded steel plates

that straddle the teeter block. The rotor blades bolt

sandwiched between the two hubbar side plates with

large horizontal bolts. There are no provisions for

adjusting either the blade pitch or the “string”

alignment of the two rotors. The blade pitch and

“string” are controlled by the very precise fabrication

of the rotor blades that provide for very exacting blade

aerodynamic and weight symmetry between the two

blades. The traditional rotor head and hubbar

configuration requires adjustments of both blade pitch

and blade “string”. (“Stringing” gets its name from the

process of stretching a string from one blade tip to the

other to adjust the alignment of the blade attachment

to the hubbar so that the stretched string centers over

the top of the hub bar. The idea is to tighten the

attachment bolts with the two blades aligned

geometrically exactly 180 degrees across from each

other.) These adjustments are necessary in less

precisely fabricated rotors in order to find the best

compromise between the rotor center of mass and its

aerodynamic center – and its spindle spinning axis.

The common rotor head and hubbar configurations

attach the blades to the hubbar with a series of smaller

vertical bolts that allow some lateral adjustment in the

bolt hole tolerances to make the “string” adjustment.

Traditional rotor configurations allow for a method

also to adjust or shim the pitch of the blades relative to

each other – to compensate for aerodynamic

imbalances between the two blades. (The

disappointing thing about this whole process is that

the stretched “string” may identify the geometric

center to the two blades. But, with less precise blade

construction or fabrication, this does not assure that

either the mass center or the aerodynamic center will

be aligned with the spinning axis of the spindle. Such

adjustments on most rotors are a compromise of all

these centers – some rotors can be made smoother,

and some just cannot because of varying imprecision

of the rotor blade mass distribution and blade/airfoil

geometry.)

Magni composite rotor blades are fabricated with such

precision that these “string” and blade pitch

adjustments are not necessary. Each blade is then

precisely matched to its partner based on very precise

measurements. The absence of such adjustments

assures the alignment cannot change while also

assuring consistent re‐assembly without timeconsuming

“stringing” of the blades. The two

horizontal bolt attachments of the blades to the

hubbar assure consistent “string” and blade pitch

repeatability.

Rotorhead teeter bearings:

Few gyroplane rotor systems, in the interest of lower

costs, use actual bearings for teeter bearings. Some

may use roller or pin radial bearings for the teetering

action, but others simply use brass and steel sleeve

bearings. To minimize teeter 2‐per‐rev rotor shake,

friction in the teeter action must be as low as possible.

Sleeve bearings can get dirty or even gall over time –

adding friction that shows up in rotor shake. Another

consideration in the teeter bearing is to minimize any

ability of the rotor hubbar to slide sideways on the

teeter bolt. Most gyro rotor systems specify plastic

shims that may allow as much as .010 inch side play of

the rotor – this is what Igor Bensen allowed in his

original Gyrocopter. Any side to side play on the teeter

bolt adds another strong significant source of 2‐per‐rev

rotor shake.

Magni rotor heads use compound bearings for teeter

bearings – mounted in the solid “teeter block”. These

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compound bearings have both radial and axial roller

bearing surfaces. With both radial and axial bearings,

the Magni teeter bolt arrangement allows ALL axial

play to be removed – to eliminate that source of 2‐perrev

rotor shake. The Magni teeter bolt configuration

also provides side‐to‐side (chord wise) adjustment of

the rotor on the teeter block – to easily fine tune any

remaining chord imbalance of the rotor. (Some other

quality rotors do also provide for precise chord wise

adjustments, but most simply require adjusting shim

thicknesses to fine tune chord balance.) For many

rotors, these adjustments are very necessary, and time

consuming to do, in order to find a less than perfect

compromise for the inherent rotor blade mass,

geometric and aerodynamic imprecision.

Rotor life:

The fatigue life of rotors is a common consideration for

all rotorcraft. While some of the simpler single‐seat

gyros do not actually rack up long operational

lifetimes, many of the current crop of new generation

gyroplanes require significant investment and should

be expected, with reasonable care and regular

maintenance, to last for many years and hours of

enjoyment. Unfortunately, there are questionable

lifetimes for several popular rotor systems on the

market today. The questions have arisen when

operators in recent years have found fatigue cracks in

aluminum hubbars and blade attachment areas on

relatively low operational hour gyros. Some producers

have necessarily required close frequent inspections

and relatively low‐time mandatory replacement of

rotor blades and other rotor components. Just the

known history of such issues, to me, makes flying with

those components a bit stressful.

The Magni composite rotors avoid the traditional

fatigue life issues of many rotors. There are Magni

rotor blade assemblies that have flown in excess of

3000 hours – most of those in rugged training hours

with students. There have never been any reported

rotor failures or even structural cracks with Magni

rotors – other than obvious rotor strikes with hard

objects. (Most Magni composite rotor damage, deep

gouges and other impact damage, are easily repaired.)

Barring an actual crash, most damage is usually

cosmetic only. Magni does now however, require

replacement of rotor blades at 2500 operational hours.

This is mostly so that the factory can evaluate such

high time rotors to see if there are any issues

developing, and to eventually determine if the 2500

lifetime limit can be extended. 2500 hours is

exceptional for rotor life on any rotorcraft, and

certainly much better than some rotors which are life

limited at even less than 1000 hours!

Full composite material construction is a major reason

for the long trouble free life of Magni rotor blades. But

the Magni hubbar attachment with large lateral bolts,

rather than vertical bolting, avoids top side and

bottom side stressor points at the bolt holes and

hubbar tips that would focus the fatigue stress at those

most critically stressed root attachments points. With

the high stress concentration points unavoidable with

common vertical attachment bolts and holes, extruded

spars and even full extrusions may be prone to stress

fatigue cracks at or near these stressor points – often

difficult to observe internally. Magni simply avoids all

of these issues with use of a full carbon fiber spar and

fiberglass construction. The Magni rotor spar consists

of a large number of unidirectional carbon fiber strips,

routed tip to root through a rounded window in a

massive aluminum attachment hub block at the root of

each blade. The horizontal configuration attachment

bolts – two very large bolts that sandwich the

aluminum attachment hub between the hubbar steel

plates – avoid the stressor points created by vertical

bolts holes and the tip of the hubbar on standard

configuration rotors. As far as we know, Magni is the

only producer that uses this entire rotor and hubbar

configuration. As far as we know, there have been no

normal use failures of Magni rotors or hubbars in the

20‐30 years that this design has been in operation.

Even a popular fiberglass rotor blade that employed an

aluminum spar and standard vertical blade attachment

bolts had severely limited life and experienced

numerous cracking issues. If there is one issue that

really takes the fun out of flying, it is probably having

doubts about the structure and reliability of the rotor!

Ground Stability:

We all tend to focus on the flight stability of gyros.

Flight instability events such as buntovers or Pilot

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Induced Oscillations have been the traditional headline

safety and fatal accident issues with gyros. With the

advent of the “Big Tail Way Back” configuration, those

stability issues are really a thing of the past for gyros

that employ that concept. However, not all accidents

are related to just FLIGHT stability. It is important also

to have strong ground directional stability in order to

avoid dangerous and damaging accidents upon takeoff

or landing. Unfortunately, ground roll‐overs are still

occurring, even with some “new generation”

gyroplanes. Ground roll‐overs cause severe damage

but can also cause severe occupant injuries – including

death! It is a bit disappointing that some Magni

“clones” have copied the important parameter of

dynamic flight pitch damping, but fail to recognize the

importance of ground directional stability also built

into the Magni gyros.

Like all tricycle gear airplanes, Magni employs a

strongly castering nose wheel. All pusher gyroplanes

land and takeoff as “tricycle” landing gear aircraft.

The advantage of tricycle aircraft is that they tend to

straighten out automatically when the nose wheel is

touched to the ground – either on takeoff or upon

landing. For a tricycle landing gear to function

properly though, the nose wheel must be able to

caster – freely align itself with the direction of motion

of the aircraft. For example, especially when landing

with a crosswind, or during full power takeoff

acceleration, the necessary cross‐control rudder

deflection may align the (rudder pedal coupled) nose

wheel in a different direction than the direction of

movement of the aircraft. If the nose wheel is unable

to freely align with the direction of aircraft motion, the

deflected nose wheel will “dart” the nose to one side

when it touches to the ground. Even low center of

gravity gyros, such as the Magni “clones” can easily roll

over when the nose is suddenly deflected away from

the direction of motion. This sudden nose “dart” may

often excite the pilot into control reactions that

exacerbate the problem.

Many gyros, for reasons I have yet to understand, use

a nose wheel without any caster. Picture the castering

wheels on a grocery cart! The touch point of the wheel

to the ground surface must be behind the vertical

steering pivot axis of rotation of the nose wheel strut.

To work properly, the angle of the nose wheel strut

must be closely vertical or perpendicular to the ground

– picture the grocery cart again! To make matters

worse, many gyros actually cant or angle the nose

wheel strut severely forward. This probably looks

good, but further prevents the nose wheel from

straightening out when touched to the ground.

Actually, when weight is applied on the nose wheel, as

upon landing, a cant forward can cause the nose wheel

to deflect away even further! Some producers even

recognize this issue and require in their training and

flight manuals to hold the nose wheel off the ground

until the gyro is well slowed down or almost stopped.

(I actually sold one of the first USA Magni gyros to a

customer who had recently rolled over his other‐brand

expensive gyro for exactly this reason!)

The potential for ground roll‐over upon a nasty

sideways or drifting touchdown is one concern here.

But, the restriction to not touch the nose wheel at

higher speeds on the ground actually limits some of

the operational and performance benefits of a gyro.

For instance, the standard FAA short field takeoff

procedure for gyros (similarly for most airplanes), and

for the Magni gyro, is to lower and hold the nose to

the ground once the rotor RPM is adequate to lift the

nose off the ground, hold the cyclic well forward to

reduce the rotor disk Angle of Attack and minimize

rotor drag, allow the gyro to quickly accelerate to best

rate of climb airspeed in a shorter ground roll, and

then rotate and climb immediately at the best angle of

climb airspeed, Vx, when it is reached on the ground.

This procedure shortens the rolling distance on the

ground by minimizing rotor drag after takeoff Rotor

RPM is reached, and avoids the need to fly some

distance in ground effect to build airspeed to Vx for

best angle of climb after liftoff. When the nose wheel

cannot be re‐touched to the ground at the higher

airspeeds – on takeoff especially when full power

actually requires more rudder deflection – the rotor

disk cannot be leveled to minimize drag and lift,

ground roll is longer, acceleration limiting rotor drag is

more, and rotor lift initiates a takeoff at airspeed well

below Vx.

The strong caster of the Magni nose wheel avoids the

potential for a “nose dart” that could cause a narrow

wheel base gyro to roll over; and allows full application

of short field takeoff procedures in even strong

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crosswinds. In my over 3000 hours of flight instruction

provided in our Magni gyros, I have experienced some

very severe sideways or drifting landings with

students. We often train even new students in hefty

crosswinds. Sometimes the ground stabilizing reaction

of the castering nose wheel straightening out the

aircraft can be startling to the student, but we have

never had a roll‐over tendency with any student.

Students often make multiple landings in a single

landing attempt, often exciting rudder control

reactions that could exacerbate the situation – and still

no real roll‐over tendencies. The point is, ground

stability issues might not be the cause of such severe

and fatal accidents as flight instability has been in the

past, but ground roll‐overs are still serious and

dangerous. Magni gyros address all types of stability –

including ground stability.

Prerotator utility/safety/reliability:

Strong prerotators are a necessity on the new

generation 2‐place gyros that are increasingly popular

today. Prerotators come in a multitude of designs and

configurations. Hydraulic prerotators are intuitively

popular, but without very heavy large diameter

hydraulic lines and large motor/pumps, prerotation

without wind help can rarely exceed about 150 rotor

RPM. Electric prerotators are also intuitively

attractive, but they require large batteries and some

sort of “soft” actuation to avoid sudden damaging

motor start torques applied to the rotor and mast and

prerotator gear. Electric prerotators are often good

for only one pre‐rotation before requiring re‐charge of

the battery on the ground or with an hour or so of

flight – one good prerotation at a time!

Mechanical coupling from the engine to the rotor is

the most popular configuration. There are two

prominent types of mechanical coupled prerotator

systems. Historically, the “flex cable” type prerotator

has had the most success and use. The commercial

versions of the “flex cable” prerotator systems were

developed mostly for lighter single place gyros with

lighter rotors. The “flex cable” itself is the limiting

factor for both the size of the rotor and the top speed

of prerotation due to the higher torque stresses

required through the flex cable.

For larger rotors on some new generation gyroplanes,

some designers have reverted to straight torque shaft

drives, employing right angle gears and a “U”‐joint

coupling at the rotorhead. Intuitively, such a system

can be designed to handle very high prerotator torque

applications. However, good intuitive ideas do not

always resolve all problems. Such systems that use a

“U”‐joint at the rotorhead, to allow pitch and roll

movement of the rotorhead, create limitations on how

the system may be used. To prerotate with a “U”‐joint

at the rotorhead, the rotorhead (and rotor) must

essentially be held in a level condition – keeping the

“U”‐joint essentially aligned straight with its driving

shaft. Otherwise damaging stresses can be applied to

the “U”‐ˇˇˇˇˇˇˇˇˇˇjoint when the shafts are rotating – prerotator

is engaged to the engine.

For such shaft drive / “U”‐joint systems, the rotor

cannot be pitched or rolled from level during

prerotation – must be held level with forward and

centered cyclic stick. That means it is difficult to taxi

with the prerotator engaged. That means that any

wind or wind from forward movement cannot be

utilized while the prerotator is engaged – can’t tilt the

rotor back to catch some prerotation helpful wind –

such as on initial roll to shorten the takeoff roll. That

also means the pilot essentially must roll onto and

align with the runway before starting prerotation. The

ability to prerotate before crossing the hold short line

before entering an active runway, the ability to allow

forward movement wind to help accelerate the rotor

RPM during roll onto the runway, the ability to have

takeoff ready rotor RPM as soon as you are aligned on

the runway, is difficult or impossible with such shaft

drive / “U”‐joint prerotator systems. On busy runways,

especially if/when a controller asks you to expedite or

trying to fit into runway traffic, you do not want to

have to stop on the runway and only start prerotation

at that point, with your back toward oncoming traffic.

The ability to achieve a higher prerotation rotor RPM

shortens the takeoff roll. But with a prerotator system

that must be held forward until the prerotator is

disengaged, the higher prerotation rotor RPM must be

achieved solely with engine power – cannot tilt the

rotor aft to collect some helpful wind for prerotation.

That means that the rotor can only be tilted back for

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building rotor RPM to takeoff RPM after the prerotator

is disengaged – when roll is first initiated. With all of

the mechanical restrictions, it can also be difficult or

damaging to have to re‐engage the prerotator if ever

needed when the rotor might have slowed down

below a safe RPM to begin acceleration down the

runway. All of this easily leads to the opportunity to

“flap” the rotor – outrun the rotor RPM because the

rotor RPM is below, or allowed to dissipate below a

safe speed for the takeoff full power acceleration.

Some prerotation systems employ a “push button”

prerotator engagement system. These systems are

intended to automatically engage the prerotator clutch

at a rate that engages the Bendix mechanism at the

rotor head, but avoids excessive torque on the system

before the rotor RPM builds. These systems can make

it difficult or impossible to re‐engage the prerotator

until the rotor is slowed to a stop – not necessarily safe

to do on a busy runway with possible traffic behind

you.

The Magni rotor system employs a large diameter flex

cable to handle the higher power of the larger rotor

and higher prerotation rotor RPM. The flex cable

allows full cyclic control range of the rotorhead during

all phases of prerotation and taxi. This allows

prerotation to full available prerotation RPM before or

during taxi into position on the runway. When done

right, and using the wind through the tilted back rotor

during this taxi, the gyroplane is ready for immediate

takeoff acceleration as soon as it is aligned on the

runway – no stopping and worrying about traffic

behind you while you prerotate! No prerotation

techniques and procedures, or third hand required

buttons to push, after you are on the runway! The

Magni prerotator system allows prerotator engaged

initial takeoff roll, with the rotor tilted back to use the

wind to build rotor RPM quicker and higher.

Prerotator engagement is applied by the pilot with a

lever that allows re‐engagement of the prerotator at

any point or RPM, while also allowing the pilot to build

rotor RPM as aggressively as needed.

The Magni prerotator system is very robust and

capable of no‐wind prerotation rotor RPM up to

around 300 RPM. (Normal takeoff prerotator RPM is

220 RPM. This RPM allows for immediate safe

application of full power, full aft stick acceleration

down the runway. Higher prerotation RPMs are

available for Short or Soft Field takeoff procedures.)

The Magni prerotator system is designed to be a

robust and reliable system, with considerations of

maximum takeoff performance, assured prerotation to

avoid possible blade “flapping” on takeoff roll, and

without complicating procedures and mechanics that

can lead to damaged parts in a hurried or stressful

situation.

4130 steel airframe:

Traditionally, gyros have been constructed with bolted

and gusseted aluminum airframes. For more durable

and long‐lasting reliability, and with a century of

experience in the processes, 4130 “Chromoly”

(Chrome‐Moly) steel structures have been refined and

adopted as a primary structure technology for the

entire aerospace industry. Lately some gyroplane

manufacturers have begun using welded stainless steel

as the primary structure in order to try to save weight

and cost above standard aircraft steel technology.

Magni may be the only major manufacturer that has

applied aircraft standard 4130 “Chromoly” steel and

associated aerospace industry standards to its primary

gyroplane airframe structure. Magni steel airframes

are professionally welded with varying tube wall

thicknesses engineered to address distributed strength

and fatigue stress requirements while minimizing total

weight. Stainless steel has a low specific gravity (low

weight per unit volume) and may be less expensive

than 4130 Chromoly. But, Magni, and most in the

aerospace industry, consider stainless steel to be

unacceptable for airframe structures because of its

much lower resistance to fatigue cracking, difficulties

in specialized welding and weld stress relief processes,

and need for thicker tube walls (defeats perceived

advantage in total weight) to offset its strength and

fatigue deficiencies. So far, gyroplane industry

experience with stainless steel airframes has incurred

structural fatigue cracking in critical areas (the mast!!).

Additional welded components have been added to

address cracking in specific high stress areas, but

typically such remedies simply transfer the high

stresses to new areas.

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4130 “Chromoly” steel is an alloy steel, containing

Chromium and Molybdenum that is widely used in the

aerospace industry because of its superior strength

and fatigue and corrosion resistance. Chromium

increases the hardness, elastic limit, tensile strength,

and resistance to corrosion and wear while reducing

thermal conductivity – a welding process advantage.

The Molybdenum further increases the strength and

the hardness and improves the response of the metal

to the various treatments post‐welding processes. The

steel Magni uses is professionally “normalized”, an

aerospace standard treatment that improves the grain

of the steel returning it to its original condition after

being worked. This leads to an improvement in the

strength and performance of the welds. Such

normalization is difficult and less proven with welded

stainless steel.

4130 Chromoly has much greater strength in both

compression and tension, and with a lower specific

gravity than other steels, including stainless steels. The

4130 alloy steel Magni uses is the aeronautical steel

par excellence. It is particularly strong (many other

steels, including stainless steels, crack and break well

before the 4130 even bends!) and is more corrosion

resistant than even many of the stainless steels.

Magni uses 4130 steel for the complete airframe

structure, all rotor head components, all control

linkage, and all metal parts that have any structural

importance. While we appreciate experimentation

with new materials and structural innovations, Magni

does not consider stainless steel airframe technology

to be properly matured and appropriate for production

aircraft structures. The truth be told, with proper

engineering, 4130 Chromoly steel still achieves

superior strength per weight performance over all

other materials ‐ with mature and decades proven

superior resistance to fatigue cracking and corrosion.

With proper engineering, 4130 Chromoly steel still far

exceeds the presumed weight advantage of lighter

steels and even aluminum – which may anecdotally be

demonstrated with the necessity of additional airframe

structural components added to later evolutions of

gyros constructed with these less proven materials.

And the fact that those manufacturers specify

relatively short life limits on AIRFRAMES and critical

ROTOR COMPONENTS suggests that perhaps even

those producers feel those technologies are not quite

ready for prime time use in aircraft. In particular,

fatigue strength is critical in rotorcraft. Magni 4130

airframes have no life limits. Magni has experience

with airframes that have over 3000 rugged student

training hours, even operating on more rugged turf

runways throughout the world. As with rotors, doubts

about structural reliability, especially concerns with ‐

often hidden ‐ fatigue cracks in more brittle materials,

can really take the fun out of flying. Here again, the

old adage, “you get what you pay for”, is more than

appropriate.

Turbulence penetration/stability:

Above we discussed the flight stability benefits of the

“Big Tail Way Back” airframe dynamic damping

configuration. That basically eliminates the potential

for the flight instability issues of buntovers and Pilot

Induced Oscillations. However, there is more to the

story of strong dynamic damping and its benefits. The

autorotating rotor also has inertia and presents

dynamic pitch (and roll) damping into the whole

system. As we mentioned, Magni rotor inertia and

dynamic response is tuned to the airframe dynamic

response so as to harmonize controls and turbulence

reactions. This is achieved with the heavier, higher

inertia Magni composite rotors. The harmonized rotor

system contributes and amplifies not only flight

stability, but improves the whole system’s ability to

penetrate and dampen wind gusts. The result is a

smoother ride through strong turbulence without

requirement for pilot corrective actions. With heavier

rotors, the gyroplane is able to penetrate turbulence

more comfortably.

No other gyroplane employs such high inertia rotors.

Although the reports are anecdotal, pilots who are

familiar with flying both Magni gyros and other models

in turbulent conditions, such as around mountains and

hot thermally deserts, report the Magni is much more

comfortable in turbulent conditions. I have an

anecdotal report to this myself. In preparing for four

Magni gyros to make a cross‐country trip from

Missouri to California this past Summer, I inquired

with another experienced gyro pilot who happened to

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fly across the same hot Southwest U.S. desert a few

years ago in a Magni “clone” – “Big Tail Way Back” ‐

but with a lighter aluminum rotor. His advice to me

was to fly in the mornings only because the thermals

are too rough in the heat of the day in the desert. The

four of us did fly, four Magni M16s, full days across

New Mexico, Arizona and Nevada in the heat of 110

degree days. Although we could tell it was indeed

turbulent, none of us were deterred from continued

flying from morning to dusk in these conditions. On

that same adventure, in the high and rough country

just west of Albuquerque, a storm wall cloud chased us

on a retreat back to an alternate airport. For a good

20‐30 miles, we were in the grip of that gust front, with

cold air and strong winds undulating against rugged

terrain. If I had had my druthers, I would have avoided

that experience, adrenalin was pumping! But all of us

out raced that storm to take refuge in a lonely airport

providing shelter from the immediate storm!

Limited takeoff rotation attitude:

This may seem like a little thing, or an excuse for

limited rotation angle on takeoff and landing. But,

Some Magni “clones” have raised tails, presumably to

be able to rotate to higher angles of attack on both

takeoff and on landings. The intuitive and promoted

advantage of being able to raise the nose further in a

landing or takeoff stance is slower takeoffs and

landings. But, some pilots have discovered that it

takes proficient skills to apply this technique without

getting into trouble. The ability to rotate too quickly to

a high angle of attack can cause the gyro to jump out

of ground effect losing airspeed and dropping back to

the ground in a rough, nose high attitude. This has

happened – with the associated roll‐over!

Magni gyros do not have raised tail booms, limiting the

rotation angle on takeoff to an angle that prevents

extreme jumps off the ground to get into this trouble.

Promoters of these high raised tail configurations also

boast that they can land at slower airspeeds – higher

disk angles of attack because they can touch down

with a higher nose attitude. This is certainly true – can

touch down at lower airspeeds and stop a bit shorter,

maybe. But, that landing attitude also invites the

ability for the rotor to strike the ground if the landing

attitude is too severe. This has happened! Magni

gyros do not encourage such tail low landings, but if

you were to land on the tail wheel first, the tail forces

the nose lower to avoid rotor strikes – maybe a bit

rougher landing, but all the parts are still together!

Another reason that some gyro configurations have

high tails is so that the horizontal stabilizer is in the

propwash – to amplify the stability contribution of the

horizontal stabilizer – when the prop is producing

propwash. The propwash can have a nearly two to one

effect on the power of the horizontal stabilizer.

Actually, this is not necessary for Big Tails Way Back

because they already have a strong leverage arm for

dynamic damping effectiveness. With this horizontal

stabilizer in the propwash arrangement, changes in

power level can change the stability/handling

characteristics of the whole machine between power

on (best), and power off (not as much). Professional

aircraft designers prefer that the control and handling

properties, sensitivity to controls, does not change for

any reason such as an abrupt power change. This is

not such an issue for pilots experienced in this

characteristic, but it can be an issue for more novice

pilots expecting to penetrate wind gusts, for instance,

with power off as well as they experienced with power

on.

Magni may have the most extensive experience of

gyroplane developers in these subtle variations and

configuration issues. Over the years they have actually

progressed through 24 (latest is the M24)

configurations (many of these being non‐production

prototype configurations to test various concepts). The

production flock of Magni gyros today take advantage

of these years of prototype and testing experience and

Magni Gyro has only released configurations to the

public upon extensive evolution to those production

configurations. Discouragingly, some designers have

simply taken an intuitive concept, applied it to an

obvious beneficial configuration (Magni “clones”), and

released production models without such extensive

evolution and iteration with prototype models. In my

opinion, this diligence to evolution and testing is the

major “Magni Difference”.

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Addendum

HTL, CLT, LTL?

(High Prop Thrustline, Centerline Prop Thrust, Low Prop Thrustline)

So, if you have worked your way this far in this paper, I’m not sure you are anxious to start another

technical subject. But if you are a gyro geek like me, always hungry to learn something new, you might

want to plunge into the following “blasphemous” subject. If you have researched gyros very deeply at

all, you have probably been exposed to all the emotional arguments and opinions on HTL, CLT and LTL.

You may even understand all the discussions about center of gravity, pitch moments, thrustlines,

balance of static moments, etc. You may have some strong opinions about what is best, CLT, LTL or

HTL. I don’t intend to get into all the technical derivations and customary arguments here. There are

just a couple of points I don’t think you may have been introduced to on the subject of prop thrustlines.

A couple of statements: Magni gyros are HTL – High Prop Thrustlines – by a number of inches! So are all

the Magni “clones”. By the popular static sum of moments analysis, this should mean that all these

similar gyro configurations should be digging burning holes almost daily from static instability Power

Pushovers (PPO, buntovers) and Pilot Induced Oscillations (PIO). This isn’t happening! For the dynamic

pitch damping reasons discussed above.

Now here’s a second statement: HTL, CLT and LTL is no longer an issue with “Big Tails Way Back”.

Neither HTL, CLT nor LTL have the important airframe pitch dynamic damping without an effective

horizontal stabilizer. Without a horizontal stabilizer, perfect CLT might be in balance, but it’s an

unstable neutral balance, and any slight disturbance can start pitch oscillations that will not be

automatically damped – the pilot has to do it. And, perfect balance with CLT is almost impossible –

don’t eat a big lunch or use the restroom; don’t use more than a couple inches of fuel in the tank!

Without an effective horizontal stabilizer, both HTL and LTL would easily diverge in higher or lower

airspeed without pilot intervention – skilled and constant pilot intervention – sometimes subconscious,

but still muscle and brain work! With the incorporation of a good horizontal stabilizer, placed “way

back” to multiply its effect on dynamic damping, close attention to prop thrustline is no longer a big

concern. Prop thrustline is even less of a concern with a bigger tail further way back. If it were,

certainly all the Magnis and Magni “clones” would be digging smoking holes. Can we all say “pitch

dynamic damping”? This is what most producers outside the U.S. are doing – and they are breaking

safety records and impressing all of aviation.

Here is a statement you will certainly have a hard time believing: HTL is airspeed stable. LTL is airspeed

unstable! What you have been led to believe is that HTL is dangerously unstable. Certainly it is without

a good horizontal stabilizer, but so are CLT and LTL without a good horizontal stabilizer – dynamic

damper. That is no longer a concern with a “Big Tail Way Back” – strong dynamic airframe pitch

damping makes them all stable and insulated from PPO, buntovers or PIO. But, aircraft designers would

also prefer that aircraft be airspeed stable – if it starts to go faster, it automatically slows down. If it

starts to go slower, it automatically speeds up – to its trimmed condition airspeed. You don’t always

want to be having to reign in airspeed if it starts to change.

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With gyros, especially less stable gyros that tend to get less and less stable at higher airspeeds, it is

important that they don’t automatically try to go faster and faster at higher airspeeds. But that is

exactly what LTL does. Here’s why:

First, understand that some gyros perceived as “CLT” may actually be LTL. On a LTL configuration, prop

thrust statically holds the nose higher, essentially slowing the aircraft slower than its actual trimmed

condition. But, as airspeed increases, real prop thrust decreases – at high airspeeds prop thrust is much

less than at lower airspeeds because of the faster incoming air. As it goes faster, the reducing prop

thrust allows the nose to drop lower, increasing the airspeed. The faster it goes, the less prop thrust

and the faster and faster it keeps going – for this situation, the pilot must actively slow the gyro with

cyclic input to keep the airspeed from running away. The exact opposite is true if the aircraft is slowing

down – it tries to go slower and slower as the prop starts to bite harder in the slower air raising the nose

and slowing it down further. This is airspeed unstable; the airspeed does not automatically try to return

to the intended trimmed airspeed, but instead continues to diverge from its trimmed airspeed.

On an HTL configuration, prop thrust statically pushes the nose lower, essentially speeding the aircraft

faster than its actual trimmed condition. But, if the airspeed increases for some reason, the prop thrust

decreases and allows the nose to rise, slowing the airspeed. If the airspeed decreases for some reason,

the prop thrust increases and pushes the nose lower to increase the airspeed back to its trimmed

airspeed. Upon increasing airspeed, HTL slows the airspeed by pushing the nose down less. Upon

decreasing airspeed, the increasing HTL prop thrust pushes the nose lower to increase airspeed back to

its trimmed condition. At higher airspeeds, or with pilot inattention, this can be an important attribute

– it certainly reduces pilot workload that would otherwise always be having to monitor and correct

airspeed constantly.

I would agree that HTL should be avoided if you just don’t have a good horizontal stabilizer – just don’t

have good dynamic airframe pitch damping. But, with a good Big Tail Way Back, HTL is no longer a thing

to be avoided. With a Big Tail Way Back, this benefit of HTL can be exploited, as it is in Magni gyros and

all the “clones”. Not to mention, with a Big Tail Way Back, designers no longer need to provide ladders

to climb into the cockpit, or worry about tipping over so easily landing badly in a crosswind. If you do

other things right – can you say Big Tail Way Back? – HTL can be a very good thing!

Thanks for your attention and diligence. Fly safe – Greg Gremminger