last update September, 2018

MT-Propeller Natural CompositeTechnology


Natural Composite History

  • Manufacturing of the first natural composite blade in 1928 (90 years ago) by Schwarz Propeller in BERLIN
  • Originally developed for high power fighters, like the FW190, Messerschmitt 109, Spitfire, Hurricane, and many more.
  • Now also used on a restored TwinMustang F82 program.
  • Latest Technology introduced for production developed by MT-Propeller using a CT (Computer tomography) for pre-selection of material and latest composite materials, like carbon fiber and glass fiber.
  • More than 72.000 blades made by MT-Propeller since production started in 1981.

Certification Capabilities:

Propeller Type Certificate (Part 35; Amendment 8):

  • Bird Strike Test
  • Lightning Strike Test
  • Static Strength Test
  • Fatigue Tests
  • Safety Assessment
  • Integration Manual
  • Propeller Type Certificate (DOA authority by the EASA and FAA)

STC Part 23 Aircraft Certification up to Part 23 Commuter:
DOA STC authority including Flight Test Part 23

  • Performance
  • Noise
  • Cooling Effects
  • Ice Protection
  • Flight Loads

MT-Propeller has NO active AD on any MT-Propeller, a safety record unmatched by any other propeller manufacturer. Total accumulated flying hrs are 150 Million up to day. A certified TBO of 4000 hrs or 6 years for Turbo Prop Applications without any life limited parts installed.


MT-Propeller has the Design Authority and certified propeller blades by the EASA and FAA for the following materials:



MT-Natural Composite Blade
MT-Natural Composite Blade

Structural Composite Design
Structural Composite Design
MT-600-Series Full Carbon Blade
MT-500-Series Full Kevlar Blade

MT-400-SeriesAluminum Blade
MT-400-SeriesAluminum Blade



Facts:


Vibration Dampening Behavior:

Due to the unbeaten vibration behavior no ground rpm limitation and in flight rpm limitation must be established for certified MT-Propeller installations using the natural composite design.


Vibration comparison composite vs. alluminum



Bird Strike:

During the take-off run a 8 lbs Stork impact , minor damage on the propeller, aircraft was ferried for 2 hours back to the home base after the impact.

minor birdstrike damageminor birdstrike damage




Lightning Strike:

Severe Lightning Strike in flight on a Turboprop propeller blade has minor damage and can be overhauled and returned to service.


Blade Tip and mid blade, minor damage.
Blade Tip and mid blade, minor damage.


Belly of the airplane with a burned spot and vaporized paint after the lightning left the airframe.
Belly of the airplane with a burned spot
and vaporized paint after the lightning left the airframe.



Moisture:

The MT-Propeller natural composite design is the only blade design selected by Griffon Hoverworks (biggest Hovercraft manufacturer in the world) after testing structural composite blade versus the standard MT natural composite design. Since year 2013 MT-propeller is the only supplier of Propellers for all new Griffon Manufactured Hovercraft. Propeller diameter up to 3,5 m (11,5 ft) are in use 3,500 hours per year without any life limitation and red bands in the harshest environment with salt water and sand.
Identical blade design are used for aircraft propeller and vise versa.

Griffon Hovercraft with MT-PropellerGriffon Hovercraft with MT-Propeller





Not all composite blades are made the same


MT-Propeller Blades – Key Features:

  • 2” wide Durable Nickel Cobalt Leading Edge. Widest leading edge on turboprop blades for best erosion protection.
  • Epoxy Paint for improved erosion protection, with minor tendency for paint cracks.
  • A lightning strike does not make the blade unserviceable compared to structure composite blade, because the MT-blade is not conductive.
  • Structural composite blades lose their lightning protection after one impact and must be retired.
  • After a ground strike the MT-Propeller single piece hub can be overhauled and MUST not be retired.

Key differences vs. structural composite blades

Aerospace grade carbon fiber combined with highly compressed beech/spruce wood core has a higher strength than aerospace aluminum with no corrosion and fatigue limit.
The MT-blade has no spar for the load carrying core.
By this, FOD on leading edge or trailing edge as well as the blade mid area can not create a structural damage requiring the replacement of a blade.

MT-Propeller natural composite blades are certified for unlimited life and can be repaired in the field or at 60+ overhaul shops worldwide.

MT airfoils are designed for a relative thickness between 3 to 10% depending on local MACH number. The propeller is designed to operate below supersonic so a certain relative airfoil thickness is needed to create the most thrust.
Thin airfoils are subject to stall flutter.

De-Ice Boots are integrated in the airfoil to keep the original shape.
By this no extra drag from De-Icing is created on MT Turboprop blades.
Not standard and available on structural composite blades.

MT - Natural Composite Blade
MT - Natural Composite Blade


Structural Composite Blade, with load carrying spar. In case of damage the blade must be retired.
Structural Composite Blade, with load carrying spar.
In case of damage the blade must be retired.



Competitive Assessment Performance


Numerous windtunnel tests within R&D programs for Airbus as the selected supplier for the Airbus Racer and City Airbus by Airbus Helicopter has refined together with the Research Institute DLR (German Research Institute) and ONERA ( French Research Institute) the best capability to improve the overall performance using MT proprietary aerodynamic software.
Better take off, better climb with high top speeds are the result.

For this, AIRBUS Helicopter has selected MT-Propeller as the supplier for the two 250+ Million Dollar R&D programs.

On the LH side the typical protection of a MT natural composite blade with a 2 inch wide Nickel Leading Edge vs a structural composite blade nickel protection on the RH side.

Natural Composite Blade
Natural Composite Blade

Structural Composite Blade
Structural Composite Blade



Competitive Assessment Performance



Shown are cross sections from MT-Propeller and typical structural composite blade.

Same thickness outside the spinner shape for minimum drag.
Independent lag screw system with up to 11 lag screws are installed in the blade root. The MT cross section shown is typical for turbo-prop construction.
No homogeny single structural material which can be damaged by FOD.

FOD on the load carrying composite shell for a structural composite blade may result to a structural damage with the need to retire the blade.

So far this never happened to a MT natural composite blade due to the unique manufacturing technology using different materials.

Capable of achieving ~10x CF loads. No Life limit in the blade retention has been introduced by the Certification Authorities.



MT-Natural Composite Blade
Natural

Structural
Structural



Natural Composite Blade Construction


MT-Natural Composite Blade

  • Multilaminated Spruce.
  • Compressed Plastified Beech Wood, called also “Superwood”.
  • Carbon Fiber Composite Shell.
  • Nickel Cobalt Erosion Sheet 2 “ wide and 5 times stronger than aluminum.
  • Aerospace Aluminum Ferrule.
  • Pressed in Pitch Change Steel Pin with no screws for fatigue.
  • Patented special lag screw design, one lag screw can hold the blade and up to 11 lag screws installed.



TEST REQUIREMENTS


The requirement for the test per Part 35.36 is as follows:

  • The applicant must demonstrate, by tests or analysis based on tests or experience on similar designs, that the propeller can withstand the impact of a four-pound bird at the critical location(s) and critical flight condition(s) of a typical installation without causing a major or hazardous propeller effect.
  • MT has performed more than 160 bird impact tests per EASA / FAA requirements since our first natural composite certification in 1981.
  • Utilizes a projectile with density equivalent to a 4 lb. (1.81 kg) bird. Blade is tested in a free state, retained at shank with no benefit from centrifugal stiffening.
  • No limitations were issued from the Certification Authorities for the MT blade design up to 2000 hp and 3 m (10 ft) diameter applications.

The MT design is certificated for the bird impact conditions calculated for the most critical flight condition (take-off rotation) for that installation The test is performed at the most critical locations on the blade.

Important factors to be considered:

  • Propeller RPM
  • Engine HP
  • Propeller Blade Angle
  • Blade Impact Location
  • Aircraft Rotation Air Speed

No significant structural damage is allowed…. Propeller must be controllable and continue to provide thrust without causing a hazardous effect.

MT-Propeller Blades passed this test without any limitation.



Aerodynamic Capabilities

Aerodynamic Capabilities

  • MT “Prop” Code is used for aerodynamic design and performance prediction.
  • Integrated code developed in-house over a 30 years period.
  • Aerodynamic unloading of the Blade Tip for lower VORTEX and higher efficiency.
  • Use aircraft flow-field information as inputs(CFD-generated velocity fields, etc).
  • Installation effects included in performance predictions.
  • Coupled with structural Finite Element design (stress, frequency) tools.
  • Correlated against AIRBUS/RUAG wind tunnel data.



MT-Applications and Multiple Blade Concept


Up to 90% of the European manufacturers and up to 30% of the US manufacturers use the MT-Propellers for new production aircraft.

Since MT-Propeller was established in 1981 more and more manufacturers changed to our system.

Since the first introduction of the 5 bladed propellers in year 1995 more than 2000+ turboprop applications like the latest OEM RUAG 228 NG, GROB 120 TP and King Airs, Jetstream, Metroliner, Cessna and many more using MT-Propellers.

It has been become an industrial standard with approximately 350+ 5 bladed Propellers shipped per year.

More than 220 STCs are available worldwide from MT-Propeller to upgrade any aircraft to a more modern higher performance, lower noise, lower weight propeller system.



With the advantages of the MT NATURAL COMPOSITE design compared to structural composite and aluminum blade materials also certified and manufactured by MT-Propeller, the majority of the MT powered aircraft using the natural composite design.



MT-Operators benefit from :

  • Higher Efficiency for lower operating costs
  • Lower Vibration- resulting in less fatigue for the crew and airframe
  • Lower Noise for higher flying comfort and less crew fatigue and reduced environmental impact
  • Renewable materials used for the lowest environmental impact