B248
MAKE: SynchroLite ~
Rotor - Blade - Composite
Outside Helicopter
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Original Date: 10/14/1988 Information : Composite Rotor Blade FabricationComposite main rotor blade fabrication at BHTI varies with blade model, but all of the blades are final cured in closed cavity metal tooling. Although many of the main rotor blade manufacturing techniques used at BHTI are used throughout the industry, BHTI has developed and uses several unique manufacturing practices. One practice is the use of prepreg roving for the automated winding of spar straps. This assures final blade balance and weight, and eliminates resin squeezeout during winding around hinge pins. Prepreg roving stock is analyzed when it is received from the supplier for resin and fiber content. In the winding step, rolls of prepreg roving are selected that together will yield the desired resin and fiber content in the final blade. Another practice is the use of a styrofoam mandrel covered with a rubber bladder for final curing of main rotor blade spars. In this approach, molded styrofoam segments are fitted onto a stiff inner support rod, and are then covered with a rubber bladder. The bladder is pressurized during the cure process in order to provide internal pressure. The mandrel is easily removed from the cured spar due to the thermal contraction of the styrofoam during the cure. |
SynchroLite - Sub-Contracting
Manufacturing:
Hollmann
C H T
Consider talking to
Powerfin Inc. in Arlington Wash.Ivo AT IVO Prop
Sourcing
Consider having Sportscopter , McCutchen Skywheels , or
Waitman produce blades.CHT is closer.
Eagle's Perch Inc.
Idea re Development Costs
Produce counter-clockwise blade first. This can be marketed to others? Then build mold for other.
Liability
Like Vortech be very concerned about liability if there is ever an thought about selling blades.
Cost
Bob Pegg had quote of $10,000.00 US for mold for 4'-6", 7" chord rotor blade.
M. Hollmann is asking $4,000.00 + US for design.
Eagle's Perch is asking $3,800.00 US for design.
Ply Layup
Skin portion
Glass fibers oriented at +/- 45 degrees for maximum torsional strength.
Spar portion
Carbon fibers; 2 plys at 0 degrees. 1 ply at +30 degrees. 1 ply at -30 degrees. for a combination of torsional and axial strength.
Leading edge sheath
2 plys at 0 degrees. 1 ply at +30 degrees. 1 ply at -30 degrees.
The Cm is considered positive when pulling up.
re: Manufacturing or Special Tool
Ideas:
Hot Oil
Consider hot oil system for pressure and temperature.
Questions
If complete blade is made at one time and compressed on foam core how are any gasses released. All the way to the ends or out the trailing edge to a vacuum line?
Remarks
Put tension on unidirectional tow when curing.
Spar
Tow
Manufacturing:
Layup with Prepreg:
Consider doing lay-up in a chiller tray (similar to frozen food trays with open tops in food stores) to extend the lay-up time.
Core:
Have a male plug over which the cloth is laid up.
This plug has numerous entry and exit ports on its large end.
Each pair of ports delivers and returns oil from a section of the cavity in the female mold. Note the mold is not sectionalized, it is just that we want an even cure temperature throughout the mold.
A vacuum is applied to the ports on the mail plug when the lay-up is being done so as to cause the material to adhere to this plug, until it is put into the mold.
Tool:
Consider having the plug and female mold approximately 20 feet long. This way the cord at the tip and root can be variable and only the taper ratio is fixed. The plastic bag will of course have to run the full length to keep the oil out of the fabric.
The oil will not circulate perfectly inside the blade so the outer female mold should be heated also.
Idea;- Could the 20 foot long "aluminum mold be temporarily twist, CW or CCW for each blade and even thought it was heated would it return to 'no twist' after it had cooled and the part was removed?
Idea:
January 12, 2000Have a blade NC machined. No taper and no twist. Just the desired profile and a span approximately 1 foot longer than the final blade radius. This is then used to construct composite female molds, both CCW and CW. This way changes can be made to the composite female molds relatively easily and also longer female molds can be made, if required.
Note:
January 12, 2000Pressure of bladder may collapse a honeycomb core because the pressure is against the side of the honeycomb. Maybe use Rohacell core.
Note:
January 15, 2000It looks like the tip (weight) should be included as part of the spar assembly because part of it must be located inside skin.
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Last Revised: November 26, 2003