B188
DESIGN: SynchroLite ~
Rotor - Blade - Composite
Use program NVFoil to look at 8H12, 0012 etc.
See also C:/NVFoil/DBJ Notes.doc
Outside Helicopters
A listing of the blades that are used on approximately 150 helicopters. Rotor Blades
Flettner:
NACA 23017, Constant Chord, 4 degree of twist, Disk loading of 1.7 lb/sq ft.
Ultrasport:
All composite
Pre-preg graphite and S-glass spar
Nomex honeycomb trailing edge.
Outer skin of pre-preg S-glass.
CA Beaty thinks that this airfoil is VR-7. I think it is actually a VR-7b with maybe -2 degrees at trailing edge.
Tungsten leading-edge weights in outboard 50% of radius for aeromechanical stability.
Each blade weighs 15 lbs of which 2 lbs is distributed at the tip.
Each blade has a linear twist of 8 degrees from root to tip.
Has an autorotation descent rate of 900 ft/min.
Polyurethane erosion strip is used on leading edge.
AH-64D Apache
The leading edge of the rotor is made up of titanium while the trailing edge is covered in a graphite composite material. Internally each blade consists of a glass-fiber honeycomb supported by five tubular spars of stainless steel which divide the blade into sections. Damage to the rotor blade should be confined to the particular section that was hit. For storage or transport, the blades can be easily folded or removed
Boeing-Vertol
This root airfoil is VR-7, tip airfoil is VR-8.
VR-8 is thinner than VR-7.
I have not been able to find out if blades are tapered or not. Taper and changing thickness might make for a very week tip.
Bombardier VTOL UAV CL-327
ARDCO designed, analyzed, tooled, defined the process, drafted the qualification and acceptance test plans and produced, the all-composite, 80 inch long, 4.4 pound, counter-rotating rotor blades for Bombardier Services VTOL UAV CL-327. The airfoil shape, the ARDCO-1, as well as the materials and structural design were completely defined by ARDCO Composites' engineers.
Carter Copter
Our rotor blades are torsionally very stiff (4 layers of +/- 45 Carbon cloth are used in the rotor blade's skin) and thus we have never measured any blade flutter tendency.
NHI NH-90
Maybe the idea of a very small downward winglet isn't so thoughtless an idea. See NHI NH-90; ILA Berlin-Brandenburg, 1998; Swept blade tips feature compound taper also. Photo by Burkhard Domke
Rotor Blade TipIt should result in 1/ less tip loss and 2/ less forward cyclic at higher forward speeds.
Chesapeake is the University of Maryland's entry in 1998
AHS student design competitionThe proposed rotor blade is to be RAE 9648 (inboard of 65%) VR-7 (from 65% to 85% radius) and VR-8 from 85% radius to the tip). The tip speed is to be 700 ft/sec. Therefore at the 85% location, where the airfoil changes from VR-7 to VR8, the speed will be 595 ft/sec. The Synchropter tip speed is 544 ft/sec.
Human Powered Helicopter Helios:
Hélios sponsors include, in addition to major support from ÉTS itself: Bell Helicopter Textron, Bombardier Canadair, 3M Corporation, Dupont, and Airtech Advanced Materials to name a few.
Team members Simon Joncas and Christian Belleau wrote software that used a combination of blade-element theory and vortex theory to predict the performance both out of and in ground effect for any given blade geometry. Joncas and Belleau ran their software in parallel on numerous computers in various ÉTS computer labs overnight for several months continuously to test approximately 3 million blade geometries. The variables explored included: airfoil cross section, blade length, chord at root and tip, chord distribution, twist distribution, and RPM - all as a function of altitude. Output from the program used to discriminate and discard blade designs included: power consumed, the distribution of lift along the blade, the distribution of drag along the blade, and the torque along the axis of the blade as a function of angle of attack.
Hélios' rotor blades - upper and lower slightly different - have significant taper (taper ratio @ 0.1) and twist (~10ƒ and the profiles are `rolled' around the axis of rotation
Using the finite-element analysis software package ANSYS
The interior structure is composed of Dow Cladmate XL foam with a density of 1.58 lbs/ft3 or 0.025 g/cm3. The sections are cut by hand into complicated, mostly hollow shapes from solid foam blocks using homemade hot-wire cutting tools guided by a set of Formica templates. Each of Hélios' wings has 22 of these foam airfoil sections that are assembled by placing them in the fiberglass molds with the CF prepreg and epoxy. The CF prepreg used (provided at a discount by Newport Adhesives and Composites) is unidirectional with a fiber areal mass of 100 g/m2 and a resin content of 33%. Strong enough to bear a load of 640,000 psi in tension, this material is 0.1 mm thick and comes in long rolls 12 inches wide. A one-inch strip of the carbon fiber when cured properly will ideally bear a load of over 25,000 lbs! The central structural element of the wing is the channel roughly rectangular in cross section that can be seen in the foam in Figure 7. This structural beam is formed of CF laid up over interior parts of the foam airfoils.
Rotor Blade Fabrication
Working with CF prepreg involves cutting and forming it into the desired shape then heating it to 80ºC for four to five hours to cure the epoxy resin. <Picture: 333 Peel Street>
Male mold forms were initially made from plaster painstakingly molded and sanded into the proper shape guided by closely-spaced aluminum templates. The aluminum templates were plasma cut directly from data from the master CAD drawing and positioned precisely on aluminum rails fastened to the floor. The female fiberglass molds used to form the CF and foam wings were then made on the male plaster forms (see Figure 9).
<Picture: Templates>
<Picture: Mold>
Figure 9: Top: Hélios team member Simon Joncas prepares aluminum templates used to construct male plaster forms which were then used to form the final female fiberglass blade molds. There are four molds in all, one for the top and bottom surfaces of both the upper and lower rotor blades. Bottom: The Hélios team and a number of ÉTS volunteers moving one of the 18-meter fiberglass molds.
The process of laying up and curing a Hélios wing in the fiberglass molds consists of several individual layups and curings using the CF, various epoxy adhesives, and a `vacuum bagging' technique to press the entire structure into the mold. The process is too tedious to describe in detail here, and is still evolving as the team makes refinements in response to problems that crop up.
The CF, epoxy, foam, Mylar, and the long molds themselves all expand by different amounts when heated to 80
o C during the curing process. For scale, the molds are over an inch longer at 80 o C than at room temperature. Thus, the long, composite structures initially develop significant internal stresses that tend to deform and weaken them. The team has resorted to making strategic cuts in the CF skins after they are cured to relieve the stresses then repairing the cuts to complete the wing. Obviously a less-than-ideal solution,
SynchroLite
For general airfoil information see:
OTHER: Rotor - AirfoilBlade Profile:
Airfoil VR-7b
|
Chord |
= 5.25" |
|
Leading edge circle is r/c = 0.0113 |
= 0.0113 x 5.25" = 0.059325" |
|
Center at x/c = 0.01055 |
= 0.01055 x 5.25" = 0.0553875" |
|
Center at y/c = 0.004 |
= 0.004 x 5.25" = 0.021" |
|
Trailing edge tab from x/c = 0.96 to x/c = 1.01 |
= (1.01 - 0.96) x 5.25" = 0.2625" [5% of chord] |
|
Trailing edge tab thickness = t/c = 0.005 |
= 0.005 x 5.25" = 0.02625" |
VR-7b w/ -2 degree tab
The Sportscopter and the Boeing Vertol both use the VR-7(b) airfoil and both helicopters are designed for optimum lift not fast forward speed. I.e. the difference in the relative airspeed between 90 degree and 270 degree azimuth is less. I.e. a very high angle of attack on the retreating side is not required.
A thinner airfoil is better for high speed therefore do not us the VR-8 profile.
Prouty states that "moving the aerodynamic center back 2% of the chord results in a 10% saving in total blade weight.
Should bend up 2 to 3 degrees. See Prouty's book p.419-20 and CA Beaty's e-mail. From NVFoil it looks like 2 degrees is best.
Because of the thinness (& weakness) of the tab and the need to clad aluminum in fiberglass it might be best to use stainless steel.
A 1" x 94 " x 0.025 piece of alum. weighs 0.235 lb, at arm of 3.7".
A 1" x 94 " x 0.025 piece of SS weighs 0.686 lb, at arm of 3.7".
Trim Tabs:
From PRA, John Frerichs
, May 22, 2000The trim tabs work by twisting the blades in forward flight. They will have some effect at hover and at 100% rotor RPM with zero pitch but not as much as forward flight. The reason for this is that lift is equal to the velocity of the air squared.. At hover in zero wind the velocity of the blade through the air is the same all the way around the circle. In forward flight this is not true. The advancing blade velocity is the hover velocity plus the forward velocity and the retreating blade velocity is the hover velocity minus the forward velocity. It does not take a big difference in the velocity to make a big difference in lift when you remember that the square of the velocity is equal to lift. The trim tabs are designed to make the blades track in forward flight the same as they do in hover.
Tip:
Consider;
Skin:
Initial idea only;
2 plies of bi-directional woven graphite carbon
Style 584
Thickness 0.013"
W & F 24 x 24
Weave 8HS
Tensile Strength (lbs./in.)
Warp 650
Fill 650
Layup 20, 70, -70, -20
Use more layers on top because the top will be in compression.??
Hinge Pin
Wrap unidirectional tape around hinge pin tube.
The tube should probably have a barrel shape to put equal tension on all strands. And/or pull unidirectional tape taught from tip end??
Hinge Bushing
If the spar and the skin are to be made seperatly the it might be best to put a lage bushing in the spar and then at assembly of the 2 parts insert an inner bushing through the upper and lower built-up skins and the spar bushing.
Taper
Do not have chord at tip so small that Reynolds number is too low.
Maybe 7" @ root to 5" @ tip. Maybe 6.5" to 4.5" & 8' blade.
Taper of 0.25 inch per foot?
Forget taper. See Prouty's book p.649. Also the extra lift at the tip of the retreating blade may be good since it is in clean air outside the other blade's disk.
Twist:
Twist, high pitch and lateral teetering may result in the training edge of the root contacting the other hub or the blades on the other rotor. Perhaps produce and mount the hubs before manufacturing final blades.
Prouty suggests -8 to -14 degrees.
Types
None
Linear
Ideal
The following table is a portion of that on Item 0721, with addition for comparative purposes. The thrust in both cases is 550 pounds.
|
Blade Element |
No Twist |
Twist of -0.667 deg./ft. |
|
|
CT w/ tip loss |
CT w/ tip loss |
|
0 |
0.0 |
0.0 |
|
1 |
0.00005 |
0.00007 |
|
2 |
0.00011 |
0.00018 |
|
3 |
0.00034 |
0.00054 |
|
4 |
0.00073 |
0.00108 |
|
5 |
0.00128 |
0.00175 |
|
6 |
0.00201 |
0.00251 |
|
7 |
0.00294 |
0.00330 |
|
8 |
0.00409 |
0.00410 |
|
9 |
0.00547 |
0.00484 |
|
10 |
0.00605 |
0.00468 |
|
Collective Pitch |
2.08 |
6.42 |
|
Horsepower |
34.801 |
33.628 (3.4% less) |
A twist of .6667 degrees per foot appears to reduce the required horsepower by 3%. This improvement may be slightly greater with an intermeshing configuration because the section of a lower blade that is directly below a section of the upper blade has less horizontal velocity and therefore the increased pitch of the lower blade will give less resistance to the downwash from the upper blade. The disk's diameter reduces and the velocity of the downwash increases as it descends down from the disk plane. That means that a segments of the downwash from the upper blade have increased in speed when they meet the lower rotor blade plus this segment is closer to the root of the lower blade, which has an even slower forward velocity. In one rotor revolution a blade will interact with the blades of the other rotor 4 times. A single disk is 236 square feet. A single blade is 3.5 square feet. Therefore a lower blade will be counteracting, somewhat, the thrust from a upper blade (4 x 3.5) / 236 = 6 % of the time. If we assume that the the diameter shrinkage of the upper rotor's disk and the 2.25 foot distance between the centers of the 2 rotor disks represents 2.3 blade elements then from Item 0721 the velocity of the lower blade at this location is about 55% of that of the upper blade. This 55% is taken from around the 75% R. location. This could result in a loss of (100% - 55%) x 6% x[efficiency of .5] = 1.5% more than the original 3%. It will probably not be this high the increased pitch will only be 0.666 x 2.5 = 1.66 degrees. This results in cooler running engines, greater safety factor, and more reserve power when required. How much more will it cost to taper blades?
The Kaman K-225 had no pitch change motion at the root. the majority of pitch change at the 75% radius point, where the servo-flap was located. This is totally opposite to the conventional concept of twist. Also the pitch at the root is fixed and it looks like it is fixed at 0 degrees.
Also where one blade passes over the other the radius of the upper blade is not much greater than the radius of the lower blade therefore the lower blade is not undoing a lot of the upper blades downwash.
Twist will have a slight disadvantage during autorotation. This disadvantage should be negligible because of the helicopter's; 2 power trains, load disk loading and heavy tip weights.
Idea:
If a master male was to be made without taper or twist and the final product is to have twist but not taper then consider producing 1 aluminum blade with a large bore at the center. Into this bore will go a 'slip-fit' steel rod. The aluminum can then be twisted CW & CCW while still maintaining a straight centerline in the X & Y coordinates?
Potential problem: The negative vertical distance at the center is so small that the 'bore' will extend below the lower skin profile. Maybes just have a small hole and sight down it for adjustments at the time of molding the half-female molds.
Coning - Dynamic:
Bob Firth at CHT and Rick have both mentioned the problem of hub loading with very stiff blades.
My thought:~ If the blade is made out of carbon only it will be very stiff (brittle). Differing loads will be placed on the disk and they will want to temporarily change the coning angle. With a stiff blade there will be no flex and a blade may break. Could consider a small offset flapping hinge, similar to the Robinson R22. This will offer a second advantage also, that of compensating for the relatively short vertical distance between center of gravity and rotor disk.
Weight & Balance
For ref. The Vortech 8-H-12 blade 8'-6" R & 4.75 chord weighs 8.26 lbs.
A full core of Rohacell 31 (8' blade) will weigh 1.4372 lbs.??
A full core of Rohacell 71 (8' blade) will weigh 3.3282 lbs.??
Note: The less the weight behind the center of aerodynamic lift the less leading edge weight must be.
Uni-directional Fiber
If width of tape (tow) that wraps around bushing is 11/16" wide, the bushing has an OD of 3/4" and uni-direction carbon tow or rods are place between the leading and trailing portions of the above tape then the width of uni-directional fibers at the bushing is 2-1/8". The blade has a chord of 6.5" to 4.5", which is a ratio of 0.6923 there for the width of uni-directional fibers at the tip should be around 2.125 x 0.6923 = 1.4712". This is very close to the 2 widths of tape, which is 2 x 11/16 = 1.375.
Consider using 0.050" diameter carbon rod in the middle since the 0.055" diameter tow will probably compress to this?
Core
Can cores be cut without twist and then twist it later during cure?
Braided Carbon I-beam
Consider taking braided carbon sleeve and forming it into a I-beam. It could have a carbon tube and 4 tows at both intersections of web and flanges, giving a 'delta' shape to these intersections.
.5" diameter = 4.7143 circumference.
Height is .6"
Initial calculations
Make flange 1"
Make 'delta' angle 30 degrees. Cos 30 = .8660. The hypotenuse of .5" is then 0.5774". Sin 30 = 0.5. The vertical member of delta is there for 0.2887".
Forget use core of honeycomb or foam.
Spar
If the root of the blade is to be VR-7 then the unidirectional material that is inline with the span probably should be fiberglass because carbon will break under the compression of blade flex. This unidirectional fiberglass may be held together by 45 degree carbon cloth.
If the root of the blade is thicker and the blades do not flex then the unidirectional material that is inline with the span could be carbon. The flex must be accounted for at the slastomeric pitch bearings.
Tow
40k tow has a cross-sectional area of 0.0022785 sq.-in.
With an epoxy to tow ratio of 60/40 the cross-sectional area will be 0.0056962 sq.-in. This is a diameter of 0.08514"
It will take 12.5 strands to come to 11/16" width.
If spar is a lay-up of tape for the top and bottom layers and some of the tapes stop short of going all the way to the tip then they should probably be cut in a chevron shape so that there is not a specific r/R where the compression in the upper layers could be concentrated and thereby collapse the core.
5,346,367 - Advanced Composite Rotor Blade
5,248,242 - Aerodynamic Rotor Blade of Composite Material Fabricated in One Cure Cycle
4,379,013 - Fine Film Pressure Bags Forming Composite Structures
3,923,422 - Taper Lining for Composite Blade Root Attachment
4,407,688 - Method of Making Helicopter Blade Spars
4,096,012 - Method for Forming a Spar Layup for an Aerodynamic Rotor Blade
4,247,255 - Composite Rotor Blade Root End
4,650,534 - Helicopter Blade Longitudinal Member and Relative Manufacturing Method
3,999,888 - Composite Tip Weight Attachment
Composite airfoil assembly ~ Application number: 20020008177
Miscellaneous
Where carbon might come into contact with aluminum or steel, the two materials are isolated with a layer of fiberglass to prevent electrolysis induced corrosion of the metal.
________________
"Another significant source of torsional moment is the position of the airfoil aerodynamic center with respect to the blade flexual axis. An aerodynamic center forward of the flexual axis will result in nose-up twisting moments as lift is increased. Some designers use swept-back tips to counteract this effect." [from Prouty p.43]
I think it looks like between 20 to 23% position? Form NVFoil.
The skin may cause the flexual axis to be further back?
Idea
Blades for Ultralight could maybe have larger chord, or maybe just bigger, than normal and thereby rotate slower than normal; with increased tip weight.
This increased tip weight will -
1/ assure good autorotation
2/ a small coning angle
3/ greater lifting efficiency
4/ allow a lengthened blade to be manufactured for larger helicopters.
Of interest, I think is -
A note in a composite book notes the helicopter blades must have core to stop stress deformation in blade. This might apply mainly to metal blade with metal skins where the metal will fatigue.
Leading Edge:
Idea re leading edge weight
Have a constant leading edge weight down the full length of the blade.
Inserting a cured composite tube in the leading edge could do this. This tube will have to have an insert during curing of the blade so as to resist pressure of cure. On a tapered blade this will give proportionally more weight at outer end. A problem with this is that as the blade gets longer the center of gravity will move further away from the leading edge. A solution to this is to use a larger leading edge tube that can be later filled with the desired mix of aluminum and lead plugs in the desired locations.
Leading Edge re: Wear & Weight
This led to the decision of using nickel for this edge due to its high hardness, high melting temperature, and most importantly its low cost. By using nickel, we can economically replace the section periodically without having the expense of replacing the entire blade. This practice is used extensively in manufacturing helicopter rotors today.
Atomic weights: Uranium = 238.030, Lead 207.190, Tungsten = 183.850, Nickel = 58.710, Iron = 55.847, Aluminum = 26.982, Carbon = 12.011.
Idea re Nose Weight (leading edge)
Have a round bar of a heavy weight material (Tungsten or Depleted Uranium) for the nose weight, but more important have this bar tapered in diameter or stepped in diameter so that it will not want to 'break loose' under flexing and centrifugal force.
Consider having a weight that has a constant weight per running inch along its length. This will weight will assume a greater roll at the tip than the root since the blade tapers but the weight does not. This is somewhat similar to Ultrasport who only put leading edge weight in outer 50% of blade radius.
Tip Weight:
From PRA:
August 11, 1999: Author: CA BEATYTip weights increase the dampening provided by the rotor. Because a rotor with tip weights tends to "stay put" during turbulence, there is a stronger restoring force on the fuselage. This is of course at the expense of more "sluggish" control response.
Though:
Idea:
Make the tool so that blades can be made up to 10.5 feet. Then there might be a market for blades for single seat homebuilts. If mold is longer than 10.5 feet then the user can cut to length off of either end.
Idea:
If one flat horizontal layer of carbon fabric was located on the chord line and from tip to root and if much of the fiber was close being perpendicular to the span then it would resist lateral bending. The main reason is that if the leading edge and trailing edge are kept apart then the blade height dimension will never increase and there for the bonding between upper ply and core and also lower ply and core will only see compression (from flapping). I.e. there is less chance of upper or lower skin delaminating from core.
Idea re Spar Web
Consider drilling (or pushing large 'pin') small holes at 1" centers down the span of the blade. This line of holes will go between the upper and lower members of the spar. Then thread carbon or Kevlar tow back and forth between the upper and lower. There should be two strands of tow, each being woven in an opposite direction through every hole. The intent is that the core willhold the upper and lower spar caps apart and this thread (in tension) hold them together.
Actually a better threading idea would be to pass the thread up through a hole, around 1 rod and then back down the next hole.
Better yet - drill at 45 degrees
Anhedral (tip droop)
See:
DESIGN: SynchroLite ~ Rotor - Blade - Composite - VR-7b - Anhedral (drooped tip)Taper:
see Form - Blade TaperNone
Linear
Not linear
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.
NV Airfoil Plotter
Speed is set at 55 knots (28.2944 m/s).
number point is set at 200.
0012
VR-7 8-H-12Idea:
Consider making a blade for single rotor ultralight helicopter first.
Have discussed this idea with
Dave @ CHT
Rick @ Dolphin
Hollmann books not yet bought
MODERN GYROPLANE DESIGN
. 2nd Edition. by M. HollmannNew book discussing gyroplane design and performance calculations. Configuration design and structural analysis of metal and composite rotor blades in flight. Listing for many computer programs for determining gyro performance, rotor blade deflection and bending moments and jump start are included. These programs are written in BASIC for the IBM PC. Tells how to design for jump-start. Many practical examples and references. 120 pages and 50 illustrations. SALE PRICE $52.00
SOFTWARE PROGRAM DISKS.
BASIC programs listed in Modern Gyroplane Design for the IBM PC. SALE PRICE $120.00
DESIGNING WITH CORE by Hal Loken and Martin Hollmann
Written for the aerospace engineer and the novice who want to know how to design core structures. Finite element analysis and hand calculations are included. Materials and properties for Honeycomb and foam cores and many practical examples are also given. Detailed, step-by-step explanation of how core structures are fabricated is included. A must for the aerospace engineer. SALE PRICE $32.00
IDEA - Hollow Trailing Section
(ie. no core in back section)This will allow for vacuum/pressure in this area, which will push forward. This is needed if blade is to be cured in one process.
Dynamic Twist
Take into account the 3 types of dynamic twist when designing the blade. See Helicopter Performance, Stability and Control. page 43.
Possible Steps in Design of Blade
From Neil on rec.aviation.rotorcraft ~ November 28, 2001
Some rotor blades use carbon fibre for the trailing edges skins ( helps torsional stiffness ) , nearly all use glass for the main spar.
Main reasons , glass has a "soft" failure mode usually an inherent failure will start with a reduction in stiffness of the blade which will be felt in extra vibration . High modulus carbon generally fails much faster and in a more catastrtphic fashion. As350 blades and 105 blades have continous fibres that are "wrapped " around the pins at the root end of the blade , high modulus carbon does not like beeing formed around a tight radius. Carbon is normally used where weight is critical , for blades the a certain mass is required to ensure good auro rotation characteristics. In most cases the bending stiffness of the blade is not critical ( torsional stiffness might be ) so again no real advantage of using carbon. An last but not least Carbon is lb fo lb many times more expensive than glass
|
|
Airfoils: |
May want to consider the newer airfoils VR-12 and VR-15. See
[Source ~ PHA p.286] Used on Boeing 360.
Leading Edge Tape:
http://www.racerstape.com/heli.html
Sub-Contracting
Outside Design: ?
Hollmann
Introduction Page | SynchroLite Home Page | Electrotor Home Page | UniCopter Home Page | Nemesis Home Page | AeroVantage Home Page
Last Revised: May 4, 2007