>> Steve, What do you think of this idea.
>>
>> Since we will not be flying forward in helicopter mode for long
or at
>> high speed
>> the leading and lagging hinges can be done away with. Same goes
for the
>> flapping
>> hinges. I think we can use GRP for the hub. Same as several
European>> helicopters
>> use. GRP has high tensile strength and a low modulus of elasticity
>> allowing it to
>> flex without failing. Same as the Long EZ main landing gear. The
>> innovative feature
>> of having a one piece carbon fiber blade with internal outer
bearing race
>> and pitch
>> change arm is also a major weight and cost saving feature. The
bearing>> balls are
>> Torlon which are widely used in off shore sail boat racing.
These are
>> subject
>> to the worst possible environmental conditions and survive. The
>> connection
>> between blade and hub is achieved by the bearing balls and they
are fed
>> into the races by one access hole on each side. We have used this
>> feature in the past of an aircraft propeller and it works well.
>> --
>> Paul Lamar ...No rotor no motor.
>
>
> Go one step further and use a standard prop internal pitch change
> mechanism.
> Milo
>
> Care to make a 3D dwg for me? I can't see how it would work with
counter> rotating
> rotors?
>
> Paul Lamar
Forgot about that! Milo
That is why I went with the tried and true helicopter pitch change.
--
Paul Lamar ...No rotor no motor.
I think it would start shaking pretty good as soon as you started
gettingsome translational lift. Did you look at that website I sent?
http://www.rotor-international.net/
It uses co-axial two-blade rotors and they appear to be underslung
withshort beams that twist for feathering, flex for coning and may
be servo-tab
controlled. Look at how far apart the rotors are. I think if you
want the
flexure to to accomplish lead and lag, the flexible portion should be
outside the feathering bearings. The stiffer the system is, the
more moment
applied to the hub and the more vibration.
I think on the model you've shown, with one bearing race, when a
moment is
applied to the assembly the loads on the bearings could get pretty
high. A
second bearing race inboard would help, especially if it were an
angularcontact type that could take high thrust loads and it was
located far enough
inboard to resist to the applied moment. I'm not sure about those
Torlonbearings being strong enough, but with two races, they might
be and you
would avoid the shear load that would occur with your model and
the loads
would be all compressive. The slight elasticity of the Torlon may
helpdistribute the load which would be a good thing as well.
Steve
I don't think so. We don't do much translational lift. It is an
arcing takeoff with
considerable vertical velocity for only a second or two.
I looked at that web site but I saw no details of the hubs. If
you see something
there in detail please do a screen capture and email that.
All constant speed props are built with only one bearing. The
negative bending
moment on the blade hinge due to centripetal force acting on the
blade CG counteracts
the positive bending moment due to thrust. Therefore it only needs
one bearing.
If the constant cord blade weighs 20 pounds
and it moves up one foot at it's CG radius position that is a
negative bending moment
of 100,000 foot pounds. The centripetal force on the 20 pound
blade is 100,000 pounds.
Weight/32.2 x FPS^2. The positive bending moment due to thrust on
the blade is only
6.5 ft x 300 pounds (each of four blades will need to generate 300
pounds to lift the
1200 pound craft.) or about 2000 foot pounds.
Obviously the rotor blade CG is not going to move up one foot. The
upwardsdeflection of the blade at its CG position will only be
about .2 feet or 2.4 inches
balancing the thrust moment. That puts a negligible bending load
on the bearing compared
to the centripetal load. All props and rotors work this way. If
not rotors and blades
would break off at the hub because they do not have the bending
strength on their own
to support the weight of the helicopter.
The bearing consists of 22 half inch dia. balls. In effect they
act like 22 1/2 inch
dia. bolts in single shear. The centripetal load is 100,000 pounds
so each half inch
bolt only needs to accept 4,500 pounds of shear roughly. A 1/2
inch bolt has an area
of about .2 square inches. So the shear stress on the bolt will be
22,500 psi
roughly. A piece of cake for a steel ball but maybe marginal for a
Torlonball. Consequently I will try to get the carbon fiber blade
weight well below
20 pounds each.
As you can see the centripetal force is orders of magnitude higher
than the
bending loads on the blade hub. It is all about numbers.
Paul Lamar ...No rotor no motor.
I don't think I can add too much to the discussion as heli dynamic's are
something I've never studied to extensively [primarily because I
never come across any books on it] but I do think there will be
times when there is signifigant translational lift. I'm thinking of
landing more than take-off. When the pilot pulls up and starts to
drop forward speed and translate into vertical flight. This isn't
a problem on your average aerobatic a/c however, so maybe
it won't be such an issue as long as there isn't abrupt control
movements exceeding some G number?
Not entirely sure..
Jarrett
A lot of prop helio hubs have lead lag dampers so they could be added.
Perhaps. I can send a dwg and you could do an FEA. I am curios about the
bending deflection of the FRP and the loads on the bearing balls.
I changed the design and did away with the inner bearing.
What would help is a simple FEA of one 1/2 inch ball and sections of the races.
I'll do a 3D of just that.
Paul Lamar ...No rotor no motor.
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