Conference vmszoo::rc

    
    Norm, You can try Hobby Lobby International. they advertize in
    RCM. They sell a line of four blade Graupner props. Also there
    have been aritcles on adapting two two blade props and splicing
    them into a four blade prop. I'll see what I can round up.
    
    						Tom

    Norm,
    
    You "are" talking about a flying prop as opposed to a static 
    [display] prop, aren't you??  That's what is sounds like but......
    
    Adios,	Al

Norm,

Ditto what Tom said... I use Graupner props EXCLUSIVELY. I think 
they're great.  They are attractive,( Unlike the "Master Screw-offs")
they come very well balanced, and above all, they take a LICK'n!!!

I'm quite sure Hobby Lobby sells just what you're look'n for.  I'd be happy
to send you my last years catalog if you'd like.  Just let me know
your LOC/MS.

Regards,

Brian

    C A U T I O N ,
    
    Just read John Preston's "Safety Comes First" column in the latest
    Model Aviation and John warns against the splicing method for making
    yer' own 4-bladed flying prop which came [I believe] from an SR/CM
    article several issues back.  John reasons that the modified/weakened
    prop hub likely will not withstand the tremendous hub loads and
    will have a high potential for shedding blades.  NOT A NICE THOUGHT!!
    
    USE ONLY A COMMERCIALLY MANUFACTURED PROP	!!!!!!!!!!!!!
    
    ADIOS,	AL

    YES AL, I AM TALKING ABOUT A FLYING PROB
    
    
    Norm

A few years back I was involved in the Asia Pacific F3A (Aerobatics) 
Championships, the China team were using laminated wood props, they looked 
FANTASTIC and appeared to perform just as well.

While the props were made by one of the team members of the accompanying 
entourage I under stood from the interpreter that they were to be commercially 
available in the near future.

Has anybody seen them, I think they would be ideal for a scale model requiring 
a wood prop.

Re: .4

I fully concur with the safety statement on home made props, I have made many
props out of glass and a few out of wood. It's not easy to do a good job and
material selection be it wood, glass carbon, or resin is critical. If anybody
is serious about making props I can share my experience. (insert here the usual
disclaimer). 

John.

    I may never make my own, but I'd be interested in hearingabout your
    experiences.
    
    Dave

Here it is Dave, it took me time to get around to doing it and I must confess I
could have put a lot more in but I am short of time at the present. If anybody
does try to make there own prop please be very very careful, it can be
dangerous, however it can be very rewarding. 

Well making props as I said requires a lot of care as the consequences of a bad
or faulty prop is serious. If you have any doubt about the finished product
break the prop and discard. 

To custom make props you will need a good pitch gauge, a good ballancer (ie.
high point ballancer) and good sharp tools. There are three basic methods of
customizing props; modifying an oversize commercial prop; making a wood prop
from scratch; and molding fiber/resin props. 

The first option of modifying commercial props has been covered in previous
notes so no further comment is warranted. 

Scratch building of wood is very similar to modifying props except it is very
time consuming and some careful drafting is necessary to ensure dynamic balance
of the finished article. I have only ever made a couple of scratch props, they
were for friends scale models, so my experience is somewhat limited.  The way I
did it was to laminate some carefully selected marine ply in to a sheet thick
enough for the desired prop. The lamination process has a the following
advantages:- 

               You know what is inside the prop (nots etc.)                It
makes a for rigid prop.                It gives a good datum lines to ensure
uniform blades. 

The process I used was to rough out the prop for pitch and profile with a belt
sander and then hand finish with conventional file and sand paper methods. The
profile is the most difficult to get but the lines from the laminations help. 

When making composite props (ie. glass or carbon or Kevlar or a blend of the
above, all bonded with a resin) resin selection is much of a trial and error
process. The problem encountered is that polyester resins are too unstable,
5-7% shrink rates are not uncommon, such shrinkage would give a prop that would
never be stable pitch so is useless. Epoxy resins while they are stable they
are more prone to heat distortion and de-laminating. Manufacturers specs help
but it does not tell the total story for resin selection. I use a local resin
that has to be heat cured at 300�F. 

Once you have found a suitable resin you must make a strong mold that can stand
the rigors of many props being pulled from it. By this I mean if the resin
cures at 300F it is no use having a mold that will destroy at 200F. 

Once the mold is constructed and prepared you load pre-wetted rovings (strands
of fiber rather than sheets of fiber) into the mould in a predetermined
measured and planed fashion. It is necessary to know you much fiber is put into
the prop for consistency and strength, it is hard to see how much fiber you
have when it is in the mold with an excess of resin. 

The method of laying up the mold is to ensure the fibers run along the prop not
across the prop, you must also ensure that extra fibers are loaded into the hub
to withstand the loads of bolting the prop to the engine. Note that Kevlar
cannot we used in the hub for filling as it tends to be too slippery, the resin
will not bond completely and the hub splits. 

After the mold is filled the upper part is attached and the whole lot clamped
together and allowed to cure. Once all has cured you split the mold and trim
the prop flashing, the prop must then be left for several days (depending on
the resin) to allow complete curing. 

Finally the prop is pitched, and balanced ready for use. 

That is a very simple description of the process, each prop will take a total
of 1 - 1 1/2 hours labor to complete ready for use. 

John