Conference vmszoo::rc

    One of the simplest ways of making a cowl is to adapt a plastic
    container of some type. I've seen the bottoms od plastic bottles
    and oil quart bottles used a number of times. Given enough
    imagination you'd be surprized what some people will come up with.
    
    
    
    Tom

    OK, I'll start...  Obviously I didn't start this note just for the fun
    of it....
    
    My Bristol M1-C Bullet (WWI monoplane, Balsa USA kit) has a huge
    fuse frontal area.  If I remember correctly, it is about 7-1/2"
    in diameter.  (And with a OS40-FSR, most of the prop area is consumed
    by frontal area!)  From a chord drawn up about 2 inches from the bottom
    of the circle, the firewall slopes back towards the tail.  From the
    side it looks like:
    
    ----------------------------|
    		                |
    				|
    <--Tail		firewall| 
    				|
    				/
    			       /
    	----------------------/
    
    
    The cowling fits cleanly over the fuse and opens to the bottom to allow
    for the engine and muffler.
    
    I made the first few flights without the cowling.  I was trying various
    props and so I was adjusting the needle valve (which can not be reached 
    with the cowl in place - time for a remote needle valve!).  The plane
    flew straight and level after an initial trimming.
    
    I then added the cowling.  After takeoff, I had to add in about 8
    clicks of down trim!!
    
    We came to the conclusion that air pressure is building up inside the 
    cowling and being forced out the bottom, thus giving it "lift".
    
    So, now my question...It was suggested that I make the mounting points 
    so that air can flow out all around the cowling, not just out the
    bottom (kinda like the Corsair cowling).  Do people think that this
    will help the plane??  It flys OK now, and it is closer to scale if
    I leave it, but I am not planning any scale meets with this so I will
    give up scale for improved performance.
    
    Do other people mount cowls with gaps all the way around?  Other ideas?
    
    cheers,
    jeff
    
    	

Back in my high school days when I was heavily into CL stunt I build a ship
that needed a cowl and wrapped the engine in tissue and tape and covered it
with clay and inverted it into (upright engine) a half gallon milk container
and poured in plaster of paris. The plaster then makes a nice mold for layering
the fiberglass into (after applying a release agent) and the cowl can have as
complicated a surface as you'd like. With the carbon fiber available today
you should be able to make a STRONG, light weight cowl.

BTW: I did this ONCE. The cowl was great and the ship flew significantly better
than when we were tweaking the engine and took a few flights with the cowl off.
I didn't feel the grief was worth it but it worked great.

    
    	You might want to check with "Fiberglass Masters" a company that
    specializes in ready made cowls. They have about 200 types in stock.
    If interested I'll bring phone # from home.
    
    Regards,
    Bob G.

    TO BOB G.
    
    YES, I WOULD LIKE THE NUMBER TO FIBERGLASS MASTERS. THANKS
    
    RANDY W
    

    Eventually, I'm going to want a cowl that hasn't been vaccuum formed or
    layed up from fiberglass.  Since I enjoy building much more than
    buying, it seems wise to include this as part of my general research.
    
    Has anyone out there ever tried turning your own aluminum cowl?
    I believe that is how commercial aluminum cowls, cheap pots, and many
    other items are made.
    
    I have a small wood lathe, and a vague recollection of seeing bowls
    formed by using a tool on each side of the aluminum to persuade it into
    the desired shape.  I've hammer forged a few things, but never tried 
    anything more agressive than a small hemisphere.
    
    Before I begin experimenting, I'd love to hear from someone with
    experience who could comment on using a male or female form as opposed
    to free form turning.

>>    Has anyone out there ever tried turning your own aluminum cowl?
>>    ... bowls formed by using a tool on each side of the aluminum 

    I've done this back in the early fifties when I set out to make a ram
    jet that way.  (Never finished the project.)

    The technique is known as   spinning.   Try a library reference under
    metalworking, spinning.

    A female form is secured in the lathe with a disc of thin metal
    pinched between the form and the tailstock.  While spinning at a high
    but still safe rate, a smooth tool like a burnishing rod is pressed
    against the metal, forcing it over the female form.  (No wise cracks.)

    When I was investigating the technique, I encountered forms that
    permitted spinning shapes like Coke bottles!  Magic.  Cowls would be a
    piece of cake using two forms sequentially.

    Alton who should have been a machinist; it was fun; the new DEC isn't

    Alton, don't you mean a "male" form or plug?  That's how I've always
    seen this done...over a male form.  BTW, many aluminum spinners are
    still made in this manner.  They're normally distinguished by a pretty
    thin wall thickness and fine 'working lines' around the spinner's
    diameter over its entire length.
						 __
				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)

    It's "spinning", not "turning", and the blank, or former, is Male.

    

    I remember, years ago, seeing guys turn spotlight shades - looked
    really neat - and quick - beats fibergalss for time to complete.
    
    These guys were spinning them by the seconds !
    
    
    Eric.

>>    Alton, don't you mean a "male" form or plug?  
    
    Ummgfhu.  At this age to mistake the female form for the male form.
    
    What can I say?  The technique could not even be started if the form
    were female.
    
    Alton, who didn't think he was that old yet.

    I am building the Carl Goldberg Sukhoi kit.  I made a mistake on the
    plastic cowling supplied in the kit (its 3 pieces and a bear to
    assemble), so I ordered a nice fiberglass cowl from Fiberglass
    Specialties.
    
    The design of this cowl makes it very difficlut to slip over the nose
    of the fuse.  It is round at the very front, tapers slightly as you get
    to the midpoint, then it changes shape to a more rectangular cross
    section to fit over the rectangular fuse back by the front of the wing.
    
    When I try to slip it over the front of the fuse, the narrower, more
    rectangular part has to be stretched almost to the breaking point to be
    able to fit over the round fuse front. I've had to sand down portions
    of the round edge to allow the cowl to fit, but even at that, it takes
    so much deforming of the rectangular part to be able to fit over a
    round section, that I've managed to cause several cracks in the nice
    smooth surface.  I'm afraid that sooner or later, it will crack apart
    altogether.
    
    Has anyone had a similar experience with this kit/cowl?  Am I doing
    something wrong?  It sure has me wondering.
    
    Regards,                                                              
    Joe