Conference vmszoo::rc

        Re:< Note 441.0 by DARTH::GAROZZO >

                From what  I  have  read  and  from  personal  experience
        there's no need  to  put right thrust on engine mounts.  I try to
        mount my engines straight,  and  if  I  can't get them completely
        stright I make sure the  thrust  is  to  the  right.    I fail to
        understand why pilots can't learn to give a touch of right rudder
        when accellerating down the runway.
        
        Anker

    I do not think I agree with the fact that you should mount the motor
    straight. 
    
    You need the right angle to compensate for the left turn
    induced by the motor torque in flight. Compensating it by ailerons
    or rudder is, to me, not the right thing to do, because you nedd
    it constantly and itit varies, at different levels of power.
    
    You also need the vertical angle (depending on the design of the
    plane) to compensate for exagerate climb at full power.
    
    My method is as follow:
    
    - I do the initial set-up as close as I can to the plan specification.
    - Try it in flying
    - Depending on the result adjust it by putting washers (temporarly)
    beyond the engine mount.
    - When I have found the right angle, I remove the engine mount and
    put it on a flat surface (a metal surface slightly oiled is the
    best one) and I reproduce the same angle(s) as the ones given by
    the washers. Once the set up is done, I lift the engine mount and
    put epoxy on the back, and I reposition it on the set-up.
    
    Once the epoxy is dry, it gives you a pefect wedge (in the two
    directions) and you can mount it on the plane having a perfect
    contact between the wall and the engine mount.
    
    It may sound cumbersome, but once you have done it once it easy.
    
    Regards
                                                              

>    THE MOUNT TO GET THE DESIRED AMOUNT OF THRUST. WHEN  YOU ARE DEALING
>    WITH HOME TOOLS AND SLIGHT ROOM FOR ERROR (1 OR 2 DEGREES) HOW CAN
>    YOU GET IT TO 0 DEGREES. ARE THERE ANY BUILDING TRICKS? 

I've been putting 2 degree thrust plates on my last few planes and believe
me you won't accidentally by building error induce 2 degrees of thrust.
After you see an engine at 2 degrees you realize that 2 is a lot.  

There is an earlier note by Dan Snow and others telling about measuring the
tips of the prop back to the tail.  Dan gave a formula for calculating the
distance variance for various degrees of thrust with various diameter props.
But zero is easy - just have equal distance from the prop tips to the tail.
Then if you want 1 degree right thrust (as per building instructions) then
put in a 1 degree thrust place between the engine mount and the fire wall.

              _!_      
Bye        ----O----   
Kay R. Fisher / \     

================================================================================

    
    	But is it torque you are compensating for or the P-effect?
    [Just kidding!  Please don't answer!]
    
    	Couple of notes back is dead on.  2� is something you won't
    do by accident!  Anyway, what I do is draw a line on the floor
    perpendicular to a flat wall.  Put airplane along this line
    nose to the wall.  Get biggest propeller you can get.  A little
    trig and measuring the tip distances from the wall and you can
    mount the motor to better than ��.
    
    	Oh, yea... don't forget to erase the line before your
    significant other gets home!

        Re:< Note 441.4 by LEDS::ZAYAS >

                Here we  have  a great argument topic again.  I'm sure Al
        and others will jump in, but here are my two bits:
        
                The problem you  are  trying to correct with right thrust
        is propellor torque.   Since  it's  torque,  which  is  trying to
        rotate the airframe counterclockwise (seen  from behind), it will
        turn the plane left if uncorrected.
        
                When you try to counteract the  left  turn  by having the
        engine pulling the plane right (which is  what  the  right thrust
        does)  you  aren't  correcting the problem, just working  on  the
        symptom.  In return, the right thrust will force you  to fly with
        the  rudder  and  aileron trims slightly off center, which causes
        drag.  Even worse, differences in engine  thrust  will cause this
        trim to affect the plane differently.
        
                If instead,  you leave the thrust straight, you only have
        to correct at  times of maximum torque, namely at takeoff or when
        making a slow fly-by  and  then  gunning the engine.  The rest of
        the  time  the plane ends up  being  trimmed  straighter,  flying
        faster and being more predictable.
        
                I belive the latest RCM issue has a  short comment on the
        fact that all serious pattern flyers have the engine  thrust-line
        straight for exactly this reason.
        
        Anker

    What do they do in full-sized planes ?

    R: .-1,
    
    While I normally install no down/right thrust [except for a minute
    amount of each to assure I have no up/left thrust], it is a fact
    that many full-scale aircraft do, indeed, have thrust [and other]
    setups set at other than zero-zero.
    
    One of the most dramatic examples of this I ever saw was a photo
    of a Piper Commanche with the cowling removed.  With all the sheet
    metal out of the way, the [substantial] down and right thrust in
    the engine was plainly visible.
    
    Many high powered [reciprocal engined] aircraft, e.g. the F-4-U
    Corsair, also had considerable fin/rudder offset to counter the 
    extreme torque effects of the very large engine/prop combination(s).
    I believe the Corsair's fin was offset upwards of 6-degrees left
    of fuse centerline which had the effect of built-in right-rudder.
    
    I don't pretend to be smarter than the full-scale designers but,
    for model applications, I find the zero-zero setup to work best
    for "most" models.  Once flight trim has been determined, I center
    all the trims on the transmitter by mechanically trimming the affected
    control surfaces and forget it.
    
    I do, however, understand that thrust adjustments can be quite
    beneficial for certain types of aircraft, most notably flat-bottom
    winged trainer types which need downthrust to counteract the always
    lifting wing.
    
    Adios,	Al

    I recall something in the takeoff checklist for P51 Mustang that
    required the pilot to crank in significant elevator and rudder trim 
    before takeoff.
    
    It wasn't just "make sure the trim is centered".  It was like 1/2
    of full trim deflection on the rudder control.
    
    Anybody got a P51 flight manual handy?
                                                        
    

    As a matter of fact, yes, I do have a P-51 pilot's manual and an
    erection [assembly] and maintenance manual.  I'll see if I can find
    the exact rudder trim setting for takeoff but I know that some given
    amount "was" indeed S.O.P for virtually any/all tail-dragger fighters,
    including the Mustang.
    
    Adios,	Al

	Re: -.5

	Nay say I!!

	Many pattern designs, including some of the very best have right
	thrust built right into the Fiberglas that forms the fuse by
	virtue of the nose not being square with 0-0.  You set the 
	"thrust" by gluing the firewall into the fuse so that the spinner
	back plate is flat and centered against the nose of the fuse with
	only an even space between the two.  Try building one that was
	designed TO have without, and you'll end up shimming the motor mount,
	which is undesirable from a rigidity standpoint.

	Bottom line is that if a design is mature, ie: the guy who published
	the plan tested and trimmed the model before publishing the plans,
	then right, left, up, down thrust and incidence are a result of
	correcting for true flight with all trims neutral, not a set parameter
	based on what might be thought to be good.

	BTW:
	You will always find the need for rudder correction in a single engine
	full scale plane during takeoff or climb because of the increased
	"P" factor associated with the higher angle of attack of these flight
	profiles.  As a matter of fact, you can readily observe the need for
	opposite rudder in decent for the same reason!  The thrust offsets
	in full scale are to compensate for torque and propeller slipstream
	effects in straight and level flight at normal cruise airspeeds.  We
	have the same forces to contend with in models, its only that their
	magnitudes are not equal or in exact proportion and of course as an
	observer on the ground, do not fell the discomfort of uncoordinated
	flight!

	How's that for stirring the pot a little?

	Ron

    In note 441.0, the question was asked about how does one drill accurate
    engine mounting holes in the motor mount.  This question was not
    answered in the note string.
    
    I have the same question.  It is most difficult to scribe the motor
    mount using the engine mounting holes(the engine majufacturer does not
    provide an engine template).  I have used a nail with the
    correct diamameter with white dope on the tip to spot the hole
    alignment.  However, most motor mounts are not built so that one can
    put then on a drill press and dirll them straight.
    
    How do you experts do this process?
    
    Your solution will be greately appreciated.
    
    
    Ollie
                                                 

For doing nylon mounts I generally put the engine in the mount inverted, 
if possible, and then use a pin in the bolt hole to scribe a line around 
the edge of the hole. I have then used a block of wood with the mount 
bolted to the face to hold it upright while drilling the the drillpress. 
If you drill out the backplate for isomounts you can use drywall screws 
in the holes to attach it to the block on the drill press bed. I have a 
small piece of 4"x4" that I can clamp to my drill press table that provides 
a good face (side) to attach it to the drill press. With the Shopsmith I 
have I can actually do it as a horizontal boring operation and raise and 
lower the table to position to the holes.

Many times I'll do one bolt and tap it and then mount the engine inverted 
and scribe the other lines. Otherwise it's difficult to hold it steady 
while you scribe the other three holes.

    As Jim suggests, I usually drill one hole and then mount the engine 
    using this hole.  I then use a drill the size of the engine's hole
    to start.  This insures that the hole is centered.  I then hold it by
    hand and use a long shaft drill to drill the hole.
    
    Accurate??  Not perfect, but it gets the job done.  If you want to be
    accurate, then you need to use the template supplied with many engines.
    
    If you are going to err, err towards giving it right thrust.
    
    cheers,
    jeff
    

    One trick suggested in a Carl Goldberg kit I built is to tack glue the
    engine to the motor mount with CA glue so it doesn't move.  This enables
    you to mark the holes, or as described earlier, actually drill the
    holes if you go in through the bottom.  Then the engine can be pried
    loose with a screwdriver to free it.
    
    -Joe

    Jim/Jeff/Joe, thanks for the suggestions.  This notes file really
    produces results for those of us with problems/questions.  I'll use
    this information and hopefully have a good installation.
    
    Thanks again,
    
    Ollie