Conference vmszoo::rc

    Re: .-1, Dave, 
    
    > Intuitively, that seems bass-ackwards." 
    
    Yeah, it sure does...I'll be interested in hearing the explanation
    for this behavior (I _sure_ don't have one).  

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

    how about this....

    a nose heavy plane forces the tail up-wards, out of the zero angle
    of attack it would have if the tail was flying "level" with
    respect to the planes over-all angle of attack, this, in turn,
    causes the tail to produce a downward moment, which forces the
    plane to climb.  A tail heavy plane does the opposite ?

    I know this is silly, but, what the heck, the idea from -.2 seems
    funny to me too.

    

With a heavy nose, the plane starts to dive and pick up speed. This in turn
increases lift which brings up the nose and subsequently starts a stall. Cycle
repeats and plane "porpoises" for a while until it finally stabilizes.  What do
you think? 

Dave 

    about nose heavy gliders recovering from a dive faster, could it
    be that up-elevator trim is used to compensate for this, and if
    so, gaining speed causes this up trim to "overcompensate"???
    kevin

    Does anybody know the proper CG point for the OLY II ?????? Right
    now, I'm balancing it on the spar and it seems ok, but I'd like
    to get it exact if possible.
    
    Steve

    Steve,
    
    I suggest to balance your OLY II statically in that way, that the CG
    is in a certain range. More important is the dynamic balancing, refer
    note 399.231 and following. In few words : When the plane is in the
    air, trimm for a steady flight speed. After this give down elevator
    and pick up some speed. Release the elevator to neutral and watch what
    the plane's doing. If it starts pumping (nose up - nose down - nose
    up....) it means, you had to trim high for steady speed - too nose
    heavy. If it would go more down, you would have had to trim down -
    tail heavy. I personally prefer to start on the heavy nose side.
    
    
    Holm- und Rippenbruch,  Bernd

Speaking of dynamic balancing...

I've been wondering about dynamic balancing ever since
Anker put his original note in.  I had since read the
same description in the sailplane digest (or whatever
that Al Ryder cited).  

I believe that they actually determine the correct CG
in full scale gliders using this technique - can anybody
comment on that?

But...

I don't believe in it.  I've had the benefit of starting with
my CG's right where the manufactures have recommended and probably
never went too far in either direction but...

If you dive your plane and it slowly pulls up it's OK.  If if porpoises
it is supposedly nose heavy.  OK - so you say - I have too much
up trim in to compensate for my nose heavy condition and when I put
it in a high speed dive it pulls up to hard.  So you take some nose weight
out and fly again.  What happens - no change.  So you take some more weight
out and fly again.  What happens - no change.  So you take some more weight
out and fly again.  What happens - no change.  So you take some more weight
out and fly again.  What happens - no change.  So you take some more weight...

Then you think - "OK - since I haven't changed my trim setting naturally
every time I dive it will pull up".  So you put in some down trim.  

Great you say - now it doesn't porpoise.  Therefore it must be balanced
correctly.

Then you think - "But is it balanced or just retrimmed not to porpoise?".

So you put all the weight back in and fly again and it reacts exactly
the same - perfect.  So now you say - "OK - was it just out of trim?
Can the trim dominate the glide test to the extent that the weight movement
for setting CG doesn't matter much?"

I maintain that the answer is yes.  But I surely don't feel like
an expert on the subject.

Opinions?

Bye          --+--
Kay R. Fisher  |
---------------O---------------
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The dive test should be performed after the glider has been trimed out for 
level flight

    re .411
    I'll agree that the trim *can* override the weight/balance in the
    scenario you present, but you should try to determine where your
    stab trim is sitting before the dive test, and hopefully it will
    be neutral. Anything else and your fighting/analyzing two conditions
    at once.
    I also don't put too much stock in dive/balance tests. I usually
    balance at around 35% initially, which is invariably nose heavy,
    then watch how it behaves on the landing approach particularly on
    the down wind turn from approach leg to base leg. I start pulling
    weight until it starts acting squirrely in some manner, then put
    a little back. It usually winds up at around 37-38%, in order to
    fly the way I like it. Porposing, in my experience, usually turns
    out to be caused by control linkages not centering.
    
    Terry
    

    Kay,
    
    	On the first flight, set trims to neutral. Take off and retrim
    for level flight. Do the dive test. If you remove weight, the next
    time you go up, RETRIM FOR LEVEL FLIGHT AGAIN. Theoretically (sp?)
    if you trimmed for a nose heavy condition and then removed weight,
    you should have too much up trim the next time up. So, you have
    to re-trim. Now do the dive test again, etc. You have to re-trim
    every time so compensate for exactly what your talking about.
    
    	What I found is that there isn't a whole lot of change each
    time. Espically removing just a quarter ounce. It's really tough
    to do in any kind of wind. I was fortunate to have almost dead calm
    and could detect the SLIGHT difference. I DID see the difference
    in the dive test.