Conference vmszoo::rc

    Thanks for start'n this one Al.  I was going to if nobody else would.
    I am an amateur in aerodynamics so I'll ask more than I answer.
    
    Could someone start with an explanation/effects of incidence and
    where, when, why it is used.  Then onto washout, trimming, building
    straight, etc....

<< To get this topic started, I'll reprint an excerpt from note 279.31 which >>
<< contained a short glossary of terms which will probably be referred to    >>
<< often during the course of upcoming discussions.  Note that I've changed  >>
<< the term "Thrust Datum Line" to "Fuselage Centerline" to enhance under-   >>
<< standing.			     					     >>

A thought occurred to me that a lot noters, newer to the sport, may not under-
stand the "incidence-ese" we're speaking in the last several notes so I thought
I'd provide a glossary of terms that will, doubtless, appear frequently in any
discussion relative to trimming:

FUSELAGE CENTERLINE:  A line drawn down the longitudinal center of the fuselage
		      as viewed from the side [or the top] of the aircraft.

INCIDENCE:  The positive or negative angular variance of the wing or horizontal
	    stabilizer measured from the fuselage centerline as viewed from the 
	    side of the aircraft.

DOWN-THRUST:  Similar to incidence; the negative angular variance of the engine 
	      thrust line measured from the fuselage centerline as viewed from 
	      the side of the aircraft.

RIGHT-THRUST:  The angular variance of the engine thrust line measured to the
	       right of the fuselage centerline as viewed from the top of the 
	       aircraft.

DECALAGE:   The angular variance between the wing and horizontal stabilizer,
	    irrespective of the fuselage centerline. Ex: 2-degrees positive in-
	    cidence at the wing and 1-degree negative incidence at the stab = 
	    3-degrees decalage regardless of the wing's, or the stab's, rela-
	    tionship to the centerline.  Similarly, 1-degree positive wing and
	    1-degree positive stab = zero-degrees decalage.

That's enough for now.  Hopefully, these discussions will be kept simple enough
for these terms to suffice and enhance understanding.  If we get too "hairy" in-
to the aerodynamics, I'm afraid we'll lose a lot of people (including yer's tru-
ly!).

Adios,	Al

Let's make the general statement that virtually any aircraft will fly reasonably
well if setup 0-0-0, i.e. 0-degrees down-thrust, 0-degrees incidence in the wing
and 0-degrees incidence in the horizontal stab. This statement, however, assumes
"any" wing airfoil "EXCEPT" fully symmetrical as more lift is generated from the
top of the wing than from the bottom, therefore requiring no positive incidence 
to provide a lifting angle of attack [though some "may" be used to cosmetically
enhance the level flight attitude of the aircraft].

With flat or nearly flat-bottom [Clark-Y type] airfoils, virtually NO lift is 
generated from the bottom of the wing and, since lift increases as a function of
airspeed, down-thrust in the engine is used to prevent or reduce ballooning at
higher power settings.  Right-thrust is normally used to counteract left-pulling
torque effect during takeoff but has no real purpose in flight so it's being 
used less and less as time goes by.  I generally try to build in about 1-degree 
of right-thrust just to insure that I have NO undesireable left-thrust.  By the
same rationale, I also build in about 1-degree of down-thrust.

With the fully symmetrical airfoil, EQUAL amounts of lift are generated from
both the top "and" the bottom of the wing so, obviously, it generates, effec-
tively, zero-lift if installed at 0-degrees to the fuse centerline.  Two methods
may be employed to overcome this: one is to use up-elevator trim [or negative
stab incidence] to provide the necessary angle of attack but this causes the 
aircraft to fly tail-low which looks awkward and produces unnecessary extra drag
so the more correct method is to set the wing a couple of degrees positive to 
the fuse centerline.

These basic statements shoud provoke some thought [and, hopefully, some under-
standing of why different types of planes are setup as they are] and generate 
some questions/discussion.

Adios,	Al

** I've opted to respond to this in this topic as, all of a sudden, we seem to 
   have trimming/incidence discussions going on in 3-or-4 different topics and
   it'd be desireable to get all such questions/discussion routed into the trim-
   ming topic.  **
    
>    					.......My PT40 requires lots
>    of down to fly inverted.  Yes, I know it is because of the flat
>    bottom wing.  The Skooter II that I flew only needed a "breath"
>    to maitain level flight.
    
>    Please excuse my ignorance when it comes to negative incidence,
>    I realize now the effect it would have on a monoplane.  Do Bi/Tri
>    planes use negative?  If so, WHY?

* Chris..., as Tom mentioned, he and I have agreed to disagree on the proper 
setup for a bipe.  My opinion, which seems to have been proven by my experience
with several bipes, is that the top wing should be set a couple of degrees nega-
tive to the lower wing to assure that it stalls last [after the lower wing]. 
I've applied this theory to a coupla' particularly nasty dispositioned bipes be-
longing to fellow local-modelers and it has tamed them right down.

The theory is that the bottom wing stalls first, leaving the ship hanging from 
the still-lifting top wing, thereby assuring stability and resistance to tip-
stalling when low/slow/nose-up in attitude as in takeoff and landing.  Many full
scale bipes are set up this way though some noter(s) report that some were/are
setup just the opposite, i.e with positive in the top wing.  A thought though is
that the top wing could be [say] 1-degree positive and "still" be negative with 
respect to a 2-degree positive lower wing.  All I know is it works fer' me!
    
Adios,	Al    

    AL,
    
    I knew you'd answer them here.  And on bipes, your actually talking
    "decalage" between the top and bottom wing, yes?
    
    Chris

    Chris,
    
    Re: .-1..., Hmmmm, yeah, I guess you "could" call it decalage since
    it's the angular difference between the two surfaces [wings], irres-
    pective of the fuse centerline, though my understanding of the term
    [decalage] had always been as applied to the difference in incidence
    angles of the wing and stab.  I'm not real sure how "decalage" applies
    to multi-wing aircraft, i.e. is it the total [algebraic] sum of
    the incidence angles of "all" flying surfaces [3, in the case of
    a bipe], or the sum of the wings plus the stab, or.......?  It would
    seem that we can have decalage wing-to-wing and/or wing(s)-to-stab.
    
    I think what's important is to understand the relationships, regardless
    of what we call them.   
    
    Adios,	Al

    Al,
    
    I agree on understanding the relationships.  I was trying to provide
    food for thought.  Multi-wing aircraft seem to throw a curve at
    the problem!
    
    Chris
    

                The thory behind having the upper (forward) wing set with
        a little positive  incidence is to ensure that the center of lift
        (terminology!) is always behind  the center of gravity.  When the
        upper wing stalls the center  of lift will move backwards and the
        plane is gauranteed to drop the  nose.  
        
                If  you  set  it  up  opposite the center of  lift  moves
        forward  when  the  lower  wing  stalls and you run the  risk  of
        suddenly having a tail-heavy plane.  Guess what if you are coming
        in too slow for a landing and the lower wing stalls, you'll  then
        start  dropping  the  tail  and the upper wing will stall and the
        next thing you know is that you plummet to the ground.
        
                Now if the plane is very nose heavy to begin with you may
        not see this problem.
        
        Anker

    Anker,
    
    That's precisely how Tom T. describes it and I won't argue or dispute
    the rationale as it appears sound.  All I can say is that I was
    turned on to the top wing negative thing by a verrrry experienced
    modeler some years ago and it has worked like a charm for me and
    I have yet to see the response you described occur.  Perhaps in
    the dynamic world, the additional drag of the stalled lower wing
    tends to rotate the nose down, counteracting the rearward shift
    in the center of lift.  Whatever happens, this setup has been
    ultimately successful for me and others I've shared it with so I
    guess, a'la the arrangement Tom and I have, we'll just agree to
    disagree on this point.  I "do" know that full-scale bipes have
    been setup "both" ways so there must be plusses [and maybe minuses]
    to both force arrangements.
    
    Adios,	Al

<< I've taken the liberty [without Tom's knowledge...hope you don't >>
<< mind, Tom] to duplicate this note in this topic as it is most    >>
<< germane to the subject of trimming/setting incidence on a model. >>
<< The method Tom offers describes a good method for determining/   >>
<< setting wing incidence without the luxury/advantage of a Robart  >>
<< Incidence Meter.  Thanx fer' the input, Tom...sounds good.       >>    
    
    For those of you who don't have a incedence meter you can and should
    still check the incedence of your wings. Here is a method how.
    
    Start by tracing the airfoil of your wing on a piece of tracing
    paper. This the the airfoil including sheeting. Not just the rib.
    
    Now cut a rectangle out of card stock larger than the tracing.Make
    sure that all sides are as parallel and perpendicular as possible.In
    the center of this card (long ways) draw a line parallel to the
    bottom edge of the card. Now transfer the tracing of the wings airfoil
    onto the card. Cut out this airfoil and make sure that it will fit
    over the wing yet still be snug.
    
    Place the plane on a flat surface and level the thrust line. Install
    the card on the wingtip and measure from the surface to the rear
    bottom corner of the card. Repeat this measuring but to the front
    bottom corner. Subtract the lesser measurement from the larged.
    You now know the length of one side of a triangle produced by the
    angle of incedence in the wing to the thrust line. Use trig. to
    determine the small angle of the triangle. If you can't see this
    in your mind draw it out and it will make sence.
    
    
    						Tom

    
      Can anybody give me the definition of "WASH OUT" I think I know
    what it means but I'm not sure.Also what is the purpose of having
    it built into the wing.Dose it make the plane more stable or does
    it make the plane able to do more percise manuvers?
    
                                              KEEP'EM FLYING
                                               JERRY

    Jerry,
    
    Washout means the wingtip is set negative with respect to the  
    center-section's incidence angle, that is to say, the tip is
    twisted trailing-edge up [or lead-edge down, if you prefer]. This
    is normally accomplished by jacking up the trailing edge of the
    wing at the wingtip during construction. 1 1/2-to-3 degrees is the 
    usual/normal amount used on models.
    
    The purpose is to assure that the tip stalls LAST, "after" the center
    section, thus preventing [or at least delaying] undesireable tip
    stalling [snap rolling] when in low/slow/nose-high attitudes such
    as landing and/or just after takeoff.  As a rule, washout is only
    seen on scale [or other heavily wing-loaded] ships and some pattern
    birds.  Pattern ships have gone more toward using thicker tip-section
    airfoils [as compared to the root section] to accomplish the same
    effect without the additional drag resulting from washout.  It
    [washout] is rarely seen on trainer and sport type models.
    
    In direct response to yer' question, washout is used to enhance
    low speed stability and has little/no [positive] impact on the pre-
    cision with which aerobatic maneuvers can be performed.
    
    Adios,	Al

    The GP PT40 has 7/8" twist applied to the 5 Foot wing.  That's alot.
    
    I have flown it so slow that the instructor was....became
    alarmed...that I flew it so slow.  Also, found out that ailerons
    are useless at that speed (remember that Al?).
    
    Chris
    

    That's 7/8" at EACH wingtip.

    Chris,
    
    Yer' right, that amount [7/8"] is a GOB of washout.  I wouldn't
    have expected to see "any" washout used in a flat-bottom airfoiled
    trainer but ya' live and ya' learn I guess.  Yeah, I remember the
    incident where you discovered that ailerons are almost totally inef-
    fective at very slow speeds.  That syndrome exists to a greater/lesser
    extent with all aircraft.  The "trick" is to design the ship such
    that the ailerons remain effective at least down to stall speed.
    You'll begin to realize that this trick is more often accomplished
    the higher the performance of the ship in question;  not so much
    because of any design miracle as due to the fact that the stall
    speed of these higher performance types has increased with direct
    proportion to performance.  Therefore, aileron control remains positive
    right down to the stall but the stall occurs at a much higher speed
    than is typical of trainer and some bottom-end sport types.  That's
    just one of the tradeoffs we pay for performance and one of the reasons
    the newcomer needs to start at the low end of the performance envelope.
    
    Adios,	Al

	OPINION: Trimming is a progressive NIGHTMARE.
    
    		 What I mean by that is if done correctly you continue 
    from one step to the next until some trimming of the ship is required.
    You do the adjuatment and then go back to zero and start over again.
    So on and so forth until the plane is flying like you want it. 
                                   
    	FACT:  
		 Trimming begins on the building board and in fact never
ends until you decide to retire the ship. On it decides to retire itself.

					  BUILD STRAIGHT.

	To begin flight trimming take the plane off and trim the elevator
and ailerons for level flight( at the normal flight speed).  Now land and
adjust the surfaces so that you can return the radio trims to the neutral
position. Again take off and check trim for level flight. Now fly the plane
past yourself and as it passes pitch the plane up into a 45 degree climb
and note if the fuse is pointing to one side or the other. If it points
straight up your in luck. If the fuse is pointing to the right add left
rudder. If it points to the left add right rudder. Now go back and verify
level flight. Adjust if required and then go back to the 45 degree pitch
step. Continue this until the plane will fly level,the fuse points straight
and the radio trims are set at neutral.  The 45 degree pitch should be done
into the wind.
	Next comes the aileron setting for adverse yaw during a roll.
Begin by flying level and roll the plane up side down. Add elevator to
fly level but don't add rudder or ailerons. Note if the fuse is pointing
to the right or left. If it points straight forward no differential
aileron throw is required. If you roll to the right and then the fuse
points to the right adjust the ailerons so that they deflect more up
than down. If when you roll to the right and the fuse points to the left
you adjust the aileron deflection so that the aileron moves more down 
than up. This adjustment is done on the ground.  After the adjustment 
go back to the start and verify all the previous steps. Adjust where
needed and continue until you get back to verifying the aileron
differential and the plane is solid. It's a lengthy process but one
that is most rewarding. The last step I'll cover on trimming this
time is knife edge flight. Roll the plane so that the right side is
on the top and see if the plane pulls towards the canopy or the landing
gear. If it pulls towards the canopy then reduce incidence in the wing.
If it pulls towards the landing gear then add incidence. If you have
an adjustable stab then all the better. For pulling to the canopy 
add incidence to the stab. For pulling to the landing gear reduce stab
incidence.


						Tom

    Great Planes supplies a very good article on trimming with many
    of their kits.  (I got one with the Super Sportster, and I know
    that Bill Lewis got one with his Cap 21.)  They go into the things
    that Tom described in .-1 and also into setting up your engine's
    thrust line.  One thing that I can add to Tom's hints is to try
    to do most of your testing on a calm day.  It is difficult to separate
    out cross wind effects from trim problems and since trimming is
    an iterative process, you can get screwed up if you guess wrong.
    
    Charlie
    

    
    For the most part you can only see a problem with right/down thrust
    just before the plane stalls in a stall turn. This is assuming 
    that the engine isn't fighting excess lift form wings. In a lot
    of older designs this fightin was quite common. 
    
    In a groovey ship for the most part slight misalignments in thrust
    arangement will be hard to see. To check thrust set up get the ship
    trimmed for level flight and get the rudder trimmed. Pull the ship
    into a vertical climb as if to do a stall turn. Bleed off speed
    and see what happens. As the plane reaches the stall speed it will
    tend to pitch right,left or towards the canopy or landing gear.
    If it does pitch then you should adjust the thrust of the engine
    in the opposite direction.
    
    	ex, Plane pitches to the right. If the engine has right thrust
    in it  then reduce the right thrust. 
    
    	ex, Plane pitches to the right and towards the canopy. Reduce
    right thrust and add a little down thrust.
    
    	So on and so forth.
    
    
    Oh pray I shouldn't forget to tell you... after the adjustments
    start the trimming opperation over again at level flight.....
    
    Have FUN :-)
    
    						Tom

    Gosh, after we spend the winter builing the plane we can spend the
    summer trimming it.  Sounds like fun! :-) :-)
    
    When do we start flying?
    
    Bye....
    
    Chris

	One item that has only been mentioned but not discussed in 
detail is what steps are taken within the building of a model to assure 
the it is built straight. I thought I would take this note down this 
hole and others will hopefully chime right in.


	To start I usually draw the thrust line on the fuse sides
right out of the box prior to any other assembly. Along with this I draw 
the location of all formers. From here the basic construction begins.
After all of the formers have been glued in place I install the engine
mount and engine/prop. Using a tape measure and or a yard stick I 
measure for the correct thrust arangement. HOW?

I install a prop on the engine and set the prop level. From the rudder
post I measure to both prop tips. Rotate the prop 180 degrees and 
remeasure. If your shooting for "0" then the measurements should be
identical. Non lay the fuse on it's side and again set the prop 
horizontal. I then pick a point on the thrust line and measure from
here to the prop tips. Rotate the prop 180 degrees and then remeasure.
If again your going for "0" the measurements should be the same.
Adjust where necessary.

TBC

						Tom

    Tom,
    
    What's the formula when you don't want 0 degrees?
    
    Chris

>    What's the formula when you don't want 0 degrees?

Another way is to adjust for zero then take off your engine mount and
reinstall it on top of thrust plates.  You can buy these at your local
hobby shop for various engine sizes and they come marked in combos.
To get 3 degrees you sandwich a 1 degree plate and a 2 degree plate together.

I find them to be pretty handy little devices - but I don't claim my
right thrust to be exactly 2 degrees.  Think next time I'll try Dan's
formula on the results just to see if they are accurate.

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

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

    Dan, Kay,
    
    Thanks, I appreciate the formula and advice.  The thust plates will
    work on the Kougar just fine, but the Jetstar can only use the plates
    for right thrust due to the motor mount construction.
    
    Chris

    Gosh!  I'm embarrassed, I was just looking back thru notes and found
    that Tom T. had already started this topic in 326.  Al, why did'nt
    you tell me? :-) 
    
    And now, since I have'nt seen it yet, how 'bout some talk on tools
    needed to trim it before it flies, like incidence meters and control
    deflection meters?
    
    Chris

    Chris,
    
    I thought so but couldn't seem to locate it at the time.  If the
    moderator [are you listening, Dave Rene?] would care to, maybe this
    topic could be combined into 326, or vice-versa.
    
    Now, are you ready for this, Chris??  And, honestly, I'm not out
    to embarrass you or make you feel lower than the aftermath of a
    riverfront grudge-hunch :-}, but you did it again!  Yup! a discussion
    on retracts already exists in topic 216.  Took me a minute to remember
    but I was sure I'd put one of my very first replies in a topic about
    retracts and, sure enough........  Maybe these two topics [216 & 402]
    should be combined as well - whatcha' think, Dave??
    
    Adios, Chris (are you blushing? :-}), 	Al

    I think that i've had a flash of insight into this on-going high wing
    vs low wing stalls first biplane controversy between Al and Tom. I
    know that this discussion started over in the pattern note but this
    seems to be more of a trimming issue. 
    
    I was looking at a top view of an Aeromaster over the holidays (Santa
    Claus, in his infinite wisdom, brought me an Aeromaster with an OS 90
    4 stroke). The thing which struck me was that there isn't all that
    much stagger between the upper wing and the lower wing. Especially if
    the lower wing is the straight version. As the plane pitches up, the
    stagger between the upper and lower wings gets smaller due to the
    vertical separation between the wings. Most airfoils stall at angles
    of attack in the 20 to 30 (more or less) degrees range. At these
    angles of attack the top wing will be about even with or maybe
    slightly behind the lower wing! So at least for the Aeromaster I agree
    with Al that the BOTTOM wing should be set up to stall first since it
    will probably be the forward most wing at the angles of attack where
    the stall occurs. If there had been enough stagger that the top wing
    would never get behind the bottom wing then my guess would be that the
    TOP wing should stall first. 
    
    This can be verified/killed if we can get a few people to check the
    stagger vs upper-lower wing incidence setups for a few full scale
    birds. I would do it myself but I don't have the data.

    What do ya' think?

GES

        Re:< Note 391.27 by TONTO::SCHRADER >

                I hadn't thought of that and think you are correct in the
        case of stalls  because  of  too high an angle of attack.  If the
        plane stalls because of  just  too  little  airspeed  the reverse
        would be true.
        
                My  experience is that high  angle  of  attack  stalls  -
        inadvertent ones - typically happen on  takeoff.    Low  airspeed
        stalls with normal angles of attack happen on landings.
        
        Anker

    ALL stalls are high angle of attack stalls. Low speed does NOT stall
    a wing. True, a wing at low speed doesn't generate a lot of lift, but
    a stall is what occurs when the airflow above the upper wing surface
    becomes turbulent and seperates. This only happens at high angles of
    attack. At low speed & low angle of attack, the airflow is still
    smooth and non-turbulent. When flying along at low speed you must
    (of course) run at a higher angle of attack to keep flying level
    and this can get you into a stall situation.

GES (Glenn Schrader - NSG - TONTO::SCHRADER)

        Re:< Note 391.29 by TONTO::SCHRADER >

                You are correct, but:  If flying  with  the  axis  of the
        plane  parallel  to  the  ground  at very low  speed  and  losing
        altitude,  the wing has a high angle of attack  relative  to  the
        wind and can stall even though the plane doesn't seem  to  have a
        high angle of attack.  It was this situation I was  referring to.
        
        Anker

    Glenn/Anker,
    
    Verrrrrry interesting, the last few replies!  I know for certain
    that full scale bipes have been setup with "both" force arrangements
    but memory fails as to specifics.  Again, all I can cite from direct
    knowledge/experience is that I've tamed some "extremely" hairy bipe
    models by setting the top wing 1-2 degrees negative to the lower
    wing and the nasty old Yeller' Peril that I fly routinely was one of
    these. (ol' Yeller' Peril is an overweight, marginally powered 1/4 
    scale Bucker Jungmeister, BTW.) 
    
    Could it be that the top-to-bottom wing relationship in a stalled
    attitude that Glenn mentions was the motivation for the Beech Stagger-
    wing??  The top wing of the Beech should "always" be behind the
    bottom in this configuration.  Hmmmmmmmmmmmmmmmmmmmm...........
    
    Adios,	Al

    I goofed,
    
    The ol' Yeller Peril is, indeed, overweight and marginally powered
    but it is a 1/5, not 1/4, scale Bucker Jungmeister from the PICA
    kit [originally designed and marketed by Dave Platt].  The 1/4 scale
    Platt Jungmeister I had was sold last summer.
    
    As to the Aeromaster's force arrangement, I recommend doing "nothing"
    in the setup category aside from building it precisely according
    to the plans.  I've yet to see a carefully/correctly built Aeromaster
    that didn't fly just fine with the force arrangement engineered into
    the kit.  No incidence meters or other gadgetry are necessary if
    the plane is carefully built per the plans, though it might be
    interesting to throw a meter on the finished product and find out
    just "what" the force arrangement of a stock Aeromaster "is."  
    
    Adios,	Al

RE: .30  Anker,

    Good case. Aerodynamically I don't think that it's
    any different. The lift force vector of a wing is always perpendicular
    to the relative wind (i.e. direction of oncoming airflow). So for a
    biplane, as the angle of attack increases the seperation between the
    lift vectors of the two wings will decrease regardless of the plane's
    attitude (assuming a configuration something like an Aeromaster
    where the upper wing is mounted ahead of the lower wing with
    the fuse. level).

RE: .31  Al,

    Yeah, the layout of the Beech crossed my mind while I was thinking about
    this. Ya know, the Beech struck me as looking a lot like a canard and
    a canard stalls about the same way as we've been talking about for
    biplanes (i.e. you've got two lifting surfaces and you set up the front
    one to stall first). Interesting...

    By the way... my Aeromaster instruction book says that the top wing is
    mounted at -1 degree with respect to the bottom wing. The bottom wing
    looks like it's set at 0 degrees.

Glenn Schrader    

    Glenn,
    
    There you go!  Top wing negative, respective of the bottom wing.
    And, the Aeromaster is one of the all-time greatest flying R/C
    bipes, bar none!  I rest my case.
    
    Adios,	Al

Kay,

I know you've been looking for my response ever since you sent me the blurb on 
biplane incidence setups.  I received the blurb Tuesday and, indeed, it supports
Tom, Anker and others who've opined that the top wing should be set positive, 
respective of the bottom wing on a plane with positive stagger (top wing forward
of the bottom wing).  What's even spookier is that I can't help but agree with 
the logic of the diagrams and related text explaining the various setups.

All I can think is that there "must" be some exception or special case situation
[not covered in the blurb] that'd explain why "some" positive stagger bipes are
setup with top wing negative.  The indisputable facts are that the Aeromaster, a
positive stagger bipe, calls for 1-degree negative incidence in the top wing and
the Bucker Jungmeister does also.  (I recently completely domesticated an abso-
lutely treacherous Jungmeister [a PICA like mine] by setting the top wing a lit-
tle over a degree negative, just like mine's setup...it became, literally, a 
pussycat after this adjustment.)  Yer' blurb suggests this setup could cause a
"catastrophic stall" but, in practice, just the opposite occured.

Now, Lew Andrews borrowed heavily from the Jungmeister when he designed the Ae-
romaster so it's certainly possible that something(?) about this/these bird(s)
is unique and excepts it/them from the rules but I can't, for the life of me,
figger' what the difference might be.  Both are quite conventional appearing,
positive stagger bipes with no unusual design aspects that I can detect.  Ac-
tual flight performance has to be the best test and the Aeromaster and Bucker
bipes are proven performers with the top wing negative setup.  Go figure....???

All I could say at the moment is follow the plans/instructions as far as what
force arrangement is recommended, whether negative or positive, and trust that 
the designer arrived at it through field testing of the design.  Then, and only 
then, if you wind up with a treacherous snap-roll tendency at the stall, be pre-
pared to try the opposite force arrangement.

Adios and thanx fer' the article,	Al

Al,

RE: Top wing incidence for biplanes

I still think that what matters here is the effective wing stagger at
angles of attack near the stall. Both the Bucker and the Aeromaster have
a small enough positive stagger that at high angles of attack the stagger
will be close to zero or negative. This is the only explanation that i've
come across that seems to handle all cases.

Glenn.

Here is a question.  I was building my Craft-Air Drifter II glider.
It has the top of the fuselage straight (presumably the ADL).
The Horizontal Stab and the Wing both go on top of the fuselage and they
both have flat bottoms.  The Stab is totally flat.  Now wouldn't
you assume that this is a setup of 0 degrees angle of incidence and
0 degrees declanage(sp)?  Now if I were to put a robart incidence meter
on the wing it would show some positive angle of attack because the meter
is made with two angled clamps on each end to center on the leading and 
trailing edge.  I haven't read my robart manual yet - maybe it shows.

So are the rules different for flat bottomed wings or is the wing
truely at some slight positive angle of incidence?

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

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

Kay,

I tried to reply to yer' question YESTERDAY but the network link was aborted 
and I've been unable to re-access the notesfile `til now.

What you describe is interesting as I've never used the Robart Incidence-Meter
on anything but symmetrical/semi-symmetrical wings.  I can see what yer' saying
[I think] but lemme' make sure; are you saying that the flat-bottom wing's lead
edge will not fit the locating bracket such that it rests in the apex of the "V"
notch?  Unless the bracket can be somehow adapted to a flat-bottom wing, you may
have to revert to blocking the plane's CL parallel to a flat surface and measur-
ing from the surface to lead and trail edges to check incidence.

The setup you described is, indeed, a zero-incidence, zero-decolage force arr-
angement, which makes sense as flat-bottom wings require no positive angle of 
attack since no lift is produced from the flat bottom of the wing.  But, while
no incidence is required, you may still desire to check it.

I'm positive I've long since trashed any instructions for my incidence-meter.
If, you discover some instruction to cover the use of the meter on flat-bottom
wings, please share it with us.

Adios,	Al

    I could have missed it, but I don't remember seeing anything in any
    of the trimming notes on "trim tabs". On full size aircraft, you have
    your normal "for us" method of trimming the elevator and on some
    planes, the rudder. But for the ailerons, there are only little trim
    tabs out on the trailing edge of the wing. These tabs are bent in order
    to achieve the proper roll trim.
    
    I've never seen trim tabs used on models. Is there a reason, or is it
    just a case of "nobody's ever tried it." Most models have almost full
    span ailerons. It seems to me that putting the ailerons "out of trim" 
    compared to the trailing edge of the wing, in order to correct a 
    condition caused by a "plane" that's out of trim for whatever reason
    (heavy wing, slight warp) etc., isn't the way to go. I would think this
    would be especially true on planes that need to be "clean" such as
    gliders and pattern ships.
    
    For example, if you need to dial in constant left rudder on a 3 channel
    glider in order to keep it from rolling right, that big rudder is 
    creating a considerable amount of drag. Where as a MUCH smaller trim
    tab out on the wing tip could do the same job with much LESS drag.
    
    Comments anyone??????
    
    Steve

    There may be other reasons, but here is my experience.  I once tried a
    trim tab (made from a piece of a beverage can) to correct the roll
    induced by a warped wing on my Sturdy Birdy.  It was a bad idea.

    In a full scale, you can retrim in flight with a trim wheel.  In RC
    that would mean another channel for the trim for each axis.  The Turdy
    Birdy approach required that I land and bend the trim tab by estimate.

    My trim tab extended out from the rest of the wing trailing edge; that
    made it vulnerable to being "re-adjusted" and even to being knocked off.

    This experience does not bear on a *planned* trim tab not extending
    beyond the control surface profile.  We adjust linkage to trim, so
    setting a static trim tab should be no different.

    Alton who doesn't have any idea about relative drag issues

    I couldn't find a place for my question so I will post it here.  Mr.
    Moderator, feel free to move it to a better location.
    
    I was flying my Skytiger last night and putting it through more paces
    than on any previous flight.  I noticed it didn't have enough rudder
    throw, and this was confirmed by my instructor.  I will add more throw,
    but here is my question.  There are two ways to do this.  One way is to
    move the clevis in one or two holes at the control horn.  The other way
    is to go to a larger arm at the servo, ie, move the push rod out
    further from the pivot point.  While on the surface both techniques
    appear to accomplish the same result, is there any difference between
    these approaches, and if so, what are the pros and cons of each? 
    Obviously, moving the clevis at the rudder control horn is the easiest
    way to go, and that's what I plan to do.
      
    An inquiring mind,
    Joe                                     

    I'll give this a try...
    
    When you move the clevis in on the rudder horn, the rudder will move
    more but the slop in the linkage (say due to the clevis pin being
    smaller than the horn hole) will be more apparent. If you move the
    clevis at the servo out, the slop stays the same but the linkage moves
    more. So, moving the servo end out will give you more throw and leave
    the slop around center due to the linkage the same.

    
    	Personally I try and keep the servo horn at it's minimum length.
    This promotes using the maximum throw of the servo and minimizes
    the sideward torque forces seen at the servos output shaft. 
    
    
    		Tom
    

    
    
    To add to my last reply...
    
    
    	I also like to use wheel arms as much as possible.  I try and stay
    away from using the slender output arms that come with most radios.
    I've seen to many of these break.
    
    
    Tom

    I agree with Jim.  I try to go out on the servo rather than in on the
    horn to reduce linkage slop.  One disadvantage to this is that slop in
    the servo gets accentuated when you go out on the servo.  If your servo
    has any deadband, you will notice it more.  Try moving your rudder to
    the left and back to center and to the right and back to center.  If it
    doesn't come back to the same center, your servo has noticeable
    deadband.  This will affect the trim, but it usually isn't that much of
    a problem unless you are flying pattern.  If so, invest in good servos.
    
    Charlie
    

    
    	I try and stay as close in on the servo side as possible for three
    reasons.
    
    	1) Reduced side load torque to the servo output shaft
    
    	2) Reduced torque load on the servo arm [also why I try and use
    	   wheels or make beefed up arms from wheels]
    
    	3) I try and use the full range on movement on the servo, front
    	   to back. This improves the precision of the servo's movement
    	   and hence the positioning of the control surfaces.
    
    
    The only way to get away from deadband is to buy good coreless servos.
    You can have the best slop free linkage set up in the world and
    deadband will kill you.  You also don't need to have great servos on
    all channels.  I run JR so usually I'll run a 4031 on elevator and
    two more 4031's on ailerons. Rudder gets a 4001 or a 401 and the
    throttle gets a 517 or a 501. If you have more than one ship flying
    you can get away with buying one radio with four good servos and
    then be selective where you put them.
    
    
    Tom

I'm trimming out a scratch built Liddle Stik.  For the record, it
looks like an Ugly Stik, with the same moments, but the span is
only 48 inches.  Its tail moment arm is rather short, as befits
the breed.  I'm using an os .25FSR in it, which pulls it just
fine.

I'm having a persistent problem with it pulling to the right.  It
also seems to turn right easier than left.  The model trims with
some left rudder (full tx trim from neutral), and a good deal of
left aileron.

I got some help with it this weekend, and on the advice added
some right thrust to the engine.  It didn't help much, and I
think this is wrong advice, since right thrust should only make
it go to the right, not left as I would like.  Please give me a
sanity check on this one.

I've also checked the balance of the wing, and add a small weight
to the right wing to balance it -- again, this won't help my
problem, right?

I'm going to put the Robart Incidence Meter on it tonight to
check for a wing warp.  Is there any other suggestion I can check
on this one?  I should add that as far as the rest of the model
goes, it is probably the straightest model I've ever built.
Since the wing is foam, I may have not properly aligned the wing
halves, but really, again I think they're very close. Not enough
to cause this problem.

Sure is a nice airplane.

Here is a recent post from the usenet on trim.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

I did this once before and here it is again.

In article <[email protected]>, [email protected] writes:
|> Would someone care to post a complete guide to trimming an airplane 
|> for best aerobatic performance?  My main interest is trimming out a 
|> 120 size EZ Diablo.  I've got the CG set exactly as marked on the 
|> fuselage, and the plane requires some up elevator trim to fly level. 
|> In vertical lines, the plane pulls to the canopy.  I'd like to trim 
|> the airplane to drop straight in vertical lines.  
|> 
|> What should my approach be?
|> Should I:
|> 1. Move the CG rearward?

Maybe.

|> 2. Put upthrust in the engine?

Down thrust, maybe.

|> 3. Put positive incidence in the wing?

Maybe.

|> I can see some potential problems with all these solutions, 
|> but #1 makes the most sense to me (unless I get carried away 
|> and the plane becomes too unstable).

If trimmed for straight and level, what does it do inverted?  It
should only take slight down elevator pressure to hold level inverted
flight.  If it takes a lot of down elevator, move the CG rearward
until it takes slight down elevator to hold inverted.  Then try your
verticals.  What happens in this case is that by moving the CG
rearward it will take less up elevator trim to hold level flight and
less up elevator trim will help in the vertical.

If after you move the CG this still persists, you should add 1/2
degree positive incidence to the wing.  Again, this changes the
elevator trim and help with the verticals.

Change the thrust last.

Now, back by popular demand, the pattern trimming chart:

-----------------------------------------------------------------------
This chart was set up for trimming a pattern plane.  However, there
are quite a few sport aerobatic planes that would fly better if they
were set up like pattern planes.  It's a lot easier to fly a plane
that's properly set up than a plane with all kinds of perverse mixing.
I also must give credit where credit is due, this chart comes from the
NSRCA (National Society of Radio Controlled Aerobatics) newsletter and
was submitted by Mike Chipchase of Australia.  Some of this
information is repeted from the last article on trimming for
aerobatics.

First let's talk about basic airplane setup.  The latest pattern
designs are set up with 2.5 degrees of right thrust, 0 degrees down
thrust, .5 degrees positive incidence on the wing (root and tip, no
washout), and 0 incedence on the stab.  Or, .5 ~ 1 degree downthrust
and 0 incedence on the wing.  Use an incedence meter to check this, or
block the plane up on a big flat table and use a scale accurate to
1/32nd of an inch. If the plans show this information use that as a
starting point. 

Control throws should be set up as shown on the plans.  It's very
important each aileron to have the same throw.  This should be setup
mechanically.  The aileron throws should be set up the same up and
down.  If the plane has split elevators make sure that each elevator
half has the same throw as the other half.  I usually set the plane up
with more down elevator than up elevator.  That way I'll have the same
control authority for up or down elevator.  Set up the rudder with
about 30 ~ 35 degrees of throw.  Of course the ailerons and the
elevator need to be gap sealed.

To start out, the CG should be placed as shown on the plans, or about
30% of the average chord.  The CG can be adjusted later.  Use the
placement of the radio to place or move the CG if possible.  This is
better than adding unnecessary weight because light airplanes fly
better than heavy ones.  Since the battery pack is the heaviest part
of the radio, its placement will have the biggest affect on the CG.
Also, laterally balance the plane.  Pick it up underneath the center
of the spinner and underneath the center of the tail.  Place weight on
the light wing tip until the plane balances.  Embed the weight in the
wing tip. 

With all that in mind heres the chart.

-----------------------------------------------------------------------
To test for			| Test procedure
-----------------------------------------------------------------------
Observations			| Adjustments
-----------------------------------------------------------------------
Control	Neutrals		| Fly model straight and level
-----------------------------------------------------------------------
Trim for straight and level	| Adjust clevices to center transmitter
				| trims.
-----------------------------------------------------------------------
Control throws			| Fly model and apply full deflection
				| of each control in turn.
-----------------------------------------------------------------------
Check the response of each	| Aileron Hi-rate 3 rolls in 4 sec.
control				| Lo-rate 3 rolls -n 6 sec.  Elevator
				| Hi-rate to give a smooth square
				| corner.  Lo-rate for a loop of 130 ft.
				| diameter.  Rudder Hi-rate for stall
				| Lo-rate to maintain Knife edge
				| flight.
-----------------------------------------------------------------------
Decalage (incidence)		| Power off vertical dive, cross wind
				| any.  Release controls when model
				| vertical.
-----------------------------------------------------------------------
A. Does model continue straight	| A. No adjustments
   down				|
B. Does model start to pull out	| B. Reduce incidence
   (nose up)			|
C. Does model tuck in (nose	| C. Increase incedence
   down)			|
-----------------------------------------------------------------------
Center of gravity		| Roll model inverted
-----------------------------------------------------------------------
A. Lots of down elevator	| A. Add weight to tail.
   required to maintain level	|
   flight.			|
B. No down elevator required to | B. Add weight to nose.
   maintain level flight or 	|
   model climbs.		|
-----------------------------------------------------------------------
Tip weight, course adjustment	| Fly model straight and level upright
				| Check aileron trim maintains wing
				| level. Roll model inverted, wings
				| level.  Release aileron stick.
-----------------------------------------------------------------------
A. Model does not drop a wing	| A. No adjustment needed.
B. Left wing drops		| B. Add weight to right tip.
C. Right wing drops		| C. Add weight to left tip.
-----------------------------------------------------------------------
Side thrust			| Fly model away from you into any wind
				| Pull into a vertical climb (watch as
				| the plane slows down.)
-----------------------------------------------------------------------
A. Model continues straight up	| A. No adjustment needed.
B. Model veers left		| B. Add right thrust.
C. Model veers right		| C. Reduce right thrust.
-----------------------------------------------------------------------
Up/Down Thrust			| Fly model on normal path into any
				| wind. When model is straight out from
				| you about 100 meters away, pull into
				| a vertical climb and release the
				| elevator.
-----------------------------------------------------------------------
A. Model continues straight up	| A. No adjustment needed.
B. Model pulls to canopy (up)	| B. Add down thrust.
C. Model pulls to belly (down)	| C. Reduce down thrust.
-----------------------------------------------------------------------
Tip weight, fine adjustment	| Fly the model away from you into any
				| wind and pull into a small diameter
				| loop.
-----------------------------------------------------------------------
A. Model comes out wings level	| A. No adjustment needed.
B. Right wing low		| B. Add weight to left tip.
C. Left wing low		| C. Add weight to right tip of remove
				|    from left tip.
-----------------------------------------------------------------------
Aileron differential		| Fly model on a normal pass and do 3
				| or more rolls.
-----------------------------------------------------------------------
A. Roll axis on model		| A. Differential OK
   centerline			|
B. Roll axis off to the same 	| B. Increase Differential
   side of model as roll	|
   command.			|
C. Roll axis off to opposite	| C. Decrease Differential
   side of model as roll cmd.	|
-----------------------------------------------------------------------
Dihedral			| Fly model on normal pass and roll
				| into knife edge flight. Maintain
				| with top rudder (do this test to the
				| right and left sides)
-----------------------------------------------------------------------
A. Model does not roll out of	| A. Dihedral OK.
   knife edge.			|
B. Model rolls in direction of	| B. Reduce Dihedral
   applied rudder.		|
C. Model rolls opposite the 	| C. Increase Dihedral
   rudder in both tests.	|
-----------------------------------------------------------------------
Elevator Alignment.		| Fly model straight away into any
				| wind.  Pull into an inside loop.
				| Roll inverted and push into an
				| outside loop.
-----------------------------------------------------------------------
A. No rolling when elevator	| A. Elevators correctly aligned.
   applied.			|
B. Model rolls in same direction| B. Elevator half misaligned. Raise
   in both tests.		|    half or lower the other.
C. Model rolls in opposite	| C. One elevator half has more throw
   directions in both tests	|    then the other. (Model rolls to
				|    the side with the most throw.)
				|    Reduce the throw on one side or
				|    increase it on the other side.
-----------------------------------------------------------------------
Pitching in knife edge flight	| Same as dihedral test.
-----------------------------------------------------------------------
A. No pitch up or down		| A. No adjustment needed.
B. Model pitches up (to	canopy)	| B. Alternate cures.
				| 1. Move the CG aft.
				| 2. Increase the wing incidence.
				| 3. Drop the ailerons.
C. Model pitches down (to belly)| C. Reverse the above
-----------------------------------------------------------------------

Notes:  Trimming must be down in calm conditions.  Make mutiple tests
before makeing any adjustments.  If any changes are made go back over
the previous steps and readjust as necessary.

Well, there it is.  For the purists out there you might note that none
of these adjustments require the use of a computer radio.  A well
designed, well built aerobatic plane can be set up very close to
perfect without any mixing.  In fact that is one measure of a well
designed pattern plane.

I hope this helps any one out there that is interested learning
advanced aerobatics.



_________________________________________________________________
 Mike Walpole     |      This space       |      [email protected]
 Mead Data Central|     accidentally      |...!uunet!meaddata!msw
 Miamisburg, OH   |      left blank!      |
(513)865-1086     |      AMA 273066       |


++++++++++++++++++++++ The full NEWS header follows +++++++++++++++++++++++++++
News Article 16818
Path: nntpd.lkg.dec.com!nntpd2.cxo.dec.com!pa.dec.com!decwrl!uunet!meaddata!msw
From: [email protected] (Michael Walpole)
Newsgroups: rec.models.rc
Subject: Re: Trimming Planes
Date: 12 Aug 1993 15:20:33 GMT
Organization: Mead Data Central, Dayton OH
Lines: 232
Distribution: world
Message-ID: <[email protected]>
References: <[email protected]>
NNTP-Posting-Host: daedalus.meaddata.com

    Kay,
    
    
    Nice stuff. Just what I needed, since I am having problems with my
    Acro-Wot. It used to fly fine but lately I have been experiencing
    problems when I roll in the vertical, say for a humpty bump (or dump in
    my case !). After the roll the plane goes off to the right. Your last
    note will help me do some more analysis of the problem and see what is
    wrong.
    
    Eric.