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the rational of trimming

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the rational of trimming

Old 12-11-2010, 11:28 AM
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protectedpilot
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Default RE: the rational of trimming


ORIGINAL: rmh

take total side area (fin rudder /landing gear/fuselage) vs total projected wing panel area.
compare areas.
If you include center section of wing (fuselage area) then the ratio will be quite a bit different
If you assume the fuselage does not contribute lift - then do not include .
Selig, et. al., did an in-depth study on wing efficiencies as pertains to thickness (in order to simplify terminology). Have you considered this in your fuse side area calculations?

bc
Old 12-11-2010, 11:58 AM
  #52  
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Default RE: the rational of trimming

Do not compare efficiencies with area!

The large fuse adds lift but not an equal amount (area to area) - nor should you likely want that -
IF efficiency were equal -things would get touchy
If you have ever made a large flat (profile fuselage) you would have noted the model does not turn as it a rolls -it simply assumes a different attitude. very strange.
However properly setup it can work to an advantage.
Old 12-11-2010, 12:35 PM
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Default RE: the rational of trimming


ORIGINAL: rmh

Do not compare efficiencies with area!

The large fuse adds lift but not an equal amount (area to area) - nor should you likely want that -
IF efficiency were equal -things would get touchy
If you have ever made a large flat (profile fuselage) you would have noted the model does not turn as it a rolls -it simply assumes a different attitude. very strange.
However properly setup it can work to an advantage.
If efficiencies were equal, everything would get EASY. Or have you ever computed a Reynold's number? And if you have, how many of the variables did you zero out? A flat surface has NO lift efficiency, zero, you're talking apples and oranges here. Point in fact, a flat surface has zero LIFT, in the context we are using the word. Flat on both sides is not an air foil. Flat doesn't fly, it channels. Area times efficiency gives you lift, when you are talking about AIR FOILS. Plus about 21(not about 21, exactly 21) other variables, if you consider Reynolds. But even then, the percentage of error will only approach 20%; so, we do the field work; like Bryan has done. Every BIT of classroom or book data came from someone like Bryan, out in the field. We learn from the field guys; academics may point the way, theoretically, on occasion; but it still gets down to what actually happens in the field. And that, on occasion, is a complete surprise to the theoreticians. Occasionally, we learn that the facts we came up with, to fit the observations we made, were wrong. In order to be proven, a fact must be repeatable. That's why it is a good idea to try Triangulation Trimming. I have a wall full of trophies this year to demonstrate its repeatability.

It only makes good scientific sense to remain open to new thoughts, to test new setups; that's why we come here and exchange ideas. We want to expand our knowledge and our capabilities. Otherwise, we'd all being flying Spads, jenny's or Sopwiths and would have never progressed to an Arrow, a Dalotel, an Aurora, Typhoon, Prophecy, Patriot, Shinden, Spark, etc, etc. We learn, we grow, we progress.

Brian Clemmons
Old 12-11-2010, 01:13 PM
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rmh
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Default RE: the rational of trimming

Well - NO airfoil has any lift till it has an effective angle of attack
a flat plate is perfectly capable of providing lift
a full symm airfoil provides NO lift either - till it is at an angle of attack
as far as "computing an Rn?

never bothered -
Obvious is still obvious.
Old 12-11-2010, 05:47 PM
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Default RE: the rational of trimming


ORIGINAL: protectedpilot

We learn, we grow, we progress.

Brian Clemmons
I was exchanging some engineering ideas with a guy from Israel a few months ago, in regard to why certain trim was "necessary" (my term). After several emails, his final email was very telling. He said to me that his 13 year old son (who all the trimming was for) just placed 2nd in their International Comp in F3A with a model that had mixes everywhere. It was those mixes they were trying to reduce but ran out of time before their meet.

Point was well taken....A moderately well set-up plane in the hands of exceptional skill, will win or place. A great set-up in moderately skilled hands will lose. A great set-up in great hands = magic
Old 12-11-2010, 08:14 PM
  #56  
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Default RE: the rational of trimming

ORIGINAL: flyncajun

while I`m talking Myths,
Another Big myth is lowering the stab to reduce pitch to the belly in knife edge LOL, BS. the only thing that causes the airplane to go the belly in knife edge is a tail heavy airplane Period!
Bryan
hebertcompetitiondesigns.com
Bryan,

Since the OP never returned to the thread with any feed back and you are discussing trimming approaches; would you mind reviewing my advice of post #4?


ORIGINAL: Lnewqban

ORIGINAL OP's question: ytell

I'm a little confused about some aspects of trimming an aerobatic model.

If your model is perfectly trimmed, so they say, you will be able to fly a perfect hands free lines on all basic directions: level, 45 deg up and down, verticals up and downs. Now how can this be true if each if for each type of line the wing is significantly loaded differently? e.g for level flight the wing creates lift which is exactly the weight of the plane anf in 45 deg. clibe lift and drag are completely diferent from a level flight?

If the plane pulls to the belly on vertical line, so they say, increase your wing incidence.
How can this be true if the elevator trim position is not changed? as fa as I understand, the elevator will keep the wing in the same AOA regardless of wing incidence change (assuming constant speed is maintained)

Yoav
The wing is what flies, and the prop helps it; the rest of the airplane just follows.

Hence, increase your wing incidence = decrease the incidence of the rest of the airplane = same wing AOA

If the plane pulls to the belly on vertical line => decrease the incidence of the rest of the airplane = stab pushes ''down'' more and increases a nose pitch ''up'' that works against the ''pull to the belly'' tendency
Old 12-11-2010, 09:43 PM
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Default RE: the rational of trimming


ORIGINAL: Lnewqban
The wing is what flies, and the prop helps it; the rest of the airplane just follows.

Hence, increase your wing incidence = decrease the incidence of the rest of the airplane = same wing AOA

If the plane pulls to the belly on vertical line => decrease the incidence of the rest of the airplane = stab pushes ''down'' more and increases a nose pitch ''up'' that works against the ''pull to the belly'' tendency[/color]
[/b]
[/quote]
Which vertical? The full power up line or the no power downline?

If it's the full power up line, the prop dominates vectors. To push to undercarriage, thrust is set much too negative against the plane's reference line (too much downthrust)

The prop pushes back alot more air mass than the wing needs to generate 1G of lift when at full power. Modern pattern model powerplants generate at least 13-14 lbs of thrust at full power

If the plane pushes to belly on "no power" downline, it is carrying down elevator trim and/or the wing is at an extremely small AOA; possibly even negative. The CG is likely too far aft, operating at close to zero static margin. This is not typical for a pattern model. They will tend to go towards the canopy on downlines when set right for the rest of the flight envelope
Old 12-12-2010, 05:11 AM
  #58  
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Default RE: the rational of trimming

Thanks, Matt.

I have edited my previous post to include the complete OP's question.

Note that he did not specify up or down vertical line, or if his was a modern pattern model.

I believe I assumed a down line, since, as you explained, the thrust angle is another factor in the balance.
Old 12-12-2010, 07:25 AM
  #59  
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Default RE: the rational of trimming

ORIGINAL: Lnewqban

Thanks, Matt.

I have edited my previous post to include the complete OP's question.

Note that he did not specify up or down vertical line, or if his was a modern pattern model.

I believe I assumed a down line, since, as you explained, the thrust angle is another factor in the balance.
FWIW-
when we were settingup IMAC/TOC models - we ran into the same old problems about thrust angles .
The problem became easy to resolve when it was noted that IF the model had enough thrust to maintain speed on the up verticals - no corrective thrust was needed
Which goes back to "a constant speed model requires far less corrective fiddling."
Note: the Up line verticals typically sapped so much speed on the up lines , the tendency was to start a pitch to the belly.
By simply increasing thrust to weight - the problem was resolved.
This was done by building to absolute minimums on weight and using tuned pipe engines
The new electric designs are far better at constant speed.

.
Old 12-12-2010, 08:18 AM
  #60  
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Default RE: the rational of trimming

I see.

Thanks, Dick.
Old 12-12-2010, 10:19 AM
  #61  
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Default RE: the rational of trimming


ORIGINAL: rmh
The new electric designs are far better at constant speed.

.

applause!! applause!!!

They actually have a hidden reserve of power, if your setup lucks up and leaves one hidden in all there somewhere. Electric motors have a characteristic that our glow or gas doesn't. They spin the prop up to their design speed if they can, and that's it. Sounds like a problem, not a benefit, right. Well, they do something more when they encounter certain conditions.

You've chosen your prop after extensive tests, right. You've got the speed you want and decent pull over the top of loops etc and noticed the magic "electric constant speed vertical". How did that happen? That vertical?

It's like something extra kicked in. You were at full throttle starting up and right where the glow/gassers would have slowed down a bit, that electric motor seemed to have found an extra bit, like the turbo had kicked in. It had found something extra. An electric motor that has reached it's design rpm won't slow down if it encounters more load, if it's got a power source that'll keep giving more. Those suckers do just that, suck power as needed. If the ESC doesn't hold them back, and the battery has more capacity in it, all you're going to lose in vertical will be from the prop slipping.

Much as I hate to admit it, electrics do have more than one worthwhile attraction. [:@]
Old 12-12-2010, 10:43 AM
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Default RE: the rational of trimming

Is this going to be a good winter for flying in Florida this year? Kinda cool therelast year...for sure. Man is it cold here now in Michigan. Capt,n
Old 12-12-2010, 10:52 AM
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Default RE: the rational of trimming

a simple example which demonstrates the BIG difference in electric vs IC engines:
Electric has MAXIMUM torque at zero rpm - from then on, torque remains same or decreases
IC engines have max torque ONLY when engine rpm reaches the point whre the flow of fuel charge is optomized resulting in maximum pressures in the power stroke.
From then on, torque decreases -at some rate- depending on engine design
So?
well , max torque occurrs at only one point somewhere in the rpm curve on an IC (design parameters determine this point)
BUT
You start with it on the electric and can potentially reach it again at any usable rpm - depending on power supply/ speed control/design limitations, ability to provide current needed .
The corker is that you also can apply a braking force to the propeller AS DESIRED-if you have proper motor control
This is accomplished by using back electromotive force (Back EMF) which is accomplished simply by shorting out the power leads (oversimplification here) and the motor -which is trying to generate power - , generates into a "short" which becomes a brake .
Couldn't be sweeter.
(This technology is about 100 years old by the way - but batteries have-up till now been incapable of producing sustained power in a light package.)
Don't believe it?
Look at the first electric cars in the early part of the 1900's
Old 12-12-2010, 03:35 PM
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Default RE: the rational of trimming


ORIGINAL: rmh

a simple example which demonstrates the BIG difference in electric vs IC engines:
Electric has MAXIMUM torque at zero rpm - from then on, torque remains same or decreases
IC engines have max torque ONLY when engine rpm reaches the point whre the flow of fuel charge is optomized resulting in maximum pressures in the power stroke.
From then on, torque decreases -at some rate- depending on engine design
So?
well , max torque occurrs at only one point somewhere in the rpm curve on an IC (design parameters determine this point)
BUT
You start with it on the electric and can potentially reach it again at any usable rpm - depending on power supply/ speed control/design limitations, ability to provide current needed .
The corker is that you also can apply a braking force to the propeller AS DESIRED-if you have proper motor control
This is accomplished by using back electromotive force (Back EMF) which is accomplished simply by shorting out the power leads (oversimplification here) and the motor -which is trying to generate power - , generates into a ''short'' which becomes a brake .
Couldn't be sweeter.
(This technology is about 100 years old by the way - but batteries have-up till now been incapable of producing sustained power in a light package.)
Don't believe it?
Look at the first electric cars in the early part of the 1900's


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Old 12-12-2010, 05:35 PM
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Default RE: the rational of trimming


ORIGINAL: captinjohn

Is this going to be a good winter for flying in Florida this year? Kinda cool there last year...for sure. Man is it cold here now in Michigan. Capt,n
Capt,n,

I believe it will be as good as the summer without hurricanes that we had this year.

We were just above freezing a couple of mornings last week.
The forecast is 31 degrees for tomorrow morning; we will see.

Other than those days, the weather has been nice to us.
Old 12-12-2010, 06:04 PM
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Default RE: the rational of trimming




ORIGINAL: rmh

a simple example which demonstrates the BIG difference in electric vs IC engines:
Electric has MAXIMUM torque at zero rpm - from then on, torque remains same or decreases
IC engines have max torque ONLY when engine rpm reaches the point whre the flow of fuel charge is optomized resulting in maximum pressures in the power stroke.
From then on, torque decreases -at some rate- depending on engine design
So?
well , max torque occurrs at only one point somewhere in the rpm curve on an IC (design parameters determine this point)
BUT
You start with it on the electric and can potentially reach it again at any usable rpm - depending on power supply/ speed control/design limitations, ability to provide current needed .
The corker is that you also can apply a braking force to the propeller AS DESIRED-if you have proper motor control
This is accomplished by using back electromotive force (Back EMF) which is accomplished simply by shorting out the power leads (oversimplification here) and the motor -which is trying to generate power - , generates into a ''short'' which becomes a brake .
Couldn't be sweeter.
(This technology is about 100 years old by the way - but batteries have-up till now been incapable of producing sustained power in a light package.)
Don't believe it?
I guess the post itself got lost.... from the power/torque/power curves in my previous post, you can see that the above statement is just wrong. I work on motors and motor drives every day, from itty bitty DC motors up to 700HP Vector control AC drives.......what we are talking about here is fixed magnet motors, or brushed motors. Back EMF, properly called counter EMF, is a purely induction motor phenomenon. DC motor with a field current: short the field and they run away in speed with little torque. I've done it, plenty of times. Golf cart service companies provide a kit to do this, they call a 'scat' kit. That's not how you slow down the electric models. You just back off the voltage. This is why you can't believe everything you read in a hobby magazine, written by the average modeler. It's hit or miss when you get accurate, factual information.

The ESC's in use in models are essential voltage controllers; period. No brakes, no back flow of current. Braking is called a regenerative drive, by the way.

The graph curves are why some manufacturers have computer tuning built into the ESC, to compensate for weight/prop/speed envelope. Better than IC? Depends on who you talk to; I know motors very well and I fly glow. Electrics are certainly simpler. At the Advanced line in Muncie, this year, there were two "flameouts". Both were fried ESC's. No glow engines failed. For the record, YS does not sponsor me in any way. I just prefer IC engines. Seems it brought me SOME success this year. But the power is a curve, not linear, and not max torque at zero only, and down from there. Nor does it remain constant.

Brian

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Edited to fix the quotes to what I think was intended.... Bruce
Old 12-12-2010, 06:27 PM
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Default RE: the rational of trimming

Brian, granted Dick was talking about permanent magnet motors.  But since that's what we use pretty much exclusively in our model airplanes his comments are valid for the most part.  Bringing the vector drive and wound field motors into it just clouds up the situation... interesting though it may be.
Old 12-12-2010, 06:33 PM
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Default RE: the rational of trimming

Brian,

I think Dick meant max torque at zero rpm when the motor is deadheaded and at full throttle. Motor drawing and controller delivering max amps under this scenario. Not for long tho!

Some electric set-ups are truly amazing in their easy delivery of power to the prop. What Dick says about the vertical up line is something I've observed with electrics too.

To get similar output from wet power, we may have to resort to belt driven and electronically governed gas power. Not in my life time tho, unless I do it. I like my gasoline powered models just fine, eventhough it's direct drive and of marginal tork at mid range. I see no reason to change what I do right now.
Old 12-12-2010, 07:12 PM
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Default RE: the rational of trimming

Thanks guys -
on slot car motors permenant magnet stuff - the car braking is accomplished by simply shorting across the the tracks VERY effective .
As I noted I really oversimplified the braking info - Just trying to note that braking is possible in the setups we fly .
I use a number of outrunners and sme of the speed controllers offer a variety of power setups
On older cars the generators -if the belt was removed -somtimes acted as electric motors -as anyone wih experience in these things knows, this type motor and generator are basically the same bits n pieces
I do fly both small and very powerful electric planes and the results are as I noted
The power consumption and shaft output are not as shown in the "chart"

Actually the power efficiency in the really good electric motors for pattern airplanes -is close to -90 %!!
And If you use really GOOD batteries capable of momentary excursions to better than 50C output- the torque available at speed, is astounding


Sadly , in some locals- there is now a very divided camp between IC and electric-for aerobatic stuff.
Old 12-12-2010, 07:16 PM
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Default RE: the rational of trimming

Dick,
Even if you include the fin/rudder gear or even spinner , stickers whatever,the fuse is still 2-300 squares smaller than the wings
the wings on the Spark are near 1200 sq.


Lnewqban,
Thanks for the chance to explain,Here is a good example of what I was talking about in a previous post.

I any airplane pulls to the belly in a up line it will be from one thing.you are using Dicks 0-0-0 setup and you have too much down thrust in the engine common mistake,in a rookie setup. This is how the Spark is set up from the factory. (I have fixed plenty of them around the world) ,No airplane will pull to the Belly in the downline unless the elevator trim was WAY off. That scenerio just can`t happen any other way.and I dout it`s what he was asking ,it`s just is not a problem any time.

Again,Not beat a dead Horse using 0-0-0 you have to run the c.g back to 30-35% to get the (BIG WING UP FRONT) like dick likes to say at a AOA that it lifts 1G and you have up elevator trimmed in as well. Then you adjust the stab to match the elevator half trim usually 1 deg neg ( same as up elevator trim).That up elevator trim is what your fighting in the upline.,,,Neg stab,= up elevator, 0 inc wing, too little down thrust. this will also give you your pull to the canopy in the downline as well ,,but without thrust on,even worse.

Now the 0-0-0 set up for Rookies and look alike ARF pattern planes from Tower,, thats fine and dandy for level flight! But you pull the nose up and guess what ,it want`s to go to the canopy with anything under 3.0 deg neg thrust in the motor. Now here is where you start chasing your tail.this begins the root of all evil to trim a airplane

Because of this pull to the canopy in the up line (i`m getting there ) you would be advised by Dick to just put down thrust in it till it stops. Yes it works using 0-0-0 But unfortunatly because you neglected to fix it "right" the downthrust will fix that problem,as long as you keep the speed the same in a up line and cause 3 more problems.and As I said ,You will also have a big pull to the canopy in the downline because you use Engine thrust to get the unloaded vertical up line straight.you may also need a throttle to rudder and throttle to elevator mix.
Next,
Your knife edge will go to the belly now ,(down thrust, tail heavy) and because of the rearward c/g ,snaps will be junk, the 45 downline will fall off and need elevator to hold the line ECT.,,,,, airplane will drop a wing (tip stall )on hard pulls, will not enter a spin clean, you can only use elevator and rudder to spin ,Deviate on any snap in any line, (snap will not stall with power) you will need a minimum of 3 mixes. just to name a few.

If you are just flying up lines under full power, and level flying you can be happy with 0-0-0 but we are talking Modern pattern Airplanes here not TOC airplanes from the 70`s underpowered ,over winged,over weight!

SO to go back to your question Technically you were correct if he were running lots of positive inc. or using alot of down trim for no reason ,But if you were to advise the guy to just reduce inc. without knowing where his other setups were ,Thrust, Inc. C/G he might try your Idea to reduce inc. and try to fly the airplane with neg inc in the wing now, and have terrible fits just lifting off the ground LOL. Then his trouble would be even worse ,just because the guy was vauge with the question,and the rest of the setting on his airplane.

Dick likes to talk about constant speed, well using full throttle or "speed" to keep the airplane flying straight up just don`t work, we fly everything at half throttle these days ,very seldom even advanced to full power, (thats why IC can still hang) even in verticals ,unless it`s very Hot or Very Windy. Using my method of trimming,the airplane never changes trim from 1/4 throttle to full throttle ,either in the up line or any other line. Pos inc forward c/g the cg forward allows the pos inc. this in turn because of the wing AOA gives you a slower flight envelope, enabling you to run a constant speed. only racers run 0-0-0 (no drag)
just common sense! HUH ?well may be not!

With 0-0-0 you have to use c/g to create AOA and downthrust to tame it in uplines so, now anything else is somwhere in between These settings, and you have to rely on your flying skills to stay on top of that. my methods ,,the airplane flys hands off in any attitude , and from 1/4 speed to wide open , taking the pilot load and cutting it way down,so you don`t have to fly it like a model Helicoptor.

o-o-o just defys logic! if you are looking for constant slow speed ,and goes against common sense once you understand how a model responds to wing and C/G settings.

re-read my second post it`s all in there,
May be Dick can try it, and report Back! Scared! probably

Bryan



Old 12-12-2010, 07:33 PM
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rmh
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Default RE: the rational of trimming

Bluntly - you are wrong .
Your comments about me are untrue and childish
Old 12-12-2010, 08:23 PM
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Default RE: the rational of trimming

HUH!uhhh,
What comments about you?
never made any comments about you just 0-0-0

Dick,
If I were wrong my reputation would not center on being known for trimming pattern airplanes.


All you have to do is try my method report back to the list if I`m wrong or not. you wont do this because you might actually find out I`m right.
My methods evolved from 0-0-0 and are refined from there, it`s why I can explain it so well. every detail.
So well in fact I`ve never been proven wrong ,,
You have seen this time and time again, every time you posted in respose to my methods some one has come on ,tried it,
and said, Yup Wow,fixed my issues every one of them ,,I could even tell them what was wrong with there airplane before they told me
Luck Nope
understanding how to trim a airplane weather it`s your setup or mine.

just do research under my trim posting here on RCU your in all of them
Bryan

Old 12-12-2010, 08:46 PM
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Default RE: the rational of trimming

I fly IMAC and am at the point where I would like to have my plane trimmed well. My trimming procedure thus far is below, please critique.

First, trim ele for straight vert. down with no power.

Second, adjust thrust for straight up till the speed slows down.

Third, adjust CG so it just falls out of 45deg inverted upline. I find this gives straight horizontal upright flight at the speed I like to fly.

Side thrust, just put in the complimentary 3deg engine side thrust and use my left stick as needed.

I have been trimming my planes like this for a long time and am use to the way they fly and more than anything am curious if I am missing anything.
Old 12-12-2010, 08:58 PM
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Default RE: the rational of trimming


ORIGINAL: MTK

Brian,

I think Dick meant max torque at zero rpm when the motor is deadheaded and at full throttle. Motor drawing and controller delivering max amps under this scenario. Not for long tho!

Some electric set-ups are truly amazing in their easy delivery of power to the prop. What Dick says about the vertical up line is something I've observed with electrics too.

To get similar output from wet power, we may have to resort to belt driven and electronically governed gas power. Not in my life time tho, unless I do it. I like my gasoline powered models just fine, eventhough it's direct drive and of marginal tork at mid range. I see no reason to change what I do right now.
Yes, we call that locked rotor. Best way to burn a motor up. Not that there is a good way. I've seen the differences between wet and electric, too; will admit there is somethig to the constant speed; but I just LIKE glow. I've made comment on occasion that it seems, at the moment, we will all eventually fly electric, but I'm hoping not. Electric motors will vary their current draw, while maintaining their speed as much as is possible, whereas the wet engine merely responds with speed available with the amount of fuel burned. An electric motor on current control would behave the same. But wet engines cannot do what electrics do.

For me, and this is personal, electrics look like toys, and wet looks like airplanes. And it is mighty confusing to me, reading all of the amateur electrical gurus explain what is happening, and how to control it, when I work with similar equipment, professionally, and know the facts.

Brian
Old 12-12-2010, 09:08 PM
  #75  
flyncajun
 
Join Date: Dec 2006
Location: DENHAM SPRINGS , LA
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Default RE: the rational of trimming

Eagleburger

You currently are using the 0-0-0 method.


There are a bunch of pattern fliers down under who use my Methods.
Please go to my website and read my Triangulation trimming article at

hebertcompetitiondesigns.com

Also you can click on my name here on RCU "Flyncajun" see all my post on the subject. Plenty!
Every possible question has been answered on this list alreadyin the pattern forum, with the response from the modelers after I helped to fix the issues.all trim questions are the same, and they all start with the same problems, so your issues are not new they are very common.they are as follows,Pull to canopy in the upline, left rudder tuck to the belly on knife edge, sometimes right rudder as well pull to the canopy in the downline , the need for lots of right thrust, the need for lots of right thrust ECT it`s all covered.

However ,I must warn you all IMAC airplanes have the wings set very forward ,some times too far forward (because they think Tail moment will dampen the airplane,,in reality the cg is just to far back ) , this effect snaps most of all now ,you have to preload the snap by faking them ( up elevator first to "show break" followed by aileron and rudder , a forgery for sure) so you may not be able to put the cg on the 25% of the MAC. unless you move the wing forward.
If you cannot balance the airplane there, you can not use my methods.

The edge 540 have a real problem with this!


But you would be a good case study if your willing to learn and do exactly as I say and report back to the list.
I`m not sure what class your flying currently that will matter to me on how to coach you to improve your setup.

Bryan

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