I am running about .5 degrees on everything from my Super Kaos to my Black Magic.

What is your wing incidence on your favorite pattern ship?

An airplane will not fly without positive incidence or an airfoil that is not symmetrical. The positive may come in the form of up elevator trim, or a wing design that creates lower pressure on the top surfaces, but that effectively creates the same results of positive incidence. Right? Then there is lift created by a fuselage....or a powerful engine that is making a propeller fly that has an airplane attached to it. All this is very confusing and beyond my scope of knowledge!

Not exactly true. A wing or any lifting body creates lift by flying at a positive Angle of Attack. Incidence is measured from some arbitrary datum line. Trimming the elevator doesn't change the incidence.

Jim O

Interesting because I recently assembled a Focus II, and the "instructions" (such as they were... good thing they really aren't needed, LOL) indicated that the wing incidence is +0.25 deg and the stab is -0.25 deg, relative (I think) to the bottom of the fuse or the canopy rails... whatever, and ignoring for the moment engine thrust line.

I explained to a friend of mine that this, in effect, created +0.5 deg incidence in the wing... or so it seems to me. The plane flies fine with the ailerons and elevators in neutral positions relative to wings/stabs, -1 deg engine down thrust, 2.5 deg right.

The H-stab will always "find" zero!

That what i believe.
Not to mention what I believe in trying to accurately measure EXACTLY 0.25 instead of 0.5 ... and I guess I've got the same instruments as you guys.
Come on... it's about 0.5deg. or +0.25wing/-0.25 stab. Yeap about 0.5.... or maybe it was 0.42?

Interesting thing about different wing/stab incidences is you're actually effecting/modifying the engines thrust angle, and the wing stab vertical positioning alone the datum line.
Want to increase your engines down thrust? Adjust the wing and stab.

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Changing the trim on the elevator would essentially change the 'zero-lift axis' of that airfoil if viewed as a whole. It is analogous to changing the incidence, as it would in effect alter the relationship of the zero-lift lines of the two airfoils. I think in the above reference though, the original post is referring to the effect of adding elevator trim, which pushes the tail down and changes the angle of attack of the main wing.

An airfoil without an angle of attack, here a setup of 0-0 incidence, will not create lift. Adding elevator (up) trim pushes the tail down and increases the AOA of the wings, creating lift.
An airfoil with a negative incidence at the stab, with respect to the wings, will effectively push the tail of the plane down and increase the AOA of the wings, creating lift.

This is, of course, neglecting the engine thrust line.

OK, I learned something... I never read before about adjusting both wing and stab to tweak the thrust line. I was aware there are stab adjusters, but just thought they were redundant if you have wing adjusters. MUCH easier than changing the engine position!

I have a couple of the Robart incidence meters, and indeed staying within an error range of +/-0.1 deg (0.2 total) takes considerable effort and guesswork to achieve. And then when I fly the plane to get the ailerons trimmed takes maybe 1/2 or 1 turn of the wing adjusters. Well, at least the incidence meters give some assurance that the plane will be flyable for the maiden, and provide a starting point for the trimming process.

It just looks funky.

But we know when flying modern designs that a plane that needs up trim has either a wing incidence issue or a forward CG issue, or possibly a thrust line problem if it varies with throttle settings.

What happens when you roll to inverted and why?

Jim

Yes, but I was being somewhat argumentative... better of changing the engine! My point here is that an airfoil need a possitve incidence to fly, not much, 0.5 is enough.Exactly how much YOU'LL need to dial in is CG controlled.Those flying with a forward GC, stab set a zero, will need a little more than those flying with a reaward CG, stab set at zero.I've always set the stab zero, flown and added wing incidence changes to dial out the elevator trim.Experimenting with the forward/reaward CG has always resulted in elevator trim changes and the corrisponding incidence corrections.Whats the right incidence for you? You'll have to find that out yourself.Regarding measuring, as stated it's a generalisation in my opinion. I own no equipment that can ACCURATELY measure the EXACT incidence.I've tried setting the airframe in a gig and measuring, but if I've sanded one LE and TE slightly different to the other, my meter wont sit in exactly the same position, thus giving a slightly different reading.I'm in the "Who cares" catagory. For me, if it looks about right, set about right, about equal it's good enough. Now go and fly and adjust from there.Exactly how it ends up... who knows but I know that it wasn't the same when I started or indeed EQUAL by the time I'm finished!

Yes, accurately measuring an angle of 0.5 degrees is difficult.

However, 0.5 degrees equates to approx. 3.9 mm (i.e. 4 mm) height difference, measured over a chord length of 450mm, which is quite typical for a 2m pattern model. So if you draw a center line, you can measure the distance down from this line at the leading edge and the trailing edge. When the difference is 4mm, you have 0.5 deg. INSTALLATION ANGLE relative to this line.
(sin 0.5x450=3.9)

(Incidence = angle of attack, and for a given aeroplane this will only be (weight and) speed dependant for level flight. For an electric model, it will only be speed dependant, as weight is constant.)

Magne

I don't think that the wing incidence on it's own will give you much useful information. In flight the wing won't care what the incidence or CoG is at. For a given airspeed and weight it will always arrive at the same angle of attack for level flight, regardless of those two variables. Same angle of attack implies same center of pressure and same lift force. Changing the incidence will change the pitch attitude of the fuselage, and as a consequence, the tail's angle of attack, which would then need to be trimmed out again to cancel any pitching moments. Changing the CoG will change the pitch moment generated by the wing, which will change the counteracting pitch moment required from the tail. But the wing will still have to fly at the same angle of attack. The point being that it's the tail incidence that really need's attention. By changing the wing incidence you're indirectly just changing the tail's angle of attack, which then requires re-trimming. I'll be honest and say I've never really bothered trimming a plane in depth and haven't thought much of the effects of downlines (with angle of attack = 0) and inverted flight but I do think that chasing the wing's incidence can result in a bit of going in circles if it isn't thought out.

Guys
I have written Many, Many Trimming guides over the years.
Even on the old NSRCA list in the late 90`s,
I`ve taught countless guys to trim their designs ,designers and joes alike.
However,
I have written a more concise article that gives you the tools to fix almost any design.
This article is running( in A few sections) in the Pattern section of Model Aviation now, because the article is so large .It explains all the reasons why I do what I do,and how we got to where we are in the current crop of designs,and the reasons behind the changes in what we now fly compaired to what used to be the standard.
all other written ,trimming methods are poor,wrong, to useless at best ,for complete trimming
on our modern designs.

I Explain how to decipher what the airplane is telling you and how to fix it.it`s all about correctly understanding of the feed back the airplane is giving you.
If you have the courage to believe, and the drive to get things right,because it makes a big difference in the end,read it.
These set up tips will directly effect your score in the end,lets face it ,thats what it`s all about.
Use my guide, and have fun learning that everything you thought you knew is wrong

I have no guessing ,surmising or ambiguity, I tell you if your airplane is doing this,or that ,how to fix it.
After designing nearly 20 top pattern models, and helping Top F3A team members from around the world trim and even design their airplanes ,you can be sure the methods are proven.
Just do some research on RCU for my previous post, and read my articles and you will be informed to make the right changes and improve your flying and scores.

hebertcompetitiondesigns.com
Bryan

Just a quick note, static rigging angles don't stay "static" much in the air.

You have a rotating prop and wing in front of the horizontal stabiliser so just because the motor is -1.5, the wing is +0.5 and the stab is set to zero doesn't mean that's the angle of attack each is seeing in the air at any given point in time. Also, with the GOC behind the centre of lift of the wing with a symetrical airfoil, stabs don't push down for the wing to sit at a positive angle of attack to generate lift, this is propogation of a misunderstanding from the real airplane world where they used to use cambered airfoils with strong negative pitching moments.

Increasing the angle of incidence of the wing and stab will force the fuse to fly with a nose down attitude which not only increases the downthrust but also raises the stab relative to the wing so adjusting the wing upsets/changes a lot more than adjusting the stab.

ok
hebertcompetitiondesigns.com
Bryan

Did the series just start in the most recent MA?

I am just starting the trimming process for a Focus II... not so "modern" of a design anymore, but your trimming procedure certainly can't hurt! I tried your older "Triangulation" system and it works very well for such a simple process.

Thanks for the link Bryan, very enjoyable reading.

0.5 for me. Very applicable thread.[sm=teeth_smile.gif]

Bryan is the dude when it comes to trimming.

you should see what he can do with a foamie even.

Bryan,

Which month magazine is your article in? I have been looking at recent issues and I could not find your article.

Also, I went online to the AMA website and could not find it there either.

Pedro

Bryan's trim article is part of the R/C Aerobatics column that appears every other month. Bryan supplied the information to Al and AC Glenn for them to include as part of their article, but it got split up into 3 parts. I think it started back in November or something like that. You can also find the full text of the article at [link=http://Bryan's Website]www.hebertcompetitiondesigns.com[/link].

Hi,
The spelling in the link is slightly mistaken.
Try; www.hebertcompetitiondesigns.com

Brian

Oops, thanks for catching that. I've corrected mine as well.

I got the article from Bryan's website. Thanks everyone. I will start the triangulation trimming process with my Giles and Ultra Sport right away.

Ron Chidgey has a neat little Angle Wizzard for about $40.00 that measures + or - .1 degree.try http://www.scratchbuilderwarehouse.com/