Incidince Meter

I have probably spelled it wrong but we got an incident meter today and I found some interesting things. (It is a great planes laser incidence meter)

1) the '59 Ares that I have been flying for a while seemed to come out at almost 0 all the way around.

2) dad's new USA1 that seems to fly well came out at almost 0 all the way around.

3) the new stab I am building I checked down it and it was 0 or so close it didnt really matter.

4) the GeoStar that I have been fighting was off and off by a good bit, the wing was different than the stab & the inboard stab was different than the outboard of the stab...
This could explain a LOT of things at least to me.

Anyone else use these??

Hey, here is some information I just received from a friend, he said it was written by our own Crist Rigotti. I think Brett Buck also mentioned that this has worked for him also.

"Build in 1/2 degree positive incidence in the LE of the stab. (I did do
this on mine.) I'm amazed how well the Legacy 40 just parks itself on the
end of the lines. You almost could fall asleep during level flight (upright
and inverted), it grooves so well."

I recall looking at the specs for the Great Planes laser incidence meter and the Robart incidence meter, and the "gravity powered" Robart unit has better claimed accuracy, FWIW. Usually more $, but not always.

I don't recall who "wrote the book" on how to use these on our stunters, but they recommended two units. Hook one to the wing, and one to the engine, until those two are zero-zero. Then transfer the one from the engine to the stabalizer, and do what you gotta there. That way, you know you have not moved the model while working with the stabalizer. No reason a couple of nearby fliers couldn't each buy one and then borrow the other, when needed. I am wondering if there is a way to use these to set the flaps and elevators at neutral. Steve

I thought every body used those incidence meters. I have two. How in the hell can you measure wing or engine incidence without one.Not very accurately for sure.I also use them as levels around the shop. I like them better than spirit levels. As far as control surface throw measurments go you can use an Ivans Magic Gadjet. or some of the other ones on the market. What I sometimes do with flaps on a ship with the flaps already installed is wrap some strips of soft balsa around the airfoil including the flaps and clamp the end of them together with a rubber band then the flap is locked in neutral. Keith (need lots of tools)Varley

>How in the hell can you measure wing or engine
>incidence without one.Not very accurately for sure.

LOL!!
Hi Keith,
The same way everyone used to do it before there were incidence meters for model airplanes. Carefully drawn datum lines, and practice.
The Ares and the USA-1 aaron mentioned, along with all the other planes we've ever built, were done this way.
I like to build I-Beam planes, and it seems it would be rather dificult to use an I.M. on those wings during construction. Even Windy on his tapes was very meticulous in drawing his "center lines".
The I.M. just verified that the planes we built, sans one of them which set for 5 years uncovered, are as accurate as can usually be accomplished, or expected.
Of course, now that we have one, it will be used extensively!
Bill <><

I just use chalk lines, plumb bobs and a transit. None of them work very well. Pencil lines work fine if you don't paint over them.
Actually I just got an incidence meter and will buy another this week.

I'm amazed at this concept that positive tailplane incidence is "good"!

Take our airplane with 3 datum lines - wing, tailplane, and thrust - all 0°. When moving forward in this attitude, the wheels are on the ground. A positive incidence is required to create a differential in pressures above and below the wing - commonly referred to as "lift". The tailplane and thrustline are also of course moving at this same angle. Quantifying this angle precisely is impossible as there are simply too many variables involved.

Because we use symetrical airfoil sections, this same angle is required for inverted level flight, BUT it is on the other side of the 0° datum.

Let's call this angle 1°. Let's also call whatever positive incidence is set on the tailplane 1°. When upright level, the tailplane is now 2°, and when inverted level it is 0°.

Added to all this is that we cannot know precisely the position in flight of the elevators to the stab, but due to the required positive incidence on both sides of 0° datum, that position differs for upright and inverted neutral. That difference is increased with any deliberately placed incidence.

This deliberate misalignment MAY work in some instances, but only to correct another misalignment somewhere else. If we create one problem to correct one problem, are we "solving the problem"? It's a little like having a headache due to a bullet in the head - a bottle of aspirin will cure the headache!

Speaking of headaches - I've got one now. (A parody of a well-known Aussie ad for beer.)

>This deliberate misalignment MAY work in some instances, but only to correct another
>misalignment somewhere else.

Thrust line, wing chord, and stab chord are usually not in line, although I have not seen how these would call for the positive incidence stab. However, gyroscopic precession from turning the spinning prop axis left in counterclockwise flight would tend to pitch the plane upward, creating this need. Inverted (clockwise), the now negatively inclined stab would again counter the (now) downward pitching moment from gyroscopic precession.

There have been enough pro and con posts to convince me that even if aiming for 0-0 incidences, it would at probably be better to err on the side of the positive rather than negative stab incidence.

I've been lucky to get my hands on a copy of Ed Southwick's article introducing the Skylark design in a Model Airplance News. (Full Page ad by Sterling, as well)

Not to digress too much on the Skylark--but I always felt, despite the popularity and fame of the Nobler, the Skylark was the definitive stunt design on my generation.

In the article that explains the success and philosophy of the design, Southwick goes to great length to impress the need for (a) building accurately, (b) stiffening the fuselage before attaching the stab, (c) not inducing stress into the structure that will cause misalignment later and (d) Thrust, Wing and Stab at 0,0,0.

Here is Southwick, with one of the best ships ever, adamant that the Stab has to be 0 incidence. And at the same time, preceeding recent geometry developments by angling the control horns so that they are 90 degrees to the actuating pushrod at neutral control deflection.

Southwick pays all this attention to alignment in the entire design and wants the Stab at 0 degrees.

His stab was up a bit out of the downwash of the wing in upright flight.

Now, years later, the more or less conventional wisdom is to set the stab at 1 degree positive or so.

So did the later experience change the way one should build a Skylark?

I've got a Smith Model Products big Skylark kit and a Tom Lay ST .46 for which it was designed.

If I build the kit, do I set up the alignment 0,0,0 as Southwick intended?

Or ad a degree to the stab because it's been 40 years since he intended?

Have had a robarts for over 10 yrs. A friend recently got one, will try to borrow it whenever I assemble the parts on the plane. Sure saves a lot of pencils and measuring before assembly. Also if you get interrupted when you come back it is easy to see if anything moved, which is the norm.

These are no more important than a pitch guage.
Got one of those?
If not better get one,
Beleive it or not , you would be surprised what you can do with a
level. assuming you have a level building surface.
I beleive this to be the most important of all.
If you have seem the old paul walker articles(pictures), you will notice he builds like the real folks. OR like the Nascar people;I.E.
the total unit frame work is built on a jig plate.this assures every-thing is straight in at least one plane.
I have a 3'x5'x 3/8' glass plate I build (assemble ) the whole thing
on. I use the g. p. incidence meter on the ship and a fixture that mounts in place of the engine that accepts a level.
Use both of these together , and you will get an education.
How much incidence do you want in the stab?The engine? I wouldn,t try to make a statement;but i,ll tell you this ;In my opinion the leading edge shape and accuracy of leading edge is all important.

DON'T GOT ONE.

I've used the Mk-108 Eyeball and ruler up to this point, but no more. I'll be doing some fab work to the units pictured below, to enable better alignment. I've purchase three and plan to use them on the engine,wing, stab to get things dialed in. Between these and the laser beams I hope to produce better work. That's a 2" dia. spinner cone for size ref.

Hey Tony:

I suspect that you will not be happy with the results from using these bevel meters. They simply don't offer the measurement resolution and repeatability that we need.

As mentioned above +/- 1/2 degree is significant.

With any of the mechanical needle types, the length of the needle becomes the readability issue. Now if that thing was 20" in diameter, it would be a different story.

See my SN review of the GP laser unit--it is equivalent of having a really long "needle"

Also, the "equalizing" fixtures that attach these to wing and stab are important for repeatable measurements. No matter what type you choose, it will take some practice with it to get repeatable measurements. Small clamping and positioning differences affect the incedence measurements more than you would think. All of the vee block type clamps rely upon true and consistent radii on the LE.

It isn't necessary to have more than one as long as you can block the plane firmly enough so that it wont move between measuremnts.

JMHO

Capt,
You may be right at that. But geeze going from "nothing" to "something" has got to be a move in the right direction. I'll have to order up one of the other units I guess. A re-read of you article is also in order. Thanks.