Setting Wing Incidence, Help
 

I am trying to set the incidence on a biplane to 0 Incidence. I purchased the Great Planes Laser Incidence Meter and now am totally confused. This is what I see. I set the fuselage in a level position by somehow finding the centerline of the fuselage, (this I don't know how to find), then I draw a line. When I set the upper wing, I would measure up from the line to the rear of the trailing edge and then set the same distance from the fuselage center line to the leading edge of the wing. Is this correct? My question is then, what the hell do I use the incidence meter for? To verify the setting? I can't quite understand what good the incidence meter is, if it does not supply a way to find the centerline of the fuse, and then use this as a reference for the incidence. Am I totally off base here? Any help would be greatly appreciated.

RE: Setting Wing Incidence, Help
 

I level my plane using the horizontal stab and set the incidence meter to zero on the stab then transfer the meter to the wing and read the difference. Its important not to move the plane during the transfer. It works for me.

RE: Setting Wing Incidence, Help
 

Usually on the plans the thrust line will be drawn on the fuselage. This line starts at the front and extends to the rear of the fuse and is the datum point for incidence set up.
All incidence and thrust settings are derived from this line.
Your plans may have the incidence built into the horizontal stab. Some are other than 0 degrees and you can use the side view from the fuse to determine it.
If you look at the side view of all the flying surfaces I'm sure there will be a datum as to the incidence.

RE: Setting Wing Incidence, Help
 

Check here: http://www.robart.com/How%20To/Incidence%20Meter.html
How to with pictures and everything ;).

RE: Setting Wing Incidence, Help
 

It makes no difference where the fuse is to start, as long as it is held firmly in place so that you may move the incidence meter from one surface to another.

Take a reading on the top wing. Let's say it shows 7 degrees positive. If the bottom wing also shows 7 degrees positive, the wings are parallell and at 0, 0 incidence to each other

If, on the other hand there is a difference in the numbers, then there is a difference in the incidence and you will need to adjust one wing or the other.

The same is true for the engine and stab. If, in this example, if all are at 7 degrees, then the incidence is 0,0,0,0

JR

RE: Setting Wing Incidence, Help
 

It does make a difference where the fuselage is. The datum has to be set at level to determine the incidence of the flying surfaces.
Maybe calling it a thrust line is a misnomer but this is an imaginary line running through the fuselage.

RE: Setting Wing Incidence, Help
 

The incidence of the engine serves the same purpose as the thrust line.

It is necessary to know what you are trying to set up. If you want 2 degrees of downthrust, that must be taken into account. Unless the stab is not yet installed, normally, all measurements are going to be adjusted to the stab, because it is the only truly fixed reference point. If, on the other hand, you are willing to uninstall the stab, then it might make some sense to worry about the fuse.

RE: Setting Wing Incidence, Help
 

Think about it like this. Set the fuse as you would normally. Now attach 4 incidence meters. Set everything (engine, top wing, bottom wing, and stab) to zero degrees.

Now, block up one end of the table 7 degrees. Everything on the plane is the same right? The only thing that has changed is that all of the incidence meters will now read 7 degrees instead of 0.

Point being that blocking the plane up so that it won't move is a pain, so... why do it?

RE: Setting Wing Incidence, Help
 

A word of caution: Not all bipes have 0 incidence on the hor. stab, very few have 0 incidence on the upper and lower wing , down thrust also veries greatly from plane to plane . BE SURE of the proper settings for your Plane per your plans .....
I would highly recomend that you set the incidence with the "datum" or "thrust" line leveled and the fuselage
stabilized . This may help reduce the chance of incorrectly setting up your plane .
With the datum line level - set your incidences to spec. , double and triple check settings
VERY IMPORTANT : ZERO YOUR METER ON A LEVEL SUFACE before attempting to setup plane .

RE: Setting Wing Incidence, Help
 

I have the same meter, infact two of them. One is not really enough. To really make life easier you need to buy or borrow another. This is also helpfull for measuring wash out and identifying warps (not that Ive ever had any warps). You plce on at the wing root the other at the wing tip.

As far as your original problem goes you would put one on the wing and the other on the stab.

I started out with one meter but eventually bought another.

RE: Setting Wing Incidence, Help
 

J_R,
I've encountered a number of aircraft, biplanes in particular, where hte horizontal stab is NOT set to zero degrees. Your advice will not work in those cases. I have a Great Lakes kit for example, where the horizontal stab incidence is NOT specified, but it clearly states in the instructions NOT to use the stab as a reference for setting the wing incidences.

I would highly recommend using that "datum" or "thrust" line for setting incidence on any plane.
Dennis-

RE: Setting Wing Incidence, Help
 

Hi Dennis

I suppose that if you are uncomfortable with the math involved, it might be easier to TRY to use the datum line running through. It is often more difficult to do that than just saying it.

If you measure the incidence of the stab on the plans, relative to the datum line ON THE PLANS, it has been my experience that it is easier to keep the model in whatever position it wants to stay in, rathter than trying to block it up.

I used 0,0,0,0 as an example. Those that understand the math will have no problem if the stab is say, 3, the wings 0 and -1, and the engine -2. It's just a heck of a lot easier to determine the incidences on a set of plans that will hold still then a fuse. If you have only one incidence meter, the problem gets worse.

You SHOULD be able to rely on measurements from the plans since they were what the model was constructed on.

JR

RE: Setting Wing Incidence, Help
 

That's a really valid point J_R. You can certainly measure the difference (if any) from the datum line to the horizontal stab, then either block the plane to get the stab at that incidence, or "do the math" and work from there. Easy enough. But what if it's an ARF without plans? ;) (I know, I know, you wouldn't have the datum line either.)
Dennis-

RE: Setting Wing Incidence, Help
 

ROFLMAO

Dennis, you have a point. Do ARF's come with incidence? I sometimes wonder.

JR