I built the vanessa cg machine, but I have a question. When you adjust the plane for flight incidence, do you level up the horizontal stab or set the plane to the wing incidence?
Any help on this much appreciated.

flynte

http://home.mindspring.com/~the-plumber/

You set the incidences relative to the thrust line. Once you level the plane relative to the thrust line you set the wing incidence and then the stabs. You have to have a reference level line somewhere on the fuse to work from. You can set the stab relative to the wing or vice versa I guess, but you have to set the 1st one relative to the thrust line.

Mike,
Thank you for the information on the proper way to set the wing and stab. incidence.
I have a question for you regarding leveling the plane on the thrust line. I have a Twist 3D, and I would like to verify the wing and stab incidence values, however I do not have a flat area anywhere on the fusealage that is level with, or inline with the thrust line of the airframe.

How do I level an airframe like this to check the incidence?

I have a Robart Incidence Meter to measure incidence.

Thanks much,
Ryan

The Twist is an ARF, right? If they do give incidence, then zero out your Robart meter on the tail. Without moving the plane, clamp it to the wings to see the incidence. Plane doesn't have to level in any way. You using the tail as the 'check'.

The only problem with that method is that you make an assumption that the stab is mounted correctly in relationship to the thrust-line of the aircraft. It sounds like RhyanO is trying to determine if the stab and wing are in fact mounted at the proper angles in relationship to the thrust-line. The vast majority of sport aircraft have the horizontal stab zeroed with the thrust-line, but you really need the plans to know for certain. A phone call to Horizon or the manufacturer may be necessary if that information didn't come with the plane.

A minor detail about the Twist.

It's got a symmetrical wing.
It's expected that the model will be upside down about as much as right side up.
It's got a very light wingloading.
It's designed as a 3D and the expectation is to pull it around with the prop, not the wing.

A setup like that almost always has the wing lined up with the CL of the fuselage.
You'll seldom see up or down thrust on the engine.

Block the sucker to sit level on your picnic table.
Stand off to the side 5-10 feet and look at the airplane.

If the stab/elevator looks to be on the same line as the wing, it's good to go. If the prop looks to be at 90degrees to the wing, it's good to go.

If you must use a tool and want to nitpick the sucker, then while the airplane is sitting on the picnic table. Put the incidence meter on the wing and record the readout. Then do the stab/elevator and you got your nits. If you're that particular, then you need to make an accurately flat replacement for your prop in order to read it's position accurately. Using the prop will not be accurate at all. A disc of 1/8" plywood works good and doesn't actually have to be a 360degree disc.

LOL,
I agree with darock... You shouldnt worry about the incidence on a Twist. Its a thumb and eyeball thing..

If you are simply wanting to practice and learn a little about incidences then as he says, level the fuselage as close as you can to the centerline of the plane, and then check your incidences.

If you are wanting to take your work to the next level, this is how the pros check their incidence,,,, with a laser like this [link=http://www.sears.com/sr/javasr/product.do?pid=00948251000&vertical=Sears&BV_UseBV Cookie=Yes]laser level[/link] that will cast a line down the side of the plane so that you can get a true level. Then get an incidence meter and go to work.. I use a digital level like this [link=http://www.sears.com/sr/javasr/product.do?pid=00940195000&vertical=Sears&BV_UseBV Cookie=Yes]digital level[/link] strapped to a GP incidence tool like this...[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXPW71&P=ML]incidence meter mount[/link]. It gives me deadly accurate results with 100% repeatability.

Thank you for the replys.


My question was how does one level a fuseage to the centerline of the plane, when there is not any level part on the airframe to reference from. Im just curious how one would go about doing such a thing. (generically speaking lets say that this plane is not a 3D plane, but rather a precision pattern plane)
I understand that one can bolt some sort of flat board onto the engine inplace of a prop.... but whos to say that the engine is correctly mounted to the engine mounts (could be 1-2deg right, left, up or down).

Thanks again for your time and advise!

Ryan

If you are wanting to check the incidence of the wing relative to the stab, level the stab and then check the incidence.

I would try to see what the incidence of the Twist is suposed to be and what the designer used as a reference for zero. That would be the best starting place.

What is it you are wanting to do? Are you wanting to change something?

You are.

The whole deal with using accurate measuring tools is to find out for ourselves.
We have a slight advantage when checking out a model when we have the instruction booklet and it's got the setup information in it and the booklet is correct. Often we don't have a booklet. Even when we do, it often has nothing about this stuff. And even when it does, it's not always the truth. I've got an "excellently complete" booklet with my Phoenix Sukhoi that says the airplane has no down thrust, no up thrust, no right thrust and no left thrust. And later on in the booklet they show a diagram for mounting the motor mount that would be perfect for a firewall that had right and up thrust. And it turns out that the bloody firewall was built into the front of the fuselage with right and down thrust.

The truth is, if you're wanting to verify that the factory built the model "correctly" you're SOL. Out of Luck.... None of them want you to know how far off or how accurate their workers do things. So don't expect to easily find all the numbers.

We find out by flying the model and putting it through some simple maneuvers and watching the results.

The measuring back in the shop really only helps us establish the starting point for adjusting for what we found with the flight tests.

BTW, with a symmetrical, very lightly loaded wing, like on the twist, the wing is going to fly at a VERY SHALLOW angle of attack. And since a wing is usually built into an airplane so that it's close to it's operating AOA with the fuselage at it's least drag orientation, you can bet that the wing in the Twist is going to be very close to the centerline of the fuselage.

And pattern planes are the same.

Now, if you've followed that..........

Most of our models don't have wings that produce a lot of pitching moment SO our elev/stab's don't need much AOA to keep the models pitched right. The Twist and other symmetrical winged models seldom have horizontal tails that differ in incidence. They don't need it.

Like Mike asked, what do you want to do? what's the problem?

Ryan, if you're really just wondering about stuff..... (I ALWAYS AM)

The way airplanes are designed is to start with what you want to do with them. Skipping past a lot of other decisions...... and after figuring out how big a wing you're going to need, and what airfoil you plan to use, you take the probable weight and look up the stats on your airfoil.

You'll find what AOA that airfoil will be when it's carrying your design load at your design speed. And you'll then draw your airfoil into your sideview blueprint so it'll be at that AOA when the fuselage is at it's least draggy orientation.

You usually want the wing to operate most efficiently when the fuselage is operating most efficiently etc etc......

Some airfoils will be relatively close to ZERO AOA at their operating speed, so will be zero incidence in the fuselage. Cambered ones will have more incidence.

And if all that didn't confuse you.....

*wanders off to get a coffee and clear his head. [&:]

Thank you all for the advise and insight into wing incidence information.

To answer the question... I am not trying to correct any problem with the Twist airplane, Iam just curious about what the incidence is for this airplane. To give a little background into why I asked the question in the first place. I recently just got done building an 1991 series UltraSport 40. When building that airplane I bought a Robart Wing Incidence meter to set the incidence values both with the Wing and both Verticle and Horizontal stabilizers. I used this meter to ensure that I glued the stabilizer in so that it was consistent to the center of the thrust line of the airframe. I also used this meter to set the wing correctly with the thrust line of the airframe.

I just completed building the Twist and I wanted to use this meter to check the incidence values of the Twist. The problem was that I didnt have any reference points on this airframe to use to level the airplane accuratly. So basically I wanted to check the incidence out just for the fun of it if you will.

I really appreciate all the advise that has been given.... Thank you.
Ryan