djr1007

I've read in many threads and such that you should :
1. Set up the plane on the bench perfectly level
2. Check and set incidence of wing/stablilizer in relation to each other and/or the planes level line or thrust line.
3. Check and adjust the engine thrust up/dw/left/right.

My confusion is with number 1. I also hear level and thrust line kinda used interchangebly. But if the engine has some down thrust built into the firewall, how can the thrust line be the "center" line?
So, how do I arrive at the refference line which all other things will be measured by?
Thanks.

Dean Pappas

Hi DJR,
It depends on the design, and upon what the plans say.
What do they say?
best of luck,
Dean Pappas

djr1007

No plans, Spot on 120 arf.

WEDJ

In General, "level" refers to the drawing datum line.
In theory, it should be parallel to the attitude the plane will have while flying level.

Kinda like the waterline of a boat.

Angle and incidences are always measured from that reference line.

The Eyeball was easy, that line went through the centerof the prop, wing, and horizontal stab. It was one of the first 0-0-0 setups.

djr1007

Sounds like (if you have no plans) you stand back and see what looks like it would be level flight, shoot a line, then zero everything out and begin working off that Line. Won't matter as long as you continue to use the same referance line as zero everytime.
Do I have it?

pimmnz

Yep.
Evan.

rainedave

My Feedback: (1)

I would bet that the stab is at 0° and that there might be 1/2° positive or so to the wing. You could prop up the plane so the stab is level and then use an incidence meter to check if the wing is the same or slightly positive in relation to the stab.

David

pimmnz

You can pick anything as a reference line, in the full size world it may not even be on the aircraft at all, and many start with the zero reference for the various stations actually off the aircraft. What you are trying to do is to find the relationships between the various items on the model. Try this as a start. place the model on a flat surface like a table. Chock the wheels so the model can't move. Raise (or lower) the tail until a ruler placed at the leading and trailing edges of the tailplane with the elevator level reads the same dimension. We will call this 'Zero' and consider that a plane passing through the tailplanes' leading and trailing edges is our reference line. Measure the wing, centre of L/E to centre of T/E. If the front measurement is higher than the rear then the wing has some positive angle to the reference, and vice versa. You can continue like this at the wing tip to establish was in/wash out, thrustlines, etc, etc. If you draw the appropriate dimensions on a piece of paper you can also directly measure the angles of the wings, tail etc. You can, by measuring distances from the front, and heights off the table, even draw an outline plan of the model.
Evan, WB #12.

djr1007

Guys:
Thanks a lot for the education, I really appreciate it. One last question. The Spot On has adjustable incidence on the stabalizer. Since the stabablizer is adjustable, seems to make sense that I could use the wing as zero and adjust the stabalizer. The instructions just said to start with the stabalizer set the same as the incidence on the wing. Nothing more on the subject.
FYI, I'm building a Big Dirty Birdy 2+2 and I have a new 1/4" steel plate magnet system, craftsman laser level and a couple other items to ensure everything is as close as possible. So I'm practicing/learning on the Spot On while I build. I know I need to put a touch right thrust on the engine. I'm following one of the "Trim" charts to set things up.
Back on the DB 2+2, the plans are not to scale and there are no instructions, I didn't know this when I bought it, but wanted to step up and try the next level. Hence the questions about level, refference line, etc.
Once again, thanks very much all of you.

rainedave

My Feedback: (1)

Yes, in that case block up the plane so the wing is level and adjust the stab to be level.

On the sixty-size Dirty Birdy and the UFO Bridi built in 1/32" of positive in the wings. That comes out to less than 0.25° which is very minor. Just to check I divided 1/32" by the root chord - 13" - and got a factor of 0.0024. So, you can multiply the root chord of the DB 2+2 by that number and it will give you the amount of positive incidence for the wing.

David

hrrcflyer

djr1007,

I have a set of instructions for a Dirty Birdy 60. If they would be of any help to you on your 2+2, I'd be more than happy to scan them into a PDF file and email them to you. If you'd like them, PM me your email address and I'll get them to you ASAP.