I'm converting a JR MDM Fox to electric. I have a drawing from the manufacturer showing the motor install.

The drawing shows 2 deg down thrust, however I don't see the 0 deg reference (thrust) line. There is a dotted line on the side view but that's the pushrod line.

The only reference line i can trace is the wing line, but than again i don't know the wing incidence.

I wrote to the manufacturer with the question (who emailed me the drawing in question) but so far no response.

Am i missing something?

Thanks in advance for any help!
V.

Vasek,

My thoughts are this................

Place the fuselage on a stand setting the horizontal stabilizer at 0 degrees of incidence. Measure the incidence of wing to see where it is set. Then work off that information most likely using the stab as the reference line. That should give you the datum line to set the down thrust.

You're right in that they have not shown a center datum line. It's not the end of the world though. The center datum like is just a reference and it isn't used for anything but convienience. It's the angle the motor is mounted to in reference to the wing itself that matters. And you've got enough on the drawing they sentyou to find that out. Measure the relativeangle from the wing section chord line (the very nose of the leading edge to the middle of the trailing edge) to a thrust line axis drawn through the motor. And then set up the motor to match that angle.

Thanks guys, i will check with both methods.

B, i did the drawing (see pic) and measured 2 deg with a proctor on my screen. So the wing appears to have 0 deg incidence. Does that look right?

That's perfect.  Use the same wing root line on the actual model to measure the downthrust angle of the motor mount.  It appears that the wing uses multiple joining rods.  If you block the fuselage up using the rods with packing blocks and shims to support the fuselage you can then use an angle jig to set the motor mount in place at the correct angle.

As to the wing's incidence it really doesn't matter since the so called center line is purely an imaginary reference.  The only angles that the air and model care about are the ones you just did and the simlar angle between the wing and stabilizer.   The measurements to the center line, when one is shown, are just a convention used by designers to have an agreed upon reference line to use for aligning all the parts. 

I've tried to say that the actual "center line" is imaginary and not important in the end in a couple of different ways now.  Hopefully it's getting through the language barrier?  But to answer your question no, that does not mean the wing is set to zero incidence.  It only means we are using the wing's chord line as our reference line for determining the motor's downthrust angle with respect to the wing itself.  Also do not confuse the purely fixed angle of incidence that the wing makes to the fuselage with the in flight angle of attack it makes to the air.  One is fixed by the designer and the other is highly variable depending on flying speed and wing loading changes that occur during turns.

BM, thanks again for your insight

I agree with all you wrote except this:
Maybe i didn't say it correctly, but if the angle that i drew on the side view is 2 deg (and it is 2 deg as measured on my screen) AND the downthrust of the motor is also 2 deg i have to assume then the wing is at 0 deg. Right?

BTW i got a late reply from the manufacturer that some info is coming my way soon (cross my fingers)

Oh, I see what you mean now. I'm not used to seeing notations like that arrow so I totally missed it at first.

Based on the angle you measured and the note on the plans that say it's 2 degrees down then I'd have to agree with the wing beeing at zero. But zero to what? SInce there's no reference line shown on the plan and given the measurement agrees with the notation I'd suggest that the manufacturer set the thrust line to the wing's chord line. So the wing's chord line is the reference line. At least the absence of any reference line on the plan plus the fact that your lines also show a 2 degree angle strongly suggests this.

update

i finally got the info needed[8D]... Steve you were right all along! The reference line is set to the stabilizer @ 0 deg.

The drawing wasn't very precise as the wing angle should be somewhere around 1.5 deg (positive).

Thanks again for the help,
V.

Glad to be of help. Looks like a nice glider should be a lot of fun.