NobelARF Alignment

I think Brett mentioned a propensity for out of alignment stabs' somewhere, but now I can't find the thread. When I level my N*ARF engine mounts, looks like the stab will be off by 1/8 or so. Easy to fix at this point by trimming and shimming. Am I correct in using the mounting rails as the starting point for 0/0, assuming that everything should be 0/0?

Best regards,

Hmm, a Nobel Arf, that must be a real prize! --sorry, couldn't resist!

Actually I think the major alignment problem is probably the motor mounts themselves (at least on my Nobler. Maybe you should take a good look at them to make sure they are straight. Also check the wing, elevator, and mounts to see if two out of the three agree with each other. I think 0-0 is what is in the design.

>Hmm, a Nobel Arf, that must be a real prize!

Yeah, it's dynamite.

good one

If you haven't glued the wing in then I would sugest using the motor mounts for your reference because you can adjust the wing and stab to match. If you have the wing glued in and it doesn't agree with the motor mounts you can shim the engine so it agrees with the wing.

>If you haven't glued the wing in then I would sugest using
>the motor mounts for your reference because you can adjust
>the wing and stab to match. If you have the wing glued in
>and it doesn't agree with the motor mounts you can shim the
>engine so it agrees with the wing.

I would guess that in general, using the wing cutout as a reference and fixing everything else would be the easiest. It will certainly result in the least amount of cutting.

I also think, that given the dimensions, that this will also form the most reliable reference point. Half the battle in measuring alignment is making sure you are really measuring it right. If you just use the 2" of motor mount stiking out from the firewall, that's not a very good baseline, and even worse, if you hang the entire fuse from it, it will sag and give you erroneous alignment *measurements". Plus, it's really easy to shim the engine afterwards, if it's off from the wing/tail - in fact, that's a trim adjustment.

As far as what to shoot for, I suggest 0-0 from wing to tail, and 0 to a little down on the engine. Given the size of the parts, there's now way to reliably hit the tiny degree of incidence that I think may be beneficial. The root chord of the stabilizer is something like 2 3/4". .2 degrees over that baseline is a whopping 9 thousanths of an inch. You'll never, ever, be able to measure that, and depending on how you put the fuse together under the wing cutoff, you can probably flex the aft end of the fuse up and down by 1/2". Shoot for 0-0, and when you are at the point of deciding "that's close enough, I'm done", make sure that the LE of the stab isn't *below* the reference point. So, in short, if there's any uncertainty, make sure that uncertainty doesn't result in "up elevator".

Needless to say, don't do the final alignment on the stab until the wing is in place and the fuse underneath is solidly glued in place!

Actually the wing alignment on the Nobler Arf is set by the mounting bolts and the front dowel. The belly pan just sort of glues onto the bottom side of the wing, and any part of the fuse you can get it to fit to. So to first order, you can get the alignment before any glue is committed.

Since I didn't actually glue my wing--I just use the mounting bolts to hold the wing on--so far so good!. The belly pan is just glued to the bottom of the wing only. I can set the alignment of the wing at any time. Hmmm--maybe I should check it before the next season!

LAST EDITED ON Jan-23-04 AT 08:19 PM (CDT)
 
When I aligned my Noblarf, I did it before putting on the flaps. This way I could grab the actual wing trailing edge with the alignment meter, not try to find a neutral flap position.

So, I used the RoBart aligning tool on the wing, and a couple of omnidirectional (the round ones) bubble levels on the engine mount and stabilizer. As Brett says, I just made sure to have the wing and motor at zero, and the stabilizer with "definitely not up elevator effect" (aiming to have the leading edge exactly even with or just higher than trailing edge). So far it seems to be awfully close to correct trim.

More flight testing tomorrow! Where's my sunscreen?

>Actually the wing alignment on the Nobler Arf is set by the
>mounting bolts and the front dowel. The belly pan just sort
>of glues onto the bottom side of the wing, and any part of
>the fuse you can get it to fit to. So to first order, you
>can get the alignment before any glue is committed.

You can get the wing aligned to the mounting hardware fine. But unless you finish he fuselage, you can't be sure that the fuse will not distort up, down, or in twist during the process. So I very strongly suggest the the wing/belly pan, whatever, be permamently in place in the final configuration before you do the final alignment, and glue in the stab.

LAST EDITED ON Jan-24-04 AT 02:26 PM (CDT)
 
I guess it depends on how you handle the belly pan. As I said, mine doesn't even connnnect to the fuselage. My wing is only held down by the dowel and bolts and as a result, still removable. At the time, the I wasn't convinced that the bellypan would add much strength to the fuse since there wasn't much "meat" to glue too. Also the Nobler Arf fuse is jig-built without the bellypan, unlike most full fuse planes where the bellypan forms an integral part of the fuse structure and alignment, and when cutout for the wing insertion, can let the fuse "spring" open.

I can see if someone applied a lot of pressure to make the bellypan fit snugly onto the fuse (and glued it in) that it might distort the fuse, causing misalignment.

> I would guess that in general, using the wing cutout as
>a reference and fixing everything else would be the easiest.
>It will certainly result in the least amount of cutting.
>

Could be right, I have never had any luck trying to shim an engine especially on wood mounts. I tried fixing the misalignment in my ARF Nobler, found Brodak shims to be too thick, will offset the engine enough to mess up the cowl alignment and a washer just sunk into the wood. The motor mounts are fixed so the wing and stab are the only things that can be easily changed unless you have access to a mill so you can make the proper angled shims.

Oh, the engine mounts..

I drilled the holes one size over and epoxied in brass tubing. Then I filed the whole thing flat and parallel. This was before doing the wing alignment. So far, NO crushing.

>The motor mounts are fixed so the wing and stab are the only things
>that can be easily changed unless you have access to a mill
>so you can make the proper angled shims.

I'm pretty sure it is possible to buy tapered shimstock, tho I looked on McMaster-Carr's website http://www.mcmaster.com/ to no avail. If somebody knows where it can be obtained, please post info. I know that there are types of epoxy putty intended for mudding in under marine diesel engines in good sized boats, tho the places I have worked always did it with custom machined tapered blocks and shimstock. It sounds like JB Weld might do the job just fine. Steve