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-   -   Effect of wing and Horz stab not paralell (http://www.rcuniverse.com/forum/aerodynamics-76/11254149-effect-wing-horz-stab-not-paralell.html)

PDF 10-07-2012 12:48 PM

Effect of wing and Horz stab not paralell
 
Hello all,
I have a ARF I'm building and the horz stab fits in a prefab slot (no room for adjustment) when installed, I measured the LE of the horz stab to the leading edge of the wing and there's a 1/4" difference. The lenght of the stab is 22 1/2" in lenght. At the moment I can't think of any way to adjust it. Is this a common issue with ARF's? What effect will I have? Any input would be appreciated.
Thanks,
Pat

David Bathe 10-08-2012 01:04 AM

RE: Effect of wing and Horz stab not paralell
 
Pat, you want them a equal as possibly but your problem could be that you're messuring from the leading edges, you must messure from the trailing edges... wing tip/aileron lines to the stab tip/ elevator hinge lines.

To line up the stab, you must first establish that the wing is seating properly.
ie, mount the wing and messure equal distances from each wing tip/aileron line- to the fin/rudder line.
Adjust wing as necessary.

Then mount stab and messure equal distances from the stab tip/elevator line- to the fuselage. Secure the trailing edge to the fuselage with a pin allowing the leading edge to move alittle for the next step.

Next, messure equal distances from the stab tip/elevator line (not leading edge as there could be some slight changes in shape)
to the wing tip/aileron line. You want 'em equal, so move the stab leading edge remembering to keep the pinned trailing edge in position.
Move/cut/sand as required.

Also note the stab and the wing need to be parallel.
View model from the back and adjust as required.

When everything is lined up, (you may need some packing) hit it with some thin CA.
Dismount the wing and continue gluing the stab as required.

PDF 10-08-2012 03:45 AM

RE: Effect of wing and Horz stab not paralell
 
Hi David, and thank you for the reply.
I measured from the trailing edges of both the wing and horz stab, it's still off a 1/4". I tried every possible way to measure and hopefully I was wrong but no matter where I measure from it's off. The way this ARF is built the stab pushes into the fuse and self aligns, there's no adjustment. As you see on my post I mentioned to all If this is a common problem with ARF's and people just assemble and go, or am I to fussy and making a big deal of it. That's also why I'm trying to find out what effects this out of alignment causes. If this was a kit I'd have more control over it since it's not covered with monokote and color scheme. Do you think I'd have any adverse effects leaving it as is. I've been out of this hobby for 10 years and this is my first ARF, the last plane I had was a trainer from a kit.
Thanks,
Pat

David Bathe 10-08-2012 03:56 AM

RE: Effect of wing and Horz stab not paralell
 
Pat, it all depends on what type of airplane you're assembling, if it's a simple run around and you don't won't to chop it... then go as is.
If you intend to do some half decent aerobatics, then I'd fix it.
I'd fix it regardless of what type of model it was.

Can't be that complex, a few mins I'd guess... can you post a picture?

PS. Just make sure it's the stab that's off... and not the wing.


PDF 10-08-2012 04:34 AM

RE: Effect of wing and Horz stab not paralell
 
Hi David,
The model is a 300 Extra .46 58" wingspan. I'm going to try to take a photo and link it. I have never done the photo post so I'll see what happens. I'll try to post later this evening. In regards to a easy fix, it won't be that easy since it'll require me stripping the monokote and sanding one side then filling in the other side. Then I'd have to apply the monokote with the paint scheme. I do want to it to fly correctly doing aerobatics.
Thanks,
Pat

David Bathe 10-08-2012 05:04 AM

RE: Effect of wing and Horz stab not paralell
 
If it's a small Extra you should fix it... and it's real simple.
I don't think i've ever made a RTF without having to remove something somehwere.
Remember that moving the tip 1/8th of an inch ( 2x =  the 1/4th you're refering to) will only result in a 1mm (ish) change at the fuselage.

It's easy to post a pic, you'll find out.


PDF 10-08-2012 05:25 AM

RE: Effect of wing and Horz stab not paralell
 
1 Attachment(s)
Hi David,
I'm trying to upload some pictures. I hope this works.
Notice in the first picture there is a reveal in the bare wood so when you push it into the fuse the sides will self align onto the fuse, therefore having no adjustments.
Thanks,
Pat

David Bathe 10-08-2012 06:12 AM

RE: Effect of wing and Horz stab not paralell
 
The pics are perfect.
You have a couple of options:
You can remove a little more of the cutout on the front of the stab leading edge, choose the side that is further in distance fron the wing.
or...

Cut of that little tab that is attached to the rear of the stab, the part that make the fuselage fillet.
Position the stab in the correct position by moving the trailing edge, leaving the leading edge locked in it's position.
When happy, draw a line and remove the excess covering then glue.
Lastly, replace the little fillet removed earlier to fill the space in the fuselage.
It's removal/ replacement will have no effect on the structural integrity.

I'm lazy, I'd do the latter option.

If you have 5 mins, possition the stab in the correct place and lets see how much it's out of line.

da Rock 10-08-2012 06:57 AM

RE: Effect of wing and Horz stab not paralell
 
Great advice. You're really only removing manufacturing errors, and it won't take but a very little time to do it.

I would suggest checking one thing first. Install the wing and check it's orientation to the fuselage. Start by measuring how far the tips are from the fuse to see if the wing is correct left/right. I usually measure along the aileron hinge line. Don't expect there to be any difference. Now, mark the very center of the end of the fuselage at the very back and measure from each wingtip/aileron hinge line end point to that mark. There shouldn't be any difference either, especially if the wing has a separate wing tube.

What I really am looking for is a straight fuselage. The fuselage sides of most ARFs nowadays is cut before it's slapped into a jig and built. If the cuts in the horizontal tail don't line up (as yours doesn't) there is a possibility the Chinese worker didn't slap both sides into the jig the same.

I've only found one fuselage to be off square in the last 5 years, but it was good to know. It saved me wasting even more time. It would have saved me a bunch if I'd measured while assembling. yeah.... :eek: I didn't check for square while assembling.

PDF 10-08-2012 08:01 AM

RE: Effect of wing and Horz stab not paralell
 
Hi David,
I contacted Tower Hobbies tech support and they told me that a few clicks of the trim will take care of that. I'm not taking that chance, I think it should be build true and square. Besides I think additional trim would create drag.
I thinking this over before I do something to the stab. If I cut and sand I'll need to match the monokote and stripes. In your suggestions you said to sand off the leading edge and move it over, but the whole piece would have to be sanded at a different angle due to the reveal rests entirely against the fuse. This would have to be done on both sides because the LE and TE on both sides are snug against the fuse. Again I'm going to have to sleep on this on.
Thanks again,
Pat

David Bathe 10-08-2012 09:26 AM

RE: Effect of wing and Horz stab not paralell
 
Pat, don't sand it, CUT IT off in one piece leaving all the covering in place.<div>Mount the stab correctly then glue it.</div><div>The piece you've removed can then be VERY slightly trimmed for a perfect fit.</div><div>You don't  need any sand paper for the entire process, just a sharp scalpel.</div><div>Don't panic to much about this, it's a 5mins max job (including setting up and waiting for the glue to dry).</div><div>Setting the stab straight is the goal, adding the fillet a secondary cosmetic procedure.</div><div>Sweet dreams.</div><div>
</div><div>
<div>
</div></div>

PDF 10-08-2012 09:39 AM

RE: Effect of wing and Horz stab not paralell
 
Hello again,
I just tried and push the stab in on a angle (not to hard but to give it a little extra pressure against the fuse) and I picked up a little. I got it down to 1/8th to 3/16th max. If you look on the second picture the area giving me trouble is the top right and bottom left, meaning I'm trying to turn the stab counterclockwise. I there a trick on compressing the wood on those areas without removing the monokote? If I could get even a strong 1/32th of an inch it might do the trick. David I'm probably not understanding about the fillet piece, what I see is the contact points are on the stab pieces that will be attached to the elevators that have the reveal that's making contact with the fuse. The little piece sticking out the back moves freely. If there's a trick on softening up the balsa under the monokote just that little bit it may do the trick.
Thanks again,
Pat

da Rock 10-08-2012 11:08 AM

RE: Effect of wing and Horz stab not paralell
 
1 Attachment(s)
If you're saying that the right tip of the horizontal stabilizer is farther aft than the left tip of the horizontal stab, then there are a couple of very simple and easy steps that can cure the problem.

Look at the area of the stab pointed out by the yellow and green arrows. See the difference? Notice that the rear tab appears to stick out where the orange arrow is pointing? The opposite side appears to be flush with the fuselage side. If you need to rotate the stab counterclockwise, try making that tab flush on the left side of the fuse. Now measure from hingeline to hingeline.

The planform (view looking down from above) of the stabilizer, with the LE projecting forward of the fuselage slots, is a limiting factor. No matter what you do aft of the forward most 2 points of the stab's LE, if the front of the stab fits the fuselage tightly, that entire stab will try to rotate around where the very front of the stab pinches the fuselage. Simply removing some of the fuselage in the slot won't allow the stab to rotate the front left and the aft to the right.

Try pushing that rear tab to the right and see how far you can go. It's already too far left in the pictures as witnessed by the way the tab sticks out to the left.

da Rock 10-08-2012 11:12 AM

RE: Effect of wing and Horz stab not paralell
 
Quote:

ORIGINAL: PDF

Hello again,
If you look on the second picture the area giving me trouble is the top right and bottom left, meaning I'm trying to turn the stab counterclockwise.
Do you mean "forward in the slot on the right, and toward the rear at the left rear"?

You're not trying to raise the right side of the stab and lower the left are you. You're wanting to move the right stab forward and the left stab rearward, correct?

PDF 10-08-2012 11:57 AM

RE: Effect of wing and Horz stab not paralell
 
Hello da Rock,
Your correct I'm trying to move the right side of the stab forward. I stripped some monokote off the top right hand side to remove some material on the LE of the stab, take moved it a bit. I'm down to 1/8" now. What's holding it back now is the right side reveal, I have to sand some out so the stab can come into the fuse a little more, I really didn't want to start doing covering, that's why I bought a ARF. I debating to stop now since I'm at 1/8". Any opinion?
Thanks,
Pat

da Rock 10-08-2012 12:46 PM

RE: Effect of wing and Horz stab not paralell
 
Simply apply some pressure to the tab at the back, pushing it right. If it doesn't stick too far out when you get that 1/8, glue it. If it sticks out more than you care it to, then razor it off after the glue dries.

The workers who put it together simply didn't have everything tight in the jig. 1/8 is borderline. It's almost close enough.

BMatthews 10-08-2012 12:47 PM

RE: Effect of wing and Horz stab not paralell
 
If that's all you're trying to do either just remove a little on the one side or add a shim of light cardstock to the other side at the front of the cutout. Or simply push it in until the short side touches then align the stab with the center line or to the wing and glue it and pack the resulting gap on the other side with a filler of some sort.

I was thinking for much of this that it was a case of the one side sitting higher than the other by 1/4 inch. In that case David was describing a good option. Other than the fact that to make up for 1/4 high at one tip the amount to remove would defy cutting it away with a knife. If that were the case I'd say simply file or sand away enough to allow the stab to sit level and then pack the upper slot with a thin wedge of wood or some file cover card stock to pack the gap.

Either way this is going to be quite typical of any ARF product. It may have sped things up but if you're building a model that is intended to perform precision flying you need to be willing to shave or sand a little here and there to fine tune the assembly. You need to assume nothing is quite as it seems and check everything. Like from the wings being balanced from side to side. that the wings fit the fuselage squarely in all directions and that things like the stabilizer sit square to the wing. Everything should be checked and checked again with a different method where you rely on nothing that is on the model as a reference line unless it is proven first.

As for checking with the distributor of the models of course they are going to give you an answer like that. And realistically they are perfectly right. The effects of this sort of misalignment are minor to unnoticable. But if you're looking to fly the model in a judged event then it's worth taking the time to make it right.

And lets not lose sight of the cost of these models. To buy what we can for the price being paid is nothing short of a miracle. To expect precision in each part is simply more than we are paying for.

da Rock 10-08-2012 12:51 PM

RE: Effect of wing and Horz stab not paralell
 
BTW, make sure before you glue that the stab levels out exactly with the wing. When we put parts together with some effort or force on the parts, they often get out of alignment some other direction. Looking from directly behind the plane, you want to see the hinge line of the stab lined up with the TE of the wing. Don't want either stab tip to look high or low compared to the TE of the wing. I figure you already know this since you spotted the other misalignment, but lots of people read through these threads.

PDF 10-08-2012 01:12 PM

RE: Effect of wing and Horz stab not paralell
 
Thanks for the advice da Rock,
Also I checked on the wing aligniment as you suggested and it came out perfect. As you can see from the pictures it would be impossible to adjust the horizontal plane of the stab being it slides into a precut and pretty snug slot. I'm now going to sand the reveal to try to get a little extra room (I'd like to get it perfect).
Thank you,
Pat

PDF 10-09-2012 12:48 AM

RE: Effect of wing and Horz stab not paralell
 
Hello all,
I want to thank everyone for there help. I finally corrected the alignment to perfect measurements, it came to the point where I had it to 1/8" to leave it but again since it was my first ARF I wanted to know if this is common having ill fitting parts, I guess this is what I'll be up against. If I'm going to build a plane I'd might as well do the best I can. I ended up cutting out the monokote on the inside edge right tip, the part that faces the fuse, and also the underside inside edge (the reveal) also facing the fuse, so none of the monokote was touched that you would see. With a sanding block I sanded the tip and the reveal out furher to the stap tip and evenually allowed my to pivot the stab right upper corner to the wing tip. I'll apply some monokote to the inside tonight (I may not even need it because as is I doesn't show) this way it can't work its way loose, it'll be about a 1/4" strip then folded on the reveal and underside. The reason the underside was sanded and not the top is that the top and bottom are pieces of balsa glued to plywood the shape of the stab and the fillet you see that slides into the fuse is actually the plywood itself. So the bottom left side of the stab was slightly longer protruding into the fillet area. I hope I explained myself well enough. I learned alot from this and really appreciate the help, It took me more time to get the courage to start cutting out monokote and sanding due to the fact I was fearfull the I would be doing something wrong and ruin the finished product.
Again thank you all for the help.
Regards,
Pat

charlie111 10-09-2012 01:14 AM

RE: Effect of wing and Horz stab not paralell
 
/     gLAD TO HEAR YOU FIXED THAT ALIGNMENT ISSUE.All The Tail alignment issues are critical!I'm Old School and use Silkspan Paper.I cold use some tips on applying (Monocoat).To My New Prototype (Rotarywing) It's Electric and a New concept check out 1st prototype on my Profile Got some (Bugs Out) by changing the directin of rotation.I can now use stock rotation on both turning motors!I'm also using typhoon motors this time! 


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