[wrongway john]

I?ve laid down and locked the HS-403?s in place in my empennage jig. I?ve run a thin red string about 1/8? of an inch on top of that to assure everything stays in line, and quadrupled checked it.

Concerning the radius for the two HS-409 pieces that fit inside the two HS-403?s, I can see a very small gap pretty much throughout the 409?s where it rests up against the 403?s, perhaps 1/64? (15 thousands or so) of an inch or less from up top. I want to work a bit more with the 80 grit, then go to the 400 grit, which I?m hoping the gap will be less than that, but I think it will be difficult to get it uniform throughout the entire lengths.

I realize that even if it looked uniform from the top view, wouldn?t necessarily mean the radius was done correctly, since one could file too much of the radius from the 409?s. I?m being careful to avoid that by fitting the pieces frequently every time I sand a bit more with the 80 grit.

I took some ?plaster of paris?, and made a mold inside my 403 pieces, thinking that would be a good guide for the 409?s when filing the radius, but that really wasn?t much help.

Is there a better way to know when you get the radius right?

 

[wrongway john]

I spent some more time the last few days on the radius, slowly filing and sanding the radius some more, setting the 409?s into the 403?s ever so often as to not to try to take off too much.

I'm close to making it fit, but still not happy with it. It appears I have about a 7 inch section on one of the 409?s where it is off the web of the 403?s by about 10-15 thousands or so. This is where I may have filed and sanded slightly too much in that area. Other parts of the 409's, appear to be off about 5-10 thousands, while about half appears to fit quite snug against the 403's web. I took the 409?s out; set it on edge on a long straight edge, and shined it against the light to the outside, and can see a very slight gap in a few areas. I made a piece of wood that has the correct radius cut out of it that I slide down the 409's to see how the radius is coming along, but I honestly don't know where to sand on the 409's anymore.

Not sure if I have to order two new pieces yet, thinking about getting a 12? flat air file on it next and see if it will keep it flatter than by doing this with file and sandpaper. Only two sentences are devoted to this procedure in the manual, saying to file down, then finish sanding the 409?s down with 400 grit sandpaper. Gosh, I can?t believe I can?t even get past the very first two pieces.

I?ve done various search engines on these pieces, and nothing is covered about it. If you have any suggestions on this radius on keeping the 409's flush with the web of the 403's throughout the span, I hope you?ll take time to share. No matter how much more I try to file or sand the 409?s now, it doesn't seem to help me any more on making it fit better.

I?ve seen a few pics of Dirk?s empennage, and it appears his 409 pieces fit snug throughout the span of the 403 webs.

Any suggestions at all would be appreciated on how you went about it.

 

[flion]

It won't hurt the strength of the spar if the radius is a little overdone. It needs to be done enough so that the bar lies flat to the web for riveting, which is what carries the combined loads. So there's really no need to order new parts. That said, the only thing I can think of to ensure the results you want are to get the parts milled. Which I wish I had thought of when I built my -6A.

After re-reading your posts, is it the web or the flange where you are getting gaps? If it's the web, the usual culprits are: not enough material removed for the radius, rivet holes need deburring, or (if not drilled yet) the bars need to be clamped into the spars better (aluminum parts may vary in 'flatness' slightly). If it's the flange side where you're seeing the gap then my prior comments hold.

 

[Dave Yost]

John,
I am at the same phase as you in the empennage construction. I had the same issue and was losing sleep over getting those gaps closed. After about 15 hours of filing on the HS-409 doublers, I went to a few builders for advice. My gaps were +/- 1/32 to a 1/64 across the length of the T.E. spare. every body that looked at them said "****, that's way better then mine looked". I don't want to speak for Van's engineering department, but the general conscious is that as long as the part fits into the radius "snug" there can be a gap at the top of the flange. This is due to the fact that the stamped u channel is not 90 degrees dead on. So, it would take a lot of effort to match fit HS-409(s) in the channels perfectly.

I am a bit of a perfectionist myself, so I feel your pain.

My home email is [email protected], send me an email and I will send you some pictures so we can compare notes.

Cheers Dave

 

[wrongway john]

Patrick. I was thinking about a machine shop too, seems like any decent shop would make short work for it, and eliminate any doubt from me that it is resting inside as good as one could possibly make it. Just never heard of anyone trying this.

After re-reading your posts, is it the web or the flange where you are getting gaps?

The worst gap is about a seven inch stretch which I believe was caused by the flange being sanded slightly too much in that area. There are a few other areas, in which I might be able to sand a bit more to get it to fit more snugly, but the last few times sanding, doesn't seem to have made any difference.

I think these pieces I filed and sanded are okay, but think I would like to have a machine shop have a go with a couple of pieces, and then compare the two sets and see if theirs is more to my liking. I haven?t drilled holes yet, so it lays down flat, and I?ll be sure and debur when I get that far, if that day ever comes. At the rate I?m going, Christmas will be here before I get to that.

As far as the radius on the ends of each flange, those are right on the money. I used a dial caliper to get the dimensions within a couple of thousands of an inch of the ?? it states.

Thanks for the feedback, Patrick, I appreciate you trying to help, and I think I'm going to look into a machine shop getting this done for me.

If anyone has a machine shop to recommend that has already done this, I appreciate letting me know.

 

[wrongway john]

Hey Dave,

I didn?t see your post as I was writing to Patrick. That is good news. I?m a bit of a worry rat, and will see if I?ll have a machine shop have a go at it, but especially after hearing what your friends had to say, I think the parts are going to be okay.

Maybe it isn't too overly critical, since Van?s only devotes two sentences to the manual on this radius telling us to file it, then sand with 400 grit sandpaper. But they don't give us any tolerances to go with here, so naturally newbies like myself run around like Don Knots in the Ghost and Mr. Chicken worrying if it is good enough.

Yeah, I'll send you an e-mail right after this. Pics don't come out too good bouncing off the shiny aluminum on this piece, but I've got quite a few.

Thanks for writing.

 

[flion]

I think we're still having a communication issue. Your flanges should not be sanded at all. They're part of your HS-403s; the web is the part that you're laying the HS-409s onto (and ultimately drilling into) and the flanges are the portions of the HS-403 that are bent and should be about 90 degrees to your work surface. The fit of the HS-409 to the flange of the HS-403 is not critical as long as it is flat to the web of the HS-403. If you over-radius the HS-409, it should still lay flat on the HS-403 web but you may see some gapping along the flange. That's Ok. As Dave mentioned, the flanges may not be perfectly bent along their entire length anyway (I believe the rear spar is supposed to be slightly more than 90 degrees but I don't have the plans in front of me). I strongly suggest you get a tech counselor to stop by before you invest a lot in machining - then go ahead if you feel like it.

 

[wrongway john]

My bad, Patrick, but yeah, I?ve been sanding the 409?s all along, and should have said the radius on the ends of those pieces is what I got to 1/2". I temporarily got sidetracked on the terminology, even though Van's has figure 6.1 explaining those.

Got something back from Scott?s at Van?s and he is in agreement with you guys. He said the only two critical areas here are no sharp corners pushing against the bend of the 403, and don?t remove so much material that one compromises the edge distance of the rivets with minimum ?? from the center of the holes to the edge of the part.

I?m looking forward to actually drilling out the holes, and have quadrupled checked what holes to avoid. Maybe by Thanksgiving, I?ll have that task complete, then move on to riveting.

I think I?m still going to order two more 409?s, because I?m curious how good of a job a machine shop could do.

 

[wrongway john]

Wow, Van?s price on the 409?s are $91.40 each, which doesn?t include the shipping. Well, I was curious what a machine shop could do with those 409 pieces, but not that curious.

 

[wrongway john]

So this is where I’m at, and a bit of advice is always appreciated from you guys before I move on.

I was careful not to drill out holes where the plans and blueprints show the ribs and hinge brackets are going at this time which it states to do.

Construction manual says right after doubling drilling with the final #30 holes through the HS-409 and HS-403 spar channel, to disassemble and debur all holes. Okay, I’ve done that. It then moves on to priming these pieces, and then start riveting. I'm sure this is also the time to take care of these four holes that it wants us to dimple the 403's and countersink the 409’s, and to put the rivets flush on the other side, which I suppose is done like this to allow for some rudder clearance.

Riveting now as the manual wants us to before getting to the hinge brackets I suppose is fine, but by doing this later in the sequence that it recommends won’t allow for complete deburring since the 403’s would be already riveted to the 409’s. Do some opt to get the holes ready for the hinge brackets while all of the other holes have been drilled and clecoed too?

Also, I know in other areas there is a particular order to the riveting sequence to keep things lined up, but with these long rows of rivets on these pieces, nothing is mentioned in the manual, but as long as everything stays clecoed, does the order one rivets matter here?

Thanks in advance for anyone that tackles these questions. I’ll be giving you guys a break for the next couple of weeks, while I get my paint and primer booth ready. And let me know if my newbie questions are getting old, I don't want to be a pain.