H

HighSchoolBuilders

Well Known Member
Hi All,

Spent the entire afternoon working on the tie down brackets with poor results. I am tempted to scrap them and redo it, but since it is non structural, I am also tempted to keep them. Any advice greatly appreciated!

1) This photo shows the overall results, note the right wing, spar to bracket holes is noticeably not balanced/offset.

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2) One of the spacer's rivet hole is very close to the edge. The only reason I am thinking of keeping it because it's non structural component. I am just hopping mad and wonder how this can happen. While we're on this photo, the countersink is disguising!

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3) Flip side of the spacer

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4) With a square, the bracket is not perpendicular to the spar. Off by 1-2 degrees.

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Those are just spaers right with the holes a bit close to the edge?...If so why on earth would you replace them?

If they carry no load then you'll never see them again and nobody will care...

Build on..Assuming I am correct in what they do..It was a while agao for me.

Frank

7a
 
I think the first temptation to scrap and redo is right. Remember it's a learning process and those parts are cheap. Good opportunity to master measuring, drilling and countersinking using non-structural parts. Clamp everything nicely and enjoy the process...
Just an opinion,
 
Looking at the -7 plans, which has a similar structure, the holes on the spacers are clearly offset (drawing 15). I'd say you're Ok edge distance wise. You can probably clean up those countersinks carefully by hand. The important thing here is that the flush rivets don't protrude; they are only holding nut-plates so the load will be carried by the bolt or screw later. Finally, your slight skew is annoying, I'm sure, but may not be a real problem. If the lower end of the bracket is in the right place, then you will be able to get the ring on and no one will probably notice (except everyone from VAF who will make a point of checking it out ... ;)). On the other hand, if it is the bottom end that is offset then you may have to redo the bracket.
 
Make it right

There's absolutely no structural or functional problem with the parts you made, but the fact you're asking the question gives you the answer you need. You should remake them if only for your own sense of quality. The parts probably won't cost $20, but it'll give you more than $20 worth of satisfaction to have them meet your standards.

Regarding the countersinks...I recommend using only single flute countersinks. I've had chatter problems with the three flute variety.

Good luck.:D
 
I've never had chatter while countersinking with a 3-flute piloted bit as long as there was adequate thickness for the pilot. If the material to be countersunk is a bit on the thin side, such as the spar flange, drill a piece of thicker stock (maybe a piece of 0.125 angle scrap) to the pilot size, cleco it through the hole for alignment, secure it with a side-grip clamp(s), remove the cleco, and countersink away. It can get a bit tedious, but the results are worth it.

I also use a ball-bearing countersink cage rather than one with only bushings, which can wear out quickly and allow the bit to chatter.
 
The spaces are big enough that the pilot hole in the countersink pilot should grab... Chatter shouldn't be a problem. Are you using a countersink cage?

Are those lightening per spec? They look small.

The holes in the spacers are not structural but I would think the parts are because they transfer some of the load off the spar web, or at the very least decrease the amount of pressure at the bolts. How does it all fit on the spar?

I've screwed up and I've been tempted to build on but these parts always end up in the scrap pile. I found that you want a scrap pile, I often dig in there to test something or even build something from that raw material.
 
Keep them

I made a personal build rule to never replace a part unless it was necessary. I developed acceptance limits and standard repairs just like the aircraft companies do to correct discrepancies and I made all the necessary production floor engineering decisions. It does not compromise your desire and motivation for perfection and it does allow you to make progress instead of getting stuck in a self defeating build loop for no good reason. Resources are valuable, don't waste them.

Bob Axsom
 
The first thing to do might be to make sure that you understand YOUR goal for the project - is it to turn out a perfect airplane, or to turn out a safe, flying airplane in a reasonable time? Either goal is valid, and I am not being judgmental - just stating the obvious.

If what you want is to be able to say that the airplane is perfect, then replace it - and expect a huge pile of scrapped parts when you finish. If you want a safe airplane, then build on.

I am like Bob Axsom in this regard - I enjoy building within a reasonable set of boundaries. I do a fair number of tech Counselor visits, and the truth is, I rarely (if ever) see perfection, and don't expect to - I know where the boundaries are for good standards, and help folks stay inside them.

Paul
 
Many thanks for all the feedbacks, I sincerely appreciated it! I countersunk those holes with a hand debur tool, never again! Lesson learned.

As with the lightening holes, I used a step drill bit. It's slightly smaller than spec but I think it serves the purpose.

From all the feedbacks, seems like I won't go wrong either way. Since it's a removable assembly where I can easily remove and redo, I will probably save the piece. If the tie down ring installs without noticeable differences, I think I will probably keep the piece. Still need to tap them, see how that goes :)

Thanks again!
Hank
 
Countersinking

Hank,
I know how you feel. I tend to want things perfect, it's the German in me! That said, the 2D [twice diameter] rule is really for sheet aluminum. Those spacers are made of plate aluminum. Those holes only retain the nut plates. As others have said, structurally, this isn't really an issue.
I've tried countersinking with both 3 and 1 flute countersinks. I found you can have problems with BOTH types of countersinks. The 3 flute style will chatter when used with a high speed air drill. The 1 flute style tend to "chip bind". The chips would curl over and sometimes create a round scratch into the piece being countersunk.
I found that it really slowed me down to have to stop and constantly clear the chips out of my 1 flute countersinks. I found that if you use the 3 flute units with an electric drill, they do not chatter. Using a cordless electric drill with the 3 flute style countersinks gave me the fastest and best results. [No cord or air line to contend with]
Just one more data point.
Charlie Kuss
 
I think the tricky part as a new (or experienced) builder is developing a good sense for those safety-based standards of acceptance. I have spent many hours agonizing (and then just sending an e-mail to Van's) over whether a mistake was acceptable for safety. Every time, they've looked at it and had me build on.

As Iron mentioned, the best way to develop that sense is to have lots of tech inspector visits!
 
I concur with Charlie. Using my portable electric drill with the countersink works best. The air drill always gives me some chatter. I have three cages one for the two most-used sized and a third for oddball bits. It is a big time saver when you don't have to reset your cage each time you swap sizes. I bought new BB cages at the local surplus store for $15 (same ones sold through snap-on).
 
I got a PM saying the same thing about the cordless drill, I think I will give it a shot, many thanks!

I am the only guy building a homebuilt in Hong Kong, no tech consoler here or anywhere near. I do have a -8 builder from Australia that come visit me once in a while. I will be asking and posting lots of questions and photo here, thanks for all the support!
 
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