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Builder Used Wrong Screw Size - Now What?

Oh, but let's not start *that* discussion again. ;)

Suggestion: It's cool you bought and fly an RV. You didn't build it so you don't know how the aircraft or methods in great enough detail to repair it or to make changes, yet you're doing so. I get it. Everyone has to learn somewhere and your starting point happens to be a completed kit.

So - get some in-person help. You live in MA, there are a lot of builders and owners in the area. Buy them a beer or whatever they like, invite them over and ask for some guidance and tutoring. As long as you're nice to these folks, you'll be amazed how helpful and willing to share skills people will be. Alternatively, if you hire an A&P, have them teach you how to do this fix the right way. One will cost a couple beers, the other will cost a couple hours of shop time. Either is a perfectly good choice.

And Chapter 5 really should be considered required reading, all of it.
To the OP: This is among the best advice you've gotten so far.

Further, and said in the spirit of constructive criticism, I also think if the you had toned down your attacks on the original builder in your initial and subsequent posts, you would have found a lot more builders on this forum ready to go out of their way to give you constructive feedback. This board has always been good about not differentiating builders from non-builders, but bashing another builder, especially when what they did was not particularly egregious, is not a great way for a non-builder to to attract the good will of builders.

Congrats on your new purchase and have fun! The EAB category of aviation is a fun place to be!
 
In addition to Van's builder's manual another good reference to keep on hand is AC 43.13-2B. This document is titled "Acceptable Methods, Techniques, and Practices - Aircraft Alterations." When I got my airworthiness certificate the inspector wanted to see that I had a copy of this in my possession. There are also several other good reference books available that might prove helpful (see the EAA bookstore for example).

Also, there are the EAA Hints for Homebuilders videos. Like this one:

http://eaavideo.org/video.aspx?v=1657896937
 
Flaming

I thought flaming like Seville did here was reason for the moderator to remove from list.

Great advice was given I thought.
 
The VAF brotherhood?

Come on now, surely somebody needs an excuse to go flying. Isn't there anybody nearby that would be willing to spend an hour helping a non builder gain some knowledge and experience?
 
Oh, but let's not start *that* discussion again. ;)

Suggestion: It's cool you bought and fly a RV. You didn't build it so you don't know the aircraft or construction methods in great enough detail to repair it or to make changes, yet you're doing so. I get it. Everyone has to learn somewhere and your starting point happens to be a completed kit.

So - get some in-person help. You live in MA, there are a lot of builders and owners in the area. Buy them a beer or whatever they like, invite them over and ask for some guidance and tutoring. As long as you're nice to these folks, you'll be amazed how helpful and willing to share skills people will be. Alternatively, if you hire an A&P, have them teach you how to do this fix the right way. One will cost a couple beers, the other will cost a couple hours of shop time. Either is a perfectly good choice.

And Chapter 5 really should be considered required reading, all of it.

Hi Greg,

Actually I have a very good A&P who can sometimes help. He did my annual last year. He doesn't mind my endless questions and desire to learn the ins and outs.

In fact he's so outstanding he's in very high demand. So it's hard to get time with him. Though he does answer any email question I send.

Another option is to get myself to EAA meetings.

But this forum is an absolute goldmine of information. Some really great; some good; some not so good but that's true everywhere.
 
Come on now, surely somebody needs an excuse to go flying. Isn't there anybody nearby that would be willing to spend an hour helping a non builder gain some knowledge and experience?

See my post just underneath yours.

Thanks!
 
I have admit it was a fun read. Lets make a sticky out of it!:D

Hi Blain,

I know you are trying to inject some levity in a thread that needs it. Nice to see that.

Your post made me consider what I had learned or been reminded of in this thread:



Things I learned:
================

1) Been web searching for a source for shear and tensile strenght of
fasteners for quite some time - BillL pointed me to MIL-HDBK-5J.

2) David Paule showed me there are other battery options I didn't
know about

3) Pop rivets will work to fasten the plate nuts in this application

4) Helpful hints on drilling out rivets.


I was reminded about:
===================

1) Section 5


All very valuable stuff.


Things I learned via experimentation after starting this thread:
=================================================

1) That K1000-8's and K1000-3's have the same "footprint" regarding rivet placement so they are interchangeable. I verified that by experimentation in the shop this evening:

A good practice sequence for beginners:

I installed a k1000-8 in a piece of 0.063" scrap

- -among other things this entails more experience with the microstop countersink

Then I drilled out the rivets I just installed.

Then I reamed out the screw hole to allow the 10-32 screw,

Then I installed the K1000-3 in the same location.

Then I turned a 10-32 into the plate nut. As someone else mentioned, the lineup of the plate nut isn't always perfect with the screw hole.

Then I did it again and again in other spots on the scrap.

The last 2 times, I drilled out the rivets kneeling on the floor, bent over double, reaching out in front of me, like I have to be when working in the plane. Just to see how much harder it was. It's easier to be off center with the drill bit.

Another thing learned:
==================

i need something in addition to the spring loaded punch to really set some deep punch marks in the rivet before I start drilling.

Thanks to all for the positive contributions.
 
Another thing learned:
==================

i need something in addition to the spring loaded punch to really set some deep punch marks in the rivet before I start drilling.

Thanks to all for the positive contributions.

If you can back up the rivet with a bucking bar when you use the center punch, you'll get a little deeper punch mark.

Skylor
 
The spring-loaded punch helps a little, but another trick is to put the bit in the drill, line the bit up on the center mark, apply some down pressure and turn the bit by hand a few turns before pressing the trigger on the drill. This sometimes helps prevent the drill bit from ?walking? off center.

There?s also something called a floating anchor nut (another name for plate nut) that can help align the threads with the nut. Perhaps someone in the group can verify that the rivet hole ?footprint? is the same as a regular plate nut, so they can be used in a retrofit situation like you?re working with.

http://www.aircraftspruce.com/catalog/hapages/anchornuts4.php?clickkey=3015615
 
Saville,

You're about 90% there on doing the job yourself, without any external assistance. But know that a center punch can actually move the dimple off center, if you don't hold it perfectly aligned. Truth is, you're overthinking it a bit. If you use a cordless drill instead of an air drill, you can start very slowly and gradually add pressure/speed. You can also help the factory head to come off by walking the drill in a circle, so the bit describes a cone. This can avoid enlarging the rivet hole, because the bit never enters the hole. If the head pops off, you can pull the shop head and shaft with a pair of diagonal cutting pliers.

But.

Have you established that you really need more cranking capacity and/or more reserve battery energy? The PC680 size batteries seem to work fine in thousands of flying a/c. Second, I haven't seen any post addressing CG changes due to the heavier battery. As I mentioned earlier, that could be a much bigger deal than #8 screws.....

Charlie
 
The last 2 times, I drilled out the rivets kneeling on the floor, bent over double, reaching out in front of me, like I have to be when working in the plane. Just to see how much harder it was. It's easier to be off center with the drill bit.

One other tip, it will be easier to do this job if you can prop up the tail to level the fuselage. I made a tail-stand out of scrap wood that serves nicely.
 
If I was closer I would offer to come assist you with that battery tray project.

Hi Charlie,

Very kind of you. I'm getting there....getting to the point where I have done the practice to do the job right as well as the understanding of what must be done.
 
I should have mentioned that the best place to find the strength of a fastener is by looking up its specification. For example, you can do a search for AN509 spec and get a link to the www.Everyspec.com site which is generally helpful.

Sometimes for one reason or another, the MIL-HDBK-5 number, which is more generic, might not match the actual specification. The spec is what counts.

The specification will also tell you about the material, the surface finish and the threads. It'll give you all the dimensions, too, and the tolerances.

Dave
 
Saville,

You're about 90% there on doing the job yourself, without any external assistance. But know that a center punch can actually move the dimple off center, if you don't hold it perfectly aligned. Truth is, you're overthinking it a bit. If you use a cordless drill instead of an air drill, you can start very slowly and gradually add pressure/speed. You can also help the factory head to come off by walking the drill in a circle, so the bit describes a cone. This can avoid enlarging the rivet hole, because the bit never enters the hole. If the head pops off, you can pull the shop head and shaft with a pair of diagonal cutting pliers.

But.

Have you established that you really need more cranking capacity and/or more reserve battery energy? The PC680 size batteries seem to work fine in thousands of flying a/c. Second, I haven't seen any post addressing CG changes due to the heavier battery. As I mentioned earlier, that could be a much bigger deal than #8 screws.....

Charlie

Hi Charlie,

I replied to your W&B post earlier in the thread:

Last November I installed a Reiff Pre-Heating system in the nose. Once I get the new battery installed, a thorough W&B will be done.

Yeah I may be overthinking it a bit. But that's just the way I am when I approach new things that I really do not want to screw up.

Thanks!
 
My apologies; I missed that post. Just went back & read it. FWIW, odds are good that a 680 would crank the plane better than the Gill, & I bet it would let you keep the original mounting tray. Still need to w&b, but going forward a bit probably wouldn't have an adverse effect. And it would more than zero out your total weight gain.
 
Thank you Bill for the #8 fastener strengths.

The PC925 battery is said to weigh 28 pounds; let's add two pounds for the tray and hold down to keep things in round numbers. Assuming all the fasteners are equally loaded and fail at the same time is quite a stretch, but let's go with it for the sake of argument. The cumulative tensile strength of those six #8 screws is 9000 pounds, which equates to 300 negative g's. This is 100 times greater than the negative g limit of the RV-8. Working the shear strength numbers in the same manner, the fasteners would fail in a 580 g deceleration. A human has survived a 46.2 g deceleration while properly harnessed. We don't have that kind of harness in our RV's. It's probably safe to assume that the RV-8 and the occupant(s) would fail long before those six #8 fasteners failed.

Looking at it another way, two #8 fasteners have enough tensile strength to lift an RV-8 at gross weight with a generous safety factor.

A consult with Van's would certainly be prudent, but casual analysis shows that the battery tray attachment is significantly over engineered.

Cheers, David
RV-6A A&P

Agree totally with the above (as an Aero Engineer myself). Vans won't analyze it because they won't take the time, but the issue is not their structure, it is the fasteners. In fact, the structure is stronger as it is, because the fastener holes are smaller, so the cross section of the angles is larger where the holes are. I think the critical case here is crashworthiness. A sudden deceleration consistent with a crash will put the largest shear load on the fasteners and if the battery comes flying forward it is a hazard to the occupants. This will be way in excess of any flight loads. Provided you are using good quality AN fasteners with high shear strength, your internal organs will be jello long before this battery comes loose. I would leave it as is and sleep very well.

I used to curse the builder of my project (I bought it half built) when I found something that I didn't like. Then I put 2 yrs into the project (and have much to go) and when I look at all the little things that I have done which aren't perfect I find myself much less willing to be judgmental. Your builder might well have looked at the numbers and decided that AN-3s were total overkill, which I would agree with. Numbers don't lie. None of these airplanes are perfect and they don't have to be. they just have to be safe.
 
Regarding the new W&B. I'm surprised I haven't seen a recommendation to run a revised W&B exercise before installing the battery. I don't know how wide the envelope for an RV-8 is, but 3 or more pounds that far aft is a pretty big moment.

Just say'n ...

George
 
Ok so lots of useful ground has been covered in this thread which brings me to the last decision topic.

The following picture shows the new battery tray i position:



6 screws attach the tray to the airframe...in this picture, 2 columns of 3.

3 of the Van's pre-drilled holes in the tray match the plate nuts installed in the airframe - the two middle holes and the lower right. I've got screws in those positions in the picture.

The builder did not use the Van's pre-drilled holes towards the top of the picture to site the plate nuts up there. The holes are about 3/8" and 1/2" down from the pre-drilled holes as you see them. I spoke with Van's about that and there is no problem having the screws in those positions. So for the top two screws I can use the plate nuts as positioned. I'll use the old tray as a template, and drill new holes in the tray to match the locations of the top two plate nuts..

The partly blocked hole in the upper left is not a plate nut but just a hole drilled by the builder that presently serves no purpose.

The problematic hole is the one on the lower left. The plate nut hole is about half-a-hole off from the Van's pre-drilled hole. Drilling the hole in that location to match the plate nut location in the airframe will result in a "snowman".

So I outlined my plan to Vans:

I'm going to make a "doubler" that will fit either under the tray between the tray and the airframe, or a doubler that fits right in where the battery sits - the battery will be sitting on top of the doubler.

In either case, Van's suggested 3 rows of flush rivets to fasten the tray to the doubler. One in between the two columns of screw holes and one out outside each of the columns of screw holes. Same rivet size as used to fasten the side brackets to the tray - 9 rivets per row.


Method 1:
=======

Here is a picture of a test doubler I made out of thin stuff just to get a feel for how it would work. You are looking at the underside of the tray, so this is the one that would fit between the tray and the airframe:



Those tabs sticking out to the sides will allow me to include the battery hold down bolts as part of the system that connects the tray to the doubler.

Pros:

The battery hold downs contribute to fastening the doubler to the tray.

Cons:

1) While the doubler helps to provide bearing surface for the countersink on the problematic hole, it doesn't really provide the ideal countersink as described in Section 5. i.e. the countersink is not entirely in the upper plate.



Method 2
=======

The other doubler method is to fit a rectangular piece inside the tray which the battery will sit on. This piece can be thick enough to handle the entire countersink of the fastening screws. However the tray section will still partly miss the grip of the screw.

A piece of aluminum under the battery will raise the battery somewhat, however, the side brackets I riveted on the tray are tall enough such that more bearing surface will exist against the battery than with the Van's supplied brackets.

Here is a picture of the new tray with the taller side brackets I installed, and the Van's supplied bracket next to it:



So even with the doubler raising the battery a little there is still sufficient height to the bracket to hang on to the battery.

Pros:

Countersinks are correct for all screw holes.


Cons:

I give up having the side tabs of the doubler ue the hold down bolts. Although, I could dismantle the side brackets, have the doubler extend to the ends of the tray, rivet the brackets back on only now the rivets go through the side bracket, the doubler, and then the tray. This would be even stronger.
 
Ok so the new battery tray is in.

Firstly, I got in there and drilled out the rivets for the plate nuts for the undersized, #8 screws. Then I installed plate nuts for the #10's. I used the squeezer on that and it JUST fit.

Next as the Builder did not use the pre-drilled hole locations for installing the old battery tray, I had to figure out a way to locate the positions to drill the holes in the doubler. To do this I enlarged the holes in the old tray. Then cut out some rectangles of metal and drilled pilot holes for #10 screws.

I then screwed the rectangles down onto the old tray using #10's into the new plate nuts. Then I traced around the rectangles; duct taped them; and then clamped them down so the rectangles would not move during transport to the shop:



Then I laid the doubler under the old tray and marked the centers of the hole locations with the drill bit. I then removed the doubler and drilled out the holes.

Took the doubler back to the plane for a test fit:



It worked!

I selected 0.125" material for the doubler so that the countersinks for the screws would not open the holes for the screw grip. As an aside, I also calculated the amount the hole would be widened if I could use the pre-drilled hole sin the 0.063 tray. If I needed to enlarge the holes I could go up to the calculated hole diameter. But I didn't need to.

Next, I drilled and countersunk 27 holes to flush rivet the doubler to the tray. I bought a micro-stop and practiced on some scrap 0.063" (the thickness of the tray), until I got the countersinks just right.

Unfortunately my squeezer didn't have enough throat height to get over the flanges to the side so I had to buck the rivets with an air gun.

Prior to riveting, I enlarged the 6 holes in the tray to expose the heads of the #10's which fastened the doubler to the airplane. This allowed me to remove the tray if necessary. Here is the final installation:



So the tray is riveted to the doubler and the doubler is screwed to the airplane with the #10's that the plans call for. I feel much better about the battery tray installation.
 
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I'm not trying to rain on your parade, I promise...but that is an ENORMOUS number of rivets on that thing. What spacing did you use and why?

I count at least 10 on each of the bottom rows, and about the same number on the upper side pieces. Perhaps a bit of overkill?

If some is good, more is not *always* better :)

And, not sure (someone else can chime in) but your countersinks for the #10 screws look too deep to me...
 
well you are certainly learning some sheet metal skills. ;)

countersinks might be ok since that was a .125 plate I think. chapter 5 has a pic.

Is that the starter contactor back there?
 
I'm not trying to rain on your parade, I promise...but that is an ENORMOUS number of rivets on that thing. What spacing did you use and why?

I count at least 10 on each of the bottom rows, and about the same number on the upper side pieces. Perhaps a bit of overkill?

If some is good, more is not *always* better :)

And, not sure (someone else can chime in) but your countersinks for the #10 screws look too deep to me...

I used precisely the number of rivets Van's told me to use: 3 rows of 9. I discussed this arrangement (using the doubler etc) with Van's thoroughly.

However those non-flush rivets on the ends only attached the angle brackets to the tray - they don't go all the way through. If you go to page 6 of the replies here, you will see a picture I posted showing the roughed out doubler as it lies on the underside of the tray. You will see that the doubler does not reach to the ends of the tray but is cut back to accommodate the shop heads. There are tabs on the doubler - with rounded interior angles - that extend to the end of the tray through which the battery hold down bolts go. So there are only 3 rows of 9 rivets which attach the doubler to the tray.

Yes I knew someone would suggest the countersinks were too deep. But you are only seeing the glint from the flashlight shining out of the tiny rim around the edge of the countersink due to the fact that the circumference of the screw is machined and not of zero thickness. I can assure you the heads of the #10's are perfectly flush with the doubler (not the tray itself).
 
well you are certainly learning some sheet metal skills. ;)

countersinks might be ok since that was a .125 plate I think. chapter 5 has a pic.

Is that the starter contactor back there?

I learned a LOT of skills on this project:

How to drill out rivets
What size drill bits to have for what size rivets.
The difference between 470 and 426 rivets and the rivet sets for the squeezer to accommodate both.
How to use a micro-stop to countersink for rivets and screws.
How to set round head and flush rivets with a squeezer.
How to buck rivets with a pneumatic gun (though an A&P did most of that)
How to order sheet aluminum from Van's ;)

Bought tools I'm not sure I'll need again also.

Even if the countersinks were too deep, it would be ok because #10's countersunk in to the original 0.063" tray DO open the holes. I discussed this with Van's after I did the calculation and they said they are ok with that.

But that's precisely why I chose 0.125" - if the countersinks are a little too deep (and they are not) the holes would not be widened. And if they were SO over-sunk as to widen the holes it STILL would be ok since that happens with the original 0.063" tray. Though if they were that much over-drilled I'd make a new doubler. But I practiced with the micro-stop (you should see the myriad of scraps with numerous holes in them laying around the shop) and got the settings just right: they are not too deep.

Yes I'm afraid that the builder put the starter solenoid back there. I discovered that to my chagrin at the same time I studied the plans and determined that the builder did not use the correct size screws to fasten the tray to the airplane. The plans CLEARLY say to only put the Master solenoid back there. If the builder HAD used the correct size screws (and therefore plate nuts) and had used the pre-drilled holes in the tray to locate those screws, a tray change-out would have taken less than an hour. Instead it took me months.

Now that the tray is completed and installed I'll be moving that solenoid forward.
 
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Not sure if I would move the starter contactor yet. If the wires
to the starter are awg2 then your main downside is probably the supply
run from the back to your main bus. Would add a bit of weight and some resistance.

I assume the alternator B lead runs to the main bus up front.

Did the builder provide a wire book with schematics?

I suggest starting a new thread in the electrical forum for
this discussion.
 
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I learned a LOT of skills on this project:

50 projects down the road you may do it differently, but good work for a first project, not bad at all!! It is complicated and you did a lot of research - good work process and surely a huge confidence builder.
 
50 projects down the road you may do it differently, but good work for a first project, not bad at all!! It is complicated and you did a lot of research - good work process and surely a huge confidence builder.

Many thanks, Bill. Yes on to the next project.......the Infinity grip...with the attendant stick clearance issues. Do I bend the stick? Cut and weld the stick? Or is the approx 1" extra height all I need? Wire bundle out the top...side...bottom of the stick?

;)
 
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