Busy Preparing for the Fuel Tanks and Tech Counselor Checks out my LE

My Technical Counselor and former long time EAA Chapter 301 President Jim Elliot has been mentoring me through all this LE mod fiasco. I had to wait a couple of weeks for him to become available to come and visit the "almost" finished LE work, and he was finally able to come out last Saturday and take a look. He is a Mooney aircraft owner and has helped several people build different makes and models of experimental airplanes. He definitely knows his way around an airplane, and with evaluating potential affects of modifications such as mine. More on that in a bit.

Since I knew I had to wait for a bit for him to be able to come over, I started preparing (for about the third time now) to get back to work on the fuel tanks. So although I have not posted in while, I have still been very busy thinking, reviewing, and planning for re-engaging on the fuel tanks to get those behind me as soon as possible. his started with a review of many previous posts where I actually started on the left fuel tank because you needed to match it up with the LE to check alignment and drill some holes in the T-712 mounting brackets for the wing spar and the rear tank baffle. This little journey took me clear back to posts from the Fall of 2017. About the last thing I remember about the tanks was fabricating the tank stiffeners for the bottom of the fuel tank skin, and countersinking skin-to-rear baffle holes per the plans.

After reviewing the stuff from the past, I ended up coming up with a list of new additional questions that required answers from Vans. As a side note, to date I have order at least 2 proseal tubes, a small sized can of proseal, and a full sized quart of proseal - ALL of which have shelf lives that have long since expired, so they will not be used to seal any part of my fuel tanks, and I will need to put in an order for more proseal yet again. Sucks to be me I guess - that's about the only way I can sum that up.

Many of these additional questions are questions that you do not see either asked or answered by others, but I find it quite strange that others are not asking the same questions. Anyway, to make sure that I don't lose the content, I am posting them here for myself and anyone else following my blog that might also appreciate the info:

385b and c SW fuel senders - for left and right - is it correct that the potentiometer scale/meter on c version for the right tank will be reversed (facing forward instead of to the rear, when installed on the side of the tank, or should the scale for both still appear toward the rear of the tank when installed correctly.

Vans says this backwards orientation is normal - important thing is that they both point down when installed either on the end rib or the rear baffle plate.

Am I supposed to scuff the back side of the sender flange of each sender if I am going to proseal it directly to the tank rib (NOT use the rubber gasket or cork as recommended by many who have been there before.)

Vans says not needed.

The left sender seems to have a dead spot at the end of travel of the arm (empty indication) - either no ohms reading at all or much higher (300 ohms or more - much higher than expected 240 ohms per the plans.) The right sender seems to be indicating correctly per the palns info. Ordered both SW senders from Vans on 4-16-18 order # 74191. SW says has a 2 year limited warranty - how do I proceed with a replacement. Go through Vans or direct with SW?

vans - Contact SW directly to replace it

Left tank will be flop tubed, so sender will be in bay #2 in rear of baffle.
1. Did I do a lot of extra unnecessary work by cutting the big hole in the aft of the end rib, when I found out that the sender needed to be placed in the second bay via the baffle in the first place.

Vans   -still good to have access t that bay due to the trap door and the flop tube/anti hangup bracket attachments.

2. With the sender in the secnod bay of the rear baffle, that means that the only way I can service that sender if necessary is to pull the entire tank, correct?

Vans - correct - you will have to pull the tank to service the sender that is mounted this way

3. For tank baffle mounted sender, do I need to cut another big round hole in the second bay AND use a reinforcement ring (T-407) as well, or just the hole big enough for the sender to fit in?

Vans says nope - no reinforcement ring or big hole needed - just a hope big enough for the sender to be inserted/mounted directly onto the rear baffle plate web. No reinforcement ring needed because the baffle plate is thicker/stiffer than the rib web.

4. Do I need to use another reinforcement stiffener ring for the T-411 cover plate on rib T-703 if no sender is being mounted in that hole, or can I just mount the cover plate, with nut plates mounted on the rib web itself instead of the combo of the rib web and the reinforcement ring?

Vans - would still use the stiffener ring here as the rib is not very thick and alot of strngth is removed by cutting that big hole.

5. Depth of tank for SW sender specs to determine what size to cut the rod - what dimension should I use for that (tank depth so I cut the rod to the correct length?

Vans - just clamp the sender in place and measure to determine based on the area where the float will be traveling.

6. Since the left tank sender will go in the rear tank baffle, do the dimensions of the float wire change from original plans for mounting in the rib on the side? Any issues with clearance of the bottom stiffeners when mounting the sending in the rear tank baffle?

Vans - measure to be sure, but should not be a change or a problem as far as they are aware.

7. Do you know a part number for a more malleable proseal for access plates that is not as hard as normal proseal to remove??

Vans - they do not use it and did not know the part number of hand - said to check Spruce and others.

8. Grounding the sender - how is this grounded to the airframe if you have the tank baffle or rib web, proseal, and the flange of the sender on the thin later of proseal. Are we supposed to run an additional ground wire from one of the sender mounting screw holes to one of the tank attach bolts or something similar?

Vans - Use a lock nut with the cut flanges that bites into the metal on the underside of the screw head and on the sender flange as it gets mashed down during screw tightening to establish contact for a good ground - so additional wire should be needed, even if screws are prosealed. Do it on all screws or just one or something in between?

As far as the tech counselor visit is concerned, Jim took a look at my unfortunate demise on the LE. Said that it is a dent and not a crease, but that it did deform the outer skin and the subskin. Then we had a conversation about acquiring an autobody or planishing hammer and a dolly that may have to be customized to try to pound (actually TAPPED) out to try to reform the skin back to the shape that it was in before. Unfortunately I can see where my unbelieveably STUPID idea t just keep pounding on the skin with the rivet gun when the rivet was not setting properly has indeed flattened it out a bit. So as a result, if I want to continue with the LE mod using what I have done thus far, I now get to learn a new skill that involves removing dents and reshaping metal, and I probably have to custom-make yet another tool = more wasted time.

So I went to local NAPA store, found a planishing hammer with a rounded head (NOT the kit you find at Harbor Freight, that only has flat headed hammers), and a Toe dolly that, when I fitted it up against the curvature of one of my LE ribs that I took with me to the store, looks like it will almost perfectly conform to the curvature of the LE skin/subskin/rib as long as it is held in the correct position. This is probably going to require a helper to hold the dolly in position while I tap the outer skin and hope like hell that I don't just deform everything beyond reasonable repair.

The last part of our visit was spent having a heart to heart about the possible structural impacts of what I am trying to do, and if I should go ahead and contact a DER (Designated Engineering Representative) to come and look at my invention and provide some further experienced insight on what I am doing. I wanted to go ahead and finish this mod regardless of the ultimate decision about its feasibility, just to see what it would take. At the end of the day I am not certain that this is a safe thing to do, and may still decide to abandon it all together. But I'm not throwing in the towel on the mod just yet.

I've got some parts to order from a number o different vendors so I am also putting that list together. I'll have some pics on the next post that show the damage from the F'd up riveting job  more clearly, and the tools I am going to attempt to use to fix it.

Dimpled the Cover Plate for the Fuel Tank rib

Well I suppose that's a long enough break since my last post. Time for some updates. In my previous post I was trying to decide what side of the tank rib to place the cover plate over the hole in the web about half way up the width of the web. After mulling that over a bit, I decided to put it on the outboard side of the rib web instead of the rib web. My reasoning for this was that MOST of the time the wings should be level, and there is a slight dihedral angle in the wing where the tip will be just a bit higher than the root.

This, combined with a slightly positive angle of incidence of the wing while it is in sustained level flight, lead me to believe that pressure from the fuel inside the tank will be greater on the outboard sides of each rib most of the time, while the small holes at the bottom rear of each rib will allow fuel to slowly escape to the next inboard bay. Since the fuel pressure should be greater on the outboard sides of each rib due to the reasons I mentioned previously, I decided to put the cover plate on the outboard side of the hole in the rib web, so that any pressure from the fuel against that rib and the patch plate would tend to push the patch plate tighter against the rib web, keeping the fuel from entering that hole, and forcing it to go through the trap door instead, as intended.

Having finally decided where to put the plate, the next step was to dimple the holes for the rivets. This turned out to be yet another exercise in "imaginative problem solving." If you haven't guessed by now, I am documenting this entire tank rib trap door fabrication process because almost nobody documents this to the level of detail that satisfies me, and as it turns out, the steps required to complete this little side assembly are a little more involved than you might think.

First problem - decide which side to put the dimples for the 4 AN426AD3-3.5 rivets. I decided to use flush rivets for this since that should be sufficient for holing this small plate in place, and flush rivets take up less space inside the tank than an AN 470 rivet. Remember, I am trying to stuff as much fuel as possible in these tanks, so every little bit helps, even if that does seem a bit anal.

I decided to put the manufactured head of the rivet on the outboard side of the rib web. Again, this is because fuel pressure will tend to push the rivet head against the rib head, instead of pushing it away.

So I put the dimple dies in my hand squeezer and set the dimples in the over plate:

Next problem -I would need to use my C-Frame tool and table to set the dimples on the rib web. None of my yokes were long enough to reach the holes in the rib web. Then another problem cropped up. The trap door was getting in the way. In hindsight, all I had to do was remove the hinge, but stupid me likes to do everything the hard way. The rib sits awkwardly on the table because of the trap door.Another problem was that my C-Frame table had been setup with the male dimple die on the bottom and the female die on the top. With this application they would need to be reversed so that the male die is on the top and the female die is on the bottom. Why is this a problem - the female die is longer than the male die, so my table no longer sits "flush" with the dimple dies in this reversed state.

So the combination of the trap door interference and the reversed setup of the dimple dies on my C-Frame table presented some challenges:

Here you can see the female die sitting very proud of the table

And it looked like this sitting on the table as a result of the trap door interference:

So how do I get the rib to set level on the dimple dies so I can pound these dimples properly: I was not concerned about the proud dimple die situation, but I did not want the dimples to be improperly set at an angle, so leveling the rib web was a concern. My solution was to place a couple of the fuel tank access plates on the other side of the rib to level it out just enough for me to set the dimples properly.

And here are the pics with all the dimples set in both parts:

I will have to use the rivet gun and a bucking bar to set these rivets. this will be the first time I have picked up the gun in a very, very long time. I will have to do some practice rivets on some scrap first, to make sure my air pressures are set properly, and I get my timing back. I want to set all of these rivets perfectly so I can move on with other much more important tasks. This little adventure has certainly resulted way too much of a time suck on the build.




I also finally called my tech counselor Jim Elliot ad he came out for another visit to help me finalize plans for the mod to the Leading Edge. I think I now have all the info that need to be brave enough to drill the final rivet and nut plate holes in the skin and the subskin, so that I can take it off the wing spar and make that all important cutout. More on that visit and the next steps for that tomorrow.

KPR

Tech Counselor Visit and more Fuel Tank Rib Fabrication

Had a little lull over the new year holiday - cold temps, getting sick, holiday obligations - blah! Nice to get back to airplane building for a change. Picking up where I left off, per Vans input about the hinge for the trap door assembly I decided to do the same - leave the rear hinge pin bent to 90 degrees and leave a small amount of excess on the other side of the hinge without bending it or peening it, etc. The idea is that the rear hinge pin will hit up against the rear baffle plate without ever coming out of the hinge, as long as there is a sufficient amount of pin left on the other side to keep from coming out or causing the hinge to hang up.

So I straightened the bent part of the hinge pin a bit more to keep that end from binding against the eyelets of the hinge, and then I made a mark on the other end after setting the bent end along the rear flange of the rib, simulating where it would hit the rear baffle plate:

 Then I cut the hinge with the dremel tool cutting wheel and deburred the end on the scotch brite wheel:

The piece of metal sticking up one the left is actually a reinforcement plate that goes on the forward part of the most inboard and outboard ribs. In this case it served quite well as a mock baffle plate so that I could verify the length of the hinge pin was correct.

Next came the cover plate for the open hole also seen in the above pic. Vans says that with the flop tube assembly this hole also needs to be covered with a patch plate so that fuel is only allowed through the trap door location. of course this is NOT in the instructions or the plans, so it begs the question, if someone was building the kit with very little or no outside help, they would never cover up this hole. How would they know f they needed to. Vans once again fails to impress me with its lack of updates to the plans of its older models that are still being built and flown. The hole is about 1.5 inches wide, so I reasoned that a 2 inch square patch plate over this hole with 4 AN426AD3 flush rivets in each corner should doe the job. this allows me to maintain 1.4 inch edge distance at each corner of the patch plate:

I cut the plate from scrap .025 inch thick aluminum sheet and deburred it on the scotchbrite wheel. then marked the location for the plate over the hole in the rib, as well as the location for the 4 rivet holes as shown above.

After drilling the 4 rivet holes in the plate, I had to match drill the holes in the rib. So I used the clamps to secure the plate on the rib and got that all done. then I deburred all the holes:

Now I get to decide which side of the rib to mount the plate. the general idea for this is that you want to put the plate on the side of the rib that might encounter the most force due to the amount of fuel in the bay at any given time. I need to decide this because I am using flush rivets to mount this thing. It is not structural so there is no need for AN470 rivets for this, and I am also trying to minimize the amount of space taken up by things other than fuel inside the tank. A rivet seems like a minute detail, but it all adds up in the end - excess sealant, excess hardware, excess rivets, and so on...... It all means less fuel in the the tank.

Since I am using AN426 rivets I will need to dimple the skins, and I have to decide which side of the rib I want  to do this.

This past weekend I had my technical counselor Jim Elliot come out again to review my plans for the cutout of the leading edge skin. He was satisfied with my planned approach. So now I am almost ready to remove the LE and make the big cut. In the coming weeks you will finally start to see what I have been planning to do all along. To think of all the research, design work, and safety evaluations I have gone through to make this seemingly rather small mod makes my head hurt. So I'll leave it at that for now.

My big problem now is that I have the fuel tank in prep mode in my only LE cradle, so in order to take off my LE I have to figure out what to do with the fuel tank. I think I may be making another cradle this weekend to give me some flexibility with handling these big parts. Not really a big problem, just yet another one that I have to deal with on this never ending journey...

KPR

Good News/Bad News

So I was able to transport my almost-complete HS up to Erie Airport past Saturday, where one of the EAA chapters I belong to, Chapter 43, was having a hangar picnic. Lots of great food and great company. There were not one, but two completed RV 10s in the hangars, and so I spent a fair amount of time gawking at them, and drueling with envy at how big and roomy this home built airplane is. I met with a tech counselor, Bill Truax, who looked over the damage to my wing skin and basically told me that it could be filled, won't ever crack, and basically told me not to worry about it, and to KPR (keep pounding rivets). That was the good news.

Now for the bad news. Later that evening, after getting the HS back home, I should have simply started closing up the rear spar and the ends and called it good. Instead, there was one rivet that attaches the end rib on the right side that did not quite get set as well as I would have liked. So I thought that I would drill out this rivet and and replace it, and then finish everything up after that. the first removal went without incident, but the attempt to reset the rivet resulted in a very badly set rivet, so I made the decision to drill it out as well, and try again. As the following picture shows, my drill slipped and I ended up drilling a new hole right through the end rib and into the spar flange that it was attached to. I then had to get creative with a pair of needle nosed pliers in order to snip away at the remaining rivet head in order to get it loose enough to remove. It did not matter, though, since the damage was already done.

A phone call to Vans yesterday, followed by a comfirming phone call to EAA HQ tech counselors today, resulted in a recommendation to:

a. Completely cut away the portion of the forward spar flange that connects to the end rib (not shown in this pic but I will add other pics as I affect this repair.)

b. fabricate a new flange part for the end of the forward spar that will need to be riveted onto the end of the web of the forward spar

c. Order a new end rib (done today), locate and final drill all the holes, debur it, dimple the holes, flute the edges, and prime it. Then finally try to rivet it in place once again.

Obviously this will set me back a bit from finishing the HS, having learned yet another very important set of lessons in the process. I'm sure this will not be the last time I have to figure out how to affect a repair like this, but, needless to say, I am very disappointed in myself right now, and in hindsight I should have left well enough alone. That said, you just have to press on when things like this happen, and realize that problems like these can still be resolved, albeit with a bit of extra effort.

The fabrication will take me some time to complete, because there are some precise measurements that have to be made for the correct size of the repalcement piece, and an 84 degree bend that needs to be made to properly line of with the web of the end rib. Lots of cutting, clamping, and drilling to do. Looks like the dimensions needed to fabricate the part are to use .032 inch thick alclad aluminum, and both sides of the piece will need to be about 1.5 inches long x 1.5 inches wide. The real dimension turns out to be about 1.65 inches x 1.39 inches in order to achieve flanges that are 3/4 of an inch wide on both sides. Bending metal is yet another specialized skill that one has to become familiar with, and it involves quite a bit of math skills and knowledge of metal properties in order to get it right. I won't bother listing out all the detailed formulas involved in figuring out the correct dimensions, except to say that I have spent most of my evening reviewing and calculating all of this. I figure this will set me back at least a week on the HS. Wish me luck I guess.

POST MORTUM NOTE AFTER RESEARCHING THIS WELL AFTER I HAD LEFT IT ALONE!! This may vary for each different model of Vans Aircraft. I have since found out that the RV-8 plans do depict relief holes in the this area, but only in the pictures. The instructions in the plan book make absolutely no mention of putting relief holes on this location, so this is an area where Vans really needs to update their instructions for the RV 8.


So, another great thing about Chapter 301, they have a lot of active RV buildes and fliers. I found one post on the Van's Air Force website where someone mentioned the need to trim this area of the front spar, and I became even more perplexed. I contacted the Chapter 301 president to ask him who I could contact about the bend line problem I posted earlier. He put me in touch with Bill Truax, a really nice person and Technical counselor who has build at least 13 airplanes I think. He took the time to come to my work shop and look at the problem in person. He told me that it probably would not be a problem and to go ahead and make the bend. So that is what I did, and it all worked out fine. On to the next step......