Friday, June 30, 2017

Fuel Tanks- Breath didnt Hold

Last report, I was holding my breath the fuel tanks would not leak.

Like all good learning experiences, my tanks leaked; both of them, mainly from the rear seam.

The one tank leaked from the seam near the fuel sender and access hole. This was easy enough to fix by removing the access panel and adding more goop. 

The tank in the picture leaked from the top seam near the middle, in 2 places. Ugh.

There were many options I found on-line to fix this:
1) use Loctite adhesive designed for just such a repair.
2) ignore it and hope it goes away.
3) cut a hole in the baffle, add more sealant and then use a new access plate to cover over hole.
4) use the really thin Proseal that is brushable, pour it in the tank and slosh it along the seam.
5) make a funky applicator with a syringe and tubing; using a USB camera, and add some more Proseal to the seam thru the filler neck or the sender access panel.

Of course, being the expert builder that I am, I did none of the above.

I decided to use option 6), which is not listed above. If that didn't work, use option 3.

Option 6) was to drill out the baffle rivets in the offending area, wrap a towel around the vacuum cleaner nozzle and tape it to the fuel filler spout. With the manometer hooked up, turn on the suction and leave the fuel sender screws out to avoid over pressurizing the tank (wouldn't this be under pressurizing?). Add some Proseal to the seam, and gently open the seam up by gently flexing the tank skin. To my surprise, the sealant sucked itself into the gap. I used a heat gun to gently heat the tank skin to help the Proseal flow into the cracks. The whole time the tank was under 27" of vacuum.

After resetting the rivets, I let the tank sit for a day. I started the pressure test tonight, and the leak check using soap bubbles showed no leakage. Normally I would say done, but I plan to let it sit over night just to make sure.

Sunday, June 25, 2017

Fuel tanks: Stop the madness, I am tired of learning

Fuel tanks are done, Yippee Ki Ya!

This last week has been fun learning how to play with ProSeal. The baffles and support brackets went on without much trouble.

For those of you building a RV9, it is important to note that the baffle doesn't naturally want to sit properly. The top and bottom skins are designed to not sit perpendicular to the back of the baffle.  So when the baffle is dropped in, it has to be forced to align with the internal ribs. Once the baffle was set down on the ribs, I pushed the baffle into alignment and pressed in a  -4 rivet thru the baffle into the ribs. This kept the baffle lined up while I inserted the gazillion silver clecos for the top and bottom row of -3 rivets, and clecos for the rest of -4 rivets for the baffle to ribs, without the brackets.

For the -3 clecos. I pushed in a -3 rivet every 10th hole to line up the skin and baffle before clecoing. Once all the clecos were inserted, I gently squeezed between each -3 rivet location with a Vise Grip welding pliers to squeeze out any excess Proseal.

I started riveting the -3's at the middle of the tank. I found I had to take the countersink (with a countersink stop) and touch up each hole before inserting the rivet; otherwise the heads were not always flush to the skin.

For the baffle to rib to bracket rivets, the pop rivets went in smoothly. I made sure I set the -3 and -4 rivets in one seating so the Proseal didn't have a chance to harden.

The sender, pickup and drain went in as per plans.

I am now in the waiting period when I am ignorant and happy, thinking the tanks are done and won't leak. Here is my leak check setup using the manometer method. I am expecting I can blow in the tubes enough to pressurize them to 27" of water. I am holding my breath hoping they won't leak.

Sunday, June 18, 2017

Fuel Tanks-Part 2

Tank assembly begins! 
The bottom stiffeners were installed as per plans. I mixed up 1 gram of Proseal per linear inch and this was just about right, taking into account losses from leaving stuff on the mixing plate, smeared on the ceiling, etc. Did I mention this stuff gets everywhere?

I decided to use the "faying surface sealing method". The next day, I mixed up another batch of Proseal per the instructions, and using the baggy technique, applied it to the ribs. I then cleco'd the ribs to the bottom skin using a cleco in every hole.

In the same session, I mixed a second batch and applied Proseal to the top of the ribs, inserted the tank into the frame and cleco'd the top of the skin to the ribs again using a cleco in every hole. Then I smoothed the excess bleed out with the tip of the plastic knife, and let it set overnight. I added tape to keep the skins from spreading due to the Proseal's viscosity.

The next day, I came back and removed every cleco four at a time, and used the #40 (-3) countersink to clean up the dimples. This removed the excess squeeze out and removed a sliver of aluminum to provide virgin material for the rivet to seal against.

I did not use "tank dies" because I don't believe in them. Tank dies are special dies only that set the rivet a few thousandths deeper. The theory being this allows the rivets to sit flush with a thin layer of Proseal in between the rivets and the skin. I think this is nonsense. Using normal dimple dies, the Proseal squeezed out during riveting and all that remained was what was needed to fill in the voids; I don't see a reason why there needs to be a thicker film of Proseal between the rivet and skin. Just my opinion.

Update-A factory  engineer wrote the following reply: I also have some concerns about the use of tank dimple dies, but in my opinion, by installing the ribs and then waiting to rivet, you just moved the thick build-up of sealant from between the rivet and skin, to between the skin and the rib.
The squeeze force of a cleco is much lower than what is exerted when setting a rivet.
The sealant is very viscous and doesn't easily squeeze out from between the rib and skin.
I am pretty sure that just installing clecos and then letting the sealant cure before riveting leaves a much thicker layer of sealant between the rib and the skin. Far less desirable than the result attained if riveted wet, in my opinion.

Comment: I still prefer the Fay sealing method I used and described above. I am afraid by wet installing the rivets, the skin may pucker between the rivets; there is heavy force on the rivets and no force between the skins when wet riveting, in my opinion.

The riveting went fine. I had to drill out a few clinchers, because the Proseal makes everything slippery. Also, if I didn't press the rivet down in the hole and squeeze out the excess, I would invariably get a rivet sitting proud. I used a hemostat to place the rivet in the hole filled with Proseal, pushing lightly to squeeze out the excess goop. Then I cleaned off the outside with a acetone-damped rag, cleaned the mushroom set, and riveted. I found using lower air pressure and feathering the trigger helped set the rivets without clinching. With 30 grams mixed, I was able to set 3 rows on the bottom,  coat the shop heads, and fillet the three ribs, before the stuff started getting hard. It took me three nights over a week to get each skin on. With this fay sealing method, there was not a rush to set all the rivets in one session; I felt this made for much better results because I wasn't stressed trying to rivet everything before the Proseal set up.

The tanks skins and ribs are all riveted now. Looking back, I don't know why I was so apprehensive, but it was a learning experience. As a side note, I used MEK to clean the faying surfaces, but switched to acetone to remove the excess Proseal to try and preserve my MEK for more important tasks; I can no longer buy MEK locally.

Monday, May 29, 2017

Fuel Tanks

I have been working on the fuel tanks. The Pro-seal is about to expire, so have been a mad man trying to get the tanks together.
Everything went per plans, but did some things that made it easier. Since I am doing both wings at the same time, the tooling and jigs get setup and taken down only once, so things go quick.
I made a template and verified the tank leading edge shape matched the outboard leading edge. The left wing I nailed perfectly, but the right I had to disassembly the ribs and tweak slightly. I also made the end ribs of the tank fit the curve of the skin as near perfect as possible to minimize the gap the Pro-seal has to fill in.

For the tank brackets I made a wood jig to hold the brackets and get the middle hole centered. Of course, all the brackets came from the factory exactly same length, except for two.Oh well.

The brackets are installed on the baffle and the line centered in the baffle holes. Then the remaining holes are drilled using the baffle as the drill guide. I found out that the baffle is not symmetrical; there is a top and bottom. In addition, the baffle flange orientation is mirrored on the right, but not shown explicitly on the plans, leading to additional confusion. You are warned.
After the brackets are drilled to the baffle they are installed on the tank, and the tank is installed on the wing for match drilling to the spar. There were several gotchas:
1) The baffle has a top and bottom, the prepunched holes are not symmetrical top to bottom.
2) The distance from the baffle to the spar is too close for clecos near the root. If I tried to use clecos to hold the tank skin to the baffle, the baffle and wing tank did not sit on the wing properly.
3) others have dimpled the baffle rivet holes; I don't see how this would work on the RV9 since there is not enough clearance; I think the baffle rivet holes need to be countersunk per the plans.

After the brackets are match drilled to the spar, the riv-nuts are installed. I used a bolt and nut to drill the brackets for the rivets as in the pic. (The hole in the wood is for the nut to rest in.)

The rest went as per plans, nothing special. Prior to priming, I edge rolled the seams very slightly using my thumb technique. Not sure if this is needed, but I do not want any of the skins lifting off the spar and I could not find anyone on line who regretted doing this.
Lastly, I primed in prep for final assembly. The plans say only the bracket needs to be primed, but my minimum amount to mix easily is 50 ml.  Not wanting to waste any, I primed the outside of the skins where they will rest on the spar and splice plate, and I primed the outside of the two end ribs, and the backside of the baffle. I am thinking the tanks may sweat when full of fuel, so I figure it wouldn't hurt to prime the outside that is exposed.

With all this work, I think I am ready for final assembly of the tanks. Hope I have enough clecos ;-)

Tuesday, May 2, 2017

Harvesting Clecos for Wings

So have started building the wings. Not much to write about as everything started out well and went as per plans. Of course as I was saying this to myself I did find some "knowledge" was needed, and a few bandages. But I am getting ahead of myself.

Here is the bountiful harvest of clecos.  And a warning. Just go ahead and order a thousand 3/32 clecos; if ordered all at once, there is a break in the price at a thousand, and the shipping is only one time. I am on my fourth cleco order; UPS is making bucks on shipping. Here is my cleco farm, ready for harvest. I am doing both wings at the same time, so this is only one of the two wings, Yes I ran out of clecos; the rest are coming in time for the tanks. Total cleco count will be slightly more than a thousand.
The main skins went on as per plans, no really drama, except I had a few holes in the rear spar where the holes in the rib, spar and skin didn't line up. Next time I need to make sure the rib holes line up with the rear spar during the rib to rear spar riveting. It is kind of tough to do it after the rib to spar rivets are in.

I didn't quite follow the plans when I put the J stringers in. I indeed drilled through my finger, even though the plans say  "be careful don't drill through your finger"

The leading edge ribs are notoriously for being hard to fit into the skin. After reading many blogs of those who came before, I decided to reshape the leading edge ribs.  During my first attempt, when the virgin ribs were inserted into the leading edge skin, the rib flanges were actually warping from straight in order to fit the leading edge radius of the pre bent skin. This is ugly, and causes scratches and bumps on the leading edge of the skin. When compared to the fiberglass tip, I think the pre-bent skins have a  different leading edge shape causing a poor fit.  After reading many blogs of those who came before, I decided to reshape the leading edge ribs. Here is a picture of the virgin rib fitting onto the skin. Notice how the tabs in front of the prepunched hole are holding the skin away.

 Everything fits much better with a small tweak to the flange. I am being careful to make the left and right wings the same, since this portion of the wing contributes to the flying qualities. Here is a picture of the reworked rib installed on the left leading edge. There is still a gap between the rib and the leading edge. I don't think it hurts anything, but I might throw some extra Proseal in there when I do the tanks.
I also had an interference on one of the rib to the spar rivets. This is the rib closest to the tank. Not hard to take care of. I am continuing on and looking forward to the Proseal Challenge.

Thursday, April 6, 2017

head...shoulders..ribs and spars

Much work has been accomplished.
I drilled out the fuel tank ribs for better venting during fueling. I used a Forstner bit so that I could get close to the rib flange. And I enlarged the wire routing holes as per the previous blog post using a home made jig to center punch all the ribs in the same location and a step drill . Easy Peasy.

The main ribs were primed with no drama. Wings stands were bolted to the floor (shhhh don't tell mom). I am building both wings at the same time so it goes pretty quick; once the tooling is set up for the left wing, it is a breeze to finish the task for the right wing. I flipped the wings up right to rivet the main ribs to the spars. This provided good access. My son was home from college on spring break, so we were able to do 1 and 3/4 wings in a few hours. I used a double offset on the gun and this seemed to really suck up the driving power. I had to crank up the pressure to 60 psi and crank up the flow. This was manageable with two of us, but the bar was bucking quite a bit. Could not have done it without a tungsten bar; that compact extra mass really help make up for the double offset power suck up.

I had to drill out two rivets just because; I should have drilled out only one... the second was best before I touched it :-(
To rivet the remaining five ribs, I  got creative and made some simple tooling. I used a sheet of hobby plywood from the aviation isle of Hobby Shack with the thickness chosen to match the no go rivet gauge. This allowed me to hold the bar on the underside and not have to worry about scratching the spar or setting the rivet too thin. I also taped the double offset to the gun so it wouldn't rotate. I used two layers of duct tape on the end to try and help prevent smileys on the rib. In addition, I used one finger around the rib and operated the trigger with my middle finger. This kept me from tilting the gun over inadvertently as I watched the bucking bar dance around. Each rivet seem to take forever to set. I was concerned about work hardening the rivets, but no problem. I also did not assembly all the last ribs at once, but rather as I went. This allowed much better access to the rivets.
I still need to squeeze the rear spar rivets, but expect no drama with that. Onward.

Saturday, March 18, 2017

Wings- Ribs

These are my wing ribs all deburred.

The two yellow spools are the sandpaper I used for deburring the holes and flange edges. I also used just a loose sheet of 220 grit pinched between my fingers for the long straight flanges. The abrasive spools were a 1/16" rope and a 1/4" flat ribbon. This worked really well. I probably used 25% of a 25 foot roll. Many of the rib flanges were fairly well deburred already, so it didn't take much more for me to be satisfied. The lightening holes needed the most effort.

I also built the rib flange forming thing-a-ma-gig sitting on the table. It forms the flanges to the perfect 90 degrees to the rib web. It works very well. However, when I tried it out, I grabbed a nose rib and looked at the flange. It measured almost perfect without me having to touch it. Then I looked at the center rib, seems perfect too. Did I spend half a day and $20 on this thing for nothing? I will finish up checking the flange angles tonight. But I will probably be too embarrassed to tell anyone how useful, or useless, this tool was. It is well worth the effort to construct for the flanges on the tail ribs, wish I had it then. But I hope I never have to  rebuild the tail feathers.

Also in the picture are the mods I plan to make to the ribs. I talked to Van's Aircraft support on Friday and they said what I had planned seemed reasonable. If you wish to follow my example, please check with Van's yourself. So here is my plan: for the nose rib, I will enlarge the internal fuel vent hole from 1/4" to 1/2". (This is not the hole the vent tube goes thru, but the one that will be at the high point when filling the tanks.) The stock hole seems really small to me, and others have complained the tanks are slow to fill. I don't plan on doing aerobatics, nor uncoordinated flight (who does?), so I am not worried if these enlarged holes cause the fuel to slosh around a little more. For the main rib, I plan to follow the supplemental instructions on the Van's Aircraft site and add a hole in the main web to the right of the first lightening hole in the picture. This will be 3/4" per the supplemental instructions. Also the RV9 plans say it is permissible to enlarge the forward tooling hole to 1/2". But the same Van's supplement says the RV7 and 8 can enlarge this to 5/8". I will follow the 9 plans and only enlarge to 1/2 ".

Lastly in the picture, behind the table, are the wings stands for the spars. I plan to build both wings at once. These stands are a God send. Thank you to the builder Billy who provided them.

So that is my plan. Onward and upward, (well not yet anyway) :-(