Q: How to finish securing the the trap door hinge pin?
A: They just bend one side of it (the side toward the rear of the rib, like I have already done). They depend on the joint between the rear baffle and rear rib flange as a hinge stop and don't even bother bending the other half.
Q: How to fabricate the rear-most anti hangup bracket for the flop tube assembly? I asked because the small drawings were not clear how this was supposed to be designed, and they do not provide any instructions for it either.
A: you can twist/bend it so that the face of the bracket is properly oriented on both the stiffener and the rib web. they said that using an "angle" is probably overkill. So attach one end to the stiffener and then twist/bend it forward enough so that the other end of the bracket is properly oriented 90 degrees from the other end.
Q: What thickness material and rivets to use to cover up the t-704 hole in the rear web of the first inboard tank rib. Needs to be done since all main fuel flow into this bay of the tank is supposed to be controlled ONLY by the hole in the lower rear of the rib where the trap door resides.
A: Use whatever scrap you have and put 4 rivets of your choosing to permanently cover with no proseal or anything - just cover that hole so the majority of the fuel entering that bay must come through the bottom hole with the trap door.
There are several other smaller tooling holes in the rib that will also allow fuel to move through them, but they are so small that they shouldn't matter much.
Q: Use the tank dies or no?
A: Says you are supposed to use the tank dies on the ribs, and the regular dies on the skins.
I don't think this is correct per Mike at Cleaveland Tools - I told the guy at Vans about a video that MIke had finally produced where he attempts to cover the proper use of the substructure dies, tank dies, and regular dies. I need to review that video again and make my final decision about which dies to use on which parts.
Q: Proper washer placement for the AN fittings for the flop tube?
A: There is no spacer(washer) placed on the T-405 tank attach bracket because that part already basically serves as a spacer since it is 3/16ths of an inch thick. So I just need to fab the part, cut small recesses in it where the rib flange/skin rivets are located around the very front of the rib, place the nut on the part and mark the rivet hole locations as best as possible to ensure clearance around the nut so that it can be secured with a wrench later on, and the nut is the only thing that rests against the face of the attach bracket.
Then my friend Mike Rettig supplied me with a few more answers to some Proseal questions:
Q: Buy and use the 1/2 inch wide x 1/16th inch deep spouts for the SEmco tubes to apply a coat on each rib web, or just use the circular tube tat comes with each tube?
A: Just use the circular applicator tube that comes with each tube, apply the bead on the rib flange only, and NOT the skin, and use a pop sickle stick or other applicator to spread it evenly across the width of the flange.
Then attach the ribs to the skin per Rick Gialotti's faying method as posted in VAF.
SO to finish up the trap door tomorrow I will shorten up the other end of the hinge pin, smooth it out, and proceed with making the cover plate for the other hole and riveting that in place.
Thursday, December 28, 2017
Tuesday, December 26, 2017
Riveting the Trap Door
Here is a pic of the lower hinge assembly with the trap door riveted in place. I used my manual rivet squeezer for all the rivets due to the slippery nature of the hinge metal and the tight quarters that the squeezer needed to fit into, requiring a bit more control than if using the pneumatic squeezer.
The rivet on the left was the first one that was set, and of course, this being the first rivet I have set in quite a while, it naturally got messed up and I had to drill it out an reset another one. In the process of that the ends of the door next to that rivet bowed a little bit, and so even the replaced rivet is not very well set. Thoroughly aggravated by this, I decided to leave it alone before I caused any more damage to everything.Here is a blurry view of the bottom side. this actually turned out OK.
And here are the flush sets that I used in the hand squeezer with a standard 3 inch Yoke:
I used the larger 1/2 inch wide by 1/8 inch thick flat set against the manufactured head of all rivets, and the smaller 3/8 inch wide by 1/2 inch high flat set for all shop heads. I did it this way to ensure that the set would not accidentally end up hitting the hing rings, deforming them so that the pin would not rotate freely. This worked OK except for that very first rivet.
For the top hinge rivets, I was able to set the first one relatively easily, but the second one required the use of my bench vise, and a spare piece of wood that would fit inside the the flat part of the rib web surrounded by the stiffener ring on the outside. I need both hands to ensure that the rivet sets would be positioned properly and not screw something up - like smashing the stiffener ring, thus ruining the entire rib and forcing me to start over.
While I did not get a pic of it clamped to the vise, here are the pieces that were positioned onto it. The vise was lightly clamped, just enough to secure the rib so that I could position the squeezer and set the rivet.
Here are the shop heads - you can see how close the one is to the edge of the stiffener ring to get an idea of just how tricky it was to position the squeezer to set the rivet.
And here is the other side with everything riveted together:
Now, can you see my next dilemma? I still have to decide how to "secure" the other side of the hinge. This turned into yet another head scratching moment, and caused me to wonder of I should have trimmed and bent the other side of the hinge pin before I riveted everything in place. Unfortunately, I did not do that. Now I have to figure out how to accurately bend this pin with everything now tightly secured to the rib web.
This revelation led to yet another interesting observation. It involves a decision about how tightly or loosely to leave the other side of the previously bent hinge pin, and the same question for the bend to the pin on the other side. too much lay will allow the pin to slide from side to side a certain amount, and over time this would run against the rib web and/or the proseal in a very critical area of the tank that is very prone to fuel leaks as a result of it not getting sealed enough in the corner between the rear rib flange and the other rib flanges. It could even start scratching against the rib web, and I have already seen some evidence of this.
But none of these things was as disturbing to me as what I discovered while checking for freedom of movement of the door. Sometimes the door would not open when the rib was in a position where the gravity should have caused the door to open easily. A closer inspection revealed that this would happen when the 90 degree bend in the hinge pin would get forced very close to the first hinge rung that it encounters. This was effectively locking the door in place, not allowing it to open, similar to this next pic - and this is NOT good.
A closer inspection of the pin revealed why this is happening:
The pin is not bent at a perfect 90 degree angle. There is a slight amount of bend on the pin just prior to where it actually bends 90 degrees, and this bend is slight enough to allow it to be inserted into that first hinge rung if that end of the pin has any force exerted on it.I think I can try to straighten it a bit where it won't be as much of an issue, but the problem is you are just trading one bend for another one - that one being the 90 degree bend in the pin. Now matter how hard you try, there will still be a potential situation where that end of the pin with the bend in it can cause friction when forced up against the rung in the hinge.
So right now I have mixed feelings about this, and they consist of everything from abandoning the entire flop tube assembly to doing the "best I can" with the hinge pin and not worrying about it too much. Whatever I decide to do, I just do not want to ever run out of fuel for any reason unless I intentionally want to drain tank completely for some reason.
I could not get the pic to focus properly, but you can still see the small bend in the straight part of the pin just before it gets to the 90 degree bend. I have some small hobby pliers that I think I can use to remove that small bend on that side of the bend and complete the bend on the other side as well.
What a pain - and look how much this has time sucked the build - all for a little door in a rib - crazy.
For the top hinge rivets, I was able to set the first one relatively easily, but the second one required the use of my bench vise, and a spare piece of wood that would fit inside the the flat part of the rib web surrounded by the stiffener ring on the outside. I need both hands to ensure that the rivet sets would be positioned properly and not screw something up - like smashing the stiffener ring, thus ruining the entire rib and forcing me to start over.
While I did not get a pic of it clamped to the vise, here are the pieces that were positioned onto it. The vise was lightly clamped, just enough to secure the rib so that I could position the squeezer and set the rivet.
This revelation led to yet another interesting observation. It involves a decision about how tightly or loosely to leave the other side of the previously bent hinge pin, and the same question for the bend to the pin on the other side. too much lay will allow the pin to slide from side to side a certain amount, and over time this would run against the rib web and/or the proseal in a very critical area of the tank that is very prone to fuel leaks as a result of it not getting sealed enough in the corner between the rear rib flange and the other rib flanges. It could even start scratching against the rib web, and I have already seen some evidence of this.
But none of these things was as disturbing to me as what I discovered while checking for freedom of movement of the door. Sometimes the door would not open when the rib was in a position where the gravity should have caused the door to open easily. A closer inspection revealed that this would happen when the 90 degree bend in the hinge pin would get forced very close to the first hinge rung that it encounters. This was effectively locking the door in place, not allowing it to open, similar to this next pic - and this is NOT good.
A closer inspection of the pin revealed why this is happening:
The pin is not bent at a perfect 90 degree angle. There is a slight amount of bend on the pin just prior to where it actually bends 90 degrees, and this bend is slight enough to allow it to be inserted into that first hinge rung if that end of the pin has any force exerted on it.I think I can try to straighten it a bit where it won't be as much of an issue, but the problem is you are just trading one bend for another one - that one being the 90 degree bend in the pin. Now matter how hard you try, there will still be a potential situation where that end of the pin with the bend in it can cause friction when forced up against the rung in the hinge.
So right now I have mixed feelings about this, and they consist of everything from abandoning the entire flop tube assembly to doing the "best I can" with the hinge pin and not worrying about it too much. Whatever I decide to do, I just do not want to ever run out of fuel for any reason unless I intentionally want to drain tank completely for some reason.
I could not get the pic to focus properly, but you can still see the small bend in the straight part of the pin just before it gets to the 90 degree bend. I have some small hobby pliers that I think I can use to remove that small bend on that side of the bend and complete the bend on the other side as well.
What a pain - and look how much this has time sucked the build - all for a little door in a rib - crazy.
Thursday, December 21, 2017
Trap Door Fabrication, Continued
Picking up from my previous post, the hinges, door, and spacer are fabricated. Now it is time to position everything on the rib and drill the necessary rivet holes.
Here some pics showing how I drilled the upper hinge rivet holes:
And here are the holes in the lower hinge:
And this is where is starts to get more challenging. The next step is to countersink the right holes in the right part. It goes something like this:
- The lower hinge is only attached to the upper hinge via the hinge pin, and to the actual trap door.
- The trap door holes get dimpled, and the back side of the lower hinge holes get countersunk.
- The upper hinge is attached to the spacer and then finally to the rib web. SO in this case the top side of the upper hinge is countersunk, and the rivet then goes through the holes in the spacer and the rib web.
So you have to make sure that you countersink the right holes on the correct side of each hinge. If you screw that up, you get to start over. Perhaps this is not an issue for other folks, but for me it was a bit unnerving. Hinges are a bit strange for me to work with, because they are made from a different alloy, with a different hardness, and a different thickness than other types of alclad aluminum.Their dimension and general shape also make them a challenge to work with.
One of those challenges is that I find it difficult to try to setup the work so that you can use a microstop countersink tool to drill the holes - mostly because the holes are typically very close to multiple edges of the hinge, an the part is small, so the tool does not sit well. The shape of the hinges also makes it difficult to butt up multiple hinge halves to give the tool more surface area to sit on, as I have done in other situations when working with flat aluminum alclad.
So, I resolved to countersink the less elegant and more error-prone way, by using my deburring bit in my cordless drill, and carefully countersinking each hole and trial fitting it with a rivet to ensure that I don't go too deep. Here I am burrowing out the holes in the back side of the lower hinge that will accept the dimples from the trap door.
And a test fit with a rivet. Not the best job, but its good enough for me:
Its OK if these are a little deeper than flush, because they will need to accept the dimples from the trap door. Next came the fitting and drilling of the holes from the upper hinge half in the spacer and the rib web. I found this to be the most challenging part of this little project. Had to get downright inventive about how to clamp that sucker down and position it exactly where it needed to go to ensure that door ends up in the right position. I found a small clamp or two that seemed to work out well enough - as able to insert it through the fuel feed hole in the rib - you know - the hole this door is trying to keep covered some of of the time:
After using the hinge to match drill holes in the rib web, I then needed to match drill the same holes through the spacer. I drilled the first hole through the rib web to the spacer, and then I needed to re-position the clamp to the corner of the spacer in order to hold it in position well enough to drill the other hole.
once the upper hinge and spacer were drilled to the rib web, next came the lower hinge and the trap door as shown here. decided to mark the hole locations in the door so I could remove the assembly from the rib, since none of these holes are going to go through the rib. I did not want to risk accidentally drilling into the rib web, so I marked the holes on the door with a sharpee so I could realign them again after removing the hinge and the door from the assembly
I put a piece of tape over both parts before removing them from the rib to help keep them aligned with each other.
Next was another trial fit after the holes were all match drilled and countersunk, etc.
And then finally is a shot of the two upper holes and where they ended up in the rib web. You can see from this pic just how close to the edge of the stiffening ring it is. This shot also demonstrates the question one has concerning how Vans seems to think that you can make three rivet holes in this area instead of the two that you see. The stiffening ring/depression makes this virtually impossible.
On that note - just one more thought about this whole situation with the fuel tank and this whole trap door fabrication business. One of things that I have become very aware of as I have continue to work the fuel tanks is the need to ensure that anything that is attached in a certain or is added to the tank assembly MUST NOT fall apart, break off, or become loose and fall off while inside the tank. In one case you might experience odd behavior with the fuel system, and in the worst case you may experience a blockage in your fuel pickup line that will cause fuel starvation at some point in the system. As such, all of the parts involved in this trap door fabrication are a concern for me, as well all the parts that make up the entire flop tube assembly.
Everything from the hinge pin to the rivets to the parts is a concern, and whatever you decide to do, you have to end up feeling confident that the added pieces and parts you are putting in the fuel tank are not going to cause a bad situation in the future. You need to k now that the extra rivets are not going to break or come loose, and the clunk on the end of the flop tube will not loosen from the tube, and so on. During my research I have read many accounts of folks that have ended up with a variety of issues with the fuel tank components from time to time. And at the same time I have also ready about folks that have had trouble-free tanks for years. I guess it all boils down to paying attention to details and being very safety-minded when working on the tanks.
This trap door assembly, fuel sending unit, and the flop tube are the only three moving parts that I am will to accept inside the fuel tank. Those 3 components provide numerous "opportunities" for things to fall apart or cause other problems. Add to this the blatant fear that most folks feel about sealing up their tanks properly, and this whole part of the project can become quite stressful. That's why a lot of builders opt to have their tanks built by someone more knowledgable and experienced. As for me, I am a builder, and the only way I will become experienced is to just dive in and do it, and seek expertise from those that are the experts.
Next up will be riveting this trap door contraption to the rib, and putting the final bend on the other side of the hinge pin.
KPR
Here some pics showing how I drilled the upper hinge rivet holes:
- The lower hinge is only attached to the upper hinge via the hinge pin, and to the actual trap door.
- The trap door holes get dimpled, and the back side of the lower hinge holes get countersunk.
- The upper hinge is attached to the spacer and then finally to the rib web. SO in this case the top side of the upper hinge is countersunk, and the rivet then goes through the holes in the spacer and the rib web.
So you have to make sure that you countersink the right holes on the correct side of each hinge. If you screw that up, you get to start over. Perhaps this is not an issue for other folks, but for me it was a bit unnerving. Hinges are a bit strange for me to work with, because they are made from a different alloy, with a different hardness, and a different thickness than other types of alclad aluminum.Their dimension and general shape also make them a challenge to work with.
One of those challenges is that I find it difficult to try to setup the work so that you can use a microstop countersink tool to drill the holes - mostly because the holes are typically very close to multiple edges of the hinge, an the part is small, so the tool does not sit well. The shape of the hinges also makes it difficult to butt up multiple hinge halves to give the tool more surface area to sit on, as I have done in other situations when working with flat aluminum alclad.
So, I resolved to countersink the less elegant and more error-prone way, by using my deburring bit in my cordless drill, and carefully countersinking each hole and trial fitting it with a rivet to ensure that I don't go too deep. Here I am burrowing out the holes in the back side of the lower hinge that will accept the dimples from the trap door.
Everything from the hinge pin to the rivets to the parts is a concern, and whatever you decide to do, you have to end up feeling confident that the added pieces and parts you are putting in the fuel tank are not going to cause a bad situation in the future. You need to k now that the extra rivets are not going to break or come loose, and the clunk on the end of the flop tube will not loosen from the tube, and so on. During my research I have read many accounts of folks that have ended up with a variety of issues with the fuel tank components from time to time. And at the same time I have also ready about folks that have had trouble-free tanks for years. I guess it all boils down to paying attention to details and being very safety-minded when working on the tanks.
This trap door assembly, fuel sending unit, and the flop tube are the only three moving parts that I am will to accept inside the fuel tank. Those 3 components provide numerous "opportunities" for things to fall apart or cause other problems. Add to this the blatant fear that most folks feel about sealing up their tanks properly, and this whole part of the project can become quite stressful. That's why a lot of builders opt to have their tanks built by someone more knowledgable and experienced. As for me, I am a builder, and the only way I will become experienced is to just dive in and do it, and seek expertise from those that are the experts.
Next up will be riveting this trap door contraption to the rib, and putting the final bend on the other side of the hinge pin.
KPR
Christmas Fun and Fabricating the Imfamous Trap Door
After the flycutter episode with the most inboard fuel tank rib, the next feat was to fabricate something known as the trap door on the inboard rib that sits next to the most inboard tank rib. So this is now becoming a process of removing the ribs from the skin to prepare for the final assembly of the fuel tank.
Before I get into that whole story, I wanted to share some fun that I had with my wife a little over a week ago at a place near a local mall called canvas and cocktails. It is a place where you can go and paint something on canvas using water based acrylic paints, and have some alcohol while you do it. An instructor guides you through the process to paint the picture step by step, color by color, and brush by brush. I did this with my wife, my oldest son, and his girlfriend, and had an absolute blast. It "almost" made me brave enough to think that maybe I really can paint my own plane when the time comes. But let's not get into a rush on that just yet....
Here are our finished masterpieces - this particular painting had so many colors an shapes going on that it took longer than usual to finish it - almost 4 hours. But it was time well spent IMHO. Can you guess what it is, and which one do you think is mine or the wife's?
Now the trap door episode. What is it? Well, in aircraft where a flop tube is to be used for the fuel pickup line, and where possible extended unusual attitudes or 0 or negative G flight might be encountered, You have to ensure several things:
1. The engine has an inverted oil system
2. The fuel tank system is designed so that fuel can continue to be delivered to the engine at all times.
Vans standard design is to install a fixed, rigid fuel pickup line that stays in the same position in all flight attitudes all the time. I had decided when I ordered my wing kit to put one flop tube in the left wing and keep the standard fuel pickup tube in the right wing, with the idea that all unusual flight attitudes and inverted flight would be done with the left tank selected so that it takes advantage of the flop tube.
If you have ever built and flown gas or glow powered RC airplanes, you always had to put a heavy weighted clunk attached to a piece of fuel line inside the fuel tank. This allows gravity to keep the end of the fuel pick line inside the tank always accessing the lowest area where fuel resides. The flop tube is basically the same concept, made with some different materials and a few more fittings, but the exact same concept.
Another contraption that is also used to help ensure that fuel is always available and in close proximity to the flop tube is a so-called trap door, that is placed over a small hole in bottom rear of the next closest inboard tank rib. The most inboard rib obviously cannot contain any holes except those that contains a vent line or fuel feed lines that will route fuel to the engine from the wings and fuselage. However, all of the inboard ribs MUST contain openings that allow fuel to transfer from one bay between ribs to another bay. IN addition, the dihedral of the wings also forces fuel to continue to flow to the lowest inboard position in the wing tank, which is right over the corner where the fuel pickup line is located.
By the time the fuel gets to the last bay in the tank where it is picked up and routed to the engine, under normal flight attitudes and conditions it should generally remain in the last bay of the tank, closest to the fuselage. However, when performing aerobatics or high G maneuvers, it is possible that the fuel may attempt to move out of that first bay of the tank and back into the outer bays, away from the fuel pickup line. So to help prevent this, a small trap door is fabricated and installed on that first inner rib so that it covers the hole that allows fuel to enter that first bay in the tank. It is designed so that it opens and closes automatically as fuel pressure is exerted into or out of that bay. Any force that is applied that would allow fuel to be removed from that bay will also close the trap door, while pressure applied in the opposite direction forcing fuel into that bay will also open the trap door. There is no control linkage or motor or wires - it is just mounted with a hinge and a plate that is big enough to cover most of the opening in the rib, and is allowed to swing freely as described above.
Now for the funny part. It seems that my original reasons for wanting a flop tube in the tank may have been misguided somewhat.It turns out that the only time you really need the flop tube is if you intend to conduct sustained inverted or negative G flight. If you perform positive G maneuvers, which most aerobatics are, you don't really need the flop tube, and can get by with the standard fuel pickup line. Further more, if you keep the aircraft coordinated, fuel should always be available in the first bay of the tank, and never allow a condition where the pickup line or tube is un-ported. This then means that the trap door should also not normally be needed either.
Oh well, too late for that. Anyway I still like the idea of the trap door anyway as a bit of insurance to keep fuel in that first bay at all times. Turbulence can have a way of putting you in some very strange flight attitudes - ask me how I know....
So I decided to put in the trap door assembly since I am also going to use the flop tube. It starts with making the door itself from .020 inch thick aluminum from your trim bundle. This is thinner than a pop can and is the same thickness as the skin that was place on the rudder frame. I measured it per the plans and cut it from the sheet using left and right hand sheers. I think this was the frst time that I realize that the left and right designation does NOT apply to which hand you use to do the cutting, but rather the side of the cut that needs to be made and the amount of extra metal on either side of the cut that needs to be kept out of the way of the sheers and the cut. Never understood that, and never used these tools until now.
Next was figuring out where to get the hinge material from. the plans tell you what hinge to use, but they don't specify a part number of if this is supplied already with your wing kit. I learned from other builders that you can use a small section of the same hinge material for the wing flaps. these hinges are 6 feet long (72 inches), and a quick review of the flap assembly plans shows that only 56 inches is needed for the flaps, so they give you plenty of extra hinge material. I measured the length I needed per the plans, and marked the line. I used my Dremel cutoff wheel to cur the hinge, but I had to slide out the hinge pin first, because you need a little extra longer length of the hinge pin so you can bend the ends to keep the hinges from separating.
Here is how I clamped everything down to make the cuts:
One part that you also should fabricate, which the plans do NOT show, is another piece of .020 aluminum shaped to match the dimensions of the upper hinge half (about 1/2 of an inch wide). This is a spacer that allows the top half of the hinge to sit even with the bottom hinge and the door assembly, and allows the door to close as flush as possible next to the hole in the rib. Here is the hinge, the door, the spacer, and the hinge pin all cut to initial size.
Next the hinge gets trimmed a bit more to match the width of the trap door and to form the upper hinge plate so that it has a small triangle on one end. More about that in a minute:
Here is my first trial fit of the assembly on the tank rib. I adjusted this a bit more later one, but this is the approximate location for the door, very near the rear rib flange:
After figuring out how to clamp the small hinge halves down on the bench so they could be trimmed to their final dimensions, I ended up with hinges that looked like this:
That little triangle on the top hinge half then gets bent 90 degrees to act as a door stop for the door. It cannot be allow to open all the way flush with the top side of the rib, because it may never close again, allowing any fuel that is currently in that first bay to escape into the outer baffles of the tank and away from the pickup line. So to prevent this, the little tab keeps the door from opening too far s that it cannot get stuck all the way open. To bend the tab, I put it in my vise like so:
Then I used a small rubber mallet to bend the metal 90 degrees. I had to position the tab properly in the vise so that the bend would occur in the proper place. the reality is that the tab needs to be a little bit inboard from the edge of the lower hinge and the door, to ensure that the door will always contact the stop and will not get stuck:
By this time I should also mention that I had already smoothed the edges of all parts on the scotch brite wheel and rounded all corners to avoid stress risers - standard deburring procedure. After the bend the parts looked like this:
Next came the painful task of marking rivet lines. I hated this part and it took a while before I was satisfied that I had the marks in the proper position. The plans do a horrible job of showing different pics with different hinge layouts that do not match each other, and they show that there should be 3 rivets on the top hinge and 3 on the bottom hinge. The only problem with this is that there is a huge stiffening ring you know - the one on the inboard rib that I cut with the fly cutter recently. So there is a huge void in the area where the upper center rivet is supposed to go (SO a rivet can't go there). And then the location of the top forward rivet is right on the edge of the rib web just on the other side of the stiffening ring, so getting the location of the rivet right is pretty important because the shop head and the hole both need to have enough room to seat properly.
Rivets for the bottom hinge can be evenly spaced as they all will fit on the rib web with no issues.To resolve this, I decided that the upper hinge could only have 2 rivets, and the bottom would have 3 rivets per the plans. The upper hinge would need rivet holes that are the right at the minimum edge distance of 3/16ths of an inch for an AN426AD3 rivet.The lower hinge rivet holes were spaced 1/4 inch from the edges, giving a little bit more of a buffer. Here are my early attempts to mark the rivet lines. found this to be very tricky because it was hard to get a straight edge on the hinges, because they are small to begin with, and the 5052 H34 aluminum alloy they are made with is very slippery. I remember dealing with this when I had to fab the trim tab hinge. It was a pain then and it is a pain now.
Since I had not had to bend hinge pins in a while, I could not remember how I did this in the past. So I decided to try to put a 90 degree bend in the hinge pin the same way I did the hinge. It did not work so well.
I ended up taking a small block of wood with a flat surface and placing it next to the pin and and then hitting the block of wood with the hammer - worked much better, the pin is much stiffer for obvious reasons, so it took a bit more force to get it to bend, but once it was started it went over pretty well.
Next was another trial fit to mark the final position of every thing after all the parts were final-formed. You leave a small opening at the bottom of the hole beause proseal sealant will be placed in this area of the rib flange, and you don't want the door to be so big that it interferes with the proseal. Also note that this hole goes all the way to the bottom of the bottom tank rib flange.Another funny thing that I saw from other folks build logs is that most folks put bends on the hinge pin on both sides of the pin, but some appeared to only put the bend on one end. Now, if yo put only one bend in the pin, and the bend is placed on the rear facing part of the hinge, that should be fine, assuming that the hinge pin is long enough to stay engaged in the hinge holes if it moves forward and backward, because the bend in the pin will eventually hit the rear rib web and baffle plate. However, I also saw some pics on some build logs where the bond was placed on the forward side of the hinge. IN this state there is NOTHING preventing the pin from falling out and causing potential blockages in the tank. I cold not believe this when I saw it. This pic shows the first bend toward the rear of the rib. I will be applying another bend on the other end when all final prep has been completed.
I decided to align the door with the rear rib flange a bit more. This should be the final position of my trap door. I have about 20 more pics of thos whole process, and if you haven't figured it out yet, this little assembly has taken quite a bit of time to research and fabricate. Most builders only show a finished pic of this door and say "here it is, already installed." Almost nobody provides the level of detail I am showing here. Hopefully this will help you with your build.
In the next post I will show how all the rivet holes were drilled and countersunk and hopefully complete the assembly of this seemingly simple little device.
KPR
Before I get into that whole story, I wanted to share some fun that I had with my wife a little over a week ago at a place near a local mall called canvas and cocktails. It is a place where you can go and paint something on canvas using water based acrylic paints, and have some alcohol while you do it. An instructor guides you through the process to paint the picture step by step, color by color, and brush by brush. I did this with my wife, my oldest son, and his girlfriend, and had an absolute blast. It "almost" made me brave enough to think that maybe I really can paint my own plane when the time comes. But let's not get into a rush on that just yet....
Here are our finished masterpieces - this particular painting had so many colors an shapes going on that it took longer than usual to finish it - almost 4 hours. But it was time well spent IMHO. Can you guess what it is, and which one do you think is mine or the wife's?
1. The engine has an inverted oil system
2. The fuel tank system is designed so that fuel can continue to be delivered to the engine at all times.
Vans standard design is to install a fixed, rigid fuel pickup line that stays in the same position in all flight attitudes all the time. I had decided when I ordered my wing kit to put one flop tube in the left wing and keep the standard fuel pickup tube in the right wing, with the idea that all unusual flight attitudes and inverted flight would be done with the left tank selected so that it takes advantage of the flop tube.
If you have ever built and flown gas or glow powered RC airplanes, you always had to put a heavy weighted clunk attached to a piece of fuel line inside the fuel tank. This allows gravity to keep the end of the fuel pick line inside the tank always accessing the lowest area where fuel resides. The flop tube is basically the same concept, made with some different materials and a few more fittings, but the exact same concept.
Another contraption that is also used to help ensure that fuel is always available and in close proximity to the flop tube is a so-called trap door, that is placed over a small hole in bottom rear of the next closest inboard tank rib. The most inboard rib obviously cannot contain any holes except those that contains a vent line or fuel feed lines that will route fuel to the engine from the wings and fuselage. However, all of the inboard ribs MUST contain openings that allow fuel to transfer from one bay between ribs to another bay. IN addition, the dihedral of the wings also forces fuel to continue to flow to the lowest inboard position in the wing tank, which is right over the corner where the fuel pickup line is located.
By the time the fuel gets to the last bay in the tank where it is picked up and routed to the engine, under normal flight attitudes and conditions it should generally remain in the last bay of the tank, closest to the fuselage. However, when performing aerobatics or high G maneuvers, it is possible that the fuel may attempt to move out of that first bay of the tank and back into the outer bays, away from the fuel pickup line. So to help prevent this, a small trap door is fabricated and installed on that first inner rib so that it covers the hole that allows fuel to enter that first bay in the tank. It is designed so that it opens and closes automatically as fuel pressure is exerted into or out of that bay. Any force that is applied that would allow fuel to be removed from that bay will also close the trap door, while pressure applied in the opposite direction forcing fuel into that bay will also open the trap door. There is no control linkage or motor or wires - it is just mounted with a hinge and a plate that is big enough to cover most of the opening in the rib, and is allowed to swing freely as described above.
Now for the funny part. It seems that my original reasons for wanting a flop tube in the tank may have been misguided somewhat.It turns out that the only time you really need the flop tube is if you intend to conduct sustained inverted or negative G flight. If you perform positive G maneuvers, which most aerobatics are, you don't really need the flop tube, and can get by with the standard fuel pickup line. Further more, if you keep the aircraft coordinated, fuel should always be available in the first bay of the tank, and never allow a condition where the pickup line or tube is un-ported. This then means that the trap door should also not normally be needed either.
Oh well, too late for that. Anyway I still like the idea of the trap door anyway as a bit of insurance to keep fuel in that first bay at all times. Turbulence can have a way of putting you in some very strange flight attitudes - ask me how I know....
So I decided to put in the trap door assembly since I am also going to use the flop tube. It starts with making the door itself from .020 inch thick aluminum from your trim bundle. This is thinner than a pop can and is the same thickness as the skin that was place on the rudder frame. I measured it per the plans and cut it from the sheet using left and right hand sheers. I think this was the frst time that I realize that the left and right designation does NOT apply to which hand you use to do the cutting, but rather the side of the cut that needs to be made and the amount of extra metal on either side of the cut that needs to be kept out of the way of the sheers and the cut. Never understood that, and never used these tools until now.
Rivets for the bottom hinge can be evenly spaced as they all will fit on the rib web with no issues.To resolve this, I decided that the upper hinge could only have 2 rivets, and the bottom would have 3 rivets per the plans. The upper hinge would need rivet holes that are the right at the minimum edge distance of 3/16ths of an inch for an AN426AD3 rivet.The lower hinge rivet holes were spaced 1/4 inch from the edges, giving a little bit more of a buffer. Here are my early attempts to mark the rivet lines. found this to be very tricky because it was hard to get a straight edge on the hinges, because they are small to begin with, and the 5052 H34 aluminum alloy they are made with is very slippery. I remember dealing with this when I had to fab the trim tab hinge. It was a pain then and it is a pain now.
In the next post I will show how all the rivet holes were drilled and countersunk and hopefully complete the assembly of this seemingly simple little device.
KPR
Saturday, December 16, 2017
Using a Fly Cutter for the Very First Time
I purchased this tool a long time ago, expecting that I would need to use it sooner or later. My initial expectation was that I would be using it to cut round holes for certain instruments on the instrument panel. I did NOT expect that I would need to use it on my fuel tank.
Basically, I needed to cut out the entire section of metal on the inboard fuel tank rib s that an access plate can be installed to allow servicing of the fuel tank in that area, should the need ever arise. Since I decided NOT to install the capacitive sender kit from Vans per their recommendation, and I am now going to switch to the normal float sender instead, the access plate would also normally contain the mounting flange for float sender, as well as the AN 833 hardware for the fuel pickup line fitting, that takes fuel from the pickup line and routes it through an elbow joint through the access plate.This will be how things get assembled for the right fuel tank, as it will be a stock tank per the plans for the most part.
The left tank, on the other hand, does not contain the stock fuel pickup line, but instead will use a flop tube as I have described previously. In addition, since I am still using the flop tube in the left tank, I cannot install the float sender in it's intended original position, as it will interfere with it. SO I will need to put the float sender in the next bay over, and mount it to the rear baffle instead of on the access plate on the T-703 tank rib web.
Aside from all that, I still need to install the access panel on the rib web, but instead of using the T-708 plate on the left tank, I will use the other solid plate that came with the capacitive sender kit. the pics will show this more clearly later. Anyway, before I even get to that, I have to cut a very large hole, so large in fact that it is too big for hole saw, and for a spade bit or other type of drill bit. the Fly wheel cutter tool was specifically designed for this situation.
The plate gets prosealed and screwed onto the rib web so that you can access from the wing after removing the wing fairing. Although it is a tight space, you are supposed to be able to remove this plate and service the tank in certain ways without the need to remove the tank from the wing. A reinforcement ring goes on the other side of the rib web and serves as the mounting bracket for the access plate. Here is a pic of that bracket with the T-410 stiffeners precut in side of it. I used snips to separate the small tangs holding each part together, and then used a small file to grind down the remaining slag. Later I found out that you can pretty much just lightly twist these parts and they will separate. am always cautious about this sort of thing from my plastic model building days, since twisting the parts of the tree would sometime remove portions of the actual part. SO you learned to use snips or clippers to keep from damaging the plastic parts.On the right is the parts removed from each other, adnon the left is the part for the right fuel tank with everything still attached as it came from the factory:
The plans do not mention how big the hole needs to be, just that you need to make one (another Vans instruction feaut-pa). So after researching some builders sites I realized that the hole needs to match the opening in the reinforcement bracket shown above - duh! So this was as easy as placing the bracket over the stiffening ring on the aft end of the rib web, and tracing the inner circle onto the web:
Next came the "art" of placing a drill board on the drill press table, followed by the rib, and then figuring out how to clamp everything down solid.I also needed to find the precise diameter and then the radius of the circle. It turned out to be a 5.25 inch diameter, with a 2 and 5/8 inch radius on each side of the center. I needed to mount the fly wheel cutter into the drill press chuck as shown, so that I could mark the center for the drill bit:
The very next thing you need to do is setup the belts on your drill press, or reduce your speed adjustment to achieve the absolute lowest RPM that you can achieve with your drill press. With mine being a standard large floor model press, I was able to adjust the belts to get it down to 250 RPM.
Next was the task of setting up the cutter as precisely as possible for the radius. Safety point - the point on end of the cutter is EXTREMELY sharp - do not mess around with this - keep your fingers clear of it at all times, and keep the drill press unplugged until you are ready to use it, and all adjustments have been completed.The tool comes with a set of Allen head screws to adjust the radius of the cutter from the center of the pilot bit, which is a 1/4 inch drill bit. IN addition, a second Allen screw is used to adjust the depth of the cutter compared to the depth of the pilot bit. The instructions say to set the cutter depth 1/4 inch higher than the tip of the pilot bit - the idea being that the pilot bit drills the hole in the center to provide a stable grip for the cutter to retain the set radius without wandering. A drill board underneath the part to be cut is also ESSENTIAL for this to work properly.
Another Safety tip: When the cutter makes contact with the metal, it emits a very loud and uncomfortable squeal. it sounds kind of like when a kid scrapes his finger nails across a blackboard - yup - it's just about that bad. So, I highly recommend that you wear ear muffs during this operation as well as safety glasses and leather gloves.
With everything positioned correctly, and the worked clamped down properly, you then dawn some thick heavy work gloves and keep all hands clear of the work piece until the drill is stopped. You start bringing the pilot bit down until it engages, and then you SLOWLY apply more pressure on the press to keep bringing the cutting bit down onto the metal. Check the cut as it engages and make sure that it does not wander from the marks that you had drawn earlier.If the part moves, or worse yet, if it becomes hung, make sure you stay out of harms way and then pull the plug on the drill press to stop it. Do NOT try to rescue the part from its demise. This is where this tool is absolutely dangerous. It can take a piece of metal and turn it into a disemboweling razor knife in a split second, and then it can take that piece of deadly metal and fling it directly at you, which is why you need to keep the drill press at the lowest possible RPM.
Make no mistake, this thing can KILL you in an instant if things start to go awry. So pay attention and take every possible safety precaution before starting the process.
If everything goes according to plan, eventually the cutter will go all the way through the metal, and you can stop the drill press. Then UNPLUG the drill press from the wall. Then and only then should you reach in with gloved hands and remove the part. Here is the new hole in the rib after the operation was complete. Notice the shavings that it creates as it cuts:
That circular piece of metal has a razor edge on it since part of the cut was made against the curvature of the stiffening ring. You could slice meat with it - or your fingers, so again, be careful when you handle this thing.
Next is a pic of the rib with its new hole, with the reinforcement bracket positioned over it, both types of access cover plates, with and without the sender and fuel pickup line hardware holes, and a cork gasket.
A couple more things I learned from my research and several phone calls to Vans - throw the cork gasket away and DO NOT USE IT - PERIOD! Over time the gasket becomes saturated with fuel and WILL START LEAKING - so NO CORK GASKET! I also learned that the mounting flange of the fuel float sender unit has a rubber gasket that you also SHOULD NOT USE, as it starts leaking as well. As I stated earlier, my left tank will use the plate on the left, and my right tank will use the standard plate on the right.
SO that is how you setup and use a fly wheel cutter tool in a drill press to cut very large, precise holes in metal. Now I just have to debur the edges of the rib a bit and continue with the remaining fuel tank assembly tasks.
On another note, There is also a trap door with a hinge on it that I need to fabricate. TO do so, Vans told me that I needed to use the hinge material from the flap hinges that came with the wing kit. Since these hinges were 6 feet long, I had stored them up on my wide garage shelf with the other long parts like the angles used for the longerons for the fuselage that are 15 feet long. The problem was that I had to get to them on the shelf, which was not exactly "easy." I had to move a bunch of stuff off the shelf first in order to get to the hinges. I finally got them down, and spent a large part of today, cleaning up the garage and putting everything back in its place.
More on the trap door fabrication tomorrow.
KPR.
Basically, I needed to cut out the entire section of metal on the inboard fuel tank rib s that an access plate can be installed to allow servicing of the fuel tank in that area, should the need ever arise. Since I decided NOT to install the capacitive sender kit from Vans per their recommendation, and I am now going to switch to the normal float sender instead, the access plate would also normally contain the mounting flange for float sender, as well as the AN 833 hardware for the fuel pickup line fitting, that takes fuel from the pickup line and routes it through an elbow joint through the access plate.This will be how things get assembled for the right fuel tank, as it will be a stock tank per the plans for the most part.
The left tank, on the other hand, does not contain the stock fuel pickup line, but instead will use a flop tube as I have described previously. In addition, since I am still using the flop tube in the left tank, I cannot install the float sender in it's intended original position, as it will interfere with it. SO I will need to put the float sender in the next bay over, and mount it to the rear baffle instead of on the access plate on the T-703 tank rib web.
Aside from all that, I still need to install the access panel on the rib web, but instead of using the T-708 plate on the left tank, I will use the other solid plate that came with the capacitive sender kit. the pics will show this more clearly later. Anyway, before I even get to that, I have to cut a very large hole, so large in fact that it is too big for hole saw, and for a spade bit or other type of drill bit. the Fly wheel cutter tool was specifically designed for this situation.
The plate gets prosealed and screwed onto the rib web so that you can access from the wing after removing the wing fairing. Although it is a tight space, you are supposed to be able to remove this plate and service the tank in certain ways without the need to remove the tank from the wing. A reinforcement ring goes on the other side of the rib web and serves as the mounting bracket for the access plate. Here is a pic of that bracket with the T-410 stiffeners precut in side of it. I used snips to separate the small tangs holding each part together, and then used a small file to grind down the remaining slag. Later I found out that you can pretty much just lightly twist these parts and they will separate. am always cautious about this sort of thing from my plastic model building days, since twisting the parts of the tree would sometime remove portions of the actual part. SO you learned to use snips or clippers to keep from damaging the plastic parts.On the right is the parts removed from each other, adnon the left is the part for the right fuel tank with everything still attached as it came from the factory:
Next was the task of setting up the cutter as precisely as possible for the radius. Safety point - the point on end of the cutter is EXTREMELY sharp - do not mess around with this - keep your fingers clear of it at all times, and keep the drill press unplugged until you are ready to use it, and all adjustments have been completed.The tool comes with a set of Allen head screws to adjust the radius of the cutter from the center of the pilot bit, which is a 1/4 inch drill bit. IN addition, a second Allen screw is used to adjust the depth of the cutter compared to the depth of the pilot bit. The instructions say to set the cutter depth 1/4 inch higher than the tip of the pilot bit - the idea being that the pilot bit drills the hole in the center to provide a stable grip for the cutter to retain the set radius without wandering. A drill board underneath the part to be cut is also ESSENTIAL for this to work properly.
With everything positioned correctly, and the worked clamped down properly, you then dawn some thick heavy work gloves and keep all hands clear of the work piece until the drill is stopped. You start bringing the pilot bit down until it engages, and then you SLOWLY apply more pressure on the press to keep bringing the cutting bit down onto the metal. Check the cut as it engages and make sure that it does not wander from the marks that you had drawn earlier.If the part moves, or worse yet, if it becomes hung, make sure you stay out of harms way and then pull the plug on the drill press to stop it. Do NOT try to rescue the part from its demise. This is where this tool is absolutely dangerous. It can take a piece of metal and turn it into a disemboweling razor knife in a split second, and then it can take that piece of deadly metal and fling it directly at you, which is why you need to keep the drill press at the lowest possible RPM.
Make no mistake, this thing can KILL you in an instant if things start to go awry. So pay attention and take every possible safety precaution before starting the process.
If everything goes according to plan, eventually the cutter will go all the way through the metal, and you can stop the drill press. Then UNPLUG the drill press from the wall. Then and only then should you reach in with gloved hands and remove the part. Here is the new hole in the rib after the operation was complete. Notice the shavings that it creates as it cuts:
Next is a pic of the rib with its new hole, with the reinforcement bracket positioned over it, both types of access cover plates, with and without the sender and fuel pickup line hardware holes, and a cork gasket.
SO that is how you setup and use a fly wheel cutter tool in a drill press to cut very large, precise holes in metal. Now I just have to debur the edges of the rib a bit and continue with the remaining fuel tank assembly tasks.
On another note, There is also a trap door with a hinge on it that I need to fabricate. TO do so, Vans told me that I needed to use the hinge material from the flap hinges that came with the wing kit. Since these hinges were 6 feet long, I had stored them up on my wide garage shelf with the other long parts like the angles used for the longerons for the fuselage that are 15 feet long. The problem was that I had to get to them on the shelf, which was not exactly "easy." I had to move a bunch of stuff off the shelf first in order to get to the hinges. I finally got them down, and spent a large part of today, cleaning up the garage and putting everything back in its place.
More on the trap door fabrication tomorrow.
KPR.
Thursday, December 14, 2017
Making Due with What You Have - The Continuation
Its been a crazy week at work, and since I am the newsletter editor for my chapter I have to spend a few evenings creating the monthly newsletter at the beginning of the 3rd week of each month. So I haven't been able to update the blog until now.
So here's the story I meant to tell in the last post. Every once in a while - and this has happened to me several times since I started the project - an opportunity arises where the materials and tools and techniques that are used to build an airplane come in handy for some unexpected purpose. One of the first things you experience when you start a project such as this, is that although you are working with metal, you sure end up spending a lot of time working with wood. All the fixtures and jigs and work benches and tables and clamping setups that you have to make out of wood in order to build a metal airplane is remarkable.
So as a result you develop a pretty good set of skills working with wood. On this particular occasion, I had a plastic tree stand for our Christmas tree finally give out last year, and I had intended on ordering a new one for this year as the holiday season started ramping up. The base was starting to crack where the legs attach to it, and it was no longer able to support the weight of the tree.
As I searched online for a replacement, I found out that there are a million different replacement stands out there, but none of them were to my liking.I was out in the garage one day staring at the fuel tank, and I turned and looked at an orange home depot bucket with a bunch of wood scraps in it that has been sitting around for years now. All of the wood in this bucket was remnant wood from the rib forms that I had cut from 2x10 boards to make the forming blocks for my subskin fabrication for the leading edge. Some of them are shown below:
The more I stared at these pieces of wood, the more I realized that I might just be able to use them to make a brand new stand for the Christmas tree. They were long enough to match to length of the original legs, and the only other thing I needed was a piece of wood to drill a 1.25 inch wide by 3.25 inch deep hole for the shaft of the first stage of the center pole of the tree to fit into. I determined this by taking the measurements from the original stand as shown below:
I figured I could use a 4x4 piece of wood to drill the new hole for the base pole, and I found some old L brackets that were removed from an old garage door frame assembly that was removed when I changed my door from a standard side spring configuration to a center spring configuration. I remember the guy asking if I wanted the old hardware, and I said, sure I'll keep those!. I had no idea what I might use them for at that time. Then I found some 1/4 inch x 5/8 inch lag bolts that were lying around, but I had to buy a few more as I realized I did not quite have enough for this holiday project.
I made some measurements, cut and trimmed all the wood with my saw, bought a 1.24 inch spade bit for the hole for the shaft, mounted it on my drill press and bored out the hole from the 4x4 piece of wood. Once all the parts were cut, drilled, and trimmed to the proper length, I took the L brackets and bolts and drilled pilot holes for them, and here is the final result:
The hardware was overkill, but it is what I had lying around, so why not use it. One thing is for sure, this stand is even more sturdy that the original one. The thing I love the most about this is that the natural curve of the wood from the shape of the LE ribs is a natural fit for this stand. I didn't even really have to do any sanding or anything, since all this ends up under the tree mat anyway. It was as if those pieces of wood were meant for this little project - amazing! Drilling out that hole was sure a trip. Saw dust kept coming out of it like a volcano as I drove the bit down deeper and deeper. As always, clamping the wood to the drill press base was a challenge, but I used a metal drill press vise specially designed for the drill press base to help take care of that. The spade bit bored a perfect 1.25 inch hole in the 4x4 wood, but now I have a mess to clean up in the basement.
So this just goes to show that you never know what your airplane building skills will allow you to do outside of your project. It is also a great feeling when you can solve a problem without going out and buying something from a store that will most likely cost you more than if you come up with abetter, cheaper solution. Unless someone reads this post, or I tell them how I did it, nobody will ever know that the legs came from scrap wood I used for the airplane project!
KPR.
So here's the story I meant to tell in the last post. Every once in a while - and this has happened to me several times since I started the project - an opportunity arises where the materials and tools and techniques that are used to build an airplane come in handy for some unexpected purpose. One of the first things you experience when you start a project such as this, is that although you are working with metal, you sure end up spending a lot of time working with wood. All the fixtures and jigs and work benches and tables and clamping setups that you have to make out of wood in order to build a metal airplane is remarkable.
So as a result you develop a pretty good set of skills working with wood. On this particular occasion, I had a plastic tree stand for our Christmas tree finally give out last year, and I had intended on ordering a new one for this year as the holiday season started ramping up. The base was starting to crack where the legs attach to it, and it was no longer able to support the weight of the tree.
As I searched online for a replacement, I found out that there are a million different replacement stands out there, but none of them were to my liking.I was out in the garage one day staring at the fuel tank, and I turned and looked at an orange home depot bucket with a bunch of wood scraps in it that has been sitting around for years now. All of the wood in this bucket was remnant wood from the rib forms that I had cut from 2x10 boards to make the forming blocks for my subskin fabrication for the leading edge. Some of them are shown below:
I figured I could use a 4x4 piece of wood to drill the new hole for the base pole, and I found some old L brackets that were removed from an old garage door frame assembly that was removed when I changed my door from a standard side spring configuration to a center spring configuration. I remember the guy asking if I wanted the old hardware, and I said, sure I'll keep those!. I had no idea what I might use them for at that time. Then I found some 1/4 inch x 5/8 inch lag bolts that were lying around, but I had to buy a few more as I realized I did not quite have enough for this holiday project.
I made some measurements, cut and trimmed all the wood with my saw, bought a 1.24 inch spade bit for the hole for the shaft, mounted it on my drill press and bored out the hole from the 4x4 piece of wood. Once all the parts were cut, drilled, and trimmed to the proper length, I took the L brackets and bolts and drilled pilot holes for them, and here is the final result:
So this just goes to show that you never know what your airplane building skills will allow you to do outside of your project. It is also a great feeling when you can solve a problem without going out and buying something from a store that will most likely cost you more than if you come up with abetter, cheaper solution. Unless someone reads this post, or I tell them how I did it, nobody will ever know that the legs came from scrap wood I used for the airplane project!
KPR.
Subscribe to:
Posts (Atom)