24-03: Riveting / Bonding on the Hinges

 The Wing Side

The wing side consists of the larger P4 hinge riveted to the wing top and bottom skins, using the cut off flange of the wingtip as a spacer. Since the wing skins are dimpled, the spacer flange strip needed to be countersunk to accept the dimples. The hinge needed no further work since the spacer flange strip is countersunk. 

The countersinking of the spacer flange strips was done using a Permagrit 100 degree countersink in the drill press - to control the depth.  The spacer strips were also primed - this wasn't really required but i did it anyway.

A test coupon was used to check the depth of the countersinks

I attempted to use the tool in my drill, but it was way to hard to control the depth and took too long. 

At the very forward part of the wing, there were 3 rivet holes where there is no hinge. These were dimpled and i installed a -3 rivet in the hole to fill it up. 

Hinge Pin Termination / Trailing Rib Prep

The wingtip side took a little longer. First up, i made up the hinge pin terminations - this is how the hinge pins will be held in position so they do not slide out. This was made up by bending each pin to a 90 degree angle at the end, such that a piece of P4 hinge (one eyelet in width) could be slid on. They were bent to be deliberately too long at the start. The pin was bent over slightly on the end so the piece of hinge could not slide off - it will stay permanently on the end of the pin. I then aligned these 2 pieces and match drilled them to the trailing ribs. I then adjusted the length of the hinge pins to the holes in the tabs aligned with the holes in the rib, when the pin was bottomed out in the hinges. The pins were labelled for their position using heat shrink tubing. The tabs be held with a #6 panhead screw into a nutplate. Hard to describe but easier to see how it came out:

The ends of the pins were bent over to stop the little tab falling off.

The trailing ribs were then primed, and riveted together with the bent hinge pieces and the angle brackets. I did not prime the flanges where the rib will be bonded to the wingtip. I also dimpled the rib web and a couple of nutplates and installed these to take the caphead screws. 

At this time, i also relieved the flange at the front of the wingtip to go around the 3 rivets which i had installed to fill the holes which came pre-drilled but were not used to rivet on a hinge. 

The Wingtip Side

Installing the hinges on the wingtip side meant i needed to countersink the wingtips for -3 rivets. I decided not to use the normal AD3 rivets (normal temper with the dimple), but elected to go for soft temper rivets - these are still AN426 rivets but instead of AD3, then are A3. The -4 length was very expensive for some reason, so i ordered -5 length (AN426A3-5 or MS20426A3-5). Had to order a minimum of 1/2 lb - so i have a couple of thousand if anyone wants any! I had planned to cut them down, but it turned out the -5 length made a nice shop head (being a softer rivet they set like butter with the squeezer). 

To do the countersinking, i was not able to use the drill press and using the Permagrit tool in the hand drill would have taken forever. So i clecod the hinges in position to act as a guide for the pilot, and used a countersink cage with a normal countersunk cutter. I countersunk a little deep so i could fill the rivet heads with epoxy and micro filler later. 

To actually install the smaller P3 hinges into the wingtip, the insides of the wingtips were scuffed heavily and cleaned with acetone. The hinges were scuffed with 60 grit sandpaper and also cleaned. I used gloves at all times from here on in. A slurry of epoxy and flox (flocked cotton) was made up and a very thin smear was applied to the hinges. The slurry would slowly move then held vertically. The hinges were clecod on and then I used the rivet squeezer / soft rivets to attach the hinge. I applied the flox slurry over the outboard side of the hinges to further hold them in place. I made sure to keep the flox slurry away from the hinge eyelets. 

A thin slurry of epoxy / flox applied to the hinge

During riveting - had to be careful not to crush any eyelets with the squeezer.

Soft rivets set. The countersinks are deliberately a little too deep.

Extra slurry was applied at the edge of the hinge

Some slurry was placed on the trailing rib also and this was riveted in place. The angle bracket was not riveted, but was just glued in place with the epoxy slurry. This was because it would have been impossible to get to it with the squeezer - it had a couple of holes in it from where it was clecod on, and these ended up being filled with epoxy so I'm confident it won't go anywhere. 

A bit messy, but the extra epoxy / flox should hold the angle bracket in place. I would not have been able to get in here with a squeezer, and didn't want to use a gun on the outside of the fibreglass surface. 

The wingtip was then placed on the wing, using the hinge pins, to cure (just in case there was any misalignment or mis-shape when laying on the bench, i didn't want this to set permanently when the epoxy went off). 

How did it come out?

Bloody great! I am very happy. 

Look Ma - no screws!

At this point the wingtips are structurally attached. They would be good to fly like this - however i reckon i can tidy up the fit a little using some micro. The trailing edges also need some trimming and alignment with the ailerons. Next post! 

24-03: Attaching Wingtips using Hinge Method - Preparation

I decided that i was not a fan of the Van's method for attaching the wingtips - namely, using nutplates and screws. Partly due to the maintenance issues with removing all those screws (and their tendency to cam out and look average), partly due to my experience with screws in fibreglass (they worry and wear and eventually need tinnerman washers), and partly due to the puckering you can get with an older fairing. 

This is what i am going for. 

The alternate method is to use a couple of hinges on the top and the bottom of the ends of the wings. The wingtips are held in place using the hinge pins, which are then retained so they don't slide out. To remove the wingtips, you just pull the 2 hinge pins and pop the wing tip off - and there are no visible fasteners. 

The pioneer in this regard was Mike Bullock, with his RV7 who did a fantastic write up on the method. I plan to follow this method closely. There are a few changes which need to be made to the method - mostly the alteration of the end rib (on the rv-14 it interferes with the top hinge by about 4 eyelets, and on the bottom by 1 eyelet). I liked the approach taken by Carl & Rafael - so i copied it blatantly!!! 

Drilling off the hinges to the Wing

The hinge method uses a wider AN257-P4 (MS20257-P4) hinge on the wing side, and a thinner AN257-P3 (MS20257-P3) hinge on the wingtip side. I ordered 2 x 6ft lengths of each hinge. The reason for this will become clear soon enough, but it is so you don't the gaps in between the hinge eyelets right under the edge of the wingtip. 

Step 1 was to add additional holes between the existing holes in the ends of the wing skins - the existing holes are designed for a screw pattern, and you need more rivets than you do screws. I used a rivet fan and carefully match drilled the holes - carefully, because the existing holes are not of a consistent spacing. 

In the corner i added a hole aligned with the existing rivet pattern.

Step 2 was to take a P4 hinge, and match drill this to the wing. I made sure to have an eyelet at the end of the skin on the top and bottom. I drew a line on the hinge which was at the required 3/16" edge distance for an AD3 rivet, and aligned this with the holes in the skin and clamped the hinge in place. I then match drilled every 2nd hole starting from the trailing edge and working my may forward. 

Line drawn 3/16" in from the edge of the hinge.

Clamped in place ready for match drilling.

Match drilled to the wing. 

Modifying and installing the Trailing Rib

On the RV14 there is a trailing rib which is installed into the ends of the wingtip, to give structure and shape to the wingtip where it is not supported by the wing skins. The plans have you install it so the flanges are outboard (leaving a flush surface). 

Since the wingtips will be secured with the pins between the hinge halves, we need some space to install and remove these pins and to secure them from falling out. The solution is to use the left trailing rib on the right wing and vice versa. This leaves the web of the rib outboard and gives you the space for the hinge pins. 

The issue is that the rib now interferes with the bottom hinge by about 1 eyelet, and the top hinge by around 4 eyelets. The rib needs to be modified to fit. The process i used to make this modification is as follows:

Step 3 I cleco'd the wingtip in position on the wing and selected an arbitrary position on the aileron and drew a line which i carried over to the wingtip. This line is used to take a measurement of the thickness of the aileron at that position. I then slid the rib into position inside the wingtip, and made sure the corresponding position on the wingtip was the same thickness. This set the correct location for the rib, and i was able to clamp this in position. If it were located too far aft, or too far forward the wingtip would be a different shape to the aileron.

I then marked the location of the rib flanges onto the wingtip, and marked the rib location so it could be installed back in the same position. I also temporarily placed the hinges in position and marked roughly where they were located. 

This measurement..

..had to match this measurement.

Step 4 With the rib flange and hinge locations marked, i was able to transfer these marks to the outside of the wingtip and mark out a hole pattern for the rivets which will hold this rib in place. I did not mark any holes where the hinges interfere with the rib (and where the rib will need to be modified). Holes were drilled in the wingtip, then the rib was placed back into the same position it came from (using the reference marks), and i clamped and matched drilled this rib to the wingtip. 

A rivet pattern was laid out and drilled onto the wingtip. 

The rib was match drilled to the wingtip. 

Step 5 Now that the rib is in it's final location, i was able to work out where the rib was interfering with both the wing side hinge (the wider P4 hinge), and also with the wingtip side hinge (smaller P3 hinge). I did this by placing the hinges together with the pins and placing them into the wingtip. 

The following modifications needed to be made:

BOTTOM

Only a small amount needed to be cut off. I removed about 1/2 - 3/4" along the bottom of the rib in the corner. This didn't appreciably affect the strength or function of the rib. 

TOP

The top was a whole other story. The larger P4 hinge overlapped the flange of the rib by about 3.5-4". I was able to place the wing side P4 hinge in place, but there was no way to place the wingtip side P3 hinge in place without removing the whole flange. I was not a fan of this idea, as I felt the rib would lose a lot of strength. The solution was to cut the wingtip P3 (thinner) hinge shorter to clear the rib, then use an offcut piece of the wider P4 hinge to make a 'bent hinge' arrangement which fastened to the trailing rib itself (sounds complicated i know). 

The idea is that instead of the wider P4 wing side hinge meshing with the thinner P3 hinge riveted to the wingtip, for the last 4-5 eyelets, it would mesh with a piece of hinge which was bent at a 45 degree angle and attached to the web of the trailing rib. A small angle bracket would be placed on the other (outboard) side of the rib to give some further support and to stop the rib moving inward / outward when installed. It is harder to describe that to see in pictures, so here goes. (This idea was stolen totally from Carl & Rafael)

Here you can see how the top flange of the rib was modified. Almost all of the flange was removed, with about a 1/4 remaining for support. Basically, i removed as much of this hinge as i needed so it did not interfere with the wider P4 hinge which will be attached to the wing. 

This shows where the flanges used to be! 

This shows the modified rib in-situ with the wider P4 hinge in place. The eyelets outside of the rib location will mesh with the thinner P3 hinge which is riveted to the wingtip. However, i could not continue this piece past the end of the rib without having to remove the whole rib flange. Instead, i removed only enough to clear the wider P4 hinge. This left a 1/4" ish wide 'foot' on the bottom of the rib to give a solid support and make sure the vertical dimension of the wingtip remains correct. You can see here i am holding the offcut piece of P4 hinge which will be trimmed, bent and riveted to the rib. 

I tried to bend the hinge like this but it didn't work - my bender was too wide for the width of the hinge and it just bent the eyelets. 

What worked much better was to clamp it between 2 bits of plywood and use a calibrated bash with a hammer!

Here you can see how it works - the wider P4 hinge which will end up attached to the wing, meshes with the small piece which is bend upward and riveted to the web of the rib. 

This was the match drilled to the rib. 

Now this method works pretty well and my plan was to bond the rib into place in this location. To give a better bond, i decided (using Carl & Rafael's method) to bend up a little angle bracket which will be riveted to the back of this rib using the same rivets as the bent hinge. This will give more surface area for bonding and more support of the rib inboard / outboard (likely only an issue when installing the wingtip).

Here is the angle bracket. It was match drilled to the lower wingtip surface just for holding in place for test fitting and when bonding. I will not rivet this in place, just bond it, as rivet access will be too hard here.  

The angle bracket is on the left, what remains of the original rib flange is in the middle. These will end up being a good bonding surface. The the load is taken by the hinge on the right. 

Match Drilling the smaller hinge to the wingtip

Step 6 The wider P4 hinge will mesh with a smaller P3 hinge which is riveted to the wingtip itself. To do this, i drew a line down the middle of the smaller hinge and used the hinge pin to put it next to it's partner (the wider P4 hinge). I could then copy over the hole locations from the wider hinge to the smaller hinge, and i drilled these to #40. 

Since the rib was modified, i was able to cleco the wider P4 hinge to the holes in the wingtip and put the smaller P3 hinge in place using a hinge pin. It was then a fairly simple task to match drill the hinge to the wingtip using my 90 degree drill. 

I made sure the smaller wingtip hinge had one eyelet at the end, and squashed the end of this eyelet to give a positive 'end stop' for the wing pins when they are installed. 

The smaller hinge was match drilled to the wingtip and i celco'd as i went. 

The BIG CUT!

So, these hinges are all match drilled in place, however the wingtip won't be removeable unless i split the wingtip at some point between the 2 hinge pieces! I wondered where this cut should be and pondered making it under the wing skin itself, however the most logical location was aligned with the edge of the wing skin. To do this, i marked on outside of the wingtip where the hinges ended so i didn't cut too far - the wingtip will retain it's flange where the nose section is located (where there are no hinges).

Step 7 I could then cleco the wingtip in position on the wing and i used my Japanese pull saw with a 1/64" kerf to scribe a line along the edge of the wing skin. Once i thought i had a nice positive line, i used a mechanical pencil to darken up this line. The wingtip was removed and i used the saw to cut off the flanges at the marks! This worked great and i've got a beautiful straight line.

I removed the blade from the saw so i could get right in next to the skin and clear the clecos.

1/64" kerf - it wrecked the saw but worth it. 

I scribed a fair distance in, but not all the way through

The scribe line was darkened with a pencil then cut off with the saw. 

Test Fit!

Step 8 The cut off flanges were lightly sanded to get a smooth edge, as was the wingtip itself. I was then able to cleco on the wider P4 hinges to the wing, using the cut off flange as a spacer. The smaller P3 hinge and the modified ribs were installed into the wingtip with clecos, and i was able to test fit the wingtips for the first time. I used some boelube liquid lubricant on the hinge pins. I was very pleasantly surprised to see they stayed in alignment! 

All parts clecod to the wingtip.

Modified rib in place. In this pic i have not got the angle bracket in place and you can see how the bottom of the rib is not well supported without it. 

Wider P4 hinges and cut off flange spacers in place

Finally! Wingtip held in place using the hinge pins

Aligned nicely!

The aileron and wingtips top surfaces stayed really well in alignment. Very happy. 

Trailing edges are aligned very well. They didn't move a whisker.

I used this opportunity to mark where the trailing edges of the wingtips will need to be trimmed to be level with the ailerons. 

Final Steps

This post has covered the nuts and bolts of how i installed the wingtips using Mike Bullock's and Carl & Rafael's methods. Obviously they are not finished. The next post will detail how i riveted the wider P4 hinges to the wings (including their spacers), and how i riveted and bonded the smaller P3 hinges and the modified rib into the wingtip. Also, how i retained the hinge pins at the trailing edge. There will be a final post in this series on how i finished the wingtips with epoxy / micro to get a good finish and hide the rivets, tidy up the trailing edges and get a nice crisp edge with the wings skins and an overall prime and sand. 

This was an enjoyable section going 'off reservation' so to speak!