Ch 21 Strakes – Fuel/Baggage

Date:  06-05-2018

Number of Hours:  7

Manual Reference:  no ref

Time for the fuel sensors to go into the strakes. I’ve spent a huge amount of time pondering and researching how to do this. My issue was using Avgas but perhaps some Mogas at times too. Once I go there, capacitance probes can be 40% out. I can’t re-calibrate on the fly and what if I shandy the fuel? This would mean completely unreliable fuel gauges. The only time this might be critical is for very long flights over water… exactly when I might not want false readings. So no capacitance probes for this plane.

My solution is a mix of optical fuel sensors and the old school sight gauges. I also need an electrical signal to work my ferry tank top up system. I’ve gone for the GEM ELS-950 level switches. These optical electric ‘switches’ just tell you liquid or ‘no liquid’. It doesn’t care about the specific gravity of the fuel as capacitance sensors do.

I used 2024 T3 1/4″ thick for the hard points. A 1/4″ NPT tap is used for the sensors. I also made a hard point for the AUX tank (or ferry tank) line which will be an AN firewall fitting.

Here I’ve cut the foam down to the inside glass for installing the hardpoints.

The positioning of these fuel sensors has been a year or so in the making. I finally realised that I have one fuel tank, not two (or three) and I don’t need sensors on both sides because the engine thinks there is only one tank supplying it.

I’ve then thought about what indications are useful in flight and what do I want the auto fill from the ferry tank to operate on which levels? I have a calculated guess that full fuel will be 300Lts in my modified strakes. Given the spar is 8″ in depth and allowing for 9″ depth maximum height as it is a little more forward, I could work out positions for the sensors as well. My decisions are:-

4/4 Full fuel at the Spar (which is not 100% full) about 275L  as high as possible (right)
2/3 about 200L    5.3″ (from the bottom of the strake)   (left)
2/5 about 120L    3.2″ (right)
1/5 about 60L      1.6″ (left)

Yes I had to make a bunch of cut outs for the hard points. Here’s the one tank thinking…. I put the ‘full’ hardpoint on the right. Then I put the AUX ferry tank fuel inlet just below this also on the right and the 2/5 of a tank (3.2″) below that. So thats three hard points on the right.  On the left we have the 2/3 full at 5.3″ and the 1/5th full at 1.6″. This is shown in the last two pics.

So whats my rationale? I like to know when I have about 2 hours fuel left. That’s my 1/5 or 60 liter indication.  I also like the 120L number which is a good one for local flights given that I rarely fly less than 2 hours and I always include a fixed reserve.  The nearly full and 2/3 or 200L are markers for my auto top up for the ferry tank. This holds 250L maximum (so I have potentially 550L at MAUW) and I like the idea of topping up the mains so if the top up fails for any reason, I always have at least 200L to feed the engine.

I’m doing these hard points in a couple of stages to ensure they are 100% fuel tight. First up is a system of washers screws and nuts to hold them in position for the initial flox to the inside skin of the fuel tanks (strakes). Also pictured is one of the fuel sensors.

Right side hardpoints floxed and held in place.

I used the castle nuts initially even though the thread was not a match but then decided to do it properly with a nut that would give me more ‘squeeze’. I’ve tried to mitigate for these fasteners getting stuck. We shall see if all the careful duct tape placement works.

Right side with just the two sensor hardpoints.

While I won’t have a full cure tomorrow, I’ll get the fasteners off and see where we are for the next lot of flox for our 100% sealed result.

 

 

 

 

 

Date:  06-03-2018

Number of Hours:  5

Manual Reference:  21-3

Like yesterday it was reinforcement tapes again. This time the prep cleanup was quicker and I left the top mouse holes for later. I wanted the layup done as I had a little bit of research to do for the next step.

You can see the edges cleaned up but no tapes yet.

Edges cleaned right and top but side tapes already done on the left. That outlet will get some work shortly to allow for the smoothest possible fuel flow.

Tapes on in this shot, you can see the slightly darker colour where the tapes are a little wetter than the strake bottom.

Still easy enough to get in there for tapes despite the smaller area.

Tapes done and you can see in this shot how the strake profile has to transition between two different NACA airfoils. This is experimental aviation after all.

Date:  06-02-2018

Number of Hours:  6

Manual Reference:  21-3

Now the plane is back right side up again I can continue on the inside of the strakes.

I did the perimeter tapes while upside down but left the inside tapes until now.

I spent a couple of hours or so just cleaning up around the edges.

The tapes are really structural so no shinny spots on the mating surface is required or tolerated for the best possible results.

After some time on the plans I confirmed that one ply of 2″ wide BID is sufficient. For this I laid out for 2″ tapes to be cut from a broader piece.

As there were so many pieces and I am only doing the left side today, I just measured and cut as I went.

The magnetometer pocket needed a few extra tapes to ensure it is sealed well. Otherwise it was just careful placement working into the night. The right side will probably get done tomorrow.

Date:  05-29-2018

Number of Hours:  6

Manual Reference:  no ref

The glass cockpit instruments use a magnetometer to sense direction as a compass does. This sensor box needs to be away from ferrous metal and other magnet fields, like say, the wires from a strobe unit. A great place for this box in a Long-EZ is right out on the end of the strakes.

I’d already made the ‘pocket’ which will be in an earlier post. Now I need to create the access.

I’d previously made the cardboard ‘map’ so I knew where to make the cuts for the pocket.

Using these thin bladed hobby saws and a straight edge works very well.

Pocket lid cut and no problems putting the mag unit in. I’ll do a final fit when its time to wire everything.

I borrowed a few tools and made those receptacles for the screws on strips of aluminium that were floxed in place. It was a few steps to get it all lined up.

Here’s the box lid now a part of the underside of the strake.

Just showing that I got the top flush which was a little tricky. We have a good result.

Date:  05-24-2018

Number of Hours:  7

Manual Reference:  21-3

Encouraged by all the work yesterday I went for it again today. The bottom skin on the left strake.

A couple of hours prep was again needed. This includes the cutout for the fuel drain hard point. Most of the work was trimming the front edge and a little around at the back for the transition onto the spar.

After micro on the bare foam I laid out the UND cloth. Lucky for me my cloth is wide enough to fit in one piece if you can live with a lot of trimming.

Despite the slightly wet micro the UND sits nicely on top. This allows plenty of time to get the fibers straight before wetting it out with a roller.

Here’s the first ply wetted out and trimmed. The golden colour of this rather smelly epoxy is one aspect of its appeal. We already know it’s proven safe for fuel tanks.

Here’s the three plies on and peel ply.

Note that I’ve peel plied the outboard area this time. The magnetometer pocket is hidden in there and I will have to cut out an access panel once the glass is cured.

Yes my workshop needs a tidy up. That’s tomorrow.

Date:  05-23-2018

Number of Hours:  8

Manual Reference:  21-3

Today was prep and execution of the bottom outside skin of the right strake.

Yesterday I made up the two fuel drain hardpoints. 1/8 NPT holes in 1/4″ 2024T3 Aluminium. I alodined these after I cut them out and thats about all I did for the day, on the actual build.

Today was a late morning start into trimming and prepping the strake for its skin.

I made an insert down to the glass for this hardpoint and then made it a bit smoother round the edges after this picture.

Finally with the strake sanded and measured and the layup planned. I microed the foam and used a little flox at the edges and for the drain hard point. Next was the first ply of UND and really careful attention to the bias direction. Its very easy for some reason to get this wrong. I really like working with UND, it just seems to behave itself better than BID and if you spend the time you can get it sitting nicely.

Once I was happy I wet the glass out using a roller and trimmed the edges.

The second ply I had all planned to roll out a ply of UND using a cardboard roll as you can see above.

This is one way to get the glass laid out close to where it needs to be. As it happens I had the room quite warm and the cloth was easily moved into position anyway. I think if you don’t have enough heat in the room with EZ-Epoxy its not too friendly.

This is with the three plies down and sorted out. That last ply is just 5″ at the outboard end.

My curve towards the leading edge worked out well even though I’ll need a little filler when I put the ‘D’ section on. Structurally it looks good.

From the afternoon start to finishing with the peel ply, its pretty dark outside now and a long day.

Date:  05-20-2018

Number of Hours:  9

Manual Reference:  21-3

Today was another big one. The bottom skin on the left side. Having done the right side I thought this would be quicker. It was easier, but not quicker. I knew what to do and all the steps got done.

The skin gets sanded and cleaned. Guidelines are drawn so I know where to prime the surface and then add flox.

I spent a while tweaking the fit, cleaning around the mouse holes and generally prepping the surface.

Ahhh, primed and wetted out with too much flox. Just the way I like it.

Primed and more flox on this side too.

Next is just fitting the top and plenty of weights and a clamped leading edge.  After this I go underneath and clean off the excess flox.

From here I worked out the ten 2.5″ wide BID strips. Wetted and cut these out which takes a little while and then the process of placing them with appropriate flox filler. A fare bit is needed at the spar and much less on the sides.

I do this laying on my back, the trouble light clamped in place and tapes with the foil method are carefully placed on pre drawn lines. After all is good I crank up the heater even higher for the ‘cure’.

Date:  05-20-2018

Number of Hours:  0

Manual Reference:  no ref

I hope you’ll excuse this post. I just want to get the strake pocket measurements documented as I’m about to cover it all up with the bottom strake skin. Please excuse this rather boring post.

Date:  05-19-2018

Number of Hours:  8

Manual Reference:  21-3

Today was floxing on the right bottom strake skin and adding boarder tapes. A big day.

I started off with more fitting of the skin. It needed a bit more off the very front baffle for the skin to get pretty close to matching the outboard end rib which in a perfect world will match my wing. Then I thought it would be an idea to have a rough template of where the ribs are. I’ll make four of these as I go. Perhaps if some time in the misty distant future I need to know rib placement for a repair, I’ll have these with the planes documentation.

Next was priming the joining surfaces which is a way of saying I bushed pure epoxy on both the skin and the rib framework it sits on.

Then it got a little ugly where I mixed way more flox that I should and put plenty on the top skin.

Next up was more flox on the rib and baffles, lots more. My idea here is I’m happy to waste a little and clean off the excess rather than have any areas starved of flox.

The top or rather bottom skin then went on as I had practiced and I weighted it down for the cure. It’s not going anywhere.

I’d previously worked out what length boarder tapes were needed. What I mean is that I wanted to tape the outer edges and do the flox skin on top thing in the one cure cycle. I really don’t want this thing to leak. So I made two ply 2.5″ wide BID tapes that go on all the outside boarders. That’s all the places a leak is possible. There are lots of inside tapes too but I’ll do those when the plane is right side up again. Its pretty challenging on your back adding flox and then tapes. My neck got a good workout.

In these shots you might see how I have tapes on the outer edges but not the internal yet. The tape is the shinny bit at the top of the pic. I just wiped the excess flox off those in between ribs and baffles, its the outside tapes that will do the work of sealing the tank. There were 10 of them and this part took some hours. I was careful using 2.5″ width rather than three inch I used previously for the hat tops. Three inches gives more error margin but its unnecessary weight so I made an effort this time. <grin>

Date:  05-18-2018

Number of Hours:  6

Manual Reference:  no ref

In correspondence with guys in the Garmin experimental division, ‘Steve’ pointed out that I had missed the significant length of the GMU11. He didn’t say anything about my work, just sent me the relevant pages in the install manual.  That manual is only 839 pages long and I didn’t know the GMU 11 was covered. I had looked at a previous version magnetometer install and just assumed the connectors were pretty standard. Oh no they are not. My carefully made pocket was about .5″ too short.

I could have cut into the D nose section in the LE but then it would have been a bit thin in that spot.  Hey, I had the heads up early, time to bite the bullet.

Yes I removed all the previous pocket work which took a couple of hours. Like a band-aid, best to just rip it off. I like mistakes in the rear vision mirror so best to get the correction done straight away. Then with a clean slate I measured for a while only to find to get the extra length comfortably, I’d be within an inch of the back wall. Might as well go all the way and eliminate a ‘back’ to the pocket. I could instead use the spar.

Structurally it made sense to do another rib type of addition. My pocket will be about 1.5″ longer than needed but overall I think this is a more elegant solution. I soon had a couple of pieces cut and fitted from my left over glassed foam. This was from when the baffles were cut out.

Here after using plenty of flox I added internal glass BID tapes and a bit of peel ply. The main work will be on the outside tapes. It they fail or have ‘pin holes’ this internal layup should prevent any leaking.

Here are the measurements. The docs say I need 6.31 inches absolute minimum for the magnetometer. So I have a bit of wiggle room to set it up. Some space also to bringing in a wire conduit with drama.

The next few hours were playing around with the ribs and baffles. I ensured all the mouse holes were smooth and that all the sides were sanded and cleaned. Above is a trial fitting of the ‘bottom’ right skin. It takes a bit of clamping but it does sit in place without doing any slits in the foam. I need a bit more fine tuning at the edges but I’m pretty close to floxing this guy in place. Maybe tomorrow.

 

Date:  05-17-2018

Number of Hours:  3

Manual Reference:  no ref

Time for a bit more glass on the magnetometer pocket. I do not want fuel to leak in here.

I’ve added flox corners here and a ply of BID to seal it.

Next was a bed of flox and then a ply of BID to all the internal corners and a bit of peel ply on the bottom just in case I have to bond something to mount the unit later.

Upper mouse holes was the next target. As the plane is inverted these seem to be on the bottom.

I hit these with the dremel. I’ll finish off when the plane is right side up but this is a very good start.

What I plan is to finish trimming these later. Then plug that hole in the hat tops up with a thin ply of glass. My idea is that when I flox the tops on I won’t be worried about filling in the mouse holes with dags of flox. I can just spread it evenly and drop the top on. If that makes no sense I’ll document it later as I do the work.

Date:  05-16-2018

Number of Hours:  5

Manual Reference:  no ref

A few things to tidy up today. My mouse holes arrived at an unexpected baffle rib intersection so that needed filling in.

I just floxed in this piece. I think these corner areas add a lot of strength so its easy enough to move a few mouse holes.

The next issue after some emails and back and forth was to admit that I needed a pocket in the strake for this Garmin GMU11 Magnetometer. It needs to live well away from stray magnetic influences that might be lurking in bolts and wires. Best to keep this guy well isolated.

Here’s the start of my pocket solution. I’m keeping the baffles the same as the rest and I’ll be going to town on tapes later to ensure its not going to leak fuel.

Lots of mouse holes sorted out for this bottom skin on both sides. Once cut I then cleaned out some of the foam, lined it with pure epoxy and then some thick micro and a bit of peel ply.

I think I have all the mouse holes I need now for the fuel to equalise quickly and not slosh around too much.