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Tom Baker

Fuel Sight Tubes

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I maintain several CT's, and I have done plenty of 2 year wing inspections. I buy my fuel sight tubes from Flight Design USA. I try to keep some on hand, and I used to just toss them in my parts box just like they were shipped. Almost always when installing the tubes there would be a spot where the tube would pinch off a little. It is not enough to keep it from working like it is supposed to, but being somewhat of a perfectionist I didn't like it.

I have changed the way I am storing the piece of sight tube that is in queue to be installed next. I am slipping it over a piece of coiled 1/4" tubing. A little silicone spray helps it slide in place easier. It slides off pretty easy. Just remove it from the tubing, cut to length, and install.

Another tip is that I slide the tube over the bulkhead fittings and place a witness mark on the sight tube. This way I know it is fully seated when I tighten the clamps.

sight tube.jpg

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Another way: use heat to shape the tube. Though it takes some skill to get right, too much and it melts or burns, too little and it still kinks when you go to put it on.

Warning: Keep that hot air gun far away from the fuel tank!

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I haven't had any issues. I have found if you have a slight pinched down spot it is caused by the length of the tube you cut. Usually too short. That said a slightly restricted spot isn't an issue since this just shows a gravity induced level and not a flow. and always install it in the direction of the tube coils natural bend. 

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1 hour ago, Roger Lee said:

I haven't had any issues. I have found if you have a slight pinched down spot it is caused by the length of the tube you cut. Usually too short. That said a slightly restricted spot isn't an issue since this just shows a gravity induced level and not a flow. and always install it in the direction of the tube coils natural bend. 

I know it doesn't cause any issue other than it doesn't look nice. I have tried long and short lengths, and many in between still with kinking issues. This method seems to be providing a nice clean looking installation.

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Use different hose. Mine never have pinch points and I use Ace Aviation poly. If yours has a pinch point cut a new piece 1" longer.

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1 hour ago, Roger Lee said:

Use different hose. Mine never have pinch points and I use Ace Aviation poly. If yours has a pinch point cut a new piece 1" longer.

 Roger, it is not a debate about which hose to use. I was simply passing along a tip that might be useful to others.

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Is there a video or instructional on changing the tubes in place without wing removal. I’ve read it can be done but is tricky and takes special technique! 

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1 hour ago, Buckaroo said:

Is there a video or instructional on changing the tubes in place without wing removal. I’ve read it can be done but is tricky and takes special technique! 

You should be pulling the wings every couple of years anyway, once they are out a bit the tubes are a cinch to change.  Just plan on changing them out with every wing pull.  

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Is there a video anywhere that can guide my AP removing the wings? I heard it’s easy but I can’t find a clear step by step instructional.

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Trying to change the fuel sight tubes with the wings  in place is not only a challenge, but a royal PITA. I wouldn’t do it either.  The opening to the sight tubes is too small and at the wrong angles to make this a viable solution. 

Like everyone said just do it at the wing pull and then it’s easy.

Wing pull:

Drain all fuel out the gas collator with the bottom cup of the gascolator off. You need two wing supports. If you allow the wings to fall it will damage your roof. You can use two 6’ ladders with a thin padding under each wing BEFORE you pull the main spar pins. Remove the nut and bolt to the ailerons just back behind the wing spar channel on each side. The ailerons will fall unless someone holds them or you slowly let the swivel bracket down with your fingers.  Remove the fuel hose that comes out of the fuel bulkhead just below the fuel sight tube. Remove the wing spar pin retaining caps.  Now make sure the ladders are in place and have someone hold the flaps because when you pull the pins and slide the wing out the flaps will fall. So long as the ladders are in place or at least someone is holding the wings up you can pull the spar pins.  Now you can slide each wing out. Some slide easy and some need to be wiggled and pulled harder. As you pull the wings have the person holding the flap guide the wires out and any tubing so they don’t get hung up and you break them. Now you can let the wings sit on the ladders. They won’t fall off so long as some of the spar is in its channel that will keep the wing from twisting and falling. 

Now do your inspection and change the sight tubes. Then reverse this process. Have someone lift the flap up to guide it into its slot. Have someone lift the aileron up in position when ready to.

this should get you through it. There are other little tips, but aren’t really needed for your first time. Your welcome to call me if you want more help.

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I did this based on Roger's instructions for the first time over the winter, it was easy.

PRO TIP:  Put one wing on the ladder and have your buddy hold the other wing tip up until the spar pins are out.  If you try to put ladders under both wings before pulling the spar pins out, the geometry is all wrong and both ladders won't fit under the airplane.  Ask me how I know...

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It is easier to have one person hold the wing especially when putting them back in. That person out on the wing tip when both wings are fully in can raise or lower the wing some which helps align the spar pin holes. I use a modified engine hoist to raise and lower the wing to align holes since I’m usually by myself. Makes it easier to line the flaps up to.

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I'll throw a couple things out. 

1. 6' ladders are to tall in my opinion. 5' ladders with solid insulation type foam for shims works better. You can adjust to just the right height by adding or removing shims or moving the ladder in or out. I have a fiberglass ladder that is just right, and a wooden ladder that I cut the legs off to make it just right. Another thing you can do if the ladders are just a little to tall is run the wheels up on some foam or wood blocks to raise the airplane.

2. I do this while I am waiting on fuel to drain. I use duct tape across the hinge line, 1 for each aileron and 2 for each flap, to hold the flaps and ailerons from falling. It makes removing and installing the aileron bell crank bolt easier, and the flaps stay automatically lined up.

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Roger and others thank you very much for this post. I’ll be studying this along with my A&P. I wish there was a video of this as tinkering with wings is intimidating to me. 

Roger thanks for the call offer! I may need this help! 👋🏻

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With respect I know Roger is a wizard but I would not do this without having three people. Also you only need to pull the wings a few inches out.

Be careful not to damage the poly tube, it is easy to disconnect if you want by undoing the blue nut but you wont need to if you only pull the wings out a bit.

Same with the wires. When reinstalling remember to lube and align the ball socket at the front of the wing cause ya need to lift the wing up at the front to align it. 

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3 hours ago, ct9000 said:

With respect I know Roger is a wizard but I would not do this without having three people. Also you only need to pull the wings a few inches out.

Be careful not to damage the poly tube, it is easy to disconnect if you want by undoing the blue nut but you wont need to if you only pull the wings out a bit.

Same with the wires. When reinstalling remember to lube and align the ball socket at the front of the wing cause ya need to lift the wing up at the front to align it. 

I always used to try and have 3 people, but have gotten to the point that I do it with 2 most of the time now.

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With my engine hoist mod I can do it by myself. I will say having the second set of hands does make it easier and faster.

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Practice makes the job easier,  and so does a tool I made by turning a taper on a brass tractor pin to use to pull into line the last bit of alignment,  by hand of course.

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I have changed my sight tubes without removing the wings. Just to see what was involved.

As I recall I had to find a really small ratcheting wrench with a head that angled, and I modified some other tool that I can't remember.

It was slow, frustrating work that, in the end, probably took as long as it would have taken to remove the wings. And as a side benefit, it'll give you a nifty pain in your neck and back before you are done.

So, it is doable but not recommended.

There ought to be a modification to install a glass sight tube like cubs have. That way it would be once and done.

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Simple push button LED array from Harbor Freight flashlight velcro behind sight tube. You won't have to change the sight tubes as often.

Larry

PICT5448.JPG

PICT5495.JPG

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I use 2" blue painter's tape at the aileron and flap ends to keep them from falling as Tom does.  Two ladders and three people best for the novice wing pullers.  I also work with the natural curl of the sight tubes to keep from kinking, as Roger says but Tom's method of "training" the hoses on the curled metal tubing is good.  I also use 9/16 OD x 1/2 ID hose and not the thicker 7/8 x 1/2 hose and size seems to matter to me (:)). I put a mark on my bench to use to cut new hose to a length that seems to keep it from kinking.   How about putting a section of door spring inside the tubes, like some of us do for the oil and water hoses, so they don't kink?  I know, some will say the spring coils will prevent seeing the fuel level - can't keep everyone happy!

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I was thinking of installing some type of small mirror device for the left one. My wife gets nervous when I start cranking my neck around trying to read the left sight. 😁

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If the sight tube hose is too short it will pinch no matter what. All the hose I have ever purchased off a roll has its own natural curl. I install it in its own natural curl state. 

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