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Wing Fuel Lines – Folding Wing Option – A Question
Currently I am building a CH 750 with the Folding Wing Option. Limited space means that I must complete the wings before I move on to the fuselage. Following some earlier advice from builders who have completed their building, I am seriously considering getting some braided fuel lines made up to replace the 3/8 inch ,heavy, plain black rubber lines supplied with the kit. I have reached the point where I have completed the building of the wing skeletons, lower wing skins, wing fold hinge, etc, and the only thing remaining is to incorporate the fuel tanks and connect with fuel lines – before closing the upper skins. In looking at photos on the Zenithair website and the FWO drawings I can see that when the wings are folded they move out and are supported on a cross tube. No where can I find pictures or drawings showing the positioning of the fuel lines when the wings are in this folded position. My concern is this – it seems that I need to build in some extra length of line somewhere. My question is this. Do the fuel lines have to ‘pull out’ of the fuselage (and therefore have to have extra length incorporated inside the fuselage) or do they have to somehow coil within the trailing edge/wing root area? Any advice will be much appreciated. Tony Oliver, Essex, United Kingdom
Replies to This Discussion
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Permalink Reply by Rusty King on
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I just found this post. Obviously no responses, but I wonder how you did yours. I am puzzling over this and it is a valid and interesting question. I suppose my fuel line slack will come from the wing area. Another question would be how are people dealing with the uprights for fuel lines? Are holes being placed in the back to help with installation and/or inspections? I know from discussions with Caleb that it's frowned on to drill any hole in the spar pickup, but wondering about the uprights?
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Permalink Reply by John Austin on
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Rusty,
The uprights seem rather substantial (my fuselage is built to Ed. 2 specs, but my wings and max gross wt are Ed. 1) but I don't remember if they were beefed-up for Ed. 2 or not. I did not run this by Caleb by I did consult with my A&P friend very experienced in aluminum airframe construction and elected to cut an ovoid hole (ovoid to accomodate the limited bend radius of the fuel line) in the side channel cover and lined it with grommet edging (Spruce). Although the braided stainless is very stiff and I have the pitot-static lines running alongside the fuel line, I still worried about fretting or chafing. Of course, the stainless would eat the aluminum channel and not the other way around! But, to be extra careful - I slid a piece of plastic corrugated loom over the braided line to further restrict it's movement in the channel and provide a barrier to chafing or fretting. I also protected the end of the channel at the bottom where the fuel line exits to prevent chafing in that area. It's really quite rigid being fixed at the top by the bulkhead fitting and at the bottom by an Adel clamp in fuselage floor, but figure you can't be too careful!
John
N750A
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John, that is exactly what I was looking for. I have the safe-air kit also.
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The Safe-Air connectors make the pitot-static connection easy. I just slid the lines from the wing through grommeted holes in the fuselage and plugged them into the connectors. They can be easily detached from the connectors if the wing ever has to be removed. You can also see the black wire loom around the nav/strobe/fuel sender wiring. It goes through a grommeted hole in the fuselage sidewall to a weather-sealed mulit-pin connector that easily disconnects. Inside the fuselage, the wiring from the left crosses through the top cross-member to the right side, where it joins up with the right nav/strobe/fuel wiring and then down the side channel with the right braided stainless fuel line. I did not interconnect the tanks with a fuel line, but can select "left, right, both, or off" with the Andair fuel selector.
I really like the concealed lines and wiring - you just have to remember they're "in there" and can't in the future go willy-nilly drilling holes in those structures!
I have zero experience with the folding wings, but I think it will be fairly difficult to get more than a few inches of slack AN6 stainless braided line within the wing. The lines come out of the tanks at the rear and have to pass through the rear spar to the TE. You're very limited to hole size in the rear spar (can't remember what Caleb told me - best check with him). In fact, to keep the hole size down, I passed the line through the rear spar and then installed the larger-diameter fitting. Much easier to install them on the bench, but it's do-able off the bench on the wing! Consequently, the only place for the slack to flex back into the wing is in the TE and there's not that much room. Looks like either put an access panel (and a cut-off valve) in the TE and disconnect the line there before folding OR if you don't want to disconnect the line, pass the line into the fuselage and perhaps construct a tray or channel just below the roof for the slack fuel line to slide inboard and form a horizontal loop laying on the tray - I don't think you'd want a loop just "dangling" vertically !
John
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Permalink Reply by Paul Bonasera on
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you will have to disconnect the fuel lines when you fold the wings. if you put any slack that can form a loop when you have the wing installed then you may loose fuel flow. also the tanks will have to be drained or the caps will need to be sealed so fuel won't drain out in the folded position.
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Permalink Reply by Mark Maltais on
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The folding wing "option" for the 750 is pretty sad. Seems like it was designed as an afterthought to compete with other kits. I looked into it and decided against it. Folding wings and letting them drag on the ground? I'd rather just take them off. Might be an option if you have a hangar and a paved runway to drag them on, but for the bush? Nah.
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I have given thought to redesigning the folding wing option but have not decided to invest the time, at least for now, or if it is even reasonably possible considering the 750 design. Key word here being reasonable. I agree that the current wing fold design leaves much to be desired. I have all the materials to weld it up per plans, except mine will be made of titanium...super duper lite weight. I really want the ability to remove the wings but I am having second thoughts about adding the draggy and bulky device.
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