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rtfm

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Hi,
I have a 6m length of 20mm OD, 3mm wall thickness 6061-T6 in the workshop. Would this be useful for the two bottom struts which are in tension upon landing? I'm assuming that it wouldn't be suitable for the top strut which is in compression.

I could, of course, buy some round tubing and use it for all the struts. From what I've seen on other light planes, about 25mm OD seems about right? One of the guys here suggested crushing hard PVC pipe into an airfoil shape and slipping it over the tubes.

Just a thought.

Duncan
 

rotax618

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If you are going to use tubes, they should be steel. Take a look at the Minimax/Himax UC, it is simple ply oner a triangular wood frame, attached to the fuselage with butt hinges, steel axle tube with a couple of angles bolted to each end - no weldingF7DA58D8-0870-4EFD-93F6-D0E24E5D338C.jpeg
 

rtfm

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Mmmm OK. Steel is fine. I think I have a set of Aeromax plans - I'll take a look and see what guage steel they use (I'm hoping they also use a similar undercarriage construction.)
 

rtfm

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I found this detail of the landing gear:
1626424087899.png
So I'm now looking for 1: OD x .095 4130 steel tube. Shouldn't be a problem...

Thanks for the tip - I'd forgotten I have some plans in the shed. This is from the 1700 HiMax

Duncan
 

rotax618

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We had to sleeve the end of the UC cross tube down to 3/4”, more common wheel bearing size (Drifter wheels) on the Himax we built. Wheel barrow wheels have 1” bearings (most are nylon - don’t use) - the rollers in the other wheelbarrow wheels are not hardened, they have to be replace.
 

sming

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Have you considered fiberglass? Like here: Sujet 2
Simple mold ( but you have a cnc ), wrap uni fg tape... not too hard?
 

WonderousMountain

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I would say that an aircraft of the fleabike weight with large balloon tires, the suspension is completely unnecessary.
Thicis a quality point, many of us WILL get carried away given the option.

Plus one on Ferrous Alloy, you need plastic deformation prior to collapse.
 

rtfm

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We had to sleeve the end of the UC cross tube down to 3/4”, more common wheel bearing size (Drifter wheels) on the Himax we built. Wheel barrow wheels have 1” bearings (most are nylon - don’t use) - the rollers in the other wheelbarrow wheels are not hardened, they have to be replace.
I bought a set of BlackMax brakes with matching wheels and axels. So I should be OK.

Duncan
 

rtfm

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Questions:
I have built the first rough prototype of the gas tank out of 3mm MDF held together with masking tape, and it fits! Ta-Daaa! Well, it's a bit snug, to be honest, so today I'm going to cut prototype #2 out of 9mm MDF, and screw it together. If that is OK, I'll commit to 9mm ply.

Question #1: What hardware do I need to include? I've been to the marine supply stores (online) and there are so many filler caps, it's hard to choose. I will have a transparent tube on the outside of the fuselage to show fuel depth, but what about fuel pumps? Is it as simple as fitting a pipe and running it to an external pump (there's plenty of space behind the engine)

Question #2: What do I seal the tank with? I've seen videos online of a guy building a fuel tank for his boat, and he seals the inside with epoxy (West). However, I've also read that I need to use vinyl ester resin. The problem with vinyl ester is that (apparently) it doesn't bind well to vinyl ester. My plan is to cut the individual sheets, glass the inside surfaces, wait for them to cure, clean up the edges, and then bond/screw all sides together, and apply a fillet. Thoughts?

Regards,
Duncan
 

TiPi

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Question #1: What hardware do I need to include? I've been to the marine supply stores (online) and there are so many filler caps, it's hard to choose. I will have a transparent tube on the outside of the fuselage to show fuel depth, but what about fuel pumps? Is it as simple as fitting a pipe and running it to an external pump (there's plenty of space behind the engine)
Duncan,

You should build a sump into the tank, lowest point with a drain valve.
The fuel pickup needs to be an accessible strainer (ala motor bike taps), agin in a location where there is no chance of picking up air if climbing or side-slipping.
The fuel pump can be a pulse pump driven by the engine crankcase. Will need to be located very close to the engine (pulse line < 25cm) and is not good at lifting fuel.
Electric fuel pump (Goss/Facet) with 2-3psi max as primary or backup.
 

Topaz

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Make sure either your cap or your fuel tank are vented. We have much more pressure variation than boats, enough on a steep descent to crush the tank right inside the airplane. It's easiest if you can just get a vented cap.
 

TiPi

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You mean something like this?
View attachment 113158
or like this (Curtis valve). The outlet needs to be at the lowest point, your valve would need to be installed vertical.
1626482108015.png

And this for the fuel outlet. The SD-1 uses a motorbike style tap with strainer, the strainer comes out when unscrewing the tap.
1626482239944.png
 

rtfm

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My fuel tank is a weird shape
1626608784757.png
Constructing this is proving to be a nightmare, so I created a flat-pack, which looks like this. Sketchup can't do this, so I had to do it by hand. I'll cut it tomorrow. Basically, I'll epoxy tape along all folding seams (red lines), and bend everything together when the epoxy is in the green stage. The top is a separate piece, to allow me to reach inside and apply the fillets. Then bond the top on. If this works, I'll commit to 9mm ply.
1626609553754.png
I have yet to find anything definitive regarding West Systems epoxy and fuel tanks (I don't plan to use ethanol-fuel). Vinyl ester worries me, because it looks like I'll have to do the complete layup on the inside in one go (including the fillets) because VE doesn't stick to VE very well.

However, I've discovered that 747 Polyester is about as gas, ethanol, diesel etc proof as one can get, and it isn't expensive. If I can find some locally, I'll go with that.

Duncan
 

Angusnofangus

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Victoria, Canada
My fuel tank is a weird shape
View attachment 113224
Constructing this is proving to be a nightmare, so I created a flat-pack, which looks like this. Sketchup can't do this, so I had to do it by hand. I'll cut it tomorrow. Basically, I'll epoxy tape along all folding seams (red lines), and bend everything together when the epoxy is in the green stage. The top is a separate piece, to allow me to reach inside and apply the fillets. Then bond the top on. If this works, I'll commit to 9mm ply.
View attachment 113226
I have yet to find anything definitive regarding West Systems epoxy and fuel tanks (I don't plan to use ethanol-fuel). Vinyl ester worries me, because it looks like I'll have to do the complete layup on the inside in one go (including the fillets) because VE doesn't stick to VE very well.

However, I've discovered that 747 Polyester is about as gas, ethanol, diesel etc proof as one can get, and it isn't expensive. If I can find some locally, I'll go with that.

Duncan
Seeing as how you already have the shape and basic bend lines, why not make this out of aluminum? Use 6061-T6, maybe .063, and then weld the seams. I don't think it would be heavier that plywood.
 

Hot Wings

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I don't think it would be heavier that plywood.
But it would be a lot more fuel proof.
If he doesn't like to weld a few 90 degree angles made of the same thickness aluminum then pop riveted with some polysulfide sealant (Pro-Seal) should work?

He can probably cut the thin aluminum on his CNC without too much trouble.
 
Last edited:

rotax618

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Good design shouldn't be a lot of afterthoughts cobbled together. There are several basic things a powered aircraft needs, a fuel tank is one of them. Surely you considered the shape, placement, material and construction of this before you got this far. Duncan, before you waste any more effort, materials and money, Stop and finish a workable design and consider how you are going to build it and from what materials.
 

rotax618

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A plywood fuel tank is not an award winning idea, the only use I could see is to use light ply as a permanent in-situ mould. I would make the ply bottom and sides out of say 3mm ply, since you have a CNC you could finger joint it to make it easier to assemble. Fillet the inside corners with micros, lay up glass/vinylester/epoxy inside to a thickness that provides the necessary strength with any baffles sumps etc, form inward flanges at the top, lay up a glass/resin top, fit the filler/fuel gauge, glue and rivet it to the flanges. Looks like a coffin.1E65BA1C-2FC5-4D45-9103-4DA4A14A54D2.jpeg
 
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