Probably a stupid fuel tank question

[Miotch]

Only tank I have that will fit in my Starduster and run inverted is an old Perfect profile wedge tank.   But I want to run both the fill and the vent line out of the bottom of the fuselage.  I've attached a drawing of what I'm doing.  My mind tells me this will work because the fill line is a fill line, unless inverted and then it is a vent line.  The vent line is a vent line unless inverted and then it is just a pipe with the bottom covered with fuel.  So, I'm thinking that bending tubing from the fill line around and having it exit the bottom of the plane should make no real difference.  This won't be a pattern plane.  Just a casual flyer (hopefully) I'd like the ability to fly inverted.  Yes I know I could buy another tank that I can make fit into the fuselage, but I'm stubbornly sticking to my "don't spend a penny on this plane" creed.  I can't believe I'd be the first person to try this, though, so I would like any opinions on whether or not this will work.  I've ran a whole lot of wedge tanks in my live, but never had a reason to route a fill line to the bottom of the fuselage.  Thanks !!

Edit: I now realize there may be a tiny bit of fuel in the bend of the fill line (which would act as a trap) when I go inverted, but would engine suction (Saito .56 not running muffler pressure) pull through this ??  I probably just think too much.

[Motorman]

Looks like it would siphon all the fuel out.

[Miotch]

Looks like it would siphon all the fuel out.

This is my understanding on how the tank is built.  Of course, since I started flying C/L around 1969, I've never actually taken a tank apart.

[Motorman]

Drawing looks right. Is your goal to avoid spilling fuel on top when filling? You could attach a length of fuel tubing on the top vent going over the side then remove it after filling.

[Miotch]

Avoid fuel spill/siphon onto top is part of it.  But the bigger part is that I simply want to avoid putting another hole in the top of the fuselage.

[Dan McEntee]

  What you have drawn as the "vent" is the overflow, and having that discharge out the bottom of the model will function but cap it off after filling. Install a tube some where that looks good that faces into the slipstream and connect that to the tube marked "fill". That will be your fill line and also becomes the actual vent. The air forced into the tube by forward flight and prop wash will help with venting and add a tinu bit of pressure to the tank. It will still lean out a bit as the tank gets below 1/2 way but not as bad.

   Type at you later,
    Dan McEntee

[Gerald Arana]

Only tank I have that will fit in my Starduster and run inverted is an old Perfect profile wedge tank.   But I want to run both the fill and the vent line out of the bottom of the fuselage.  I've attached a drawing of what I'm doing.  My mind tells me this will work because the fill line is a fill line, unless inverted and then it is a vent line.  The vent line is a vent line unless inverted and then it is just a pipe with the bottom covered with fuel.  So, I'm thinking that bending tubing from the fill line around and having it exit the bottom of the plane should make no real difference.  This won't be a pattern plane.  Just a casual flyer (hopefully) I'd like the ability to fly inverted.  Yes I know I could buy another tank that I can make fit into the fuselage, but I'm stubbornly sticking to my "don't spend a penny on this plane" creed.  I can't believe I'd be the first person to try this, though, so I would like any opinions on whether or not this will work.  I've ran a whole lot of wedge tanks in my live, but never had a reason to route a fill line to the bottom of the fuselage.  Thanks !!

Edit: I now realize there may be a tiny bit of fuel in the bend of the fill line (which would act as a trap) when I go inverted, but would engine suction (Saito .56 not running muffler pressure) pull through this ??  I probably just think too much.

That will work just fine with the fill line "plugged" for flight.

Cheers, Jerry

[Peter in Fairfax, VA]

Yes, that arrangement will kinda sorta work OK if the fill line is plugged after filling. 

Issues:

1.  If you don't plug the fill line, it will be a siphon arrangement.

2.  With the advised plugging, the vent will work OK flying right side up, the vent will be "dry," allowing atmospheric pressure above the fuel.

3.  Flying inverted, the vent will be "wet," sitting in the fuel.  In that case, air that enters will bubble in, which requires slightly more suction, influencing the mix lean to a greater or lesser extent.

4.  Typical designs either have a dry vent both upright and inverted (standard Perfect) or a wet vent all the time (uniflow.)

[Steve Helmick]

I keep thinking that a "Starduster" is a Sal Taibi free flight design. I built a 1/2a Starduster X, a Starduster 900, and I met the real Sal Taibi once or twice at Taft, CA. I'm also thinking that RSM kitted a stunter with a similar name, but RSM's website doesn't seem to be operational right now. Maybe that was the "Stardust", IDK.

Per the sketch, it'll siphon fuel for sure, unless securely capped. Also, I can't imagine a Perfect tank being the largest tank that will fit, yet still hold enough fuel for the 6-7 minutes or so kinda sorta needed. Even a 4 oz clunk tank would be better, IMO.  Steve

[Tim Wescott]

I keep thinking that a "Starduster" is a Sal Taibi free flight design.

And more... https://outerzone.co.uk/search/results.asp?keyword=starduster

[Miotch]

Also, I can't imagine a Perfect tank being the largest tank that will fit, yet still hold enough fuel for the 6-7 minutes or so kinda sorta needed. Even a 4 oz clunk tank would be better, IMO.  Steve

Oh, I could buy a tank that is larger and fit.  But part of my weird goal is to only use stuff I already have and not spend a dime on this plane.  None of my uniflows will fit and my clunk tanks are either too big or too small.  I have this 2.5 ounce tank or a rectangular 3 ounce tank to choose from that fit.  And the rectangular tank has two top fills and not plumbed for inverted.

This isn't the old time Starduster plane.  It is a scratch design Starduster Too I built to replicate the one dad built when I was a kid.  Here are some pics with photos of the plane I was trying to mimic

[Steve Helmick]

OH! THAT Starduster. I see you have a Saito, so fuel economy should be pretty good. Will you have throttle and a desire to land with the engine still running? Biplanes typically don't glide very far, but I think I'd opt for engine-out landings. The models I've seen (mostly Navy Carrier) look to be pretty twitchy on landing approach, and seems likely that's from propwash giving more elevator effect than expected and desired. Having it quit during final would be sketchy.  Steve

[Miotch]

OH! THAT Starduster. I see you have a Saito, so fuel economy should be pretty good. Will you have throttle and a desire to land with the engine still running? Biplanes typically don't glide very far, but I think I'd opt for engine-out landings. The models I've seen (mostly Navy Carrier) look to be pretty twitchy on landing approach, and seems likely that's from propwash giving more elevator effect than expected and desired. Having it quit during final would be sketchy.  Steve

I've never had a throttle on a C/L.  It's all I can do to make one that has two strings !! If it flies at all, it will either land in one piece or many pieces when the fuel runs out.  I'm hoping that it at least flies until it runs out of fuel.  Of course, I've perfected the art of taking a plane home in a very small trash bag, so that's always a possibility.