external fuel tanks

JBanes,
Please keep in mind those pressurized tanks you see were on bigger or more highly tuned engines than a Cox Reedie.

External tanks on Babe Bees (and similar) require drilling a hole through the tank side wall so the external tank line can be plugged on to the backplate fuel nipple inside the tank. That ruins the Bee tank and relegates it to being an awkward/fancy engine mount.
Babe Bee tanks are more expensive than regular backplates. You can install a regular backplate on your Bee. Then you can benchtest the "Bee" just like a "product" engine. Once done testing, switch the backplate out for your Babe Bee tank. Basically, tank vs backplate is an issue of convenience vs appearance.
Something to consider is that those Babe Bee, Golden Bee, Black Widow, Texaco engines can be difficult when it comes to sealing the tanks. Pickup lines inside the tanks can be positioned improperly, the sealing surfaces can be less than perfect causing leaks, and backplates can be deformed by heavy-handed installation trying to seal the whole assembly (or just due to old age/repetitive maintenance).

Do you have a particular model in mind? What engine and tank are you planning to run? Is this plane "Freeflight," RC, or CL (Control Line)? Even just bench testing will require considerations that will not necessarily work on your airframe. That's why som test jigs have adjustable fuel tank mounts.

Generally you want the tank as close to the engine as possible, and centered on the spraybar. You don't want to gravity feed (no float in the venturi, or air inlet like a car or motorcycle carb), nor do you want to pump uphill. Also try to kee Ifthe tank inline behind the engine, and not outboard of the engine with respect to your flying circle.If it is outboard, you will most likely wind up pumping (muffler, bladder, or crankcase pressure) against g-forces trying to pump inward towards the engine. A lot of the older British plans  show the tank cut into the fuselage so that the "center mass" of the tank is on (or inboard) of the fuselage/engine centerline.

For most 1/2A (little) engines, you shouldn't need a pressurized fuel system. But if you are talking high-end rotary valve engines, then pressurized fuel is recommended. Examples would be Cox Tee Dee's, Norvel AMEs, AP Wasps.

I have a profile DH Mosquito model. The first tanks were one-ounce beauties just barely outboard of the engines, and on top of the flat-plate wings. They were normally vented (to atmosphere). I could never get both engines running because either one, or both would gravity feed and flood out before I could get them running cleanly.
I got both engines running just fine once I built built.smaller, thinner (heightwise) tanks that sat just behind the engines. I did leverage muffler pressure to ensure the fuel pumped inward to the engines once the plane was flying. The failed tanks are early in the thread, the good ones are later. Keep in mind this is a bigger, heavier plane with bigger engines.
I did two-line tanks.to avoid having to play with vent caps, so my fueling process is a small pain (I can describe that if you wish).
https://www.coxengineforum.com/t10666-bhm-mosquito-in-ms-build?highlight=BHM+Mosquito.

That P-40 I emailed you the picture of has the wedge tank mounted so the fuel pickup was a smidge lower than I wanted, but that was because where it was mounted on  the fusleage prevented me from mounting the tank higher. Another 3/16" higher would have been ideal, but goofy looking. Also check out how the outboard edge of the tank was about an inch outboard of the centerline of the engine/venturi. If I rotated the engine so the cylinder was horizontal, then the tank would have been just a smidge high because the venturi would have been positioned lower than the tank. The venturi would have been more inline with the outboard edge of the tank too, requiring less pressure to fees the engine.

Everything on these little engines/models is about balancing  limitations against desires. Keep asking questions!

You only need a very smal hole in the tank on a babe bee (it can be sealed up later with JB-weld in order to be reversible). The reward is much longer and more stable runs.

Here is one I did +30 years ago....

Now that is quite the neat muffler/exhaust there. Looks 'steampunk'. I am guessing that that exhaust was done that way for a specific application? Or was it just a fun project?

As Kris said. Just fill the external tank, fill the regular Bee tank. Hook up the feed line from your external tank to the Bee. You can then also top up the fuel line between the two by adding a bit more fuel through the remaining 'open' nipple, then cap it off with a small piece of fuel tubing that is plugged and let er rip. I see that Kris mentions that it will draw the fuel through the line, and will work fine also if he said. I had just personally filled the line as well. I will post a picture later as I just got to work so will do so later on when I get home.

Sorry, I am having trouble finding the picture right now. Anyways, again, just hook one line of teh Babe Bee to the external tank fuel line. You can fill the big tank first then hook up to the Bee, or hook it up and fill both through the other nipple on the backplate. Once full, keep the vent line on the external tank open and plug the second line on the Bee. Again, if I come across the picture, I will post it for you.

NEW222 wrote:Sorry, I am having trouble finding the picture right now. Anyways, again, just hook one line of teh Babe Bee to the external tank fuel line. You can fill the big tank first then hook up to the Bee, or hook it up and fill both through the other nipple on the backplate. Once full, keep the vent line on the external tank open and plug the second line on the Bee. Again, if I come across the picture, I will post it for you.

I did a set up like that several years ago...worked fine, though I have yet to try it on a plane: