Fuel tank on scale project

[Gary Dowler]

PICTURE POSTED WRONG. Imagine it rotated 90 deg clockwise!

Close to committing to a fuel tank on my PT-26. Scale, so no need for uniflow.  Tail dragger that will be required to taxi at the end of the flight when fuel will be low.  My tank bay is able to fit a tank that is 3" long. Don't need a big tank, 3oz with this FP will suffice.
Y concern is fuel pickup at the end while doing the taxi and stop then shutdown. Plastic tanks are too long. A metal tank with a clunk might work.  Then I had another idea.
A wedge tank set at a slight angle with the pick up being on the low side. See sketch.


Ideas? Suggestions?  I want to keep it small as practical to keep weight down, but again I need reliable fuel pick up on the ground at low speed or stopped when fuel level is low.


Funny, just looked at my post and the drawing is posted 90 deg wrong!  How do I correct this? Needs to turn 90 deg clockwise.
Gary

[Trostle]

Here is my experience with tanks for CL Scale.  I have had success with this approach.

First - Are you planning to do a series of maneuver like loops, figure 8's, inverted flight, wingovers - those maneuvers allowed by the CL Scale rules?  If so, then you might need a wedge tank.  The problem you will have with a wedge tank is that at the end of the flight for the taxi and throttle demonstration, the fuel pickup will uncover and starve the engine of fuel.  Then you might want to use the approach you outline.  However, you have better alternatives than your "sidewise tank" mount idea.

An idea, but one I do not recommend is to use install the wedge tank as on a stunt ship, make it big enough so that at the end of the flight, the fuel pickup tube does not uncover at the end of the flight.  In other words, you will still have a tank the is still about half full after the landing, but with a tail dragger, there will still be fuel to the pick up.

There two better approaches.  Either way, I strongly recommend that you use a uniflow system.

1.  Use a clunk tank,  then the fuel pick up will always be where the fuel is.  For a "stuntable" scale, use a cylindrical tank clunk tank, set up for uniflow, just like used on a stunt ship.  There is material on this forum you can search on this.  You essentially have a stunt ship fuel system that will work throughout the flight, including the taxi to engine shutoff.

2.  If you are not planning to try to do an entire stunt pattern, which would not do you any good anyway because most of the CLPA maneuvers are not in the scale rule book anyway, what I have used is a square tank with the fuel pick up on the bottom outside corner of the tank and the uniflow tube just forward of that still on the bottom of the tank.  Even this will allow you to do the basic maneuvers listed in the scale flight rules, like a wingover, a simple loop, a figure eight, the wavy flight thing.  The tank/uniflow system will still function, though I would recommend not to do extended inverted flight (not required anyway for inverted flight) towards the end of the flight.

Remember, if you are doing a series of manuevers, the rules only allow 6 options.  If you have a throttle, then you do not need very many maneuvering flight options.  You can do a touch and go, taxi, throttle demonstration, so you only need, at most, 3 maneuvering options.  If you do the maneuvers early in the flight and with this flat bottom tank, the fuel will still cover the pick up.  Then for your touch and go, landing, and taxi, the fuel will still cover the pick up tube and the uniflow will still function.  Yes, you will still want to have fuel in the tank at the end of the flight through to the engine shut off.  The uniflow venting makes this approach work.

No matter what your approach is, use a uniflow venting system.  This helps to get a consistent run though out the flight, regardless of the tank configuration.

Keith

[Gary Dowler]

Hi Keith.  Great reply.  By the way, my pic posted wrong, its off 90 deg.  Should be rotated 90 deg clockwise.  No, there will be no aerobatics of any sort with this one.  The PT-26 was a simple, low wing, 2 seat primary trainer.  It was not an acrobat of a plane.  The only maneuvers will consist of the required 10 laps of level flight, then options like a couple laps at a high angle, slow flight with flaps down, touch & go, then land, taxi, stop, shutdown.  No steep climbs, no inverted, etc.

Gary

[Tim Wescott]

Gary, you didn't mention whether you felt comfortable building a tank from scratch.  I like building tanks, so I would build a tank to fit into the available hole, either arranged like Keith recommends, or with a clunk if there's room.

There was a thread recently that was either about modifying tanks or turned into being about modifying tanks.  Apparently you can cut up a plastic clunk tank and weld it back together with a soldering iron.  I have not tried this, so I have no opinion on how well it would work -- but it's something to think about.

[Gary Dowler]

Gary, you didn't mention whether you felt comfortable building a tank from scratch.  I like building tanks, so I would build a tank to fit into the available hole, either arranged like Keith recommends, or with a clunk if there's room.

There was a thread recently that was either about modifying tanks or turned into being about modifying tanks.  Apparently you can cut up a plastic clunk tank and weld it back together with a soldering iron.  I have not tried this, so I have no opinion on how well it would work -- but it's something to think about.

Hi Tim.  Yes, Ive built a couple of tanks and this is indeed an option.   A tank building question though for the experienced tank builders.  Ive heard of a few people building metal tanks and rather than soldier, using JB Weld to assemble them.  Anyone here ever tried this method? Results?

Gary

[Peter Grabenstein]

I would say JB Weld is for sure NOT fuel proof.
I use "Stay Brite" for soldering tanks.

 
Peter

[Dave Harmon]

Ive heard of a few people building metal tanks and rather than soldier, using JB Weld to assemble them.  Anyone here ever tried this method? Results?

Gary

Gary.....I have used JB Weld...the slow stuff.
I found a stash of tanks that were NIB but decades old so I took off the back cover, replaced the tubes with aluminum tubes and glued them in.
I should have used copper tubes but were not available locally at the time.
Five years later...the JBW is still good and no leaks.
This is with 25% nitro fuel.

[Tim Wescott]

JB Weld really stinks when it touches the soldering iron, so I prefer real solder.  You don't have to use anything fancy -- plain old rosin-core soft solder should work well (I haven't tried the fancy new lead-free stuff yet, but will probably be forced to before I die).

[Trostle]

Hi Keith.  Great reply.  By the way, my pic posted wrong, its off 90 deg.  Should be rotated 90 deg clockwise.  No, there will be no aerobatics of any sort with this one.  The PT-26 was a simple, low wing, 2 seat primary trainer.  It was not an acrobat of a plane.  The only maneuvers will consist of the required 10 laps of level flight, then options like a couple laps at a high angle, slow flight with flaps down, touch & go, then land, taxi, stop, shutdown.  No steep climbs, no inverted, etc.

Gary

Gary,

So, with that flight plan, I would strongly recommend a square tank with the pick up on the bottom at the rear and the uniflow vent just forward of that, still on the bottom of the tank.  You could used muffler pressure to the uniflow vent, or just vent the uniflow from the atmosphere in a position that makes sense, particularly so that it does not drain the tank prior to starting the engine. 

I have used this approach on a number of successful competition scale models without muffler pressure.  Just remember to have a tank large enough so that there is residual fuel to get through all of the maneuver, the taxi, through the engine shut off to keep the fuel pick up covered with fuel to that point.  The uniflow helps assure consistent engine runs, even with constant use of the throttle.

I have also used uniflow clunk tanks with success on a four engine scale model for the Tuscon 1/2A multi-engine scale contest and on another twin model flown at this same contest venue as well as a third place with that model in the profile event at the Nats.

Keith

[John Rist]

I have had good results with a RC style clunk tank on muffler presser.  Good to the last drop of fuel.      Much easier to set up than a custom built uniflow tank.