How ared you getting enough flight time with a 4 oz tank and LA46?

I am considering an experiment to install a 4 oz Sullivan rectangular slant 'flex-type' clunk tank on my Vector40 (inverted engine).

Reason: I currently run a Brodak 4 oz uniflow wide-wedge metal tank on my model and have been running with muffler pressure. My model uses a stock OS 46LA w/ stock muffler.  Current setup runs pretty well with the only real issue being unequal (slightly slower) lap time when inverted. For equal inverted time, it seems that I need to raise the tank slightly, but cannot because the current metal tank is up against the underside of the maple motor mounts.

I wanted to try a clunk tank set up for uniflow. I have a Sullivan 4 oz slant rectangular flex tank that fits well in the tank bay area w/ plenty of room for the fuel tubing. Sullivan also makes a rigid slant tank, but I would have to trim the cowl slightly to allow the rigid tank to fit (not really an issue if needed). (FYI, the Sullivan rectangular flex tank is 2" wide, 3-1/2" long and 1-3/8" tall)

My current plan is to set up the clunk tank for uniflow with the ability to adjust the uniflow exit up or down as needed for equal lap times.

So, I guess my questions are:

1. Uniflow exit point at around 1" from the back of the clunk. Is this OK? (Clunk tank is 3.5" long)

2. Not sure if muffler pressure heat will have a negative effect on the tank softer flex material. As an alternative, stay away from muffler pressure and just use ram air pressure from the foreword facing open vent line.

3. Any fatal flaws in the concept above.

4. Any other issues I should be aware of?

Thanks in advance.

Sure, it works. Here's a picture of another Vector 40 ARF that I "adopted" and rebuilt the nose on. Sullivan square nose "flexi tank" sitting on the bearers. If you have the patience to carefully bend the tubing I don't immediately see why you couldn't get a slant front to work, but the fuel will get more of a rollercoaster ride. I have the uniflow about 1" back from the front of my tank. It works fine on this and several other installations I've tested. Twist the uniflow tube for tuning the tank. Don't twist the whole cork or you risk screwing up the clunk clearances in the tank. That also messes up your overflow tube position. I wouldn't put a clunk on the uniflow. I tried that and didn't like it. One thing to watch is whether the in situ tip of the uniflow tube is correct after you have it installed in the plane. It is real easy to squeeze one of these tanks trying to push it into place and either twist the uniflow tube in the cork, or end up with the uniflow tube pressed up against the side of the tank and causing a restriction.

Don't worry about any heat effects on the Sullivan tank from running pressure. It is miniscule. I've done it with no problem. So try both ram air pressure and muffler pressure and see which one runs better for your specific setup. But reset the needle after making either change.

I had a similar setup in an ARF Nobler. It worked fine. The current setup I'm running on a modified Twister has an OS .46LA (with a hard tank) is pretty thirsty, and I'm getting only about 5:30 for ~4-7/8 oz. So things vary a bit engine to engine. You will likely end up short of time for a full pattern with just the 4 oz. unless you are running a small venturi. And that (and the stock muffler) can make the  tuning a bit more finicky. Still, it's an OS .46LA, one of the sweethearts of sport flying.

On a marginal tank, you can play the game with less nitro and less oil. Less nitro since the .46LA is overkill for the Vector 40. Less oil means less margin of safety on settings and unexpected problems (pressure line blows off, etc.)  The OS electroless nickel isn't always the most robust. (We can have that internet war again, I suppose, or we could just put links to the past battles of documented issues....) My thought would be run a safe fuel while you get all your tank issues sorted out. If you aren't close on time, try a smaller venturi and less nitro and see if you still have adequate power and are not overheating. If that looks good, then try dropping the oil to something like 18% and see if you can still get an easy needle, no overheating and no metal coming out your exhaust pipe.

You can shim the engine if you don't have far to go and you're not worried about spinner/cowling alignment. On my Vector, the fit is quite close and I chose to use a more adjustable tank rather that live with the spinner offset.

This is all just my personal opinion. Lots of others will (likely) disagree. That's ok--if what they are doing is working for them, great! There's more than one way to do most of this.

Dave

  I would not put the slant in that direction. look at the difficulties it presents. The location of the main body is what's important. I still think a RST type tank would be best/ Save the slant for a profile. Look at Dave's picture closely and duplicate.
 Type at you later,
  Dan McEntee

What's the theory on how this is going to fix it? Fuel mass is stil gonna' be in the same place relitive to the NVA, right? 

I don't have much experience with clunk tanks. But it is my understanding that if you can raise or lower the uniflow vent exit relative to the spray bar elevation it can affect the lap times. If this is not true, then yes, the clunk tank experiment will be a waste of time.

  The problem as I see it is with the angles that you will have to bend the pick up tubes and the uniflow/vent tube. You will have to tank the tank out of the airplane and apart to make any adjustments. Not to mention that it's going to be a royal pain to simply attach the fuel lines. Other than just dropping in nicely, I see no advantage here. It helps to envision the engine and the tank as one unit, and then try to keep fuel lines as short as practical. I'm not a fan of how you have the needle valve installed. To me, it's on the wrong side. That isn't affecting the run you are getting, but it adds length to the fuel line, and everywhere it has to pass through a bulkhead or rub against something is another potential place for a pin hole or leak of some kind or a kink that restricts fuel flow. I think shimming the engine will be the least amount or work and headache. Or, just keep flying it as is.
  Type at you later,
   Dan McEntee

you could try it , test it , with the cowl off . & if it works take a chainsaw to the inside of the cowl . Either way up ( the tank ) .

Dan , do you think theres anything to a more even run with the fuel line inboard ( needle adjust outboard ) so it always draws the fuel across ( uniflow or not )
rather than it pushing the fuel across to the intake , with less weight of fuel reducing the positivity ( big word ) of the feed toward the end of the run . Perhaps .

Jim Casale I think was on about assymetric tanks . A FSR .40 / 45 , anyway . Talking about 1 inch depth tank bays . The FSR's you need the tank 1/8 down .
For a matched run upright & inverted . The conclusion was , if you only had one inch , move the feed & uniflow down the 1/8 th  on the 1 inch deep tank and youd be in the game . Youd do it UP ,

( Ive got FSRs and always put the ' normal ' tank down the 1/8 th . Wonder on the assymetric hight ones . ( latest build ive found to my relief I did 1/8 ply surrounds
to the 1/8 steel engine pads . So ive a extra eighth ( or two . One each way ) as ive only 100 length & 45 width to play with . ) . THAT ASIDE -

#!* keybrd .

Another THING , STEEL Clunk Tanks are popular here . Usually both , with maybe just a brass tube on the uni line , Not Quite hitting the rear wall so it dont get stuck ( blocked / bulked ! )
Cunning sods if to short - throw a can top thread on to  the underside , with a screw cap . Not only can they get into the flex lines - the can fly longer with the extra volume .

ONE THING you DONT DO with clunk tanks is store nose down . or you may get a front clunk , or more likely a front clunk with a folded obstructed fuel tube inside the tank , often stuck there .

So , the other thing'd be cut an ole inna da bottom , aft , and knock the fuel tubes higher with a cold chisel , or something less offensive . Or just take the back off and realign them .
To test the inches ( fractions of  )  you could test as is with differant hight pads under the engine , on the ground , for even speed , and how far ya gotta shiftem .

Any ' ground run ' ive done , flipping the plane over and seeing rpm's and angle nose up - for the switch / break ( speed up ) the same angle either way up
has matched the air setting - being even .

To cut a long story short , better to do this to test you run , on the ground ( in your hands - feet on ground -if you want to quibble ) and also check the vent hight there
rather than pontificate endlessly up & down . Though I do wonder say the pipe ended 1/3rd hight ( if it spraybar level - whatever , is the clunk going twice as far away
one way up going to influance the effort . perhaps .

Youd generally be best to discard the cowl till youve perfected ( big word ) the run . saving endlesss off'n'oning . & rmember it's no sweat to butcher the INSIDE of the cowl ,
nobody'll ever see the surgery - for if throwing the tank in with the feed pipes accessable is gunna save endlessly ining & outing of THAT , too .

ONE BLANKETY THING - inexplicably - going from  a SF 46 muffler to a tounge muffler , on my Strega , got the run even . same tank hight . I think the pressure line had woven around from the away side .
So just shiffting the  nipple position on the muffler ( to close and hady the the fuselage thing ) for minimum tube lengh , could get it right . Drill a hole - ive used nearest ive got bolts with a side V cut to start a thread & screwed the nipple in
to form a self rolled compacted base ! thread . No Worries . Or started with a nearest tap , tapered , just thru . To get a start - then wound the fiting in . Lubed ( of course ) . A thought. Specially if youve a spare muffler .

Throwing it in the middle of the flat bit ( duct to tube ) wouldnt be a bad idea . the nipple .

Air Miniseries,

NO WHACKING! (I had to go along with you on that one....)

I also modified an ARF Nobler years ago to fit a Sullivan tank. That, after the metal kit-tank spewed a ton of rust out of it (but the outside was nicely painted in a gray hammertone paint), and then the replacement plastic kit-tank split in flight dumping nearly a full load of fuel into the fuselage causing the engine quit while inverted. After fixing the rudder, nose and wing scrapes (pavement rash, you know) I took a Dremel with a burr and carved enough of the bearers to fit in the Sullivan. Much easier than a chisel with poor access and angles on something "wots aready dun."

The Divot

I don't have much experience with clunk tanks. But it is my understanding that if you can raise or lower the uniflow vent exit relative to the spray bar elevation it can affect the lap times. <snip>

Right, but you can do the same thing by reworking a tin tank or learning to make one yourself with some assymetry... raise the point of the wedge higher.

When I needed another ounce of fuel in my PA .51/SV-11, I made a "sump" and soldered it onto the bottom of the 6 oz square wedge tin tank. Speed upright vs. inverted didn't change, because the uniflow tube wasn't moved, and the tank height didn't change. It fit, barely, under the pipe header, with about 1/16" clearance. Fuel heating has not been a problem.   

I would expect your .46LA would need more fuel, because I'd expect it would need a bigger propeller to haul a seriously overweight model, therefore burn more fuel. An alternative to a bigger tank is to add 1 oz of Coleman fuel to a quart of glow fuel to make it run longer. It's also worth mentioning that R/C plastic tanks typically hold more than the nominal rating.  Steve