usable fuel
 

Hello,
I just finished breaking in a Magnum 91 and have started to fine tune the thing. I have found that when the plane runs out of fuel there is still about 10% of fuel left in the tank. It used to be worse, but I "T"ed the fuel hose, putting a pickup both at the front and back of the tank which helped. Is this common among nitro powered planes-having fuel left over in the tank?
Thanks everyone!

RE: usable fuel
 

Not sure the "tee" in the fuel tank is a good idea. Depending on the attitude of the plane in flight ,one of those lines may not be in the fuel.............draws air.....engine quits.

RE: usable fuel
 

This is absolutely correct. As soon as one of those pickups is out of the fuel your engine is going to die. You need only one clunk in the tank and it should extend to within ~1/8" of the back of the tank. It should move freely when you turn the tank upside down. This setup will let your engine draw almost all of the fuel out of the tank.

Ken

RE: usable fuel
 

The clunk should be just short of the back of the tank and be able to get close to the corners in both inverted and upright flight. You'll never get every drop of fuel out of the tank, but if yours is quitting with 1/4 (10%?) tank left, you may have a pin hole in your fuel line at that level and as long as the line is submerged in fuel does not affect it, but soon as you burn up enough fuel, the hole is exposed and viola--she conks out. Flatspin is right--dual pickups, one is bound to suck a little air in a dive/climb when the level gets low. Put a new piece of fuel tubing on and make sure your clunk flops around just short of the back of the tank.

RE: usable fuel
 

Thanks fellas,
I'll go back to the one pickup setup. I put it in there becaue when I would hold the airplane in a nose low attitude, the engine would quit. Maybe I just have the pickup too far back, I'll look at it.
Thanks again!

RE: usable fuel
 

The silicone fuel line in the tank should be VERY flexible.. When you put your plane in a nose down attitude, the klunk (the metal piece at the end of the line) should fall to the front of the tank.

RE: usable fuel
 

Uh-Oh....

I made this assersion once in another thread only to be lamblasted by a bunch of people.

Here it comes! DUCK!

But this is how I've purposely set up my tanks and it works very well.

RE: usable fuel
 

Heh, actually in flight, you don't need to have the clunk move to the front of the tank. And in practice it doesn't.

When you dive, there's enough G-force to hold the fuel at the back of the tank, so your plane runs out of air before your engine runs out of fuel. Holding the plane still and nose-low isn't something that happens in flight unless you really work at it.

And yes, you CAN take most models up really high, and do a shallow dive long enough with a nearly empty tank to get the engine to die. But it's actually rather hard to do, and not worth worrying about.

I have several tanks where the clunk can't move to the front of the tank except during a sudden stop, and when it does, it gets stuck. Those planes do as good a job as any at emptying the tank.

(I also don't run the tank dry with the engine anyway. I land with a little fuel in the tank most of the time, the pump the tank empty. When pumping out if I want the last bit of fuel, I'll hold the plane up at a slight angle, which helps, but I usually don't bother).

RE: usable fuel
 

Eh... this is a misconception.

We covered this ad-nauseum in the other thread.

The plane does not accelerate in a nose down attitude fast enough to hold the fuel at the back of the tank.

To keep the fuel back there it would need to maintain an ACCELERATION rate equal (rather greater than) to 1G/(percentage inclination to the horizon)*some factor.

e.g. the further the nose is down, the higher it must maintain a constant acceleration rate.

Of course that can't happen so that means, even in a slight nose down attitude the clunk can become uncovered esp. when say coming in for a landing on a long glide.

This is not too problematic until the plane starts running down on fuel.... that is at less than half a tank the problem starts to surface, but at about 1/4 tank it really kicks in as all it takes is a -15 degree or so attitude to uncover the clunk. The uncovered clunk makes the plane behave as if it were out of fuel prematurely.

Of course one could argue that why fly this amount of fuel... but then I like to maximize my flight times.

RE: usable fuel
 

Depends on what you're doing. If you're in a steap dive, such as near-vertical, then acceleration and lack of altitude is doing it. If you're in a very shallow dive, then yes, it's just a matter of not having enough fuel in the tank. Which is basically what I said.

Also, don't discount the amount of time it takes the fuel to go through the lines, and the fact that a single bubble won't usually be noticeable. (you can test this by pinching off the fuel line when the engine is running and time the amount of time until it dies, probably a couple of seconds. Figure out how high you have to be to avoid hitting the ground in a dive for that many seconds).

Anyway, the agree on the main point that the clunk doesn't move to the front of the tank in a dive, and it doesn't matter that it doesn't.

RE: usable fuel
 

OK OK OK all I know is if the clunk moves to front of the tank, it folds the fuel line over and the engine quits--not insantly, but it will quit.

RE: usable fuel
 

Where would I get fuel tubing flexible enough to move the clunk to the front when at a nose low attitude? I know none of the fuel tubing I have ever used is that flexible.

RE: usable fuel
 

That's the point, you don't want the clunk to move to front of the tank, and I've never seen a tank where it could easily do that with out getting stuck. And it getting stuck is a bad thing.

Maybe it could work in some of the really large tanks out there, but even the 12 or 14oz (I forget which) tank I have wedged in to an LT-40 won't do it, and shouldn't do it.

Don't worry about it, just put the tank together with a single clunk just a little bit from the back of the tank and go fly. You won't have any problems from that. If you really want to fly for an hour, put in a bigger tank (like I did in that LT-40 above. I have no idea how long it will go on a tank, but based on fuel left after long flights, I'd say 45min of aggressive flying, over an hour if I just put around).

RE: usable fuel
 

if the point is getting all the fuel in your tank used up then go to a bladder tank, they cost a lot more. I have been flying models for over 30 years and haven’t had much worry with my planes cutting off in flight due to fuel starvation. most fuel lines are long enough and have fuel in them to keep an engine running when you are in a dive. I don’t run my tanks dry I know pretty much how long I can run on a tank of fuel depending on the model, but on occasion I do have a dead stick due to empty tank and when I remove any remaining fuel there is about half ounce left. if you have your fuel lines/tank set up properly it will siphon almost all of the fuel out. most of the maneuvers we do don’t last but a second or two. it happens but not a common thing at least not in my experience and not that much of a worry. I suppose if I were flying something like a jet or high end model I would make those assurances. but for sport flying or just putting around I don’t bother.

RE: usable fuel
 

If you just must have fuel tubing to do what you think needs to be done, then go to SIG, http://www.sigmfg.com/cgi-bin/dpsmar...FV4.html?E+Sig, and get yourself some SURGICAL TUBING to fit your desired equipment.

Then you just might find that good ol' Montague was the man to listen to.

Now good ol' 'opjose' may be on track also, however in 60 years of playing with toy airplanes from CL, FF, and RC including CL Stunt Competition where fuel management was of ultra-extreme importance to assure a stopped airplane (no throttles, just needlevalves) 8 minutes from first prop flip, to pylon racers to Pattern, sport etc., etc., I have never expereinced fuel problems that required a clunk to go to the nose of the tank. Actually just the opposite.

An aircraft in a vertical dive is constantly accelerating under the gravity acceleration schedule as is the mass of the fuel in the tanks. Drag being produced at 1/2 the square of the airspeed, constantly retards that acceleration of the flying machine.
As one that has been supersonic in a vertical dive, as well as near zero speed at the reversal of maneuvers such as a flop-over from a vertical tailslide, I have never experienced any looseness of the shoulder-harness during the vertical descent portion of any such maneuver. My RC experience for 31 years of RC leads me to believe that the fuel also stays firmly planted near the lower aft portion of the tank, aft being the portion closer to the earth.
Of course when performing maneuvers exceeding 1G, the other factors come into play. Fuel and clunk follow the higher forces. It really doesn't take a lot of G force to move things around, so a fuel line like surgical tubing can tie itself into a knot in short order, however one must do as one thinks best!!!
Of course some Professor of Physics from John Hopkins University, having flown an RC across the Atlantic Ocean plus several other record performances, may well be able to dispute my theories. :)

edit: add 1G+ info.

RE: usable fuel
 

What we need is a nice ROUND tank with the clunk tube originating in the middle of the tank. That way the clunk could travel with the fuel no matter the attitude without getting stuck anywhere... or better yet a round bladder :D oh wait....

RE: usable fuel
 

As you rally don't want the clunk at the front of the tank, many peopl actually install a shrt section of brass tubing in the feul line inside the tank to ensure the clunk can not get tangled and move to the front of the tank.

RE: usable fuel
 

I want my clunks in the fuel, no matter where the fuel happens to be at, which does include the front of the tank... untangled of course.