dumorian

My Feedback: (6)

I'm planning to use a dual gas tank setup on one of my models. The reason? The space for the main tank is limited and I just can't get a bigger tank in there. It is a 16 ounce tank on a 27 pound plane. Not as much flight time as I would like.

My question:

Does it matter if the second tank is under the primary tank?

The primary tank is slightly above the carb level, the second tank will be below the level of the carb. It is a standard Walbro pumper. I'm just concerned that the when the fuel is being sucked from the lower tank to the upper tank that the siphon effect might change the mixture.

Tanks!

w8ye

My Feedback: (16)

Have one tank feed the other

The pump should take care of the height situation

dumorian

My Feedback: (6)

Thanks Wy8e! That was a fast reply!

Yes, I plan to fill from a T between the carb and the clunk of the upper tank. I'll then run the vent from the upper tank to the clunk on the lower tank. The lower tank will have the overflow vent line, which I believe will need to run up to a point above the upper tank before exiting the fuse? I suppose if the vent was lower than the upper tank, gas could run out from the upper tank if the carb had any air leaking back through the lines when just setting around in the pits.

w8ye

My Feedback: (16)

You are correct

Truckracer

My Feedback: (19)

Make the bottom tank your primary tank that feeds the engine and you won't have any vent problems. Hook the tanks in series as suggested and I doubt you'll have any problems. I have used tanks like this in glo planes and helis before without problems. Have also seen them in Jets, though mostly back in the days of ducted fans. Stacking the tanks should make them pretty much like one big tank ... just a more friendly shape to fit in the plane though.

dumorian

My Feedback: (6)

Duh... sure! I only just considered doing this for the first time this evening. Haven't thought about it a lot. But having the bottom tank the main tank makes good sense. The pressure from gravity will be the same when they are full either way. I'll just be sucking gas up on the second half of the gas instead of sucking it up from the start. I won't have to worry about vent routing and not letting it fall below during any service. I like this.

spaceworm

Since you are running a gasser with a Walbro pumper carb, have you considered a single large tank further back in the fuselage? This would help minimize cg shift as the fuel is used also and eliminate the extra plumbing and failure potentials of the dual tank setup. JMHO

dumorian

My Feedback: (6)

Yes I have and that's a very good point. This is a model I picked up at a swap this past Saturday. It's a quarter scale Stinson L-5. It has a seat and person up front and in the back for that matter. There is a rather large area where I could place a very good sized tank just under the existing tank, but it would be fairly low... for certain below the carb by a few of inches. I'm worried that even though it is pumped, that it would be a bit harder to start. Some days, these things can be a little cantankerous anyway and lack of fuel doesn't really help much. The thing weighs a ton for what it is... 27 pounds with a 102" wing! I'm thinking that where the gas is won't matter a whole lot. I do like to stay with KISS as much as possible. I've even considered a header tank and a large tank, but the line connections are pretty much the same, so no real gain. The area I have to work with has a fairly small footprint, about 3" x 7" but is rather tall. I'm not sure I could find a larger tank without standing it upright and if I know myself, somewhere along the line I will try to fly this thing upside down! After all, how are those Marines in there supposed to be observers if they can't look at the ground through the completely clear roof?

Now, if this were a Yak or other high performance model, I would certainly be thinking along the same lines as you. In fact, I set my tank back as far as I could in my Extreme Flight Yak just for that reason.

Yes, I do have a variety of models. I enjoy each one for what it is. They all have their merits.

I do really appreciate your input. It is an extremely valid point and certainly would hold true for most models. A single larger tank would almost always be a better solution.

Tired Old Man

My Feedback: (1)

Dual tank installations work fine. An over-under installation reduces CG shift more than a single large tank.

arobatx

We did this rather often on the larger hydroplane boats back in the day, and though they were usually installed side by side, the system worked great. Even in helicopters you've seen the use of 'header tanks' to reduce the possibility of bubbles in the feed line. Check out the various shapes and sizes of Nalgene bottles if you want to run one tank, they probably have a bottle that is narrow and tall that would work.

rc bugman

My Feedback: (30)

Multiple tanks work well when plumbed in a line (sequence, overflow tank 1 to clunk tank 2). I have a couple of planes with 3-1 gallon tanks plumbed this way. The only word of caution is that if you plan to run a significant portion of the time at full throttle, increase the size of fuel line hooking the tanks together and on the clunk line. The increased line size eliminates any problem with flow resistance across the tanks. Some say that the carb pump overcomes this resistance but in my applications with large fuel loads and full throttle engine runs, the extra fuel line size is necessary.

Elson

Bass1

Sounds like those little marines haven't missed many meals!

dumorian

My Feedback: (6)

Yeah, I keep looking at it and pecking around on the covering trying to figure out where the weight is. It is fabric covered and looks to be painted with latex house paint. I guess that adds up! Otherwise, there isn't a whole lot that is solid vs. stick built. It is a big model though. It's giving me a new challenge as it's too tall when on the workbench to reach into the top. So, internal work at the moment is on the floor. My knees don't care much for this. I'm dreaming up an adjustable height table/workbench. I could benefit from this with a few other models as well.

Meanwhile, at this moment the top tank has it's new gas stopper in it. And yes! When they say don't use a glow tank stopper with gas, believe it. This one had the regular stopper in it and it had gotten soft and was rapidly degrading. The back half fell away into the tank in the process of me handling it. I'm 'really' glad I took the time to pull the engine box and get to this! Eek! Anyway, that top tank is plumbed, I'm about to go back out to finish up the system with the new bottom tank. Then it'll be put the engine back on, loosely and test fill the tanks to be sure they are working as I have it figured. Murphy says that if I bolt it all down tight, I will have done something wrong. If I just sort of hang it there, all will be right.

Then, I'll work out new battery locations, decide where the receiver is going, plug it all in and start programming the radio! About the only thing I don't have for it as of yet is an optical engine kill. I guess for the first flight, I'll just rely on the throttle servo and failsafe to do it's job. It does have a separate ignition switch on the fuse, so I can turn it off it needed after landing. Something I do when it's like this is I always approach a running model from behind the wing to turn it off. That way if for whatever reason it decide to idle up, like running out of gas, the wing can't turn the prop into me and me into hamburger.

Yeah, this dual tank setup is working out really nice. It will be pretty much hidden, or at least hard to see and I do feel better having one tank up at carb level, not that pumpers really need this so much, but I do think it makes starting easier. I notice that most weedeaters and such have the tanks above the carb. I guess when things aren't ideal, this might help. If nothing else, if the carb dries out a bit, at least it can get some gas to soften things up.

And I guess I'll leave those well fed Marines on the ground for at least the first few flights!

dumorian

My Feedback: (6)

Alright! The tanks are working great! It's interesting to watch the bottom tank and the flow of fuel into it from the top tank when emptying it all. Pump, pump, pump and the gas level doesn't drop but there's a swirl at the top! Just like it should, just something new to see.

I got the receiver in all the servo wires run and the tail functioning. I'll do the wings tomorrow and all I lack is the ignition battery and programming/tuning.

Thanks for all the suggestions, help and input here. I was surprised that I could find almost nothing about doing this on any of the Big 3 forums. I did find one small section in one thread which had a nice graphic which verified the way the lines run. Good input here however made me feel comfortable with this setup. It always seems to work in my mind, but every once in a while in reality it doesn't.

GaryM

My Feedback: (14)

I know this is a little late since you have the dual tanks working but here is a company that a lot of flyers seem to overlook and he has been around for years catering to the large scale birds. His gas and smoke tanks are heavy duty and are of unusual dimensions compared to Sulliuvan and Dubro .

B & B Specialties

www.bennettbuilt.com

GaryM

dumorian

My Feedback: (6)

Humph... I didn't think about him for special tank sizes. I was just on the site last week looking at both Quadra and Zenoah engines. Seems he is the one to go to for parts and advice on these engines. Good to know this.

jeffpits

Something you may want to check. Due to the deteriorated stopper you replaced you may want to check your filters and the screen in the carb. I wonder if some of that stopper gunk could cause a problem.

Jeff

dumorian

My Feedback: (6)

Good idea! When I first pulled the stopper I just noted it was the wrong type but it looked to be in one piece. I didn't really look 'close'. The stopper was in and out several times so that I could do some measuring. After this, I noticed the ring of rubber in the bottom of the tank. I'm pretty certain it was not there when I originally removed the stopper but I now cannot swear to it. I was at the time of first removal simply trying to get stuff apart for other reasons. I knew not putting the cowling back on was a good idea! I will pull that cover on the carb and take a look pre-flight.

I read [link=http://www.rcaer.com/pages/files/Aerovate%20-%20Tuning%20a%20Walbro%20Carb%20the%20Right%20Way. pdf]this article[/link] on tuning a Walbro carb. These folks have a lot of great info on their website. This seems to be a very thorough method for tuning. I thought I'd give it a shot today to see if I can have one 2 stroke that doesn't 4 stroke at some point in the throttle range. What I really need is a carb adjusting screwdriver. Something with a cub around the slot to fit the Walbor screws. I normally tune on our flight bench with the model all strapped down for safety. It's just too painful of a process to start and stop the engine before each tweak. And, the vibration makes it pretty hard to keep a slotted screwdriver in the screw while at the same time trying to make micro adjustments. Hmmmmm.... I guess it the screwdriver blade was just a little larger across than the diameter of the screw, a simple piece of tubing clamped to the screwdriver would do the trick.

I will take the camera if we get to fly today. I will also plan to take the camcorder if I have any blank tape....

Meanwhile, buying a used model. I noted that the servos in the wing look to be epoxied in place. [>:] They are at least on a plywood tray, but it doesn't look to be designed for removal. If I had done this build originally, I would have made those plates removable and on those plates would have been blocks that would have been used to screw the servos to. As the servos lay on their sides, at this point I really can't replace horns, adjust horns and if I have a servo failure, it will be bust something out to remove it. The access cover is plenty big. Perhaps 3" x 4". I guess the builder had never run across installing servos inside a wing like this? Another method would have been to use a slightly heavier cover and to have mounted the servos to the cover, however I don't think this would have worked as the linkage will not swing up out of the box. Still, it would have been easy to have the base screwed down, and the servos screwed to blocks on that base. The servos used are high torque, but not metal gear. I guess on this model, with the weight, the vibration might not transfer out to the wing tips and ailerons and servo gears. I noticed on the Hitec website, they recommend metal gear for 'all' gas engines due to the extra vibration.

Hmmm... let see... if an aileron servo locks full up..... I'll just throw the flaps full down, give aileron input to put the other one in full up and bring her in under crow steering with the tail? [8D] It does have a nice I think it was a 5645 for the rudder! It's an ecumenical model. Has Futaba (elevator), Hitec (wing and rudder) and JR (throttle) servos in it!

n0kjf

This might be a few days late, but speaking as the local endurance flyer champ, my son and I put together a Hobby Lobby Senior Telemaster ARF as a endurance plane. It was gasoline powered, 6 fuel tanks in series. We flew for a little over 7 hours and landed 2 minutes after our last competitor ran out of fuel. We could have flown for a "little" while longer.

The carb pumps are very capable, we had a pinched line on one flight and the "pony" (header) tank was collapsed from the suction.

dumorian

My Feedback: (6)

Well, I blew it yesterday. In the process of getting everything back into the trailer, what did I forget? Yes, the camera! But, I did manage to get to the field with everything else needed. I can say it wasn't an uneventful day, but it was a day in which everything came home in one piece.

The dual tank setup worked great! The flights were a bit short... the first very short as I forgot to check the plug cap. It fell off on the second trip around the field. Not enough time to even get it fully trimmed in much less start feeling out how slowly it might fly or to test the flaps... But, I just brought it around, deployed the flaps and dove her in to an excellent landing. I would rather be lucky than good. It even stopped right in front of the pit entrance! I can't do this if I try. So, the screw on thingy on the plug didn't exist and the plug cap needed one... Another bug! It took a hose clamp to hold the cap on. The next flights were uneventful. I don't feel like I flew all that long but each time I was into the second tank before landing. I'm thinking 32 ounces is just right for this model. I cannot believe how slow it flies! At one point I deployed flaps, kept throttling back and pulling up and I'm positive I could have walked faster. I just don't really get how this model at 27 lbs and a 102" wing has enough lift. It really is a very sweet model to fly, although the ground manners are a bit lacking.

So, it was a very good day. It will have to be the next outing before I can get shots. It is getting colder here finally. Even a chance of snow coming up, so it might be a while before we get to fly again, but one never knows. I guess I could start working on a set of skis? I might need to add another gas tank for a heater to keep those Marines warm though!

That's an awesome amount of time in the air! That starts to create issues even for transmitter batteries and such. I guess one could fly with a charger plugged in? Or, two 72mhz radios on the same channel? Interesting. I guess it took a pretty good pack in the model as well. 6 fuel tanks! Hmmm... I would have thought you could have at least gotten 8 in that fuse! Those are floaters for certain... flying tail and all. This is good to know that a pump will suck a tank flat.

n0kjf

We custom built a Hobby Lobby Senior Telemaster kit from the ground up as an endurance / night flyer. It has wing tanks and a single large center tank. It will hold more than 2 gallons. I think it will fly for a few hours. We had some great tests with it last fall in Summersville WV at the Walley's Squadron Fly-in.

My regular Senior Telly carries 48 oz. of fuel and can go for 3+ hours. I fill it once and fly all weekend. 10+ flights on one fill. It has 2 tanks, a 32 and 16. The 16 is on top and that one feeds the Zenoah 20ei. Great engine but the ignition draws 2.5 amps!! Wow. We use lipos in the endurance flyers, 4,000 mAh packs, 2 for the reciever and 2 single cells hooked parallel for the ignition. The endurance flyers have SPE 26's. I bought 5 from BCMA before he quit and one more at Toledo last year. The Zenoah has at least 150 hours of run time on it by now. We should have kept a log. A few of the SPE's are pushing 50 hours.


Transmitter batteries were a little tougher but we worked it out. Large internal pack connected to the trasmitter via a Y. One lead of the Y external, and velcro an external pack on the back. Swap the external pack every hour or so and it keeps the internal pack charged. The fres battery will discharge into the internal pack rapidlly so we did not let the voltage drop a lot. In retrospect, the internal pack would have gone for close to 6 hours and the external pack would have pushed it to 12 hours. We were planninging on an endurance flight so we were ready, willing and able to fly longer.... much longer. But our competitors ran out of fuel so we landed shortly after securing the win. No sense in giving away the length of our legs, we felt like the next year's event would have been better, but no one would fly against us. Oh well. Spring 2010 we are going to fly most of a day to see if we can go dawn to dusk+. We had a great time. I had a half dozen pilots and our closest competitor was alone, so we spelled him, and he even took a turn or three on our plane. We had a great time and everyone left happy.

Anyway, I know multiple tanks work great, I use the 2 tank set up everytime I fly, and 6 worked well too, just watch for pinch points.

dumorian

My Feedback: (6)

The tanks in the wing is interesting. I'm trying to consider the plumbing for this. If each of them was in series, the trim would need to be corrected often. Then, one would need to pull from maybe outside left then outside right... working towards the middle... a lot of lines running from wing to wing. I have had a couple of STMs and done some work inside wings. There certainly is plenty of room in there for flat tanks! The lift that these things have is awesome while the drag seems very low and unless someone else shows up with a Tele, you just might keep that 1st place trophy for some years! Mine never wanted to land. I dumb thumbed one of them when I first started flying, actually my first flight. A radio problem took my second one.

n0kjf

We use valves for each wing, if a wing gets light, we shut down the flow from that side of the plane so it draws fuel from the heavy side. Without some way to control the flow, it could get real out of balance.

dumorian

My Feedback: (6)

OK, that makes sense, I was seeing in series... if six tanks in wing... outside left to outside right to middle right to middle left to inside left to inside right to middle main tank in fuse. Still, a constant change in roll. Valves would certainly be a lot easier. I suppose you only need to series the tanks in each wing individually and then Y them into the main tank vent? If you're filling from the main tank, I guess you need to use the valving during the fill process as well and would have two overflows, one from each wing?

Plumbing is a very interesting science. We're still figuring out new/better things for houses all the time. One would think a drain running at 45 degrees would empty better than one running with a 1/8" drop per foot, but no. Add suds from a washer and you have problems with air lock. Vertical no problem as the liquid swirls to the sides, almost horizontal, liquid lays on the bottom, anything in between and you get waves and possible air lock trouble. One would never think moving liquid around would have so many variables.

jrichardj

I have a problem with vertical downlines and spins when the fuel tank gets down to about 3/4 full....l..The pick up line and klunk rests against the side of the tank and air enters the fuel line. I can't find a fuel line flexable enough to allow the klunk to fall to the nose during these manuevers and was wondering if a header tank would be the best fix or is there a better way???