Round Tank vs Square tank???

[Paul Taylor]

So my Tutor 2 came with a round tank. I noticed yesterday that when getting to the end of the tank that is seems to surge for about 10 laps. Sounds like Up and down and up and down as it picks up the last of the fuel.
Would a square tank give it a cleaner shut off?

Paul

[Alan Hahn]

I don't think so. The on-off-on is basically due to the fuel sloshing forward and backwards as the motor quits, catches, quits...and the nose yaws back and forth. The way to "fix" it is to make sure the back of the tank is further outboard than the front, so the pickup stays in the fuel (or fix the outward yaw of the plane by moving the leadouts forward would also work).

[Leo Mehl]

So my Tutor 2 came with a round tank. I noticed yesterday that when getting to the end of the tank that is seems to surge for about 10 laps. Sounds like Up and down and up and down as it picks up the last of the fuel.
Would a square tank give it a cleaner shut off?

Paul

I dont think the tank shape has much to do with it and I have had this happen myself. I think if you run the tank on Pressure it will pretty much stop this. I think it has more to do with the plumbing tha it does with tank shape. When this happened to me it was a tank that I bought and not one that I built. Most of the time a square tank will work just as well as a tapered tank. Plumbing is very important and sometimes boughten tanks do not have the tubes soldered in the right place. Tanks are one of the most important parts of your setup for without a good engine run you cannot trim your plane.

[Paul Taylor]

Thanks guys,
This is a round plastic clunk tank on pressure. The Tank i use more often is square clunk tank on pressure.

I wish I could mount a camera on the tank to see what it is doing.

Will give it another look over.

Paul

[Garf]

Shimming the tank back outboard stops this problem. BUT........at the end of the fuel, the engine quits like someone threw a switch...no warning at all. The first time I tried this, I crashed.

[Kim Mortimore]

Paul,
Round vs. square tank doesn't matter.  Pressure doesn't matter--the pick-up tube can't draw fuel if it isn't immersed in fuel, whether the tank is pressurized or not.  What the camera on your tank would show is what Alan described, fuel sloshing forward and back, uncovering and then recovering the clunk as the engine sputters, restarts, sputters, etc, causing the nose to yaw alternately in and out. 

Mounting the tank so the rear is farther outboard than the front is the classic solution, as mentioned twice here.  As for sudden shut-off with no warning, especially if you are not keeping an eye on a watch and don't know when to expect the engine to quit, one solution with uniflow is to locate the uniflow vent farther forward in the tank, so it uncovers well before the pickup uncovers, causing the engine to lean out maybe two or three laps before it quits, giving you the hint that it's time to level out and prepare for a nice, safe return to Mother Earth, ready to fly another day. 

What is vent arrangement on your tank?

Your plane may also be trimmed for excessive outboard yaw, commonly seen with guys who really like a lot of rudder/engine offset.

Hope this helps.

Kim Mortimore

[Larrys4227]

Theres alot more experience in here than what I can offer on this subject, but this is one of my 'to do' problems I need to work on. My first tank I put together was a Sullivan square, with a FIXED pickup to the back of the outboard corner. This got me through the initial 're-learning and re-tread' flights, but obviously didn't work well when I got to doing some stunts. It worked pretty good as the end of the tank neared. A lap or two of surging, and then it would quit. My 2nd tank was a larger Sullivan square, with a clunk to the outboard rear corner. It was pressurized, but foam-mounted to the inboard side of the fuse. I would get surging for at least 10 laps as the tank drew down. The further the tank would empty, the worse the surge would be. With a strong headwind, it was always a scampering effort to keep the plane flying.

My current tank is a Brodak standard vent wedge. Its pressurized, foam-mounted on the outboard side of the fuse, and a 1/4" or so above c/l of motor. At the very end of a run, it will surge for about a lap or so, and then quit. However, about 2/3 through the run, I have to listen for a 'burp' in the engine run. This is my warning not to attempt anymore stunts. If I do any stunt that makes the plane inverted, the motor will sag badly making it VERY difficult to pull out of the stunt. I've saved the plane a number of times when this happens .... but someday my luck will run out.

Something that I want correct ..... once I hear that first 'burp', I generally practice my straight and level flight (but can throw a wingover or two in if I'm gentle on the handle) but I've got ALOT of fuel left to burn off before it gets empty. I can't see inside the tank, so I dont know where the fuel pick up is. I know its in the wedge of the tank, but is it in the middle of the wedge, or at the back of the wedge? I was thinking about shimming the back of the tank outboard to toss fuel to that area, but I've spent alot of time getting the tank in just the right spot. 

Am I on the right track to get better fuel delivery as the tank emptys out? Or is this something I'll have to live with.

FlySafe!  Larry (Larrys4227)

[Larrys4227]

.........
Your plane may also be trimmed for excessive outboard yaw, commonly seen with guys who really like a lot of rudder/engine offset.

Hope this helps.

Kim Mortimore

--- see previous post ---

My plane (Flight Streak) has both the offset rudder and engine. The offsets are per the manual, so nothing excessive. I've been told that the plane flies level and straight, but I cant tell if they are missing anything ... I'm always inside the circle. The plane has a good amount of tension in my estimation and I kind of like it that way (might be a newbie-thing).  But if its counterproductive to steady flights, I might have to do something about it.

Thanks a bunch Larry (Larrys4227)

[Paul Taylor]

I will kick out the back of the tank and report back. Thanks guys.
The rudder has no off set.

[Kim Mortimore]

Larry,
You mentioned that your second tank was a Sullivan square clunk mounted on the inboard side, and it surged a lot.  Several guys at one of the clubs I fly with have been amazingly successful with Hayes square (rectangular actually) clunk tanks mounted inboard on FStreaks.  The obvious advantage of an inboard tank is more room on the very short-nose plane. 

What engine are you using?

As for the Brodak wedge mounted outboard, that burp at the 2/3 point is not so good, and is something you shouldn't have to just live with.  It sounds like the tank may be mounted a tad high at 1/4" above center.  1/8" to 3/16" is more common.  One of the most useful things on any stunt plane is a tank that is easy to adjust for height.  On profiles, the best way to do this is with slotted tabs (several ways to do this) in front of and behind the tank, each tab secured with a 4-40 bolt and blind nut thru the fuse.  Unfortunately, this takes up even more room and requires at least an inch longer nose to install, which the FStreak ain't got.   

An easier method on a short-nose plane is to make a mount pad out of balsa, same "footprint" as the tank, carved into a wedge shape so the rear of the tank is farther outboard.  Fuelproof the pad however you want, then attach it to the tank with double-sided foam tape (the stuff about 1/16" thick).  Apply the foam tape also to the bottom of the pad and attach it to the fuse about 1/8" to 3/16" above center.  A rubber bank or tie wrap is good for insurance, but be sure you allow for raising and lowering the tank.  See how that works.  Then if you want to raise or lower the tank, it's just a matter of prying the tank/pad off the fuse with a flatblade screwdriver, scraping the old tape off (alcohol or acetone might help), then retape, reposition and remount.

Hope that helps,

Kim Mortimore 

[Larrys4227]

Kim - Guess I should have mentioned a couple of things. Its an OS25LA-S, and the fuse is modified -- 2" longer in the tail, and 1" longer in the nose. Originally, I did not have the room for the Sullivan tank on the outboard side, but since I made such a habit of smashing up planes, I've been making my own and took some advice to lengthen the fuse. Its worked well, and I kept the tank on the inboard side until I got the Brodak.

Since I'm sitting here next to the plane, I took a good effort to measure the height of the tank, and its currently at 3/16". But as I'm looking at it, I'm noticing that the rear of the tank is closer to the fuse than the front. Its not much .... maybe a 1/16" at most. But that is contrary to what we've been discussing. I've got foam padding between the fuse and tank .... trying to eliminate any foaming, etc. It really helped with the Sullivan on the inboard side. The way I have rubber bands holding the tank, its pulling the rear of the tank more than the front. Gonna have to work on this stuff .... Rootbeard and yourself have given me a mission .... 

This Brodak tank probably has a dozen flights ..... its done well since I got the height just right. It was a bear the first few flights, but I got it tamed. It would be nice to get rid of this 'burp' though. Once it does it and I stop stunting, I bet I go around 20-30 times before the engine quits. Its practice time that I'd like to use!!!

Heres a pic of it from last sunday (maiden was on saturday).... its a newly rebuilt Streak. For me, its REV #2. I fixed alot of bad things I did in REV #1 and its been excellent so far.

Thanks for the advice .... I might just try the double sided foam trick ... !!

FlySafe!  Larry (Larrys4227)

[Just One-eye]

One of the simplest adjustable tank attachment systems is hook and loop fabric, simply glue one kind to the plane, and the other to your wedge fixture.  I like a backup in the form of a long cable tie, myself, however. 

[Garf]

I use coathangar wire bent into a "U", stuck thru holes drilled thru the fuselage, then bent into hooks for rubber bands.  I put foam under the tank with a little extra under the rear of the tank. You can use R/C foam, but I use Dr Scholls 2X shoe pads cut to shape.

[Larrys4227]

You can use R/C foam, but I use Dr Scholls 2X shoe pads cut to shape.

Are your planes 'Gellin'??!! 

[Garf]

Always seems to be one in every crowd. 

[Jim Thomerson]

What I have seen with some engines run on an open vented uniflow tank is that the engine goes rich when the fuel uncovers the uniflow.  Get a couple of rich laps then a half lap lean out as the fuel runs out.  I don't see this with all engines, and I don't see it with muffler pressure. 

I've made uniflow tanks with the uniflow ending everywhere from the front outside corner to near the fuel pickup and they all seem to run about the same. 

[Russell Shaffer]

Question for Kim - exactly how are the guys doing the Hayes tanks?  Are they mounting them in the normal way with the bulge down and the tank flat against the fuselage, or are they setting them on edge?  Anything special about the venting, do they just use the existing vent, or drill out the second one?  I plan to do this on an Acromaster soon.  Thanks for any help on this. 

[Paul Taylor]

This not a real good picture but if you look close you will see that the boot is mounted to the side of the plane. I then ran the fill tube up and thru the fuse to the other side of the fuse.
It only used two lines. I stand the plane on the nose to fill it. I leave the fill tube open getting air pressure from the prop. Works good.

[Bob Reeves]

Hays 4 ounce on inboard

[Bob Reeves]

Sullivan 4 ounce tank outboard.. The rear is shimmed out 1/8th inch..

[Wynn Robins]

SINTERED BRASS CLUNK

will only shout it once  - although I have told you a 100 times before Paul - sheesh.   

[Paul Taylor]

SINTERED BRASS CLUNK

will only shout it once  - although I have told you a 100 times before Paul - sheesh.   

Wynn,
I know, I know.... I thought about that too but this tank came with the plane. So I am using what I had.

It seems to pick up fuel fine and there is foam between the tank and the fuse. I do not see any foaming in the tank. I think it is the fuel sloshing up the side of the tank and then falling back down as the plane slows down. When fuel falls back down the wall to the bottom of the tank the engines comes back to life.
So I will kick out the back of the tank to see if that will fix it. If that does not resolve the problem then off with the round tank and on with a square tank with a SINTERED BRASS CLUNK!!!

And it not shouting unless you put three bangs after the words in caps.


Paul 

OBTW--- How is Jr? Got him a plane yet?

[Bill Adair]

Paul,

Sounds like the clunk fuel line is too stiff.

Try to find more flexable fuel line for the clunk, and use the heaviest clunk weight you can find. That's an easy change to try, and won't cost much.

Bill

[FLOYD CARTER]

I've used commercial "wedge" tanks, plastic clunk tanks and all the rest.  When I make my own tanks, they are formed around a rectangular block with uniflow.  I prefer rectangular instead of a wedge because I get several laps of sputtering before fuel runs out.  Therefore, I never get caught in some awkward position when the motor cuts.  When the motor makes final surges, I have time to get ready instead of crashing!

Floyd in OR