clover burp finally got me

[Chris Belcher]

So i have had a problem with my os la 46 burping at the upward leg of the clover after the first outside loop. On the way up it just shuts off..most of the time it comes back on and I gulp and finish the pattern. Already crashed once dead stick but yesterday it burped, lines went slack, regained control right when the engine came back on and pancaked it...broke its poor little back. So....I'm gonna fix it and remount the tank inboard, don't really care if it does that great of a pattern anymore as it has gained lots of weight from the first repair.
Said all that to ask this question...I had the tank and engine (OSLA46) outboard. It is a Brodak ATF 4.5 oz on uniflow with muffler pressure. Venturi is a .272 with tigre needle. What will moving the tank inboard do. What about moving the engine inboard? I had rather move the tank in and leave the engine out. The only way i could get it to stop burping ws to run it in a solid 2 with 4 pitch prop. Loved the run that way...but every 10th flight or so it would still burp. Running in a 4 stroke it would do it every time. I'm gonna use the ol' bugger as at test bed cuz i have a new one a flying buddy gave me and want to get it running right on this one and then just swap everyhting over to the new one. what ya'll think?

[john gunn]

you got an
la from Fox?

[John McFayden]

Did you try tilting the rear of the tank away from the fuselage about an 1/8 inch with a shim to force the fuel into the end of the tank and covering the end of the pick up tube as long as possible?

John McFayden

[Dave_Trible]

You are simply running out of gas and/or the last of it is falling away from the pick up tube at the wrong time.  When you set it faster you are setting it leaner ,  coasting on through.  The possible answers are:
1. Stay faster
2. Smaller venturi
3. More fuel
4. Baffle in the tank to hold fuel 'in the pocket'
5. More nitro to stretch the run a bit

Mounting the engine or tank inside won't change much of anything I can think of.

Dave

[Howard Rush]

5. More nitro to stretch the run a bit

Oh?

[Dennis Moritz]

Tank. Uniflo getting uncovered. Maybe. 1/2 ounce bigger tank. Choke area already at minimum. Probably. Running a fatish needle and medium sized venturi. Run engine a click or two leaner. Wait. Tigre needle. One or two clicks on an OS needle equals how many quarter turns on a Tigre? Next time FIX PROBLEM WHEN YOU GET WARNING. Easier than repair and rebuilding. How many laps did you run after finishing pattern? Bigger tank would probably work to cover issue. Eric Rule makes very nice profile tanks. Try a 5 ounce with the same setup. Actually more nitro will shorten run. Less nitro will lengthen run.

[Dave_Trible]

Oh?
[/quote Well  as I last recall but it's been awhile since I messed with that- the last on my list for sure.  Could have been less nitro maybe but it's of minimal use. 

[Steve Hines]

Maybe back plate leaking. Had a problem last year with one Sams planes was not in just one place. How long does it run after the problem and still run. We tryed tanks, plugs. Allways lower fuel hard turn. Lew W. at brodak helped, just a little silicone.

Steve

[Tim Wescott]

Did you try tilting the rear of the tank away from the fuselage about an 1/8 inch with a shim to force the fuel into the end of the tank and covering the end of the pick up tube as long as possible?

+1.  Actually, +1/8: I kick my tanks out by 1/4" rather than 1/8, because 1/8" always seems to be just enough to tease, but not enough to satisfy.

You may also want to consider going to an RC-style clunk tank.  I know it's anathema to some, but a 4 or 5 ounce Hayes tank, run on muffler pressure, bumped out 1/4" in the back, will run the tank dry and then shut off cleanly every time.

(I use a 4-ounce tank.  With PowerMaster 10/22 mix I have to fine-tune the engine run by adding Coleman fuel to the mix to get the last dozen laps or so after the pattern.  Sane people might solve this problem by just using a slightly bigger tank).

[Randy Cuberly]

Oh?
[/quote Well  as I last recall but it's been awhile since I messed with that- the last on my list for sure.  Could have been less nitro maybe but it's of minimal use. 

Uhhhh....Dave,
More nitro typically requires a richer needle setting and uses more fuel.  It does supply more power at a lower RPM but the total result is more fuel usage.  How much more depends on a lot of things but it will definitely use more fuel!

That's why Howard was pulling your chain and being just a little incredulous!

Randy Cuberly

[Dave_Trible]

Randy I know I can count on Howard to keep me on my toes.  I don't do a whole lot of playing with the nitro (and probably should have simply not mentioned it). I keep 10% and 15% in my supply,  using the 15 most of the time unless it's cold.  The run times are a little different and I'd forgotten which way.  Happens when you sit on your tail all winter waiting to fly!

Dave

[Chris Belcher]

OK...I do the pattern with 3.5 ozs of 5/22 with 10-15 laps to spare. Set rpm at 9.8-10k with eather 11.5 x 4.25 prop....oh yeah, forgot to mention that was the part that hurt the most...lost one of 2 eather props i bought back in the 90s....loved the way the plane flew with this set up. Last nite when it quit I sucked out the remaining fuel and there was 1/2 oz left. Yes the rear was canted out 1/4...tank height was right as upright and inverted lap times were same. Tank was as far forward as possible.
 How could moving the tank inboard not change anyhting...why does one mount the tank inboard a la Tom Farmer/forerunner. I fly with Tom here in Fort Worth regularly...maybe I'll ask him next time I see him..he doesn't come out as often as he used to. What issue(s) does inboard tank solve?

[Tim Wescott]

The inboard tank setup is going put a positive head on the fuel at the needle, like what would happen in a stationary setup if the tank were above the engine.  When you turn faster laps, the effect will increase, tending to richen the mixture and slow down the engine.  With an outboard tank, the effect is reversed -- the faster you go, the leaner the engine gets, and it's up to the engine's natural regulation to overcome this effect.

Have you checked the leadout location?  Whenever I whine about fuel cutting off late in the pattern, Mark Scarborough asks me if the leadouts are too far back (which effectively cants the rear of the tank in, along with the rest of the aircraft).

Have you pulled the back off the tank to make sure the toobs are in the right places?  For that matter, are you absolutely sure that you haven't plumbed the uniflow to your venturi?  I'm sure that you'd never do something like that, but there is surely sufficient stupidity between my ears for that to happen!

[Steve Helmick]

OK...I do the pattern with 3.5 ozs of 5/22 with 10-15 laps to spare. Set rpm at 9.8-10k with eather 11.5 x 4.25 prop....oh yeah, forgot to mention that was the part that hurt the most...lost one of 2 eather props i bought back in the 90s....loved the way the plane flew with this set up. Last nite when it quit I sucked out the remaining fuel and there was 1/2 oz left. Yes the rear was canted out 1/4...tank height was right as upright and inverted lap times were same. Tank was as far forward as possible.
 How could moving the tank inboard not change anyhting...why does one mount the tank inboard a la Tom Farmer/forerunner. I fly with Tom here in Fort Worth regularly...maybe I'll ask him next time I see him..he doesn't come out as often as he used to. What issue(s) does inboard tank solve?

 3.5 oz in a 4.5 oz tank seems like a bad deal to me. I'd suggest a bigger venturi to burn more fuel, and probably more nitro. Besides that, the tank might still be the problem, with tubes not perfectly located. I would also say to kick the back of the tank out and check for too much yaw....leadouts too far aft.  Steve

[Brett Buck]

So i have had a problem with my os la 46 burping at the upward leg of the clover after the first outside loop. On the way up it just shuts off..most of the time it comes back on and I gulp and finish the pattern. Already crashed once dead stick but yesterday it burped, lines went slack, regained control right when the engine came back on and pancaked it...broke its poor little back. So....I'm gonna fix it and remount the tank inboard, don't really care if it does that great of a pattern anymore as it has gained lots of weight from the first repair.
Said all that to ask this question...I had the tank and engine (OSLA46) outboard. It is a Brodak ATF 4.5 oz on uniflow with muffler pressure. Venturi is a .272 with tigre needle. What will moving the tank inboard do. What about moving the engine inboard? I had rather move the tank in and leave the engine out. The only way i could get it to stop burping ws to run it in a solid 2 with 4 pitch prop. Loved the run that way...but every 10th flight or so it would still burp. Running in a 4 stroke it would do it every time. I'm gonna use the ol' bugger as at test bed cuz i have a new one a flying buddy gave me and want to get it running right on this one and then just swap everyhting over to the new one. what ya'll think?

     Put in more fuel, and just live with the excess run. The wedge angle on the Brodak tanks (which is the same as a Veco) is too shallow to ensure it will run cleanly through the last few maneuvers unless you have a lot of excess fuel.

   An alternative is to make a tank with a steeper wedge angle. It needs to be more or less twice as wide as a Veco T-21 tank.

 Fuel is running away from the pickup, that's why it is quitting (and that is the classic case, first loop of the clover). It almost certainly has nothing to do with the internals of the engine or how it is mounted. If it sucks air into the pickup, it doesn't matter much if the overall head pressure is higher.

    BTW, what is wrong with running it in a 2-stroke all the time?  That's more-or-less how they are supposed to run. Running with lots of pitch is not the way to go.

     Brett

[John Leidle]

 A wild guess says Steve hit it on the head,, low fuel going lean in a bad part of the pattern,,, I believe if the tank had been full the plane would still be with us .
  john

[Scott Richlen]

When mine did that and crashed, I finally just built my own tank.  Problem went away.  Ask Paul Walker how to plumb it.

BTW, my LA-46 uses 4 5/8 ounces to get through the pattern in cool weather.

See the shape of the tank in the wooden buck I use.  Note how its pinched at the back.  Note where my uniflow line is positioned.

Scott

[RogerGreene]

All,

I hope that I am tooting my horn too loud, but I have been making tanks for a while. Stunt News was gracious to publish "How I Make Fuel Tanks". It appeared in the September / October 2013 issue. It tells how to make a profile and in fuselage fuel tanks. I haven't had a blurb problem.
 

[Steve Fitton]

Nice work on that tank Scott!!!

One of your club how to sessions could be on how to make a tank, I would love to see that done in person   

[Tom Luciano]

I had this exact problem on my twister and my Vector when I used a 4oz tank. I agree you need more fuel. I have since opened up the exhaust(more grunt) and gone to a 5 oz. tank and never had a problem.

my la is very reliable and consistent!

Tom

[Scott Richlen]

Hey Steve - we're hoping to schedule a tank-making clinic sometime this spring.  Hopefully we can squeeze it in between flying sessions and trying to get our P-51s done.  I better get Roger's article out and review it too.

Scott

[Brett Buck]

I had this exact problem on my twister and my Vector when I used a 4oz tank. I agree you need more fuel. I have since opened up the exhaust(more grunt) and gone to a 5 oz. tank and never had a problem.

   The issue with simply putting in more fuel is, while it works, you end up with a lot of laps left over at the end. The angle of the wedge needs to be just enough to get it through the 4-leaf with about 1/4 ounce of fuel, so it can be cut off with a cutoff loop 3-4 laps later.

     The wedge angle of the typical Veco T-21-style tank (current sold by Brodak) is usually about 1/2 the angle necessary. Make a tank with the angle about twice as much and you should be OK.

     It depends a little bit on how the airplane is trimmed (lots of rudder offset makes things worse, for example) but usually kicking the rear of the tank out 1/4" or so, or making it with about the same amount of taper, is sufficient.

     Brett

[Mark Mc]

When mine did that and crashed, I finally just built my own tank.  Problem went away.  Ask Paul Walker how to plumb it.

BTW, my LA-46 uses 4 5/8 ounces to get through the pattern in cool weather.

See the shape of the tank in the wooden buck I use.  Note how its pinched at the back.  Note where my uniflow line is positioned.

Scott

Okay, being a Noob, I have a couple of questions.  The pics of your tank look pretty self-explanatory.  My questions are:
1)  What material do you make the tank out of and where do you get it?
2)  What type of solder do you use?  I assume you use solid core with paste flux rather than flux core?
3)  What kind of soldering iron/gun do you use?
4)  Any special tips on closing out the tank after the interior is all soldered up?
5)  Any good videos/web pages on making tanks?
6) I have commercial tanks that some say are prone to leaking.  Use the same iron/gun and solder you use on your tanks to go back over those commercial joints?

Thanks,
Mark

[Tim Wescott]

I'm not Scott, but here's my take:

Okay, being a Noob, I have a couple of questions.  The pics of your tank look pretty self-explanatory.  My questions are:
1)  What material do you make the tank out of and where do you get it?

Tin-plated steel.  If you buy sheets it'll probably just be called "tin", although "tinplate" and "tin plated steel" will appear too.  K&S sells it, or you can start using Powermaster fuel and use old fuel cans.  If you have other flyers in your area you may be able to beg some.  Some grocery-store items still come in tinplate cans, mostly stuff that has pineapples in it.  Grocery-store tinplate cans work, but has ribs, which leads to ribbing from your flying buddies.

2)  What type of solder do you use?  I assume you use solid core with paste flux rather than flux core?

Nearly anything will work.  Some people prefer rosin-core ("electrical") solder because it doesn't leave corrosive flux behind.  Some people use paste or liquid flux.  Pick your poison -- if you use tinplate that's in good shape it'll solder like a dream with just about anything.

3)  What kind of soldering iron/gun do you use?

Just about anything will do.  I'm a freelance circuit designer, metalworking hobbyist, and modeler.  In addition, my wife used to do stained glass.  So we have a LOT of soldering irons around.  Just about every one I've tried works.  My preference is for one with a massive tip, because the ones with a light-weight tip tend to cool down as soon as they touch the tank, and take some time to heat up again.  But people have reported success with just about everything.

4)  Any special tips on closing out the tank after the interior is all soldered up?

Start by making sure everything fits really well before applying a drop of solder, and buttoning up the tank will just happen.  Be sure to double-check that all the tubes are in the right place and tacked down an both ends before you button it up though -- I never get as good of results when I have to open a tank and re-close it than I do the first time around.

Be sure to pressure test when you're done.  I plug off all the tubes but one, hold the tank underwater, and fill it with a fueling syringe.  Usually everything is fine the first time out, but sometimes there's leaks, which you then identify by the bubbles and fix.

5)  Any good videos/web pages on making tanks?

Yes, but I can't point you to any.  Google is your friend.  There are magazine articles and threads right here on Stunthanger, too.

6) I have commercial tanks that some say are prone to leaking.  Use the same iron/gun and solder you use on your tanks to go back over those commercial joints?

Yes.  Use the same pressure test, then fix with a soldering gun/iron/whatever.

Thanks,
Mark

You are welcome, for whatever my babbling is worth.

[Chris McMillin]

Oh?

LOL.

[Bob Hudak]

Tank. Uniflo getting uncovered. Maybe. 1/2 ounce bigger tank.

1/2 oz. more fuel and he will over run the pattern, it happens when he is doing the clover. I would try the Armorall or silicone like Steve suggests.

[Brett Buck]

1/2 oz. more fuel and he will over run the pattern, it happens when he is doing the clover. I would try the Armorall or silicone like Steve suggests.

I am not sure why - this is an  absolutely classic "t-21" wedge angle" problem, and a big reason they aren't used that much any more. Do you think there is some sort of foaming going on?
 
   Brett

[Bob Hudak]

I am not sure why - this is an  absolutely classic "t-21" wedge angle" problem, and a big reason they aren't used that much any more. Do you think there is some sort of foaming going on?
 
   Brett

Yes I do feel foam is creating some grief for him. He stated that the engine always quit then came back on(except the wrecking flight)in the climbing leg. Short of building a tank Armorall may cure the foam suck.

[FLOYD CARTER]

Not sure all the suggestions are the right ones.  I run the LA46 with a 4 oz RECTANGULAR home-brew uniflow tank. No baffles or such things.  I like the rectangular tanks precisely for the reason that the engine takes a couple laps to "cough" out, and thus preventing sudden stops.  Any kind of a wedge will burn all the fuel, but that might not be a good thing.

A fuel starvation issue can be identified simply by adding more fuel, like Brett said.  We normally fuel enough for 10 laps after finishing the pattern.  That's better than running out in the clover.

Floyd

[Randy Powell]

Back in my ST60 days, I built tanks with a hopper on the side (about 1/2 oz) and a bleed system in the tank to keep the fuel from sloshing around. Thing would run to the end of the fuel and shut off like a light switch. Worked for me.

[Brett Buck]

Yes I do feel foam is creating some grief for him. He stated that the engine always quit then came back on(except the wrecking flight)in the climbing leg. Short of building a tank Armorall may cure the foam suck.

   I got the symptoms, but I don't think you need foam for that to happen. If I run short, mine will do exactly the same thing - almost quit in the inside top loop, but if it makes it through, it will always get through the rest of the maneuver. Outside loops won't cut it (since the nose yaws in a bit, running the fuel to the rear) and the lower inside loop will usually work (because there's more lateral G in the bottom loop, as opposed to the top).  That's why an inside cutoff loop works, but the outsides don't.

    I'm not there, so I will defer to the people hearing it in person -  but the symptoms appear to be absolutely classic "not enough wedge".

     Brett

[Brett Buck]

Not sure all the suggestions are the right ones.  I run the LA46 with a 4 oz RECTANGULAR home-brew uniflow tank. No baffles or such things.  I like the rectangular tanks precisely for the reason that the engine takes a couple laps to "cough" out, and thus preventing sudden stops.  Any kind of a wedge will burn all the fuel, but that might not be a good thing.

A fuel starvation issue can be identified simply by adding more fuel, like Brett said.  We normally fuel enough for 10 laps after finishing the pattern.  That's better than running out in the clover.

   In most cases, you can't afford or can't tolerate enough extra fuel to get around it, particularly in FAI or if you run slow lap times. I needs to run *absolutely no different* through the clover, and then cut off a few laps later. Most cases, particularly with a T-21 style tank, if you get the fuel load under the limit, it starts going occasionally lean as early as the hourglass. I can tell when I am in trouble when I get a couple hundred RPM rise across the bottom of the hourglass(because the fuel ran to the front and down of the tank during the pullout on the descending leg).

   The Veco tank used to work fine in Noblers with a Fox, because it just didn't turn tight enough, but that's not the case any more.
 
   The key is the wedge angle, and taper/cant. It only has to be a little steeper than a T-21  - the really sharp type as shown above works even better, but it doesn't have to be that steep, and that deep a wedge cut into the capacity a lot.

     Brett

[Scott Richlen]

Brett:

It's hard to tell by the pictures in my previous post, but my tank is 1.25 inches tall (deep? thick?) and not .75 inches like most commercial tanks.  So a steep wedge is easy to have without any loss of fuel capacity.

Another advantage of making your own tank.

Scott

[Scott Richlen]

Okay, being a Noob, I have a couple of questions.  The pics of your tank look pretty self-explanatory.  My questions are:
1)  What material do you make the tank out of and where do you get it?
2)  What type of solder do you use?  I assume you use solid core with paste flux rather than flux core?
3)  What kind of soldering iron/gun do you use?
4)  Any special tips on closing out the tank after the interior is all soldered up?
5)  Any good videos/web pages on making tanks?
6) I have commercial tanks that some say are prone to leaking.  Use the same iron/gun and solder you use on your tanks to go back over those commercial joints?

Thanks,
Mark

Mark:

In addition to what Tim said (thanks Tim, you saved me a lot of typing) I'll add:
1.  Although I have made tanks from old lacquer cans, K&S is better.  I get the larger sheets of .008 tinsheet (you may have to order it since many hobby shops carry only the smaller pieces since they don't understand what it is used for.)  The K&S is easier to solder and ends up being a lighter tank.
2.  Same experience as Tim.  I get my solder either at Radio Shack or Home Depot
3.  I use a stick iron made for stained glass.  I found the electronic Weller much harder to use as it doesn't have enough heat capacity being designed for soldering thin copper wire and the like.
4.  You've identified the fun part
5.  You'll have to show up at our shop session this spring on making tanks (or tell Steve F to bring his camera...)
6.  Throw the commercial tanks away and build your own.  Here's a good starting point: get a tank kit from Brodaks.  They come in various sizes.  It already has the shaped endings and all the tin formed.  You just have to solder it together.  However, if you want to build the tank with a pinched back end, you should make a wood buck like I did (easy to do with a scrap of 2x4) and form the K&S around it.  (Just remember as you are making your first two or three tanks to keep saying to yourself:"this is building character, this is building character, this is building ... etc.")

Scott

[Tim Wescott]

(Just remember as you are making your first two or three tanks to keep saying to yourself:"this is building character, this is building character, this is building ... etc.")

What, he's not supposed to remember not to leave the buck in?

[Chris Belcher]

OK...I'm with Brett on this one. I do have enough fuel to do at least 10 laps after the pattern, sometimes 15 depending on needle setting, i.e. a little leaner setting if windy. I also always use armor all in my fuel, I know there are debates over this one too but I have been doing that since the 90s. It OBVIOUSLY keeps fuel from foaming and i only use about 4-5 drops in a gallon. (I used to use a couple of squirts but have now seen a few drops works pretty well.) My gut tells me it is simply the pick up sucking air at the exact wrong time due to fact that it ALWAYS happens at the exact same place in the clover...at the bottom of the outside loop on the way up...worst place really...it's n the way straight up and man does it slow down fast an lose tension in a heartbeat.
Does anyone sell tanks with the angle Brett is talking about?
And Brett...I LOVE a solid 2 stroke run with a 4 ish prop.Seems the speed stays the same throughout and no wind up. The ONLY issue i have (well...other than the clover burp) is if i set a little too lean it sags at certain places but then I just back off about 200 rpm and its back in the sweet spot. Tach is a must...

[Brett Buck]

Does anyone sell tanks with the angle Brett is talking about?
And Brett...I LOVE a solid 2 stroke run with a 4 ish prop.Seems the speed stays the same throughout and no wind up. The ONLY issue i have (well...other than the clover burp) is if i set a little too lean it sags at certain places but then I just back off about 200 rpm and its back in the sweet spot. Tach is a must...

  I make my own tanks, it's really pretty easy once you have a good template. I don't use any sort of mold, just a CAD-drawn paper templates. Glue it to the metal with spray adhesive, cut it out with good scissors, bend along the lines, and soak the paper off in lacquer thinner.

    If it's sagging off in the maneuvers, I would start with 5% more nitro, which should let you back off on the needle and get the same RPM, and thus run a bit richer. If 5% is too much, mix 50/50 of each type in the syringe. Alternately, .002 or .005 more venturi, or .002 or so less head clearance. Or trim 1/16" off the prop (or even just smooth out the airfoil at the tip). I would certainly start with nitro, it's trivial to change it on the fly. At least one well-known modeler has been known to adjust for variation throughout the day with nitro (mixed in the syringe, say, 2 ounces of 15 and the rest 10, that sort of thing) instead of needle adjustment!  I haven't quite gotten there, but certainly, my buddies and I have been compensating for location/altitude changes with nitro for a very long time.

    Brett

 

[RogerGreene]

Chris,

I made these tanks using the Tank Bender found in Stunt News Sept/Oct 2013.