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PUSHER engine - fuel flow problem w 2 tanks

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PUSHER engine - fuel flow problem w 2 tanks

Old 02-21-2007, 12:14 AM
  #1  
suzonka
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Default PUSHER engine - fuel flow problem w 2 tanks

I have a canard , my first and I had to set up a header tank so I could come up with at least 6 oz total fuel ,now the tank clunks are facing the rear of the plane and the engine is a pusher 25 BB with a stock muffler I added a short 5 inch extention on the muffler to get more back pressure to the tanks, it ran a little better Now but seems still starving for fuel so should I add a longer silicon tubing muffler extention to get even more back pressure say 8 inches? and when I raise the engine on a regular plane to set the high speed neele valve isnt it the opposite with a pusher so you lower the engine towards the ground to set up the needle valve? Will a smaller prop that revs the motor more also help give me more back pressure because now Im useing a 9x6 on the 25BB engine and I dont hear the full rpm range sound as I open it to full throttle?? whats your opinions,thanks anyone.
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Old 02-21-2007, 09:28 PM
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cwesh
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

Humm...

Looking at your picture, you do want the clunks to the rear of the plane, otherwise you could starve the engine of fuel in a climb.

Checking the needle setting, you still need to raise the engine like a front mounted one, however, don't raise it too much, 45 degrees should do, otherwise you could starve the engine of fuel if the clunk does not fall forward and comes out of the fuel. Personally, I don't do this check on them, if the engine is above the fuel, you are heading downhill [X(] , and climbing out the fuel is above the engine, I set the needle valve sitting level on the starting stand and go fly.

As to the lean condition, not much advice there, on my glow powered canard, the Starliner Mk IV, I have 14 inches of fuel line, running from the front of the tank to the engine. Never had any problem with a lean condition, always runs great. I do run my engine slightly on the rich side, I set the mixture to produce a slight smoke trail at full throttle. Also, it is a O.S. .91FX and the size may be the difference in why it works fine. My smallest pusher was a .45, had non problems with long fuel lines on those one either.

Later!
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Old 02-21-2007, 09:57 PM
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Villa
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

Hi suzonka
I have the Canard shown to the left of this note. It uses an 8 oz tank located in front of the main wing(very far away), plus a 1 oz tank just to the front of the engine. The fuel lines and clunk orientation is just as you have shown. The 1 oz tank is always 100% full. I think that is the difference between yours and mine. I never, ever, have a problem with the engine. I use an OS 46FX engine. My rule is to get the plane into the air within 30 seconds of starting the engine, or the engine will overheat. If the two mixture screws need adjustment, I first replace the pusher prop with and identical tractor prop, then do all adjustments. I can point the engine up and it acts like a standard set up. No problem. The secret is to have the small tank next to the engine where it will be 100% full all of the time. Let me know what you do and how it performs.

Old 02-21-2007, 10:50 PM
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Tall Paul
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

My pushers use a single tank, with the clunk at the rear.
Never noticed any problem with fuel feed.
Old 02-21-2007, 11:07 PM
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Villa
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

Tall Paul
The center of my main tank is about 18 inches in front of the carburator. I was seeing a great deal of engine RPM change in manuevers.
Old 02-21-2007, 11:34 PM
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suzonka
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Default RE: PUSHER engine - fuel flow problem w 2 tanks


ORIGINAL: Villa

Hi suzonka
I have the Canard shown to the left of this note. It uses an 8 oz tank located in front of the main wing(very far away), plus a 1 oz tank just to the front of the engine. The fuel lines and clunk orientation is just as you have shown. The 1 oz tank is always 100% full. I think that is the difference between yours and mine. I never, ever, have a problem with the engine. I use an OS 46FX engine. My rule is to get the plane into the air within 30 seconds of starting the engine, or the engine will overheat. If the two mixture screws need adjustment, I first replace the pusher prop with and identical tractor prop, then do all adjustments. I can point the engine up and it acts like a standard set up. No problem. The secret is to have the small tank next to the engine where it will be 100% full all of the time. Let me know what you do and how it performs.

@@@@@yes Villa I have my small tank in the front of my main tank because I wanted to keep the fuel feed line close to the engine and I was wondering about how a short clunk will work if I swap the tanks around because the shorter line in a small tank dont move as flexable as a larger tanks longer clunk line. I had it running but it wants to stall if I diconnect the glow plug wire because I cant get the needle valve set right, and another problem I may have is does it matter if I have such a larger prop a 9x6 on this 25 BB engine because when I had a 8x6 it reved up much more so do you think I should stay with the smaller 8x6 prop to let the engine reach its maximum RPM and produce maybe more muffler pressure to the tank? any opinions ? by the way the smaller tank does empty first and keeps the main tank full. but if you think I should reverse my set up it will be a large job I have everything just set in right to fit.
Old 02-22-2007, 05:31 AM
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jaka
 
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

Hi!
If you use a conventional R/C tank the clunk should be at the rear...but why use a clunk in the first place! It's not needed in a sport model.
All R/C models can be flown without a clunk in the tank...all you have to do is to bend the sucktion tubing down so that the engine gets fuel when the nose points upward. OK! You can't do any lenghty inverted flights but all other maneuvers will work just fine. If you have long fuel hose it's no problemn to fly inverted for, lets say 5-10 seconds.
Best solution obviously is to use the Tettra"Bubbleless" tank which has no clunk at all. Fuel and air are separated with silicon bladder inside the tank and fuel is pressed forward to the carb by the pressure developed by the silencer/pipe.
I have had a 6oz Tettra tank in my .40 size "Pushy Cat" pylonracer for years and it works very good.
Old 02-22-2007, 08:23 AM
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Villa
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

Hi suzonka
You must solve each problem as you come to it and in some order of importance. If the engine dies when you remove the glow plug, go no further. Either solve that problem or give up the hobby. Once the engine is responding reliably, you can decide on the prop. I don't know what a 25 BB engine is. Maybe others will help you with that. Below is something I put together for myself, from info I have seen at this site. Step 4 and 5 is what you reported.

Alternate Method for Tuning 2-Cycle Engine (None Air Bleed Carb)(Air Bleed is similar)

1. High-speed needle controls from ¾ to full throttle.
2. Low speed valve controls from idle to ¾ throttle. Low speed valve dominates.
3. Start engine and after warm up go to full throttle, leaving glow driver connected. Lean out for max RPM then richen about ¼ turn.
4. Slowly reduce throttle to lowest RPM engine will run reliable, then remove glow driver.
5. If engine dies immediately it is too rich. Lean out LOW SPEED VALVE 1/8 turn, start engine and go to full throttle to clear out excess fuel. Go to idle and remove glow driver. If RPM drops it is rich. We are looking for no drop in RPM.
6. Once you feel you are there, go to full throttle. If it hesitates it is too lean. If it BLUBBERS and puts out a lot of smoke it is too rich. Make changes in 1/16 increments.
7. Now go back to the HIGH SPEED NEEDLE. Peak to max RPM and richen 1/8 turn. Hold plane vertical. If RPM drops a little richen in 1/16 increments. If RPM increases a little but keeps running it is perfect.
Old 02-22-2007, 11:44 AM
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Tall Paul
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Default RE: PUSHER engine - fuel flow problem w 2 tanks


ORIGINAL: Villa

Tall Paul
The center of my main tank is about 18 inches in front of the carburator. I was seeing a great deal of engine RPM change in manuevers.
.
No doubt! Why must the tank be that far away?
Old 02-22-2007, 03:40 PM
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Villa
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

Tall Paul
My SPAD Canard uses a 1 inch square aluminum tube as the fuselage. The 8 or 10 oz fuel tank sits on the square tube in front of the wing. The system works perfect the way it is so why change it. As it is the main tank is just about centered on the CG which is always a plus.
Old 02-23-2007, 04:40 AM
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suzonka
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Default RE: PUSHER engine - fuel flow problem w 2 tanks


ORIGINAL: jaka

Hi!
If you use a conventional R/C tank the clunk should be at the rear...but why use a clunk in the first place! It's not needed in a sport model.
All R/C models can be flown without a clunk in the tank...all you have to do is to bend the sucktion tubing down so that the engine gets fuel when the nose points upward. OK! You can't do any lenghty inverted flights but all other maneuvers will work just fine. If you have long fuel hose it's no problemn to fly inverted for, lets say 5-10 seconds.
Best solution obviously is to use the Tettra"Bubbleless" tank which has no clunk at all. Fuel and air are separated with silicon bladder inside the tank and fuel is pressed forward to the carb by the pressure developed by the silencer/pipe.
I have had a 6oz Tettra tank in my .40 size "Pushy Cat" pylonracer for years and it works very good.
Hi Jaka I went nuts and did everyhting I hope is right I got rid of the clunks and saved a lot of uneeded tubing that way I bent the suction tubes down,I dont plan on going inverted to much with this canard, I also changed my tank arrangment to the smaller 2 oz in the back near the motor and the main tank away towards the nose, I used a metal tubng extention so I wouldnt pick up pulsing from the muffler pressure with silicon tubeing. I siliconed all the joints ,no leaks, so lets see when I set the needles what happeneds? Thanks heres a picture.
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Old 02-23-2007, 09:12 PM
  #12  
suzonka
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

ORIGINAL: jaka

Hi!
If you use a conventional R/C tank the clunk should be at the rear...but why use a clunk in the first place! It's not needed in a sport model.
All R/C models can be flown without a clunk in the tank...all you have to do is to bend the sucktion tubing down so that the engine gets fuel when the nose points upward. OK! You can't do any lenghty inverted flights but all other maneuvers will work just fine. If you have long fuel hose it's no problemn to fly inverted for, lets say 5-10 seconds.
Best solution obviously is to use the Tettra"Bubbleless" tank which has no clunk at all. Fuel and air are separated with silicon bladder inside the tank and fuel is pressed forward to the carb by the pressure developed by the silencer/pipe.
I have had a 6oz Tettra tank in my .40 size "Pushy Cat" pylonracer for years and it works very good.
JAKA IS IT TRUE THAT YOUR IN A LOOP AND YOU HAVE1/3- 1/2 TANK OF FUEL LEFT OVER ,NOW THE PLANE COMMING OUT OF THE LOOP DOWN NOSE , WHERES THE CLUNK ,ITS FACEING UPWARD IN THE PLANE AND THERE ISNT ANY FUEL UP TO THE TIP OF THE CLUNK, AM I RIGHT SO FAR . SOME GUYS SAY THEY PUT A PIECE OF STRAIGHT METAL TUBING RIGHT TO THE CLUNK SO IT DOESNT GO FORWARD ON HARD LANDINS. SO IF YOUR FLYING DOWNWARD SHARPLY AND THE TANK IS 1/3 LOW ON FUEL THERES NO WAY THAT LINE IS IN THE FUEL UNTIL YOU STAIGHTEN OUT AGAIN.
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Old 02-23-2007, 09:43 PM
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suzonka
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Default RE: PUSHER engine - fuel flow problem w 2 tanks

hI HERE IS ANOTHER PICTURE
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