3w 70 fuel consumption

[barrie burton]

I have a 3w 70 in a glider tug.It has a 1 pint metal fuel tank.Anyone any ideas if that tank is large enough.It is very difficult to fit a larger tank in the cowl area.On the tow,I expect the motor to be running flat out,but throttled back there after.

Barrie B

[John Greenfield]

Barry

As a guide we have 1.5 litre tanks in out Greenley tugs powered by Zenoah 62's and can easily get 15 tows to 1200ft on a tankfull so it really does depend on how much towing you want to do between fills and how high you tow to.

John

[barrie burton]

Thanks,John,we do about 6 tows in succession,this gives the other normal flyers a chance to fly.What I did not mention,is that after about a 10 min flight,not towing,I seem to have run out of fuel and had to make a dead stick.No leaks were apparent and the tank was full.I was wondering if the 3 W 70 was a thirsty engine

Barrie B

[Tony Collins 1073]

Just a thought Barrie. If the clunk pipe has come off inside the tank you will only have half a tank to use before the engine cuts. Happened to me once.
Tony.

[barrie burton]

Tony,no clunk,the outlet to the engine is via a soldered pipe out of the bottom of the tank.

[Tony Collins 1073]

No hairy batics then Barry.

[Arthur Fielding]

Hi
Just an idea
I found out some time ago now that petrol engines need a felt clunk/filter to stop air bubbles that form in the tank due to engine vibration, being sucked up to the carb causing the engine to stop.
Could be when you tank runs down it sucks air bubbles and stops .Might be worth a new tank with a felt clunk.
Good luck
Arthur.

[John Greenfield]

Barry

We have a few warbirds in the club that use the 3W 70cc motor and they all exhibit "normal" fuel consumption. I would however suggest that a 1 pint tank is quite small for the size motor.

Not having a clunk system will also mean that you will never use up all the fuel in the tank so reducing the amount of fuel practically available.

John

[Cary Bailey]

I have a 3w 70 in a glider tug.It has a 1 pint metal fuel tank.Anyone any ideas if that tank is large enough.It is very difficult to fit a larger tank in the cowl area.On the tow,I expect the motor to be running flat out,but throttled back there after.

Barrie B

Short fuel line from a metal tank that will vibrate/resonate causing fuel to froth, will not not settle the fuel before reaching the carb intake. The intake will collect the "air" until a glug of it gets released from the chamber into the motor then the motor quits! You try and find out why this is happening but no "air" is found. I have had this happen on race engines when the fuel tank has been close to the carbs. We raised the tank so that the "air" was able to release itself back into the tank. We could see the problem when we extended the fuel line to 3 times it's length and the results that the observed were that air locks formed at the top of the fuel line. (I used clear fuel line for this purpose). Once the air lock formed it could then be seen to be drawn into the carb when the throttle was opened and the motor stopped. The fuel tank we were using was a pit pick up type, no clunk, the tank was causing the frothing of the fuel.
You could reposition your tank above the carb slightly or even move it to the CofG position within the fuselage & fit a bigger tank (which also will cause less frothing)!
Cary

[barrie burton]

Thank you for your help,gentlemen,I am going to fit a 1 litre clear tank in the cabin area,that way I can see fuel usage.I don't do hairy batics with it,it is a Max Holste Broussard,a very sedate aircraft.

Barrie B