i have .26 O.S. 4-stroke engines on my PBY catalina. in a previous thread i found that there are no good fuel pumps for this engine with confines of the engines housing. i currently have small primmer tanks behind the engines and a large tank in the belly well below the engines. i want to redo this system since the primmer tanks make a mess. can i eliminate the primmers? im not sure how well the engines draw fuel from that distance and being a twin loosing one engine from fuel starving a really bad. is there any good exaust booster i can use to pressurize the tank other then the standard exaust nipple? i know this may seem silly but this is my only fuel plane and i have only flown it once in 8 years so im not fimilar with gas engines

Jeff,


Header-tanks don't solve any problems!

Since fuel that is used from them must be replenished constantly, it eventually needs to be drawn all the way from the bottom tank.

Just use a 4-5 ounce tank for each of the engines, located in the wing right behind it.

I have often contemplated light weight, low power consumption methods of delivering fuel from a remote tank. I have never found a good solution, but I think it is worth discussing.

I have had ideas that probably will not work, like using a light weight dry fish aquarium bubbler that runs off 12 volts to pressurize the bottom tank but decided that it is probably too heavy. Also depending on how large your remote tank is, the pressure differential between a full tank and an empty tank will have a noticeable impact on the tuning of your engine - even if you are applying a constant pressure (unless that pressure is something like 10X the pressure differential or something like that - again probably outside the scope of a fish aquarium pump).

Another idea would be to buy a fuel pump intended for jets. Pump the fuel from the clunk line of your remote tank, to an input line near the top of your header tank. Then have a relief line set near the top of your header tank feeding back to your remote tank. Your remote tank would be open to the atmosphere through a third vent line. The idea here would be to only fill the remote tank (say 1L) and then turn on the pump which would fill your header tank (s) (50 mL).

This method could be around 150 ish grams but it is complex. I do not know if a jet fuel pump will tolerate methanol-based fuels. It is also expensive and complex. If the pump goes out, you will only have a few minutes of fuel. Circulating fuel throughout the plane is wasteful in energy.

So - I am kind of out of ideas....

Originally Posted by jeff262

i have .26 o.s. 4-stroke engines on my pby catalina. In a previous thread i found that there are no good fuel pumps for this engine with confines of the engines housing. I currently have small primmer tanks behind the engines and a large tank in the belly well below the engines. I want to redo this system since the primmer tanks make a mess. Can i eliminate the primmers? Im not sure how well the engines draw fuel from that distance and being a twin loosing one engine from fuel starving a really bad. Is there any good exaust booster i can use to pressurize the tank other then the standard exaust nipple? I know this may seem silly but this is my only fuel plane and i have only flown it once in 8 years so im not fimilar with gas engines

You can use the crankcases as minitaure compressors to pressurize the tanks, but as with an pressurizing system, it must bleed off quickly when RPM are dropped quickly or the engine will flood.

my next question is how many ounces of fuel will the .26 4-stroke burn at full throttle per minute?

Originally Posted by jeff262

my next question is how many ounces of fuel will the .26 4-stroke burn at full throttle per minute?

The rule of thumb is 1oz per cu in per minute so figure .26oz per minite.

A 4oz tank will give you 15 minutes flight time on one engine.

If you want to run a common tank for both, an 8oz tank will do.

I have a 20fs in an EFLITE EXTRA 260, with a 3oz tank!

I have too keep the speed up, so I am flying from 3/4's too full throttle, and I have never ran out of fuel yet!

Originally Posted by whiskykid

I have a 20fs in an EFLITE EXTRA 260, with a 3oz tank!

I have too keep the speed up, so I am flying from 3/4's too full throttle, and I have never ran out of fuel yet!

So you converted an electron burner to a 4-stroker?

OP, if you PM me I could probaly draw you up a plumbing diagram for using the engines as compressors.


It can all be done W/inexpensive inlne check valves & fuel line. You'll need an old spray bar to make a bleed off regulator.

Using the crankcases on single cylinder 4c engines to prssureize the fuel systemis a proven concept.

Saito uses it on the dual carb 300Ts. It's cheap, simple, reliable & if you tap into your engine right for the pressure outlet, you will improve engine oilnig to the main crank bearing as the valve train.

OP, if you PM me I could probaly draw you up a plumbing diagram for using the engines as compressors.

It can all be done W/inexpensive inlne check valves & fuel line. You'll need an old spray bar to make a bleed off regulator.

Using the crankcases on single cylinder 4c engines to pressureize the fuel system is a proven concept.

Saito uses it on the dual carb 300Ts. It's cheap, simple, reliable & if you tap into your engine right for the pressure outlet, you will improve engine oiling to the main crank bearing as well as the valve train.

http://www.rcgroups.com/forums/showt...ght=old+school

yup had ta do it!

i had no idea i could run a 4-stroke inverted, cool. well anywas if i wanted to keep the primer tank and the main tank how should i vent it? i currently have vents on the primmers and on the main tank and this is why i hate it because fuel keeps comming out of the primmer before everything is filled, can i just use the main tank vent and remove the vent from the primmers?

Originally Posted by jeff262

i had no idea i could run a 4-stroke inverted, cool. well anywas if i wanted to keep the primer tank and the main tank how should i vent it? i currently have vents on the primmers and on the main tank and this is why i hate it because fuel keeps comming out of the primmer before everything is filled, can i just use the main tank vent and remove the vent from the primmers?

Originally Posted by jeff262

i had no idea i could run a 4-stroke inverted, cool. well anywas if i wanted to keep the primer tank and the main tank how should i vent it? i currently have vents on the primmers and on the main tank and this is why i hate it because fuel keeps comming out of the primmer before everything is filled, can i just use the main tank vent and remove the vent from the primmers?

yes! it's only inverted till it leaves the ground!

ok judging from what you say here, I assume that you are not running a pressurized system! I know that in a perfict world, a 4 stroker will draw enough fuel to run, if the tank is level and in-line and venus lines up with mars, blah blah!
I personaly would never run a non gas engine without atleast muffler pressure!

"if it where mine" I would plumb the muffler pressure to the main tank, then split the pick-up and run those too the vent line of the header tanks, then the pick-up of the headertanks too the engines!

with a 3 line set-up on the main tank, 1 the pick-up, 2 the vent,3 a fill line!

the trick would be filling them up! start by filling up the main, then you would hafta plug the vents to the engines untill the headertanks get full!

just a thought, I am not that great with splaning things with the writen word! but I tried!