nrad2000

Why is it that they put fuel tanks in front of the CG? Would it be more ideal if they brought it closer or ontop of the CG?

goirish

My guess would be so the tank would be closer to the engine. Less plumbing I suppose.

RCKen

My Feedback: (9)

The reason is because of the distance the fuel has to be pulled. If you are using just muffler pressure on the tank then normally the tank ends up sitting to far away from the engine when it is moved to the CG of the plane. However, if you have an engine that has some sort of pump system for fuel then you can easily move the tank back to the CG. Pattern planes do this alot for the very reason that they want to have the CG of the plane be constant throughout the flight.

Ken

Jetdesign

My Feedback: (8)

Getting fuel from the CG to a glow engine, for some reason, is a lot harder than it sounds. There are pumps and regulators, but all add areas for problems to happen.

Best option, in my opinion, is a pumped engine (engine that comes with it's own pump, designed to work with that engine and carburetor).

I believe the most successful add-on system is a Cline regulator. This system has you pressurize the fuel tank with muffler pressure and a check valve, then regulates the fuel before the carb - it uses a diaphragm that operates as the engine demands fuel (using the compression, as mentioned above). Cline regulator is very similar to a Walbro carburetor that guys use on Gas engines, and is somewhat similar to a YS glow engines that use pressurized tank and diaphragm as well.

Perry pumps are just that- pumps. They pump fuel from the tank to the engine. Tuning is difficult as the carbs on these engines are not designed to work with pressurized fuel. They are accommodated by closing the low-end valve (almost fully closed), then adjusting the high end to best performance. It is tricky, but it works.

I tried all this stuff and ended up switching to electric, mostly because I like the CG at the fuel tank.

nrad2000

I've got an OS FS 91 w/ pump. You guys think this is enough pump power to draw fuel from a tank thats located close to the CG? I'm finishing the build of an Phoenix Extra 330s and the fuel tank that it came with seemed awefully small. So I picked up a 12oz tank - w/ full fuel I'm guessing the plane will be awefully nose heavy. I can easily bring it back towards or very close to CG. So I guess what I'm trying to ask is - with my OS FS 91 w/ pump and the fuel tank pushed back to CG - will this combination work for the plane and it's flying?

Jetdesign

My Feedback: (8)

With a pumped engine you can put your tank on the CG.

That is a good engine

da Rock

Because they can, and because it makes the rest of the design easier.

Does it affect the flight performance enough that it matters? Only really matters to precision pilots who are sharp enough to see the difference and feel the need to deal with the problem of fuel feed.

da Rock

Will it pump well enough? It was designed to pump from as far back as the CG can be in a model designed for a 91. Yes, it will pump well enough unless you plan to use it in a much larger model.

Will the 12oz tank be enough? It should be adequate. I get a normal flight time out of 7oz worth of fuel from regular sized tanks in 5 planes powered by 91FXs and 4strokes are supposed to be more efficient.

Will the plane be "awfully nose heavy when full of fuel"? Nope, not even slightly nose heavy. They are designed to take off with a full fuel load. And the aeobatic ones are designed to execute maneuvers in front of judges immediately after take off, and do. And designed to execute maneuvers in front of judges just before landing. No reason to re-think something that's been common practice forever.

Yes, your combination will work. Like gangbusters.

HighPlains

My Feedback: (1)

I thought you were studying to be a mechanical engineer. Maybe you should rethink that statement and try again.

ES CONTROL

a under powered plane needs full thro. in a vertical position. A pump is not needed .

Gray Beard

My Feedback: (-1)

The pump on a OS .91 will draw fuel as far as you want to put the tank. I use both the pumped OS and YS engines and if the plane design allows it I put the tank over the CG. Is it important?? Not really but there is no trim changes during flight but most people wouldn't notice that anyway. It is often easier to set up a plane when it doesn't mater where you put the fuel tank, high, low, way back, way close. There are more important reasons to use pumped engines but again, most people wouldn't notice that either.

Jetdesign

My Feedback: (8)

This is why I generally stay the heck away from this forum.

HighPlains

My Feedback: (1)

Come on Joe. Job interviews will be much rougher than this forum. If you succeed, then you get to ask the tough questions after your manager tosses a stack of resumes on your desk.

Jetdesign

My Feedback: (8)

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HighPlains

My Feedback: (1)

Carbs:
Really?

Jetdesign

My Feedback: (8)

.

HighPlains

My Feedback: (1)

If that was the case, then venturi size would not matter to fuel draw. Your pumped engines are marvels of great design with terrific power output compared to the normal sport engines. All of this may not matter too much longer with the way electrics are taking over.

Are you about finished with school? Ready for the "real world" or what ever the phrase is today?

nrad2000

Off on a tangent - is there another way of securing the wings to the fuse without the nylon bolts?

p51Dpony

two things

scenario one: my 15 yr old has one of those "predator UaV" arfs designed for electric, has about a 45" wing span, rather than go electric I'm planning to put a magnum .15 on back cause it fits nice, gonna put a main tank at CG (which is quite a ways away on that rear engine configuration) but planning to put a small header tank near engine. The engines pressurizing muffler will feed to main tank which then sends its fuel to the head... just like we do w/ helis.  Any doom and gloom predictions?  If someone suggests I need stay electric w/ that design I will ask the moderator to permanently ban you from this site  [:'(]

scenario two:  I see the statement of carb not handling pressure because engine draws the fuel was attacked.... you need to then clarify why statement is wrong, Obi Wan Kenobi explained it best when he said certain things are true in a certain context or point of view... if you cant explain your gripe I will ask the moderator to permanently ban you from this site [:-]

oh wait, , a 3rd scenario, wouldn't it be wonderfull if fuel injected engines were more available for models!!??  All those heli tuning issues, all those cg issues, all those overheating or flame out issues would have programming or jetting curves to make our lives more focused on flying than dead sticks.  I think I saw one awhile back, more expensive than a gas saito or ys which means $ is the limiting factor but the technology is feasible right?  If someone says it could never happen, you know what I'm gonna do....

rcacro

steel bolts, rubber bands, string, epoxy, Zeus fasteners, dowel and clips

jetmech05

The tanks are forward of CG for the reasons given....better to be nose heavy than tail heavy...so as you burn fuel you are burning into CG...even a dead stick right after take off with a full tank won't be a CG issue...
Nylon bolts work very well...I have never seen a nylon bolt strip or break in the air......I've seen wing tubes bend and the bolts hold
Good flying

cessnaflyer54

My Feedback: (68)

Go gas and you will not have a problem finding a pump or regulator. Put the tank where ever you please and
a whole cleaner than glow. For the same amount of glow to gas, your flight times are longer and cheeper.
Just a thought.

RCER88

My Feedback: (25)

If you are concerned put a small tank like a 4oz "feeder" tank close to the engine then put the "main" tank on the CG. We use this technique all the time on glow engines so we can install retracts in the nose. The 4oz tank will keep the motor running as the exhaust pressure pushes fuel from the main.

That system works.

Good luck.

Gray Beard

My Feedback: (-1)

If in doubt then set the engine and tanks up on a starting stand and give it a try. I have seen a few header tanks solve a problem and seen others do the set up and feeding problems were still there. I gave it a try last year on one plane and it was no help at all. Then I discovered it was the engine with a problem so the tanks may have worked? You can also set up the engine and tank on a stand and see how far your engine will draw fuel. Some are just better then others so your engine may work with just one fuel tank. Never know until you try it.

ArcticCatRider

My Feedback: (6)

There are very few planes out there that can have a tank right at the CG. A mid, and shoulder wing design would make it next to impossible....and a high wing you wouldn't bother with. So that leaves you with low wings and biplanes, and putting the tank typically where all your radio gear is.

I've never tried a "long range" set up. I think an engine at WOT might handle it, but I think you'd loose it on the idle. You'll notice when you put your finger over the venturi and make a perfect vaccuum, it seems the engine can pull infinite fuel, but this just isn't the case when it's naturally aspirating.

It's a good thought though. Don't let a shifting CG make you go electric...if you wanted to get uber creative you could use an extra channel on your radio to operate a moving ballast in the aft section of your fuse, to negate the effect of diminishing ballast up front.

If it was me, I'd just fill the tank up and fly it.