Why can't we simply increase tank size for more flight time?
 

Other than considering increased weight, what are the disadvantages and contraindications to plugging in a larger fuel tank in glow planes to maximize air time, if the tank sits at or near the COG? For example, if you're only getting 8 minutes on a 10 oz tank, why not put in a 14+ oz tank? Thanks

RE: Why can't we simply increase tank size for more flight time?
 

I generally fit the largest tank which fits into the tank compartment, and then fill her up and fly until its within a couple of minutes of its empty time.

The only problem is the weight and position, but you have already considered those things, so go ahead and fit the largest tank you can get in, you don't have to fill it up.

RE: Why can't we simply increase tank size for more flight time?
 

I agree with hamishrock. If it calls for a 10oz and a 14oz will fit I go with the bigger. I"ll even consider differant shaped tanks to get more fuel. I've even enlarged the tank compartment, with a ARF it may not be possible, but building a kit - changes can be made by thinking ahead.

RE: Why can't we simply increase tank size for more flight time?
 

You have already touched on the reason as to 'Why Not?' [:o] Weight.

These AC are designed to fly with certain weights IF you increase the weight they do not fly - very well - [&o]

So - what am I talking about? The performance of the AC. If you increase the fuel from 10 - 14 oz ... fine you just bought yourself and extra 5 minutes of flight time - BUT the first 5 minutes thw plane flies like a brick because it is too heavy. [:@][:'(]

You will spend this time lumbering into the air (If you can get off the ground) and then any manouvers that you do will be slow and sloppy. Once you burn off some fuel - the responsiveness of the AC will improve dramatically.

I see this with my AC daily, I can do some manouvers only after 1/2 a tank has been burned. :eek:

Your call - Happy Landings

RE: Why can't we simply increase tank size for more flight time?
 

Agreed with bbbair. Plus, it all does depends on what type of flying you do. If your only goal is to fly circuits around the field heck put two tanks in, you’re not going to notice or care that you have a brick for a plane.

However for those that are putting a plane through its paces and constantly expanding the boundaries of there abilities don’t care to have expanded flight time. After 8-10 minutes of getting your adrenalin pumping… Need to stop and take a break anyway.

To me if you don’t feel mentally spent and ready to land after a 10 minute flight you didn’t fly fast enough, low enough, or bold enough.

RE: Why can't we simply increase tank size for more flight time?
 

I have noticed that some engines don't run well with larger tanks. I don't know why, maybe it's something to do with pressurization from the muffler.

RE: Why can't we simply increase tank size for more flight time?
 

This has been my experience also. My Magnum 15 used a 4oz tank, I switched to 3oz and it ran better from full to empty.
On the other hand, my Saito 45 will run 35 minutes on an 8oz tank without a hitch. The 45 was replaced with an 82, 8oz is the perfect size. I used to like a flight lasting 20-30 minutes, 10-12 is more enjoyable for me now.

RE: Why can't we simply increase tank size for more flight time?
 

JPMacG has the right idea.
Although I can't remember or recite the exact technicality of it, there is something called the "tank head."

It has to do with the size of the area the fuel is being drawn from, and the size of the engine drawing it.

I'll poke around some old notes and try to get back to the thread.

RE: Why can't we simply increase tank size for more flight time?
 

Yeah, that's what I thought... having to do with the pressure in the tank or something like that. Please keep us all updated!

RE: Why can't we simply increase tank size for more flight time?
 

it's called head pressire and fuel draw.a large tank that os full has alot mire head pressure than a small tank.the fuel will want to gravity ffed to the engine so you atart with a needle that is closed more than normal.as the fuel depletes the head pressire decreases as does the fuel draw and the engine starts runnong lean and dies or overheats and gets damaged.

RE: Why can't we simply increase tank size for more flight time?
 

If the engine is positioned correctly, with the spraybar of the carb within 3/8" of the centerline of the center of the tank, any engine will gravity feed from full to half a tank. The pressure coming from the muffler to the fuel tank is just barely over atmospheric. Whether the tank is full, or you're running on fumes, there is the same ammount of air pressure in the tank. The head pressure comes from the weight of the fuel from the full to 1/2 tank. If your engine is set up correctly, although it is harder with an airbleed carb setup, the little bit of pressure the tank gets from the exhaust should be more than enough to assist in drawing fuel. The biggest problem I have seen with bigger tanks isn't so much the weight itself, but where the weight is. All the extra weight is forward of the center of gravity making the plane really nose heavy. You could compensate by moving the tank farther back, but then you would run into head pressure and draw problems, but it's nothing a #3 bolt through the end of the muffler won't cure...

RE: Why can't we simply increase tank size for more flight time?
 

Now, if you use a YS engine with a built-in pump, will any of this matter?

RE: Why can't we simply increase tank size for more flight time?
 

As far as the pressure problems and fuel draw, no. But you would still have to move the tank back toward the CG to avoid being nose heavy.

RE: Why can't we simply increase tank size for more flight time?
 

Don't forget that after 10 --14 minutes YOU may becoming a frequency HOG. ENJOY !!! RED