Fuel Tank placement

[Bud Shupe]

I know that this is probably a simple question, but where does the fuel tank go? AT the cg ? or ahead?

[KeithLuneau]

Usually right behind the firewall. Balance it with the tank empty though.

[Bud Shupe]

Thanks Keith, I can see that the plane will be nose-heavy with a full tank and perfect when empty.
Thank you.:)

[KeithLuneau]

Yeah, it's easier to deal with a nose-heavy plane on take-off, than a tail-heavy one on landing... :) I've tried mounting the tank on the CG, but had problems getting the fuel to the engine, I guess it didn;t like the long fuel lines for some reason.

[Bud Shupe]

I thought I knew a lot about IC, but I truly don't understand the relationship between 2C engines and thier fuel tanks. I am contemplating a EP to Glow conversion,1/2A, Wasp .061 and I see that MAX fuel tank size is 2oz. Any tank larger can "lead to excessive leaning" or "erratic engine operation and is not recommended". What is happening here and how doe's that work?

[KeithLuneau]

Hmm, not sure really. My best guess is that the smalle motor can't hold enough pressure in a larger tank to get good fuel flow. 2 oz. should be plenty though. I've never ran a Norvel, but all my Cox's get around 10 minutes on 1 oz.

[Bud Morrison]

yeah with a 2 oz tank your gonna fly for a lonnngggg time

[T. Lyttle]

The draw varies from engine to engine as well. The Wasp was a hot engine, and the draw wasn't that great, but a reed Cox seems to be able to draw fuel from as far away as the tailcone... I have seen kids mount tanks in the goofiest places, and still get good runs.

I run diesels exclusively now (closest glo fuel is 80 miles away), and my PAW 50 runs forever on a 1/2oz tank, with reasonable draw; you just run what you can when you can!

[KeithLuneau]

I run diesels exclusively now (closest glo fuel is 80 miles away)...

I know what you mean, that's why I fly primarily electrics. Just what is involved with running a diesel though? I miss flying IC stuff.

[Tony Oliver]

With most engines, it's not really the fuel draw that's the problem with the tank away from the engine, it's the change of fuel level during flight.

If you consider a small model with the tank at the usual 2/3 level with the spraybar, but 8 inches behind the engine. It starts with no problem, draws fuel and runs without any difficulty at full revs and at idle. Point the nose vertical, and the tank's now 8inches below the carb and it has a long way to pull the fuel up, so the engine runs lean or dies of fuel starvation. Point the nose down vertically and you've got a fuel level 8 inches higher than the spraybar - fuel will syphon into the tank and it's likely to run rich as the fuel is not being pulled in any way - it's being pushed.

We are asking a lot of an engine. It burns fuel but needs air to burn it, and only 20% of that is oxygen. Out-and-out racing engines have a huge hole as an intake but the downside is that it will not pull air in with the suction needed to add fuel, so a high pressure system is needed to force fuel in.

The opposite - small hole, lots of suck will be what beginners engines have. There's less power but more flexibility.

Give your engine a break - put the tank as close as you possibly can to the engine, and at the right height.

The one thing which is required in all these is an air-leak free carb as anything which allows air to bypass the needlevalve will reduce fuel reliability. You must keep 'O' rings which seal the carb to the crankcase, (and in some the barrel has them too) in good condition. Some people seal the area with silicone sealant or epoxy - a bit drastic, but sometimes necessary.

I hope this helps

Tony

[T. Lyttle]

All absolutely right. My comment had to do with a PGF Chinn test that showed the Cox Bee series engines pulling ~36" before leaning out to stop! Unmatchedby any other; one only has to look at the venturi size of the Bee and, say, the Wasp to see why.

As far as the diesels are concerned, everything I need is available from the hardware store, or NAPA here, ie, kerosene, oil, ether, and amyl. The kerosene is usually stove fuel, the oil is 30w and castor (sometimes you have to go to the drugstore for that), the ether is starting fluid (here's the tricky part: the fluid is usually 50% ether, 50% kero, so one adjusts the mix to suit) and the amyl shows up as "diesel ignition improver (wattch this stuff, is ain't friendly!), the mix being 50%kero, 15%mineral, 15%castor, 18%ether, 2%amyl. Start there, and adjust to your needs.
Diesels are tough. I have a 2.5 that was bought in 1953, runs better each time, and my PAW30 pulls at least as hard as a Cox reed. Check out Eric Clutton for more info.

[Tony Oliver]

....and aren't diesels fun to use!

Like you, I'm using an early diesel all the time (Frog 100) and have PAWs from the little .5cc up to the .34cu in (why do they change to cu in?). The snag withthem is they can be very messy, but it's offset by the smell - wonderful!

For anyone wanting to mix their own, there is plenty of info for different mixes at www.modeltechnics.com

Tony

[T. Lyttle]

Hoo, brave lad, running a prop as tough as that on there; got a spare crank, or are you just lucky?

I just love my PAW50, good beginner's engine, unlike the Miles 5cc that I ran a few times until my nerve ran out... At one time I had a couple of hundred diesels, including your Frog, flew my Frog 3.5 for many years in a Bristol Scout. Also had a pair of PAW 2.5s in a Aeromodeller ME110 profile; man what a fun machine, it would do ANYthing except land inverted! Still own a select few diesels (Doonside Mills, Sesqui, ETA Elite, etc), gonna will them to my flying buddy if he outlives me...

[Tony Oliver]

Great stuff, this nostalgia - especially when you can still live it! (why keep it in the past?).

I'm not as brave as you think - if the model noses over, the prop cuts grass and stops but doesn't hit the ground due to the wing overhang and undercart. A three point landing. It's been flying now for about 6 years so it's trimmed now. (and I normally launch over long grass).