john491

My Feedback: (13)

I am working on a new, for me, design. It is kind of freehand. The length of the finished plane will likely be about 60", wingspan about 50" and an all-up weight of about 11 pounds. I will power it with a Xicoy X-45.
I have been under the impression that the fuel tank should be, as close as possible, centered on the CG. I have seen build threads here however that have the tank, or tanks, well forward of the CG. I have the option of making the center of the tank directly on CG, but can make the fuse about an inch thinner and hence the plane lighter if the tank is forward somewhat of the CG. In this case the location of the tank and size ( height of the fuse ) is determined by a wing spar.
I'm only talking about two inches with a 1200 cc tank.
Thoughts on location?
John

Springbok Flyer

Getting the main tank centred on the cg is the best if at all possible.

JanR

CARS II

My Feedback: (7)

If possible, if not then a little forward is not a big deal, look at jets like the Excalibur or the Kangaroo, their fuel tanks are located completely forward from the CG point.

Dave Wilshere

If you end up with the tank forward of the balance point ensure the stabiliser has generous area, and maybe have a curved canopy shape forward of the balance to generate low pressure (lift)

Always the ideal is to have it over the balance.

highhorse

My Feedback: (2)

Centered is best, but I have flown a scratch-design turbine with fuel equivalent to 10% of the gross weight located at just 11% of the MAC with no ill effects of even noticeable trim changes. You didn’t mention your chord length, but I am guessing that moving the center of your tank to a point 2” fwd of your intended CG should not produce much of an issue.

Joseph Frost

It's good to have fuel tank forward of the GC, 'not center!' You don't want to have model landing tail heavy as the left over fuel is all the way back at the end of the flying session.
Better to be nose, than tail heavy!

Placing mine well fore of the CG in my latest EDF to turbine convert.

highhorse

My Feedback: (2)

With apologies to my RC comrade, I will vehemently disagree with the logic in this post.

First: While nose heavy is indeed better than tail heavy IF the correct CG cannot be attained or is unknown (as is often the case until a newly built model), a nose heavy CG has it’s own issues/trade offs is not necessarily better than a correct CG.

Next, the “…end of flying session” aspect of the above opinion is remiss, as a fuel tank located forward of CG unavoidable dictates that the CG continuously moves aft as fuel is burned and that the end-of-flight CG is at its most aft location (and the pitch is in its least stable, most sensitive state) during the most critical phase of flight - the landing. There is NO inherent advantage of an aft-shifting CG over a stationary one, as would be implied by insisting that the tank be mounted forward.

The statement that fuel which remains in a a tank which is collocated with the CG is somehow “…all the way back…” is nonsensical, as it is moves neither forward or aft from when the tank was full unless the shape of the tank makes this so, in which case the issue is tank shape vs tank location.

If one’s goal is simply to accept the trade offs of a deliberately nose-heavy (and therefore more stable airplane) AND the option exists to place the fuel tank on the CG, then do indeed place the fuel on the CG while attaining the nose-heavy state through other methods which do not involve continuous trim changes and a counter-productively lessening of longitudinal stability as the fuel is burned.

Last point: To restate all of the above in a neater package, I suggest asking the following question of anyone who has the option to place a tank over the CG but instead chooses to move it forward…”Why is it better that the CG move continuously aft as the flight progresses?”

That’s my opinion, at least, and other’s mileages will obviously vary. Best wishes to all :-)

Joseph Frost

In exception of 3/D stunt models I rather fly any jet model extremely nose, than aft heavy, (easiest way to find out the effects after flame outs, LOL) so I always place my fuel tanks well in front of models CofG. With some model you have no other option, anyway.

highhorse

My Feedback: (2)

Fair enough. Keep in mind though, 1) that (nose vs tail heavy) wasn’t the OP’s question and 2) your jet isn’t gliding as far after a flameout if it’s nose heavy, more so if it’s “extremely nose heavy”, because nose heavy pays a price in wing loading.

Joseph Frost

It is only natural we like doing thing different way, I'm only sharing my experience and it's up to an individual to choose what's the best option for each scenario. In my "F9F" Panther the center of fuel tank is 6.5 inches ahead of CG. No drama at all, as I find from my experience every jet model is a pretty good glider if nose heavy to keep the speed up, when the worst happen to land dead stick. Certainly not the opposite, with the alfa stall and certain dead. LOL.
See my 1st. landing attempt couple days ago with one of my giant EDF jet, I have purposely set pretty tail heavy with 4 kilo of batteries way back than normal just as a test trial for my other project I'm currently finishing off. If I didn't have 10+ kilo burst thrust I would be most likely dead man, after that high alfa flare stall, LOL. The model was so tail heavy I actually had to force it nose down, which is not my favored, I rather gently pull up during landings. LOL. (BBB very tail heavy load flight)

A great f/tank design to minimize tail heaviness at low fuel level.