Fuel tank orientation and "aerobatic" fuel supply?

[Russ1974]

Hi,

 

At present I haven't securely fitted my fuel tank as I was unsure whether to have it perfectly flat or at an angle.  Then it got me thinking.  If it was perfectly flat, and if I put the plane in a nose dive with anything other than a completely to the brim full tank, wouldn't the engine be starved of fuel and cut out?

 

So two questions;

 

1) Should I install the tank securely or leave it loose so it can flop round a bit, and if secured, should it be flat?

 

2) How does the plane get fuel when pointing downwards?  I understand the "clunk" on the fuel pipe will give fuel during rolls etc but can't work out how it would work when the plane is pointing down.

 

Thanks!

[Ultymate]

Russ,

1/.  Deffinately secure the tank firmly if not the weight of the fuel slopping around will end up breaking the tank loose a sure recipe for disaster

 

2/.  Even in a nose down dive the fuel in your tank, thanks to inertia, will be pushed to the rear of your tank and your clunk will have no problems picking up your fuel.

[Simon B]

Go electric, then it won't matter

 

Sorry, couldn't resist

[Russ1974]

Ulty - thanks.   Simon - electric is for girls.

 

 

[Simon B]

Heheh

[Russ1974]

Fuel tank is now secured in place

[Simon B]

Here's a quick question from someone who knows little about IC.  If you're flying and the fuel tank isn't full, do you get issues with the CoG, as the fuel moves about the tank?

[John Privett]

The Cof G will move a little rearwards as the fuel gets used up.  As it's usually safer to have the C of G too far forward rather than too far rearwards the C of G is checked before the very first flight of a new plane with the tank empty. The difference is not generally noticed on sports planes and the difference between a full tank and an empty tank will be greater than a half-full tank with the fuel sloshing around.

 

"Ordinary" engines need the tank close to the engine.  Those with pumps can have the tank on the C of G and that is not uncommon with aerobatic competition models.

[Simon B]

Ah ok.  Cheers for that. 

[Russ1974]

John - a very technical and useful response.  I, on the other hand, just "shoved it in"

[Ross Clarkson]

Posted by Russ1974 on 25/09/2009 09:17:20:

Ulty - thanks.   Simon - electric is for girls.

 

 

 Ha Ha, brilliant response.

 

A little off topic but, do any model aircraft incorperate wing fuel tanks like real aircraft and if not, why not?

[John Privett]

Somebody posted a link to a video recently.  I don't recall if it was on here or another forum, but I'll keep my eyes open and if I find it again I'll post the link here!  The video was shot specifically to show how the contents of the fuel tank (ie. the fuel!) moved around during a flight.

[John Privett]

Posted by Ross Clarkson on 25/09/2009 11:07:25:

A little off topic but, do any model aircraft incorperate wing fuel tanks like real aircraft and if not, why not?

 

I've never seen it done, and I can only think of one example where I've heard of it being done.  That was on the original prototypes for the model that Maynard Hill and his team flew across the Atlantic a few years ago.  The original design had a very slim fuselage (to minimise drag) and there wasn't sufficient space to carry all the fuel required other than by putting some of it in wing tanks.  But they subsequently modified the design, making the fuselage a little bigger (for very little extra drag) and managed to fit all the fuel in the fuz.

 

For most normal, everyday model i/c engines the tank needs to be at the same height as the carb and as close behind it as possible.  Otherwise you run into problems with the mixture varying when upright vs. inverted and when climbing vs. diving.  The other problem would be having to connect/disconnect the fuel supply every time you assembled and dismantled the model.  As we haven't got to worry about pilots, passengers, cargo etc. in our planes there usually isn't a problem putting the fuel tank in the fuz - so why make things difficult by using wing tanks?

[Russ1974]

My guess is that the only reason they do this on "real" planes is to free up the fusealage for passengers and luggage.  Because on a model plane you don't have that requirement, it's much simpler just to shove the electronics and fuel in the big empty middle bit.

 

The extra strengthening and technology required to put fuel in the wings is pointless on a model plane.

 

 

 

[Ross Clarkson]

Yeah, fair points but i know how some people are just crazy for scale detail and wondered whether anybody had actually done it.

 

Cheers,

[David Davis]

The first model to fly the English Channel, a Radio Queen in the early fifties, was modified to incorporate fuel tanks in the wings.

[Myron Beaumont]

Going back to the question of tank height position -OK I always line up the centreline of the tank with the spraybar / needle BUT I ask myself ,does anyone know the pressure provided by the muffler to the tank & if enough,wouldn't it really be better to have the spraybar aligned with the tank top to avoid any flooding whilst static ? I recently changed from a 2st to a 4st in a model Both engines using exhaust pressure feed .The spray bar on the 4 stroker is a good 1/2 " higher than the 2 st . There are no discernable problems

(good job 'cos there's no way of highering the tankbay.)  I havn't tried the 4 st without pressure - I will ,just to see what if anything happens -Then again ,I'll have to alter the settings  & I don't really want to .

To repeat ,has anyone used a manometer or similar to measure the head of pressure provided by the exhaust ?

G-UMPY 1

[John Cole]

I once fitted a transparent cover to my fuel tank bay (so I could easily see how much fuel was in the almost-transparent tank).  I was amazed to see what happened when I ran the engine.  Despite the tank being mounted in plastic foam, the vibration turned the fuel into a froth, filling the complete tank!