An interesting video of what happens to fuel tank in flight, shows how many times the clunk is exposed, brings me to the point of having an header tank

watch it, worth it

www.youtube.com/watch?feature=player_embedded&v=WtbSqEtLQX4

Looking at this, we could discuss, some mods to ensure continuous supply of fuel, i am holding my thoughts, to generate discussion.

That is an excellent instructional video to teach new pilots how the fuel pickup line works in fuel powered planes. Among the first thing I teach new pilot is to bring engine to idle during downline. One other solution in situations where the clunk is out of fuel but still have some fuel available to avoid a deadstick is to use felt type fuel clunks.




Another good solution is the RotoFlow fuel tanks... they are good design and can help to some extent.

http://www.jlproducts.net/ProductRotoFlow.html

My favorite are the Fourtitude Fuel tanks. With these tanks, I have seen guys coming with literally empty tanks and still with a running engine so they are proven to pick fuel till the last drop but of course one has to be careful during their downlines.

http://www.fourtituderc.com/



Here is one in my Dalton Extra 260

Quote from: rcpilotacro on May 05, 2013, 08:44:49 AM
Looking at this, we could discuss, some mods to ensure continuous supply of fuel, i am holding my thoughts, to generate discussion.

Need to know your thoughts and experience on this.

How will the Roto-flow tank pick up, if the fuel is in the front, i.e. model decelerating or in a nose-down position?

Something new is needed e.g. multiple pick-ups in the tank

I need to think hard of a situation where I need to be in a straight downline for lets say more than 5 seconds and in most cases will be in a close throttle (idle). A standard clunk system is supposed to build fuel reserve for 10 to 15 seconds at idle and according to the company the Rotoflow system will supply fuel to the engine in a straight downline for 25 seconds. They say there is more reserve build into the Rotoflow in case the pick up line does not  contact with the fuel.

I also think the felt type clunk systems build more reserve for those long downlines.

Albeit complex to make, but here's what comes to my mind of the top of my hat... (See pic)

The reservoir is the actual tank, the FDC (fuel delivery comaprtment) is something like a "reserve" tank in bikes. A thin sheet separates the two and this sheet has nipples/nozzles delivering fuel from the reservoir to the FDC, so it does not return to the reservoir. The clunk always hangs in the FDC; not a 100% failsafe solution, but here's a start of a new design . The reservoir has an input pipe that fills the tank and the pressure return pipe can also be connected to the reservoir so fuel return is minimized...

Inputs?

GS

Nice idea GS!      Instead of the bladder complications, several non-return valves could be put; the simple cone-ball types

Right chief, I originally though of non return valves (spot on - ball cones came to mind), but I have zero idea of their availability etc so thought of what could be simpler...Non returns will also let the clunk move unrestricted

good we are throwing ideas now, good one Girish

Girish,

these are there in real aeroplanes, and are called baffles, job of baffles is to minimize the slosh, kind of shock absorber of the fuel. Making couple of baffles with holes as shown in the image will, to a large extent ensure the clunk is never exposed. Some pics for more ideas

Woah! I never imagined I'd get so close... I just worked on a simple approach of "one area always filled". Yups, I know "baffles" as they're also called in acoustics, help in stopping sound from returning and interfering . I am now thinking of how to put that baffle inside a tank without cutting the tank

Quote from: girishsarwal on May 08, 2013, 12:28:00 PM
how to put that baffle inside a tank without cutting the tank

(a) OHP Sheets and CA, friend of mine tried it with mixed results
(b) Make your own can two piece tank, baffle and seal them

A solution has existed for the last >40 yrs ... But as usual ignored by the
Rc community in their craze to commercialise everything.

Do a search on the uniflow system .... Very much in vogue with control line
Stunt flyers

Next Idea is how do you build a tank, custom tank, Sandy Jain and i went hunting for fuel tanks ( picked up like 30 of them) as good if not better than 3M tanks. Will post pics of how i build them, any ideas before that  ?

PS
This question is still alive, of how do we prevent an exposed clunk, Salam has shown us waht the industry has to offer, anything beyond ?

PPS
We can further the discussion on baffles as well

c) some kind of an assembly to the "dhakkan" (cap) that cups the cap from the inside forming the FDC, and it can be screwed/snapped on.

We could test this easily on a coke bottle and one of those plastic pill bottles... . Maybe a gasket in between to avoid leakage. 20ml fuel reserve should be good? I have no idea...

d) make the pill bottle as the plug for the coke bottle, so the pill bottle acts as the FDC. easier to construct as long as the right size bottles can be found

Gusty ,
A simple hopper 6oz with a centered clunk fed off your main tank will solve all the problems. I've been using such systems on my jets for over 10 yrs now.
Lots of helicopter pilots use a hopper tank with excellent results

Wow great ideas... I like the idea of two tank or two clunk systems. I still think a good felt type clunk has sufficient fuel reserves for long downline so a modified tank system may not be needed.

Gusty, let me play a different role here.. .... Do we really have a problem which we need to fix? How many of us have seen or experienced crashes caused by fuel starvation due to fuel pickup system while using an existing line of fuel tank systems?

I am thinking which IMAC sequence or a hard 3D move will require a modified fuel tank system which the existing available products have failed to deliver?

Quote from: xantos on May 08, 2013, 07:45:42 PM
A simple hopper 6oz with a centered clunk

Nandan mentioned something similar, isn't it Nandan ? However when i flew your Jet i did notice a header tank (refer my first post), like we do in Helis. In real aeroplanes we call it the   Service Tank . More on Service Tank later

Quote from: Salam on May 08, 2013, 08:39:09 PM
Do we really have a problem which we need to fix?

Salam Bhai, you are right, however i have seen many crash, esp newbies not paying enough attention to building and positioning tanks correctly (me inclusive), also idle down line and a large non felt/non ceramic clunk, does lead to occasional splutter of the engine , once i have back to back cuts  post blender recovery, changed over to ceramic clunks issue was sorted, like you covered little bit of soaked up fuel helped.

Quote from: Salam on May 08, 2013, 08:39:09 PM
I am thinking which IMAC sequence or a hard 3D move will require a modified fuel tank system which the existing available products have failed to deliver?

precisely, for which we need to know what all are possible, 9 out of 10 that i have asked had no idea of what is possible/ how important is to build your tanks properly.

Some more issues we intend discussing are , uniflow, suction feed condition, cavitation, ebullism, frothing etc.

what else can be done to ensure positive fuel feed ? any one can join in & throw some ideas, may be we can make'em fly'em and videograph them to know the result

also did you notice at one point there was a lot of waves kinda thing in the fuel, why could that have happened ? any thoughts  

I accept with most humility that ive been one of those newbies

I maybe incorrect but those waves were probably loads of ripples from sudden vibrations.

I am also a newbie when it comes to glow/nitro engines. I stayed electric throughout and moved directly to gas engines. I think this could be more of a problem for glow engines where bubbles developing in the fuel line will kill it while gas carburetors are pretty good in that aspect.