Engine doesn't lean out....

[Disc]

Guys,

I was flying last evening and someone pointed out to me that I was well into my Header tank about 2/3 empty. I landed the machine.

Now on my Raptor Titan and Raptor 60 when you reached the header tanks the engines ran lean very quickly. Engine noise level change etc.

My Voyager with Hyper no note change at all it just ran as smooth as anything no hints I was into the header tank...

So whats normal for it to run lean once the main tank is empty or not to lean out?

[Ade_Law]

it depends on the height of the header tank.

if the header is above the carb it will richen when the main tank is fully empty. if its below the carb it will lean out.

Ade

[robgt]

Not to lean out - as long as the pipe work is all ok.
I ran my 600n almost completely empty (including the header tank) just the other night... oops
It's so good to fly I get a bit "lost" flying it sometimes and I usually forget to start my timer (tut tut tut) so I have to bring the heli back in to check the fuel level
It doesn't run lean though.
Cheers,
Rob

[robgt]

Ade, is there any chance you could explain why this is, as I don't fully uderstand why this happens in a pressured system on a 3D heli?

i.e. Consider that the heli can be at any particular attitude in the sky, why does placement of the header tank make any difference at all?

Much appreciated
Cheers,
Rob

[Ade_Law]

there isnt actually much exhaust pressure so the weight of the fuel has more of an effect than you might think.

the reason why it happens when you come off the main tank and onto the header alone is down to the weight of the fuel in the clunk line. if your header tank is high its going to have to be pulling this up hill normally luckily the weight of the fuel back down to the carb evens this out.

when the header tank empties its not having to pull the fuel up from the tank so now there is "a head" of pressure from the tank to the carb so it goes rich.

Ade

[Disc]

my header tank is roughly inline with the Carb..

but it is just sooo smooth.

found out what happens when you run an engine lean with 9% oil though

Not a lot actually... it looses power but doesn't make that harding up noise at all. Rather like Pro Synth fuel apart from its like a black Ink

[robgt]

Thanks Ade, it kinda makes sense...
I just have trouble getting my head around the idea that th eposition of a header tank in relation to the carbs spray bar has any effect when the heli is vertical, for example.
I can understand the principle when hovering normally... but... hell I don't know - maybe I'm just being thick

Cheers,
Rob

[Ashley Davis]

nope, not being thick, header tank is only above the carb if it's up the right way

[robgt]

This is what I'm struggling to get my head around - why does it matter if your (my) heli spends most of it's time any which way up except normal

Cheers,
Rob

[moyesboy]

The heli can't actually spend all that long in any attitude other then upright or inverted - probably not long enough to hear the difference on the motor. The heli has to return to right way up or upside down OR pull G force in one or the other direction, as in a tick tock or high g turn, quite regularly (unless you have the BobJ gravity on/off switch available).

A fixed wing has to be able to run well with the nose pointing straight up ( yuo can't fly a heli straight up). Thats why those plank fliers are always holding their models nose up in the air, and almost always spraying all the exhaust onto their transmitters!

[kevinh]

Not to lean out - as long as the pipe work is all ok.
I ran my 600n almost completely empty (including the header tank) just the other night... oops
It's so good to fly I get a bit "lost" flying it sometimes and I usually forget to start my timer (tut tut tut) so I have to bring the heli back in to check the fuel level
It doesn't run lean though.
Cheers,
Rob

is it better to stop flying once your on the header then?

[raptor-flyer]

I was under the impression the reason a header tank was fitted,was that it is easier to see in flight than a tank which is partially hidden by the frame work.
From what most flyers are saying the only reason they fit the header tank is for more flight time.
was always taught onto header tank land soon.

[Ade_Law]

its only an issue when the main tank is empty and if your header is spot on the carb you wont see any difference either. i see what your saying tho, eg in tic tocs where the tank is below the engine it should lean out..

maybe it does you just dont notice it?

Ade

[moyesboy]

eg in tic tocs where the tank is below the engine

The heli can produce no lift when it is pointing straight up (or straight down or on its side).
So the fuel is always weightless if the heli is pulling no G perpendicular to the rotor disc.
during a tick tock the fuel is at the top of th tank, then the bottom, then the top, but it wont ever all run to the back (or the front if it was nose down).

[Steve]

If you convert your tank plumbing to the uniflow system, then the pressure is equalised throughout the system, and does not change throughout the flight.