Fuel in tank foaming after half tank...

[1helimech]

My fuel foams after about 3 minutes of flight it looks like the tank is full when it foams it's like the fuel is rolling up the tank's vertical right hand side, when I set the Helli down the foaming slows to a minimal amount I hovered for the rest of the tank with no recurrence of the massive foaming...It has done this several times and I'm at a loss as to what is going on with it...  

Thanks in advance for any and all help..
Galen

[Kevin Dalrymple]

What motor? Is it regulated?

[1helimech]

The engine is regulated...It's an OS Max 91HZ-PS It doesn't use crankcase pressure but does use Muffler pressure to the tank... I just put a new cylinder liner , piston, ring , connecting rod and crankshaft bearings in it....

[Roger]

Do you have any kind of vibration monitoring software onboard the Heli that you could check for vibe levels. 

ROG

[1helimech]

I'm running an  ikon I don't think it has vib monitoring software. Sure wish it did though
Galen

[Kevin Dalrymple]

Why do you use muffler pressure a
Bad not crank case pressure?

What are your needles set at? Sounds like a tuning issue.

[Ross Lawton]

Hi 1helimech,

Fuel foaming can be caused by numerous things, engine mixture, something out of balance, something bent, something loose but hopefully we will be able to find the cause and get this sorted for you. 

I have a couple of questions which may help in finding the cause of this issue for you:
Has the foaming always been present or has it started recently?
Has the heli had a crash, tip-over?

There is a couple of things i would try:
The OS Max 91HZ-PS engine from memory can be a little fiddly to tune, check to make sure it is running the correct shims in the head for the fuel you are using and install a fresh plug just to rule it out.

Check to make sure nothing is loose, anything that is loose can cause a vibration. I would check the boom supports to see if any of the epoxy bonds have broken. If any have then this could cause a slight vibration. A good tip for the boom supports and is something i carried over from the N9 is to drill through the carbon tube and install M3x10 button head bolts through the plastic boom support ends and carbon tube. This along with the epoxy is a belt and braces method but i have never had a boom support come loose. I also rough up the area being bonded with epoxy and use a long setting epoxy as it is much stronger than quick setting epoxy.

It may also be worth trying a different set of main and tail blades if you have a spare set or able to borrow a set from a flying collegue. Do the mains first and then the tails or vice versa so you know which one is the cause if it cures the issue.

The next thing is the reason i asked if the heli has had a crash or tip-over and is where some parts will require changing. A rule of thumb i go by with things like this is: if it rotates, change it. So that means things like shafts, hubs, bearing etc.. In cases like this i usually change the following first:
Main Shaft
Head Axle Shaft
Head Dampers
Tail Output Shaft
Tail Rotor Hub

I also check and change any bearings that are feeling rough. This is usually either after a crash or a long period of time and i will change them as a matter of maintenance.

Hope this helps, keep us informed and hopefully we will be able to get this sorted for you. 
Cheers,
Ross

[1helimech]

I do have the Engine running "rich" due to the new internal parts.. I run muffler pressure due to the engine is pumped that is to say there is a pump on the back case of the engine...I'll lean up the mixture and see how that helps. I have looked for loose things and have not found anything yet my Heli only has 7 or 8 flights on it, no crashes and it has done this for all flights ...I did install a different set of blades still the same thing....Thanks for all the input you  guys !!!! it might well be that the engine is running way to rich she smokes allot and stumbles when i throttle up to get on the Governor... I have to work for the next six days away from home so it will be until then before i can try it out and see...Thanks you guys for the help you all rock !!!

Galen

[david harlan]

i had fuel foaming issues,decided to get rid of the fuel filter,just straight tubing,and what do you know, problem solved,check your pluming,and filter your fuel in the bottle before it gets to your heli,worth a try.

[flyercld]

You say in your post, it foams after three min. of flight. So, when you put the heli in a hover its ok? Have you had a tip over? Check your tail output, and main shaft. If that's ok take a look for loose bolts start at the head and work your way back to the tail.

Next, check tuning. Hover the heli in normal mode with no GOV. Your needles should be set for break-in, high side 2.5 out from close and mid 2 turns out from close. Do not make any adjustment to your mid, just work with the high and idle screw for now. Do this with a new plug. Check your idle and adjust for a good hover not lean a little on the rich side.

Check to make sure you have no leaks in all you lines as well, a small pin hole can run you nuts.

Check back with us on your progress.

Charles

[mdu6]

From your description I doubt the 'foaming' comes from a helicopter mechanical problem.

If it were heli mechanical - it would normally be present all the time - not after 3 minutes of flight.

Since you say it is a PS -  It is a fairly old engine - was the engine running regularly before you installed it in the N7 ?

When 'foaming' occur - are there other signs (RPM increase, RPM drop, helicopter shaking etc) or nothing else happens -  it might simply be your fuel pressure that varies (muffler seal, tuning etc) end what you are seeing is normal fuel pressure in the tank (dishwasher effect !).

[1helimech]

First off I'd like to say thanks for all the input !!!!

  #1: I will check for fuel system for leaks
  #2: I will set the needles as recommended
  #3: I smoked the engine in my Velo. 90n2 so I rebuilt it and installed it in my N7 ( i know i know it's old BUT so I'm I ....LOL ) I put in all new boca ceramic bearings, a new piston and ring,  a new cylinder liner and a new connecting rod.  This Vib seems only to be induced by fwd flight and as soon as I land it's gone and doesn't return in a hover even... I work on real Helios and this Vibe. coming on in flight and going away on landing has really got me going crazy.
  #4: I just read that the Main blades should be loosy goosy ...I have mine what I call fairly tight as in they hold there own weight when I hold them 90 to vertical with the helicopter tipped on it's side, is that to tight for this helicopter ? Maybe ?
Galen =)

[mdu6]

Are there other visible signs of this 'vibe' ?

When you bring it back into hover - are you keeping the engine at the same RPM ?

Basically - try to see if it is RPM or Forward speed related - (different set of causes)

[Ben Kerr]

I run my main blades really tight so I wouldn't worry about that. Does the foaming effect the heli's engine performance at all? Every nitro I have ever seen will foam some, without seeing it I can't say if it is a normal or excessive amount. I would second what Ross said to look for, but if nothing is bent I would look at the engine.

[1helimech]

It's like Ground resonance in reverse ...as soon as a skid tube sets down the Vib stops and then i pick it back up into a hover all is good i have not gone into FWD flight to check that out yet.  RPM stays close to the same on the ground and in a hover.