Inverted Fuel Oil Necessary?

[rph142]

I?m having trouble trying to decide how much inverted capability I should put into my IO-320 powered RV-3B. I plan on flying gentlemen aerobatics, loops, rolls, cuban 8's, hammerheads, slow rolls, and 4+ point rolls. I don?t intend to fly any true -g, but I suspect some of those maneuvers will require 0 to +-1/2g. I understand the inverted oil systems dont really protect the engine from the 0 to +-1/2/g range so I probably wont install a full inverted oil system (dont have the space either). So the question I have is, would an accumulator and the raven air/oil separator suffice? Would just the air oil separator work? I bought the accumulator already so I could test its capacity.

The second problem is on the fuel side. My tanks have the non inverted pick up's and are closed up. Would it be possible to mount a small .5 gallon header tank downstream of the AFP fuel pump? I was thinking about making the tank out of a 4" diameter, 6" long aluminum cylinder. I cold put a check valve on the discharge side of the AFP pump, just before the mini tank. When the plane bumps negative g the engine fuel pump would draw fuel from this mini tank.

Any thoughts?

[Mel]

Rob,
For the acro that you list you don't need any inverted systems. Most RVs do not have anything and do just fine. Unless you plan on sustained inverted the standard system works fine. The air/oil separator will help keep the belly clean but still not necessary.

[sandifer]

You can do all the maneuvers you mention without inverted fuel/oil - you just wouldn't score well if you ever wanted to fly an IAC contest...not that that even matters as long as you're having fun. I'd like to see more RV's compete. But they're better suited to gentlemen's acro anyway. Since you admit you will not be sustaining neg. G, you wouldn't need to worry about flop tubes/header tanks either. Even if you went briefly negative, momentary engine sagging never hurt anything. In those situations, oil pressure is much more critical. I used to do all the positive G maneuvers in my RV-3 and never really wished I had inverted systems. I did end up buying a Pitts, though.

[Andy Hill]

Rob... My limited understanding experience, order in which to "fit" inverted things:

1. IO engine. Without it, the slightest 0/-ve 'g' will see engine cough / stop
2. Some sort of Air/Oil separator, and/or effective breather routing i.e. into/at exhaust. With a separator though you need a routine / method of emtying it. Keeps belly clean, doesn't save oil if the manoeuvres are inclined to lose it
3. Improve 2 to the Tank part of an Inverted system which not only "blocks" off some oil loss, but collects the rest and returns it to the sump when upright again.
4. Full Inverted Oil system - keeps +ve Oil Pressure under -ve 'g'
5. Flop Tube.
6. Aerobatic Prop (if you're C/S).

We started with 1-2, and now have 3 - which is a vast improvement for what I tend to do (2-3s -ve 'g' at a time, quite a lot of vertical stuff). Most of the time nothing comes out, but sometimes a combination and/or extent of manoeuvres does dump some oil.

Someone who knows more might say how long an IO engine will run inverted without a fuel system - asking a few people got varying replies, but I've never heard the engine stutter, and loss of Oil Pressure seems a more immediate concern

Not sure what you mean by an accumulator? Is this Oil or Fuel? Any links would be great / of interest.

As above, I do not think you need to worry about Flop Tubes / Header Tanks...

Andy Hill
RV-8 G-HILZ

[rph142]

The oil accumulator is a device that will supply pressure to the oil system when the oil pump loses suction. I have the Moroso 1.5 qt version. My thought was to put it downstream of the oil pump with a check valve just before it. If the pump stops pumping then the accumulator squirts out 1.5 qts of oil until the pump starts pumping again. Im not sure if im going to use it now though. I would really like to know how long the Lycoming will run at 0g. Ill never be 0 for more than 2-3 seconds i suppose, basically just the time it takes to roll out of an inverted 45 down line from a cuban 8 or inverted section of a slow roll. If thats all it takes to kill the engine then i might need to figure something out.

[RV8iator]

To do a true slow roll, you will need an inverted oil and fuel system. When passing the 90 on the entry side you will be pushing until you pass the 90 on the exit. Done properly, will take several seconds of negative G. You can speed it up but it's not as pretty.. IMHO

[frankh]

I have the Morroso 1.5 qt version plumbed into a fitting screwed into the oil cooler..Can't use a check valve as the oil need to go in and out of the accumulator.

Its great for providing constant pressure through all monouvers and I use it to pre-lube the engine prior to start as well.

I like it!

Frank

[Dan Blumel]

Originally Posted by frankh

I have the Morroso 1.5 qt version plumbed into a fitting screwed into the oil cooler..Can't use a check valve as the oil need to go in and out of the accumulator.

Its great for providing constant pressure through all monouvers and I use it to pre-lube the engine prior to start as well. I like it! Frank

I have the larger Moroso 3 quart version (manual hand valve) to maintain oil pressure for my CS prop and the engine. I also use it to pre-oil my engine before starting. Mine is mounted behind the seat back on My Glasair 1 RG. I have quick disconnect fittings on it (for Hydraulics) so that it is easily removed (quick straps also) and I can operate without it.

My mounts will also take an oxygen bottle in its place.

I can bring it inside a warm hotel room overnight with 80+ psi charge for 3 quarts of VERY warm (keep it by room heater) oil for better winter prelube before cranking.

[Dmadd]

Rob,
I took it (the inverted system) all off my "bought" O-320 powered RV-4 shortly after starting the re-build process.... If you decide you want inverted stuff, PM me and I'll make you a good deal on all the parts... They are in a box somewhere in my hangar with everything else I've removed while upgrading the plane... Personally, I've never missed it. ;-)

good luck with your decision,

Dennis

Originally Posted by rph142

I?m having trouble trying to decide how much inverted capability I should put into my IO-320 powered RV-3B. I plan on flying gentlemen aerobatics, loops, rolls, cuban 8's, hammerheads, slow rolls, and 4+ point rolls. I don?t intend to fly any true -g, but I suspect some of those maneuvers will require 0 to +-1/2g. I understand the inverted oil systems dont really protect the engine from the 0 to +-1/2/g range so I probably wont install a full inverted oil system (dont have the space either). So the question I have is, would an accumulator and the raven air/oil separator suffice? Would just the air oil separator work? I bought the accumulator already so I could test its capacity.

The second problem is on the fuel side. My tanks have the non inverted pick up's and are closed up. Would it be possible to mount a small .5 gallon header tank downstream of the AFP fuel pump? I was thinking about making the tank out of a 4" diameter, 6" long aluminum cylinder. I cold put a check valve on the discharge side of the AFP pump, just before the mini tank. When the plane bumps negative g the engine fuel pump would draw fuel from this mini tank.

Any thoughts?

[mvs163]

Hi Rob,
If you decide you need inverted systems...I was able to install the flop tube, flapper and guide in my QB -3 wings. I purchased the oil system from Rob Halas at Raven, he sells a smaller diameter breather pot for RVs. It sticks out into the "cheek" of the right cowl and you will need the "swivel fitting" for the rear sump fitting to clear the mount.
Also, depending on the vintage of you're sump you may need to weld a boss on for the return. I'll be using an Ellison Throttle Body, I've had good results from these units.
Good luck
Mike