N429EM

Boy, do I open myself up for criticism.

Anyway, I had a brainstorm, last night, while reading some threads concerning the oil spray on the outside of the plane. Some of the discussions were referencing where/how to vent the crankcase on 4-strokes. Well, I thought it might help cut down on the different sources of oil spray. The drawing below is a Pitts-style muffler, but I'm sure it could be adapted to other 4-stroke mufflers. My idea is to install a small pipe in the exhaust stream and use it to direct the crankcase venting into the exhaust stream. If it gets burned, great. If not, at least it's in the same area as exhausted oil, from the ignition process. And, not spraying oil somewhere else on the plane.

Depending on responses, I may be doing this to my Saito FA80, as a test.

So, what do you guys think?
Criticisms, be brutal. If this is a dumb idea, at least I put it on paper and my mind will stop thinking about it.

Sport_Pilot

I think I understand, but not sure about the extra tubing.

N429EM

The 'Extra tube from fuel tank" is a left over fuel tube. That's just describing what kind of tube it is.

Make sense?

Birman

That's exactly what they do on the RCV-91 engines and the users have the blessings of the manufacturer.

Square Nozzle

My Feedback: (1)

If the oil doesn't burn and you want a clean airframe after flying, I've heard of putting the crank case breather into a small tank that's carried in the plane. The tank is emptied after flying. Maybe I read that in my RCV manual.

pe reivers

I know a lot of oil is expelled from the vent tube. Running it into the exhaust is a good idea. If it is run in as close to the exhaust valve as possible, it may even provide some extra smoke trail, because more of the oil is evaporated.

Charley

My Feedback: (2)

The crankcase breather sucks and blows as a function of piston motion. When the piston goes up the crankcase breather sucks; when the piston goes down, the breather blows. That's why its called a breather. Don't know what will happen if you hook it to a pressure source like a muffler. In automotive applications the breather is hooked to the intake manifold.

CR

Hobbsy

My Feedback: (102)

When it is running, the piston blowby causes it to be mostly out, if you watch the vent tube carefully you can see the outward migration of the used lube oil.

proptop

My Feedback: (8)

I've also been thinking about an air/oil seperator...

Suppose, if you have the room for it, you took a 2oz. tank, and stuffed some of that plastic pot scrubber "wool" into it? That would increase the surface area for the oil mist to cling to (without causing too much backpressure to outward flow ) and hopefully seperate?
The tank would need to be vented of course, but I bet the vented vapors from the crankcase would have a lot less oil in it.

Maybe instead of a 2oz. tank, something like a "Gascolator" as used in the fuel system of full scale A/C could be used...something that could be easily drained?

broke_n_bummin

If you'll look at the way OS set up the FL 70, it's done the same way. Only, they go a bit further and tell you to hook it to the tank for better pressure regulation on sport and 3D models. The pressure coming out ogf the crankcase is greater than the pressure coming from the muffler.

proptop

My Feedback: (8)

All this reminds me of the late 60's - early 70's cars and emissions controls, PCV valves, etc. etc.

I think one reason the Japanese do it is because they have very strict emissions rules over there?

broke_n_bummin

Instead of JB welding the tubing to the exhaust, you could tap a 6-32 hole into the exhaust pipe, then screw a 1" screw into it with a lock nut, then drill through the middle of the screw. I've had to do that a couple times when the nipple broke.

rxAxilleas

hi guys,
why not to dril a hole on the intake pipe and atach a niple. then route the tube from the breather to that niple.i see that os surpass II engines do that way. the previus versions route the breather in open air. os have think it that way to improve their engines, why we dont do that the same way?
anyone tried this?
achilles

DarZeelon

I see a potential problem here...


In a normal (Saito, OS, clones and TT) four-stroke engines, if you hook the crankcase excess oil nipple to the intake manifold:

At low throttle setting the manifold vacuum is high and the blow-by is minuscule...

A long period at low throttle could potentially lead to bottom-end oil starvation, as most of the oil is sucked out from the crankcase.

At high throttle settings this problem disappears, as blow-by increases and manifold vacuum decreases.


If you hook the crankcase excess oil nipple to the muffler, at high throttle settings the pressure in the muffler should be higher than in the crankcase. The result could be 'lubrication' of the bearings with hot exhaust gas...

If we just leave it, your model will just be a bit dirty, after a day of flying...
Isn't this a pretty normal situation, with our 20% oil mix fuel???


Just stop being spoiled brats and wipe your model with Windex™ at the end of the day.
Is it so much of a bother to even raise this issue?

If you can't stand the oil, glow engines are probably not for you...

rxAxilleas

my question was how OS did this (route the breather to intake manifold) .
1)did solve the problem with the oil drain at low throtle?(as the engines firing how it is posible to have increased suction on the niple to drain the oil)
2)the problem is there for all the surpass II engines but none of us noticed it
3)parhaps this problem you mention is very very very litle to bother the engine function?
i have an old surpass 91 and thinking to route the niple to intake.i had a small botle to cache the oil ( i route the breather to small botle and then vendilate this botle)
i flew the plane 5-6 days and didn t empty yet the botle . the botle was from a 35m film container.

DarZeelon

Axilleas,


The average pressure in the intake manifold is not dependent on the engine's firing...

When the engine fires, the manifold is separated from the combustion chamber by the closed exhaust valve.
The cylinder pressure may marginally and temporarily raise the pressure in the intake manifold, as the intake valve begins to open, before the piston has reached TDC and also some residual exhaust pressure goes out the intake valve.

The pressure soon becomes strongly sub-atmospheric, as the piston begins to descend, sucking fresh mixture into the cylinder.

On average it is a strong partial vacuum, in all engines and in most engines, it never gets as high as atmospheric, even at full throttle.

wcmorrison

My Feedback: (2)

Why not buy a Magnum four stroke, it already has the PCV hooked up to the intake manifold. Their set ensures the oil flow from blow by comes through the main bearing to the cam shaft area. That ensures positive lube for the front end and sends the unburnt oil back through the intake valve into the combustion chamber and out the exhaust valve to the muffler. No complicated plumbing from all the ports and fuel tank.

Cheers,

Chip

proptop

My Feedback: (8)

Been thinking about the venting of the crankcase to the exhaust...

If you wanted to make something like an augmentor tube, that would help to create a slight negative pressure to help evacuate the oil vapors/mist from the case vent, without causing any positive pressure to push it back (or any exhaust gasses either ) into the engine.

I believe the vacuum provided by the augmentor tube would be considerably less than the vacuum at the I. manifold, and would also be somewhat proportional to r.p.m. (instead of inversely like the I. manif. source )

Kimhoff

My Feedback: (22)

I give what is a augmentor tube and please provide a diagram.

gkamysz

My Feedback: (19)

Dar, is the above an observation? The OS Surpass 70 and larger have been using a PCV system connected to the manifold for a few years now. Has anyone had any issues? I'm sure OS did their homework. It must work well enough that after a few years they integrated the PCV into the the engine design and the user doesn't even have to think about it. The newest engines (FS-200, FSa-56) vent gases and oil past the cam followers into the rocker well and into the intake port via a small hole in the head. The user isn't even involved anymore.

Don't use a window cleaner containing ammonia as it will etch the plastic covering and take the luster right out of it.

What's wrong with asking for cleaner engines?

broke_n_bummin

gkamysz is correct. The 2 diagrams I posted above are straight out of an FL 70 manual.

DarZeelon

No Greg, I was just crunching the theory...

The residual amount of surface oil, left in the bearings and even on the cam-lobes, for as long an idle period as one will endure, could just suffice.

After the .70FL used a sealed rear bearing that in theory, kept all the oil in the crankcase, away from the cams and followers, I could believe anything.

gkamysz

My Feedback: (19)

The Surpass engines with PCV have a small hole in the crank to pass lube into the cam box. The cam box is were the crankcase vent is. They use the same method in the new engines but it is plumbed internally rather than with the tube from the cam box to the intake manifold.

As far as sucking all the lube out of the crankcase, I just don't see it happening. Shortly after going to idle the manifold and crankcase pressures will balance. The small amount of circulation that does occur will be caused by blow-by. It's not like a vacuum cleaner.

I had an FL-70 apart recently. I didn't take many notes and I'm not sure if it had a passage into the cam box. One thing to note about the FL-70 and plumbing the breather to the exhaust. The nipple supplied to use in the muffler has a small passage. It's much smaller than the pressure fitting for the fuel tank.

Newc

Not for keeping the plane clean, but, for what it's worth...

Since the 70's automotive race engines have been using crankcase scavenging to increase HP. By creating a vacuum in the crankcase one reduces the aerodynamic forces acting to slow down the crankshaft counterweights, rod ends, etc., with the resultant HP boost. The key to this is to have the crankcase ventilation entering the exhaust stream in such a way that the exhaust stream is strongly pulling the crankcase vapors out, and this is accomplished by a properly shaped tube directly in the exhaust stream. I don't believe that this sort of scavenging can be accomplished by simpy having a nipple like is used for using exhaust pressurization of the fuel tank. The tube in the exhaust stream needs to actually create a vacuum using the flow of the exhaust.

Another method to reduce parasitic loses in the crankcase on the race engines that we used was a crankshaft scraper. This is a piece of metal that was shaped such that it would be within about 0.005" of the rotating crankshaft compnents, including the counterweights, journals, etc.. It was mounted on the interface between the engine block and the oil pan/crankcase and angled such that the oil was scraped off as the crankshaft rotated. Slow motion photography through a clear plexiglass oil pan was able to quite easily show the benefits. Without the scraper there was as much as a quart of engine oil resident on the crankshaft (from the oil coming out of the journals) and this is the mass that was scraped off resulting in less rotating mass and the resultant increased acceleration and HP. Obviously there are many differences that would keep this from being applied to our little engines, but it was first used on full scale aircraft engines. When the DC-3 was being certified it was to have been able to take off in a specified distance (I seem to recall 1000') but the first flights weren't able to do so. A couple of engine engineers took the engines back and developed the scrapers and the result was a 10% reduction in take off distance - more than enough to certify the plane.

DarZeelon

NewC,


It is no secret that model engines are designed 'down to a cost' and not up to a power...

For an engine to sell (street price) for ~$200-250, its production costs must be $15-20.
Yes, that is the net residual cost to the manufacturer, to produce a four-stroke engine.

All the rest is profit for the entire chain.

If actual production costs determined the 'street price', a Saito 1.80 would cost ~10% more than a Saito .40.

Yes, the market theory does work and you are (actually, we all are) willing to pay significantly more for a larger engine.


All of what you had suggested in your post, will not be incorporated into any model engine, since its cost would skyrocket...

The motto is KISS (Keep It Simple, Stupid).
You want more power? It is much cheaper to just get a bigger engine...

Scraper plates and PCV can be good if you are modifying your own, full-size 'drag racer', but cannot good for a production model engine.