Oily glow powered models

[Former Member]

[This posting has been removed]

[Martin Harris - Moderator]

Baby wipes are great for cleaning off oil - they seem to grab it. However, we're getting away from the purpose of posting the question about how some glow engined models and exhaust locations/orientations end up with negligible oil deposits and others using the same engines, fuels and state of tune can be more productive than a medium sized middle eastern oilfield!

I think we all accept that petrol engines produce less oil residue with their higher fuel to oil ratios but that wasn't what I was researching.

Any more examples of glow engined models which don't get a covering of oil?

[Denis Watkins]

As already suggested, their is a difference with 2 and 4 strokes.

An upright mounted 2 stroke can be the worse culprit, leaving a trail front to tail on the silencer side of the model.

The cleanest mounts appear to be side mounted 4 strokes, where the exit is at the bottom bulkhead, either side of a model.

It would appear that it is possible to get a cleaner exit in certain parts of the air stream, as suggested.

[Jon H]

I have found that an exhaust mounted a 90 degrees to the airflow is usually quite clean. Our exhaust gasses have significant velocity and will easily travel an inch or more even when the model is zooming along.

Dont forget than a great deal of oil will come from the crankcase breather on a 4 stroke (75% of the goo from a laser is from the breather) as well as carb spit on both two and 4 stroke engines.

Carb spit will be the cause of all that oil inside your cowl that you cant work out how it got there. It is usually easy to spot as it will be the colour of your fuel and not be brown like exhaust residue.

[Don Fry]

Here's an odd one. Model is an artf 60 odd inch semiscale P40. The lipped air exit is the only air duct out of the cowl. The black tape you can see is cosmetic over a silicone exhaust exit from the Laser 75 lurking in there. The pipe is cut at an angle, about 30 degrees so the airflow tend to suck the exhaust. The model is oily from on the bottom of the cowl, for 2 inches in the area in front of the lip at the rear of the cowl. There is absolutely no trace of oil anywhere else on the airframe, and I mean none. Motor runs on 15 % oil in the fuel.

I can only conclude that the air exiting the exhaust provides a boundary layer between the model and the exhaust.

[Engine Doctor]

A velocity stack minimises carb spit.and a messy engine bay .Added benefit especially noticeable with piston ported  two stroke petrol engines is that it improves fuel economy. 

[charles aldous]

Best place to buy a velocity stack to try on my Saito 56 anyone?

[charles aldous]

**LINK**

Just ordered the above, hope it helps.

[Bob Cotsford]

That's blown my theory out of the water, I've just maidened a Wots-Wot which has the exhaust exiting dead centre under the nose and that was well lubricated underneath from nose to tail after 2 flights.

[Former Member]

[This posting has been removed]

[Tim Flyer]

This is the Laser 80 mark1 anti splash velocity stack fitted on my Wot 4 😉

Edited By Timothy Harris 1 on 17/05/2017 11:36:12

[charles aldous]

I added the velocity stack to my Saito 56 and attached the crank breather to the muffler pressure tube. I think I have a little less slick in the cowl, but still present, and underside of model stills gets covered.

[charles aldous]

Update on Saito 56 Oil residue.

I tried moving the breather tube from under the cowl, attaching it to the muffler pressure tube, but made no difference to the amount of fuel/oil residue deposits on the model, so now reluctantly accepting that the breather residue is what it is.

To address the slick in the cowl, I fitted a velocity stack but this hasn't helped at all. In fact, when holding the model vertical at full throttle during mixture checking, I can see this stuff running down the inside of the cowl, although slightly less noticible at idle. Older posts on forums elsewhere suggest fitting an air filter to the velocity stack to contain the fuel spit, but I can't find a readily available one.

Any views or comments most welcome on a suitable filter arrangement, or other possible causes of what seems to me to be excessive amounts of unburnt fuel/air slick in my cowl.

Edited By charles aldous on 31/10/2017 12:06:57

[Jon H]

Has the engine ever been apart? seems strange its spitting so much. perhaps the cams arent right

[Peter Miller]

Posted by Martin Harris on 02/05/2017 00:43:19:

Any more examples of glow engined models which don't get a covering of oi

Peggy Sue 2 remains spotless after over a dozen flights.

[charles aldous]

Posted by Jon Harper - Laser Engines on 31/10/2017 14:01:23:

Has the engine ever been apart? seems strange its spitting so much. perhaps the cams arent right

Hi John, I have had the engine apart to check the timing and valve clearances whilst trying to eliminate reasons for the fuel spitting. I put it back as per the info onine for timimg mark alignment etc. At one tooth off the alignment is way off so I am pretty sure I have it correct as the engine gives around 8500 rpm with a 12x 6 prop and bags of power. Any views on an air filter, or better still any other thoughts on possible causes?

[Denis Watkins]

Posted by charles aldous on 01/05/2017 09:59:38:

This is my set up of a Saito 56 that produces a lot of oil residue in the cowl which then exits from the rear underside, covering the fuselage belly. I am new to Saito FS's. My questions: Is it likely that this oil slick is only coming from the vent and if so why is it ending up in the cowl? Are there any ways of reducing it or deflecting it away from the model?

Many thanks in advance

Is this motor

Run in Charles?

[Jon H]

I recently ran in an enya 53 4 stroke and saw 10k on a 12x6 so your 8500 is rather slow. What fuel are you running?

[charles aldous]

Dennis, yes, the engine is run in thanks. Had at least 100 flights since I bought it second hand, engine pulls Toledo Special around very well.

John, I'll double check my numbers at the weekend. It might have reached 9000 or so before richening back a few hundred from peak, but i can't be sure. I'm running Optifuel 12% slv. The cam setting method I used is below, although I used a 2mm hex driver instead of the described tool, same effect though.

 

http://users.tpg.com.au/gmustang/saitotiming/timing.html

 

Edited By charles aldous on 31/10/2017 15:34:31

[TartanMac]

Charles you should get more than 8500 rpm I think out a 56. I'm sure from memory my Enya 41 4C does more than that on a 12x6 and it has no compression left at all. 12x6 @ 8500 rpm is 0.55hp you should get 0.9 out of that so around 10,000 rpm would be more like it.

If you want an air filter look at 1/10 scale car filters 1/8 would be too big I will put up pics later as I was going to do the same thing, as my cars are bone dry under the shell and you don't loose hp with a filter or at least nothing that you will notice. you want one with a bolt on it somewhere so you can connect a wire to it so it wont move or come off or fold the rubber tube in flight. But I would say there is something wrong with that engine.

[charles aldous]

Thanks Mac, I might even have the prop size wrong from memory, so I'll post again when I have checked the rpm and prop size. Where is the calculation you use available please?

Suppose I had the timing out by one tooth either way, with that prop and fuel, would even 8500 rpm, smooth idle, great transition etc be achieveable?

[Jon H]

Posted by charles aldous on 31/10/2017 15:22:07:

It might have reached 9000 or so before richening back a few hundred from peak,

Edited By charles aldous on 31/10/2017 15:34:31

Dont run it rich. You arent protecting anything and are just running rich all the time. This is likely the cause of the mess.

Lean it off slowly to max rpm, then either leave it alone or, if you must, 2 clicks richer. If the engine is rich enough for you to notice an rpm drop vs peak revs then its too rich and you have gone too far.

I run my saito 45 at peak rpm on the Laser 5 fuel i use in everything. it never misses a beat. Your optifuel is a slightly messier fuel, but running rich like this will make the problem so much worse, not to mention increasing fuel consumption significantly

[Denis Watkins]

• Saito-30 9x7, 10x6
• Saito-40a 10x7, 11x6
• Saito-50, 56 11x8, 12x6, 12x8
• Saito-62a 12x8, 13x6
• Saito-65 13x6, 13x8
• Saito-72 12x8, 13x6, 13x8
• Saito-80 12x9, 13x6, 13x8
• Saito-82a, 13x8, 14x6, 14x8

[charles aldous]

Posted by Jon Harper - Laser Engines on 31/10/2017 16:23:25:

Posted by charles aldous on 31/10/2017 15:22:07:

 

 

Lean it off slowly to max rpm, then either leave it alone or, if you must, 2 clicks richer. If the engine is rich enough for you to notice an rpm drop vs peak revs then its too rich and you have gone too far.

Thanks John,

 

 

 

Edited By charles aldous on 31/10/2017 16:58:09

[TartanMac]

Posted by charles aldous on 31/10/2017 15:47:00:

Thanks Mac, I might even have the prop size wrong from memory, so I'll post again when I have checked the rpm and prop size. Where is the calculation you use available please?

Suppose I had the timing out by one tooth either way, with that prop and fuel, would even 8500 rpm, smooth idle, great transition etc be achieveable?

I doubt that you would get a good idle but I'm not an expert. That said I have seen some people tune an engine call it great and it is not good at all. Locked down in a bench where the engine does not move at all I would expect 2,000-2,200 rpm idle assuming it is well run in. But if it is shaking around in the air frame it will be higher as you don't have the maximum flywheel effect.

The website I use is really only good for APC readings but in testing some props it seems I get the exact same rpm on graupner super nylon props the only APC prop I have that I get a false reading on is my 10.5x4.5 as the blade shape is not the same but apart from that it is pretty good.

http://www.godolloairport.hu/calc/strc_eng/index.htm

I don't know how to create a link you can click