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10% oil - 5/6/2003 9:06:12 PM   
futaba1024


 

Posts: 139
Joined: 1/21/2003
From: staffordshire, UNITED KINGDOM
Status: offline 		Hi Guys.
Been usung a comercial fuel, Model Technics Dynaglo 5 that has a total oil content of 10% (8%syn 2%castor 5%nitro 85%methanol) with absolutely no ill efects on various 2and4 stroke motors, according to most people there is not enough oil content. how come I've not wrecked several of my engines?
Cheers
       Post #: 1

10% oil - 5/7/2003 1:22:11 AM   
tps


 

Posts: 9
Joined: 5/7/2003
From: Tellus
Status: offline 		I agree! Car engines runs just fine on just 8 or 9% oil together with 25% nitro. 3,5cc car engines produces almost 3 bhp @ 30-40 000 rpm

I think the 20% oil limit is an old leftover from the stoneage... ;-)

(in reply to futaba1024)
       Post #: 2

10% oil - 5/13/2003 4:43:24 AM   
tdriver



Posts: 185
Joined: 11/9/2002
From: Athens, GREECE
Status: offline 		[QUOTE]Originally posted by tps
I agree! Car engines runs just fine on just 8 or 9% oil together with 25% nitro. 3,5cc car engines produces almost 3 bhp @ 30-40 000 rpm

I think the 20% oil limit is an old leftover from the stoneage... ;-) [/QUOTE]


..............couldn't agree more..............new engines are running on methanol last time i checked,not on oil.

(in reply to futaba1024)
       Post #: 3

10% oil - 5/13/2003 11:07:44 PM   
JWN



Posts: 4722
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		My guess is the answer is two fold.

1) There are no thrust loads on the bearings in a car, or radial loads. This would beg the question on why helicopter fuel usually has more oil instead of less compared to airplane fuel.

2) The oil used in the Model Technics Dynaglo fuel is very high quality and therefore 10% total content is all that is needed.


Read the article on Power Masters site written by Don Nix about oil content. Also read the article Stu Richmond wrote a month or two ago, I believe it was in RCU, about oil content. Both agree that it's the quality of the oil, not the quantity, that provides the protection.

John

(in reply to futaba1024)
       Post #: 4

10% oil - 5/16/2003 1:57:01 AM   
tps


 

Posts: 9
Joined: 5/7/2003
From: Tellus
Status: offline 		Thrust load, maybe not, but I'm certain that a car engine have a much more stressful life than a airplane engine - full throttle, brake, full throttle, brake etc. Remember, 3bhp @ 40 000 rpm with an 3.5cc engine - thats impressive.

One thing that comes to my mind is fuel consumption. 3.5cc on-road engines consumes about 125cc fuel in 5 minutes. More fuel throu the engine, less oil is needed?!

I run my car engine with 25% nitro 3% synthetic and 6% castor - total 9% oil. The engine runs just fine and has no loss of compression after running over 15 liters of fuel throu it :-)

I remember reading an article in an old issue of a UK magazine called RC Car Racer or something similar They were successfully running 3.5cc car engines with only 2% oil. The only downside they had was that the engines were harder to tune. I wonder what type of synthetic oil they were using, perhaps turbine oil?

(in reply to futaba1024)
       Post #: 5

10% oil - 5/16/2003 3:02:25 AM   
JWN



Posts: 4722
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		Even though you are running through the oil that fast, the total percentage, and quantity, is still very low. I agree that the cars have a much more stressful life. In addition to the on/off throttle usage, there is almost more heat and dust.

My gut still tells me it's the lack of thrust loads which allow the low oil percentage, but then, I don't run cars

John

(in reply to futaba1024)
       Post #: 6

10% oil - 5/16/2003 8:24:58 AM   
downunder-RCU



Posts: 1125
Joined: 12/27/2001
From: Adelaide, South Australia
Status: offline 		I've often wondered how they get away with it too. It won't be because of the lack of thrust loads because that's carried by the ball races and they're the part of the engine needing the least amount of oil.

No matter how fast they're revving, if they're tuned right then the total amount of oil passing through per rev will be the same (and if you work it out, the volume is amazingly small!). Maybe because of the revs and because they're only peaked for a very short time then the oil doesn't get much chance to burn off? Maybe backing off gives them a chance to load up with some excess oil to help carry it through the next high rev cycle?

The most highly stressed engines I know of are the 2.5cc CL speed engines putting out 2.7HP (genuine, not manufacturer's inflated figures ) at 40K+ using zero nitro and 20% castor. This is a regulated fuel though so possibly they might develop even more power with less oil or one with less drag.

(in reply to futaba1024)
       Post #: 7

10% oil - 5/16/2003 10:12:12 AM   
tps


 

Posts: 9
Joined: 5/7/2003
From: Tellus
Status: offline 		Another interesting thing is that if I run my car engine with high % oil fuel, the engine will run just like crap.

I still think that this has to do with fuel consumption. I dont think airplane engines, in general, consumes 125cc of fuel in just 5 minutes. More fuel throu the engine - more oil to lubricate the internals. Lets say that a car engine uses the double amount of fuel per revolution compared to an airplane engine, this should mean same amount of oil in both engines at a given time. (using 20% oil for the airplane engine and 10% for the car engine) ???

(in reply to futaba1024)
       Post #: 8

10% oil - 5/16/2003 7:41:05 PM   
JWN



Posts: 4722
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		Ducted fan, pylon and CL racing engines all use amazing amounts of fuel as well. Heck, my OS BGX burns through 24 oz. in less than 10 minutes at full throttle which is far more than your car engine burns.

Car engines don't have thrust loads, only radial loads. Airplane engines have both thrust and radial loads.

John

(in reply to futaba1024)
       Post #: 9

10% oil - 5/16/2003 9:52:17 PM   
Homebrewer



Posts: 1335
Joined: 12/29/2001
From: Colorado Springs, CO, USA
Status: offline 		Just exactly what kind of ill effects are you expecting? I don't think your engine will last more than 2-3 years of summer weekend use as opposed to much much longer.

(in reply to futaba1024)
       Post #: 10

10% oil - 5/17/2003 9:22:36 AM   
downunder-RCU



Posts: 1125
Joined: 12/27/2001
From: Adelaide, South Australia
Status: offline 		[QUOTE]Originally posted by tps
Lets say that a car engine uses the double amount of fuel per revolution compared to an airplane engine,[/QUOTE]
Then the car engine would have to be tuned slobbering rich. Doesn't matter if it's a car, aircraft or boat engine, if it's tuned correctly then they all run the same air/fuel ratio (so long as it's the same fuel mix). The car engine only has a higher fuel consumption because it's turning far higher revs.

(in reply to futaba1024)
       Post #: 11

10% oil - 5/17/2003 2:15:49 PM   
tps


 

Posts: 9
Joined: 5/7/2003
From: Tellus
Status: offline 		I have tried running a Novarossi 3.5cc car engine with 18% oil fuel, the engine ran very erratic. In other words, it's useless.

3 years of engine life... That must be very rare with a car engine. I get one season, if I'm lucky. Somehow dust seams to find it's way into the engine and scratches the piston and other moving parts... ooch!

(in reply to futaba1024)
       Post #: 12

10% oil - 5/17/2003 2:24:28 PM   
tps


 

Posts: 9
Joined: 5/7/2003
From: Tellus
Status: offline 		[QUOTE]Originally posted by downunder
Then the car engine would have to be tuned slobbering rich. Doesn't matter if it's a car, aircraft or boat engine, if it's tuned correctly then they all run the same air/fuel ratio (so long as it's the same fuel mix). The car engine only has a higher fuel consumption because it's turning far higher revs. [/QUOTE]

Good point !!!

What about nitro, I guess nitro fuel allow a richer mixture compared to non-nitro fuel.

(in reply to futaba1024)
       Post #: 13

fuel/oil mixtures - 5/18/2003 6:24:30 PM   
Waco Driver



Posts: 157
Joined: 1/16/2003
From: Paris, ON, CANADA
Status: offline 		This discussion is not taking into account the fact that since cars are operated in the horizontal position, they have a relatively constant fuel head at all times. This means that fuel/air mixture ratios are little affected between a full and nearly empty fuel tank.

In an aircraft flown aerobatically however, fuel heads may change thru a range of perhaps 12 or more inches from nose up to nose down. If mixture is set slightly too lean on the ground with the model held in the horizontal position, it will be severely lean in the vertical climbing position. This is where the 18-20% oil in the fuel mix saves the day.

If a model aircraft were always flown in a relatively horizontal position, say doing just circuits, with takeoffs and landings, you could probably get away with using 8-9% oil in the fuel mix also.

_____________________________

MAAC 6273 L

(in reply to futaba1024)
       Post #: 14

10% oil - 5/18/2003 8:47:29 PM   
downunder-RCU



Posts: 1125
Joined: 12/27/2001
From: Adelaide, South Australia
Status: offline 		[QUOTE]Originally posted by tps

What about nitro, I guess nitro fuel allow a richer mixture compared to non-nitro fuel. [/QUOTE]
When you use nitro or use a higher percent you have to open the needle valve more. Methanol has a air/fuel ratio of 6.5:1 but nitro starts at 2.5:1 and can go much richer.

If you use 10% oil and 20%nitro then you have 70% methanol. But the ratio of methanol to nitro (the actual fuel) is 7:2 or 3.5:1. If you up the nitro to 30% then you cut back the amount of methanol to 60% so now your ratio of methanol to nitro is 2:1 which is closing on twice as much nitro in the fuel as you started with. But because of the difference in air/fuel ratio you have to open the needle valve quite a bit to get the correct mixture. You're now flowing far more fuel which also means you're flowing far more oil and this might go some way to explaining why a car engine gets away with so little percent oil in the mix.

The only problem now is helicopter engines. They tend to use 30% nitro but around 24% oil. Not only that but they run them rich! Go figure

(in reply to futaba1024)