STG

My Feedback: (26)

4 strokes typically do have a flatter torque curve than 2 stokes. That means that, although peak torque is similar between 2 and 4 stokes the 4 stoke will typically produce more at lower RPM. How does that translate to model airplane motors? Well if both my 2 stokes (OS108) and 4 strokes (YS110) can transition from (almost no load or thrust) about 1800RPM to full load & thrust (~9000 rpm) in a fraction of a second then where is the torque difference? How can this torque difference be a factor?

It is not a factor because the props we use impose very little load on the motors at low rpm. As the rpm increases the load on the motor is exponential.

For instance with a 16 x6apc prop:

4000rpm----.2hp
5000-------- .35
6000-------- .6
7000-------- .9hp
7500-------- 1 hp
8000--------1.3
9000--------1.9hp
9500--------2.3hp!


As you can see the prop does not load the motor much from down low--2000 to 6000 rpm-- That is why I say these motors do not need much torque.

The down low power that people I think are attributing to 4 strokes has more to do with how fast they experience them to spool up (go from idle to full throttle). This has more to do with how well the carb meters fuel at lower and mid settings than the actual torque curve of the motor. A 4 stroke is less sensitive to the correct needle settings when it comes to spool & transition.

That is why the YS motors have an edge over the other 4 strokes on spool up. Not because they have more torque, but because the pressurized and regulated fuel system lets them meter fuel needs more accurate at lower and mid power settings.

That is also why 2 strokes get a bum rap--because it is harder to get them to meter fuel accurately from idle all the way thru to full(and some 2 stokes may not have a good enough carb to get it right). My experience has been if they are just a little bit lean or rich at idle or on the high end the transition and mid range running suffers a lot. That is why a pump has often been the answer for me as it allows for a leaner setting at idle and at full as the fuel supply does not change when you put the plane in the air.

Now I am not speaking for all 2 strokes only OS.25fx, OS46FX, OS.91FX, OS108, OS1.60fx.

STG

My Feedback: (26)

Please, I did not mean to be come across as rude when asking about the posts being bold-ed. I only asked because for some reason the contrast is hard on my eyes. Sight impaired people do come in all ages.[8D] Sometimes I do not pay close enough attention to my posts. Bill, you are no doubt a great asset to RCU.

BTW, do you use glasses at the computer? I was not sure if I needed them, but went in for an eye exam--when I got my glasses I could not believe what I had been missing.

coveredup

My Feedback: (1)

4 strokes sound better. I cant stand my buddies 2 strokes when he hovers down low.

STG

My Feedback: (26)

Yep, I fire up weed whacker & imagine I am flying my OS108/F90, then I go on to mowing and think about my YS110/Yak, then I go on to my electric hedger and think about flying my foamy. [sm=lol.gif]

britbrat

I missed something somewhere -- where was I being aggressive? If I did so, I appologize, but I believe that 2slow2matter was referring to someone else's post(s).

Flyboy Dave

My Feedback: (21)

I'm sorry, Sir....there is no two stroke application currently on the market that I
know of that is more economical than the 4-stroke engine. Case in point....two
stroke engines are banned in California. The reason is....two strokes lose aprox.
25% of the fuel charge from unburned combustion, at he same time (when the
transfer ports open) when a fresh charge of fuel is entering the cylinder...flushing
out, or "scavenging" the engine of burned fuel....setting up the next fresh charge
of fuel to be compressed and burned.

That means too much raw fuel goes out the exhaust to consider the two sroke
"efficient" in any way, shape, or form.

There have been experiments with two stroke engines, in which fuel injection
has been used to deliver fuel to the "top" of the engine, while the normal air
charge is brought from the crankcase. While these experiments have been
promising....none (that I know of) have made it to market. []

Sorry....

FBD.

Motorboy

Correct, 2 stroke engines are not economical while the engine has carburator and fuel wasted while transfer- and exhaustport are open. Do not forget the heavy diesel 2 stroke engines has injector therefore not waste of fuel for nothing. But 4 stroke heavy diesel engines win in fuel economy cause each 2. revolution are fuel injected in the engine.

Jens Eirik

DarZeelon

Actually, Jens, it is every 2 strokes...

In every revolution of the engine, there is a power stroke.

Look up Detroit Diesel and Orbital two-stroke Diesel engines to see this.

The intake is controlled by sleeve ports, unmasked by the piston and there are (mostly) 4 exhaust valves per cylinder, in the head.

Since the entrance and exit are at either end, scavenging is as efficient as that of a four-stroke engine.

But this has nothing to do with model engines, surely not with glow-engines.

Roby

Jigeye,

I suggest that you get a 4S and decide for yourself what seems to
be best for you and your needs. As pointed out above 2S and 4S
each have pros and cons.

I've flown with several friends for many years and most of these
guys WERE 2S only flyer's. Shortly after getting their 1st 4S they
showed less and less interest in the 2S. Don't know why. Don't
care either. They just like them and it seems now to be
the 1st engine of choice within our group.

Try it and see for yourself.


Regards
Roby

STG

My Feedback: (26)

Again, I do not disagree the your theory.

I don't think that most of these new Saitos or YS's were engineered with economy as a top priority.

In a practical application-----

http://www.rcaerobats.net/MotorCostComparison.htm The 2 stroke used .8oz min and the 4 stoke used 2.2oz min -- Same plane flying the same sequence by masters level pilot.

My OS108 does better than my YS110 on mileage flying a mix of 3D and IMAC. The OS108 is on a plane that weighs 1 pound more. Both motors turn the same prop the same RPM. 16x6 ~9500 set for flying.

Most will agree that the 1.6FX does just as good or better than the SA180 or the YS1.4.

STG

My Feedback: (26)

x

William Robison

My Feedback: (3)

STG:

California has indeed banned two stroke engines in motorbikes and lawn/garden equipment. So far the Eco-Nazis haven't banned two stroke airplane engines. Either model or ultra-light.

Bill.

STG

My Feedback: (26)

x

William Robison

My Feedback: (3)

Practical? No. But it sounded good to the California majority, it's purely political. Remember that many voters can not think for themselves, they go with the loudest and best sounding lie. A much better solution to the California smog would be involuntary sterilization of all breeding age people.

The only real effect the ban has had is making people drive into Nevada to buy their weed whackers. Made California businesses lose the profit, and the state to lose the tax revenue.

This is typical of all things the Eco-Nazis do. Much more harm than benefit.

Bill.

STG

My Feedback: (26)

x

Red B.

This is only true if you consider conventinal two stroke engines.
FWIW, it may interest you that the most efficient two stroke engines are large, low-rpm long-stroke marine engines. Their specific fuel oil consumption is is of the order 170 g/kWh, i.e., a thermal efficiency approaching 50%(!). This efficiency is virtually identical to what can be acheived with the most efficient four stroke diesel engines.

BTW, large in this case implies engines with a cylinder bore of more than 40 in. and a stroke of more than 100 in. HUGE!
In the figure below the efficiencies of some common types of engines are given.

1. Low speed two-stroke diesel engine
2. Medium speed four stroke diesel engine
3. Combined cycle gas turbine
4. Gas turbine
5. Steam turbine

/Red B.

STG

My Feedback: (26)

Are they allowed to dock on the shores of California? [&:]

Hobbsy

My Feedback: (102)

OK gentlemen, back to RC please, everything after post 60 is totally off topic.

STG

My Feedback: (26)

You ever learn anything interesting by accident?

Off topic? That is crazy.

tukkus

My Feedback: (2)

after reading all of the previous posts i have come to the conclusion that this one ^^^^ is the best

B.L.E.

I think 4-stroke glow engines, while they don't overscavenge like 2-strokes and spill part of the fresh charge out of the exhaust, waste fuel by the need to have a very rich mixture at full throttle.
A 4-stoke engines compression changes with throttle opening. If you turn the prop with the throttle completely closed, you will notice very little compression because the throttle does not let any air into the cylinder during the intake stroke. What feels like the top of a compression stroke is actually the engine going over bottom dead center with a vacuum in the cylinder.
On the other hand, a 2-stroke engine have just as much compression with the throttle completely closed as it does wide open. The gasses not replaced by the fresh charge just stay in the cylinder. The surging, misfiring idle of a 2-stroke is the result of the large amount of exhaust gasses left in the cylinder from the last power cycle.
This makes me think that the compression ratio of a 4-stroke, in order to have enough compression during idle to fire has more compression than is desirable for full throttle. In order to control the ignition point of this overcompressed engine, the fuel/air mixture must be extremely rich. At low throttle openings, the dynamic compression is low and the mixture can be lean.
I have also noticed that many 4-stroke engines have a curiously large amount of timing overlap, 80 degrees being typical. The exhaust valves typically close 40 to 50 degrees after top dead center. This may be to allow the engine to suck back some exhaust during the intake stroke so there will be more gasses in the cylinder to compress when the throttle is nearly closed.

B.L.E.

Thanx for your vote of confidence

MinnFlyer

My Feedback: (4)

A 4-stroke is Majestic
A 2-stroke is A Peasant

A 4-stroke is Ballet
A 2-stroke is The Twist

A 4-stroke is A Symphony
A 2-stroke is Rap

A 4-stroke is Lady Godiva
A 2-stroke is Phyllis Diller

A 4-stroke is A fine Oil Painting
A 2-stroke is Etch-A-Sketch

William Robison

My Feedback: (3)

Mike:

I like your comparisons, 'specially Phyllis Diller. But I would have used Gina Lollobrigida for the four stroke, and Moms Mabley or Michael Jackson's sister for the two stroke.

Haw.

Bill.

britbrat

For me, it's more like the "Ride of The Valkeries", vs "The Marriage of Figaro" .