STG

My Feedback: (26)

Beauty lies in the ear of the beholder.

A lot of guys that want to get into 4 strokes have just had a .40 2 stoke on a 6-7 pound trainer. Take offs and climbs were done at full throttle with motor buzzing @ high rpm. If they wanted to do anything aerobatic again full throttle was needed. Most people that aren't into racing don't find that high rpm 2 stoke sound nice.

With the 2 stroke if you can keep the revs @10,000 or less with a nice pitts muffler or pipe the sound is nice. With the bigger motors (.91 & up) this is easy to do -- especially if you are not racing. Powering a bird properly--putting a .91(with a 15x6) in a 8 pound plane instead of a .61 (with a 13x6) is part of making this sound right--then you can use throttle management and run at lower throttle settings for most of your flying.

Even with my OS25FX I find myself using a bigger prop (10x3) only because the motor sounds a lot better when I am 3Ding it right in front of me.

Check out this film clip with the OS25FX turning a 10x3. Sound is good to me until I pull out aggressively(~13,000rpm). With a 9x4 pull out is just as good, but 3D RPM is higher and does not sound as good to me.

http://home.comcast.net/~stgflying/MINI3D.wmv

Beauty lies in the ear of the beholder.

Richard L.

My Feedback: (24)

I bench ran both the OS .91FX 2-stroke and the OS .91 Surpass III 4-stroke on the same 15% fuel and 14 oz tank. At full throttle, the OS .91 four stroke ran for 20 minutes swinging a 14x7 prop @ 9600 rpm. On the other hand, the OS .91FX two stroke only ran for 8 minutes swinging a 14x6 prop @ 10,500 rpm.

STG

My Feedback: (26)

Full throttle is not what I ment by "in practice in a lot of applications" . It would have made a lot more sense to me to have backed the .91FX back to 9600rpm for the test to see how it really faird against the .91fs. This is still not a practical test (at least for me) becuase I do not power my planes to fly at high throttle settings.

Also, Notice I did not name the .91FX as one of my motors that did well on fuel? I don't really know, though, as I never checked that motor. I do admit though that the OS four stroke line is one that is known for it's good economy, but not for its good power to weight. I would expect the .91Fs to do well on economy against the .91fx even if you ran them in a fair test. If I did the test it would be with a 15x6 on the .91FX as that prop gives the best thrust with still plenty of forward speed(unless you are racing) How well....I would like to see.

I do know that my OS1.6FX and OS108 flying a mix of 3D and IMAC do better in mileage to the top performing 4 stroke competition.

Check out this practical application of the 1.6fx against an YS1.4. The 2 stoke uses .8oz min and the 4 stoke is @ 2.2oz min

http://www.rcaerobats.net/MotorCostComparison.htm

_________________________

If you are running the 2 stoke or 4 stoke too rich (high and low needle) or with too much nitro or to hot of a glow plug you can go thru much more fuel than needed to get the job done.

My SA100 4 stroke does great on 15% and a 6.5 pound plane. I get close to .6oz min. (Again mix of 3D and IMAC) I run a vp20 and have my low speed leaned to the point that if I go from full throttle to none and back to full fast it is too lean and will quit (easy to do during waterfalls[:@]). This plane is @ full power for brief periods only.

DarZeelon

Richard,


If you replaced the glow-plug plug your engine came with to the cold A5 (which the [link=http://www.os-engines.co.jp/english/line_up/plug/pluindex.htm]OS Jap web site[/link] says is the right plug), you could close the needle more and get better fuel consumption. You would not be risking a lean-run.

Reduce the nitro and fuel consumption will be reduced further still.

It would not come close to what you saw with the Surpass III, however.

Sport_Pilot

Is that the best OS can do? I have an old ASP Redhead that will swing a 14-6 with 5% fuel at 10,800 RPM and it will take almost 20 minutes to empty a 14 ounce tank, not sure how long running wide open all the time as opposed to most of the time but I figure it is about 15 minutes. I have a .91 four stroke that will run only about 15 minute flights on a 15 ounce tank. But it has to run 15% or more nitro to turn a 14-6 at about 10,300 richened up to about 10,000. Hey maybe if you used the same prop? Or leaned the mixture on that two stroke?

BTW the standard for a .90 two stoke is one ounce per minute.

djlyon

" BTW the standard for a .90 two stoke is one ounce per minute."

Yea well my Nelson 40s (Q500) when on song burn 4oz a minute. Top that if you can in ozs burned per cubic inch.
[sm=punching.gif]

bla bla

No questions about the fuel ecom'
550cc tetra, YS 140 timer set at 14mins. OS 1.40 RX timer set at 8mins

STG

My Feedback: (26)

Isn't that funny. Your redults are the opposite of mine and Bob Pastorello http://www.rcaerobats.net/MotorCostComparison.htm Or is that a typo?[&:]

I just maidend a 11 pound plane with a 1.6FX and pipe. Two 8 min flights throttle over 15% (mix of IMAC and 3D) both flights used about 6-7oz of fuel(less than half my 16oz tank) With this amp;e power I did not need high throttle settings to get the job done.

http://home.comcast.net/~ccrsfield/giles2.wmv

William Robison

My Feedback: (3)

Gentlemen:

Let’s put an argument to rest here, please.

Some say a four stroke engine burns less fuel than an equivalent two stroke, others say the opposite, and some even say there’s no difference.

To get X amount of power you have to burn Y amount of fuel. Basic physics. In theory, a two stroke engine of X bhp will burn exactly the same amount of fuel as a four stroke engine of X bhp. Please note this is power, and not piston displacement.

This is obvious, but it must be said: We get power from our fuel by burning it in the engine’s cylinder. Any fuel lost to back spray from the intake, or lost through the exhaust contributes nothing to the engine’s power, and decreases the fuel efficiency.

A two stroke engine can be set up for good efficiency in burning its fuel, but the developed power is not high for its size and weight. Would you like to fly a “91’ engine that would only turn a 9x6 prop at 8500 rpm? Of course not.

When we alter the port timing for high rpm and high bhp we lose a lot of the efficiency we had in our econo-motor, a lot of fuel is lost in back spray from the intake, and a fair amount of fuel goes out the exhaust unburned.

A normally aspirated four stroke engine can not be expected to deliver the same power as a two stroke of the same displacement as it is only burning its fuel every other revolution, while the two stroke engine has a power stroke on each turn of the crank shaft. The four stroke does not take a 50% hit in power though, for several reasons. First, the four stroke engine has much greater pumping efficiency, using one entire stroke to force the burned gases out the exhaust, and another complete stroke to draw fresh fuel/air mix into the cylinder. The two stroke has to do both in a small fraction of its cycle, doing both while the piston is near the bottom of its stroke.

The four stroke engine also burns its fuel at a higher temperature, and this again raises the efficiency of the engine. A quick comparison of muffler/exhaust temperatures will confirm this to anyone who has doubts.

Both two and four stroke engines benefit greatly with the use of a stack on the intake, not as a tuned length, purely to catch the fuel sprayed back from the intake, holoding it to be drawn in on the next intake stroke. Even more benefit is realized with the use of an air filter, again not so much for increased engine life but to catch the last bit of fuel that would be blown back out.

Similarly, a tuned exhaust can give large gains on a two stroke, but for maximum benefit it’s only effective in a narrow rpm band. A four stroke engine can also benefit from a tuned exhaust, but it has to be set up differently, it’s roughly twice as long as the one for a two stroke engine, and the gain is not as great.

In summary, a two stroke engine of a given power will burn a similar amount of fuel as a four stroke engine of the same power, but usually the two stgroke engine, due to its inherent inefficiency, will have a higher fuel rate. Again please note, this is power, not engine displacement.

Also note I have not mentioned supercharged engines. Even so, the YS engines when developing X bhp will burn Y amount of fuel. Or more.

Bill.

donkey doctor

Hello; I prefer four strokes to two strokes, I don't fly at full throttle hardly at all. If you fly at maximum output (lots of two stroke people do) all the time, then likely yopu'll be happier wearing out a two stroke. Most of the posts I see here must fly at full throttle, it seems that maximum output is the only subject. In the real world, how often do you fly at full throttle? If that is your criteria for selecting an engine, you're wasteing your money on a four stroke, because you'll never use what four strokes excell at.

I see most two stroke flyers at our field just put the throttle to the top and leave it there for their entire flight. If that's the way you fly, or want to fly, get a two stroke. Leave the four strokes for the guys that actually fly the plane (and move the throttle around) and don't try to figure out why four strokes are so popular.

britbrat

That was an interesting collation of your personal opinions on other folks alleged behavioural traits.

Do you have anything to add to the discussion of the engines themselves?

STG

My Feedback: (26)

Bill, why do you bold your posts?

I agree with your theory...

... but in a practical application (flying a mix of 3D and IMAC--not full throttle or even high throttle settings) when comparing the 2 stroke to the 4 stroke (OS108 OS1.6FX) I do not see the "2 stoke inherent inefficiency" hurting them for mileage when you compare power to power.

Motorboy

With respect!
Do not forget, there are older peoples in RCU who need bold or bigger letter/alphabets cause reduced sight of age..

Jens Eirik

2slow2matter

My Feedback: (1)

Unbelievable.

Why can't "cool" be enough. I mean, it's my money. If I want to spend twice what you do on an engine simply because it's Cool to me, then that's fair enough. I didn't ask you for any money when I went to purchase the engine, so don't give me any grief for "wasting my money."

Afterall, people, this is a hobby. The cool factor can not, should not, and will not be ignored! Why do I buy four strokes? Because I like them, and for no other reason. Why do I like them? I'm not getting into that argument.

William Robison

My Feedback: (3)

STG ( and others)

Quote:

ORIGINAL: STG
Bill, why do you bold your posts?
I do not see the "2 stoke inherent inefficiency" hurting them for mileage when you compare power to power.

While I can still count the feathers on a sparrow at 150 yzrds, the computer screen at four feet is a different matter. As Jens said, some of us find it much easier to read a bolded post than a plain one.

Power to power? My point. To get the same power you're going to burn the same mount of fuel. And at part throttle there's not as much out spray or unburned fuel out the exhaust.

Bill.

britbrat

There's nothing wrong with "cool" [8D] & there's nothing wrong with personal preferences [sm=thumbup.gif]

I didn't see anyone saying that you should buy, or should not buy one or the other. All I see are folks expressing their personal preferences & why they like what they like.

For sure, the "folklore" issues & relative performance issues are are being discussed, but no one (with one apparent exception) is criticizing anyone for their choices.

BTW -- I'm one of the "old" folks & I don't like the bold type [:'(] -- it hurts my eyes [] -- too much contrast [:@] -- but that's a personal preference

Bodge

Bold? I hadn't noticed. Now that's OLD...

Anyway, I have an MVVS 91 that out fourstrokes my ASP 91FS. It pulls a bigger prop, throttles very well and uses little fuel - and it's cool!

I do like fourstrokes, though. I think they are easier to hover. But I'm not sure why.

bldrums

I just DO NOT agree ....with 2 strokes ...or 4 strokes..or anything

Naa, just joshin' I love it all

My "problem" is that I like too much of this cool RC stuff! May be too many $$$ but, way cool fun and cheaper than therapy! Ok not cheaper , but so what

(Saito .56, .82, .91 , 1.25 on the way)


how do you get the bold to work?............emm...[img][/img]

krayzc-RCU

My Feedback: (31)

i have 8 of them

blw

My Feedback: (3)

Britbrat,

Maybe you should stop being so aggressive when someone expresses a point of view.

B.L.E.

Even at low rpm's, a two stroke sounds like a two stroke, you will never mistake a horizontally opposed four cylinder four stroke engine turning 6000 rpm for a two stroke engine turning 12,000 rpm, even though they theoretically should sound the same.

DiscoWings

My Feedback: (76)

Why go with 4-strokes?
WIDE POWER BAND, torque is distributed at many differnt rpm readings, great for aerobatics & 3d. Put put put is a nice sound.


Why go with 2-Strokes?
More power at peak RPM power band is very exponential... if you want to haul ass, get a 2-stroke. Many people have disagreements on scale planes, some peple want to go fast, some people want realistic sound.


2-strokes dominate the hobby, probably 3-1. 4 strokes have more novelty many modelres like they way the run even if they have to pay a performance penalty.

DarZeelon

B.L.E.,


Well,


A four-stroke just sounds like a Briggs & Stratton lawn mower that lost its blade, or on steroids..., doesn't it?

NM2K

My Feedback: (14)

----------------


Thank you, Jens. Bold print does help some of us. Oops! <G>

sknx

My Feedback: (4)

As net etiquette in chat rooms and forums, bolding your hole post or using too much chromatics is impolite and seen as shouting. In any browser there is a decent feature that changes all the fonts on the web pages ( you can make them red, 77 px and italic if you like them that way).
Usually I skip reading when I see bolded posts. I don't like to be poked because someone wants my attention.
Hope I did not offended anyone.

Boby

I got sucked by /dev/null