RE: Considering a large Glow engine ??? For big engines, GAS is better in every way :)  
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RE: Considering a large Glow engine ??? For big en... - 10/5/2006 7:40:20 PM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		This thread is great. Tons of info in one place. Finally.



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RE: Considering a large Glow engine ??? For big e... - 10/5/2006 8:06:17 PM   
Sport_Pilot



Posts: 7727
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From: Acworth, GA, USA
Status: offline 		Checking the motocross online ads. The 80 cc two strokes are getting replaced with 125cc four strokes. 150 with 250 etc.

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RE: Considering a large Glow engine ??? For big en... - 10/5/2006 8:24:41 PM   
XJet


 

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From: Tokoroa, NEW ZEALAND
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quote:

ORIGINAL: RVM
Humm, so do 4-strokes have more torque than 2-strokes or not?


Four-strokes definitely have more peak-torque (ie: the maximum turning force applied to a 4-stroke crankshaft is greater than that applied to a 2-stroke of the same displacement. Unfortunately it's only applied every second revolution -- so the *average* torque (at maximum power) is less.

However, 4-strokes also create far more torque at lower RPMs than a 2-stroke. This means that the torque-curve of a 4-stroke is flatter than a 2-stroke of the same maximum power output.

This means that when you hit the throttle from low RPMs on a 4-stroke, it revs up much more quicky than a 2-stroke. This is one of the reasons why those who fly 3D prefer 4-strokes.

Not a simple answer eh?


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RE: Considering a large Glow engine ??? For big en... - 10/5/2006 8:35:30 PM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		Actually a great answer, since I understand torque curves and how they apply to automobile engines (and various other devices other than engines). I just wasn't sure where the torque on a 4-stroke was, and whether or not a 2-stroke had more or less of it.


quote:

ORIGINAL: XJet

Four-strokes definitely have more peak-torque (ie: the maximum turning force applied to a 4-stroke crankshaft is greater than that applied to a 2-stroke of the same displacement. Unfortunately it's only applied every second revolution -- so the *average* torque (at maximum power) is less.

However, 4-strokes also create far more torque at lower RPMs than a 2-stroke. This means that the torque-curve of a 4-stroke is flatter than a 2-stroke of the same maximum power output.

This means that when you hit the throttle from low RPMs on a 4-stroke, it revs up much more quicky than a 2-stroke. This is one of the reasons why those who fly 3D prefer 4-strokes.

Not a simple answer eh?



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RE: Considering a large Glow engine ??? For big en... - 10/5/2006 8:53:33 PM   
rmw00



Posts: 116
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From: Indianapolis, IN, USA
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quote:

ORIGINAL: XJet

Compare the weight/power of the average 40-sized 2-stroke with the weight/power of something like a Saito 82.

the Saito is about the same weight but has *more* power and, more importantly, more *usable* power.


Uhh... NO. If you compare a .40 to an .82 there is no question what the result will be.

How about the OS LA .65??? Same weight as the .82, more HP, a bit less torque but spins a 13x8 pretty well, for less than half the price. Or a Moki .61LS, mine spins a 14x6 at 9000rpm on a cool day, wieghs the same as the .82 and costs less. And the .82 sucks fuel really fast.

The best 4-stroke .90 I ever had was a K&B .65 Sportster . Swung an 13x8 prop better than any current .90 4-stroke (in 1999) weighed less, and cost $99.

I'll put my Moki .61LS up against a Saito.82 any day, we'll see what *usable* means. If you really want to get *used*, I'll put a pipe on it.


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RE: Considering a large Glow engine ??? For big en... - 10/5/2006 8:56:48 PM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		rmw00, wouldn't the comparison depend on what you were comparing? You would have to set up some standards. For instance, comparing engines, are you basing the comparison solely on power/CC, or power:weight, or weight:CC, power/fuel consumed, ([power:weight]/CC)/fuel consumed etc.

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RE: Considering a large Glow engine ??? For big en... - 10/5/2006 9:53:35 PM   
Ed Cregger



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From: Ringgold, GA, USA
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quote:

ORIGINAL: RVM

rmw00, wouldn't the comparison depend on what you were comparing? You would have to set up some standards. For instance, comparing engines, are you basing the comparison solely on power/CC, or power:weight, or weight:CC, power/fuel consumed, ([power:weight]/CC)/fuel consumed etc.



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


And this is precisely why I try to discourage folks from relying on manufacturer's test data. Without established parameters and agreed upon terms, the data is meaningless most of the time.

In the end, all that matters is how it flies your model with a certain level of reliability and a price that the end user can afford.

Engines are a separate hobby for me. I love them all, so you aren't likely to see me sticking with just one type or any one brand. I enjoy extracting the maximum for the engine that I am using at the time. However, my maximum is not always horsepower. In fact, horsepower is seldom my prime consideration. Tractability, reliability, sometimes economy and the ability to swing a useful prop at a useful rpm are my goals. This makes owning and flying virtually any engine fun. I have YS, Rossi, Webra, Enya, OS, Super Tigre and a Jett SJ.46. But I also own and enjoy the cheapest Asian engines too.



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RE: Considering a large Glow engine ??? For big en... - 10/6/2006 1:56:04 AM   
rmw00



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From: Indianapolis, IN, USA
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quote:

ORIGINAL: RVM
rmw00, wouldn't the comparison depend on what you were comparing? You would have to set up some standards. For instance, comparing engines, are you basing the comparison solely on power/CC, or power:weight, or weight:CC, power/fuel consumed, ([power:weight]/CC)/fuel consumed etc.


Exactly!!! This thread started out stating that gas was better for everything, then changed to 4-strokes are better. The post I was replying to had stated that a 4-stroke had better power to weight than a 2-stroke and compared a .82 4-stroke to a .40 2-stroke. My point was that for most standards, but not all, 4-strokes would not be better than 2-strokes, particularily power to weight.

Every perforrmance based model competition I can think of except pattern is exclusively 2-stroke.


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RE: Considering a large Glow engine ??? For big en... - 10/6/2006 2:08:04 AM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		A lot of the IMAC guys that I've talked to who are still running glow engines are using 4-strokes. Also, nearly all the 3d glowies use 4-strokes.



quote:

ORIGINAL: rmw00

Exactly!!! This thread started out stating that gas was better for everything, then changed to 4-strokes are better. The post I was replying to had stated that a 4-stroke had better power to weight than a 2-stroke and compared a .82 4-stroke to a .40 2-stroke. My point was that for most standards, but not all, 4-strokes would not be better than 2-strokes, particularily power to weight.

Every perforrmance based model competition I can think of except pattern is exclusively 2-stroke.


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RE: Considering a large Glow engine ??? For big en... - 10/6/2006 4:25:20 AM   
XJet


 

Posts: 3462
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
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quote:

ORIGINAL: rmw00


quote:

ORIGINAL: XJet

Compare the weight/power of the average 40-sized 2-stroke with the weight/power of something like a Saito 82.

the Saito is about the same weight but has *more* power and, more importantly, more *usable* power.


Uhh... NO. If you compare a .40 to an .82 there is no question what the result will be.

How about the OS LA .65??? Same weight as the .82

I don't know where you're getting your figures from but I believe they're wrong.

The OS65LA is several ounces heavier than the Saito 82 -- remember that OS quote their weight (18oz according to this page *without* a muffler (most other sites say 18.9oz without muffler (example) and those 2-stroke mufflers are *heavy*. The SA82 is only 17.6 ounces *with* muffler according to this page.

As for the power difference, Saito claim 1.5HP, OS claim 1.7, but this is at 16,000 RPMs. Show me any regular plane where you'd be propping a plain-bearing motor to turn 16,000 RPMS and you'll see what I mean by "more usable power" in reference to a 4-stroke.

On a power-to-weight ratio, the Saito is still a long way ahead.

quote:


more HP, a bit less torque but spins a 13x8 pretty well, for less than half the price. Or a Moki .61LS, mine spins a 14x6 at 9000rpm on a cool day, wieghs the same as the .82 and costs less. And the .82 sucks fuel really fast.


The 82 doesn't suck fuel, unless you're still running the bottom end too fat -- you've got to lean them out by about 2.5-3 turns once they're run in.


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RE: Considering a large Glow engine ??? For big en... - 10/6/2006 5:24:26 AM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		My .91, when I started leaning it out, hardly used any fuel at all. I'm sticking a BruLine filter and velocity stack on it when I get it back from being repaired so it should get even better. Also, I only had about 2 gallons through mine so it still had a bit of leaning left to do. I use a lot less fuel than other people I fly with who run 2-strokes.

quote:

ORIGINAL: XJet

The 82 doesn't suck fuel, unless you're still running the bottom end too fat -- you've got to lean them out by about 2.5-3 turns once they're run in.



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RE: Considering a large Glow engine ??? For big en... - 10/6/2006 5:58:52 AM   
JettPilot



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From: Paradise, USA
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quote:

ORIGINAL: Sport_Pilot

When they went to the schnurle ported models the differance between milage and evironmental issues shrank, but the two stroke also jumped in power.



The four stroke motorcycle will develop more power and a LOT more torque than a 2 stroke at low RPM. For a 2 stroke to take advantage of its porting and expansion muffler, it must be at High RPM. The expansion chamber only works in a narrow RPM range ....

Who wants to have to run thier motorcycle at 8000 RPM all day to have available power My four stroke puts out loads of power from low RPM to High RPM. When you run a 2 stroke at high RPM's, they DRINK fuel like there is no tomorrow.

As far as 2 strokes being as reliable as 4 storke motorcycles, only an ignorant person that knows nothing about engines makes a statement like that. Be it Motorcycles, or Ultralights, or anything, you see 4 strokes for long distances when reliability can be a life or death situation.

Its easy to talk big in these forums, but when its real life, and people are educated, that changes. I dont see any 2 stroke bikes way out in the middle of nowhere, and almost all ultralight guys that fly long cross country ( transcontinental ) fly 4 strokes. The 2 strokers almost never make it without engine troubles

Here are some pictures of a friends ultralight, he has been a pioneer in flying them cross country for many years... He used to keep two have to keep two 2 stroke engines ready at all times, because they always went bad and he would always have engines go bad and change them... Since having a 4 stroke, he flys all over the country inculding to Alaska and back and has never had engine trouble

JettPilot




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< Message edited by JettPilot -- 10/6/2006 6:00:27 AM >

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RE: Considering a large Glow engine ??? For big e... - 10/6/2006 7:41:10 AM   
bla bla


 

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Status: offline 		Here we go, it's that Honey again.
She's lookin' FINE Jettepilot.

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RE: Considering a large Glow engine ??? For big e... - 10/6/2006 1:15:28 PM   
skiman762



Posts: 1166
Joined: 12/1/2005
From: Nashville, NC, USA
Status: offline 		I know this much, if you are in this hobby to save money you picked the wrong hobby
We should spend more time flying to improve our skills then worrying about who has the best engine.
I had the chance to spot for Jerry Smith at a flyin a few weeks ago and he flew an 11lb funfly stick with a os 160
He did things the 3d boys weren't doing how about a powered flat spin 20 feet off the ground with about 10 rotations before he pulled out.
I got wrapped up in the more power thing myself then I relized all I was doing is making deeper holes in the ground
now I'm working on my flying skills rather then hoping my overpowered plane will get me out of trouble.
but the great thing about this hobby is to each his own.
Happy landings

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