How is it possible that 4C's are lighter than 2C's??
03-09-2007, 09:29 AM
#26
Senior Member
Join Date: Mar 2002
Location: Indianapolis,
IN
Posts: 116
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
I wonder if 2 strokes need to be heavier in order to deal with the increased power from the same displacement? Also, why do 2 strokes spin clockwise in the Southern hemisphere??
03-09-2007, 10:11 AM
#27
RE: How is it possible that 4C's are lighter than 2C's??
Also, why do 2 strokes spin clockwise in the Southern hemisphere??
03-09-2007, 01:11 PM
#28
Senior Member
My Feedback: (14)
RE: How is it possible that 4C's are lighter than 2C's??
ORIGINAL: Sport_Pilot
Actually the hole should make the crank lighter not heavier, though that would also depend on the transition from the solid part of the crank to the hollow portion. I suspect the four stroke crank is heavier because it must put out more torque at the same speed.
ORIGINAL: RunningMan
Never weighed a 4s crank vs a 2s, but not having to have that great big hole that is in the middle of a 2s crank, would make a 4s crank lighter.
Steve
Never weighed a 4s crank vs a 2s, but not having to have that great big hole that is in the middle of a 2s crank, would make a 4s crank lighter.
Steve
Actually the hole should make the crank lighter not heavier, though that would also depend on the transition from the solid part of the crank to the hollow portion. I suspect the four stroke crank is heavier because it must put out more torque at the same speed.
---------------
Four-strokes do NOT make more torque than two-strokes of an equal displacement. Remember, the two-stroke is firing twice as often. I'm talking model airplane engines here that are atmospherically aspirated, not Offenhauser or YS. <G>
Ed Cregger
03-09-2007, 01:50 PM
#29
RE: How is it possible that 4C's are lighter than 2C's??
Remember, the two-stroke is firing twice as often. I'm talking model airplane engines here that are atmospherically aspirated, not Offenhauser or YS.
03-09-2007, 03:34 PM
#30
Senior Member
My Feedback: (14)
RE: How is it possible that 4C's are lighter than 2C's??
ORIGINAL: Sport_Pilot
You are right Ed. However, I didn't explain it well. This is going back to college and studying kinematics, but as I recall the important thing is the peak thrust through the power stroke. The four stroke only has a power stroke every other revolution, but that one stroke is more powerful than the two strokes power stroke.
Remember, the two-stroke is firing twice as often. I'm talking model airplane engines here that are atmospherically aspirated, not Offenhauser or YS.
--------------
I agree, but the single power pulse of the four-stroke, although stronger than the single power pulse of the two-stroke, is not stronger than the two power pulses of the two-stroke. But I'm sure you know this.
The problem we have today in most comparisons is the automatic increase in displacement that is given to four-strokes when we compare the four-stroke .91 to the two-stroke .61. Then, there can be more power developed by the four-stroke, but people forget about the displacement increase, it is so engrained in our thoughts.
Ed Cregger
03-09-2007, 05:47 PM
#31
Member
Join Date: Feb 2006
Location: Christchurch, NEW ZEALAND
Posts: 44
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
Here are the specs for 2 OS engines that are the same displacement. How can an engine with 1hp more produce less torque? Also note the weight of the twoas the 2 stroke is almost 2/3rds the weight. The info is from the O.S. website so I gather both are weighed either with or without muffler.
OS 1.20 AX
Displacement 1.20 cu in (20 cc)
Bore 1.197 in (30.4 mm)
Stroke 1.083 in (27.5 mm)
Practical rpm range 1800-9500
Power Output 3.1 hp @ 9000 rpm
Weight 21 oz (650 g)
O.S. FS-120S111-P Four-Stroke
Displacement 1.218cu.in (19.96cc)
Bore 30.4mm(1.197in.)
Stroke 27.5mm(1.083in.)
Practical rpm range 2,000-12,000r.p.m
Power Output 2.1ps/12,000r.p.m.
Weight 920g(32.5oz.)
OS 1.20 AX
Displacement 1.20 cu in (20 cc)
Bore 1.197 in (30.4 mm)
Stroke 1.083 in (27.5 mm)
Practical rpm range 1800-9500
Power Output 3.1 hp @ 9000 rpm
Weight 21 oz (650 g)
O.S. FS-120S111-P Four-Stroke
Displacement 1.218cu.in (19.96cc)
Bore 30.4mm(1.197in.)
Stroke 27.5mm(1.083in.)
Practical rpm range 2,000-12,000r.p.m
Power Output 2.1ps/12,000r.p.m.
Weight 920g(32.5oz.)
03-09-2007, 10:03 PM
#32
Senior Member
My Feedback: (3)
Join Date: Dec 2004
Location: Martinsville,
IN
Posts: 1,486
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
The OS web site has known to be wrong. I question the 9,500 peak RPM of the 2 stroke to the 12,000 peak RPM of a four stroke. And I think you quoted a pumped 4 stroke about 2 OZ heavier. These 2 engines are not a normal comparision.
03-09-2007, 11:54 PM
#33
Member
Join Date: Feb 2006
Location: Christchurch, NEW ZEALAND
Posts: 44
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
It is the pumped but the hp is the same. I don't understand why people compare different size engines. If I was looking for a V8 I wouldn't look at a Mini. Earlier in the thread some one said about comparing similar sized engines and that is why I put the specs up as they have the same capacity. Yes the 1.20 (20cc) four stroke will have more grunt than a .91 (15cc) 2 stroke but there is .29ci (5cc) difference.
03-10-2007, 03:50 AM
#34
Senior Member
My Feedback: (14)
RE: How is it possible that 4C's are lighter than 2C's??
ORIGINAL: baldrick
It is the pumped but the hp is the same. I don't understand why people compare different size engines. If I was looking for a V8 I wouldn't look at a Mini. Earlier in the thread some one said about comparing similar sized engines and that is why I put the specs up as they have the same capacity. Yes the 1.20 (20cc) four stroke will have more grunt than a .91 (15cc) 2 stroke but there is .29ci (5cc) difference.
It is the pumped but the hp is the same. I don't understand why people compare different size engines. If I was looking for a V8 I wouldn't look at a Mini. Earlier in the thread some one said about comparing similar sized engines and that is why I put the specs up as they have the same capacity. Yes the 1.20 (20cc) four stroke will have more grunt than a .91 (15cc) 2 stroke but there is .29ci (5cc) difference.
--------------
It is an old habit that stems from the days of all the kits being made for standard sized two-stroke engines and folks wanting to know what size four-stroke would provide similar power. It amazes me that it hasn't caused more problems than it has over the years.
Today I see folks trying to pretend that two and four strokes produce the same amount of power ('cept different) in order to outfit their models with the proper size engine. There is one exception to the general rule (YS), but other four-stroke engines, especially the lower tier in the price range, are pretty much the same as they were twenty plus years ago.
Ed Cregger
03-10-2007, 11:22 AM
#35
Senior Member
My Feedback: (29)
Join Date: Jan 2005
Location: San Antonio,
TX
Posts: 1,402
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
BaldRick,
The two stroke fires every revolution, while the four stroke fires everyother rev. This is why four strokes produce only about 2/3rds of the raw power of a two stroke. The engines would be closer in weight if the 4 stroke wasn't a pumper and both included stock mufflers. The 4 stroke's power is somewhat more useable because of a flater power band and the ability to swing a bigger prop without overheating. This is because of the intake stroke cooling the cylinder between power strokes.
Dave
The two stroke fires every revolution, while the four stroke fires everyother rev. This is why four strokes produce only about 2/3rds of the raw power of a two stroke. The engines would be closer in weight if the 4 stroke wasn't a pumper and both included stock mufflers. The 4 stroke's power is somewhat more useable because of a flater power band and the ability to swing a bigger prop without overheating. This is because of the intake stroke cooling the cylinder between power strokes.
Dave
03-10-2007, 02:21 PM
#36
Member
Join Date: Jul 2004
Location: NA, SINGAPORE
Posts: 47
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
Not sure about that, I had a OS 120 Surpass II-E w saito pump unit. It could manage 15x8.
My OS 120ax could swing a 16x8 prop no problemo. Its throttle IMHO is very linear too.
The all up weight with muffler of the OS 120ax is closer to 850 gm just slightly lighter compared to the four stroke 120.
One apparent advantage the 4 strokes has, is its ease of mounting on the airframe. Its easy to direct the exhaust to the bottom of the plane. Not so with the 2's.
My OS 120ax could swing a 16x8 prop no problemo. Its throttle IMHO is very linear too.
The all up weight with muffler of the OS 120ax is closer to 850 gm just slightly lighter compared to the four stroke 120.
One apparent advantage the 4 strokes has, is its ease of mounting on the airframe. Its easy to direct the exhaust to the bottom of the plane. Not so with the 2's.
03-10-2007, 04:14 PM
#37
Senior Member
My Feedback: (1)
Join Date: Sep 2004
Location: STOCKHOLM Akersberga, SWEDEN
Posts: 1,116
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
How is it possible that 4C's are lighter than 2C's??
03-10-2007, 08:50 PM
#38
Member
Join Date: Feb 2006
Location: Christchurch, NEW ZEALAND
Posts: 44
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
I knew I'd rock the boat a bit with my comments 
. I agree with what every body says but we need to mention when we are compaing them with. ie power or capacity. The older day engines didn't have the same output as the modern engines. The modern .46 is swinging the oldschool .61 props with relative ease. I've got an ESM Extra 330 which a friend had an O.S. 1.20 four stroke in. It flew ok on that motor but I have powered it with a Magnum 1.20 2 stroke and it's swinging a larger prop, motor and muffler is lighter than his and now has unlimited vertical. The choice of engine / airframe combination is always an interesting one
. I agree with what every body says but we need to mention when we are compaing them with. ie power or capacity. The older day engines didn't have the same output as the modern engines. The modern .46 is swinging the oldschool .61 props with relative ease. I've got an ESM Extra 330 which a friend had an O.S. 1.20 four stroke in. It flew ok on that motor but I have powered it with a Magnum 1.20 2 stroke and it's swinging a larger prop, motor and muffler is lighter than his and now has unlimited vertical. The choice of engine / airframe combination is always an interesting one
03-10-2007, 11:47 PM
#39
Member
Join Date: Jul 2004
Location: NA, SINGAPORE
Posts: 47
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
After looking at my comment a little bit, I believe I was pretty biased towards the 120 sized engines.
When ya want to compare the smaller ones in the 60 range, example such as (the exemption) YS63 is lighter by a hair compared to the OS 55ax. Prop wise the YS on 14x4w and OS on 13x4w. The older 60 size two strokes are way way over the hill.
So.... a sweeping statement of 4c over the 2c or vise versa doesnt hold true. I digress, choosing yur killer combination has never been better; 2c or 4c has its place.
When ya want to compare the smaller ones in the 60 range, example such as (the exemption) YS63 is lighter by a hair compared to the OS 55ax. Prop wise the YS on 14x4w and OS on 13x4w. The older 60 size two strokes are way way over the hill.
So.... a sweeping statement of 4c over the 2c or vise versa doesnt hold true. I digress, choosing yur killer combination has never been better; 2c or 4c has its place.
03-11-2007, 02:02 AM
#40
Senior Member
My Feedback: (14)
RE: How is it possible that 4C's are lighter than 2C's??
ORIGINAL: ir
After looking at my comment a little bit, I believe I was pretty biased towards the 120 sized engines.
When ya want to compare the smaller ones in the 60 range, example such as (the exemption) YS63 is lighter by a hair compared to the OS 55ax. Prop wise the YS on 14x4w and OS on 13x4w. The older 60 size two strokes are way way over the hill.
So.... a sweeping statement of 4c over the 2c or vise versa doesnt hold true. I digress, choosing yur killer combination has never been better; 2c or 4c has its place.
After looking at my comment a little bit, I believe I was pretty biased towards the 120 sized engines.
When ya want to compare the smaller ones in the 60 range, example such as (the exemption) YS63 is lighter by a hair compared to the OS 55ax. Prop wise the YS on 14x4w and OS on 13x4w. The older 60 size two strokes are way way over the hill.
So.... a sweeping statement of 4c over the 2c or vise versa doesnt hold true. I digress, choosing yur killer combination has never been better; 2c or 4c has its place.
-------------
Now you're talking. It does depend upon the intended usage of the particular engine, two or four-stroke, and how it is tuned.
Ed Cregger
03-19-2007, 01:11 AM
#41
Member
Join Date: Feb 2006
Location: Christchurch, NEW ZEALAND
Posts: 44
Likes: 0
Received 0 Likes
on
0 Posts
RE: How is it possible that 4C's are lighter than 2C's??
Just a quick note on the O.S. 1.20 2 stroke.
The specs I put on earlier are about right. The 1.20 is a long stroke engine thus lower revolutions. Long strokes are in general gruntier than the standard short stroke engine with less rev's.
Any one got the newer O.S. 1.20 4 stroke with the sealed pre-greased bearing????
The specs I put on earlier are about right. The 1.20 is a long stroke engine thus lower revolutions. Long strokes are in general gruntier than the standard short stroke engine with less rev's.
Any one got the newer O.S. 1.20 4 stroke with the sealed pre-greased bearing????
