Sportflyr

My Feedback: (1)

I know this question will make a lot of people chuckle but, having never
owned or even held a 4-stroke before,I just wonder if someone could
give me an explanation. Is it the engine block itself? More use of aluminum?

Another reason I ask is this doesn't translate as such in the full- scale world.
A 4-stroke with more parts, will always be heavier than any 2-stroke in full-scale mode which are
commonly used in ultralights for their light weight, simplicity and power. Having been involved
in motocross many years ago (amateur mechanic for my brother), I also see that the new generation
4-strokes are a little heavier than the 2-strokes (albeit, not by much).

I'm looking to get into a larger scale Cessna-150 Aerobat and I need to
make a pertinent decision on what to power it with...most likely a twin, pumped 4-stroke.

Without getting too much into metallurgy, if it is indeed the use of more
aluminum that makes these 4-strokes lighter, then why can't the 2-strokes be
made light as a feather with the same technology?

This is a question that has been in the back of my mind forever but, always
kinda shy about asking so please be easy on me. I own two ST .45's which
I hold very near and dear, an old K&B .40 and an OS LA .46.

P.S. there has beeen no one at the field that can give me a straight
answer for this phenomenon just that, "they are". And again, sorry for the loaded question![sm=confused.gif]

DarZeelon

Sportflyr,


If you weigh a two-stroke engine and a four-stroke engine alone, they would weigh about the same.

The valve mechanism of a four-stroke is comprised of pretty light parts that despite their sheer number, add very little to the weight difference.

But the muffler we are accustomed to have on our two-stroke engine is much heavier than the one on a four-stroke engine, making up a major weight difference.

asmund

Right on My 91 fs weighs just about the same as my 91 fx when neither has the muffler attached

Motorboy

The 2 stroke engine can be lighter than a normal 2 stroke engine as here: http://www.modelenginenews.org/cardfile/gp2.html

This is a light engine: 98 grams. In comparison, an Oliver Tiger Mk 3 comes in at 175 grams.

Jens Eirik

B.L.E.

A lot of two stroke engines use chrome plated brass cylinder sleeves and brass is heavy. I believe that Saito uses chrome plated aluminum cylinders in most of their newer four strokes. Also, the cylinder and head is one piece, no head bolts. This helps to make these engines very weight competative with two strokes of equal power. There is no reason that this can't be done with 2-stroke engines in fact you see this construction a lot when you go to gasoline spark ignition two strokes. A lot of glow engines have not changed much during the past couple of decades.
Norvel was offering a line of two strokes that featured ceramic lined aluminum cylinders that was supposed to offer a weight savings over ABC (Aluminum piston, Brass cylinder liner, Chrome plated) engines.

As stated before, two strokes come with bigger mufflers and as a result, they are usually quieter than four stroke engines. The people who fly in F3A (pattern) use mufflers that resemble two stroke tuned pipes inside the fusilage in order to get the four strokes to meet the strict noise limits of F3A competition.

downunder

Well you do it to everyone else so I figured it was your turn. I've overlooked the misplaced comma

I've often wondered why RC 2 strokes are so heavy too. There are many (but not commonly available) .60 size, ball raced, ABC 2 strokes that weigh in the area of 12-13 ounces including muffler. The engine in the photo is one example and I have one. Their RE 51 weighs 10.4 ounces with muffler.

DarZeelon

Touché!

The new RCU has removed the 'Spell Checker'... It is easy to ovelook.

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So, is this one of your Stalkers?

Sportflyr

My Feedback: (1)

Very interesting answers, thanks so much for all of them.

I never took the muffler into account which I should have
especially running two of the heaviest on the market...the
ST Quiet mufflers which are gargantuan and have a separate
header to boot.

Also didn't realize four-strokes used a different cylinder sleeve. I can see
where that chunk of brass can make a big difference.

Is it a matter of thermo-dynamics with the 2-strokes which I guess produce higher heat
and RPM?????

Thanks again for the insightful responses.

WycheG

My Feedback: (4)

I don't know if you can generalize on the cylinder liner thing. My YS 4-strokes and 2-strokes all have cylinder liners (and, as was mentioned before, the liners are quite beefy) but my Saito does not have a separate liner (so it is much lighter).

B.L.E.

Didn't K&B make a series of linerless two strokes called the Sportsters? I think they were an 'inside out' design. Instead of an aluminum piston in a chrome plated cylinder, it used a chrome plated piston in a plain aluminum cylinder. They also had bushing bearings for the crank. I think they were pretty light for their displacement.

NM2K

My Feedback: (14)

As Dar Zeelon pointed out, the two-stroke's muffler (for a given displacement) is quite a bit larger and heavier than that of the four-stroke.

Additionally, the two-stroke's crankshaft will be larger because it needs to be able to pass enough fuel/air mix through its bored center to feed the engine adequately, plus it needs to be larger in order to handle the higher level of power that is produced by a two-stroke versus a four-stroke.

Then we must consider the gas passages that are routed through a two-stroke glow engine's crankcase casting. This calls for the use of more heavy metal that the four-stroke simply does not need, since all of this is handled in the four-stroke engine's head and not the crankcase.

If one looks at it from a power versus weight context, instead of a displacement versus weight context, then the two-stroke begins to look very light.


Ed Cregger

Sportflyr

My Feedback: (1)

OK, I think I'm getting the hang of it. I read here a lot more than I post and there are a few
threads I've come across that suggests using four strokes for models that will come out just
too nose heavy for even a smaller two stroke.

Sounds like Saito has the edge with the one piece cylinder setup but, how are they as far as ease of use?

Most guys at my field are running OS FS's or Magnums with lots of success. I'm looking forward to getting into one.

I noticed that Tower lists weight and power for most of their motors...how reliable is that info?

Also, I notice Saito doesn't doesn't give specs on power output at least on the Horizon site, and what
is an "AAC" cylinder type?

NM2K

My Feedback: (14)

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Yep, they sure did.

I still have my wife's .28 Sportster and I bought Frank Schwartz's .65 Sportster a while back. I hated Sportsters when I first encountered them over a decade and a half ago, but since then I have learned to appreciate them. I only wish that mine were equipped with bushings for the crankshaft. If they were, I would invest in a couple of Davis Diesel Development conversion heads for them.


Ed Cregger

NM2K

My Feedback: (14)

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The original four-strokes were quite a bit heavier than many of today's four-strokes. You have to start somewhere. Some of today's four-strokes are still using "old designs" in so far as the bulk and girth of their engines are concerned (Enya, OS, Sanye, Thunder Tiger). Saito and YS tend to be the trendsetters in the design and manufacture of glow four-stroke engines intended for model airplanes.

The real problem of the "heavy four-stroke syndrome" is the fact that it still takes a lot more displacement in a four-stroke engine to equal the power output of a much smaller two-stroke engine. This is especially pronounced when the four-stroke engine is an OS (non FL), Magnum, ASP, SC (all Sanye products), Thunder Tiger, or Enya engine. I'm not saying that these engines are bad. I am saying that they are considerably heavier than Saito engines of equal displacement. Running 30% nitro in a four-stroke does not make up for the power difference between it and a hot two-stroke engine. But it helps.

I don't know of any modern four-stroke engines that are not reliable.

While Saito's all-in-one cylinder/head design (YS too) is lighter than having a separate cylinder head, it is also much more expensive to replace should the liner get seriously scratched or the head suffer some type of damage. Everything is a compromise. You have to consider what is important to you.


Ed Cregger

Hobbsy

My Feedback: (102)

Sport here is an example of an AAC setup, Aluminum piston, Aluminum cylinder with Chrome bore, this cylinder is from an Enya .60 XF. You can see the thin Chrome lining in this verticle view. The difference is that the Saito does not have a sleeve, the Chrome is plated right on the inside of the cylinder, hence, no sleeve==less weight.

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

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.

Sportflyr

My Feedback: (1)

Thanks, You guys sure know your motors![X(]

B.L.E.

AAC.......Aluminum Aluminun Chrome, aluminum piston in a chrome plated aluminum cylinder

ABC.....aluminum brass chrome, aluminum piston in a chrome plated brass cylinder sleeve

ABN......aluminum piston in a nickel plated brass cylinder sleeve


I suspect that Saito refrains from making horsepower claims because they don't want to have to lie in order to compete with some of the inflated claims made by the competition.

downunder

I just checked the crankshafts in a little .15 and a .60 and surprisingly enough the holes in both of them weighed exactly the same!

Hobbsy

My Feedback: (102)

Are you sure, I thought a larger hole in the southern hemisphere would be heavier.

baldrick

The Magnum 1.20 2 stroke I have weighs less than a friends 1.20 4 stroke including mufflers. Also the 2 stroke has more power.
Question here in a similar note. Manufacturers recommend say for instance a maximum of a .91 2 stroke or a 1.20 4 stroke. How come with modern engines is there such a difference in performance? I'm looking at engines for my Ultimate before I start construction.

NM2K

My Feedback: (14)

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speedster 1919

My Feedback: (3)

One thing not mentioned is cost or price. Take any manufactured product. When you start to make it smaller and use thinner pieces and casting . You have to have more precise tooling and labor intensive operations and also have more rejects. Now if you get too thin and light every crash would probably require a new engine. A 2 stroke muffler has to stay large for expansion and to be less restrictive.

wcmorrison

My Feedback: (2)

No No No. It is the torque that is backwards, spins the other way. Right!

Good to see you back on line.

Cheers,

Chip