2-Stroke Vs. 4-Stroke question

2-Stroke Vs. 4-Stroke question

Post by Jason Parke » Wed, 06 Oct 1999 04:00:00



    I have a question I have not been able to get a strait answer for from
any dealer.  Can anyone tell me if there is some rule of thumb or chart that
will directly compare 2-strokes to four stroke engines.  What I mean is if I
am given a range between 60 and 90 for 2 strokes what is my range for a four
stroke?  Please email me if you can help me out.

Jason

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Learjet3 » Thu, 07 Oct 1999 04:00:00


Quote:
>I have a question I have not been able to get a strait answer for from
>any dealer.  Can anyone tell me if there is some rule of thumb or chart that
>will directly compare 2-strokes to four stroke engines.  What I mean is if I
>am given a range between 60 and 90 for 2 strokes what is my range for a four
>stroke?  Please email me if you can help me out.

>Jason

then go 90 to 1.20 (even 1.50) for 4 stroke


<remove NO-SPAM from email address to respond>

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Ivo » Thu, 07 Oct 1999 04:00:00




Quote:
>     I have a question I have not been able to get a strait answer for
from
> any dealer.  Can anyone tell me if there is some rule of thumb or
chart that
> will directly compare 2-strokes to four stroke engines

This one generates endless debate because the engines don't produce
power in exactly the same way. I'll leave the theoretical discussion to
the engineers out there, but heres's a practical comparison:

Many people equate 60 2-strokes to 90 4-strokes because they might have
similar hp ratings, but in the real world that doesn't really check
out, and here's why: A 2-stroke will produce good power at considerably
higher rpm than a 4-stroke, So say, for example, you're looking to run
a 14X6 prop on your "60 size" sport/aerobatic plane, the OS 61 FX will
only spin it at around 8600 rpm because this large a prop doesn't allow
the engine to ever enter its power zone. An OS 91 Surpass (4-stroke),
on the other hand, will spin the same prop at 9500 rpm which will
result in excellent vertical performance. So for that type of airplane
the 91 4-stroke will give better overall performance.

Now, say instead, that you're looking for top speed in a pylon racing
or jet type airplane. The 2-stroke's ability to safely rev up to 14,000
rpm and higher will result in an level flight speed for beyond the
reach of the 4-stroke. Being limited to about 11,000 max, the 4-stroke
simply cannot safely rev as high as the 2-stroke so therefore cannot
keep up in the "speed contest".

Think about the type of flying that you like to do, and the flight
envelope your plane was designed for and the choice of engine will
become more apparent.

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

2-Stroke Vs. 4-Stroke question

Post by go.. » Thu, 07 Oct 1999 04:00:00



Quote:
>    I have a question I have not been able to get a strait answer for from
>any dealer.  Can anyone tell me if there is some rule of thumb or chart that
>will directly compare 2-strokes to four stroke engines.  What I mean is if I
>am given a range between 60 and 90 for 2 strokes what is my range for a four
>stroke?  Please email me if you can help me out.

>Jason

There really is no straight answer.  A general rule of thumb is to go up 1 size but
as 4 strokes have become more powerful, this is not always true.  I have found
my OS91FS(pumped) to be extremely powerful with a three blade prop and would
not hesitate to use it anywhere a 91 2strk is called for.  A lot also -in my case anyway-
depends on what sort of planes one likes to build and whether one is power
hungry or not.  I like scale and I like the sound of 4 trks and I would never
compromise the look of a scale plane by having the motor*** out somewhere.

So, there is one person's view and I think that you will get many other different
answers to this very good question.

Gord Schindler
MAAC 6694
Toronto, Ont.
Canada

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Mike Wizynajty » Thu, 07 Oct 1999 04:00:00


Jason,

The reason you aren't getting a "strait answer" is because there is no such
thing to this type of question. The issue is muddled by pilot expectations. You
might find that you wouldn't be happy with the plane's performance even if you
went to the largest recommended engine, the .90 2-stroke. You may really want a
1.20 2-stroke in your plane.

Generally speaking, you would probably find most 1.20 4-stroke motors will do
the job. If you want more power a 1.40-1.80 4-stroke can work well. If you want
a really light plane and are willing to do some extra work to save weight during
construction then a .91 4-stroke may fill the bill.

Tell us a little about your project (type of plane, proposed weight ect.) and
your expectations and we can better help you choose a power plant.

Wiz

Quote:

>     I have a question I have not been able to get a strait answer for from
> any dealer.  Can anyone tell me if there is some rule of thumb or chart that
> will directly compare 2-strokes to four stroke engines.  What I mean is if I
> am given a range between 60 and 90 for 2 strokes what is my range for a four
> stroke?  Please email me if you can help me out.

> Jason

 
 
 

2-Stroke Vs. 4-Stroke question

Post by mkirs.. » Thu, 07 Oct 1999 04:00:00




Quote:
>     I have a question I have not been able to get a strait answer for
from
> any dealer.  Can anyone tell me if there is some rule of thumb or
chart that
> will directly compare 2-strokes to four stroke engines.  What I mean
is if I
> am given a range between 60 and 90 for 2 strokes what is my range for
a four
> stroke?  Please email me if you can help me out.

Generally, a kit will specify a range of 4-stroke engines in addition to
the range of 2-strokes it lists.

In my experience, a kit recommending a .60 2-stroke will
traditionally recommend a .90 4-stroke.

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

2-Stroke Vs. 4-Stroke question

Post by FozzyBe » Thu, 07 Oct 1999 04:00:00


this is my rules of thumb

2c ===>>>4c

.15-.20      .26
.40- .50     .52-65
.60            .75-.91
.91            1.20-1.40

Quote:

> >I have a question I have not been able to get a strait answer for from
> >any dealer.  Can anyone tell me if there is some rule of thumb or chart that
> >will directly compare 2-strokes to four stroke engines.  What I mean is if I
> >am given a range between 60 and 90 for 2 strokes what is my range for a four
> >stroke?  Please email me if you can help me out.

> >Jason

> then go 90 to 1.20 (even 1.50) for 4 stroke


> <remove NO-SPAM from email address to respond>

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Paul Rucke » Thu, 07 Oct 1999 04:00:00


Roughly 40 to 50% increase in Cubes of the 4-stroke over the 2-stroke, i.e.
.60 2-stroke equals .90 four stroke. .90 2-stroke = 1.20 four stroke, etc...
Sport 2-stroke vs Sport 4-stroke. Of course the equation skews when you use
High Performance engines like Rossi 2-strokes, vs YS 4-strokes. But the
equation is a good rule of thumb.


Quote:
>     I have a question I have not been able to get a strait answer for from
> any dealer.  Can anyone tell me if there is some rule of thumb or chart
that
> will directly compare 2-strokes to four stroke engines.  What I mean is if
I
> am given a range between 60 and 90 for 2 strokes what is my range for a
four
> stroke?  Please email me if you can help me out.

> Jason

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Paul Mcintos » Thu, 07 Oct 1999 04:00:00


Jason,

The range of two strokes you gave is probably equivalent to .70 to 1.20 four
strokes.  It all depends on which specific two stroke you are trying to
replace.  Just as there are a range of engine sizes to consider, there is also a
range of engine power within each size.  For example, a .61 K&B has far less
power then a YS .61.  They could both be used in the same plane, but the
difference in performance would be dramatic.  The same is true in 4-strokes.
Compare the Magnum .91 to the YS .91 for example.  In real world useable power,
I believe that the YS is nearly double the Magnum.  An airframe that is marginal
for the Magnum would be no problem for the YS.

I guess that I am trying to say that there is no hard and fast rule for
converting generic 2-stroke sizes to 4-strokes.

Quote:

>     I have a question I have not been able to get a strait answer for from
> any dealer.  Can anyone tell me if there is some rule of thumb or chart that
> will directly compare 2-strokes to four stroke engines.  What I mean is if I
> am given a range between 60 and 90 for 2 strokes what is my range for a four
> stroke?  Please email me if you can help me out.

> Jason

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Michael Gre » Thu, 07 Oct 1999 04:00:00


So what you are saying is 4-stroke = power/verticle performance and
2-stroke = speed?

Mike

Quote:



> >     I have a question I have not been able to get a strait answer for
> from
> > any dealer.  Can anyone tell me if there is some rule of thumb or
> chart that
> > will directly compare 2-strokes to four stroke engines

> This one generates endless debate because the engines don't produce
> power in exactly the same way. I'll leave the theoretical discussion to
> the engineers out there, but heres's a practical comparison:

> Many people equate 60 2-strokes to 90 4-strokes because they might have
> similar hp ratings, but in the real world that doesn't really check
> out, and here's why: A 2-stroke will produce good power at considerably
> higher rpm than a 4-stroke, So say, for example, you're looking to run
> a 14X6 prop on your "60 size" sport/aerobatic plane, the OS 61 FX will
> only spin it at around 8600 rpm because this large a prop doesn't allow
> the engine to ever enter its power zone. An OS 91 Surpass (4-stroke),
> on the other hand, will spin the same prop at 9500 rpm which will
> result in excellent vertical performance. So for that type of airplane
> the 91 4-stroke will give better overall performance.

> Now, say instead, that you're looking for top speed in a pylon racing
> or jet type airplane. The 2-stroke's ability to safely rev up to 14,000
> rpm and higher will result in an level flight speed for beyond the
> reach of the 4-stroke. Being limited to about 11,000 max, the 4-stroke
> simply cannot safely rev as high as the 2-stroke so therefore cannot
> keep up in the "speed contest".

> Think about the type of flying that you like to do, and the flight
> envelope your plane was designed for and the choice of engine will
> become more apparent.

> Sent via Deja.com http://www.deja.com/
> Before you buy.

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Ivo » Thu, 07 Oct 1999 04:00:00



Quote:

> So what you are saying is 4-stroke = power/verticle performance and
> 2-stroke = speed?

> Mike

That's condensing the discussion an awfull lot, but basically yes. Note
that you see not a single 4-stroke engine in use in pylon racing or
ducted fan applications, but you see lots in pattern, where they have
dominated in recent years, despite the 2-stroke's max hp advantage.

I'm frequently amused by some manufacturers' hp claims for 2-strokes,
like for the new OS FX .91 2-stoke which they dare compare to MUCH
larger gas engines. Well, they get their hp rating at 15,000 rpm! Now
really, how many sport/aerobatic flyers are going to prop their engines
for that kind of revs?!

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Francis Garci » Thu, 07 Oct 1999 04:00:00


Most of the people I know multiply the 2 stroke displacement by 1.5 to get
the 4 stroke equivalent.
 
 
 

2-Stroke Vs. 4-Stroke question

Post by Mike Wizynajty » Thu, 07 Oct 1999 04:00:00


Ivo,

That was an excellent post! Very simple and very clear and to the point....

Wiz

Quote:



> >     I have a question I have not been able to get a strait answer for
> from
> > any dealer.  Can anyone tell me if there is some rule of thumb or
> chart that
> > will directly compare 2-strokes to four stroke engines

> This one generates endless debate because the engines don't produce
> power in exactly the same way. I'll leave the theoretical discussion to
> the engineers out there, but heres's a practical comparison:

> Many people equate 60 2-strokes to 90 4-strokes because they might have
> similar hp ratings, but in the real world that doesn't really check
> out, and here's why: A 2-stroke will produce good power at considerably
> higher rpm than a 4-stroke, So say, for example, you're looking to run
> a 14X6 prop on your "60 size" sport/aerobatic plane, the OS 61 FX will
> only spin it at around 8600 rpm because this large a prop doesn't allow
> the engine to ever enter its power zone. An OS 91 Surpass (4-stroke),
> on the other hand, will spin the same prop at 9500 rpm which will
> result in excellent vertical performance. So for that type of airplane
> the 91 4-stroke will give better overall performance.

> Now, say instead, that you're looking for top speed in a pylon racing
> or jet type airplane. The 2-stroke's ability to safely rev up to 14,000
> rpm and higher will result in an level flight speed for beyond the
> reach of the 4-stroke. Being limited to about 11,000 max, the 4-stroke
> simply cannot safely rev as high as the 2-stroke so therefore cannot
> keep up in the "speed contest".

> Think about the type of flying that you like to do, and the flight
> envelope your plane was designed for and the choice of engine will
> become more apparent.

> Sent via Deja.com http://www.deja.com/
> Before you buy.

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Paul Mcintos » Thu, 07 Oct 1999 04:00:00


Four strokes are VERY popular in SWRA pylon racing.  As a matter of fact,
they dominate the winners circles.  The other pylon events that you refer
to are so structured and so restrictive that 4-stroke manufacturers are not
interested in making engines for them.
Quote:



> > So what you are saying is 4-stroke = power/verticle performance and
> > 2-stroke = speed?

> > Mike

> That's condensing the discussion an awfull lot, but basically yes. Note
> that you see not a single 4-stroke engine in use in pylon racing or
> ducted fan applications, but you see lots in pattern, where they have
> dominated in recent years, despite the 2-stroke's max hp advantage.

> I'm frequently amused by some manufacturers' hp claims for 2-strokes,
> like for the new OS FX .91 2-stoke which they dare compare to MUCH
> larger gas engines. Well, they get their hp rating at 15,000 rpm! Now
> really, how many sport/aerobatic flyers are going to prop their engines
> for that kind of revs?!

> Sent via Deja.com http://www.deja.com/
> Before you buy.

 
 
 

2-Stroke Vs. 4-Stroke question

Post by Jason Parke » Thu, 07 Oct 1999 04:00:00


The aircraft is a Model Tech 60-90 P-51D Mustang and I am trying to keep the
scale look.  I have modified it to accept a tail retract which it was not
supposed to be able to have but works well with a robart system.  I have
also put OEL strut retracts on it from Century models.  I have nav light and
landing lights on it as well and those are from RAM electronics.  I plan to
fiber glass the model and paint it with automotive pain as well to keep the
realistic look for the plane.  My main concern was the extra weight of the
fiber glass on the airplane vs. the power of the engine, the model is really
no longer the model tech it started out as but the base of it still remains
as far as the outer lines of it are concern, I want it to look like a P-51
and not something that looks kind of like one. I hope this will help you
help me out more.

Jason


Quote:
> Jason,

> The reason you aren't getting a "strait answer" is because there is no
such
> thing to this type of question. The issue is muddled by pilot
expectations. You
> might find that you wouldn't be happy with the plane's performance even if
you
> went to the largest recommended engine, the .90 2-stroke. You may really
want a
> 1.20 2-stroke in your plane.

> Generally speaking, you would probably find most 1.20 4-stroke motors will
do
> the job. If you want more power a 1.40-1.80 4-stroke can work well. If you
want
> a really light plane and are willing to do some extra work to save weight
during
> construction then a .91 4-stroke may fill the bill.

> Tell us a little about your project (type of plane, proposed weight ect.)
and
> your expectations and we can better help you choose a power plant.

> Wiz


> >     I have a question I have not been able to get a strait answer for
from
> > any dealer.  Can anyone tell me if there is some rule of thumb or chart
that
> > will directly compare 2-strokes to four stroke engines.  What I mean is
if I
> > am given a range between 60 and 90 for 2 strokes what is my range for a
four
> > stroke?  Please email me if you can help me out.

> > Jason