stunthanger.com
News:
CLICK HERE---->    <----CLICK HERE
 
 
*
Welcome, Guest. Please login or register. March 27, 2017, 12:48:21 AM


Login with username, password and session length



Pages: [1]   Go Down
  Print  
Author Topic: Why 4 Stroke  (Read 1273 times)
Motorman
Trade Count: (0)
Admiral
******
Offline Offline

Age: 60
Location: North East USA
Posts: 2975


Millville NJ PDQ Flying Clown Country


« on: February 17, 2017, 09:03:37 PM »

I don't know anything about 4 strokes on model planes but my take on it is why use a heavy engine that puts out less power? What's the thinking on using 4 strokes.

Thanks,
MM
Logged

There will be a sunny day and we will fly our airplanes.

Dan McEntee
2015
Trade Count: (0)
Admiral
*
Offline Offline

Age: 61
Location: St. Louis, MO
Posts: 2138


« Reply #1 on: February 17, 2017, 09:54:54 PM »

   
      You should try reading all of the sections on this forum.
   Search this section for anything by Bob Reeves, or Saito .56 or .72. If you haven't flown one, you should try one that is properly set up. If you get into four strokes, forget everything you ever  learned about running and proping two strokes and start from scratch. They require shorter nose moments due to the extra weight as suspected. They can swing more prop and the torque they put out is remarkable. I have a Top Flite Score with a Saito .56 in it that I bought to get some experience with them to see what they are like. I messed with it off and one for two seasons and could see why some guys loved them and why some guys would use them for trot line weights. It was when I read up on what Bob Reeves figured out  that I started getting really constant runs. The combination is responsible for a few trophies in my possession.  It's really a very different type of power plant, and if you can grasp the concept behind them,they are a very useful and viable power system. Paul Walker won one of his Walker Cup NATS wins with a four stroke. Like I said before, some people swear by them, some swear at them, but they are just one of the several different power choices that a guy has available to him these days.
     Type at you later,
     Dan McEntee
Logged

AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)
Brett Buck
Trade Count: (0)
Admiral
******
Online Online

Age: 240
Location: Sunnyvale, CA
Posts: 7223


« Reply #2 on: February 17, 2017, 11:11:10 PM »

I don't know anything about 4 strokes on model planes but my take on it is why use a heavy engine that puts out less power? What's the thinking on using 4 strokes.

   The all-up weight isn't a lot different from a piped 40 once you add up all the parts and consider the difference in the fuel weight, and the power is more than sufficient (from a 56 on up) for any current competitive airplane. Overall power, for stunt, hasn't been an important factor since the mid-late 80's, because you can get far more than you can use.

    The pros and cons have been debated endlessly. One thing that 4-stroke definitively solve is the "excess power burst" problem that you can get with 2-strokes if you don't set them up right. The aren't going to spin up much beyond about 11,000 rpm no matter what you do, which, conveniently, is about what you need in the air for a 4" pitch prop. In fact, the low-rev systems are seemingly intended to overcome the tendency of the engine response to be too "flat" because it regulates a little too well at 4" pitch rpm.

    The cons are the tendency towards random fuel consumption, and generally inflexible response. You can't just dial in the amount of power boost/brake you want like you can with a tuned pipe engine or a feedback control electric. The Berringers used an intentionally flexible prop to help, and also invented the venturi system that Bob Reeves and others use to adjust the speed over small ranges. The random fuel consumption is mostly due to trying to control the speed with the needle, and it's a very weak effect on RPM but a big effect on fuel usage.

    At the time of the original experiments (Ted Fancher in the mid-80s), the power characteristics were a huge improvement over the ST46 and similar, with much less problems than you got with muffled schneurle engines like the 40FSR. But a few years later, along comes Bob Hunt/Dean Pappas/Rich Tower with piped 40s, which solved the schneurle engine problem, and was much more amenable to tweaking. The whole idea died until Windy/Bob Zambelli and others ran out of ST60s and discovered 4-strokes, at which point tuned pipes were a turnkey operation with far more flexibility. Some liked the heavy line tension to you tend to get, and tried it with some success, but it wasn't a breakthrough that you had to have to be competitive.

     Later, Igor Panchenko invented (as far as I know) the very-low-rev system that "freed up" the engine to be more responsive, at the cost of less speed control due to the very high pitch required. Bob Reeves applied the Berringer-style venturi, with resolved the issue with the speed adjustment, but by then, Mike Palko and others were experimenting with electric, with quite obviously more potential. So after a brief second heyday, interest sort of faded away. Some people (like those here) are still enthusiastic about it and get very good results, hence the forum for it.

     Any of these systems (tuned pipe, electric, 4-stroke, and the very advanced 4-2 break engines like the Discovery-Retro and Belko {ST60's with 20 more years of aerospace-quality development work}) is plenty capable of providing sufficient performance for any purpose, if you know what you are doing. Electric clearly has the most growth potential at this point. The others have pretty much been refined to the point that not much new is being developed. David Fitzgerald and I have made changes only in the area of fuel flow and carburetion over the past 10+years. We learned some very interesting things and have refined the run to our needs, but nothing that would be classified as a breakthrough.

      Brett
Logged
Dane Martin
2016 supporter
Trade Count: (0)
Admiral
*
Online Online

Age: 34
Location: las Vegas, NV
Posts: 1279


heli pilot BHOR


« Reply #3 on: February 18, 2017, 10:36:34 AM »

I don't think they are less "power", just less RPM potential.  So prop selection for CL is tricky at first.

Mostly, it's Cuz they sound so bad @$$
Logged
Chris Behm
C/L Newbie
2016 supporter
Trade Count: (0)
Captain
*
Online Online

Location: Los Angeles, CA
Posts: 866



« Reply #4 on: February 18, 2017, 03:27:01 PM »

Subscribed.
How does vibration compare, 2 cycle to 4 cycle? I would assume the 4C would shake less, but that is just a guess on my part.
Logged

Regards,
Chris

AMA 5956
2008 F3F USA Viking Race Team
CL-flyer
Trade Count: (0)
Lieutenant
***
Offline Offline

Age: 59
Location: WA
Posts: 62


« Reply #5 on: February 19, 2017, 04:53:21 AM »

Check out the RC forums for a more complete coverage of four-stroke engines in general before focusing on CL usage. I like four-strokes a lot but only use them on my RC planes. Only two-stroke and electric for CL.

In a nutshell the four-stoke uses more of its power stroke than a two to generate more torque.
Logged
Brett Buck
Trade Count: (0)
Admiral
******
Online Online

Age: 240
Location: Sunnyvale, CA
Posts: 7223


« Reply #6 on: February 19, 2017, 05:57:55 PM »

Check out the RC forums for a more complete coverage of four-stroke engines in general before focusing on CL usage. I like four-strokes a lot but only use them on my RC planes. Only two-stroke and electric for CL.

In a nutshell the four-stoke uses more of its power stroke than a two to generate more torque.


   That's certainly not true in general, a PA61 puts out ~50% more torque at typical 4-stroke revs as a Saito 56, and even more difference at lower revs. The data is available here somewhere - we measured it. But that's not particularly important, since you can't really use the full capability anyway. 4-strokes (and to a lesser extent, 4-2 break engines) use large props at low revs because they have to, not because they are somehow "torquers".

    The energy from a given amount of fuel and air is generally more efficiently used for given amount of power in a 4-stroke but the power, even at low revs, is much less. As long as it is sufficient, you decide based on other issues (like the ability to regulate at usefully low revs, which the 4-strokes definitely do).

     Brett

p.s. I thought I had dug this up before, but here are the numbers. At 9000 RPM a Saito 56 puts out about 90 in-ounces (based on data from Saito/Pete Bergstrom posted here).  My PA61, set up for a launch RPM of 10100 rpm with a normal prop, dragged down to 9000 by a much draggier prop (Rev-Up 14-6) was around 140 in-ounces. We were initially surprised by this, but then it occurred to me that to run at a stable speed with an inflight RPM of 10800, 9000 is probably pretty close to the tuning peak. We run well past the peak in flight, of course. The Saito 72 peak torque is around 118 in-oz, so, still not there. Even the venerable ST60 is in between the 56 and 72.

  I also presume that the Saito data was taken at ideal mixture with the throttle wide open. The PA needle was set at the position necessary to get the launch revs with the flying prop, and then left alone as we changed to a 14-6 Rev-Up to bog it down, and had just enough load to run in a 2-stroke. A little tweaking at it could have been more, another .015 of venturi would have been dramatically more, etc.

   Note that this tells you only a little bit about how effective any of these engines might be in flying a stunt plane, but the notion that 4-strokes are "torquers" is way off. A different way of saying it is that they will *only* put out significant torque at low revs, i.e. they won't breathe at higher revs. The torque and HP curves are dropping dramatically at 11,500 rpm and look like a brick wall. Take the pipe off the PA, or shorten it by two inches, and it will happily thunder out 2-3x the power at much higher revs, meaning it keeps putting out torque far beyond the 4-stroke. Note also that this is a mere PA61(!) - and you can get an engine 25% larger!

    
« Last Edit: February 19, 2017, 06:46:51 PM by Brett Buck » Logged
Paul Smith
2016 supporter
Trade Count: (0)
Admiral
*
Offline Offline

Age: 70
Posts: 3984



« Reply #7 on: February 20, 2017, 05:37:16 PM »

It seemed like the whole rationale for 4-stroke was a slight reduction on noise.

But with the advent of cheap and easy electrics, the need for lower dB's is satisfied and the 4-stroke is nothing but heavy, expensive, complicated junk.

If you want power and performance use 2-stroke.
If you want quiet use electric.
If you want 4-stroke use 4-stroke.

There are still a few die-hards who make Sterling engines run.
Logged

Paul Smith
Robert Zambelli
2016 supporter
Trade Count: (0)
Admiral
*
Offline Offline

Posts: 1381



« Reply #8 on: February 20, 2017, 05:38:57 PM »

Around 15 years ago when I was tinkering with 4S engines, I did a comparison regarding weight.
I did a weight comparison between the ST 60 and ENYA 53 4S.
Tanks included.
More info to follow.

Bob Z.
« Last Edit: February 21, 2017, 12:39:44 PM by Robert Zambelli » Logged
Chris Wilson
Trade Count: (0)
Admiral
******
Offline Offline

Age: 56
Location: Sydney Australia
Posts: 1411



« Reply #9 on: February 20, 2017, 09:02:28 PM »

I like four-strokes a lot but only use them on my RC planes.
Probably because they throttle better when swinging scale sized props, and people can relate to them far easier.
Logged

MAAA AUS 73427
Paul Smith
2016 supporter
Trade Count: (0)
Admiral
*
Offline Offline

Age: 70
Posts: 3984



« Reply #10 on: February 20, 2017, 09:13:17 PM »

That was the theory.  But in actual scale contests it doesn't seem to prove out.  4-strokes seem to have MORE trouble dead-stopping the model than two-strokes.  Maybe this has to do with one-cylinder engines needing to coast through two revolutions. 

The bigger 4-stroke props might be developing too much thrust at their lowest idle speed.
Logged

Paul Smith
Bob Reeves
2016 supporter
Trade Count: (0)
Admiral
*
Offline Offline

Age: 72
Location: Tulsa OK
Posts: 3325



WWW
« Reply #11 on: February 26, 2017, 03:07:12 AM »

My reason for going to 4 strokes was mostly financial. I wanted to be able to compete at the highest level of Advanced and knew I wouldn't be able to get there with a Fox 35 or FP-40. Having to invest four to six hundred in a piped engine set up just wasn't in the cards. On top of that if I wanted to have a back-up engine I would have to spend another four hundred or so. Discovered I could buy a really good Saito 56 used from an RC guy for a hundred bucks and for less than $300.00 have two engines ready to go.

My 4 stroke story has been told a couple times on the forums so not going to go into the whole process of how I ended up with a Saito 56 powered stunt ship that won Advanced at Brodak's twice and in my opinion could compete with the big boys in Expert under any conditions. I reached my goal which was to win Advanced at Brodak's with a $100.00 engine competing against pipes and electrics flown by some of the best Advanced flyers in the country.

I did not move to Expert simply because I have other interests and wasn't willing to invest the effort it would take to get to the top of Expert. I know myself well enough to know if I went into Expert I wouldn't be happy till I was winning. I had no doubt my 4 strokes could get me there if I was willing to invest the time it would take to get good enough. I wasn't willing to invest that time.
Logged
Chuck_Smith
Trade Count: (0)
Commander
****
Offline Offline

Posts: 281


« Reply #12 on: February 26, 2017, 05:37:09 AM »

For some of us, mucking about with the engine is as much or more fun than the flying. I've been flying the same pattern since 1970, nothing new there. But engines, always something fun to try next. As noted earlier, ample and consistent power is no longer a differentiator in this hobby. Anybody can have it.

If a 4 stroke floats your boat - take up the challenge. Main thing is...have fun! One of the early drawbacks was expense. Nowadays you can pick up gently used 4 strokes pretty reasonably.

Me, I'm looking at gas now. Obscene power to weight, torque for days, reliable, super easy starting, consistent, easy cleanup and your fuel is 2 bucks a gallon. The only drawback so far is that the smaller gas engines use so little fuel that the carb passages are tiny, and ANY dirt is not-so-good, so the challenge is going to be assuring good filtration.

All IMHO and YMMV,

Chuck
Logged

AMA 76478
Chris Wilson
Trade Count: (0)
Admiral
******
Offline Offline

Age: 56
Location: Sydney Australia
Posts: 1411



« Reply #13 on: March 03, 2017, 08:24:41 PM »

....... I wouldn't be able to get there with a Fox 35 or FP-40.
In this country an FP 40 in a profile won many titles in a Sukhoi profile model - so it is possible.
Logged

MAAA AUS 73427
proparc
2015
Trade Count: (0)
Admiral
*
Offline Offline

Location: Mesquite,Texas
Posts: 2239


« Reply #14 on: March 05, 2017, 09:29:03 AM »


Me, I'm looking at gas now. Obscene power to weight, torque for days, reliable, super easy starting, consistent, easy cleanup and your fuel is 2 bucks a gallon. The only drawback so far is that the smaller gas engines use so little fuel that the carb passages are tiny, and ANY dirt is not-so-good, so the challenge is going to be assuring good filtration.

All IMHO and YMMV,

Chuck

Gas has come on like gangbusters in the RC world. All for the reasons you mentioned. The DLE line of engines has really been responsible for a lot of that. My Saito 72 has been without question, one of the MOST reliable and consistent CL motors I have ever owned. I own 3 Saito's, and I am looking for a 4th.
Logged

Milton "Proparc" Graham

Tags:
Pages: [1]   Go Up
  Print  
 
Jump to:  


Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines

Valid XHTML 1.0! Valid CSS! Dilber MC Theme by HarzeM