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Author Topic: Why such low RPMs?  (Read 36045 times)

Online Brett Buck

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Re: Why such low RPMs?
« Reply #50 on: August 28, 2012, 09:46:35 AM »
Thanks Bob, Brett and Randy,
  I am not trying to cause trouble with such an innocent sounding question. I am too old, infirm and broke to try out all of the different styles of power plant in stunt. I am not even a particularly good stunt pilot! But I am interested in the science and engineering behind our toy aeroplanes. So I am asking such an apparently simple question to those who know what they are talking about. As Chris Wilson says, I am very happy using a big diesel in stunt, so that puts me beyond salvation.
  Seems to me that once you have more than enough power to handle the job in hand (and I mean the scientific definition of power Brett!). The only difference is in how this power is delivered to the end user. Without a description of the power delivery from each solution, it leaves people like me (and I suspect many others) totally in the dark as to which way they should go!

  Understood. It is a perfectly innocent and very good (and important) question.  I am planning on answering it legitimately (in my personal evaluation, of course) but every time we had this discussion it turned into a flame-fest when I or someone else pointed out some of the less-stellar characteristics of one engine or prop, and the supporters/cheerleaders for that engine or prop took offense. Actually, it was more like if you said anything that was not effusive praise ("Engine X is a better than inventing the wheel or discovering fire, and everyone who buys one is a genius and really handsome"), it turned in to a war. Of course if you don't compare pros and cons of various things, you can't actually make any sensible evaluation.

   Veering OT  - My personal preferences are quite well-documented. I think among the IC engine options, the PA75 and the RO-Jett 61 BSE "Brett Version", both set up the way David and I said to in our article, are the best in terms of performance and consistency that I have personally flown and appear to address most of the issues we found, and can still see, in other systems. Paul's 40VF setup is a very close second, and in any rationally-sized airplane, will provide nearly equivalent performance with excellent feel and dead-nuts consistency over a huge variety of conditions. Ted's 46VF setup is brilliant at times but had the propensity to just fade in some circumstances for reasons we never figured out. And to give credit where credit is due, Ted's 46VF run from the mid-90's is the template we are using. David figured out how to get the PA to run a lot like a gigantic 46VF (with an assist from Frank Williams and his spigot venturi), and I translated that to the RO-Jett - which ended up timed like a 46VF BY ACCIDENT.  And I think our thinking was coalesced when Paul Walker and I did entirely independent development of one particular engine in the 90's and then compared notes - both coming to the conclusion that this particular engine was not going to do what we wanted, and more importantly *why*.

    But note that this took a LOT of trial and error, and many of the things we tried didn't work, and occasionally, some things we tried worked unexpectedly well. Almost everything we are doing right now, someone told us wouldn't work, that the problems we were having weren't real, or that we were the first people ever to have that problem.

    Back on the original topic, this means you can't dismiss anything out of hand. You can make educated guesses and the more educated the guess, the more likely you are to be right, but the only way to tell for sure it to try it and see. If nothing else you will learn something. If I was working on 4-strokes I would start with a standard setup the way Steve is doing, use that to get a baseline, and then try Bob's way and see what it does better or worse.

     Brett

p.s. BTW, at the current moment, it would appear that all the players (Bob Reeves, Randy Smith, and Richard Oliver) are all  irritated with me to one degree or another. So no one can accuse me of playing favorites! Although I guess I need to figure out how to needle Bobby Hunt again, just to prove my objectivity.

Offline proparc

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Re: Why such low RPMs?
« Reply #51 on: August 28, 2012, 11:00:14 AM »


Brett

p.s. BTW, at the current moment, it would appear that all the players (Bob Reeves, Randy Smith, and Richard Oliver) are all  irritated with me to one degree or another.

Normally, the 4 Stroke Forum is a closed little shop just between us devotees. I have to admit, no matter whats been said, it was sure nice to see some fresh blood come in here and hang out with us.

Hmm, maybe I'll have to figure out a way to drum up some business again. Such as, the the state of the BOM and 4 strokes. Or, 4 strokes and abolishing the 8 minute rule, or, the use of 4 strokes and allowing someone else to paint your plane.

I know, how about allowing the use of 4 strokes with escapements. That should get this place going again. LL~
Milton "Proparc" Graham

Offline Andrew Tinsley

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Re: Why such low RPMs?
« Reply #52 on: August 28, 2012, 11:25:29 AM »
Thanks for that Brett,
  I hope you don't get flayed for the description of how you got to the engine combo you now use. I have tried the OS 40VF and am certainly impressed with the run. I was about to say it was on a par with a big diesel, but strike that out, as there seems to have been too many ruffled feathers! Seriously, the only problem I seem to have had with the piped 40, is that it seems a little too lively coming out of corners. But then I am only a very poor stunt pilot, so maybe it is just my lack of ability.
  If one of the large stunt engines acts similarly to a piped set up, then I am not too interested in going that route. Mainly due to expense and pilot inability to appreciate the difference.
  I have done the ST60 route and it doesn't suit me at all, mainly because I grew up on diesels and I do not like ring problems. I actually prefer the old Merco  61 to the ST 60, so user preference is creeping in!
  I can afford a Saito and I am in the process of sorting out my preconcieved ideas about 2 strokes. So I shall dip my toes in the water and try Bob 's set up. (I actually did this for a friend and wasn't put off the resulting run!).
  So your comments are much appreciated. Not all of us are competition minded or indeed have much piloting ability. No matter, it is a very interesting exercise to try out the various aproaches and sample what the expert pilots use.
  So my thanks to you Randy and Bob, for taking the time off from the robust discussions, to give me some insight into the various setups.

Regards,

Andrew.
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Offline Bob Reeves

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Re: Why such low RPMs?
« Reply #53 on: August 28, 2012, 01:08:07 PM »
Andrew, if you like diesels you will really like the way a Saito 56/62 will run. Same type of constant speed without the stink or critical needle and compression settings. Now I'll be in trouble with the diesel guys...

The main reason I have spent so much time playing with 4 strokes was simply because I didn't have the expendable capitol to go buy 2 or 3 $400.00 engines. If I could have I would probably have been using a pipe like everyone else and probably be in the process of changing over to electric. As it is I'm perfectly happy with my four strokes, they will do what I need done.

Online Brett Buck

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Re: Why such low RPMs?
« Reply #54 on: August 28, 2012, 01:18:24 PM »
Thanks for that Brett,
  I hope you don't get flayed for the description of how you got to the engine combo you now use. I have tried the OS 40VF and am certainly impressed with the run. I was about to say it was on a par with a big diesel, but strike that out, as there seems to have been too many ruffled feathers! Seriously, the only problem I seem to have had with the piped 40, is that it seems a little too lively coming out of corners


  Interesting that you should say that. For fear of incurring the wrath of various people, that is *exactly* why we (David, Ted, and I, with Paul thinking along the same lines) are running the engines the way we are.  And that is also the essence of the discussion Paul and I had on the topic of the engine back in the mid-late 90s WRT to one particular model. That's what I mean by always having sufficient power and that control is they key. We are doing what we do almost entirely because it reduces the boost in the corners and in specific parts of the square 8. Many that I fly or observe have what I think is grossly excessive power boost. I have flown some individual setups that went halfway through a corner, kicked, and practically pulled the handle out of my hand.

   If you used the 40VF, put Paul's setup on it. Start with the standard prop-  11.3 or 11.5-4.25, a .270 venturi, and 18.5". Launch at 10800. then adjust the needle to get a decent airspeed. If it wants to go into a 4-stroke at all in level flight (like coming around into the wind) at a decent speed, go down to a .265 venturi and try again. Keep going until you are launching at 10800 or so, have a level flight speed you like (maybe 5.3-5.4), and it *stays in a 2 the entire time*, just barely at the richest point. If it's too lean, increase the venturi by .005 and try again. Then if it is putting out too much boost in the corners, lengthen the pipe in 1/4" increments until you either like it, or it sags off in the maneuvers. If it's too "flat" in the corners or sags, push it in 1/4". Problem solved, that will get you more-or-less the same run that won the NATs repeatedly and the WC.

   If it's a new engine, and it wants to quit on hard insides near the end of the pattern (like bottom of the hourglass or pullout from the overhead 8) push the pipe in 1/4. You can go back out when it gets broken in more.

   In the other cases, I think we have published our settings for the PA61, RO-Jett 61 BSE "Brett Version", PA75, etc and those are our best efforts to manage the issue you describe. And it would be tough to argue with the success. Although someone undoubtedly will. The ones I have published (mostly on SSW) are the ones that worked well. We have tried *many* other settings and adjustments that we didn't publish. It takes A LONG time to do a valid evaluation, in some cases it has taken me several seasons to figure out what the good and bad points were.

   I also think that's most of what people like about 4-strokes, too. I mentioned it above but it definitely solves any problems with excess power bursts. In fact, I think the low pitch setup for 4-strokes may do it a little too well, which is probably why the low-rev thing seems better to people - because the low pitch 4-stroke system simply can't speed up even if you want it to, there's just no room left. The low-rev system certainly can. Whether that advantage is mitigated by having to run a corresponding high pitch, I have no idea. I am a little skeptical but Bob says it's better so I say its worth a try.

    Brett

Offline RandySmith

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Re: Why such low RPMs?
« Reply #55 on: August 28, 2012, 01:40:27 PM »
 "Brett

p.s. BTW, at the current moment, it would appear that all the players (Bob Reeves, Randy Smith, and Richard Oliver) are all  irritated with me to one degree or another. So no one can accuse me of playing favorites! Although I guess I need to figure out how to needle Bobby Hunt again, just to prove my objectivity. "


UH  no,  I am not irritated with you or anyone else..no problems here.  ;D
and if you have any problems sticking Bobby.. let me know I can give you a couple of things to get him going  .... >:D

Randy

Offline Andrew Tinsley

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Re: Why such low RPMs?
« Reply #56 on: August 28, 2012, 03:12:30 PM »
Hello Bob,
 Now you really have done it! The scented aroma of diesel fumes is the main reason I like big diesels (and small ones come to that!). Setting up the needle and compression are second nature when you get the hang of it!
The only problem that I have ever had is in the time limit for an F2b run. Minute changes in NV settings give large changes in run time. Still I understand that one can now use a timer in FAI competititions (?). Not that I ever compete in anything.
I really believe that if more people tried diesel power, they would be very surprised. Best I can describe it as, is a piped run without ANY variation anywhere in the pattern. But then no one is going to be converted to diesel power, there seems enough aggro with glows as it is!

Regards,

Andrew.
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Offline proparc

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Re: Why such low RPMs?
« Reply #57 on: August 28, 2012, 03:57:31 PM »
Hello Bob,
I really believe that if more people tried diesel power, they would be very surprised. Best I can describe it as, is a piped run without ANY variation anywhere in the pattern. But then no one is going to be converted to diesel power, there seems enough aggro with glows as it is!

 

Regards,

Andrew.
Andrew, I own a diesel, and have flown diesels and, Jim Thomerson flies his diesel every single week here in Texas. When they are running, they are just as good as anything else.

But, they don't meet my personal standards for flight-to-flight consistency. Generally speaking, the standard I look for in flight consistency is based on MY ST46. Any engine that meets that standard is good-to-go. My Saito's meet that standard. PA's would certainly meet that standard. Not sure if the Stalkers would.

I am quite aware of the PAW line of motors popularity in Europe. If you’re a diesel flyer, you’re probably going to be very happy with a Saito. Once you open that white box and get a gander on what’s inside, you might never be the same. If you stick with the 40A, 62A, and 72B, you’ll be good to go. Avoid the 82B, it’s a turkey. The 91 is FAI legal, and may be the smoothest runner of them all. Warning, it is enormously powerful-trust me.
« Last Edit: August 28, 2012, 05:40:21 PM by proparc »
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Offline Andrew Tinsley

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Re: Why such low RPMs?
« Reply #58 on: August 29, 2012, 04:49:49 AM »
Hello Milton,
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Offline Andrew Tinsley

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Re: Why such low RPMs?
« Reply #59 on: August 29, 2012, 05:16:40 AM »
Hello Milton,
  Think I pressed the wrong button on the last post! I run PAWs but not the big ones. I have had problems with getting repeatable runs with the 49. I am sure that it is my fault rather than the engine. Other people manage to do so without too much trouble I am also a little overawed at the weight of the big PAWs too! I actually run an MVVS 49 diesel and that gives me total repeatability as far as I am able to ascertain (run time per tank being variable!).
  A great engine, a pity they are no longer made even in glow format. I keep looking for another one without any luck so far. I am sure I am going to enjoy the Saito runs. Let us face it 4 strokes must be better, because they have more parts to fiddle with (I wonder if Brett will take the bait?).
  I don't much like ringed two stroke engines, even though I am a fan of Merco 61s. They always seem to fall over with ring problems just at the most inconvenient time, so no ST46s for me (even though I have run the ST 60!)

Regards,

Andrew.
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Offline RandySmith

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Re: Why such low RPMs?
« Reply #60 on: August 29, 2012, 09:45:21 AM »
Andrew there are 3 MVVS 49s for sale in the classifieds 2 rear new ones and 1 side used 49

Randy

Offline Andrew Tinsley

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Re: Why such low RPMs?
« Reply #61 on: August 29, 2012, 11:46:32 AM »
Thanks Randy!
I haven't looked at the classifieds for sometime. Serves me right!

Thanks again,

Andrew.
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Offline Chris Wilson

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Re: Why such low RPMs?
« Reply #62 on: August 29, 2012, 05:27:57 PM »
Andrew (off topic I know, but......) if you go for another MVVS 49 diesel conversion go for the side exhaust and block off the entire boost port and the vestige of lower crank case port under the exhaust port.

And side mount the engine, this way it minimizes the 'gear change' misfire during maneuvers as the active transfer ports are front and rear and not top and bottom.

Shameless plug here, any chance of a 'Diesel Stunt' forum?
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Offline proparc

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Re: Why such low RPMs?
« Reply #63 on: August 29, 2012, 05:37:55 PM »

Shameless plug here, any chance of a 'Diesel Stunt' forum?

I am sure you could but, your probably going to end up like the "Maytag Repair Man".
« Last Edit: August 29, 2012, 07:49:24 PM by proparc »
Milton "Proparc" Graham

Offline RandySmith

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Re: Why such low RPMs?
« Reply #64 on: August 29, 2012, 09:53:35 PM »
No , I don't think there is any chance of  a diesel forum because you can ask any diesel questions on the engine forum, so it is not needed

Randy

Offline Andrew Tinsley

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Re: Why such low RPMs?
« Reply #65 on: August 30, 2012, 05:10:08 AM »
Hello Chris,
I have mine with rear exhaust, but I don't seem to get the problem that you indicate. It is probably there, but I just don't notice! It takes all my time and gritted teeth to attempt the schedule, so I am probably concentrating on beating gravity!
Thanks Randy for the heads up on the MVVS sales. I did say I was old, infirm and broke and right now I can't afford the asking price! Maybe I can catch up with them when I am in a better finacial shape, (next pension cheque, unless my wife has that earmarked for something!)
I like the sound of a diesel forum, but suspect that it would only be read by us two and Jim Thomerson! So Randy is probably correct in saying, it should be part of the general engine forum. Hm! I note 4 strokes have their own section! No ............ Let us face it, diesels have such a bad press in the US, we don't stand a chance of influencing anyone!

Regards,

Andrew.
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Offline proparc

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Re: Why such low RPMs?
« Reply #66 on: August 30, 2012, 11:59:42 AM »
Andrew this is for you-enjoy. H^^



Thought I would add this also. Saito 40A CL.
http://www.youtube.com/watch?feature=endscreen&v=5ut6pJ8sc_k&NR=1
« Last Edit: August 30, 2012, 04:48:14 PM by proparc »
Milton "Proparc" Graham

Offline Andrew Tinsley

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Re: Why such low RPMs?
« Reply #67 on: August 30, 2012, 12:18:20 PM »
Thanks Milton,
I will be firing up my own Saito 62 soon. I enjoyed myself helping a friend out with his 62. Both are the C/L version and I really had to block the intake in order to get the revs down to a suitable level for running in. I could have done with an R/C carb!
Once it is run in, I shall go with Bob's low rpm route. People that deliberately run them in valve bounce mode, must be made of money, what a way to treat an engine!

Regards,

Andrew.
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Offline proparc

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Re: Why such low RPMs?
« Reply #68 on: August 30, 2012, 12:35:02 PM »
Thanks Milton,
I will be firing up my own Saito 62 soon. I enjoyed myself helping a friend out with his 62. Both are the C/L version and I really had to block the intake in order to get the revs down to a suitable level for running in. I could have done with an R/C carb!
Once it is run in, I shall go with Bob's low rpm route. People that deliberately run them in valve bounce mode, must be made of money, what a way to treat an engine!

Regards,

Andrew.

I agree with you, I certainly don't roll like that with my babies! Years ago, you could get away with that-not anymore. Saito stop bushing the heads on their motors, so you can’t do a valve job like the old days.  The RC boys think, and I agree, that Saito did that to force you to have to buy their very expensive one-piece-leak-free cylinder heads, as a replacement part. They make more money off you that way.
Milton "Proparc" Graham

steven yampolsky

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Re: Why such low RPMs?
« Reply #69 on: August 30, 2012, 01:51:46 PM »
Andrew this is for you-enjoy. H^^



I have two of these(one's in a nice profile):

Offline Gordan Delaney

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Re: Why such low RPMs?
« Reply #70 on: August 01, 2013, 05:59:42 PM »
   Everyone I knew doing that had stock engines. They have no significant reliability issues at 10000 rpm or so, and valve float may be a feature rather than a bug.

   Can't say the same for the reliability of the airplanes they were attached to. A fair number of four-stroke airplanes have self-destructed in many interesting and otherwise unheard of ways that we had never seen before in two-strokes - like Paul's Mustang exploding up the fuselage in flight, and Gordan's control horn upright breaking in half. Both of those were large Saito's but that might have been because that's about all anyone was using. And they were all running in the 9500-10500 rpm range with around 4 and a half inches of pitch.

     Brett
Brett, On my saito 82 I was launching at 10200rpm and the prop was 13.375x3.75pitch. The Tony flew 5.35 lap times. The power was  unreal. I wish I had left it in. I now have a .81 two stroke.

Online Brett Buck

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Re: Why such low RPMs?
« Reply #71 on: August 01, 2013, 07:01:52 PM »
Brett, On my saito 82 I was launching at 10200rpm and the prop was 13.375x3.75pitch. The Tony flew 5.35 lap times. The power was  unreal. I wish I had left it in. I now have a .81 two stroke.

   That's about as I recalled it, and that was right in the ballpark with what everyone else was doing as far as RPM goes.

    Bob's method is very similar to what Igor Panchenko was doing  - very very low launch revs with very large amounts of pitch.

     Brett

Offline Dan McEntee

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Re: Why such low RPMs?
« Reply #72 on: August 06, 2013, 05:25:59 PM »
   I just want to add my own experiences with the 4 stroke set up. I had been wanting to try them out just for giggles and grins, but had not seen anything at contests that turned me on about them. Then I had the opportunity to buy a Top Flite Score with a Saito .56 in, and it was equiped with a hand made 4 ounce uniflow clunk tank.
   I tried "playing it straight" with the Saito and tried running it like my ST.51s and it would cork screw me into the ground almost. I tried running lower RPM and higher pitch and I didn't have enough fuel to do the pattern. If I went back to higher RPM and lower pitch, I could get a decent run one flight, and then the next all hell would break loose and it would drop 2 seconds on the lap time. I got to a point where I understood why some liked them and some hated them!
   Just as I was about to put it up for sale, I read somewhere that 4 strokes don't like uniflow, not enough fuel delivery, and that a standard plumber Sullivan tank on muffler pressure was recommended. I tried that and things improved. I discovered Mr Reeves' set up soon after that and installed a nylon screw in the smallest UHP venturi I had, and tuned the intake as per Bob Reeves' instruction, and things got rock solid and way better. I have the opportunity to talk to Gilbert Berringer each year at Oshkosh, and asked him about his intake set up and he confirmed he ran venturis in the 5 to 6mm range with a straight through needle valve, and that kind of matched up with what I ended up with. I asked him to fly it in an afternoon demo a few years back, and he gave me a thumbs up on it. He noticed one thing on my engine that I have noticed my self when comparing it to ther 4 strokes, and that is that my engine is much cleaner, no baked on oil crust with the exception of the muffler. I take that as an indication that my lower RPM run is much cooler that a high RPM set up, and after almost 5 years of running the engine, I have never felt the need to reset the valves. The engine , to me , runs the same now as it did three years ago, so why mess with it. I run Powermaster YS-20/20 fuel, a Rev-Up or Vess 13-7 prop, take off RPM around 7800, fuel load about 3 and 3/4 ounces, 70 foot lines from handle to fuse center line, and 5.3 lap time. Each run is very consistant and repeatable and I am very reluctant to try anything else. Very little to no whip up in wind, which I think  is due to the fact that there is no power delivery on every other stroke, and that in turn helps regulate the speed? A more of a pulsing type of power? I really don't know.
    I found the whole learning process of the 4 strokes pretty interesting, and I'm happy with the results. It has surved me well in contests, but I am not going to sell off my inventory of ST.51s and St.60s! I find each type of engine has it's own attributes and I kind of like swapping around every now and then. In this day and age, we really do have a pretty wide variety of different types of power plants, and a person should be able to settle on one that they understand and are comfortable with, and I think that is the important thing, understanding the power plant and being comfortable with operating it, no matter what kind it is.
    Type at you later,
   Dan McEntee
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Offline Allan Perret

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Re: Why such low RPMs?
« Reply #73 on: August 08, 2013, 10:10:25 AM »
 Understood. It is a perfectly innocent and very good (and important) question.  I am planning on answering it legitimately (in my personal evaluation, of course) but every time we had this discussion it turned into a flame-fest when I or someone else pointed out some of the less-stellar characteristics of one engine or prop, and the supporters/cheerleaders for that engine or prop took offense. Actually, it was more like if you said anything that was not effusive praise ("Engine X is a better than inventing the wheel or discovering fire, and everyone who buys one is a genius and really handsome"), it turned in to a war. Of course if you don't compare pros and cons of various things, you can't actually make any sensible evaluation.

   Veering OT  - My personal preferences are quite well-documented. I think among the IC engine options, the PA75 and the RO-Jett 61 BSE "Brett Version", both set up the way David and I said to in our article, are the best in terms of performance and consistency that I have personally flown and appear to address most of the issues we found, and can still see, in other systems. Paul's 40VF setup is a very close second, and in any rationally-sized airplane, will provide nearly equivalent performance with excellent feel and dead-nuts consistency over a huge variety of conditions. Ted's 46VF setup is brilliant at times but had the propensity to just fade in some circumstances for reasons we never figured out. And to give credit where credit is due, Ted's 46VF run from the mid-90's is the template we are using. David figured out how to get the PA to run a lot like a gigantic 46VF (with an assist from Frank Williams and his spigot venturi), and I translated that to the RO-Jett - which ended up timed like a 46VF BY ACCIDENT.  And I think our thinking was coalesced when Paul Walker and I did entirely independent development of one particular engine in the 90's and then compared notes - both coming to the conclusion that this particular engine was not going to do what we wanted, and more importantly *why*.

    But note that this took a LOT of trial and error, and many of the things we tried didn't work, and occasionally, some things we tried worked unexpectedly well. Almost everything we are doing right now, someone told us wouldn't work, that the problems we were having weren't real, or that we were the first people ever to have that problem.

    Back on the original topic, this means you can't dismiss anything out of hand. You can make educated guesses and the more educated the guess, the more likely you are to be right, but the only way to tell for sure it to try it and see. If nothing else you will learn something. If I was working on 4-strokes I would start with a standard setup the way Steve is doing, use that to get a baseline, and then try Bob's way and see what it does better or worse.

     Brett

p.s. BTW, at the current moment, it would appear that all the players (Bob Reeves, Randy Smith, and Richard Oliver) are all  irritated with me to one degree or another. So no one can accuse me of playing favorites! Although I guess I need to figure out how to needle Bobby Hunt again, just to prove my objectivity.
Hey Brett:  Can you elaborate on "Ted's 46VF setup" or point me to where I might find it.
Allan Perret
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Re: Why such low RPMs?
« Reply #74 on: August 08, 2013, 12:02:14 PM »
Hey Brett:  Can you elaborate on "Ted's 46VF setup" or point me to where I might find it.

  I think the article that David and I did has that, if not, I would have to dig a little. I may have been one of the first people to run the 46VF in a stunt plane (the same engine Ted subsequently had AACed and then used to win the 95 NATS, and may now belong to Jim Pollack) but I didn't see any way to use the power available at the time (1988). Ted figured it out later, using Eather UC props and later Eather pipes.

   It was magnificently good when it was working, and it almost always worked. 1993 Team Trials, where David and Ted both ran it, for example, it was so good Baron and Windy thought they were cheating. At one NATs, however, it just sort of went gutless and we couldn't figure out why, and Ted switched to the PA61 during the contest. May have been 98 or 99, but it's getting a little hazy. Maybe 98, because 99 was when I first ran the PA.

    Brett

Offline Allan Perret

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Re: Why such low RPMs?
« Reply #75 on: August 08, 2013, 02:49:41 PM »
 I think the article that David and I did has that, if not, I would have to dig a little
You talking about the pipe article in Stunt News, 2009 Special Edition ?     
I just looked thru that and only see set-up specifics for the 40VF.
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Offline Gordan Delaney

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Re: Why such low RPMs?
« Reply #76 on: October 16, 2014, 09:17:21 PM »
    That's the theory. When 4-strokes were an active area of investigation, people were claiming to intentionally run it to valve float. They also had some evidence of that, including chewed-up cams, bent valves, bent pushrods, and funny smile-shaped spots on the tops of the pistons - after they went too far and the piston hit the valve.

   I would be surprised if any of this was important, the power falls off drastically at high revs even without the valves having to float. Near as I can tell the low-rev thing works precisely because it gets further away from the RPM range where breathing goes over the cliff, so it has less regulation. That's probably why it doesn't have the "dead-overhead" problem, at least. I haven't ever seen any sort of analysis from the gurus, so that's my external evaluation for what little it is worth. 

 Based on limited dyno testing the cutoff revs were a little lower than where we ran the PAs at the time. My PA setup of the time (2002ish) pretty much wouldn't go over 12000 with any prop we dared to start it with (set up for normal flying at a 10000 rpm launch revs with the needle set at a constant launch setting) and as I recall the OS52 was looking like it was running into a brick wall around 10000-10500. That's consistent with needing 4.5" of pitch or so for the 4-stroke and 3 3/4 with the PA. That's just the shape of the curve, of course. The actual power/torque was much less with the 52 at any rpm we tested but that's no surprise. They crossed at about .45 HP at the inflight rpm - also about what you would think given the required power is the same in level flight.

   The difference of course was that running at 10,800 in flight with a cutoff at 12000 gives you some breathing room. Running 10000 in flight with a 10500 cutoff means you have nowhere to go to pick up revs. The experience seemed to back this up, hence the weak overheads. Running 8000 in flight with a maybe 10000 cutoff (from reduced venturi size limiting the breathing) gives plenty of headroom, which seems to be the trick of the super-low-rev system. I would expect other less-positive effects but I am sure that those will not be discussed here.

    Brett  on the saito 82 I launched at 10200 rpms. Prop was 13.250-with 3.75 pitch. Had tons of power. Hauled my Tony at 5.35 lap times. Tony is 743 Sq. inch
Just my thoughts.
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Re: Why such low RPMs?
« Reply #77 on: November 09, 2014, 02:32:42 PM »
   Everyone I knew doing that had stock engines. They have no significant reliability issues at 10000 rpm or so, and valve float may be a feature rather than a bug.

   Can't say the same for the reliability of the airplanes they were attached to. A fair number of four-stroke airplanes have self-destructed in many interesting and otherwise unheard of ways that we had never seen before in two-strokes - like Paul's Mustang exploding up the fuselage in flight, and Gordan's control horn upright breaking in half. Both of those were large Saito's but that might have been because that's about all anyone was using. And they were all running in the 9500-10500 rpm range with around 4 and a half inches of pitch.

     Brett
    Yes, I was using 3.8 pitch and 13.250 dia. at the nats I set the needle at 10,200 on the ground and lap times were 5.35 sec. lap times. I repaired the Tony and put in a double upright horn and repaired the plane. It flew great again. But sad to say It broke a lead out yesterday and this time not repairable. But it had lots of power.

Offline REX1945

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Re: Why such low RPMs?
« Reply #78 on: May 19, 2015, 12:17:48 PM »
For me the only negative is the higher vibration level.

    For sure, you need to be balancing your props. Even then, the 4 Strokes can shake a lot of stuff loose
and make your engine mounts squash.  Be sure to check the mounts after the first couple of flights.

    My experience with 11,000 RPM was not good; lots of variation in the flight time
for the same amount of fuel. Also, use an OS "F" plug.

    My Four strokes seem to run a lot better after they've seen a couple of gallons of fuel.

    I'm using an XOAR 13-6 on my Saito .56 with a double star venturi and 15% Wildcat fuel.
It turns about 9,000.

    Airplane is a Legacy that weighs 62 Oz.

Rex

Offline David Felinczak

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Re: Why such low RPMs?
« Reply #79 on: July 15, 2015, 08:07:18 PM »
Bob,
I am ready to break in my new Saito 56FA, CL you modified for me a few years back. I am going to put it in one of my profile Pathfinders.

What do you recommend as far as bench time, fuel, prop and RPM for break in.

I spoke to you at one of the Brodak Fly In's and if I remember correctly you told me that the Saito engines are more consistent mounted as a sidewinder
vs inverted. Does this still ring true? If so, is it due to increased crankcase pressure when the engine is mounted inverted?

Thank you in advance for your expertise and assistance.
David Felinczak
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Offline Bob Reeves

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Re: Why such low RPMs?
« Reply #80 on: July 16, 2015, 10:56:46 AM »
Probably would have been better to start a new thread, this one has about ran it's course.

In my opinion, the most critical part of the break in process is the initial low speed running recommend in the Saito manual. This is much easier to do with an RC carb because you can control the speed much easier. I keep an RC carb just for the low speed part and have never tried it with a fixed carb. Would guess the best approach would be to block off as much of the intake as you can and still have it run. Use a tach and try as best you can to follow the book.
After the initial low speed run I usually run it at 8 to 9000 with a 13-5 or 13-6 in 10 minute intervals letting it completely cool between runs for about an hour total run time.

I have posted a few threads on why I feel they work better mounted sidewinder, here is one, searching for my posts will probably bring up more.
http://stunthanger.com/smf/index.php/topic,13537.0.html

Bob,
I am ready to break in my new Saito 56FA, CL you modified for me a few years back. I am going to put it in one of my profile Pathfinders.

What do you recommend as far as bench time, fuel, prop and RPM for break in.

I spoke to you at one of the Brodak Fly In's and if I remember correctly you told me that the Saito engines are more consistent mounted as a sidewinder
vs inverted. Does this still ring true? If so, is it due to increased crankcase pressure when the engine is mounted inverted?

Thank you in advance for your expertise and assistance.


Offline David Felinczak

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Re: Why such low RPMs?
« Reply #81 on: July 17, 2015, 09:01:31 AM »
Thank you for the info.
I will choke off the intake and open the needle and this should do the trick.
Sorry about the thread.
Take care and be safe sir.
David Felinczak
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