Saito 56, 62 & 72 Torque & HP Curves

[PeteBergstrom]

Guys,

I finally received the Torque curves from Saito that i promised a while back.  These are hand developed by the guys at the factory and the first time I have known them to release these figures.  I really interested in everyone's input from this information.

Have fun!

Pete

PS - I'll post the 72 chart in the next post

[PeteBergstrom]

Here is the 72 chart.

pete

[Bob Reeves]

Downloaded for further study... Any chance you can get the 40a?

[Leonardo.STUNTI]

Great, thanks for share!

[proparc]

I don't know what the torque curve for my 40A is, but it has a ton of torque!!

[Bob Reeves]

Studied the graphs a bit, have first hand experience with the Saito 56 and believe I have a fairly good understanding of what works and what doesn't so it is the only one I can relate to. It is interesting that the RPM range that works best for stunt is about where the torque is the highest 82-8300. When I was running a lower pitch prop at 9 grand it wasn't well behaved at all.. Speeding up on the down legs and sagging overhead.. With a 7 pitch prop at 82-8300 it's as close to a perfect stunt run as anything I have seen.

So can some engine guru explain why as it relates to the graphs?

[john e. holliday]

Thanks to Bob Reeves he tamed down my little 4 stroke.  Flies the Skyray better than any engine that been on it.  The engine is going into a Cardinette.  Plans available from Brodak.  Bob Z. may not like my wing tips as I don't like carving that much.  I am taking pictures as I go along.  DOC Holliday

[Doug Moon]

Studied the graphs a bit, have first hand experience with the Saito 56 and believe I have a fairly good understanding of what works and what doesn't so it is the only one I can relate to. It is interesting that the RPM range that works best for stunt is about where the torque is the highest 82-8300. When I was running a lower pitch prop at 9 grand it wasn't well behaved at all.. Speeding up on the down legs and sagging overhead.. With a 7 pitch prop at 82-8300 it's as close to a perfect stunt run as anything I have seen.

So can some engine guru explain why as it relates to the graphs?

I think I can.  This just my idea of what might be happening.

As you have pointed out you are operating on the top of the torque curve.  The torque is what gets things moving.  Like drag car at the start.  It is in the lower RPM range for the engine and it blasts off the line.  Then once it is moving the HP curve keeps it going.  Then it levels off a bit and you shift to the next gear and hit the top of the torque curve and go faster and the hp takes over and pushes it further.

In stunt we operate in a much more narrow rpm range.  We also increase and decrease loads on the motor all throughout the flight BUT we need the speeds to be constant, or near constant.  We need to utilize the torque curve more than the hp curve to achieve this. Your findings prove this very point.  You are setting up the engine through prop load to operate right up on top of the curve.  You fly level and it cruises along steady.  You point the nose up and the motor has enough torque to keep the prop at or near the requested RPM.  But it is loaded enough so it cant over rev either.  So you get a nice clean steady paced run throughout the flight. 

When you under load it and run the RPM up and get on the HP curve you have no torque left when you dramatically increase the load like a we do in stunt.  The motor is running over the curve and nothing is there to keep the prop spinning.  The HP curve tries but it doesnt have the booty.  The under load lets it rev and it works some but not well and you get erratic runs.

At least that is what it looks like to me.

[Martin Quartim]

I am just curious to know how Saito did this test.  Did they use one of those fancy Dyno that can measure the RAW power on the shaft of the engine, regardless of a propeller, or one of those Dyno that measures Torque of the Engine spinning a propeller (Net Power)

I bet, they used a Dyno that measures NET POWER, now which prop and fuel was used?

I believe this chart gives you an idea of what the engine does. However, just replacing the prop would produce a different chart, with different peaks of torque and power. It would be interesting to see how the curves would change for different propellers, fuel and climate conditions.

Martin





Martin

[bob branch]

I may be interpreting this wrong and if I am someone please correct me. But it looks to me like the .72 has a distinct advantage over the other two motors for stunt applications. The torque curve is much broader and does not fall off as quickly as the other two motors. Also there is considerable horsepower available to allow a broader prop selection. I had a Saito .72 on a Brodak Strega last year. It will turn a Zinger Pro 13X6 at 8500 to 8750 rpm. Lost of people gave me different numbers and implied it would do more. It did not. I used the UHP manifold with the medium venturi and was running powermaster YS 20/20 fuel on suction. Lap times were in the 5.4 sec range on 67 ft lines. Unfortunately the plane was killed due to failure of the flap horn boxes before it could be trimmed out. From a weight perspective there is very little difference in the weights of these motors. There is alot more power in both hp and torque in the .72 from this data. Take a look at the percentages at 8500 rpm. My motor now resides in an RC 3D plane and the instant spool up torque is wonderful when hovering or punching out of a hover vertically.. it is instant power on demand.

I am not working with this power platform this year, but please correct me if I am misinterpreting these numbers.

bob branch

[ash]

I may be interpreting this wrong and if I am someone please correct me. But it looks to me like the .72 has a distinct advantage over the other two motors for stunt applications. The torque curve is much broader and does not fall off as quickly as the other two motors. Also there is considerable horsepower available to allow a broader prop selection.

Thats the way I read it too, but it seems to me that the 72 has lately fallen from favour amongst erstwhile Saito72 stalwarts. Why is that, if it is even true?

[Doug Moon]

Thats the way I read it too, but it seems to me that the 72 has lately fallen from favour amongst erstwhile Saito72 stalwarts. Why is that, if it is even true?

Because you can get the 56 to swing the same prop with authority at 3 less oz in the nose.  The 72 has more juice for sure and will wing a larger prop than is needed in a typical 60 sized stunt plane.  So you tame it some and end up using what the 56 will use.  That was my experience.  As well as others I know. 

[Alan Hahn]

One thing all of you should remember is that these curves are for a specific venturi (as noted it is the one "without" the insert--if I understand the meaning of the caption).
Since I think most everyone is operating with different sized venturis, their curves will be different. So if you have a smaller opening, I would expect your torque curve to fall off faster with rpm than these plots. At a lower rpm, then the smaller venturi will admit most of the air/fuel mixture the engine need, so then the torque will probably get nearer the curve in the plots (but still lower since the engine is fighting the higher pull to get air through the smaller hole).

Finally when you pull the nose up, the fuel head will drop a bit, so the mixture will get a little leaner too. I would expect this effect to matter some too.

[Bob Reeves]

First, Martin Quartim and Bob Branch... Please go to your profile and delete your Zip codes it is slowing down the works.. If you need to know why just do a forum search for "Zip code".. Thanks..

Doug, what you said makes sense to me.. I always heard that HP curves really do not give any insight as to how a particular engine might work on a stunt ship but the torque as you described your theory computes in my pea brain.

My personal take on the 72 is the 56/62 is more than enough for anything I would want to be hanging on to. The 62 is only 0.2 ounces heavier than the 56 and can supply a little more punch if needed. I'm with Doug, why add two ounces to the nose when a 56/62 will swing the same prop at the RPM we need. Of course this is thinking of stunt ships at the top of my size/weight limit... Under 700 sq/in and 60 - 64 oz tops.

[bob branch]

Not sure the zip code issue. I did not have a zip code listed in my profile. I removed my location, maybe that will do it.

I am not pursuing the .72 as a power plant in large part due to the weight issue. I do not think the power was an issue. The plane did not pull more than I would expect any .60 size plane its weight to pull. But I am not into delving into stunt design on my own. I'm not experienced enough and prefer to let designers much more accomplished than I will ever be to design my planes. There just isn't much out there designed to carry that much weight up front. I chopped 1 3/4 inches off the nose of the strega to try to deal with it and that was not enough. This year I am going to be utilizing PA .51's on a pipe for my power system.  My analysis was just from a power torque curve an power perspective.

thanks,

bob branch

[Martin Quartim]

Alan,

The venturi is one of many variables, these charts are valid only for that climate, for that specific prop, for that fuel, for that venturi and plug (things we don't know). Changing the prop for example will result in a very different curve.


The auto industry has a Standard to bench mark engines, as matter of fact two standards SAE and DIN, and one could compare two engines by looking at the curves of HPxTorque. The Model Engine Industry has no standard, and no one can really compare engine performance by looking a chart where you have no idea how it was done.

The link below has some good information about measuring Torque and HP using a Dyno for Model Engines. Notice how different propellers change Torque and Power.

http://www.clcombat.info/dyno.html

Martin

[Alan Hahn]

Martin,
These are engine curves---they do not depend on the propeller.

[Martin Quartim]

Alan,

Are you sure?  how do you know that? I have recently been doing a lot of research about dynos, measuring power and torque of model engines and I really would like to know how Saito have done these tests.

If these are raw power and torque curves then it is even harder to make any relationship between these curves and  our pratical experience, because it doesn't have the effect of the prop reistance loading the engine.


Martin

[Doug Moon]

Martin,

These curves seem to be right in the wheelhouse for out applications.  It is no secret we run stunt engines in the high torque range, not the HP range, unless you run a 2s 40 on a pipe screaming its guts out. 

The saitos perform best, from my experience, in the 8000-8800 range.  The chart is showing that is where the torque is highest and steady.  I would think the charts are good info. 

Mid 8s on the tach and those motors are HAPPY and will have little trouble.

[RandySmith]

Martin,

These curves seem to be right in the wheelhouse for out applications.  It is no secret we run stunt engines in the high torque range, not the HP range, unless you run a 2s 40 on a pipe screaming its guts out. 

The saitos perform best, from my experience, in the 8000-8800 range.  The chart is showing that is where the torque is highest and steady.  I would think the charts are good info. 

Mid 8s on the tach and those motors are HAPPY and will have little trouble.

HI Doug

I think what Martin is saying is that you cannot determine much of anything from the chart shown.
The most likely way that they got this chart was to run a Engine with a  carb, and turn it across  the 7500 to 12,500 that they show on the chart.
Or they ran a large range of differant props,or loads, on the machine to get these figures, We really do not know what was run, how it was run, what prop was used, if an RC carb was used, what nitro was used, what carb-venturie size opening was used, and about another dozen or so questions.
The best way to get a HP and Torque plot on a motor using a venturie for our purposes ( CL Stunt) is to run a range of selected props with the engine running wide open and see where the curves plot out.
This is what I do when plotting  curves. In my mind it is the only way to get useful information.
The plots shown are useful for people using a RC Carb as you can see how the engine performs across a range of RPMs

An example at ST 60 turning a 13 x 5 Rev up prop included in my set of test props will make 86 in oz. of torque and right at .85 Horse power. This is turning 10,250 RPMs.
The 14 x 5 turns 9150 and equates to 96 in oz of torque, but that is the point where the curves starts to fall.
 Any engine that turns the same prop 10,250 will make the exact torque and HP so if you put my 13 x 5 test prop on another engine you would get a good comparison.
In order to get a good curve with a venturie equipped motor you need to run a series of test props.
This way you can look at the different  props (loads)  and see how they corresponds to the torque curve of the engine, as it will rise and fall with the different props (loads).

Another example of a series running
The ST 60 was tested using a 15 x 6  , 15 x 5  , 14 x 5  , 13 x 5  , 12x 5 W , 11 x 5W :
 it makes it highest torque  , and is the flattest curve with the 14x5  and 13 x 5.
Using the 15 x 6 it fall off very fast, same with the 11 x 5 w it fall off fast

Regards
Randy

[Bob Reeves]

The chart says "CL" & "no insert".. This tells me the charts were not done with an RC carb. One would expect Saito engineers have the equipment and a pretty good idea of how to properly measure torque and HP.

[RandySmith]

The chart says "CL" & "no insert".. This tells me the charts were not done with an RC carb. One would expect Saito engineers have the equipment and a pretty good idea of how to properly measure torque and HP.

So Bob  how do you think they got an RPM range of 7500 to over 12500  out of a  C/L motor with no carb?
That was one of the points I think Martin was trying to make, we don't know how it was done. the fact the have equipment and know how to use it , is not really germane to the post I made, Point was  "useful info"
We all know these are good engines, and the engineers at Saito know what they are doing and how to use their equipment. As far as "properly" measuring.. proper for one application may not be for another? Just another question?
They could have used a dyno that put a lot of load on the engine?
That could explain the RPM  range? maybe so? maybe know? another question.
The dyno loading is good for getting a graph, maybe as you have found isn't so good at getting a useful torque  curve for a stunt engine.
It looks like to me you found out that information a swhat one of my good friends like to call "dirty knees" testing. That is  gettin gto the flying field and trying all sorts of different setups.
The reason you find the higher pitch props  work better, is a good reason  to see how the chart out on a chart of Torque- HP.
Maybe I will have time to run one and chart it soon


Regards
Randy

[ash]

I would have thought it appropriate that a company like Satio would have a serious brake dyno and all the required skills to run it. And it would be in their best interests to do so as a torque curve determined by sweeping the carb range would be a pretty sad looking display of performance. If Lothar Henschel can make a brake dyno at home out of a vacuum cleaner motor, I reckon Saito can too.

[Bob Reeves]

Ash said what I was thinking much better than I did. Maybe I'm reading it wrong but why can't we assume Saito knows what they are doing and the graph is a very good representation of the engines preformanced on paper. I'm just trying to figure out how and if this will relate to my trial and error findings.

[RandySmith]

Hi Bob and Adrian

No one here said that Saito didn't know what they were doing.
No one here said that the engineers  didn't have test equipment.
No one here said that the graphs are not correct.
Please do not insinuate that was said.
My post was explaining some of Martin's very legitimate question.
I am sure that Saito has a Dyno that they can load a motor up with, However NONE of us know for a fact what ,and how this was done, it can be done in differant ways.
Also you may not be able to run these motors with out the "insert" as tested, you may have to have the insert  installed in the engine? or maybe not? we don't know.

Everyone here knows Saito is a first rate company and produces excellent engine. NO ONE is knocking Saito.
What was asked is how this related to practical-usable information for C\L stunt flyers. Information is like air ...more of it is better.

Regards
Randy

[Doug Moon]

Well, it is interesting that the curve that Saito came up with here happens to coincide with a very good usable way to run your Saito as a stunt engine.   

From years of messing with 4 strokes running them down on the RPM range produced a more powerful, usable, tunable, run.  We run stunt motors in the torque range of the curve because we apply load so abruptly time and time again we need that power to keep moving.

Look at the chart.  It shows the upper torque range of the motors, 56-62 in the 8000-8500 range. 

In flight getting that RPM will be different for everyone.  I got that range (8800 with the largest UHP venturi) with Bob's old 56 with an Eather 14-4.5 half UC Wide 2 blade.  Bob was getting this same RPM range using a 7 pitch or higher prop but different diameter.  We both report the best flight performance when the motor was running in this rpm range.  How much torque I was producing and how much he is producing is irrelevant.  The peak performance gained and where it is gained is.

If it were me and I looked at the curves, without any other info about the test and had heard what others real world testing told me, I know where I would need to prop the motor to get into that RPM range yet fly the plane at usable speed.  There is a balance there and the plane plays a large role in it.

I think Saito probably used a Brake Dyno and stating no insert means max air input.  This would be a max power output.  Needle set appropriately and see what you get.  The power numbers themselves mean very little and if there were an insert installed the curves would probably look the same just at lower rpm numbers.  But if you are talking inserts like we use it wouldn't be too far down the range.  BUT you can see the curve and know ABOUT where your upper torque RPM range is and where your Upper HP range is.  Gives you a very good starting range to work in.  Seems pretty straight forward.

It would be nice to know what instrument they used.  That would answer alot of questions. 

BUT it does coincide with world findings in stunt use if you ask me.

[Rudy Taube]

Hi Pete,

Thank you for posting these useful charts.

I received my CL Saito .72 a few weeks ago. Like my other Saito's this is a very nice engine, it is going into a Strega. Thank you for your efforts in helping to get us these CL 4 strokes. :-)

I have a question for you, but it is an engine question so I am asking it over in Randy's engine section. TIA for your ans.

Regards,  

[PeteBergstrom]

Gentleman,

Regarding the Torque and horsepower curves.  One of the reasons that I rarely provide torque and hp curves on any of our engines is because of the confusion they can cause.  The measurements for these curves were taken from a brake dyno at the Saito factory.  The torque curves that I have provided do indeed provide useful information for what we do.  They were developed using the venturi system that we provide with the new CL series of engines, and measurements were taken without the insert that is supplied with the engines. 

To develop the curves one needs to run the engine at the optimum fuel mixture for the air being allowed to pass through the venturi, and then you vary the rpm by placing a load in the form of a brake or propeller.  In this case the load was changed through the brake mechanism on the test stand.  The load provided to change the rpm doesn’t matter whether it is a propeller or a brake type mechanism. The downside to using a fixed pitch propeller as a load is that it takes many different propellers that will load the engine to different levels to develop a complete torque curve.  A brake dyno is much easier and less time consuming to develop the same numbers.  The hp curve is simply a calculation based on the measured torque and the rpm of the engine.

Here is where the confusion usually comes in.  Until Bob Hunt starting playing with tuned pipes, and then Randy and others developed them to the point where the rest of us could use them, the traditional way to control rpm was to vary the rpm by adjusting the mixture, then secondarily adjusting the amount of air through the engine. (This gave us the traditional 4 – 2 – 4 engine run we have all tried to tame for so many years.) If you are still working a system that involves using the mixture ratio to control your final rpm, then these curves will provide little information.  But in today’s world of 2 stroke engines running at a 2 cycle on pipes, and four strokes running at a 4 cycle (imagine that), with a properly set mixture these torque curves provide exactly the info we need to make intelligent running choices about our engines.

Without readily available torque curves we have all played the ‘try it and see’ method of finding the sweet spot for our engines (2 & 4 stroke) and the way we want to apply them to the world of stunt.  In the Saito arena, I can tell you that these curves reflect real world use.  What modelers have found from empirical trial and error testing is that the sweet spot to run Saito 4 strokes is between 8200 and 8700 rpm.  These rpms work for most all of the applications, and ours in particular, because we are most interested in the engines quick ability to recover rpm lost when we change the load on the engine (i.e. square corners, etc.).  If we were looking for ultimate speed and didn’t care about engine acceleration, then we would want to run the engines with a load that gets them much closer to the top of the hp curve, not the torque curve.  But if you notice at that point, there is very little torque, and the engines ability to recover from a change in load is much diminished.  Not a good situation for our use of these engines.

I think that if we had readily available torque/hp curves available for the 2 stroke engines we are running on pipes right now, you would find that the sweet spot on the torque curve is in the 10,500-12,000 rpm range, while the real hp is created somewhere between 18-20K.  Once again, through trial and error testing, the modelers have learned what serves them best … torque, not hp.

Please trust me guys, there is no black magic going on here.  These are honest numbers developed by established testing methods.


Pete Bergstrom
Category Manager - Air Team
Horizon Hobby Inc.
217-403-3202

[Bob Reeves]

Thank you...

[Marvin Denny]

  I was touting this very  theory (it was back then) of running "just above" the peak torque  back in the mid 70s to mid 90 s in combat and was essentially told that I was full of  uh um er  aaa-- Baloney.
  Nice to see someone that has some sence posting  on the subject.

  Bigiron

[RandySmith]

To add more information and clarify the torque curves , I was able to measure and find this out today:

The smaller Saito comes with a 240 venturie as delivered, The .240 insert was removed and the Graph was plotted using the .272 venturie.

The larger Saito comes with a 255 venturie set up as delivered, and this was removed to run the Saito with the .295 size venturie.
So the graphs were done using the 272 and 295 venturis.

Depending on what size you run it will change the graph.
 It also looks very much like if the graph had been extended a little wider all of the engines have a very flat curve from 7500 to 9500 RPMs, and in the case of the 62 it may even be as wide as 7000 RPMs. That is a very good range.
Then there the case of the best running Saito I have seen, was running well above 10,000 RPMs, so go figure?

A very well made product and I particularly like the mufflers.

Regards
Randy

[RandySmith]

Please trust me guys, there is no black magic going on here.  These are honest numbers developed by established testing methods.


Pete Bergstrom
Category Manager - Air Team
Horizon Hobby Inc.
217-403-3202

HI Pete

The new CL Saito engines look great, I think they will be a big hit with the CL guys.
I don't think anyone here thought there was any black magic , or the number were not honest, there were just some natural questions asked wanting more information. Hence my quote from back up in the thread from a day or 2 ago.

""Everyone here knows Saito is a first rate company and produces excellent engine. NO ONE is knocking Saito.
What was asked is how this related to practical-usable information for C\L stunt flyers. Information is like air ...more of it is better.""

We appreciate the time and effort it took for you to get the info for us.

Regards
Randy

[Martin Quartim]

Pete,

It is just great that you have come up with this charts and brought Saito Engineering close to us.

I am impressed with this report and that Saito has a brake dyno for testing engines. That answers some of my questions thank you.

I graduated M.E. many years ago and worked at VW Research and New Tecnologies Department,  so I have some  back ground on Engines, Dynos and interpreting charts. I quit Engineering 25 years ago, so I am very rusty and I guess dangerous 

Also I fly with a Saito 72. I use a venturi developed by a friend that using 10/22 fuel it will do a noticeable 4-2-4 with a 13x6 prop and a very light 4-2-4 with 20/20 fuel and a 14x6 prop.

Now I am starting to understand how this chart was created and I can start figuring things out.

For example if I take my Saito 72 with say a 14x6 prop and find it peaks at 8900rpm, then  it will match torque and power with this chart (if I use same venturi, fuel, same climate….)  Now if I keep the same prop and change the needle to a rich setting to go down to  8000rpm (not best air/fuel)  then it will not match the chart at 8000rpm. To keep in the curve at a lower RPM I would need a different prop, with more load, to keep the needle setting at best air/fuel mix, would that be right?

I guess it is obvious that a Saito 72 at 8000rpm with 14x6 will be spiting a lot more torque and hp then at the same 8000rpm with a 11x6 prop for example.

Now I wondering  what the curves would look like if I keep the same prop and go from a very rich needle to a lean needle setting   


Martin

[proparc]

Thats the way I read it too, but it seems to me that the 72 has lately fallen from favour amongst erstwhile Saito72 stalwarts. Why is that, if it is even true?

The 62 is more of a "mainstream" motor for the less experienced.

[Bob Reeves]

The 62 is more of a "mainstream" motor for the less experienced.

Huh?

[Doug Moon]

The 62 is more of a "mainstream" motor for the less experienced.

Huh?

[Bob Reeves]

Guess he's not going to explain his post.. I sure don't get it..

[Mark Scarborough]

Studied the graphs a bit, have first hand experience with the Saito 56 and believe I have a fairly good understanding of what works and what doesn't so it is the only one I can relate to. It is interesting that the RPM range that works best for stunt is about where the torque is the highest 82-8300. When I was running a lower pitch prop at 9 grand it wasn't well behaved at all.. Speeding up on the down legs and sagging overhead.. With a 7 pitch prop at 82-8300 it's as close to a perfect stunt run as anything I have seen.

So can some engine guru explain why as it relates to the graphs?
[certainly not an engine guru, however I did stay at a holiday inn last night  ,lol
I actually just finished reading the article by Dean Pappas on tuned pipe setups, IF ( a big if I may add) I understand correctly what the article said. Operating on the peak or backside 0f the torque curve is part of what helps keep the plane from accelerating on the downhill side. In other words, there is no more torque available to accelerate the propellor.
Understand, and I reiterate, I am NOT and engine expert, only posting this as a paraphrased version of what I understood hoping to be corrected if need be.

[phil c]

I guess it is obvious that a Saito 72 at 8000rpm with 14x6 will be spiting a lot more torque and hp then at the same 8000rpm with a 11x6 prop for example.

Now I wondering  what the curves would look like if I keep the same prop and go from a very rich needle to a lean needle setting   


Martin

Martin, from what I've seen, richening up the motor just drops the torque curve down some.  How much depends on the motor/prop/fuel, and how much you richen it.  Four stroke engines can run with a rich, burbly run.  I don't think anyone has documented it to be similar to a two stroke engine breaking between a 4 cycle and 2 cycle.  Some pretty good test published in Stunt News years ago show pretty definitively that a 2 stroike motor goes from firing every other revolution to firing on every stroke when it breaks.  I don't think four stroke engines do that- call it an 8-4 stroke!  They seem to have a pretty narrow operating range and like to run at a very specific rpm for a given fuel/prop.  Running it rich slows it down some, but nowhere near as much as a 2 stroke engine.

[john e. holliday]

I think Bob Reeves has it nailed.  You run the rpm where the engine is happy and prop for it.  I know my Enya 46 when it got over 9,000 would just quit.  I also learned that it didn't like the stock muffler pressure setup.  Need to get it repaired one of these days even tho it is heavy.  DOC Holliday

[Martin Quartim]

Hi Phil,

Have you measured that or do you think the torque is reduced when richening the needle from peak?  I always thought the engine would loose HPs and gain torque from peak to a more rich mixture, but I never measured it, I just thing it works like this.

Sorry about the confusion using the term  4-2-4. What we have achieved is an significant increase in RPM when the nose go up, similar to what a 2S 4-2-4 engine does.

This video was recorded when we were doing just a duration flight test with 10% fuel MAS Scimitar 13x6 wood prop.



Perhaps some computer guru can find quite accurately the engine RPMs by analysing the sound track.

Martin

[Ted Fancher]

reply to bump this interesting thread back to the front page.  I missed it the first time round.

Ted

[Bob Reeves]

Hi Phil,

Have you measured that or do you think the torque is reduced when richening the needle from peak?  I always thought the engine would loose HPs and gain torque from peak to a more rich mixture, but I never measured it, I just thing it works like this.

Sorry about the confusion using the term  4-2-4. What we have achieved is an significant increase in RPM when the nose go up, similar to what a 2S 4-2-4 engine does.

This video was recorded when we were doing just a duration flight test with 10% fuel MAS Scimitar 13x6 wood prop.



Perhaps some computer guru can find quite accurately the engine RPMs by analysing the sound track.

Martin

Hi Martin, you probably have already heard this as I've posted it many times but I am running a 13-7.5 on my 56 which takes us back to the "Why run a 72 when the 56 will turn the same prop" discussion. I know the 72 will turn a larger prop but if a 13-7 is enough for the airframe why add two ounces of engine you are not using. Not really questioning your choices just think it's an interesting subject that I'm hoping more will comment on.

[Allan Perret]

Does anyone know if the 56 and 62 share the same case?

[Bob Reeves]

Does anyone know if the 56 and 62 share the same case?

For everything we care about yes! The UHP manifold for the 56 fits the 62 and the mounting holes are the same. Internally I would guess you would find a few differences.

[Mike Alimov]

Sorry for a late reply to this, I just signed up to this forum; these curves were not posted on Stuka...

Very interesting info, and thanks to Pete for convincing the Saito factory to acquire and release these curves.

Incidentally, I have already taken torque-vs-RPM readings on my own (summer of '06) on the Saito 56, to understand better how to run the beast.  I assembled a torque engine stand from a kit by American Hobby Products, and used different props as loads.  My curves correlate to the factory data pretty well, considering the difference in methodology etc.  My process is very time-consuming, and gives more point-to-point noise than the variable dyno setup.

I have read the many opinions in this thead on how to interpret the data we have.  Everyone agrees that the Saito's are "happy" in the mid-8000 RPM range, so the answer seems to load them up with the prop to get into that RPM range, and it's done!  My own experience shows that to be about right.  But is this the end of the story?

The only set of (factory-supplied) torque/RPM curves that seems near ideal belongs to... the Saito 72. Why do I say ideal?  Because at 10k RPM, both the torque and power curves start falling off pretty steeply, and that's the point where we want to operate.  For those who did not read Dean Pappas' article "CL Stunt's New Tune", available from PAMPA website, I strongly recommend it.  To summarize, we achieve near-constant airspeed by operating an engine on a steep falling side of the torque AND power curve: if the engine loads in the corner, RPMs drop, torque is up, plane accelerates, and speed is restored; if the engine unloads in the wind (wind-up), RPM is up, torque AND horsepower is down, prop acts as a brake, and speed increase is contained.  Dean clarifies that *steep* fall-off means 8 - 10 % change in torque/HP in response to a change in 500 RPM.

By looking at the Saito 56 and 62 curves, mid-8000 RPM does indeed put us at the beginning of the torque curve decline (albeit not very steep), BUT - this is improtant - the power keeps rising all the way to 12000 RPM.  So while the torque is down, the RATE at which this torque is delivered is way up, and until the RATE is peaked, speed will be increasing.  Which means that engine will respond to wind-up under severe weather conditions, with plane gaining speed on each consecutive loop downwind. 

I did not believe that 4-strokes are capable of wind-up until I personally witnessed a flight by a Japanese F2B team member at the '04 Worlds in Muncie.  I think he was using OS70 Surpass spinning a stock wooden Zinger 14-6, but don't quote me on that.  One thing I'm sure of, it was a 4-stroke.  Those who attended probabaly remember the high winds (15 gusting to 20 MPH) that year.  His plane was whipping out of control.  By the end of the 3rd consecutive loop, the speed he picked up was scary.  I remember making a comment to someone standing next to me, "so much for the constant speed 4-strokes".

How do we cure the tendency to wind-up? By shaping the torque/HP curves to fall off steeply at some preset RPM.  How do we shape the torque curves?  In 2-strokes, we do that by tuning the length of the pipe to the exhaust timing.
Not sure how to do it in 4-strokes, but here are some ideas.  First, you could play with valve timing, but it's hard to do (either grind custom cams, or do some kind of variable valve timing, like Honda's VVT-i).
Another method (partially applicable to 2-strokes, by the way) is to take and engine of larger displacement and choke the intake down.  I think this is exactly why the 72 curves look like they do - displacement is significantly bigger than 56/62, but intake size is proportionally smaller.  As the RPMs increase, the large engine quickly runs out of air, torque and HP drop, and you get speed control.  The smaller engines with larger intakes (note - the factory curves were taken WITHOUT carb inserts) continue to breath well into the high RPM, and so support the HP increase. 

It would be interesting to get factory curves with inserts (Pete?..), and overlay those on the first set.  I predict that while torque peak will remain in the mid-8000 RPM range, the fall-off after that will be steeper than with large intake. Which in turn will bring peak HP point down the RPM range, and make for a more stunt-able run.

[Bryan Higgins]

Im just learning about Torque and Horsepower as well as prop pitch. By doing research on the latest
engines available for a mid 50 or 60 size stunters you can't leave out the purchase price.

After getting back into control line and wanting to build a full sized stunt ship not everyone has
five hundred dollars to lay down just for a engine and pipe.  By carfully studying all the most
popular engines available , you just can't ignore that the three Saito C/L series engines price.
I paid $209.00 for my Saito .56 c/l  while others where as much as $150.00 or more adding up to
close to five hundred dollars.

For someone just getting back into this great sport.  And seeing all those fantastic stunters being
built and wanting one for himself this is definitely a great purchase.....

I recieved mine last week and can't wait to get my Strega built.

[Bob Reeves]

Price was the reason started playing with 4 strokes and performance has kept me using and buying more.

I think Mike has hit on an important aspect of setting up a 4 stroke. Load it to take advantage of the torque then choke it down so it runs out of poop and doesn't wind up.

The first time I had my Score/Saito 56 out I was running a Bolly 13-6 with a stock (wide open) Dixon venturi. That day the wind was blowing 12 to 15 MPH and the Score was doing about 9000 MPH at the bottom of the vertical eight. On top of the wind up it would slow down (sag) overhead and in the square eights. Needless to say I was less than impressed.

After some trial and error along with a great thread on the old UHP forum with Doug Moon and Brad Walker giving me advice I made up a couple hardwood blocks drilled and taped for a 1/4-20 nylon screw that went right into the intake of the Dixon venturi. This gave me a means to infinitely adjust the choke area.

Then while at the Brodak FlyIn I discovered several 13 - 7.5 Rev-Up props. Shortly after returning from Brodaks I stuck on one of the Rev-Up props and started screwing in the choke screw.  I am flying on 63 foot eye to eye lines, the first flight wide open the Score was doing just over 4 second laps but showed promise as the overhead sag was gone.

It was about the 5th flight I finally had it choked down enough to get the lap times down around 5 seconds. All the bad things magically went away, no wind up or sag just one speed everywhere. Another interesting thing happened, the engine was using more fuel choked down than it did wide open.

After looking at the info spewed forth in his thread I believe by trial and error I found the right combination of prop and choke area to get and keep my 56 running at the torque curve decline as Mike talked about above.

[Bryan Higgins]

Hi Bob

Between your post on your Score and Saito engine set-up's along with Doug Moon and Bradley Walkers
post on four strokes.  It gave me my final decision to buy the saito .56 .  I  was opting for the .62 but
as many of you have said the larger engines slowed down to fly stunt correct was about where the .56
starts.
I saw the choke screw set-up on your Score and it is a very simple way of taming the runs to where you
like them along with setting the RPM's to your liking .  I purchased some Rev-up's and Zingers for my
.56 until i save enough for some Bolly's.
By the way i liked the way your Somthing Extra turned out. It's quite impressive.

[Bryan Higgins]

Hello Mike

Thank you for the post. It's very good reading and helpful.