Author Topic: 4 stroke venturis, does size matter (Read 9391 times)

Bob Reeves · « **on:** September 21, 2008, 08:26:05 AM »

I'm experimenting with the first control line version of the Saito 40 I have played with and have ran into a situtation I don't fully understand.

I have extensive time and experience with the Saito 40 RC version in two configurations, one is a mod to the RC carb that basically turns it into a CL venturi, the other is using the UHP manifold. Both versions work fantastic, gobs of power, consistant bla... bla...bla... Both version have my infamous nylon screw for adjusting the choke area and typically burn about 4 ounces of fuel for a <> 7 minute flight...

Now comes the CL version, same prop, fuel (YS 20-20) etc. Install a nylon screw so we can adjust the choke area, set the screw and needle for 81-8200 just like my other engines and the darn thing runs for 15+ minutes on 4 ounces and exhibits all the tendencies that almost made me give up on 4 strokes.. Time after time my experiments concluded that if a Saito 40 doesn't burn <> 4 ounces of fuel it isn't going to provide the rock solid constant speed run I'm after.

The only difference that is obvious is the CL version uses a conventional spray bar and I calculate the choke area at the spray bar to be .011 with the insert and .021 without. Both versions of the RC engine use a spigot with the choke area (again at the spray bar) .037 for the RC carb and .039 for the UHP. On the UHP version my adjustment screw is above the spraybar which reduces the intake area but doesn't really change the choke area at the spray bar.

Hoping I laid enough ground work above to ask my question but not real sure what question to ask. OK the engines with the larger area at the spraybar work, the one with a smaller area at the spray bar doesn't. However when I have the UHP version set right I am closing off about 2/3rds of the intake area.

One would think it shouldn't matter if you are restricting the choke area what size the hole is to start with, right? If that's true then why doesn't the CL version act the same as the other two versions? Why can't we get the CL version to use the same amount of fuel using the same RPM and needle setting?

Baffled in 4 stroke land..

Bradley Walker · « **Reply #1 on:** September 21, 2008, 11:54:37 AM »

It is the spraybar, it is too small and restrictive.

Use only the PA spraybar.

BTW, this is the cause, it is not a theory. The 4 stroke needs a very high flow fuel system to be able to run rich. If you use the Saito CL version system it will run too lean and will never make top power. The fix is simple, never use anything but a PA spraybar on a 4 stroke.

Spraybar size, and the exit hole in particular, is one the most overlooked things in stunt engines. They are not all the same.

I feel an article coming on!!!

Bob Reeves · « **Reply #2 on:** September 21, 2008, 01:54:54 PM »

Problem is you can't use the PA assy in most four stroke setups and for sure in none of the 40 configurations. The Saito CL engines have a spraybar that is nothing like what we are use to seeing.., It looks to be a two piece assembly and none of the PA spray bars are long enough even if you could make it fit.

I did look at the fuel exit hole and it looks to be close to the PA, the needle and spray bar are well made and seem well designed. I am just not sure about the small choke area...

Bradley Walker · « **Reply #3 on:** September 21, 2008, 05:33:56 PM »

Quote from: Bob Reeves on September 21, 2008, 01:54:54 PM

I did look at the fuel exit hole and it looks to be close to the PA, the needle and spray bar are well made and seem well designed. I am just not sure about the small choke area...

Doug had one on his new Saito 62. It did not work anything like the UHP with PA needle.

Bob Reeves · « **Reply #4 on:** September 22, 2008, 06:47:25 AM »

The eyes can be a little deceiving when trying to compair small holes... I measured the outlet holes in the PA and Saito spray bars this morning using numbered drill bits and as close as I can judge the PA is .046 and the Saito is .038.. To me that is a significant difference...

Sometime after our contest this comming weekend we are going to put the engine back on the test stand and start doing a little experimenting.

Think we will start with one of my modified RC carbs or a UHP both of which we know work, get it set for the RPM we also know works and see how long it takes to burn an ounce of fuel. Then install the stock CL carb, set it for the same RPM with and with out the restrictor and again note the run time for one ounce of fuel.

This should give us a good reference to compair the two (3) configurations and I highly suspect the CL version will run much longer on the same amount of fuel even without the restrictor.

If the results are what I expect, first we will drill the spraybar hole out to match the PA and recheck. If that doesn't get us in the ball park I need to figure out how to get the Saito spray bar apart so I can open up the choke area and see if that helps. Worst case is we will mess up the stock Saito parts but they are available from Horizon.

Hey Pete, you reading this? Tell me how to get the Saito spray bar out of the insert without breaking something...

Added: Never mind, Found the parts breakdown in the CL Suplement which shows how the spraybar is assembled.

Mike Alimov · « **Reply #5 on:** September 25, 2008, 03:05:49 PM »

Bob -
I've re-read your original post, but still could not figure out if we are comparing oranges to oranges. After all the configuration changes you've made to the Saito 40 CL version (insert or no insert, nylon screw, etc), what was the final choke area that resulted in 8100 RPM? Now, how does that compare to the choke area with UHP setup (you said 0.039 but 2/3 closed, which gives me 0.029 - still bigger than 0.021 without insert - which would explain the fuel consumption difference). Also, I assume when you compare RPM, that both engines are swinging the exact same prop (which means they develop same power)?

Brad -
you say "The 4 stroke needs a very high flow fuel system to be able to run rich. If you use the Saito CL version system it will run too lean and will never make top power. " I thought max power is developed by any internal combustion engine under most optimal settings, including fuel-air mixture. A rich setting may give you constant speed, but does not correspond to top power. I've tried your theory of "high-flow" setup including large spray bar hole, but did not see any difference in either run quality, or power developed.

I've successfully tested a CL version of the Saito 56 using its factory venturi / spraybar, and it ran identically to my other engine (with Dixon venturi). Very good power and consistency, using 2.5 - 3 oz for full pattern on 10% nitro fuel. Hmmmm....

Bob Reeves · « **Reply #6 on:** September 25, 2008, 03:42:37 PM »

Hi Mike, don't have allot of time right now as I am getting ready for our contest but one thing I did discover when putting many flights on both my Saito 40's and 56's was if they don't drink fuel they do not run consistently. The problems show up with losing speed in the square eight and some overheads. I could get the same RPM on the ground (same prop) with several different setups but they sure didn't act the same in the air.

This is the same thing we are seeing with the CL 40, we can easily get it set for the same RPM (same prop) on the ground as I am running but it simply doesn't preform like my 40's do in the air.

Joe Yau · « **Reply #7 on:** September 26, 2008, 12:53:23 PM »

I'm just thinking.. could it be the valves needs to be adjusted? (most likely needs to close up the rocker/valve stem gap a hair). so it opens up the intake more.

Mike Alimov · « **Reply #8 on:** September 26, 2008, 03:08:35 PM »

Joe, that valves needs to be properly adjusted and engine fully broken in goes without saying; based on the history of Bob's postings with his 4-stroke experiences, I'm assuming all that has been taken care of.

We're back to the fuel supply debate, and the infamous "burnout" as described by 'Zilla.
I've noticed similar symptoms as Bob describes on his new Saito 40 CL, but that was only the case when engine was needled to the MAX RPM on the ground and then released. It did go lean and sag overhead. All that was required to fix that is to richen it a bit (1/4 turn?) until it dropped about 300 RPM from max, and bam - perfect runs.

Joe Yau · « **Reply #9 on:** September 26, 2008, 03:46:10 PM »

]

Quote from: Mike Alimov on September 26, 2008, 03:08:35 PM

Joe, that valves needs to be properly adjusted and engine fully broken in goes without saying; based on the history of Bob's postings with his 4-stroke experiences, I'm assuming all that has been taken care of

I do realized that, just trying to eliminate other possibilities.

Bob Reeves · « **Reply #10 on:** September 27, 2008, 04:32:09 AM »

Good Morning,

Have a few minutes before we start getting the first day of the Tulsa Contest underway. I didn't go into the details of prop, fuel, valves, or needle settings because none of these items really changed between the engines and didn't feel it was necessary to get the point across. Please assume we know how to set the needle and check the valves. I've been flying/campaign 4 strokes for two seasons and lets just say everyone that has seen one of my 4 strokes run or has test flown one of my airlanes has been pretty impressed. Not saying the formula I ended up with is the best or only way to get it done but it works and has worked on every Saito I know about that duplicated it.

We put 6 or 7 flights on the CL engine before deciding it really wasn't going to work and I started looking for the reason why. We may end up with a bunch more before I have the answer because I also know that test stand results may not corespond to what it will do in the air.

Please stand by, after this contest is over I will find an answer...

Dick Fowler · « **Reply #11 on:** October 12, 2008, 06:32:31 PM »

Quote from: Mike Alimov on September 25, 2008, 03:05:49 PM

Bob -
I've re-read your original post, but still could not figure out if we are comparing oranges to oranges. After all the configuration changes you've made to the Saito 40 CL version (insert or no insert, nylon screw, etc), what was the final choke area that resulted in 8100 RPM? Now, how does that compare to the choke area with UHP setup (you said 0.039 but 2/3 closed, which gives me 0.029 - still bigger than 0.021 without insert - which would explain the fuel consumption difference). Also, I assume when you compare RPM, that both engines are swinging the exact same prop (which means they develop same power)?

Brad -
you say "The 4 stroke needs a very high flow fuel system to be able to run rich. If you use the Saito CL version system it will run too lean and will never make top power. " I thought max power is developed by any internal combustion engine under most optimal settings, including fuel-air mixture. A rich setting may give you constant speed, but does not correspond to top power. I've tried your theory of "high-flow" setup including large spray bar hole, but did not see any difference in either run quality, or power developed.

I've successfully tested a CL version of the Saito 56 using its factory venturi / spraybar, and it ran identically to my other engine (with Dixon venturi). Very good power and consistency, using 2.5 - 3 oz for full pattern on 10% nitro fuel. Hmmmm....

MIke, good to see you today. I must say I was impressed with how well your setup works when I watched you fly a few patterns with the Vector today. Smooth power and very even pull at all atitudes... I'd say you have it dialed in pretty well.

Bradley Walker · « **Reply #12 on:** October 12, 2008, 08:19:10 PM »

Quote from: Mike Alimov on September 25, 2008, 03:05:49 PM

I've successfully tested a CL version of the Saito 56 using its factory venturi / spraybar, and it ran identically to my other engine (with Dixon venturi). Very good power and consistency, using 2.5 - 3 oz for full pattern on 10% nitro fuel. Hmmmm....

I am sure if you have completed your tests and found no difference, then that must be it then. Everyone else must be wrong.

Please feel free to bring your 4 stroke to Dallas in the middle of the summer and we will see if you are making "very good power". When your 2.5 oz to 3 oz of 10% nitro turns into 2 oz of fuel consumption due to the heat and low air density I am sure it will be very impressive.

The engine will be so hot at the end of the run that the paint will be boiling off of the nose of your plane, and if you have an aluminum spinner you will not be able to touch the thing for 20 minutes after the flight for fear of burning the skin off of your fingers. If you are using a pressure line from the muffler, you might see the silicone fuel tubing burn through from the intense heat of the exhaust after 10 flights...

BTW, Bob Reeves might have the most impressive 4 stroke run I have ever seen....and I have seen a couple. Smooth, quiet, steady, and not fast.

Allan Perret · « **Reply #13 on:** October 13, 2008, 07:20:33 AM »

BTW, Bob Reeves might have the most impressive 4 stroke run I have ever seen....and I have seen a couple. Smooth, quiet, steady, and not fast.
[/quote]

Brad: Which of Bob's setups are you referring to here ?

Bradley Walker · « **Reply #14 on:** October 13, 2008, 07:24:10 AM »

Quote from: Allan Perret on October 13, 2008, 07:20:33 AM

BTW, Bob Reeves might have the most impressive 4 stroke run I have ever seen....and I have seen a couple. Smooth, quiet, steady, and not fast.

Brad: Which of Bob's setups are you referring to here ?

Pretty much all of them really. I saw the Saito 56 in the Score at Tulsa and it was simply incredible.

Bob Reeves · « **Reply #15 on:** October 13, 2008, 11:06:54 AM »

Quote from: Mike Alimov on September 25, 2008, 03:05:49 PM

Bob -
I've re-read your original post, but still could not figure out if we are comparing oranges to oranges. After all the configuration changes you've made to the Saito 40 CL version (insert or no insert, nylon screw, etc), what was the final choke area that resulted in 8100 RPM? Now, how does that compare to the choke area with UHP setup (you said 0.039 but 2/3 closed, which gives me 0.029 - still bigger than 0.021 without insert - which would explain the fuel consumption difference). Also, I assume when you compare RPM, that both engines are swinging the exact same prop (which means they develop same power)?

Brad -
you say "The 4 stroke needs a very high flow fuel system to be able to run rich. If you use the Saito CL version system it will run too lean and will never make top power. " I thought max power is developed by any internal combustion engine under most optimal settings, including fuel-air mixture. A rich setting may give you constant speed, but does not correspond to top power. I've tried your theory of "high-flow" setup including large spray bar hole, but did not see any difference in either run quality, or power developed.

I've successfully tested a CL version of the Saito 56 using its factory venturi / spraybar, and it ran identically to my other engine (with Dixon venturi). Very good power and consistency, using 2.5 - 3 oz for full pattern on 10% nitro fuel. Hmmmm....

Hi Mike,

Now that I have a little more time I can make a few comments on your post.. My Score has a Dixon venturi but I sure wasn't happy with the way it ran with the stock spray bar and stock choke opening. The issues I had were all the same as when I first started playing around with my Saito 30 with a low pitch high (relative) high RPM set ups. It would sag at the top, wind up in the rounds and loose speed in the squares. It also was only burning about 3 ounces of fuel.

I then started applying the info I discovered during the time I was fine tuning my Saito 40 setup. Most of what sent me in the proper direction (except for the magic nylon screw) came from Brad and the Dallas gang. I replaced the spray bar with one of Randy's, ran a 1/4 - 20 nylon screw down the throat of the Dixon bell to adjust the choke area and stuck on a Rev-Up 13 - 7.5 prop.

Once I got the choke area set for the prop and the needle properly adjusted the fuel consumption went up to 4 ounces, it no longer had any tendency to wind up, it looses 0 speed in the horizontal square 8 no matter how hard you hit the corners and when you pull up for the wing over you have no doubts about the power.

There is allot about what happens I do not understand... like how can an engine possibly use more fuel with a smaller choke area... but it does.. Same with my 40's, choking down the intake made it go from using 2 ounces to 4 with a noticeable increase in power and consistency.

This what prompted me to start this thread, hoping someone that might better understand flow rates can shed some light on why the stock CL won't get there from here.

One additional note in my way of thinking is I simply can't agree with the Saito engineers on how the 40 should be ran. They recommend an 11-4 and running it at 10.5 or 11 grand. First I believe my set-up with an 11-7 running at about 8100 will be allot less stressful on the engine making it last longer. I also believe I am putting more fuel through it which means more lubrication and more power. I know the Saito guys are allot smarter than I am but it just doesn't compute in my pea brain logic.

Added: Still haven't had time to get back on the CL Saito 40.. Stuff keeps getting the way but I will and let everyone know the out come.

James Lee · « **Reply #16 on:** October 13, 2008, 12:31:48 PM »

Just a note... I'm not a big four stroke fan... I ran an early Saito 45 for several years in a Magnum, basically Pratt's prototype set-up... After a year or so of struggles it became very dependable with some of the most consistant runs I'd ever had.... But it was not overly powerful, enough, but not too much... Went to a 50 when they first came out and went back to the hair pulling

Decided I'd rather have a two stroke!!!
At the Neosho fun fly this last Saturday, I had the opportunity to fly Bob's Score with the Saito 56 (Thanks, Bob!!

)... I was VERY impressed... Just a low growl all the time with identical lap times at the start and end.... And power was NOT a problem

and his Score is 68 oz....
In my opinion, Bob does know what he's talking about on the subject of four strokes!!
Thanks
Jim

Bob Reeves · « **Reply #17 on:** October 13, 2008, 03:40:26 PM »

Thanks Jim, I sure had a good time and glad you liked the Score.. I really hate that the best airplane in my fleet is a darned old ARF but what can you do.. As we all know the engine is a big part of the equation and that Saito really makes the airplane what it is.

Back to the original issue... May have found an answer to the CL 40 (and maybe others) in the form of an OS needle I found in my junk. If I can't make the stock CL venturi work and I have my doubts I will make another insert and stick this needle assy in the side. I should be able to roughly duplicate the choke area of the UHP using this as a spigot. With any luck it will even be somewhat adjustable... This needle is available from Tower for around 10 bucks, I just hope I have the proper tap..

Bradley Walker · « **Reply #18 on:** October 13, 2008, 04:12:58 PM »

I am still not sure about this spigot. I have tried it also.

Greg L Bahrman · « **Reply #19 on:** October 13, 2008, 04:46:24 PM »

<There is allot about what happens I do not understand... like how can an engine possibly use more fuel with a smaller choke area... but it does.. Same with my 40's, choking down the intake made it go from using 2 ounces to 4 with a noticeable increase in power and consistency.>

It appears that as you restrict the venturi you are getting better suction or fuel draw thus the increased fuel usage. like putting your finger over the venturi....My guess

Bradley Walker · « **Reply #20 on:** October 13, 2008, 06:36:41 PM »

Quote from: Greg L Bahrman on October 13, 2008, 04:46:24 PM

<There is allot about what happens I do not understand... like how can an engine possibly use more fuel with a smaller choke area... but it does.. Same with my 40's, choking down the intake made it go from using 2 ounces to 4 with a noticeable increase in power and consistency.>

It appears that as you restrict the venturi you are getting better suction or fuel draw thus the increased fuel usage. like putting you finger over the venturi....My guess

I think the cam works properly at high load and low RPM.

Greg L Bahrman · « **Reply #21 on:** October 13, 2008, 07:28:05 PM »

<I think the cam works properly at high load and low RPM.>

You think the longer open duration at lower RPM's thus the increased fuel usage?? Well that would make sense too.

Bradley Walker · « **Reply #22 on:** October 13, 2008, 07:38:31 PM »

Quote from: Greg L Bahrman on October 13, 2008, 07:28:05 PM

<I think the cam works properly at high load and low RPM.>

You think the longer open duration at lower RPM's thus the increased fuel usage?? Well that would make sense too.

Yes, and the intake stroke requires time to work.

Bob Reeves · « **Reply #23 on:** October 14, 2008, 04:14:29 AM »

Quote from: Bradley Walker on October 13, 2008, 07:38:31 PM

Yes, and the intake stroke requires time to work.

That has to be the $64,000.00 answer.. Keep the intake valve open long enough to suck in a big fuel charge which makes for a bigger bang which equates to power. Makes sense to me..

Mike Alimov · « **Reply #24 on:** October 14, 2008, 11:29:11 AM »

Guys, it is not my goal to stir controversy just for the sake of it, or to declare that I hold keys to the best 4-stroke setup while everyone else is wrong. In fact, my setup was largely borrowed from those used by the Australians and French, who use 4-strokes at the WCh level.
After re-reading a bunch of older posts on 4-strokes (Saito 56 specifically), I've concluded that the main difference between mine and Bob's setups (and those preached by the Dallas group) is in the fuel system. We seem to agree on pretty much everything else: relatively large-diameter, higher pitch props (I use APC 13x6 and Bolly 12x6.5 3-blade on my 56); modest RPM - mid-8000's up to 9000; prefer a fixed venturi over RC carburator; set needle a few clicks rich of the peak RPM.

The only thing that's different is that I use uniflow tank. I've tried to make non-uniflow systems work (hard tank, clunks, etc), but the result was a significant speed-up from beginning to the end of flight (about 0.3 sec). In making my custom uniflow tank, I kept in mind the need to GUARANTEE good fuel flow to the engine. Due to much smaller fuel consumption, I was able to keep the tank short, resulting in only ~ 4" of fuel line from NVA to the pick-up. With this 3 oz tank, I get about 7+ minute runs, with lap time change less than 0.1 sec from beginning to end.

My guess is that the reason why "Dallas non-uniflow setup" setup consumes to much more fuel is because you need to compensate for fuel pressure differences simply by "flooding" the engine with so much extra fuel, it does not "feel" fuel head pressure differences. This also explains the "burnout" effect - i.e lack of power in overheads if set lean. At the top of the circle, the centrifugal force is offset by the gravity, causing less fuel pressure. Being very sensitive to fuel pressure, 4-strokes start to lose power... unless set rich. Uniflow systems seem to be less affected by that.

That's all I have to say.

Bob Reeves · « **Reply #25 on:** October 14, 2008, 02:09:34 PM »

Hi Mike,

I think we are all trying to learn and come up with the ultimate way to run our valved wonders.. Like most I quit when it worked and haven't really explored anything beyond that. Like you I am not sure my setup is the ultimate, in fact I think it's a little complicated and sometimes difficult to find the proper choke area and needle sittings. The saving grace is once you find it you can just about forget it's even adjustable. Now I would like to go further by trying a few new ideas. May or may not work but at least I have a good base line in my present setup.

I don't believe one can use "to much fuel", if my 56 used 6 ounces for the pattern that would be fine with me. I think the more fuel used the better the engine gets lubed and the more power it's making. This like most of my theories are only based on the logic that stems from my experience without a thorough understanding of the actual science.

This is of course assuming the needle is set at the proper air/fuel mixture which I believe everyone agrees is just a tad on the rich side of peak RPM. Also why I tend to discount the idea we are simply running a richer mixture. If the needles are set relatively the same, just on the rich side of peak, engine A is using 3 ounces and engine B is using 4 ounces which one is making more power? My vote would be for engine B..

I for sure want to try a uniflow tank, last time I tried it I was still trying to make a lower pitch higher RPM setup work and it didn't help. I do know one of the symptoms of not having a setup just right is a greater difference between a full tank and an empty one. If the lap times drop during the flight more than a tenth or so something isn't working or adjusted right.

Just trying to throw what I think I know out there and hoping to get a better understanding of why it works (or doesn't).

Bradley Walker · « **Reply #26 on:** October 14, 2008, 02:14:17 PM »

Mike, I do not think you are controversial, I just think you are wrong. N offense.

I explained what your setup will do under extreme conditions. I have done it. I have seen other people do it. I also know how to fix it.

The Berringers get away with their setup because they are using a Saito 56 to fly a plane with the parasitic drag of a heavy Nobler. At the WC's in 2003 Berringer did not look like he had an excess of power, although it was very good for his airplane (which weighs about 54 oz and has flaps that are about the size of a Veco Smoothie---with an airfoil to boot).

I guess there are varying opinions on what "great power" actually is...

Bob Reeves · « **Reply #27 on:** October 15, 2008, 11:24:33 AM »

Quote from: Bradley Walker on October 13, 2008, 04:12:58 PM

I am still not sure about this spigot. I have tried it also.

Tom Martin brought over about 20 RC carbs with this needle valve assy. Ordered a couple tap's yesterday for the metric thread and as soon as they show up I will have all I need to make new inserts. Haven't done any measuring but the needle assy. UHP supply's with the 40 manifold is almost identical with the exception of the way it's mounted. I can see no reason why they shouldn't work just fine.

Not to get in competition with UHP but am thinking of going into a limited production of replacement inserts for the CL 40, maybe even the 56 and 62. I'm already modifying the 40 RC carb into a CL venturi for $45.00 and so far everyone I have done one for is happy with the results.

Scott Hartford · « **Reply #28 on:** October 15, 2008, 11:41:45 AM »

I have 2 of the 40s done by Bob and they run beautifully! Ingenious design that absolutely works! Saito should have copied Bob!

Bob Reeves · « **Reply #29 on:** October 21, 2008, 09:24:33 AM »

Quote from: Scott Hartford on October 15, 2008, 11:41:45 AM

I have 2 of the 40s done by Bob and they run beautifully! Ingenious design that absolutely works! Saito should have copied Bob!

Well we know that ain't gonna happen but appreciate the good word..

Have decided that size does matter so I ordered the taps and went to work on the lathe.. The result is functionally the equivalent of my UHP venturi mod. The choke area (at the spray bar) is withen thousands of what my UHP calculates and see no reason it shouldn't work the same.

In the foreground is the stock Saito CL insert showing the difference and it also shows how I added my nylon screw choke area adjustment. This setup would work great on a profile but in a built up fuselage the screw would be a little difficult to adjust. Think the best bet for a built up is either a UHP or a modified RC carb as the screw can be adjusted from the side rather than the rear.

On the other hand I have set the screw on the test stand and all it needed in the airplane was a slight tweak. Once the adjustment is made for the prop it's pretty rock solid.. I haven't touched the screws in my 40's or my 56 in two seasons flying in everything from 100 deg to 65 deg in four states.

Willis Swindell · « **Reply #30 on:** October 21, 2008, 05:24:16 PM »

I think if you work hard enough you can make any system work for you. I have messed around with these 4 strokes for about about ten years and tried many different ways but the system that works for me is exactly the same one Mike Alimov uses. Jim welch fly’s with me and he uses muffler pressure and a regular tank and runs as well as mine . Both of us use RPM from 8200 to 9000. usually about 8600 and 8700.
Willis

Mike Alimov · « **Reply #31 on:** October 22, 2008, 12:49:40 PM »

Willis,
I've been told that I'm plain wrong, therefore that makes it impossible for mine and yours (and French and Australian) setups to work as well as they do. We all must be delusional. I haven't come to grips with this realization yet, but if I work hard enough, I might. Just repeat: This cannot work, I must be dreaming, This cannot work, I must be dreaming...

Bradley Walker · « **Reply #32 on:** October 22, 2008, 02:38:38 PM »

Quote from: Mike Alimov on October 22, 2008, 12:49:40 PM

I've been told that I'm plain wrong, therefore that makes it impossible for mine and yours (and French and Australian) setups to work as well as they do. We all must be delusional.

I am sure it works...

4 strokes work. I think I am pretty sure of that.

I guess it just depends on your experience with failure with systems that "work", except when the chips are down and the conditions are tough.

Like I said, please bring your 4 stroke burning 2.5 oz of 10% nitro fuel in the Northeast to Dallas in August...

It will be even better if you bring a big fat winged plane with HUGE flaps too. That would be perfect.

BTW, Steve Fitton has flown Willis's plane and he said it was really good. I have no doubt that is true. I think the point of what I have been posting has been twisted by Mike.

I have never said that Mike's system "won't work" or "does not work". I said that Mike's system will not work as well as OTHER systems, and lots have testing has proven that.

In fact it is Mike who has been saying that proven improvements "make no difference".

THAT is what I said was "wrong". I stand by that assertion.

Martin Quartim · « **Reply #33 on:** October 22, 2008, 08:05:36 PM »

Are there other people running the Saito 40 CL and having similar problems?

I was hopping this engine would work nicely stock, but had doubts since the beginning that an R/C body adapted into a venturi would work well. Any way, I can't wait to see this problem resolved so I can get me one of these.

I may be wrong but I believe the shape of the venturi is the trick, as well as a good NVA such as the PA, like Bradly mentioned.

Making a lot of fuel passing through the engine can help cool the engine, but just because the engine is sucking up more fuel it does not mean it is producing more power. Could it be that the extra fuel is just passing through the engine and not burning Kcal into RPMS?

Martin

Martin

Doug Moon · « **Reply #34 on:** October 22, 2008, 08:37:08 PM »

Good thread here lots of info for sure.

Bob,

I been thinking about your question about how can they burn more fuel when the whole is smaller. I wonder if it could have to do with ignition. Follow me here. The motor runs on a glow plug with pretty high compression to keep things warm and toasty. So if you have a big hole for the intake it will have to be a leaner setting or it will get to cool and stumble and or shut off. Example. With hole size of A you run prop A at 10K max rpm. That uses the least amount of fuel correct? Performance is suspect. So you richen some and change to Prop B with a higher pitch. You use a little more fuel but not much and you are down to 9500 RPMs. You are also going faster as well. Go to pro C with more pitch RPMs go down 9000 working in your upper torque curve, fuel consumption should start going up. But you are hauling A$$! So try and richen some and it falls on its butt. Ignition goes out. You could try to prop it even steeper but the speed will be excessive due to the toque available while using that large opening. If we had an ignition on these things we could run them as fat as we want. So we close the hole and start the whole process over and get down to a range that has the correct speed and works in the meat of the toque curve while keeping the plug nice and hot. Most engines will always use the more fuel in the torque curve. You burn more fuel because you are in the torque curve with a smaller opening than in the HP curve with the larger opening while getting the correct speed for stunt.

You also said you felt your motors would last longer than the Saito prescribed method. I dont know if I agree, not that that means anything, but you are running your motor with more load on it than they say and load will wear it out faster. If you have a car that hauls a trailer all the time and another one that cruises highway speeds the cruiser will out last the hauler every time. At least that is how I see it.

I have a Saito 62 with CL setup. I used the stock setup for quite some time trying to get it to come in. Running 3oz of fuel. The time of year was mid August temps ranging 90 at a 11 pm to 100+ during the day. Yep 90 at a 11pm means you dont get a break from the heat ever and the density is nil! The hole is large and the NVA cross section is small. I bet I could get it to use fuel and run in the lower curve like I want but a 14x8 or 14x9 prop isnt going to be usable on a 60 sized stunter. I went to a PA NVA and the UHP manifold. The opening is considerably smaller and I run 4 oz of fuel, 20/20. I run a 14x5-4.5 and it a solid runner. Still need some tweaks on the prop.

Word on the street is the Reeves 56 kills! I and another around here think there is something to that old spun 56 muffler. My 62 has a tiny muffler that is just an extension of the pipe with a pressure fitting and a reduced hole at the end. Good and light but not much chamber. Has a loud popping Harley sound as it runs. I like it but I think there is some performance gain with a chamber muffler.

john e. holliday · « **Reply #35 on:** October 23, 2008, 07:41:48 AM »

Watched Bob fly at Tulsa(Terry Bolin's place) and was amazed at how well that engine run. The engine/plane combination flew like there was no turbulent wind. Even watched Jim Lee fly the combination after the official events were over. DOC Holliday

Bob Reeves · « **Reply #36 on:** October 23, 2008, 10:52:29 AM »

This is a good thread and maybe we will all gain a little insite into the magic of obtaining the perfect stunt run.. If the perfect stunt run can ever be defined in words..

Doug's post leaves me pondering and wanting to think through a few things, will probably be back when my brain is working better.

Not sure how to answer Martin, "Are there other people running the Saito 40 CL and having similar problems?".

Might not but are they flying in 15 MPH wind on 90+ deg days. The stock CL engine we tried wouldn't do it.. On the other hand I can't say we really gave it a fair shake as after 6 or 7 flights I went for the throat and started thinking about how to get from the stock setup to what I knew would work.

Lots to think about, problem is we are running out of flying weather and further experimenting is going to slow down.. Man I hate winter...

Bradley Walker · « **Reply #37 on:** October 23, 2008, 11:24:19 AM »

Quote from: Bob Reeves on October 23, 2008, 10:52:29 AM

Might not but are they flying in 15 MPH wind on 90+ deg days. The stock CL engine we tried wouldn't do it..

EXACTLY!!!

Bob gets what "good" means.

Bob Reeves · « **Reply #38 on:** October 24, 2008, 09:22:25 AM »

Quote from: Doug Moon on October 22, 2008, 08:37:08 PM

Good thread here lots of info for sure.

Bob,

I been thinking about your question about how can they burn more fuel when the whole is smaller. I wonder if it could have to do with ignition. Follow me here. The motor runs on a glow plug with pretty high compression to keep things warm and toasty. So if you have a big hole for the intake it will have to be a leaner setting or it will get to cool and stumble and or shut off. Example. With hole size of A you run prop A at 10K max rpm. That uses the least amount of fuel correct? Performance is suspect. So you richen some and change to Prop B with a higher pitch. You use a little more fuel but not much and you are down to 9500 RPMs. You are also going faster as well. Go to pro C with more pitch RPMs go down 9000 working in your upper torque curve, fuel consumption should start going up. But you are hauling A$$! So try and richen some and it falls on its butt. Ignition goes out. You could try to prop it even steeper but the speed will be excessive due to the toque available while using that large opening. If we had an ignition on these things we could run them as fat as we want. So we close the hole and start the whole process over and get down to a range that has the correct speed and works in the meat of the toque curve while keeping the plug nice and hot. Most engines will always use the more fuel in the torque curve. You burn more fuel because you are in the torque curve with a smaller opening than in the HP curve with the larger opening while getting the correct speed for stunt.

You also said you felt your motors would last longer than the Saito prescribed method. I dont know if I agree, not that that means anything, but you are running your motor with more load on it than they say and load will wear it out faster. If you have a car that hauls a trailer all the time and another one that cruises highway speeds the cruiser will out last the hauler every time. At least that is how I see it.

I have a Saito 62 with CL setup. I used the stock setup for quite some time trying to get it to come in. Running 3oz of fuel. The time of year was mid August temps ranging 90 at a 11 pm to 100+ during the day. Yep 90 at a 11pm means you dont get a break from the heat ever and the density is nil! The hole is large and the NVA cross section is small. I bet I could get it to use fuel and run in the lower curve like I want but a 14x8 or 14x9 prop isnt going to be usable on a 60 sized stunter. I went to a PA NVA and the UHP manifold. The opening is considerably smaller and I run 4 oz of fuel, 20/20. I run a 14x5-4.5 and it a solid runner. Still need some tweaks on the prop.

Word on the street is the Reeves 56 kills! I and another around here think there is something to that old spun 56 muffler. My 62 has a tiny muffler that is just an extension of the pipe with a pressure fitting and a reduced hole at the end. Good and light but not much chamber. Has a loud popping Harley sound as it runs. I like it but I think there is some performance gain with a chamber muffler.

No Question I am running in the torque curve and believe that is a big reason my engines run more like tractors than Toyotas. Being raised on a farm guess tractors are in my blood. You could very well be correct and/or a combination with what Brad said above, the valves being able to breath better at a lower RPM. All I know is it seems to work and every time I have tried to run one like a Toyota it looses speed climbing hills.

My thinking on longevity is the smaller parts are what wear and break at high RPM, rocker arms, push rods etc. I am making the engine work but the stress is on the crank, rod and piston which may or may not be more bullet proof than the rest of the parts but they are bigger and stronger. Guess I'll discover the weak point when something breaks (knock on wood) which hasn't happened yet.

I thought the new CL 56 and 62 came with the old lighter 56 muffler instead of that cast thing my RC 62's came with?? I went so far as to order the old style mufflers from Kaz in Japan for my 62's. Now that Saito has started supplying them with the CL engines I believe they can be ordered from Horizon..

I'm running a 13-7.5 on my 56 and would probably stay with the same prop on a 62.. Still haven't done anything with either one of my 62's have UHP manifolds and old style mufflers for both just need a stunt ship. Anyway for me the 56 seems to be all the motor I could ever possibly need, not even sure why I bought the 62's other than a new and exciting 4 stroke. The Score is big enough and even at 68 ounces the 56 has enough balls to fly it in anything anyone else would fly in.

As a small side note.. Before I started messing with 4 strokes I was basically scared to death of wind and turbulence, you may remember me woosing out a few times in Dallas when the wind was coming over the tracks. I have been so bad my hand was shaking when I was flying. If I had to sum up what 4 strokes have done for me, it would be one word "Confidence".. I no longer worry about if the airplane will do what I ask, I know it will without a doubt. Granted part of it is I have learned a little more about trimming and have a few more flights under my belt but next time I am able to come to Dallas I won't chicken out because it's a little windy.

Well I've rambled long enough.. Spent the morning in the shop and this is the result.. Two Saito 40 RC conversions, and a Saito 30 RC conversion. the CL 40 conversion was already done. The drill bit is just to hold one of the 40's so the camera could look down the throat.

catdaddy · « **Reply #39 on:** October 24, 2008, 09:42:27 AM »

Quote from: Bob Reeves on October 24, 2008, 09:22:25 AM

Well I've rambled long enough.. Spent the morning in the shop and this is the result.. Two Saito 40 RC conversions, and a Saito 30 RC conversion. the CL 40 conversion was already done. The drill bit is just to hold one of the 40's so the camera could look down the throat.

WAY KEWL!!!
Is one of dem mine?
Do you have some 20/20 on hand for sale?
I'd like to come out and break mine in, the wind can blow all it wants and I can at least get that done.

Bob Reeves · « **Reply #40 on:** October 24, 2008, 10:09:08 AM »

Yep one is for you..

Am pretty sure I have an extra gallon of 20-20 but I wouldn't use it for break-in.. I use anything I happen to have for break-in fuel, you have complete control on the test stand so no worries about lean runs or over heating... Usually several partials mixed together or who knows what.. Stuff I wouldn't fly with but as long as it has enough oil I don't worry about what it is, just use after run oil in case it contains moisture.

Allan Perret · « **Reply #41 on:** October 24, 2008, 12:28:11 PM »

Hey Bob:
Did you know that Dubro sells a 10-32 nylon bolt with a socket head. It's easier to use a ball driver if you make adjustments with the motor running.

Bob Reeves · « **Reply #42 on:** October 25, 2008, 05:13:58 AM »

Quote from: Allan Perret on October 24, 2008, 12:28:11 PM

Hey Bob:
Did you know that Dubro sells a 10-32 nylon bolt with a socket head. It's easier to use a ball driver if you make adjustments with the motor running.

Yep, thanks for the tip but I get mine from Small Parts in packs of 20 or 50 for a whole lot less. Have both kinds, the hex head just happen to be closer. Haven't really found it to be an issue one way or the other. A 5/16 nut driver works as well as a ball driver and either way you need to carry another tool.

Just in case someone is wondering... The nylon nut isn't really needed but once the screw is set it gives a little added insurance it won't move. Also once you get the screw set for your prop you can pretty well forget it's even there.

Author Topic: 4 stroke venturis, does size matter (Read 9391 times)

Willis Swindell