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Author Topic: 4-stroke fuel?  (Read 920 times)
FLOYD CARTER
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« on: May 02, 2017, 02:55:42 PM »

I have acquired a gallon of Power Master "4-Stroke" fuel.  The label says--for YS and others.

I have been running it in a Saito 62.  The fuel is 20% nitro!  

I am trying to get the engine to run slower and with a bit less power.  I've tried lowering prop pitch, inserting a venturi restrictor,  but still  need less power.  

I don't understand why 4-strokes need 20% nitro.  I would like to use SIG 10-10-10 because I have lots and I use it in many 2-stroke engines.

Any issues with that?

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George Truett
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« Reply #1 on: May 02, 2017, 06:19:15 PM »

Floyd,

In my experience it has been R/C pattern and 3D fliers behind the increase in nitro in 4 stroke fuel.  In classes like SPA with displacement limits guys started using 30% heli fuel to get that last bit of vertical performance.  Saito recommends 20% oil and 5-15% nitro.  OS says use 16-20 % oil and 5-15% nitro.  Both say a castor/synthetic blend is fine.  You should be right in there with your 10-10-10 fuel.  George
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Robert Zambelli
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« Reply #2 on: May 04, 2017, 06:06:19 PM »

Hi, Floyd.
The 10/10/10 will work perfectly in the SAITO.
I've also run Powermaster 10/11/11 and Brodak 10/11.5/11.5 with excellent results.
I've been told that the higher nitro content should be used when the weather is very hot, like 90 and above, but I've never tried it.
The real expert here is Bob Reeves. As far as I know, he has more experience with SAITOs than just about anyone.

Bob Z.
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Steve Shackley
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« Reply #3 on: May 11, 2017, 04:42:28 PM »

I've been using Rich's Brew 15% 11-11 in my OS .56 and Saito .62 4 strokes here in Albuquerque.  We're over 5000' in elevation and increase the nitro, particularly in the summer.  When I lived in California at sea level it was 10% 11-11 in both 2 and 4 strokes.
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Mike Callas
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« Reply #4 on: May 17, 2017, 09:20:56 PM »

Floyd,
I would stay away from castor, use all synthetic. The castor will gum up a 4 stroke. YS 20/20 is all synthetic.

http://stunthanger.com/smf/four-strokes-only/why-not-to-run-castor-in-a-4-stroke/
 
What RPM are you running? Did you do the Reeves mod? Don't use a low pitch prop, you need to load the motor, so 6" pitch prop or more.
Hate to be a jerk but is a 56 available?
Mike
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Brett Buck
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« Reply #5 on: May 18, 2017, 07:43:30 AM »

Don't use a low pitch prop, you need to load the motor, so 6" pitch prop or more.

   It takes less shaft power to fly the airplane with a 6" pitch prop than a 4" pitch prop, substantially so.  That sounds like less load, not more. Which is also why it works at all - you are trading a much less good prop for unloading the engine so it can respond more in flight. The fact that you lose some power is moot, because the power is still more than sufficient.

    I would also note - the only perceptible competition success with a 4-stroke were with props 4.5" at around 10,000 rpm - like the 2003 NATS. The ultra-low-rev approach (first used in this country by Igor Panchenko as far as I can tell) came later.

    The Berringer-style venturi is a *great* idea that definitively solves one of the biggest problems - trying to adjust the speed using the mixture - by allowing you to change the choke area instead. One day, when I am retired and have some time to fiddle, I might make something similar for a 2-stroke.

      Brett
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Dan McEntee
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« Reply #6 on: May 20, 2017, 03:53:21 PM »

   It takes less shaft power to fly the airplane with a 6" pitch prop than a 4" pitch prop, substantially so.  That sounds like less load, not more. Which is also why it works at all - you are trading a much less good prop for unloading the engine so it can respond more in flight. The fact that you lose some power is moot, because the power is still more than sufficient.

    I would also note - the only perceptible competition success with a 4-stroke were with props 4.5" at around 10,000 rpm - like the 2003 NATS. The ultra-low-rev approach (first used in this country by Igor Panchenko as far as I can tell) came later.

    The Berringer-style venturi is a *great* idea that definitively solves one of the biggest problems - trying to adjust the speed using the mixture - by allowing you to change the choke area instead. One day, when I am retired and have some time to fiddle, I might make something similar for a 2-stroke.

      Brett


    Brett;
     The speed limit combat guys have been using a "variable " venturi to help regulate speed almost since the event was conceived. It lets them dial in the speed appropriate for the atmosphere at the site for that particular day. That may be where Bob Reeves got the idea, but also maybe not. . I have a Saito .56 in a Top Flite Score with that set up, and it worked right from the get go in giving me nice consistent engine runs with the power dialed in like I like it. I don't think I have ever had a bad run since I put that set up to use, and my engine still looks like new with a whole bunch of flights on it over 5 or 6 years or more. While I like it a lot, I haven't sold off my hoard of other two stroke engines either! Like you, I wonder what a ST G-.51 would run like with it and how would it be installed. My uneducated wild guess is, that it may help you find the "sweet spot" for venturi size a whole lot quicker, it may not be the big revelation that it was for four strokes. I think maybe two strokes flow a lot more air a lot faster, and would having a big lump in a venturi actually hurt air flow? Cause a bunch of turbulence in the intake? I haven't witnessed a speed limit combat engine at full song, but at the rpms or peak rpms that they run, and the type of run they require, it might not make any difference. Interesting to think about, though.
   Type at you later,
   Dan McEntee
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Brett Buck
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« Reply #7 on: May 20, 2017, 06:53:16 PM »

     The speed limit combat guys have been using a "variable " venturi to help regulate speed almost since the event was conceived. It lets them dial in the speed appropriate for the atmosphere at the site for that particular day. That may be where Bob Reeves got the idea, but also maybe not.

    I am sure Bob could clear up where he got the idea, but certainly its very close to the Berringer venturi. Of course, they didn't invent the idea of a variable choke area, but the Berringer venturi was a very good implementation that is ideally suited to the application.

    Brett
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Bob Reeves
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« Reply #8 on: May 25, 2017, 03:02:49 AM »

Been busy working on tractors and just saw this..

Have posted how I got to the spigot with nylon screw a few times, short version..
Panty Hose ---> Nylon screw through the side of a UHP intake ---> Nylon screw down the throat of UHP and Dixon intakes ---> Carb Mod.

Longer explanation with proper credits here.
http://www.tulsacl.com/SaitoCarb.html

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Brett Buck
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« Reply #9 on: May 25, 2017, 05:51:06 PM »


The Berringer version is shown here:

     http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=257986&mesg_id=257986

   But Bob's is superior because it uses normally available parts. The Berringers build aerospace parts for a living, so knocking this out from a block of aluminum isn't an insurmountable problem but might hold up everyone else. If you took the drawing above to a machine shop, it's surely going to cost more than $40!

      Brett
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