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Author Topic: Engine orientation for best 4-2-4 running?  (Read 1213 times)

Offline Frank Sheridan

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Engine orientation for best 4-2-4 running?
« on: June 05, 2009, 04:40:13 PM »
Hello all. I'm sure this has been discussed before but is there one engine mounting position relevant to level flight that is best for achieving a 4-2-4 run characteristic? In other words, will an inverted engine exhibit better 4-2-4 tendencies than an upright one? What about profile mounted engines?
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Online Brett Buck

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Re: Engine orientation for best 4-2-4 running?
« Reply #1 on: June 05, 2009, 08:53:43 PM »
Quote from: Frank Sheridan on June 05, 2009, 04:40:13 PM
Hello all. I'm sure this has been discussed before but is there one engine mounting position relevant to level flight that is best for achieving a 4-2-4 run characteristic? In other words, will an inverted engine exhibit better 4-2-4 tendencies than an upright one? What about profile mounted engines?

   Depends on the engine. Generally an upright or inverted engine works better, but a Discovery Retro is said to run better as a sidewinder. Some engines don't work well at all on their side, but if you have to, they usually run better if the cykibder is inboard rather than outboard.

    Brett
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Offline Frank Sheridan

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Re: Engine orientation for best 4-2-4 running?
« Reply #2 on: June 05, 2009, 09:40:51 PM »
I've never seen anyone run a profile engine with the cykibder... I mean cylinder... on the inboard side! (Sorry Brett, I couldn't resist that!) Now, when you say run better do you mean better overall,  or better as far as a 4-2-4 run is concerned?  Now my lifetime of inexperience is beginning to show. Take, for instance, a Fox 35 mounted on a profile plane. If it were mounted on the inboard side of a profile fuselage, would the tank be on the inboard side as well? Would it still exhibit the Fox "burp" during maneuvers?

« Last Edit: June 06, 2009, 11:41:31 AM by RandySmith »
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Offline RandySmith

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Re: Engine orientation for best 4-2-4 running?
« Reply #3 on: June 06, 2009, 11:40:54 AM »
Hi Frank

There have been many people fly profiles with the engine mounted to the inside, The Forerunner kits  were mostly setup for inside locations, and other profiles were done this way too.
Frank Williams started using this setup on profiles and the ST 60. The inside cylinder setup helped keep the glo plug clean, so the engine ran with a much cleaner 4-2 than having it setup with an outside cylinder.
I have talked to several people using the older  FSR 40 and 45 motors and they claimed much better 4-2 cycling with and inboard cylinder mount also.
The reason it works is when you transistion the plane in manouvers ,and if there is a loaded up fuel charge ,centrifugal force will load the plug area of the head outboard mounted, cooling the plug some, and this results sometimes in a "ratty" run.
With inside mounting centrifugal force helps keep the glo plug cleaner, resulting in a cleaner 4-2 transition

As far as the FOX burp, people report yes it still is there, but not as bad, and happens the opposite way

Regards
Randy
« Last Edit: June 08, 2009, 10:22:26 AM by RandySmith »
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Online Brett Buck

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Re: Engine orientation for best 4-2-4 running?
« Reply #4 on: June 06, 2009, 12:57:49 PM »
Quote from: Frank Sheridan on June 05, 2009, 09:40:51 PM
I've never seen anyone run a profile engine with the cykibder... I mean cylinder... on the inboard side! (Sorry Brett, I couldn't resist that!) Now, when you say run better do you mean better overall,  or better as far as a 4-2-4 run is concerned?  Now my lifetime of inexperience is beginning to show. Take, for instance, a Fox 35 mounted on a profile plane. If it were mounted on the inboard side of a profile fuselage, would the tank be on the inboard side as well? Would it still exhibit the Fox "burp" during maneuvers?

     Spelling flames on Stunthangar, my God what have we come to...;-)

    Frank Williams is the expert on the topic, but he reports the burp is still present but happens on insides instead of outsides. Actually he had tried it to fix the burp and found it didn't and then went on to develop the bypass volume reducer.

    The theory is that the inboard cylinder makes any puddles of fuel that accumulate in the bypass (and occasionally drip into the cylinder causing rough running) run down into the crankcase instead. The 2 1/2 Gs or so also alters the flow of gasses in the cylinder, making it less likely to fling raw fuel droplets on the plug element.

    The only real downside is that you have all the weight on the inboard side, and thus need much more tipweight than you would otherwise.

   Go through the PAMPA bibliography and find anything by Frank Williams, and read it. Not a word written that is not pure gold.

     Something that just occurred to me - I bet if they ran the Discovery Retro with the cylinder *inboard* they wouldn't need the plug shield gadget in the head.

    Brett
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