OS mixture question
DaveL322 at comcast.net
DaveL322 at comcast.net
Tue Apr 19 11:18:25 AKDT 2005
Wayne,
In practice, yes and no. When I flew both props back to back on the OS EFIs, I found that the amount of unload was about the same with either prop (7700 ground vs 8300 in air). All other things equal, the 2 blade will unload more in the air than an equivalent 3 blade (which does effectively make the pipe longer), but, because of the greater efficiency of the 2 blade, I typically don't crack the throttle open as much with the 2 blade. I think the most I ever saw on the 3 blade was 8600, and the most on the 2 blade was 8900 - and that only happened on very windy days.
I think I tend to fly in a bit closer and slower than the average guy - and I think I am using the throttle a bit more than the average guy (ie, I've recently flown both the P05 and F05 and had 1+ ounces left in a 12 oz tank). Running the throttle that much in the midrange and with an average lower flight speed (and lower RPM) benefits from the slightly longer pipe.
I think the ideal pipe length will change depending on glow plug, compression, nitro, prop, and barometer. Sometimes, the pipe length will be shorter than ideal, and other times longer. Being longer results in a slight power loss, whereas shorter results in a cranky engine. Ergo, I'd rather leave the pipe a bit long so I don't have to fuss with it as much. The pipe length is really tied to RPM (1st order effect), but pipe length can be effected by the plug, nitro, compression, etc. as these things may change the RPM of the engine or the amount the engine unloads in the air (1st order)- and then that change in RPM results in a differing pipe length being better (2nd order) . Simply changing the pipe length can also influence what plug, compression, nitro work best - all are ways of adjusting the amount of "heat" (or timing) in the engine.
Dave
-------------- Original message --------------
Dave,
Do you find that a 2-blade prop will unload more or less then a 3 blade?
Maybe the reason for your longer pipe length is due to the fact that your running a 3-blade prop. I too have a longer pipe setup on my 16x11
3-blade then I do on the 17x12 2-blade prop Pipe length will certainly be determined by the load the prop puts on the engine and the amount of nitro you use. That's why I like to keep the fuel thing at a constant and I use 15% Cool Power only so I know that it is the prop changing the load and not other variables.
Wayne Galligan
----- Original Message -----
From: DaveL322 at comcast.net
To: discussion at nsrca.org
Sent: Tuesday, April 19, 2005 12:34 PM
Subject: Re: RE: OS mixture question
Agree. Good stuff.
I have found a couple of setups (for my flying style at least) that perform best in the air with the pipe more like 1" longer than what would be peak RPM on the ground. And I've found several setups that behave very differently in the air than on the ground.
It is always easier to start long - the engine will be friendly with a long pipe, but cranky with a short pipe. And cutting is easier than adding. So I usually fly with what I know is a long pipe setting and evaluate shortening the pipe based on how it flys.
Dave
-------------- Original message --------------
> This is good info, no doubt!!!
> Just a thought - many folks want a "starting point" for pipe length.
> Experimenting with different props/pipes and motors - all things being about
> equal (I know they're not, really, but it's okay), I've found the 17 x 12 APC or
> similar load starting point to be about 23.75 -24" plug to reflector, following
> headers curves, and the "wave" length.
>
> This measurement will get a person who's in a hurry in a flyable condition
> pretty fast, with minimal additional tweaking.
>
> Of course, YMMV, depending on a lot of things, but the most frequently asked
> question I get by the newbie two-stroke convert (or a former 2 stroker who has
> RE-converted)is "what's a good starting point for 1.40 - 1.70's in today's
> planes?"
>
> Hope this is helpful to someone.
>
> Bob P.
> >
> > From: "richard.lewis"
> > Date: 2005/04/19 Tue AM 11:08:47 EDT
> > To:
> > Subject: RE: OS mixture question
> >
> > Thanks again Wayne...:) Very well spoken, clear, and concise 2-stroke
> > tuning methodology.
> >
> > Richard
> >
> > _____
> >
> > From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org] On
> > Behalf Of Wayne Galligan
> > Sent: Tuesday, April 19, 2005 9:12 AM
> > To: discussion at nsrca.org
> > Subject: Re: OS mixture question
> >
> >
> > I helped a guy with the a similar issue this weekend on his Mintor. Way
> > too lean on the bottom end. His would pop on acceleration or die coming out
> > of the outside loop.
> >
> > For the OS 1.40 RX Try this:
> > Use an OS "F" plug.
> > 15% nitro
> > I have not had to adjust the pump on any of the OS's I have set up to date.
> >
> > Set the top end till it peaks in rpm(use a tach if you have one) and back
> > off one click to the rich side.
> > Bring it down to an idle and try to set the idle to about 18-1900 rpm.
> >
> > Let the engine idle for at least 20-30 seconds and do not touch the
> > throttle.
> > 1. if it speeds up or surges at any time during this time the bottom end
> > is lean.
> > 2. if the engine gradually slows down and dies...its rich.
> >
> > Advance the throttle with medium speed and observe:
> > 1. if it burbles and picks up speed or burbles and dies bottom end is
> > too rich.
> > 2. if it falls flat or hesitates then accelerates or dies it is lean
> >
> > This may take several tries to get but once its set then its just minor top
> > end adjustments depending on weather conditions.
> >
> > Changing pipe lengths will also effect the low end transition. A longer
> > pipe setting will allow you to set the bottom end a little richer and give
> > better downline braking.
> > I find that running the bottom end as rich as possible with out it loading
> > up gives the best downline deceleration.
> >
> > Setting your pipe is a whole other story. My best method is on a test
> > stand. Set the pipe long and run engine, tach the top end at peak rpm.
> > Shorten the coupler or pipe about 1/4" at a time and observe the peak rpm.
> > It will increase with each shortening of the pipe.
> > Once it peaks in rpm or no longer increases or drops in rpm this is the top
> > tuning spot for your engine and pipe for max rpm(not really the desired
> > tuning).
> > At this point back the pipe off about 3/8 to 1/2". This will give you a
> > good starting point. I usually lengthen the pipe if I go to a higher loaded
> > prop or
> > shorten it with a lighter loaded prop.
> >
> > The OS 1.40 is a very predictable engine. If it starts to load up and
> > stall in the midrange for no apparent reason or drops rpms
> > after the glow plug is removed first check the plug . If it continues to do
> > the same thing then the bearing is probably on its way out.
> > Replace the bearing with a sealed bearing or a stainless steel bearing that
> > goes in the EFI version. I have about 200 flights on one
> > of my OS's that has the sealed std steel bearing from Bearings Limited in it
> > and it is still going strong. Another way to check the bearing is move the
> > prop by the tips
> > perpendicular to the engine and if you can feel end play the bearing is
> > getting loose.
> >
> > Wayne Galligan
> >
> > ----- Original Message -----
> > From: Kurt Bozarth
> > To: discussion at nsrca.org
> > Sent: Monday, April 18, 2005 7:22 PM
> > Subject: OS mixture question
> >
> >
> >
> > OS 140 RX (non-EFI) question:
> >
> >
> >
> > When I advance the throttle, the rpms remain at idle for approx. one second,
> > "pop" and then advance to full throttle rpms I am not quite sure if this
> > "pop" and hesitation is a result of having too lean of an idle mixture or
> > too rich. This is an older motor released back when Hobby Services offered
> > a free needle valve assembly replacement to correct for mid-range richness
> > issues. I do not know if this was done or not - something I will check for
> > tonight. I have never adjusted the pump setting. Let me know your
> > thoughts. Thank you.
> >
> >
> >
> > Kurt Bozarth
> >
> >
> >
>
> Bob Pastorello, El Reno, OK, USA
> rcaerobob at cox.net
> www.rcaerobats.net
>
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