Model Forum / Radio Controlled / Air Models / June 2004

As an aside to the OS46. A chap at our club came down yesterday with a OS 46
with a tuned pipe, and a 8X6 prop put on the tacho a it turned at 16,000
rpm.

On 6/14/2004 7:06 AM Ted shuffled out of his cave and grunted these
great (and sometimes not so great) words of knowledge:

Sounds like the temperature and very possibly the nitro content of the
fuel.  I use 10% and have had no problems, however there are other
people at my field using 20%+ nitro and consistently have problems on
hot days.

An 11X4 is on the low end of the desireable range, but the higher heat more
likely affected the mixture than the prop.  With higher heat comes less
dense air and you need to lean the engine slightly more.  This gives less
power and the 11X4 would be more suitable.

FWIW, I flew for years in the Phoenix summer where temps regularly were
95deg when I got up in the morning.  Never had any heat problems, maybe
because I let them run a little richer for the extra cooling of the fuel
coming in.

--
Paul McIntosh
http://www.rc-bearings.com

An 11x4 is a little on the low pitch side for a 46FX, especially in a
model with as small as and with such a low wing loading as a 4 Star
40. Try a Bolly 11.5 x 5. Of course it doesn't matter how low you prop
any engine if you know how to use the throttle and have ears.

Too lean a mixture with too high an RPM will cause overtemp & or
detonation, whichever occurs first. This could of course be
exacerbated by nitro content, oil type/content leading to a dead cut
and even seizure, especially on an extremely hot day.

I run my 46FX with a 12X8 and 5 or 10% nitro - whatever is in stock.  It
runs great on that.  It is not uncommon for the temps to be in the 30'C
range here is S. Ont. in the summer.  I tend to run a tad rich though for
extra cooling.
Gord Schindler.
MAAC6694

So . . . you had one dead-stick landing and the engine still seems to be
working fine?  As long as the engine doesn't make a habit of it, and as
long as you're sure that you're not running too lean and cooking the
engine, I'd say don't worry about it.  These are glow engines, after all.  
As someone else has pointed out, "If lawnmowers used glow engines,
everybody's lawns would be 4 feet high."

BTW - despite what some of the other posters said, I've had very good
static thrust with an 11x4 on my .46FX, too.  Actually, I usually run an
APC 12.25x3.75.  It seems to be a tad better for static thrust, although
you'll never win a race with one.  

Well you asked for experts but I am going to reply anyway.
I have heard many tales of people running big props on their 46 size
engines, I have tried lots of props on mine and it pulls the best for what I
want to do with the APC 11x4. I am located in Texas and we have plenty of
100+ heat in the summer too, never have had a cooling problem with this
engine. So I think the 11x4 is a fine choice. Someone else has commented to
the effect ...... one dead stick and you are worried ?? ...... I would
immediately be concerned if my 46 deadsticked (just doesn't happen). If mine
still has fuel and it deadsticks, the glow plug will fail completely in a
few more flights. Its just the way this engine works. I run my engine
slightly rich on the high end and it is extremely reliable. I would retune
the engine and fly it cautiously for a couple of flights, if it deadsticks
again or just doesn't run right I would put a new plug in it and see if that
fixes it.
For what it is worth I have a TT46 vs the OS46, but they are all basically
the same.

Charlie