Years ago (early-mid 80's), I was very involved in the rc air hobby --
mostly pattern and sport acro. I left the hobby for years, and have
returned with a vengence over the last few of years.
One of my favorite planes was the built-up Super Sportster (don't
ask), and I had a particular fondness for the SS 20. That plane was
powered by a ST .25, which had a very aggravating problem. It would
invariable quit about 5 minutes into a flight. It didn't sound lean,
rich, or seized, it just QUIT. You could run it on the test stand all
day long, and you could also run it in the plane on the ground all day
long -- in mixed attitudes and throttle combinations. I learned a
great deal about spray bar positioning, low and high needle setting,
and even managed to get past the ubiquitous mid-range stumble (or at
least thought so). The 2 ST .61's I had, after their initial
teething, were great engines. The .25 ALWAYS suffered the sudden
inexplicible sudden stoppage about 5 minutes into flight, but ONLY
during flight. Eventually, that stoppage killed the plane when it
happened in a low-level maneauver over rocks. The engine was cleaned
up, after-oiled and stored.
I was very recently given a SS .20 from an estate that had a used-up
OS on it (no compression). Initial thoughts went to trying to find
some way to use the ST .25 (other than as a boat anchor). Have any
new thoughts about the older ST's come up while I've been away? I
tried multiple different glow plugs, the carb settings, replacing the
fuel, clunk, filter, and all tubing -- all to no avail. I've tried
many different fuels, and while the ST .25 seems to prefer the 5%
nitro, even at out high field altitude (>3000 feet). The one thing
that I never remembered trying was going to a larger-than recommended
I susupect these answers have been dealt with years ago, and from the
old comments I've found, it looks like ST's may be more suited to
decorative uses than others. The engine has been torn down, with no
signs of wear or corrosion, and there is no evidence of carb leakage.
Fuel is pressurized using muff pressure. Compression is good. Starts
easily. The glow plugs look okay. Not burned out, and the catalyst
looks okay, with no obvious burning/flaking. Would a Perry carb be
likely to solve the problem? If there was a good chance of it doing
so, I would be willing to go that route. The ST .25 was a great match
for the SS 20, at least when it was running.
Should I even attempt to resurrect this engine, or would I be best in
pursuing another brand? Whilst on that subject, what do you think
about the GMS engines? I have a couple of larger GMS's I'm pleased
with, but nothing this small. Just for sake of principal, I'm
inclined to spend more and order an Irvine (or GMS) from Just Engines,
before payig less at Hobbico/Tower.
I have several other reliable .25's, but these are all on funtional
combat ships, and I hate to start stripping them as combat is a nearly
weekly thing here with a couple of local friends. On a few occassions
we actually have some out-of-town guests and have a real "group".
Sorry for the long post. I have no local resources. For years, I was
the only on in this region interested in RC, and even now, with the
friends I've interested, our "club" numbers 4, and I'm the "old-hand"
(scary, no?) The nearest real club is a bit over 100 miles away, and
aren't particularly friendly to non-locals (even if you're a
dues-paying out of town member, you're welcome to watch at their
flights or meets, but they don't really want you flying, or even
appear to be interested in mentoring). The "LHS" is the same way, a
bit over 100 miles away, and not too knowledgeable at that. Basically
carry Hobbico/Great Planes and that's it.
- posted 15 years ago