Any hope? ST (Itlaian) ST .25 ? (ATTN: LONG)

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
prop diameter.
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.
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On Sat, 14 Oct 2006 05:15:39 -0500, Bob wrote in :
Well, just to make yourself happy, clean it up, put on a new glow plug, grab some fresh fuel, and go fly it. That's the only way you can make yourself feel that you gave it everything you could.
I've never tried to heal an ST, so I don't have any miracle advice. I did spend a few hours on an ASP .25 to no avail. I forget the symptoms now. I traded it in for $20 at RJL for a GMS .46, which gave me loads of fun for a couple of years until a friend broke the plane it was in. The net cost of the .46 was something like $60 plus shipping.
I think the RJL trade-in may still be available.
Two brands I have confidence in at the low end: Thunder Tiger and GMS.
My one Magnum didn't give me happines (.15 XLS). Others have had success with that same engine. Must be my fault.
And, of course, there is always OS. Except for the FX stinkers (all .46 size?), every other OS engine I've had or helped to run was a sweetheart. They cost more, but, as a general rule, they work right out of the box.
I had an Irvine .40 hand-me-down. Once I picked a piece of trash out of the needle-valve barrel, it worked great. I didn't like the plastic backplate. I over-tightened it, had a lean run, and ruined the backplate. My bad. Go and do otherwise!
I have a GMS .32 and a TT .36 on two Gremlins. They both have given long service. Both have been crashed. The carb for the TT is being held on with JB Weld. I think the TT may have more power--but that may be a biased judgment, influenced by the small difference in displacement and cost.
The sound of the GMS engines is generally more annoying than that of the TT or the OS engines (even with the baffles removed from the mufflers). It bothers me a bit, but the low cost of the engines helps take the edge off the irritation.
Reply to
Martin X. Moleski, SJ
Oh, I had actually already done that. It doesn't appear that being stored, then stripped and cleaned (even new o-rings), has changed one iota about the engine. I had thought perhaps some saner mind had come up with a solution in the last 20 years or so. It's handy to remember that this engine has tought me more about dead-stick landings than the rest of my engines combined.
I think I've moved beyond it now. Hot furnaces and very large sledges sound more like repair equipment at this point. Certainly more satisfying.
Good to hear about the GMS's. I have a few of their larger engines and have been very happy with them. I have a moderate form of hearing loss that affects only certain frequencies, and until you (and a few neighbors) had brought it to my attention, I thought GMS was about the quietest running engine on the planet. One quick GMS question, though.... The GMS engines I have are new, but prop over very easily, as though they are very low on compression. They start quite easily, and once running "low compression" is definitely NOT the case. How do they do that? Some sort of (taking advantage of) differential expansion of the sleeve/ring/piston), or what? So, far (knocks on wood), haven't had a bad (or even weak) one.
Yeah, there are. But most of my OS experience has been in the .40 to .61 range, and I haven't been very impressed -- at least not to the the tune of the advertising hype. When you get a good OS, you "usually" get a good one, but when you get a bad one, it's a disaster. that OS (at least through our "Local" HS does nothing about, even during the peeling liner craze. Besides, I'm more or less perpetually pissed at OS, and would be as likely to buy the newest chinese import.
I'll probably go with the GMS .32. Same weight and footprint as the .25, but with a bit more horsepower. My deceased friend tended to build beautifully (although sometimes heavily). This SS is covered in one of the iron-on "tex" coverings and has been lightly painted, so may benefit from a little more oomph than my monocoted version did.
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On Sat, 14 Oct 2006 11:09:05 -0400, "Ed Cregger" wrote in :
Let me know how the 'speriment turns out.
If you don't like the sound, I'd be happy to buy both of them from you at a premium used-once price. :o)
Reply to
Martin X. Moleski, SJ
wrote in
sorry its a bit long but this is how to set up the carb and as recommended by the UK importer a few years ago
Super Tigre carburetor adjustment procedure
The Super Tigre carburetor has two needle valves for adjusting fuel mixture. The # 1 needle is the high speed adjustment needle (on left as viewed from rear of engine, the needle closest to the fuel inlet nipple) . The # 2 needle (on right as viewed from rear of engine, and close to the throttle linkage attachment) is for slow speed adjustment. Newer Super Tigre carburetors have gone to a recessed screw in the barrel for slow speed adjustment. The idle speed adjustment screw is located to the left of the carburetor throat (as viewed from rear of engine). The screw on the right of the carburetor throat (as viewed from rear of engine) is the barrel retaining screw. Super Tigre carburetors have been maligned by some modelers as being hard to adjust and too finicky. My 30 plus years experience with Super Tigre engines has taught me to make any carb adjustments in very small increments, and once they are properly set they stay that way. If you are used to cranking a needle ¼ to ½ turn to try and improve a condition, you will never get a Super Tigre carb adjusted properly. I have had properly adjusted Super Tigre carburetors go from too rich to too lean in less than a ¼ turn of the low speed needle.
To set up this carburetor you will need a short piece (1 foot) of clean fuel tubing.
First the idle speed adjustment screw needs to be adjusted so that the throttle barrel is open about the diameter of a modeling T pin. Later after the idle and mixture has stabilized and the engine is mounted in the aircraft this setting can be backed off so that the throttle barrel will close all the way with low throttle and low throttle trim to kill the engine.
Open the throttle barrel wide open, then with the length of clean fuel tubing attached to the fuel inlet nipple, blow through the tubing. Screw the high speed needle in until you hear no air escaping. Now open the high speed needle 2-1/2 turns.
Now with the throttle barrel at the previously established closed position, gently blow through the tubing. Adjust the low speed needle in until you can barely hear air escaping. Now open the low speed needle ½ turn from this position.
Bear in mind if your change the position of the throttle stop you will have to reset the low speed needle. Also the setting on the high speed needle will affect the low speed transition. I have had the best luck trying to get a reliable idle and good transition with brand new Super Tigre engines after they are properly broken in. I have run as much a two gallons of fuel through Super Tigre ringed engines before the idle and transition stabilized to an acceptable level. The breaking in of a Super Tigre engine is time consuming and if not rushed, will reward you with an engine that should almost last a lifetime.
With the engine mounted on your aircraft it is time to start it. Fill the fuel tank and open the carburetor wide open. With your finger over the carburetor throat (and glow plug driver NOT CONNECTED) Bring the prop up on the compression stroke and slowly turn it through one revolution. You should see fuel flow into the fuel line and into the carburetor, flip through about two more revolutions with your finger over the throat. If when you remove your finger from the carburetor throat and the fuel in the fuel line flows back into the tank, this could be an indication that your fuel tank is too low relative to the carburetors center line. Go to low throttle, high throttle trim on your radio. Connect the glow driver and with a ckicken stick flip the prop through until the engine starts. Some of the hotter Super Tigre engines that I have had had a propensity to start in reverse. If this is the case try rotating the prop backwards against compression and letting it pop back. Usually the engine will start and run in the proper direction. If the engine starts and will idle fairly well, let it run for a minute or two to allow the engine to come up to operating temperature. Advance the throttle slowly to wide open. Listen to the engine and determine if it?s four stroking or two stroking. If it?s four stroking screw in the high speed needle until the engine transitions to two stroke. Now open the high speed needle until the engine just goes into four stroke. Back off the throttle to idle and have a helper hold the aircraft. With the helper holding the aircraft advance the throttle to wide open. Have your helper point the nose of the aircraft to the sky. If the engine speeds up to a stable two stroke, the high speed needle is set properly. If the engine is new, I generally open the high speed needle about 1/8th turn additional to ensure a rich high end until it?s broken in.
Once the high speed needle is set, return the aircraft to the level position and set the throttle to low throttle/high trim. If the engine is idling let it idle a few seconds then slowly advance the throttle. If the engine burbles, and it may spit fuel out the throat, it?s too rich. If this is the case, close (clockwise) the low speed needle about 1/8th turn. Run the engine to full throttle to clear it out then return to idle for 10 to 20 seconds then slowly advance the throttle. Repeat the above procedure until you have a smooth throttle transition. If the engine sags and hesitates with no burbling it means the low speed needle is too lean. Open (counter clockwise ) the low speed needle about 1/8th turn and try it again. This is the most time consuming part of adjusting any model engine carburetor so be patient. Once you are satisfied with the idle and transition return the throttle to wide open and recheck the high speed setting as per the previously outlined method and make the necessary small changes, then fly.
Note: Do not be tempted to short cut the break-in, burn at least a gallon of fuel with the high speed set rich. After break-in is accomplished do not try to adjust to the last few higher rpm?s, as this is the quickest way to turn your Super Tigre engine into a so-so performer (or worse) rather than a star performer. Also do not use the glow plug that came with the engine, substitute an OS #8 plug.
Some have reported that the venturi can be rotated from it?s straight down position to a slightly forward facing position to improve low speed transition. I have never encountered a problem that made this necessary, but it remains something to consider if all else does not give satisfactory results.
Reply to
On Sat, 14 Oct 2006 10:47:28 -0500, Bob wrote in :
The bigger engines may have a nicer exhaust note.
I dunno.
There were things called "Dyson rings" (I think) that were designed to expand against the cylinder wall under compression. Perhaps there is some effect like that even with regular rings?
I'm familiar with two OS disasters:
.46 FX -- peeling liners
1.20 Supercharged -- never figured out what we were doing wrong with that. We broke it bad and OS no longer supports it. It's a $750 doorstop. :o(
I don't like the LA's. I loved the FPs. They're almost bulletproof if you don't hydraulic-lock them.
TT GP series has got that covered.
Sounds reasonable to me.
Let us know how it turns out.
RJL/MECOA sells the GMS engines. You may be able to get $20 for your ST from them.
Reply to
Martin X. Moleski, SJ
While I cannot help with the ST.25 I do own a GMS .32. Early in its lifetime (maiden flight after break-in to be exact) it came into violent contact with a boulder. I replaced the cracked crankcase and ginched head (head was more for cosmetic reasons) and currently fly that engine on a "SPAD" pizza box flyer. Excellent power, response, idle, you name it. Same can be said for the GMS .76 ringed I have. I also am a fan of the SS and I fly an SS20 with an OS .25FP. I chose that engine from my inventory due to looks more than anything (plus it was shown as the engine used in the plans). I also had the choice of the GMS .32 and an Irvine .25. Didnt use the Irvine due to its red color which would clash with the Gold & Black Steelers color scheme. Didnt use the GMS as it hadnt been repaired yet. The .25 FP has enough power but I wish I had been able to use the GMS .32. I suppose I could retrofit the GMS but that would entail completely rebuilding the nose of the plane. Got that .25FP fitting in there too good!
Anyway, I think the GMS would be a good choice for your SS20 and parts are very easy to get from Tower. I might eventually bite the bullet and swap out the OS for the GMS. Eventually.
Reply to
Fubar of The HillPeople
The smaller GMS engines are not ringed. My .32 was literally "squeaky" tight at the top when I bought it. Its of the ABN, ABL, ABCDEFG, whatever it is, type of engine. My .76 is Dysen Ringed I believe. The ring has an "L" shaped cross section. The .32 sounds about like any other 2 stroke engine I have but the .76 (with the original GMS muffler) did have an odd note to it. Kind of a tinny ring. When buying a replacement from Tower I found out they are using a more conventional muffle style now. My .76 was purchased from MECOA taking advantage of their trade-in policy to unload a magnum xl .40 POS.
Reply to
Fubar of The HillPeople
That's "Dykes" ring, Dan.
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And speaking of that Meccoa trade-in policy, I also have a hopeless Magnum to trade in..... :-)
Good flying, desmobob
Reply to
Robert Scott
I appreciate the time you spent in answering my post (and yes, I still have the manual). However, unfortunately, BTDT. I actually burned a bit over a gallon of fuel on the test stand before even putting the ST in the plane. You are correct in your statement that the ST needles, especially the low-speed needle can be finicky. Once broken-in and tuned, the engine ran like a champ on the stand. Also, ran like a champ in the plane, at least on the ground. No evidence of overheating, so far as I could tell. No loading with prolonged idle, good transition, and excellent higher throttle response, and no ebvious evidence of leaning out in flight. My early thoughts were leaning out when the engine unloaded, but even running it rich didn't fix the problem. The problem would occur anywhere from 5 to 7 minutes into the flight, with the engine suddenly quitting. No sputtering first, as though it was going rich or lean, and not the very sudden stoppage I associate with an engine that is seizing. Breakdown of the engine never revealed any noticeable wear or scoring. Although I fiddled with the positioning of the spray bar, I really wasn't able to notice a difference unless I really got it way our of it's correct location. I tried many different glow plugs (and fuels), and settled on an OS#8 as it seemed to work best. This was all back in about 1985. After the plane was killed during a low-level engine stoppage with nowhere to deadstick it (bunch of big rocks), I tore down the engine, which still looked fine, oiled it up for storage, and it sat there until a few months ago. By now the engine has had probably 4 - 5 gallons of fuel through it. Tore it down and inspected it, reassembled it and re-tuned it, and it's back to its old tricks just as before (but did the air-testing on a SPAD this time). And yes, it got new gaskets, etc. I simply don't understand it. Runs GREAT on the stand, in any position, ditto in the plane whilst being held in any position, but about 5-7 minutes in the air it simply abruptly quits -- almost as though the fuel is being shut off very close to the fuel inlet. I've changed tanks, clunks, tubing and filters to no avail. About the only thing I haven't done is change the carb or put a pump on it - but would just replace the engine prior to doing that. I think my next step will be just to replace the engine, perhaps taking advantage of one of the trade-in programs. A bit of a shame, because when it's running, it runs very well, but I'm not willing to limit all my flights with it to 4 minutes.
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Yep, it was a GMS .76 that I was specifically referring to. Compared to the ABC, ABN, whatever, that most of my engines are, it felt to have poor compression when hand propped cold. I guess that's the difference the Dykes ring makes, because once this thing gets going, it appears to be producing very good power, and pulls better than any .60 I've used (other than a maybe an injected YS), and will keep up with some .90's. Lots of bang for the buck, although I haven't had mine long enough to know about their lifespans. Very easy to break-in and tune, also, IMO. My .76 GMS has the longer muff (?hush pipie?), so maybe this is why I don't notice the strange sound.
Based on dimensions, it looks like the GMS .32 will squeeze into the space currently taken on the SS by the old OS. I received some appropriately-colored "tex" material when I was given the plane, so any mods should look okay if needed.
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Yeah, I don't know why I'm such a fan of the SS series. Generally, I prefer pattern ships, but I really enjoy the SS's. I've been working into 3-D, but at this point don't think I'm going to enjoy it as much as pattern or just a good all around ship like the SS. I also enjoy more extreme acro like the Hot Canary and the Hots, but prop hanging and the like just doesn't do anything for me, at least not yet. Maybe as I get better....
I also enjoy kit-building, and hate seeing most everything going ARF, even though that's probably a cheaper way to go if you consider your time worth anything. I considered my building time a form of therapy. At least I still have quite a few kit boxes stashed away,
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Your description of it running fine on the ground but having problems in the air is the typical description of a model suffering fuel foaming from vibration.
As soon as the landing gear is lifted from the ground, the models tendency to vibrate at a given frequency changes, throwing off the needle settings beyond a human's ability to adjust in anticipation.
Isolating the fuel tank from vibration, or, in a worst case scenario, spritzing a couple shots of Armor All into your fuel and shaking well, will often cure this malady.
The Super Tigre engines had nothing wrong with them to cause such a problem. I think real world physics are giving you a hard time this time.
Ed Cregger
Reply to
Ed Cregger
The use of a Dykes ring in their construction would provide identical characteristics. I'm not aware if GMS utilizes a Dykes ring or not.
Ed Cregger
Reply to
Ed Cregger
"Ed Cregger" wrote
Excellent, Ed. I think you hit it on the head.
Time to more carefully balance the prop, and check to see that the tank is well padded with closed cell foam, not the other kind like that is found in chairs, and that there is not a long length of fuel line that is unsupported and vibrating like a string.
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That's an excellent thought, Ed. The tank was well encased with closed-cell foam. If anything it may have been wrapped too tightly. The lines were kept as short as possible, with no unsupported segments or loops that could flop around, both on the tank outlet (carb side) as well as as much as possible on the inlet (muff) side. At one point, I had been using a quick-fill valve, but removed that thinking that it may have been leaking either allowing pressure loss or bubbling, but that was removed long ago. I did use a sintered clunk, thinking that it might filter bubbles or foam out ahead of the true filter, rather than a standard clunk, but that obviously didn't help. However, I never thought to try a defoamer such as armor-all. I'll give that a shot, and I'll revisit the tank wrapping as well. It may be that I have the tank wrapped tightly enough for vibration to be transmitted in that manner (it's a very snug fit in it's present location). I never noticed foaming in the fuel line after a dead stick, but I don't really remember looking for it, either.
Your idea just makes more sense than anything else that I've been able to come up with, particularly when you consider the engine normally works so well up until the point that it quits, and that it only quits during flight. Even more indicting (in retrospect) is the fact that regardless of the flight time prior to the stoppage, the tank was usually about 2/3 full after the dead-stick (based on what was removed from the tank at the end of the flight).
Thanks for the ideas, and you can be sure I'll investigate this and let you know if it fixes things. I'm going to feel really stupid if this turns out to be the source of the problem. I do find it a bit strange that the same thing is presently happening during testing on a SPAD, where the foam wrap as well as the mounting is quite different. I'm using cool-power fuel, and don't have a foaming problem with any of my other ships, at least not so far as I know -- and certainly not to the degree to cause this problem.
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