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Author Topic: Inside loop during heavy wind: Wet plug causes engine flame out  (Read 1319 times)

Offline Paul Van Dort

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Hi all, yesterday during a most enjoyabel contest in Orp-Jauche in Belgium, I had to fly in very windy conditions. Luckily no turbulence.
I like my engine setup. (ST51 with new piston ring, blocked boostport and low compression head. OS 6 plug, 5 % nitro, 23% oil 50/50 mix castor/ klotz) 13-5 Brian Eather undercamberd prop) .
This setup usually gives me a steady run, no acceleration on manoeuvers . Decent power. No issues between upright / inverted.

Yesterday during that windy flight, When entering the loopings, I heard the engine getting richer and almost cuting out. Finishing the loops was not an issue due to wind. However in the first loop of the vertical eigth, the engine quite at 45  degrees, so I had to make an inverted landing. Minimal damage thanks to the grass circle.

When I removed the plug, it was completely filled with fuel/ oil. The clear cause of the flame out.

Now I am wondering how I can avoid this in the future, without altering too much the setup I am now happy to fly with.
A hotter plug will affect the running and will cause the engine to run faster in manoevers. Something I don't want.
More revs with a smaller prop will reduce the phenomenon, but I like the big prop pulling the plane trough the air with authority

So I feel something has to happen with the combustion chamber, to block oil from killing the plug. Any suggestions?

Making the plug stick out further in the combustion chamber will be my first attempt in resolving this. eventually I can use a longer plug than the OS 6. Any suggestions?

Thank you for any help!

Online Dennis Nunes

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #1 on: June 20, 2022, 06:30:46 AM »
When I removed the plug, it was completely filled with fuel/ oil. The clear cause of the flame out.

Might it have been a plug that was dying or failed? Have you tried a new plug to see if the flame out happens again?

Dennis

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #2 on: June 20, 2022, 08:37:38 AM »
Might it have been a plug that was dying or failed? Have you tried a new plug to see if the flame out happens again?

Dennis

It is certainly possible that the plug quality was not optimum. I can try a new plug, but the test conditions will be more difficult to achieve in teh near futur. It was really blowing... Thanks!

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #3 on: June 20, 2022, 08:51:00 AM »
An other idea: Typically the squishband gap of an ST51 is a big 0.9 mm. reducing compression by adding gaskets can even increase the gap to 1.1 or 1.2 mm. Not good because this way the effect of the squish is reduced.
Therefore I think that reducing compression should happen without increasing the squishband gap. I even think that the squishband gap should be reduced to something between 0.3 and 0.4 mm to have the full benefit.
The only way to reduce the compression in that case is to make the dome higher. This will enable me to have the plug stick out a bit, protecting it from oil getting in.
Reducing the squishband gap requires some machining to the head, but my friend and clubmate Jef Lemmens has done this nicely on his lathe.. I still need to try it out....

Again finding the correct balance between compression/ glowplug heath range / nitro content/ squishband gap...   Interesting.  So much fun. Who needs electric motors anyway  :-)


Any takers on this?

Online Lauri Malila

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #4 on: June 20, 2022, 10:29:58 AM »
What plug are you using? A 4-stroke plug has a better thermal inertia, it may stay better hot in wet conditions.
Another possibility is a plug shield, press-fitted in combustion chamber.
Your squish band clearance is far too big to be fine-tuned to something that works well. I'd rather use a chamber shape that makes squish less critical. L
« Last Edit: June 28, 2022, 11:22:08 PM by Lauri Malila »

Online Brett Buck

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #5 on: June 20, 2022, 10:51:56 AM »
An other idea: Typically the squishband gap of an ST51 is a big 0.9 mm. reducing compression by adding gaskets can even increase the gap to 1.1 or 1.2 mm. Not good because this way the effect of the squish is reduced.
Therefore I think that reducing compression should happen without increasing the squishband gap. I even think that the squishband gap should be reduced to something between 0.3 and 0.4 mm to have the full benefit.
The only way to reduce the compression in that case is to make the dome higher. This will enable me to have the plug stick out a bit, protecting it from oil getting in.
Reducing the squishband gap requires some machining to the head, but my friend and clubmate Jef Lemmens has done this nicely on his lathe.. I still need to try it out....

Again finding the correct balance between compression/ glowplug heath range / nitro content/ squishband gap...   Interesting.  So much fun. Who needs electric motors anyway  :-)


Any takers on this?

      You are worried about using a hotter plug changing the way it runs, but are willing to cut away parts of the head and otherwise radically change the compression?
BTW, this might actually work because you would have to run the engine much leaner due to the extreme loss of power your head mod would induce. But it would also greatly alter the run quality.

       In any case, I would strongly suggest using less oil, and in particular much less castor. If I run 22% 50/50 oil, my engine does something similar. 22% 5/17 castor/synthetic is fine and 18% 50/50 is also fine (although they run differently). An ST51 probably does not benefit from excess castor oil. It is a lot easier than cutting something and easily reversible.

     I also note that you have greatly reduced the power with the other modifications, so it's not that surprising that something bad happens when extremely unloaded.

       Brett

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #6 on: June 20, 2022, 01:11:14 PM »
      You are worried about using a hotter plug changing the way it runs, but are willing to cut away parts of the head and otherwise radically change the compression?
BTW, this might actually work because you would have to run the engine much leaner due to the extreme loss of power your head mod would induce. But it would also greatly alter the run quality.

       In any case, I would strongly suggest using less oil, and in particular much less castor. If I run 22% 50/50 oil, my engine does something similar. 22% 5/17 castor/synthetic is fine and 18% 50/50 is also fine (although they run differently). An ST51 probably does not benefit from excess castor oil. It is a lot easier than cutting something and easily reversible.

     I also note that you have greatly reduced the power with the other modifications, so it's not that surprising that something bad happens when extremely unloaded.

       Brett

Indeed, in heavy wind the engine is unloaded, causing enrichening, which helps in braking. Combined with the inertia pushing the oil to the top of the cylinder and the plug suffers. I have the impression that the engine is now more powerful  than the original, especially in the range I want to use it (more torque). It pulls the 2 kg model with authority in a burpy 2 stroke, keeps a steady run, resists running away in loops etc. I only never tested it in such a heavy wind. So I will take into account all the suggestions. In 1996 at the Wch in Sweden, I used a 11.5 x 4 APC on the ST51, running in much faster modus of course . But I was not able to control the power and the risk on a runaway was always there.  It suddenly could take off for 4 seconds lap times. Now I am happy with the stability. And the experiments are great fun. I will keep you posted. Thanks for the feedback.

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #7 on: June 20, 2022, 01:16:00 PM »
What plug are you using? A 4-stroke plug has a better thermal inertia, it may stay better hot in wet conditions.
Another possibility is a plug shield, press-fitted in combustion chamber.
Your squish band is far too big to be fine-tuned to something that works well. I'd rather use a chamber shape that makes squish less critical. L

If I am not mistaken this seems to be a retro discovery engine? It is clear that the combustion chamber has a specific shape to keep oil from entering the glowplug. Very interesting. The "drop catcher" is really special...

Online Lauri Malila

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #8 on: June 20, 2022, 01:48:31 PM »
No, itís not a Retro, but some details are indeed stolen from Yuriy. L

Offline Air Ministry .

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #9 on: June 20, 2022, 10:50:32 PM »
( if your a pesky rush rush type . go to bottom & up 13 to SUMMARY . We assume others are entralled by deatailed explanations .   :##   LL~   ;)  )

Guess ive flown the G - 51 as much as any other engine , this century , at least .

Had one in a 2 kilo ' Hurricane ' thing running a 13 x 5 or so APC 'dagger 'prop .
Usually run 5 pitch but 10 or 11 or 12 , 3 or 4 blade , 12 x 5 2 blade T F wood .

HOWEVER , as Brett says !  OIL .

First hour or twos running , the 30 / 25 oil indeed . But the most run one , ive
used a lot of cheap ?? comercial fuel . Hot Stuff etc etc ( brand ) which might be 18 % oil .
So cunning sods actually go by the WEIGHT im told , to write a larger number on the lable .
20 % Weight isnt 20 % volume , we're told .
Whatever .
This Engine has NO WEAR on the RING . Sits at 5 thou. clearance , on a recent strip & inspect .
Mustve used say 10 Imp. Gallons so far , not a lot but not insignificant .

TWO THEORIES ive read ,
1/.  Backplate radial gap - Fuel Oil accumulation - Ungloops under high strees ( like you get in wind )
and ' dumps ' Rich cut & plug foul results .

Maybe so . Particularly with excess oil .

2/. Excess oil . theory . 18 % recomended . ( from my observations this is no problem at all . WEAR
is not going to be an issue . Grit Ingestion is to be avoided - screen on intake if 'desert / dusty 'use ! )

same bleedy issues , up in the backplate & dumps , so we're told .

3/. Mangey pattern Enya Plugs ! these work for six runs . If your lucky . Then do as yours does .

SO MATCH YOUR PROBLEM PRECISELY .  While we're on PLUGS , if theyre white & chalky , theyre past it, and'll DO THAT .

4/. BEARINGS . Ive had to replace 10 year old bearings . As they DO THAT . If the bearings feel at all notchy in the least
this could well be the problem . Ive had it . story is minute metal particals 'short out 'the plug . Like they do . Not Unusual .

My engines are always afterun oiled . but if youve an 'of season 'where it is UNFLOWN , unless its been thoroughly rinsed , the NITRO RESIDE
is CORROSIVE , hence disintegrateing bearing surfaces - forign matter - metalic - Plug trashed . Litte brown or black speks on the element .

So there we are .

Start up , aFTER AFTER RUN OILED , ive found if I pull the plug ( Its OILED ) flush it , and give the engine a generous flooding prime , say 20 cc .
turn through 10 times then belt through / spin over ten times . WELL , six at least of each , anyway . She fires up straight of , into a clean run .

Whereas if you dont the after run oiled plug aint gunna do the trick till its cleared after faffing around some time .
While where at it , the 'element Pushed Back 'into the plug - is generally said to be from to much Comp. ( ratio ) .

however , Uncleared of storage oil , the hydraulicing can do the same thing . Push the element back into the glow plug .

So there you are . SUMMARY . 18 % oil is plenty ( at least untill 30. C. Atmo temp . maybe add a iota in a heat wave )
                           =======
Your best with at least 3 % Castor or Syn. as precaution . Usually Half Each Syn. &  Castor is a safe bet .

PLUGS . Check Them . White & Chalky element , its trash for stunt .

Watch yer Bearings - Theres no uva real ''issues 'wiffem .
====================================

My only rotten run thing was into insides in owling gales . Stock Intake about level with the 3 inch spinner edge .
A sort of rich cut ? baulk , hestitation . Into up leg of inside squares . When it were windy as eck , near two hand
stuff . Like 18 Kt costal , hard & billowing . Old on tight & dig in your heels stuff . Mightve been 'Cumulative'

Bob Gieske & cohorts ( one stunt fuel supplier ) ran some ( a few % ) of 'keep it going 'range extender STUFF ,
not ipa or petrol . Slips my mind at the moment . But was definately 'anti flame Out '. Bob Hunt was in league with the supplyer so should recall the stuff . Maybe Lighter fluid ?

Versatile engines these G-51's . But the first thing I did on my Bunged Boost one was UNBUNG it , merely a personal preferance , an 'as its made 'is goodenough .'
Only Other Issue I can see with them , is a big tank level with the stock spraybar in the venturie , vertical mount . Close in . Could Obstruct 'through flow 'of cooling air .
The Big Jim / Urtnowski . And by Bob Gialdini , Cowl Top ventilation , to stop percolation / fuel vapouriseation . Parked . For good restarts & running case pump efficiency
in worth a thought .

 H^^

Offline Air Ministry .

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #10 on: June 20, 2022, 11:06:47 PM »
AND you didnt mention if you run MUFFLER PRESSURE ,

First , If shess pullinglike blazes , on the wires , into the loop , The conflicting forces - can push the fuel ' DOWN ' in the tank . Its early in the run - so the fuel level is UP .
Also if its FREEZING weather , the whole L.J.K. Setright '  thermodynamics - a engine is a series of holes = the metal is just there to hold them in place - trip , isnt
thermodynamicing as it should . Hence the need for IGNITER ( as oposed to oxegenation / Nitro )

But a G 51 can fly 2 kilo on 80 cc of fuel , for the pattern . Nitro is hardly  NECCESARY . Gets to 'operating temp. / fuel consumption stuff . But understanding it 'no nitro 'helps maybe .
If freezing could be 'overcooling 'too.

Anyway , with the wee tank in ROUGH air , it keeps a more even fuel feed pressure . Bulbous Fuel FILTER Posn . Can act as 'dump 'feed too .

Oviously youve too much oil Though . And check yer plug . AND BEARINGS .  %^@

Offline Air Ministry .

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #11 on: June 21, 2022, 07:58:35 PM »
Other THINg'd do it .

Big Bore ( 3 / 32 ) thin wall brass tank uniflow / vent tube . Head ' G 's Surge .

1 mm bore tubes best , or 1/16 copper plubrs tube . Whole Length .

Known Fact .

Bumpy air & your rooted if its not .

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #12 on: June 22, 2022, 04:20:18 AM »

1/.  Backplate radial gap - Fuel Oil accumulation - Ungloops under high strees ( like you get in wind )
and ' dumps ' Rich cut & plug foul results .

Maybe so . Particularly with excess oil .

2/. Excess oil . theory . 18 % recomended . ( from my observations this is no problem at all . WEAR
is not going to be an issue . Grit Ingestion is to be avoided - screen on intake if 'desert / dusty 'use ! )

same bleedy issues , up in the backplate & dumps , so we're told .

3/. Mangey pattern Enya Plugs ! these work for six runs . If your lucky . Then do as yours does .

SO MATCH YOUR PROBLEM PRECISELY .  While we're on PLUGS , if theyre white & chalky , theyre past it, and'll DO THAT .

4/. BEARINGS . Ive had to replace 10 year old bearings . As they DO THAT . If the bearings feel at all notchy in the least
this could well be the problem . Ive had it . story is minute metal particals 'short out 'the plug . Like they do . Not Unusual .

My engines are always afterun oiled . but if youve an 'of season 'where it is UNFLOWN , unless its been thoroughly rinsed , the NITRO RESIDE
is CORROSIVE , hence disintegrateing bearing surfaces - forign matter - metalic - Plug trashed . Litte brown or black speks on the element .



Thanks fo the feedback. I was not able to understand everything you wrote as English is not my first language but I get most information

1.I think it should be easy ro make the backplate radial gap smaller. I will give it a try.
2. Oil content. I will reduce the percentage and/or go with more synthetic than castor
3. Plug looks god, but I can experiment more .
4. Bearings feel ok.



Start up , aFTER AFTER RUN OILED , ive found if I pull the plug ( Its OILED ) flush it , and give the engine a generous flooding prime , say 20 cc .
turn through 10 times then belt through / spin over ten times . WELL , six at least of each , anyway . She fires up straight of , into a clean run .

Whereas if you dont the after run oiled plug aint gunna do the trick till its cleared after faffing around some time .
While where at it , the 'element Pushed Back 'into the plug - is generally said to be from to much Comp. ( ratio ) .



I use afterrun oil after every session. Before the first flight of the day I start the engine upright on 1 or 2 primes. This should get the afterrun oil out without "punishing" the plug.


Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #13 on: June 22, 2022, 04:23:08 AM »
AND you didnt mention if you run MUFFLER PRESSURE ,

First , If shess pullinglike blazes , on the wires , into the loop , The conflicting forces - can push the fuel ' DOWN ' in the tank . Its early in the run - so the fuel level is UP .
Also if its FREEZING weather , the whole L.J.K. Setright '  thermodynamics - a engine is a series of holes = the metal is just there to hold them in place - trip , isnt
thermodynamicing as it should . Hence the need for IGNITER ( as oposed to oxegenation / Nitro )

But a G 51 can fly 2 kilo on 80 cc of fuel , for the pattern . Nitro is hardly  NECCESARY . Gets to 'operating temp. / fuel consumption stuff . But understanding it 'no nitro 'helps maybe .
If freezing could be 'overcooling 'too.

Anyway , with the wee tank in ROUGH air , it keeps a more even fuel feed pressure . Bulbous Fuel FILTER Posn . Can act as 'dump 'feed too .

Oviously youve too much oil Though . And check yer plug . AND BEARINGS .  %^@

I no longer use muffler pressure as it made the needle too sensitive. There also was some richening as the flight progressed. Both problems solved when going to atmospheric pressure. I reckon the Stalker muffler I use on the ST51 generates too much pressure.
No filter between tank and engine. The fuel is clean before it goes into the tank.

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #14 on: June 22, 2022, 04:24:56 AM »
Other THINg'd do it .

Big Bore ( 3 / 32 ) thin wall brass tank uniflow / vent tube . Head ' G 's Surge .

1 mm bore tubes best , or 1/16 copper plubrs tube . Whole Length .

Known Fact .

Bumpy air & your rooted if its not .

I did not catch that completely. Are you making the vent tube smaller to have less effect on the fuel pressure from the changing airspeed?

Offline Dennis Toth

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #15 on: June 22, 2022, 08:14:31 AM »
This is an old trick that is meant to reduce the uniflow pressure upwind/downwind variations by using a smaller vent opening so the partial tank vacuum is less impacted by a strong wind force. It works on some ships.

Easy way to try it is to make up short pieces of various size tubing and install it on the uniflow vent line with a small piece of fuel line. You could even solder one end and drill various sizes down to very small. They used to do this to make pressure taps for crankcase pressure through the tap to adjust the amount of pressure.

Best,   DennisT

Offline Air Ministry .

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #16 on: June 22, 2022, 08:36:58 PM »
Wottitis , Pressure / Head / Flow - SURGE .

A open ended can , Shaken .

A Can with a Pin Hole & a 6 in tube , shaken !

Both 2/3 full of fuel . Er , the results fairly obvious .

======================================================

A short deep tank / The Pressure Head over the centerline , under high ' G ' , is sudden .

So instanter , the ' feed ' , at the spraybar - has a sudden pressure / flow surge . Rich Cut .

Tho a neoprene vent line cap , melted over , with a pin hole helps . The full length off the vent tube at  say 1.2 m.m. bore , I consider gives the most stable run .

Really , the only way youll beat it , if you fly in costal storm air , is perhaps a Chicken Hopper Tank . Where the supply feed is ( Hopefully ) so small and removeed ! ? from pressure surges
that life goes on as normal .



Id ended up going to 4 in pitch for flying in gales , to get a bit of punch in 20 knot gusts .
The G 51 sounded musical , the case resonateing as if it were on the road to blowing the cylinder off . ( have a G 45 ABC s/h to try 4 in pitch on ) G 51 your stuck around 5 in. pitch . perhaps .
So threw the Irvine RE 40 in the Spit . But the funny noise was the cracked pushrod end . Prior to that It'd seemed to ' lock in '  good , But Flaps Only out of the wingover wasnt entirely sucessfull .

G 51 MB 3 Flew good in a big wind , but big gusts need steering through  in manouvres , when your hatless . Threw in a Torpedo 40 with perry pump . some resolutions but not 1.000.000 sucessfull .

We have to settle for excellent , as few are perfect . ( no matter what Honda Says . )

The COMO 51 is a drop in for the G 51 . and is a FOUR INCH PITCH Motor . BUT the ( crank ) nose is short ( spinner nut issue with thick spinner backplate ) and the prop drivers 1/4 in. Aft or G 51 .
As Randy Smith says theyre " The Best Supre Tigre Stunt Motor " we will put a picture on . Essentially Ex G 40 case Version BIG SHAFT  P.D.P. baffled  Kin to Last P D P ST 60 V but G 51 Size .



But this is getting rediculous ! Unless youre going to fly when the wreckage will be blow into the next county , Dont get strung out .
If your into really rough bumpy air , try playing chicken - hopper .
If its COLD try Bob Gieske's Patent GO restorer .
And get rid of the oil . If its Quality 18 % , no more'n 23 % ( 20 C / 3 Syn . ) for heat wave conditions ! .

Quote
Coleman fuel (called Shellite in Australia) is a form of very pure petrol but only has an octane rating of 50-55 so wouldn't take kindly to too much ignition advance. However it's a mineral fuel while castor is vegetable based so can't mix together. Acetone is a cosolvent which allows them to mix. Same goes for diesel fuel where kerosene (mineral base) has castor but, happily, the necessary ether is also a cosolvent.

Actually , acetone is usefull in damp humid weather to absorb moisture . And WE DONT LEAVE THE FUEL CAN CAP OFF , do we ! ( Still looking to Autenticate - I D wot it was I thought . )

(m Ho Kay , and I hope weve got this RIGHT . Bob says AMYL   ACETATE  was what they used , pre pipe era . I think 2 % .

oh dear . -Octanol is the most effective surfactant compared to biodiesel and ethyl acetate for stabilization of ethanolĖdiesel fuel blends.
                                                                                                              -----------------
Might get into my FILES and check period info to a authenticate . Think its in the 40 FSR stuff or Gieske .)

INKOREKT !  Dont swear by the previous THREE lines !

« Last Edit: June 24, 2022, 11:06:47 PM by Air Ministry . »

Online Brett Buck

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #17 on: June 23, 2022, 01:08:32 AM »
This is an old trick that is meant to reduce the uniflow pressure upwind/downwind variations by using a smaller vent opening so the partial tank vacuum is less impacted by a strong wind force. It works on some ships.

Easy way to try it is to make up short pieces of various size tubing and install it on the uniflow vent line with a small piece of fuel line. You could even solder one end and drill various sizes down to very small. They used to do this to make pressure taps for crankcase pressure through the tap to adjust the amount of pressure.

Best,   DennisT

  If you want a neutral pressure inlet, I suggest (as in another recent thread) a blanking plug with very small (like #50) cross-drilled hole, which is pressure-neutral.
 
    But, again, I think we are looking for really complicated solutions when a far simpler and far less invasive seems obvious - if you really think it is loading up on oil, put in *less of it*. On the surface, it seems to directly address the problem you have, not to mention not gumming up the engine with unnecessary varnish over time.
 
    Brett

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #18 on: June 24, 2022, 11:13:40 PM »
May 81 Flying Models .

C?L Stunt .

Bob Hunt .
K P Stunt Fuel . Ken Purzysck .
FUEL . 2 % Propalene oxide .

BEWARE . This may / might ( delete as Reqd . ) Turn you hair grey , have your eyes fall out , contibute to global warming , the black holes in the universe & the end of mankind , as we know it .
Propylene oxide is an acutely toxic and carcinogenic organic compound with the molecular formula CH₃CHCH₂O. This colorless volatile liquid with an odor similar to ether, is produced on a large scale industrially.

Might be better to stick to Shellite or Lighter flluid ( Which is I think the Bob Gieske trip .

N. B. The Adamisin tribe consider OIl to lower the octane , reduce the volitity of the fuel , the power , and the economy .
Therefore 18 % and itll boggey along nicely .

So Less is Best

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #19 on: June 28, 2022, 07:19:31 PM »


FUEL .

Quote
and don't go beyond about .010 head clearence if you can. Don't load it up with a lot of oil. Oil lowers the octane of the fuel and causes detonation which can lead to heat. My nephews engines have never been run on more than 18%  pure ucon. fp's hate castor.......... We also use an assymetric combustion chamber which runs a cleaner four cycle. We use venturi dia's from .281 to .312 depending on the power required with St needles. Props have been easy: 11x6 Power Prop (no longer available) to very special: 10.5x5.25 Eather three blades. Uni-flo tanks with muffler pressure.

DAVE ADAMISIN . https://stunthanger.com/smf/engine-set-up-tips/os-40-fp-set-up-q's/msg569552/#msg569552

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #20 on: June 29, 2022, 02:00:05 AM »

FUEL .

DAVE ADAMISIN . https://stunthanger.com/smf/engine-set-up-tips/os-40-fp-set-up-q's/msg569552/#msg569552

"don't go beyond about .010 head clearance"   in the positive or negative direction?

Online Lauri Malila

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #21 on: July 02, 2022, 01:23:55 AM »
"don't go beyond about .010 head clearance"   in the positive or negative direction?

 Paul,

 I think in that case you shouldn't go to less than 0,01"/0,25mm. I don't know what propylene oxide does for combustion behaviour, but in my experiments with my bigger (.77) engine, I've gone safely down to 0,2mm squish clearance (parallel squish, 40..50% area). In our low revving engines that seems to be a safe mechanical limit, even during much higher rpm that you'll never (hopefully) experience during flight.
But as usual, there is no universal answer and experimenting means a lot of work by the lathe and at flying field, if you really want to isolate and understand the effects of squish- and head volume changes.
But, in a non-piped engine with no shortage of power, I came to conclusion that it's better to use a combustion chamber design with no squish effect, or a very mild squish effect.
The problem with squish, as I see it, is that in varying load and temperature and natural cycle variance of a stunt engine, you cannot expect a stable combustion- and flame propagation behaviour from a squish head.
With my current combustion chamber shape, I have a very logical combustion behaviour between 0,5 and 1mm squish clearance, that makes life sooo much easier.
If I still want to (I certainly do) continue experiments with squish band, then I want to make a head with fixed squish clearance and individually adjustable combustion dome volume. L

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #22 on: July 03, 2022, 10:42:15 PM »
Quote
"don't go beyond about .010 head clearance"   in the positive or negative direction?

thats in the FP 40 direction - s ! .  ;D

In orstrawla , the theory is = 1 per 5 % nitro . Checking one I run on anything , I found TWO in it . Gaskets .

Kiwiland and No Nitro , one head gaskets fine , if its STOCK SPEC .

The general theory is High Comp. gets a HARD break , Low ( ering ) comp. gets a SOFTER break . This is assuming powers adequate .
Ive had no trouble around 2 kilo with a G 51 . But 80 ounce Strega was a step to far .

the Black Tornado 10 x 6 3 blade ( actual 5 or so pitch ) snarls away supurbely . However a 10 x 4 ditto has a harsh resonant echo . to say the least . Pre Ign. Im told . Needs a few extra gaskets there then
on 4 in pitch .

hook up the link to the Big art FP 40 , with its blocked boost its not incomparable to your G 51 set up . Incidently , all the late 4 bolt big fin 40 / 45 / 51 heads interchange - for various combustion chamber
bowls & squish band widths . Tho ive only tried it ' on the bench ' .

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #23 on: July 03, 2022, 10:48:34 PM »
Hers their FP 40 head . the flat piece adjacent the blocked boost .



AS THEY SAY , they were trying for " Traditional " engine runs , in the early scneurle era . round 1980 .

WHAT the head did , they say , is STEADY The FOUR STROKE Cycle . Its a head insert . If someones running a G 51 steady in the four stroke ,
with a blanked boost port passage , youd think a similar head would do it there ( steady the 4 cycle ) If it needed steadying .

The " 10 thou. " relates to this HEAD primarily .

Offline Steve Helmick

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #24 on: July 04, 2022, 07:08:45 PM »
I'm skeptical of statements about oil being stuck somehow, suddenly dousing the glowplug.

First thing I would do is fit a 4-cycle glowplug. If the ones you get have a shield of some sort, then be certain it clears the piston. Note that OS glowplugs (some models?) are now metric in length, so probably don't come flush with the combustion chamber surface. Don't know about Enya or other manufacturers...all I've ever used were made in USA, either Short or Long reach. A short plug in an engine designed for long plugs will barely run, so I'd speculate that a medium length (i.e., metric like the OS) would not be optimal.

I'm curious why you don't run a fuel filter? We never did back in the 1960's, but I'm also not sure there were any available. So far, I like the Sullivan "Crap Trap". A new one every year works. Make certain you pay attention to which direction fuel flows through it...it matters.

NEVER run a gasket between the muffler and engine!  H^^ Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #25 on: July 05, 2022, 05:02:49 AM »


I'm curious why you don't run a fuel filter? We never did back in the 1960's, but I'm also not sure there were any available. So far, I like the Sullivan "Crap Trap". A new one every year works. Make certain you pay attention to which direction fuel flows through it...it matters.

NEVER run a gasket between the muffler and engine!  H^^ Steve

I fill my 2 liter fuel container via a coffee filter. The  container is never opened, except when filling it. The pickup of the fuel in this container is about 2 cm above the bottom to avoid picking things from the bottom. and there is a big filter in the tube towards the handpump. I am confident that the tank contents is super clean and I take good care avoiding debris while filling the tank .

A fuel filter can get contaminated , affecting the NVA setting. I never used a filter in the last 25 years.

And absolutely no gasket between muffler and engine. A perfect fit and good heath transfer.

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #26 on: July 05, 2022, 05:17:19 AM »


       In any case, I would strongly suggest using less oil, and in particular much less castor. If I run 22% 50/50 oil, my engine does something similar. 22% 5/17 castor/synthetic is fine and 18% 50/50 is also fine (although they run differently). An ST51 probably does not benefit from excess castor oil. It is a lot easier than cutting something and easily reversible.

     I also note that you have greatly reduced the power with the other modifications, so it's not that surprising that something bad happens when extremely unloaded.

       Brett

The switch from 11/11 to 5/17 was painless and not affecting the way the engine runs. So that will be my new mixture. I did not test in the wind yet. But I am optimistic.
I did test with a reduced squish gap and a larger (higher) combustion "bowl". Very powerful but with a higher fuel consumption because I had to run it richer. Different running characteristic  inside versus outside rounds. Nothing dramatic.
Then a test with hemihead with almost no squishband: Less powerfull, but very stable in a burpy 2 stroke. Low fuel consumption. No difference in feel inside compared to outside rounds. This leaner setting also can help avoiding my flame out issue in the wind. To be proven :-)  So many things to test. So little time :-)  Fun!

Offline Steve Helmick

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #27 on: July 06, 2022, 03:24:34 PM »
I fill my 2 liter fuel container via a coffee filter. The  container is never opened, except when filling it. The pickup of the fuel in this container is about 2 cm above the bottom to avoid picking things from the bottom. and there is a big filter in the tube towards the handpump. I am confident that the tank contents is super clean and I take good care avoiding debris while filling the tank .

A fuel filter can get contaminated , affecting the NVA setting. I never used a filter in the last 25 years.

And absolutely no gasket between muffler and engine. A perfect fit and good heath transfer.

Yes. I'm pretty sure that's what they're supposed to do!

I see you're not using muffler pressure anymore. I hope you have an air filter on your uniflow air inlet. I've found lots of tiny bugs and seeds in my filter...if I don't do one or the other. If you have some clogging (not the dance type!) in the NV and suddenly it clears out itself, it's going rich, right?

Another potential problem is if your engine swallowed a bee or similar...as I witnessed happen to Ted Fancher. I like to run at least one layer of nylon mesh over the venturi inlet to prevent that sort of rot.  H^^ Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #28 on: July 07, 2022, 08:55:43 AM »

I see you're not using muffler pressure anymore. I hope you have an air filter on your uniflow air inlet. I've found lots of tiny bugs and seeds in my filter...if I don't do one or the other. If you have some clogging (not the dance type!) in the NV and suddenly it clears out itself, it's going rich, right?



That's a good point. Never thought about that.

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #29 on: July 07, 2022, 10:42:09 PM »
With your no. 26 post ,

the tank hight if you stuck to the uneven one , can get varying things from varying things !

Like a change from tube ( uneven ) to Toungue , got it even ! ! ( Bizarre ! ) . obviously , if
you did stick to that set up , youd reshim the tank to suit . Theres a thing .  n~

What I was going to say . . . Aus. a lot use steel ( tin ) clunk tanks , your conventional tin
tank , with dual tubes to a dual clunk . some openable , a can top removeable for replacing
the flexable fuel lines in it .You dont stand the plane on its nose - using clunk tanks .

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #30 on: July 08, 2022, 02:31:54 AM »
With your no. 26 post ,

the tank hight if you stuck to the uneven one , can get varying things from varying things !

Like a change from tube ( uneven ) to Toungue , got it even ! ! ( Bizarre ! ) . obviously , if
you did stick to that set up , youd reshim the tank to suit . Theres a thing .  n~

What I was going to say . . . Aus. a lot use steel ( tin ) clunk tanks , your conventional tin
tank , with dual tubes to a dual clunk . some openable , a can top removeable for replacing
the flexable fuel lines in it .You dont stand the plane on its nose - using clunk tanks .

I indeed experience that less obvious parameteres can affect the  inside -outside  engine behaviour. Mufflers are a good example but also plugs, fuel, venturi size, prop size - engine RPM...
I stick with the clunk tank. I like the engine shutting off 5 laps after the clover leaf :-) 

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #31 on: July 24, 2022, 03:35:28 AM »
Yesterday I was flying the setup  where I had the flame out issue with.
Differences:
1. About 13 degrees celsius hotter. Humidity about the same
2. Fuel from 11/11  to 7/15  Castor/ Klotz

Issues: I did not experience any braking from the engine. It used to stay in a burpy 2 stroke in the loops, but yesterday it took of in a 2 stroke, returning slowly to the correct setting.

Obviously heath is the problem. Switching to a medium fireball plug gave a less stable run, so I quit that idea. Perhaps an OS8 plug might have been better.

So my main question is how to re-establish the braking properties of the ST51.

My options as I see them:

- More oil or just a higher castor percentage?
- A smaller prop. E.g. 12-6
- Less compression?
- More compression with a medium plug?
- ...

Hope you guys can give me more inspiration.

Sorry to hear the issues at the nats (Thunderstorm and crashes)


Online Lauri Malila

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #32 on: July 24, 2022, 06:47:19 AM »
-Smaller prop/improved cooling. Especially in hot weather the engine has no time to cool after the loading part of manoeuvre, and instead of going rich when it unloads, it starts burning the residual fuel in the system and accelerates. This is also typical when using a too big prop. Try something like 12x5...6" 2-blade.
-Higher compression.
-Hotter plug (if CR allows). Try OS A3 or LC3 if head design allows (LC3 is a long reach plug).
-Less or thinner oil, if engine construction allows.
-I very rarely touch the CR or Venturi after initial tests/calculations, but play more with prop pitch. But in very very hot weather I may change from Ý5,3 to Ý5,4mm venturi. Then I observe very carefully the engine sound/possible increase in vibration. if it detonates too early, I add a 0,02mm shims until it stops detonating.

It's difficult to say for sure without knowing more, but what you describe sounds logical after your "improvements" to the combustion chamber shape. You have effectively narrowed the top of power curve. L

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #33 on: July 24, 2022, 11:37:28 PM »
INDEED . Dead Stock theyre fine . The 12 x 5 Top Flite ( NOT the power point ) is good . The bundled drone ones ! . You want good grain though .

Pinching the fuel line the rpm should , after release , drop straight back . A big 13 x 5 or 6 APC would get swung , but NO ' powerband / Switch .

I wouldnt trim down past 11 5/8 in Dia . Tips'll wear in grass !



If this is the 10 x 6 3 Bl Tornado / Grish , itll snarl away in a perfect run . The Master 3 bl are weightier & thicker , but a 11 x 5 , maybe trimmed , might be o.k.

Id do a big blow with long tube on your tank . If its a CLUNK the weight can have KINKED the fuel tube , or twisted in . And youre shot . Sounds like it could be it ! ??

Muffler Pressures almost mandatory in rough air , in my opinion . FRILLING 1.5 mm through the spray bar & fuel hole in it , can improve NEEDLING & run .

If its had over TWO HOURS USE , Id Doubt over 20 %oil is a good idea . You need to get FUEL throught to cool it . Alcohol . ' The Book ' says 11.000 rpm on a G 51 STUNT .

Think your trying to run it uphill in top gear , sluggish & no throttle rsponce . Try Chhangeing Down a gear ! Look at the PROP MASS , ( weigh it ) If you halve the mass . its going to GO . Good .

Nuther instance is Dual 11 x 5 4 blade , Itll run it , but the power bands all to buggery . flat & soft , no step , up or down . 13 in. your overpropped on a G 51 . 12 x 5 max , the 10 x 6 3 blade is 5 true pitch .
4 3/4 to 5 1/4 is my observation on what they behave well on , at around 5.0 per lap around 65 + to 70 lines . They haul .018s fine like that .

ALSO , I find normally theres 3/4 turn on the needle , between full solid 4 stroke thru into full solid 2 stroke . The best way to SET IT , is do that . then . Go Back 1/4 turn ( from solid 2 stroke .)

It may be a touch under or over dead right , but darn close . for a TEST . ( setting it ' off ' the 4 stroke setting is TO DECEPTIVE , you want to get a steady 2 stroke , motors then hot ,
then go back 1/4 turn richer . Or you can hunt about all day for a setting & get nowhere )

Stick a little prop on & let it H O W L , it not a steam engine .
« Last Edit: July 25, 2022, 12:14:11 AM by Air Ministry . »

Offline Paul Van Dort

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #34 on: July 25, 2022, 03:47:07 PM »
Any experience with OS 6 and OS 8 glowplugs? Next experiment is with OS 8, replacing the OS 6.

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Re: Inside loop during heavy wind: Wet plug causes engine flame out
« Reply #35 on: July 25, 2022, 11:10:43 PM »
HACTUALLY !  na na na naarrgghh !

The Lew Woolard Silver Fox 40 Schneurle ! info , goes on about , I think its .180 MAX piston Crown to glow Plug . Or it stops & wont work .

The big write up was in Stunt News . as youve got a Hemi head / i wondered if the ' plugs up ' beyond a usefull hight . at T D C .180 max gap !


-------------------------------------------------------------------------------------------------------------------------------------------------------------------

Also wondered if youve tryed a 4 stroke plug ?



Only real trouble with plugs is cheap nasty Enya copies which might do six flights before they emulate yours . CUT going level outta loops . Or short battery leads popping them as it kicks . :(

Quote
Sep/Oct 95 issue of Stunt News has a good article on Lew Woolard's Silver Fox mods for the 40.

for plug / piston clearance data .


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