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Author Topic: Inside loop during heavy wind: Wet plug causes engine flame out  (Read 391 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!

Offline 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 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

Offline 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, it’s 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 ethanol–diesel 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: Yesterday at 11:06:47 PM by Air Ministry . »

Offline 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: Yesterday at 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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