Super Tigre 90 Quits When Inverted?

[craig procter]

I seem to be for ever having problems with this old glow Super Tigre 90. I have have been having so many problems with it being inverted on the plane that I have had to bench run it and adjust the needle settings as to get it to run nice but as soon as I turn it upside down it quits again.

 

I have taken it apart, cleaned it and inspected it, checked the spray bar positioning, etc.. but the dam thing will still quit when inverted.

 

It seems that if the glow stick was permanently attached to the glow plug it would then stay running. I've heard of these onboard glow units before but I believe they only stay on for about 20 seconds. Is there away to have it set so the glow plug is constantly getting power from a battery?

Edited June 2, 2022 by craig procter
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[Jason Channing]

Try an OS F plug, hopefully should clear the problem.

 

[Simon Clark]

Onboard glow devices such as those supplied by Model Radio Workshop switch the plug on at low throttle settings and are not time limited. You can adjust the switching point easily. They also turn off when you apply throttle cut. I use them in every glow plane I have except for club32 pylon racers ans swear by them:

https://modelradioworkshop.co.uk/product-category/glow-plug-switch-devices/

I also agree that OS F plugs are the best for this size of engine

Simon

[Ron Gray]

Where’s the tank position in relation to the spray bar as the symptoms you have posted suggest that the plug is getting flooded.

[craig procter]

7 hours ago, Simon Clark said:

Onboard glow devices such as those supplied by Model Radio Workshop switch the plug on at low throttle settings and are not time limited. You can adjust the switching point easily. They also turn off when you apply throttle cut. I use them in every glow plane I have except for club32 pylon racers ans swear by them:

https://modelradioworkshop.co.uk/product-category/glow-plug-switch-devices/

I also agree that OS F plugs are the best for this size of engine

Simon

Oh excellent thanks for that. I have an idea now being a cheap skate lol, I could set something up with a 1.2v battery with a metallic strip screwed onto the throttle servo arm that touches another metallic strip when the throttle is a low position and then once I cut the engine I could even rig up a switch to turn it off afterwards or move the throttle back up so it's not making the connection anymore, I think it will work...

[craig procter]

The tank position in relation to the spray bar is something else I need to look at it seems from what people are telling me, thanks for the info...

[craig procter]

9 hours ago, Jason Channing said:

Try an OS F plug, hopefully should clear the problem.

 

Thanks, another thing in my arsenal to combat the engine quitting...

[Frank Skilbeck]

It should run fine inverted, so check the tank position etc. I have a couple of the model radio shop remote glows, useful for engines where fitting a glow stick isn't easy. But if you want to go the cheapskate route one of these activated by the throttle servo control horn might be more reliable than a couple of metal strips.

[Peter Christy]

Super-Tigres - in common with a lot of older European engines - were designed to run on long-reach plugs. The only long-reach plugs currently available (of which I'm aware) are 4-stroke plugs, hence the recommendation for the OS "F" plug.

 

4-stroke plugs are also "hot" plugs, which makes them better suited to the straight fuel (no nitro) recommended for Super-Tigres.

 

As mentioned above, its also worth checking the tank height. Also, are you using a pressure feed?

 

A short-reach plug in a long-reach head will work, but it will be much easier to flood the plug - especially when inverted - as the fuel will tend to collect in the "cup" formed by the empty part of the threaded section of the head.

 

--

Pete

[craig procter]

1 hour ago, Frank Skilbeck said:

It should run fine inverted, so check the tank position etc. I have a couple of the model radio shop remote glows, useful for engines where fitting a glow stick isn't easy. But if you want to go the cheapskate route one of these activated by the throttle servo control horn might be more reliable than a couple of metal strips.

Okay cool, that would work great I reckon with that micro switch, thanks..

[craig procter]

43 minutes ago, Peter Christy said:

Super-Tigres - in common with a lot of older European engines - were designed to run on long-reach plugs. The only long-reach plugs currently available (of which I'm aware) are 4-stroke plugs, hence the recommendation for the OS "F" plug.

 

4-stroke plugs are also "hot" plugs, which makes them better suited to the straight fuel (no nitro) recommended for Super-Tigres.

 

As mentioned above, its also worth checking the tank height. Also, are you using a pressure feed?

 

A short-reach plug in a long-reach head will work, but it will be much easier to flood the plug - especially when inverted - as the fuel will tend to collect in the "cup" formed by the empty part of the threaded section of the head.

 

--

Pete

The tank is pressure fed from the exhaust if that's what you mean? I didn't occur to me about the plug not being long enough and I can imagine what you mean with the fuel collecting in the head. I have been using OS no8 plugs mostly, maybe I should try a long reach one then as well..

 

Thanks Pete 

[Jon H]

If you have tuned the engine to work well upright and it stops as soon as you turn it over then tank placement is my suspicion just as the others have said. 

 

I recommend you level the top of the tank with the centreline of the carb. This will prevent fuel syphon when the engine is sat on the ground and prevent ground flooding. 

 

the OS F plug trick is a good one and can work well. However once fitted the first time be very careful when you turn the engine over as you may find that the plug is too long on some engines and you will punch a hole through the piston if you just fit it and try to fire it up. 

 

I would also consider the fuel you are using as ST engines tend to like less nitro. 

[craig procter]

1 minute ago, Jon - Laser Engines said:

If you have tuned the engine to work well upright and it stops as soon as you turn it over then tank placement is my suspicion just as the others have said. 

 

I recommend you level the top of the tank with the centreline of the carb. This will prevent fuel syphon when the engine is sat on the ground and prevent ground flooding. 

 

the OS F plug trick is a good one and can work well. However once fitted the first time be very careful when you turn the engine over as you may find that the plug is too long on some engines and you will punch a hole through the piston if you just fit it and try to fire it up. 

 

I would also consider the fuel you are using as ST engines tend to like less nitro. 

Okay noted, with a longer plug I'll turn the engine over by hand with out the glow stick connected of course and check for clearance, thanks for the info...

[John Wagg]

My original thought was try a different plug. Then came tank position. Regarding the tank I also wondered if the pick-up was jammed so that when inverted the pick-up sucked air. Unlikely but I have known it happen. Easy to check as wobbling the plane vertical you should hear the clunk of the pick-up.

Edited June 3, 2022 by John Wagg

[craig procter]

4 hours ago, John Wagg said:

My original thought was try a different plug. Then came tank position. Regarding the tank I also wondered if the pick-up was jammed so that when inverted the pick-up sucked air. Unlikely but I have known it happen. Easy to check as wobbling the plane vertical you should hear the clunk of the pick-up.

Yes I know that can happen or the classic one is where the clunk double backs on itself perhaps after a hard landing and the next time you go to run the engine you get problems or people use too stiff a tubing etc, I'm wise to these things but thanks for your help...

[craig procter]

Okay I still haven't got the engine back in the plane yet but I have got it running better bench testing it. I will of course from peoples help on here check the position of the tank in relation to the spray bar.

I have made some fittings on the glow plug so I can run a 1.5v battery internally in the plane and have it setup mechanically so that when the throttle servo arms moves to idle it will make a connection and put power the glow plug and hopefully keep the engine running that way. I could of bought an onboard glow system for this purpose but I'm tight lol.

Here's what I have done so far in the photo. I crimped a wire to a electrical ring connector so it is help in position when the glow plug is put in and I used an old cog with a grub screw in so I can tighten it to the top of the glow plug and screwed in another wire to the top of it, Just got to sort out the other end now.

[Ron Gray]

The problem with an on board glow that automatically comes in at low revs is that it can hide an underlying issue with your setup. Far better to get it running correctly without it, if setup correctly it will run without an on board glow. A flying buddy of mine had a Saito which would cut out at low revs so he fitted an on board glow do that it wouldn’t cut out. I persuaded him to revisit the setup and tuning, funnily enough he never had that problem again, even without the on board glow. 

Edited June 3, 2022 by Ron Gray

[craig procter]

I hear you Ron thanks, this is more of a backup really if I can't nail it...

[Ron Gray]

I’m sure you will nail it Craig. 

[Martin Dance 1]

Looking at your photo and taking into account the angle at which it is taken I think your fuel tank is too high. In an inverted setup I would expect the bottom of the tank to be almost level with the top of the head so that the top of the tank is level with or just higher than the spraybar. I've used ST engines a lot and they do idle reliably. If you have an engine test stand. Set the motor up in an upright position with the top of the fuel tank a little above the spray bar, about 8-12mm. I aim for the motor to idle reliably at around 2000rpm for one minute and then to accelerate to full power with a brisk opening of the throttle without sagging or mis-firing or producing clouds of smoke. My reasoning for choosing  one minute of idling is two fold. 1 It gives the engine time to cool a little and this will magnfy any poor carb  setting. 2. If you are doing a landing approach, chances are you will be closing the throttle going downwind just about in front of you. by the time you turn onto finals the engine will be at idle., If you decide to go around you need the motor to accelerate cleanly. For many models the time taken to complete the dowwind leg, crosswind leg and finals is about a minute. So aiming for at least a minute idle is a reasonable goal.

Once your engine is set up in the upright position it should need little or no further adjustment

 

[Peter Christy]

6 hours ago, craig procter said:

The tank is pressure fed from the exhaust if that's what you mean? I didn't occur to me about the plug not being long enough and I can imagine what you mean with the fuel collecting in the head. I have been using OS no8 plugs mostly, maybe I should try a long reach one then as well..

 

Thanks Pete 

Re: Tank pressure - yes that is what I was referring to. If the tank is too high (as suggested), then the pressure feed will make matters worse! Depending on the bore of the carb, you may not need pressure, but it is one more variable to consider. If the engine runs fine without it, then its something else to go wrong, but it is often useful if the tank is some distance back from the engine, and it is a big bore carb (not enough venturi suction to keep the fuel flowing!).

 

Regarding the plug, yes an OS 8 is a very good plug, but it is also a bit short for the ST! If you take the head off you will see that it stops several turns short of the combustion chamber! As Jon has suggested, best to turn it over by hand first to make sure the clearance is OK with a 4-stroke plug, but I've never had an issue with smaller STs (up to 60-size) or Webra Blackheads using them.

 

--

Pete

[craig procter]

4 hours ago, Martin Dance 1 said:

Looking at your photo and taking into account the angle at which it is taken I think your fuel tank is too high. In an inverted setup I would expect the bottom of the tank to be almost level with the top of the head so that the top of the tank is level with or just higher than the spraybar. I've used ST engines a lot and they do idle reliably. If you have an engine test stand. Set the motor up in an upright position with the top of the fuel tank a little above the spray bar, about 8-12mm. I aim for the motor to idle reliably at around 2000rpm for one minute and then to accelerate to full power with a brisk opening of the throttle without sagging or mis-firing or producing clouds of smoke. My reasoning for choosing  one minute of idling is two fold. 1 It gives the engine time to cool a little and this will magnfy any poor carb  setting. 2. If you are doing a landing approach, chances are you will be closing the throttle going downwind just about in front of you. by the time you turn onto finals the engine will be at idle., If you decide to go around you need the motor to accelerate cleanly. For many models the time taken to complete the dowwind leg, crosswind leg and finals is about a minute. So aiming for at least a minute idle is a reasonable goal.

Once your engine is set up in the upright position it should need little or no further adjustment

 

Thanks Martin I found this very interesting as well as the other useful information people have kindly given too. It's funny when you say about the landing part because I had that very thing happen to me where I came in a little bit too fast (idle was set fast to keep the dam thing running) so I decided to go around and try again, I blipped the throttle and the motor cut (oh bugger), because I was dead stick and still going at some pace I gave a little to much bit too much elevator to bleed some speed off, slightly stalled it and hit the ground too hard and it broke the nose off along with the motor.

If the Spitfire which I was flying was fitted with flaps it might have been a successful landing even though the engine was idling fast. So yes it would help a lot if I didn't have to worry about the engine potentially quitting on me especially when taking off or on finals!

Oh I thought I would upload another photo the engine in my crudely setup in my vice showing the tank and in it's temporary position.

 

[craig procter]

4 hours ago, Peter Christy said:

Re: Tank pressure - yes that is what I was referring to. If the tank is too high (as suggested), then the pressure feed will make matters worse! Depending on the bore of the carb, you may not need pressure, but it is one more variable to consider. If the engine runs fine without it, then its something else to go wrong, but it is often useful if the tank is some distance back from the engine, and it is a big bore carb (not enough venturi suction to keep the fuel flowing!).

 

Regarding the plug, yes an OS 8 is a very good plug, but it is also a bit short for the ST! If you take the head off you will see that it stops several turns short of the combustion chamber! As Jon has suggested, best to turn it over by hand first to make sure the clearance is OK with a 4-stroke plug, but I've never had an issue with smaller STs (up to 60-size) or Webra Blackheads using them.

 

--

Pete

I am overwhelmed with all the help and useful information everyone has sent me, it's amazing. I did at one stage take the pipe off the exhaust to see if that would make a difference but at the time it didn't, I figured I was still doing something wrong. The setup at the moment as you can see in the photo's is working a lot better after tweaking the settings however when I turn this upside down it still cuts on idle. I now know the tank isn't in the ideal position but this is just temporary until I can get back to work on it.

Thanks about the plug thing I understand and I will get one me thinks for sure...

[Engine Doctor]

That glow clip you have fitted is a large heat sink and will try to cool the plug. Try  a lighter commercial type 

What fuel are you using. Too much oil will puddle into the plug when inverted. Try a lower oil content  say 15 %. Still plenty for the engine.

When you stripped send cleaned it did you make sure that crankcase compression is good ? Any leaks will cause erratic running.

Is cylinder compression good ? If piston ring is worn and compression is low this can also add to erratic running.

Hope you get it sorted.

[craig procter]

43 minutes ago, Engine Doctor said:

That glow clip you have fitted is a large heat sink and will try to cool the plug. Try  a lighter commercial type 

What fuel are you using. Too much oil will puddle into the plug when inverted. Try a lower oil content  say 15 %. Still plenty for the engine.

When you stripped send cleaned it did you make sure that crankcase compression is good ? Any leaks will cause erratic running.

Is cylinder compression good ? If piston ring is worn and compression is low this can also add to erratic running.

Hope you get it sorted.

I can imagine it would act like a heat sink. I have been using different types of fuel one of them being Opti Fuel 20% nitro and 18% oil. I haven't taken the piston out to check the piston ring but compression is very good and I'm pretty sure there aren't any leaks.

Thanks for your help too...