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Petrol engine cutting out on take-off

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chris larkins24/05/2019 15:39:17
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192 forum posts
124 photos

I recently bought a second hand Black Horse FW-190, it was fitted with all servos, battery x 2 and an NGH 25cc petrol. It was minus any retracts so I have fitted some E-flite units with Hobbyking oleos.

I fitted a 16x10 wooden prop to try to keep the revs & noise down, all was well until just after lift off when the engine died suddenly with not much runway remaining, damage was limited to a broken prop, bent axles and a split retract mounting.

Flight no.2, the retract mounting was repaired, tank filled with fresh fuel, a tube was soldered into the hole on the diaphram plate and a line run into the fuselage (just in case airflow in the cowl was upsetting the carb). A 16 x 6 prop fitted and with a tweak of the high speed needle I was getting almost 900rpm more than before with plenty of pull...……….. Take-off was smooth but a little bit higher this time the engine died again, damage this time is a little more with a cracked cowling, broken spark plug and both retract mountings pulled out of the wing. I have checked the tank and all appears to be well and it is fitted with a felt clunk (one suggestion was that if it had a normal clunk fuel frothing could have caused it.

Does anyone have any ideas what could be causing this? Repairing the model is not the end of the world but is it going to happen again the next time round? On the ground it appears to run lovely, during the noise test it was on full throttle for some time with no hesitation.

Edited By chris larkins on 24/05/2019 15:40:18

Steve Balaam24/05/2019 16:42:54
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94 forum posts

I had a very similar problem, I found the carb air intake airflow was being restricted by the cowl. I cut a hole in the cowl to allow the air in and the engine ran fine after that.

Paul C.24/05/2019 16:54:22
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587 forum posts
143 photos

Just wondering if it's worth a test flight with the cowl removed , that would remove any possible restriction.

Paul.

Ron Gray24/05/2019 16:59:43
1447 forum posts
363 photos

I’m not a fan of the nose up test, but in this case it could eliminate some possible problems. I would suggest only holding the model at 45 degrees, not vertical, and see what happens then. I had a similar issue with one of my engines which, on closer inspection, was a small split on the fuel feed, when level it was fine but as soon as the nose was raised air got in and the engine cut. New fuel line cured the problem.

cymaz24/05/2019 17:04:39
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8656 forum posts
1175 photos

Riches the HS needle at little. I’ve just given up on a RGC ET-30. Mine would die nose down. Never did get to the bottom of it....sorry to be a killjoy.

bert baker24/05/2019 17:20:07
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1423 forum posts
303 photos

my Mate has similar problems,,, the plug was bad,,, plus he wasn’t aware the plug cap needed a quarter turn to lock it on and he had lost a spring that was inside the cap

bert baker24/05/2019 18:45:28
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1423 forum posts
303 photos

Just watched the video,,, probably learn,

Martin McIntosh24/05/2019 21:12:04
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2927 forum posts
1073 photos

Sounded as though dirt was being pulled through the fuel line. Filters from the fuel pump and tank to motor need to be much finer than for glow fuel. Once crap is in a diaphragm carb. it can be difficult to find and remove. I have had more motor cuts for one reason or another on petrols than any other type.

Martin Harris24/05/2019 21:59:48
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8800 forum posts
215 photos

With my recent record of petrol woes I'm not sure that I should comment but the problem seems to only affect the model in flight. Static runs are perfect for extended periods but that engine cuts almost as soon as the model is in the air.

The only two differing factors that come to mind are acceleration effects and different airflow.  Although the model climbs quickly in both videos, it was not significantly nose up and as soon as the engine stuttered on the second "flight" the nose was dropped to maintain level flight before it lost power completely.

Edited By Martin Harris on 24/05/2019 22:04:47

chris larkins25/05/2019 22:06:38
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192 forum posts
124 photos

Thanks for the replies so far..... a couple of people have said about the cowl. When I got the model there was just a large hole in the front, with the engine clearly visible. I decided to 3d print a dummy engine fan to make it look more scale, I thought that this would also limit some of the airflow into the cowl as there could have been too much.

I wonder if this is upsetting the carb? The engine ran fine on the ground with this, but didn't have any airspeed

dsc_1070.jpg

Edited By chris larkins on 25/05/2019 22:08:01

Engine Doctor25/05/2019 22:16:34
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2298 forum posts
27 photos

Suggest you fill in the holes in the dummy engine and only leave the holes in front of the cylinder open. Also have an exit hole two to three times bigger than the inlet to draw cool air through the cowling . You may have to fit some ducting /baffles to guide the air flow. Radial cowls are notorious for cooking engines unless they have some form battle to guide air over the engine.

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