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Mounting of sc 46 abc engine

Upside down, does it need to be at an angle?

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Craig Spence23/01/2009 23:09:38
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Right, hi all, I went to my model club for the first time the other day and before I had my first flight the engine was hard to start. After some uming and ahing the instructor found the problem, I put the fuel tank together the wrong way lol!. Well that aside he said the plane was fine and the only thing I should consider is changeing the the engine round to an angle or cylinder up as upside down aint great. However, once I had my first lesson the plane was up in the air for over fifteen minits, the instructor run it until dead stick and was very surprised it stayed up so long. He said that it was a good set up and when I said should I change it he said what do you think.
So I havent changed it and will be taking it down the field tomorrow for its third flight (second flight was just as long). Does upside down mounting of an engine effect performance as the instructor said that the plane I was flying with the engine and tank only normally lasts for 8 to 10 minits, most flyers that day were quite impressed with the time it lasted.
Any feedback appreciated and will look forward to an explanation.
Oh the plane is a Prangster with an SC46 engine and it was only getting flown on very low throtle.
Cheers all.
Garry Pollard24/01/2009 00:07:07
1091 forum posts
Hi Craig
For what it is worth, 20 yrs ago when I flew ic engines we always tried to mount them upright so there wasnt the prob of fuellock,ie fuel in the upside down cylinder head causing it to be impossible to turn over. We were lazy in those days
Comming to the lenght of flight, I dont know if you drive a car, but if a car is driven on low throttle it will not consume as much petrol as if it was driven flat out. To my mind that is why your flight was so long, you were flying on tickover. If it isnt broken dont try and mend it. The model flies well and any improovement may change all that
Garry
Craig Spence24/01/2009 09:01:59
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Hi Gary,
thanks for the feedback, common sense rules really but its good to get as much info as I can.
Cheers.
 
Craig Spence24/01/2009 09:03:29
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Hi Gary,
thanks for the feedback, common sense rules really but its good to get as much info as I can.
Cheers, Craig.
 
Alan B24/01/2009 22:21:33
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Hi Craig
 
I have a Prangster 3D with the same SC 46 abc engine.  The position of your engine is probably the same as mine as per the build instructions - Inverted at a angle.  I have had no problems with the position at all.  I get on average about 12 - 15 minutes on a tank of fuel, a bit longer if you just cruise it around.
 
As Gary says above "If it aint broke then dont fix it !" 
 
The Sc engine will run quite happily all day in that position as per the planes design.
If these budget engines are set up correctly - then you will find they almost start first time every time.
 
Al
Craig Spence25/01/2009 00:10:23
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Hi Alan,
my engine was just mounted inverted (no angle) and I found out today why this has its disadvanatages, the spar in my wing broke causeing the wing to fold and make my plane decend from around 500ft like a pigen shot in one wing, fast and totally out of controll lol!.
 
It landed on a hill on the horizon and looked fine with the wing silouted towards me looking like it was ready to take off, however when I got there the engine had snapped off the cowel, apart from that the plane was fine. I mean the damage from a 500ft fall would cripple a balsa, however because my engine was totally inverted it was also totally submerged in mud ive spent all night digging it out and am hopeing it is ok when i retune it tomorrow.
 
Total damage, broken spar, prop, tie wrap on under carriage, dirty engine and well see if it works tomorrow, oh ive mounted it at an angle now as well and your right it does start first time every time lets see if it does it for me tomorrow.
 
Cheers.
Alan B26/01/2009 09:45:29
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Hi Craig
 
As previously discussed in your previous threads- thats the "Prangster for You !"  Virtually indestructable.
 
I wouldn't have thought the engine position would have broken the wing spar!  However mounting the engine at a angle thus putting the Silencer at the opposite angle would probably suggest to me it gives the model a better weight balance.
 
Try to get less shot pigeon impressions!
 
PS  I have also noticed with these, if you put the model into a fast dive - the Rudder flaps like a good Un ! (Perhaps that might just be the 3D version)
 
Al
flytilbroke26/01/2009 10:54:26
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Impacting with the ground. It is pure luck at which angle the engine hits, so how it is mounted does not matter. For that spar to break it must have been bad wood, or extreme stress
 
I found that when the Glass re-forced tape was applied well, the wing would NOT fold even with broken or damaged spar. They are tough indeed.
 
Agree with Alan B re the engine and balance.
Craig Spence26/01/2009 22:12:59
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Hi Alan B,
thanks for the feedback, I dont think that the position of the engine broke the wing spar either. I went to the model shop and asked the man who designed it, he said that what probably happened was that it was poor wood and also that the wing probably lifted from the plane on the bands causeing more pressure and thinking back and looking at where the spar broke hes probably right. It snaped just about where the bands are mounted.
 
I have now got reinforced engine cowl and have mounted it at an angle, lets hope I dont have another mishap tomorrow.
 
Cheers flytilbroke as well, my instructor said that I could have hit turbulent air causeing the wing to lift sharply, who knows one of lifes little mysteries I suppose.
 
Cheers all.
Lee Smalley26/01/2009 23:50:24
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the engine mounting does not matter to its ability to run most problems stem from the tank installation as the engine is rotated the carb position changes and as a result the tank will need adjusting in centre line height most people forget or cant be bothered to do this and as a result the tank is in too high a position and and during periods of low throttle excess fuel can syphon through cooling the plug to a point it just quits, for people to be suprised it lasted so long shows what they know about tank position  
Craig Spence27/01/2009 09:02:51
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Hi Lee,
thanks for that bit of info, I never knew that but you cant move the fuel tank in the Prangster without modification (cutting foam and weakening the fuselage). However I will remember that for future models, the fuel tank in the Prangster is in line with the engine, the carb line is in direct line with the engine shaft, is that ok?.
 
Cheers Lee.
flytilbroke27/01/2009 11:13:06
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Hi Craig, for an ideal instalation (which does not happen often) look at the position of the spray-bar inside the Carbureter, that should be in a horizontal position inline with the centre of the fuel tank. Again, this seldom is the case.
 
In an inverted position and when an engine is ticking over, oil can "pool" where it is least wanted, over the plug coil. We are lucky in that this happens fairly rarely with a run-in and properly tuned engine.
 
Have fun
Craig Spence27/01/2009 20:31:25
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Cheers flytilbroke,
when you say oil can pool over the plug coil is this why the engine sometimes splutters, when otherwise ok.
Cheers.
Lee Smalley29/01/2009 22:05:47
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its not really the oil pooling but rather excess fuel, as we never really tune our engines perfectly ( or at least i don't) as a result when you open the throttle the engine coughs as it burns off the excess fuel in an ideal world the tank level should be slightly lower than the center line of the carb / spraybar but obviously this is somtimes impossible and not all engines are the same, take the Laser engines their carb is mounted at the top of the engine !! try getting your tank level with that !!! and yet they run so well scalers swear by them!!!  so im afraid you are back to square 1.
Find out what works for you and stick by it 
Garry G31/01/2009 15:43:24
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On a side mounted engine you are looking at the spray bar running vertically up the air intake, is the centre line of the carb. the same as the c.l. of the crank shaft?
flytilbroke31/01/2009 16:46:30
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Think of a line drawn through the middle of the tank base end and tank neck, extended out the front of the model. Ideally, on that line is where the spray bar should be. Practically, for most of us, as near as we can make it usually works fine. We have to take what we get as to position with so many ARTF models and some other ones too.
 
As our glow engines use "sacrificial" oil it is not burned in our engines, it is ejected through the exhaust. When slow running and inverted, some accumulation tends to take place at the head, hence the inverted engine can be more prone to stopping as the plug oils up.
 
A rich fuel to air mix can make this worse.
 
Gary G. Nope
 
Have fun now lads
Lee Smalley01/02/2009 13:31:14
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"On a side mounted engine you are looking at the spray bar running vertically up the air intake, is the centre line of the carb. the same as the c.l. of the crank shaft? "
 
yes mate but as flytilbroke says we try our best to get tank in right position but somtimes its impossible and i have yet to come across an engine where this has been critical, the only time it is a problem is when we have stopped flying and while we are not watching fuel siphons through and floods the engine without us knowing so when we come to restart our engine the silencer is full and so is the engine i have 1 aircraft that does that so i have to ensure that when im finished flying i leave it nose up somehow, but in the air it doesn't bother it !!
Peter 'Ivanna Crashalot' Savage01/02/2009 18:00:41
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You could just always fly upside down!!!

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