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46AX on Cowled Extra 300 SP kit

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Old 11-18-2012, 10:29 PM
  #1
CrashedTrainer
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Default 46AX on Cowled Extra 300 SP kit

Dear All,

I am about to get an [link=http://www.greatplanes.com/performance/airplanes/gpma1022.html]Extra 300 SP[/link] "Extra 300 SP" kit for my OS 46AX engine. This will be my first intermediate plane after flying my standard 65" WS trainer.

I downloaded the construction manual for the above mentioned kit. Since this is a cowled kit which completely encloses your engine, I have a couple of questions answers to which I couldn't find in the manual:

- How am I supposed to fuel up the plane? normally i just use the fuel tank line connected to the needle valve.
- How can I do the initial priming of the carb (which i do by blocking the carb air inlet and silencer exhaust using my fingers and then hand cranking the propeller 2 or three times)
- How much affect will the side mounting have on the engine startup and normal performance?
- Lastly will the already available air inlets on the cowl suffice to cool down the engine while in the air and more importantly on the ground during initial startup and checks??? Also how much is flying without the cowl recommended???

For needle valve & glow plug access i can drill a hole in the cowl so no issues there.

I would highly appreciate a detailed reply.

Thanks!
Crashed Trainer
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Old 11-19-2012, 12:10 AM
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Default RE: 46AX on Cowled Extra 300 SP kit

Hi Crashed,
Quote:
ORIGINAL: CrashedTrainer

Dear All,

I am about to get an [link=http://www.greatplanes.com/performance/airplanes/gpma1022.html]Extra 300 SP[/link] ''Extra 300 SP'' kit for my OS 46AX engine. This will be my first intermediate plane after flying my standard 65'' WS trainer.

I downloaded the construction manual for the above mentioned kit. Since this is a cowled kit which completely encloses your engine, I have a couple of questions answers to which I couldn't find in the manual:

- How am I supposed to fuel up the plane? normally i just use the fuel tank line connected to the needle valve.

It's usual to use a third line to the tank. Plumb it to the bottom of the tank either with a second clunk or a bent fuel tube (don't let the tube rub on the bottom though). You can seal the other end with a screw and let it dangle out the bottom of the cowl, or use a fuel dot to mount to the cowl or fuselage.

You can also buy special 'fuellers' that fit in the line between the tank and the carb if you want to stick with a two line system. These work by blocking off the line to the carb and connecting your refuel system to the tank.


- How can I do the initial priming of the carb (which i do by blocking the carb air inlet and silencer exhaust using my fingers and then hand cranking the propeller 2 or three times)

Sometimes it's possible to poke your finger in the cowl, block the carb, pull the prop through one blade, remove your finger, pull through a bit further, reinsert finger etc. This works but is a pain. Alternatively it should be easy to block the exhaust only and then hand crank six or more compressions. A third method is to squirt a small amount of fuel down the carb from your squeeze bottle or refuel pump.

- How much affect will the side mounting have on the engine startup and normal performance?

Very little as long as the tank is the correct height relative to the new height of the spray bar. Priming is easier, flooding is harder. Performance should be unchanged.

- Lastly will the already available air inlets on the cowl suffice to cool down the engine while in the air and more importantly on the ground during initial startup and checks??? Also how much is flying without the cowl recommended???

If the model is well designed yes (some are better than others). You will more than likely be fine as designed but probably the single best and easiest thing you could do is put a baffle in the cowl. A baffle will ensure that all the air that goes into the cowl will be used for cooling instead of missing the engine all together. The baffle is made from a U shaped piece of balsa glued sideways in the cowl and then sealed with paint or varnish. Position the baffle so that the engine cylinder head fits in the open part of the U. You will have to make cut outs for the engine mount, muffler, throttle link etc. It's a wee bit of mucking around but well worth the effort (use a paper or cardboard pattern to get the right shape).

Air inlet size is important but so is the outlet size to get the hot air out again. Some people will tell you that the outlet has to be three (or two, or four) times larger than the inlet. This isn't quite true but one or other of them will be limiting the air flow. If you need more cooling there's no point in opening up one if the other is limiting the flow eg no point opening up the outlet if the inlets are too small. Having said that the outlet which is parallel to the streamlines, will generally be larger than the inlet, which is at right angles.

A correctly cowled engine will actually provide better cooling, and far less drag, than an engine sticking out in the breeze.

Test flying without the cowl used to be quite common and probably won't hurt anything. It's a good way to eliminate overheating if you are having engine issues


For needle valve & glow plug access i can drill a hole in the cowl so no issues there.

I would highly appreciate a detailed reply.

Thanks!
Crashed Trainer
That's been my experience and I hope that's detailed enough for you, if not feel free to ask more.

Dave H
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Old 11-19-2012, 12:59 AM
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Default RE: 46AX on Cowled Extra 300 SP kit

thats more than enough actually! I might get my hands on that kit hopefully by the end of this week... then i have a whole week off to work on it so its going to be awesome!!

hopefully i wont need it but will come back here if i do need any more help... thanks Dave for sharing your experience here!!!

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Old 11-19-2012, 06:50 AM
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Default RE: 46AX on Cowled Extra 300 SP kit

I will add my ten cents to the previous answer as far as priming the engine goes as I have the same engine. It is a very good one and doesnt faulter.
What I do is to open the throttle all the way (no battery attached) and use the electric starter to spin the engine for a few seconds. This draws fuel into the carb. Next, add glow battery power throttle down to 1/4 or 1/3rd and use the starter again, should fire up. Dont get discouraged if it takes a bit longer to start up as that is normal.

Good luck

Rafeek
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Old 11-19-2012, 09:49 AM
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Default RE: 46AX on Cowled Extra 300 SP kit

McDaniel makes a remote glow connector which will eliminate one hole in the cowl. Another starting tip: with glow disconnected, throttle wide open, put your finger over the muffler outlet and hand-prop 5 or 6 times, reduce throttle to just above idle, connect glow and start up.
Less likely to get a hydraulic lock that way.

Which kit is it?
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Old 11-19-2012, 10:31 AM
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Default RE: 46AX on Cowled Extra 300 SP kit


Quote:
ORIGINAL: CrashedTrainer

Dear All,

I am about to get an [link=http://www.greatplanes.com/performance/airplanes/gpma1022.html]Extra 300 SP[/link] ''Extra 300 SP'' kit for my OS 46AX engine. This will be my first intermediate plane after flying my standard 65'' WS trainer.

I downloaded the construction manual for the above mentioned kit. Since this is a cowled kit which completely encloses your engine, I have a couple of questions answers to which I couldn't find in the manual:

- How am I supposed to fuel up the plane? normally i just use the fuel tank line connected to the needle valve.
- How can I do the initial priming of the carb (which i do by blocking the carb air inlet and silencer exhaust using my fingers and then hand cranking the propeller 2 or three times)
- How much affect will the side mounting have on the engine startup and normal performance?
- Lastly will the already available air inlets on the cowl suffice to cool down the engine while in the air and more importantly on the ground during initial startup and checks??? Also how much is flying without the cowl recommended???

For needle valve & glow plug access i can drill a hole in the cowl so no issues there.

I would highly appreciate a detailed reply.

Thanks!
Crashed Trainer
To fuel it I either use a three line tank and the fuel dots, clean looking and easy. You can also do a split line and plumb like normal with the main line looped out of the cowl and a piece of copper or brass tube between the lines so you can remove the line halves to fill and drain the tank. Perhaps JOhn Buckner will post a photo to show you this?
To prime you just open the throttle and stick a finger over the exhaust then roll the engine over. If you use an electric starter you don't need to prime, it will do it itself in a few seconds.
Side mounting has no effect on the engine, set up is the same as an upright engine.
The air intake is fine but you want to have an opening about twice as big for the air to flow out or it will over heat. If the head of the engine is sticking out of the cowl there isn't a lot of problems. If it does over heat then open up the outlet holes more.
I make my own remote glow drivers but you can buy them pre-made. You can simply drill a hole in the cowl for glow plug access, same for the needle valve. There is a drilled and tapped set screw in your needle valve for you to attach an extension. It's just piano wire that you make a bend in at the top so you you can turn it. The shorter the better.
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Old 11-21-2012, 01:21 AM
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Default RE: 46AX on Cowled Extra 300 SP kit


Quote:
ORIGINAL: CrashedTrainer

thats more than enough actually! I might get my hands on that kit hopefully by the end of this week... then i have a whole week off to work on it so its going to be awesome!!

hopefully i wont need it but will come back here if i do need any more help... thanks Dave for sharing your experience here!!!

You're welcome, best of luck with the model.

Dave H.
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Old 11-21-2012, 04:05 AM
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Default RE: 46AX on Cowled Extra 300 SP kit

Gene could you take a pic or describe your remote glow driver please ? Both ends...Do you use an old glow plug? Thanks
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