Cowling Issues

[linw]

Hi, guys. I am building a cap232 ARF and am looking for advice on how to install an ASP46 engine and cowling. I am not experienced at this so all help appreciated. The photos show the current state with the engine temporarily fixed in the correct (hopefully) position as per the (feeble) instructions. The engine is almost at the end of the mounting rails but it still is about 5 mm too far inside the cowling. The carb and the cylinder head are touching the front of the cowling.

I guess I have to open up holes for the carb and cylinder head. Bit ugly but I will need access to the glow plug and access to the carb throat may be handy as well. Hopefully I can then get the cowling back the 5 mm I need.

As far as plumbing goes, I will need to bring the filler tube out and I am pretty sure I can get access to the muffler tube for tank full check.

I have tried cutting similar fibre glass before with tin snips and the paint chips at the edges pretty badly. I bought a Dremel look-alike today with a fine cutting disk. Is this the go for cutting the glass? I will have two long cuts along the side to allow the muffler to slide through so any tips as to how to get a good straight edge would be welcome.

Sorry for the long post but perhaps others can learn as well.

Lindsay.

[isxism]

The Dremel is definately the correct tool for this job, but use extreme caution while cutting any fibreglass. Use proper PPE. (safety glasses, mask...) Use a straight edge to successfully perform a straight cut. Looks like you did a fine job with the 232!!! Send us pics when it is complete!

[abenn]

I doesn't really matter to the aircraft which way the engine is sitting, so you want to angle it so that its exhaust is pointing down and, hopefully, the head fits within the bulge in the side of the cowl. Seems like yours is about right.

As for cutting the cowl, I stick masking tape on so that I can draw my cut lines, and to help prevent chipping the edge while cutting. A Dremel cutoff wheel is the easiest way to do it, and I cut the hole about 1/8" undersize first and then finish it off with a fine file.

If your head fits within the cowl there's no need to make an access hole for the glow plug if you don't want to: You can fit a remote glow assembly like this http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXBC35&P=ML and mount the contact anywhere handy on your fuselage or cowl.

When you cut your hole for the exhaust exit it's probably good to leave a lot of space around the exhaust (a) to stop the heat from damaging the cowl and (b) to leave a nice large exit hole so that the air coming in at the front of the cowl can pass through and cool the engine. With insufficient exit hole, air will stagnate inside the cowl and your engine may overheat.

[linw]

Thanks for the great suggestions, guys.

As for the engine orientation, a 90 deg mount looked really good as the head fits within the cowl bulge and the needle valve would be easily available at the top.

The front of the muffler would need to protrude through a hole forward but the muffler outlet is well up within the cowling as the cowling is quite deep at the aft end. Should I just make a longish sausage shaped longitudinal hole (plenty of air flow) and route the exhaust mess down under the plane via an exhaust extender?

[abenn]

... The front of the muffler would need to protrude through a hole forward but the muffler outlet is well up within the cowling as the cowling is quite deep at the aft end. Should I just make a longish sausage shaped longitudinal hole (plenty of air flow) and route the exhaust mess down under the plane via an exhaust extender?I've had a setup that sounds like you describe: I made quite a neat hole (say maximum 1/8" clearance round the muffler) where the muffler fouls, and then a larger air-exit hole towards the back underside of the cowl where I let the exhaust outlet (extended, as you suggest) go.

[linw]

Thanks for that confirmation. Indeed, your described setup does sound like mine.

The added photo shows it with the cowl top on the left. The rectangular front cutout will also allow air to flow directly over the head, too.

Sounds like a go.

Thanks for your help.

Lindsay.

[linw]

Only one slight problem - the muffler would hit the firewall :o The firewall is quite deep and the fuel tank is close to the top. Should really have looked at more than dropping the engine into the cowling!

Back to the plan positioning, then.

[abenn]

Only one slight problem - the muffler would hit the firewall :o ...You might then need to look for an after-market "dustbin" silencer or a "Pitts" type silencer like this http://www.justengines.unseen.org/acatalog/Pitts_Mufflers.html :cool:

[linw]

Thanks for the site pointer. I have used JustEngines once and they were great. Four days to get a carb from UK to NZ! Yes, a Pitts muffler would do the job. Pity we don't get an option to buy this type with our engines. Buying them as an add-on is about half the price of my ASP 46!

Another suggestion made was to cut a half moon out of the lower firewall to accommodate the rear of the standard muffler. There would also need to be a hole for the front of the muffler as well, of course.

Thanks heaps for the helpful input. I will go away and ponder!

[abenn]

In one of my models (long since deceased) I installed 15mm copper water pipe long-radius 45 degree bend through the firewall to exit from the side of the plane somewhere in the fuel tank bay. My silencer was a standard OS with a straight-back exit pipe, and simply pointed into the open end of the bend.

A half moon cutout, lined with brass sheet or something, may possibly be your easiest way.

My OS120AX engine comes with a silencer that can be turned through 90 degrees so it fits within a cowl like a pitts. I believe all their AX engines come with that type of silencer now.