FCC

I need everyone to share some comments, the problems and solutions of the cowled engine that we normally face. I know there are always some tips that everyone has that makes life easier, so please go ahead and share.

MinnFlyer

My Feedback: (4)

One unique idea I saw once was used on a Goldberg Chipmunk.

Instead of gluing the 2 halves together, this gentleman took a scrap of the ABS and CA glued it to one side so that it protruded from the seam by about 3/8". that made a bed for the other half to rest on where it was screwed in place. Now, the 2 piece cowl can be opened, and the engine can be removed without removing the spinner and prop. Neat trick!

LDaba

My Feedback: (2)

Cowled engines, especially on warbirds, have a tendency to run on the hot side. This detracts from reliability and reduces engine life.(not good)
I have found that having an exit area 2-3 times the size of the inlet area will greatly assist in the cooling of the engine. Also, the use of baffles in the cowl to direct incomming air over the cooling fins of the engine body and head and out to the cowl exit will also greatly improve cooling and ultimately, reliability.
I also overpower the plane and then run the engine on the rich side.The rich mixture cools the engine better. ( ex: I use a .90 for a .60 or .75 application)This way the engine works less to provide the required amount of power and runs cooler.
Well that's it 'bout that.
Happy landings, Tony

Ted Farmin

one rule of thumb is to have 25% more exit air than inlet air.

Spaceclam

probably the most irritating problem with cowls is when they don't fit or the hole for the engine shaft is in the wrong place and you don't want to undo everything. another is when it is the wrong shape. that is pretty annoying too. about the overheating problem though, i just use an os four stroke and they run really cool, but generate a ton of power. i mean this thing swings trees for props. (considering the engine's size) on a lot of cowels, especially with aerobats, they seem to have these ferrings around the top of the cowel, widening it. this allows for some ram-air holes. they seem to protrude more on show planes and aerobats than on your average "ARF". mine runs so cool that after a flight, i can actually touch the engine and it is just hot. not really hot, but just hot. while at the same time, i can't kill the engine for beans, it never dies on it's own, and it chews up grass, debris, and even mows lawns at idle and it still powers through. back to the beginning, does anybody know how to do a minor reshaping of a cowl?

tdwise

One of these days I'll do what MinnFlyer suggested about a 2-piece cowl - I like the benefits and it sure beats removing the prop/spinner/needle valve to get at the engine. But that's for the next plane.

Cooling is always an issue whereby as long as there's ample openings for hot air to escape, the engine should run fine.

But priming a cold engine sometimes can be difficult esp. when the carburetor cannot be readily accessable for choking. I've learned that by plugging the exhaust outlets with your finger tips while flipping the prop through works just as well - if not better than trying to choke the carb. At least it does on 2-strokes.

Ted

Stick Jammer

On new planes with a new engine and a fully enclosed cowl, it's best to do the first few flights with the cowl off. This way you can concentrate on flying, trimming, and landing your new bird without having to worry about overheating, especially with warbirds. Once all the bugs are worked out and the motor is broken in, then put the cowl on and test for sufficient cooling.

Spaceclam

i did ten runs on the ground before i went into the air. it ws well broken in enough to be used with a cowl. and here is a secret. my os .91 is the pumped version of the classic .91 surpass 2. it takes about 1.5 seconds without choking, priming or anything on it's first flight. if any of you are looking for a new engine, spend the extra $50 on an engine with a pump. you can run it without a muffler because it doesn't siphen fuel, it does not lean out when you torque roll, it performes just as well upside down as it does right side up, and if nothing else, the pump works to incredibly low rpm's (it is crankcase pressure powered) so spool up is really fast.

Spaceclam

and it started in 3/4 of a second on it's first run.

TexasAirBoss

My Feedback: (22)

I like to have about 2 1/2 times the inlet area for my exhaust area. That works best for me.

I highly recommend finding Maple for the cowl mounting blocks. The stuff is the wooden model building equivilant of STEEL. I epoxy AND srew them to the firewall. I use servo srews or tiny socket head srews to actually attach the cowl to the blocks. The Maple WILL NOT STRIP. Just think of Maple as steel.

Make sure that absolutely no part of the engine or muffler touch the cowl.

Spaceclam

sounds like a good idea, but i never thought that far. I just screwed the cowling directly into the plane on the top and the sides using 5 screws. Once they got loose, i wicked some ca into it and it never got loose again. that means i have a lot of space at the bottom, but that is ok. Looks better, and still has the air flowing that is necessary. plus, I have my rocker cover sticking out of the bottom, so the engine is plenty cool.

JL1

My Feedback: (93)

Internal ducting/baffles help a LOT. be sure that all of the inlet/exit air goes over the cylinder head and through the cooling fins.