Cowl Vents

[Harleyman]

I've read that the exit vents of a cowl should equal three times the size of the inlet vents.
I'm working on the cowl for a Vector ARF, but the photos and instructions don't show any more than an opening for the venturi muffler and engine head. 

Is that enough?   

Any advice or photos?

[bruce malm]

I sealed of the tank area to keep the fuel out and then modified the cowl and put a good size opening just a ways behind the engine on the bottom. Can't quite remeber if that put it in the cowel or the fuselage it self. I put angled dams where needed and sloped the exit hole so extra engine oil and fuel would run out.

Bruce

[Wynn Robins]

Chris,
I will take some pics of how I did my one tonight and post here...> I added a vent to cowl and directed the air out there with a 1/32nd ply plate....will take pics

[Paul Taylor]

OK I will need to watch this one. Sealing off the fuel tank is something I did not do on the Green Stunter. I will wait and see what Wynn shows us.

Where have you been Chris? And don't say working cause I know you have my dream job.  And that ain't a real work.
Having to test ride Harley's has to be fun.

Later

[Wynn Robins]

Chris, Paul

Here is how I did my first Vector cowl.....just added a 1/32 ply sheet to the top of the cowl to create a cavity and direct air out of the fuel tank compartment.

Cut a vent at the rear of the cowl where the ply cover meets the bottom of the cowl so the air can flow out.....I dunno how well I explained it...but that is how I did it...  see pics...

cowl is a bit dirty as it has been used for a year and a bit without a decent clean, but you get the idea....

[Bill Little]

I believe the "key" to getting correct cooling of the engine can also include some "directing the airflow" inside the cowl.

I have seen pictures of some of Mr. Rabe's "cowls" where the inside of the cowl is pretty close to the cylinder on purpose.  It is smoothed into and away from the cylinder to direct the air around the cylinder, sort of a venturi effect.

A properly cowled engine will run cooler than an exposed engine on a profile from what I have been told over the years.  All due to directing the airflow.

Bill <><

[Harleyman]

Thanks guys!

Wynn,  looks nice.  Is that a LA 40 or 46 you have in the nose?  I have both a FP40 (which have been working great for me) and a LA 40 and am trying to decide.  I have not yet flown an LA 40.
Also, any problems with the needle/fuel line comming off the muffler side of the motor?  My instructions don't address it directly, but show the NVA mounted with the fuel line comming off the bypass side (closer to the tank pick-up).

Thanks again.

[Wynn Robins]

Chris,

have had ZERO problems with the motor running as displayed....maybe it is the muffler pressure I dont know....but it works every time and works perfectly.

the motor is the 46.....probably overkill on power, but it is the same size, but lighter then the LA 40....so that might help some on weight up front.....