• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Hinged piece on Lower Cowl -- Needed?

It keeps ram air from entering the back of the engine compart and disturbing the the pressure air coming out of the top of the engine and exiting out the lower lip. There has to be a pressure differential for the engine to cool properly. Have done some tests with an airspeed indicator on the front and rear of the back baffle and everything you do to keep air from entering the cowl from under the engine helps increase this differential and increase the airs cooling efficiency.
 
For some reason, it made a large difference with mine as to the effectiveness of carb heat. Taxied out on an icey day, and couldn't get an rpm drop with carb heat. Shut down, and did an eyeball inspection of the engine....the door was cracked open with the screws missing.....replaced the screws from my kit, and got an rpm drop with carb heat...replaced the felt seal on the inside of the door, and got more rpm drop....

But, no measured improvement in differential pressure across the baffles*...

*Between old felt and new felt....
 
Thanks for the replies. One of the things that got me wondering about the value of this hinged piece is the fiberglas CC lower cowls I've seen that have no similar panel incorporated in them -- at least I believe that is true because you can look in around the round filter and see the carburetor.
 
Where can you get the felt from? Are staples the typical way for install?
 
It keeps ram air from entering the back of the engine compart and disturbing the the pressure air coming out of the top of the engine and exiting out the lower lip. There has to be a pressure differential for the engine to cool properly. Have done some tests with an airspeed indicator on the front and rear of the back baffle and everything you do to keep air from entering the cowl from under the engine helps increase this differential and increase the airs cooling efficiency.

Do adding the stock louvers to each side of the lower cowling help the engine run cooler. Question: Would they not effect the differential pressure also... Or do they help to evacuate the hot air better. I am looking for any real world difference. Has anyone built the cowling without and then added them later to see if there was any difference in engine temperature.
 
Last edited:
I feel like engine cooling is voodoo magic stuff.
There is a Smith Cub here that has a Titan 360. Sutton exhaust. No hinged air box baffle. If you look past the air filter, you can see all the way to the firewall.
It runs cool. He had to tape off 1/3 of the baffle mounted oil cooler to get decent oil temps.
 
A standard Cub cowl has cheeks that effectively evacuate hot air. Adding louvers with cowl cheeks can’t do as much as just increasing the cheek opening. In a tightly cowled airplane louvers work well. Like a Husky. One of the most popular mods for Skywagons is to add cowl louvers, and it works well for 15-20° reductions in cruise CHT with cowl flaps closed.
 
Back
Top