Larry,
I have not measured the temperatures in the lower cowl, but I have participated in lower cowl temperatures in several GA aircraft and it is very difficult to find a source with adequate volume and temperature. Additionally the temperature in the cowl varies with AOA, IAS, and engine power. Plus there is heat loss from the source to the carb.
When this is all considered it is virtually impossible to find a suitable source for hot air to provide carb deicing. Then consider under proper conditions the temperature drop in the venturi can be 90 degrees F. So you really need hot air at the source to produce at least 100 degrees at the carb.
The FAA spec for this was written in blood, so it is very critical, airplanes have been lost in the past.
Jack Webb
BASE
L360, LIV
From: Larry Henney <LHenney@charter.net>
To: lml@lancaironline.net
Sent: Friday, November 21, 2008 6:27:54 PM
Subject: [LML] 320 Carb Heat Box
Guys,
I've got a friend looking at his 320 carb heat intake box. The question is; Does lower cowl air have enough heat in it to prevent carb ice? He is considering muffing an exhaust pipe to make sure the heated air is adequately hot.
I was wondering if others have ever had carb ice with the standard Lancair carb heat box (using just lower cowl hot (warm) air)?
We'd appreciate your thoughts.
Larry Henney