Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9 Posted (10 years 2 months 1 week 4 days 18 hours ago) and read 3784 times:
The NACA type ducts that are used on airliners as ram air inlets for the A/C pack's heat exchangers all look the same regardless of the type of aircraft (from what I can see) ....... except for on the Lockheed L-1011.
The L-1011's NACA ducts have the same basic shape as the ducts on other airliner types, but, they also have a raised lip that outlines the shape of the duct, whereas other airliner's ducts are flush with the fuselage. I guess the purpose of this lip is for enhancing the function of the duct.
My questions are: Are the raised lips on these L-1011 NACA ducts heated? Do the cockpit switches for the anti-icing system in the L-1011 include a switch for heating these ducts?
Even though I've learned from this forum that one of the main reasons for the unique shape of a NACA duct is that it won't allow ice to form on it's surface which could block the inlet, I can't help but think that ice could form on those raised lips around the L-1011's ducts just like it can form on pitot tubes, etc.
I'm simply curious about this, and finally decided to ask about it.
Here's some photos that show the difference between the NACA ducts on an L-1011 and a few other airliner types.
Unlike the L-1011 and DC-10 (which have their A/C packs near the nosegear), I think all/most of the newer airliners today have their A/C packs near the main landing gear bay, thus the location of their NACA inlets in their bellies/wing roots.
Here's some info about NACA ducts from previous posts ..........
"NACA (who designed these ducts), is named for the National Advisory Committee to Aeronautics - the forerunner of NASA"
"They will not allow ice to form on their surface. They are used as ventilating inlets/outlets for fuel tanks and they must not be blocked by ice. NACA found out that the specific aircraft like shape is ideal to slow down air at that specific point and moisture will not freeze. So, the duct will always stay free of ice."
"They scoop air with very little drag, much better than the typical scoop that protrudes into the airstream."
"A NACA duct is simply a duct designed to draw air into itself without creating a load of turbulence behind the duct. It does this because the divergent part of the duct creates a lower pressure zone into which the surrounding air is drawn."
PS, My question about whether or not the L-1011's NACA ducts require anti-icing heat on the raised lips is very simple to answer with just a Yes or No reply - and perhaps an explanation as to why. I'm sorry for this long "overkill" post!
Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 2, posted (10 years 2 months 1 week 4 days 15 hours ago) and read 3699 times:
Thanks for your reply.
OK, so the simple answer is that they're not heated.
I thought it looked possible that ice could form at the forward part of the raised lips where the sharp points of the lips are very close together (as can be clearly seen in the first L-1011 photo). I guess the small pointed gap area at the front of the inlet didn't cause an icing problem.
As far as I know, these raised surfaces aren't even made from metal. They could be made of fibreglass.
Yikes! From Canada, joined Oct 2001, 284 posts, RR: 1
Reply 4, posted (10 years 2 months 1 week 4 days 13 hours ago) and read 3644 times:
I was about to post a quick "JET's right." post, but got this Administrator's message saying my post of "JET's right." is "too short". So after giving long and hard thought towards my original thinking of "JET's right.", I would like to conclude this explanation of a forum-board idiosynchrasy (sp??) with my original post of "JET's right."