BigGiraffe
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Posts: 256
Joined: Sat Jan 29, 2000 7:58 am

Secondary Air Inlet Doors

Tue Feb 22, 2000 10:31 pm

Some commercial jets such as the Fanjet 707s and early 737s (747s too, I think) had secondary air inlet doors on the engine nacelles to allow extra air flow with high thrust and low speed. (These doors are located around the circumference of the nacelle near the engine inlet). Later 737s and today's aircraft don't have these doors. What design changes and improvements allowed their deletion?

Thanks,
BigGiraffe
 
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DL_Mech
Posts: 2070
Joined: Fri Feb 18, 2000 7:48 am

RE: Secondary Air Inlet Doors

Tue Feb 22, 2000 10:38 pm

I've been wondering this myself, my guess would be aerodynamics. UA still had this on older 732's-- are there any UA people that know for sure?
This plane is built to withstand anything... except a bad pilot.
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

Sucker Doors

Wed Feb 23, 2000 12:49 am

That's what these were called, informally, on the 737s at least. Their purpose was to allow additional airflow into the engine at higher aircraft angles-of-attack, and they were on the 737-100s and only the -200 "basic" models. For the 737-200 "advanced" model (produced after 1974 or so), Boeing made several design changes to the forward engine cowling (including lengthening it) that all resulted in significant enough aerodynamic improvements such that the sucker doors were no longer needed.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
BigGiraffe
Topic Author
Posts: 256
Joined: Sat Jan 29, 2000 7:58 am

RE: Secondary Air Inlet Doors

Thu Feb 24, 2000 6:58 am

These doors are spring-loaded shut and would open when pressure was low enough on the intake side. Once the aircraft is up to speed there would be enough ram pressure to keep them closed. They are sort of a pain on USAF C-5 aircraft because you get corrosion and cracks around them. I can see why owners would want to be rid of them. But still I wonder how things were changed so they are no longer needed?