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19AB67

Fins on plane for various reasons

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Hi folks, 

 

partially the issue was already discussed...

 

http://forum.avsim.net/topic/6476-small-fins-in-b737-800-tail-cone/

 

but not all: 

 

1. There are the fins on top of the tail cone. They follow the airflow, and therefore I don't believe that they are vortex generators as brought forward in the thread above, rather to streamline the airflow. But why? 

In German we say the lolly is suck or the cookie is swallowed... why do they need them milliseconds before the flow layers leave the skin? 

 

2. There are real vortex generator just below the front cockpit windows. As they stick out disturbing the airflow

              \ / \ / \ / \ / \ / \ / \ / \ / \ / \ /

they truly let little vortices rush over the cockpit windows. On the one side this will induce a lot of noise, on the other side they might clean the windows more efficiently from rain drops? 

 

3. There is one fin on each inboard engine side, which directs the airflow a little up onto the wing. I wonder that they are a benefit for all flight phases with different speeds. I assume their purpose is noise reduction. 

(Have you noticed the howling noise, wheneven the BAe146s move their flaps?) 

 

Who is able to provide more information? Thanx in advance. 

 

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To your point number 3:

As far as I know good old McDonell had a patent on having two of those on both sides of the engines. As far as I am aware they reduce the approach speed by 5 knots.

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This excellent 737 technical website explains what these vortex generators are for and their history on the 737.  They were for drag reduction and now help control the airflow over the elevators to reduce vibration.

 

It may be at "the end of the lolly", but if separated flow prevents the air rejoining behind the tail smoothly it can cause a lot of base drag, as if the tail cone was not tapered at all.

 

At the bottom of the page they talk about the radome vortex generators, which are to reduce noise. I imagine they do this by preventing the flow in front of the windscreen becoming detached.

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Ya the vortex generators at the nose actually bring the noise down. With the Section 41 basically dating from the 707, the flat glass windshields make a lot of noise. By encouraging the airflow to follow the fuselage, the airflow hits the windshields at a flatter angle than at rightish angles to it.

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