upsmd11
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What Are The MD-80 Fins?

Sat May 17, 2003 11:20 am

I have always wondered what the fins are on the fuselage of the MD-80's. A friend of mine who works for DL once told me they were steps so MX could wash the windows but I doubt this as the DC-9's don't have them.

Regards,
John


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Bruce
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RE: What Are The MD-80 Fins?

Sat May 17, 2003 12:11 pm

They are called "strakes" and they help improve the aerodynamic stability of the MD80. They have them on the engine nacelles too. Probably need them due to the md80s length and overall design.

bruce
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cdfmxtech
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RE: What Are The MD-80 Fins?

Sat May 17, 2003 1:05 pm

friend of mine who works for DL once told me they were steps so MX could wash the windows

I hope this is all your friend advises you about!!!
 
techspec
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RE: What Are The MD-80 Fins?

Sat May 17, 2003 2:09 pm

If my memory is correct. The MD80 strakes were installed to assist airflow across the Vertical Stab and elevators during high angle of attack situations. Prevents what is called "tail" stall. From what I was told in certain flight profiles (nose high) the wings had a tendency to rob airflow from the elevators. So the story goes....
Also, the engines have similar strakes on them also.
 
FBU 4EVER!
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RE: What Are The MD-80 Fins?

Sat May 17, 2003 6:25 pm

The nose strakes were introduced on the DC-9-50 to improve the directional stability and aerodynamic airflow at high angles of attack and certain flap positions.The DC-9-40 had an internal mechanical solution to this problem,but this was deemed uneccessesary with the arrival of the strakes.On the DC-9-50 and MD-80 series the strakes are anti-iced by bleed air via the airfoil anti-ice switches,on the MD-90 they are electrically heated.
The engine nacelle strakes were introduced on the MD-80 series for another reason,namely stall recovery.They add area which in turn adds drag and in a stall condition,this will help the nose drop faster than the tail.On the MD-90,with it's much heavier engines,there are small "flaps" at the trailing edge of the engine pylons in addition to the nacelle strakes.These operate only in the air and when the control column has reached it's fully forward position.The nacelle strakes are not heated in any way.
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liamksa
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RE: What Are The MD-80 Fins?

Sat May 17, 2003 6:45 pm

The Beech 1900 has ventral strakes which hang from the T-tail. The increase in side area combined with the relatively long moment arm improve directional stability.

They supposedly also increase rudder effectiveness in a sideslip by providing a vortex.


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ConcordeBoy
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RE: What Are The MD-80 Fins?

Sun May 18, 2003 12:14 am

While we're on this subject... what is the purpose of the small vertical fin?

It's above the "W" in "World" on the DC9 photo in the first post.
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RE: What Are The MD-80 Fins?

Sun May 18, 2003 12:32 am

It's the VHF Com. Radio #1 antenna.The one for the #2 Radio is underneath the fuselage.
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citationjet
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RE: What Are The MD-80 Fins?

Sun May 18, 2003 1:20 am

Since the Beech 1900 is based on the original King Air, Beech did everything they could to avoid designing a new tail for the 1900D.
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