Nose Strakes ?
 

Please forgive my total lack of knowledge.

Background is part of an Avionic Apprenticeship etc etc .

Was reading a fairly recent issue of Flight today particularly about the new 717-300X.

It mentioned 'heated nose strakes'.

Errrm - what are nose strakes ? And what are heated ones ??

Thanks

The nose strakes are to attach the flow and can be seen on any MD80 or 90. The heat is so ice does not buildup and fly off and go down the engine.

:ok:

They're those things that look like broken off canards or step boards just aft of the nose.
They smooth the airflow over the horizontal stabilizer believe it or not.

Ah ha ! Thanks guys.

747 Focal and avioniker:

Close, but not quite correct. The strakes are aerodynamic in nature. At high angles of attack crossflow on the forebody of a fuselage is substantial. The large moment arm between the forebody and the center of gravity results in that side force creating large yawing moments. When McDonnell Douglas stretched the DC-9-30 to the DC-9-50 the strakes were added to offset the change in directional stability caused by the increased fuselage length ahead of the center of gravity. They were kept in the MD-80 and MD-90. The difference in the MD-80 and MD-90 strakes is that the MD-80 strakes are pneumatically heated while the MD-90 strakes are electrically heated. The reason for the heating is as 747 Focal says.

I wish I had my old MD-80 manual because there is a brief description for the reason of the strakes. I believe it said something to the effect of reducing the fuselage vortex at high angles of attack. Someone with a manual care to dig that up ?

I guess the 717-300 will have the longer fuselage therefore it will require the strakes.


Typhoonpilot

Typhoonpilot,
I flew the MD80 when it was still called the DC9-80 so my memory, never that good, is a bit vague, but I remember being told that the vortex from the strake would, in a sideslip, impinge on the vertical stabiliser and cause the a/c to roll towards wings level.

- or was that the vortilon on the wing of DC9's ?

At high AoA, the flow around the a/c fuselage can break up and cause turbulence around the stabiliser. The strakes prevent this by adding vortex energy into the flow, I think...

Just a thought but....

In deep stalls, T-tailed aircraft suffer from lack of elevator/stab authority due to the wing turbulence spilling back into the horzontal stab airflow.

The nose "chine" may provide a means of offering increased elevator effectiveness in a deep stall by providing "cleaner" air for the stab to work in. (It essentially pushes the disturbed wing turbulence out of the way of the tail allowing a few more degrees of elevator effectiveness than would ordinarily be found.)


PT