Ziggy
Topic Author
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Joined: Thu Jun 21, 2001 11:07 am

Vertical Fins?

Thu Feb 21, 2002 2:31 pm

On the Beech 1900 series there are vertical fins or stablizers set below the horizontal stablizers. (like upside down winglets) I'm wondering if their purpose is like the winglets, to use the vortices to enhance proformance?


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 Big thumbs up Ziggy
 
Illini_152
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RE: Vertical Fins?

Thu Feb 21, 2002 3:52 pm

I doubt it. If you look at the vertical stab on the 1900, is is amost identical in size to the stab on a 350 King Air and a 99 Airliner. More than likely the extra vertical surfaces were needed to increase lateral stability in the event of an engine failure, and rather than redesign the whole tail, Beechcraft just added a few extra surfaces on there.
Happy contrails - I support B747Skipper and Jetguy
 
Mr Spaceman
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RE: Vertical Fins?

Fri Feb 22, 2002 1:13 am

Hi guys.

I've always wondered about those vertical fins on the tail of a beech 1900 myself. I also thought it had something to do with stability, as Illini_152 mentioned, because I'm used to seeing winglets on an aircrafts main wing at the very tip...not on the horizontal stab. Just an observation.

Hopefully someone will let us know for sure what they do...Illini_152 didn't seem certain, however I suspect he's correct about stability.

Regardless of their purpose do they have a specific name?

The MD-11 also has winglet type devices which are on the bottom surface of the wingtips. I feel these devices must deal with the forces of tip vortices because of their location.


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P.S. Some people think that winglets are used to enhance performance, as mentioned by Ziggy, and some think their purpose is to reduce drag by reducing the vortex at the wingtip. Which is it? Can their purpose be for both reasons at the same time?

Chris  Smile

"Just a minute while I re-invent myself"
 
bio15
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RE: Vertical Fins?

Fri Feb 22, 2002 5:47 am

Well, reducing drag is enhancing performance.

-bio
 
Metwrench
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RE: Vertical Fins?

Fri Feb 22, 2002 2:48 pm

A Native American, (A&P Mechanic), told me once, "Indians never put that many feathers on an arrow".
 
apathoid
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Metwrench

Fri Feb 22, 2002 4:24 pm

As opposed to the Fairchild Merlin with the huge placard that says "don't stall with the SAS system inop." ???? At least with a Beech a stall isn't a death sentence.  Smile/happy/getting dizzy
 
Turbotrent
Posts: 146
Joined: Tue Jan 01, 2002 8:43 pm

RE: Vertical Fins?

Fri Feb 22, 2002 10:35 pm

Could anyone explain to me how the winglets really work, I mean how do they reduce drag? I hope someone can help me.

Greetings,

Tom
Man's flight through life is sustained by the power of his knowledge.
 
Staffan
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RE: Vertical Fins?

Fri Feb 22, 2002 11:08 pm

Tom,
The basics behind a wing is that there is high pressure under the wing and low pressure on top of it to create lift, this pressure differance is achieved by shaping the wing so that the air has to travel further to go above the wing than the air going underneath it.
Anyway, when you have this pressure differance, the air under the wing will try to 'escape' to the top of the wing by curling across the tip of the wing, this has two negative effects. The first is that you loose pressure under the wingtip, and the second is that a vortice is created. A vortice is very turbulent air spiraling off the tip of the wing, a motion started by the air flowing across it, this creates drag.


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So, by mounting a winglet you can somewhat reduce the vortice and at the same time gain something from it. The winglet is shaped like a small wing, with a carefully calculated shape and and angle of attack, and when the secondary flow (across the wingtip) hits the winglet, alot of the energy in this air is used to create a liftforce pointed inwards and slightly forward (somtimes referred to as thrust), the result being that the air is slowed down and a much smaller vortice is created at the tip of the winglet.

If you do a forum search on the subject you'll find more info on it.

Hope that helps,

Staffan
 
Turbotrent
Posts: 146
Joined: Tue Jan 01, 2002 8:43 pm

RE: Vertical Fins?

Fri Feb 22, 2002 11:19 pm

Thanks a lot Staffan, I understand it now  Big thumbs up

greetings,

Tom
Man's flight through life is sustained by the power of his knowledge.
 
AJ
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RE: Vertical Fins?

Sun Feb 24, 2002 7:29 am

The vertical fins below the horizontal stabiliser and the fuselage allow for directional stability at high angles of attack due to the large (monsterous) bulk of the fuselage blanketing the tail.
The horizontal fins allow a more flexible CofG range.
 
Mr Spaceman
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RE: Vertical Fins?

Tue Feb 26, 2002 4:14 am

Good info gentlemen.

It's interesting how the Beech 1900 has these vertical fins to help it's stability, but other similar aircraft such as the Beech King Air 350 don't. It just goes to show that every bird is different.

Thanks.

Chris  Smile
"Just a minute while I re-invent myself"
 
UALPHLCS
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RE: Vertical Fins?

Tue Feb 26, 2002 1:22 pm

Thank you for this thread first of all its a question i always wondered about. In addition to the vertical surfaces on the tail could someone tell me about the little horizantal surfaces under the tail on the fuselage? In the first pic they are clearly visable right above the registration.
A little less Hooah, and a little more Dooah.
 
FredT
Posts: 2166
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RE: Vertical Fins?

Tue Feb 26, 2002 5:39 pm

UALPHLCS,
quoting AJ, two posts above:
"The horizontal fins allow a more flexible CofG range."  Big grin

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
speedbird001
Posts: 28
Joined: Thu May 04, 2000 5:12 pm

Wing Physics

Wed Feb 27, 2002 5:31 am

This is quite an interesting subject which I have heard the usual theory of lower pressure below the wing pushing up etc, but I have also heard another theory that the air molecules "stick" more to the top of the wing. Does anyone have more information on alternitive theorys for wing lift generation?
Many thanks

Concorde 001
 
delta-flyer
Posts: 2631
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RE: Vertical Fins?

Wed Feb 27, 2002 8:24 am

The directional stability is the same reason for the large vertical surfaces on the space shuttle carrier 747 and on Hawkeye


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Ziggy
Topic Author
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Joined: Thu Jun 21, 2001 11:07 am

RE: Wing Physics

Wed Feb 27, 2002 11:28 am

What happens is that you have a High pressure below the wing and low pressure above it. You have what is call a boundary layer or a still or slow moving air. This layer is if at most only 1/16 of an inch and could be smaller, but yet it's present. I'm sure a aero engineer could go into far more detail about this than I can. But that's it in a nut shell.

Ziggy  Smile
 
EssentialPowr
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RE: Vertical Fins?

Wed Feb 27, 2002 12:01 pm

I've watched this thread with some interest...

With regard to the 747 and the E2, the end plates on the vertical stabilizer are to enhance directional stability, as mentioned above. The reason for the endplates, as opposed to the std config, is due to the fact that the space shuttle on the 747, and the radome of the E2, certainly impedes airflow to the vertical fin...Grumman chose to build 1 tail, and used it for the C2 and E2 for the same reason as described below:

The 1900d is, as most know, simply an evolution of the B1900C, and of the King Air series. In particular, the tail shared by the -200, -300, -350, -1900c and -1900d is the same tail as introduced by the F90 in 1979, for a 750 shp application. As the a/c was lengthened to the -200 and above, the same tail worked simply b/c increasing the length of the a/c compensates for tail area.
(Witness the 747SP, the "short" 747 that has one of the largest vertical tails in the history of a/c production, to include the C5, AN 124, and B52.)

As horsepower increased, the vertical fin area reached a point where it HAD to be increased for the 1900d. So why not use the same part and not have to retool? BINGO.

So for the 1900d, which has a great deal of single engine Reserve HP to accomodate and engine out situation), extra vertical surface was needed, hence the endplates on the tail. It's also greater than 12,500 lbs, which places some additional constraints on the design.

The directional stab topic surfaced about 2 wks ago; my assumption for the hozizontal surfaces on the 1900d is the same as the for the endplates...it's cheaper to build the same vert tail for a variety of a/c, and simplify the 1900d as needed to account for its specific requirements in the pitch and yaw (and therefore roll) axes.

Cheers-
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Vertical Fins?

Wed Feb 27, 2002 6:04 pm

In short, the viscosity of the air will tend to make it follow the curved upper surface of the wing. This means there is a downward acceleration of the air. There's never an acceleration in a fluid without a negative pressure gradient, i e a region of lower than ambient pressure in this case. This is what generates lift.

You can also say that lift is generated by (mainly) the top surface of the wing accelerating the air downwards, creating a lift force proportional to the downward momentum (downwash) given to the air.

BTW, boundary layers can be well over 1/16th of an inch. The boundary layer thickness can be calculated from the reynolds number and the distance from the leading edge. It will increase in thickness faster in turbulent than in laminar flow. To get an appreciation of boundary layer thickness, note the distance between the fuselage and the intake lip on the radiator of a P51 or the #2 engine on a DC-10/MD-11. This distance is there to prevent boundary layer ingestion.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.

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