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Ventral Fin...Required?


FlyingMonkey

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Hey all, this just occurred to me:

 

Is the ventral fin on CTs serving some essential purpose?  I assume it's there to give a little added directional stability, but is that really true (or maybe, not the whole story)?  Has anybody here ever flown a CT without the fin installed, and care to comment on how it flies in that state?

 

Just curious...

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Protects the stabilator from impact.

 

Hmm...that be, I've never hit the fin but I know some others have.  I think you'd have to just about be in a tail slide over the runway to bang the stab.

 

Is that a guess or deduction, or info you got somewhere from FD or others?

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Hmm...that be, I've never hit the fin but I know some others have.  I think you'd have to just about be in a tail slide over the runway to bang the stab.

 

Is that a guess or deduction, or info you got somewhere from FD or others?

 

I've taken mine off and lowered the tail to the ground. It will touch.

 

It also protects the tail itself too. The fin will break and absorb the energy.

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The fin is required for directional stability. If you try flying with it removed you might find the aircraft uncontrollable.

 

Really, uncontrollable?   :o

 

I could see it being more yaw-happy than it already is (which is a lot!)...but it's doesn't seem *that* critical to safe flight.  I always assumed it was there to tame some annoying tendencies, but not critical to flight control.

 

I concede that I could very well be wrong.  That's why I'm asking, it's something I don't think we've had a thorough discussion on.  

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I will echo Bill and others.

 

Things like extra fins and strakes and do-dads often come about from flight testing, that reveals idiosyncrasies the designers did not anticipate.

 

Let's take some hypotheticals...

 

Hypothetical one:

 

They fly the plane with no fin, and find it has an unpleasant and cyclical yawing motion when displaced around the vertical (yaw) axis.

 

Hypothetical two:

 

In spin testing, they find recovery slower and more problematical than they like.

 

In both cases, they could have redesigned the entire vertical stabilizer, maybe making it larger or extending it forward. But, since the cg is trending a little towards the nose (let's say), they decided a ventral fin which could also protect the tail and provide a more easily replaceable structure should a tail strike occur.

 

Those are just guesses. My point is, it's safe to assume the fin is there for a reason, and to fly with it removed is to take on test pilot status without test pilot pay.

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With regard to flying without the underfin:

 

Besides a nose heavy CG shift, the absence of the fairing could very well influence the flight control characteristics of the stabilator and vertical stabilizer.

Another consideration is how it would affect the "Spiraling Slipstream."

I think it has additional purpose besides just protecting the tail structure.

 

Oh, I'm sure it has aerodynamic purpose...I am just curious exactly the purpose(s) is/are.  If they just wanted to protect the stab a simple metal skid hanging down 6-12" would be lighter, stronger, and have less drag.  The rear of a CT almost looks dart-like with that big underfin, so there must be a reason for such a large area surface.

 

To be clear, I would never fly with it removed.  It's just such a prominent feature, I want to know how it works!

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Oh, I'm sure it has aerodynamic purpose...I am just curious exactly the purpose(s) is/are.  If they just wanted to protect the stab a simple metal skid hanging down 6-12" would be lighter, stronger, and have less drag.  The rear of a CT almost looks dart-like with that big underfin, so there must be a reason for such a large area surface.

 

To be clear, I would never fly with it removed.  It's just such a prominent feature, I want to know how it works!

 

Andy, what happens if you remove part of the fins from a dart?

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Andy, what happens if you remove part of the fins from a dart?

 

If you remove enough, the dart will swap ends in flight because the CG of the dart is very far forward and it would not have enough stability.  But a dart doesn't have wings, and many airplanes have very forward CG and no under fin, yet don't swap ends.

 

My *guess* is that the CT has even worse vertical axis (yaw) stability without the fin than it does normally.  The CT is pretty tail happy anyway, and without the under fin it might be a real handful when the air is not smooth.  It might also have very poor crosswind control in landing without the fin, and every little gust would knock the nose around and mess with runway alignment.

 

Just my speculation though.

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Of course the downside us weathervaning. Especially when taxiing. Also probably a pay off why we need to be more active on the pedals than a lot of other similar planes.

I do agree that it is necessary or it wouldn't be there.

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The fin is hollow and will crush easily. On the new planes they added a teflon block on the bottom of the fin for tail strikes.  The fin is not small and is is no doubt there for stability.

 

The whole airplane is hollow, and the construction of the sub fin is the same as the rest of the airplane.

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The whole airplane is hollow, and the construction of the sub fin is the same as the rest of the airplane.

 

No it's not.  Push on the sides of the fin...it's constructed like a child's plastic toy.  The rest of the plane is nothing like it.

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Remember the flight testing of the C-162?

There were two crashes due to stability problems. The under fin was added for stability control and most importantly, stall recovery.

It may be the same for the CT

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