Ventral Fins
 

Hello all,
Pardon my limited knowledge.
But why is Ventral Fins installed in some Aircraft type not others?
How does Ventral Fins affect Directional Control?:confused:

Raisbeck put out a promo video for the strakes on the King Air, had some good animations on how it directed airflow. For the Dornier, the venteral fins had the affect of reducing the required rudder defleciton during engine out situations.

Think of it as a "fence" to prevent excessive yawing. I'm sure someone much smarter than I will give you a much more detailed answer! :}

In simplest terms, it adds to the overall fin area where other vertical fin options are limited. Also useful if the fin needs to be aligned with a low thrust line. An example of both being the CFM Shadow.

http://p.!!!!!!!!!!!!!!/photos/middle/9/1/0/0386019.jpg

Hello.

usually it is a good sign of a screw up during the design that was found too late in the flight test process or after EIS (entry into service).

You can rarely see it today (on new model a/cs) except on some older models that got new engines, for example, or some other form of upgrade.

Cheers,

"screw up during the design" ... how gauche ... flight test fix, please ...

Don't forget that the ventral is in much 'cleaner' air at high AoA than the dorsal; it doesn't have to be a 'screw-up' at all, but could be a considered design choice for high AoA directional stability.

The modified B737-700IGW that is now the AEW&C airplane for the RAAF has a couple of ventrals fitted under the aft fuselage, reason, additional directional stability during engine out flight.
The perception is that the vertical stabilizer is partially in the wake of the MESA antenna and is therefore not quite as effective.

In addition, they've moved both the elevator feel pitot tubes to the top of the leading edge of the vertical stabilizer because of turbulence left by the MESA antenna wake in their original position.

These are design features, not screw-ups!

Cheers, FD :hmm:

Thanks fellas for the info.:ok:
"be yet wiser"

Ok, ok, screw up is a hard statement...

What I wanted to say is that adding ventral fins usually is not something that you pout on your original design...at least, not lately...

Flight test fix - yes...high AoA (after flight test) - yes...

As for 737 in RAAF - this was not the original design neither for 737 nor for its military counterpart...therefore it is still a fix...

Any mod, whatever the purpose, is still a fix...

Not a screw up:) maybe, only sometimes...:E

The Boeing 707/720 had to have a ventral fin fitted before it was allowed onto the British register.
But after the incorporation of other mods the requirement was dropped.
Not sure but I thought that they also insisted on a taller fin:confused:

If you want to see how additional Fins have to be added to straighten an aircraft's performance - Look at a Beech 1900!
Additions to the Tailplane, Keel and Ventral areas, all in a concerted effort to keep it straight.

All those "flight test fixes" made for quite a nice flying aircraft. Incidentally you can ferry the thing with some of those doo dads missing entirely.

The Learjet 35 has ventral fins to stop it dutch rolling. These were fitted in lieu of a yaw damper. And I think this is why they were fitted to some 707s. It had no yaw damper and dutch rolling was a bit of a problem on these aircraft.