Bell 212 Shark Fin?

[R7000]

Can someone reply with the function of that bid old shark fin on the top of some 212's?

Thanks

[BlenderPilot]

Give it a little more stability in the Yaw axis, basically you will see that fin in all the SCAS equipped 212's. It does make it nicer to fly.

[Aser]

I did the same question some time ago , I was told is about the sperry autopilot in the 212.

[remote hook]

It was to help with Yaw axis control, don't see them much anymore.

RH

[SASless]

The Dihedral Sail (Fin) was only installed on the Bell Scas machines and not on the Sperry or Sfena equipped birds. When the Scas worked it was great...the Sperry with out the FD's were okay, with the FD's it was wonderful, the Sfena was useless for reliability....never did fly with one that worked.

[Aesir]

Yes the fin used to be required for SCAS but is no longer needed. A company I used to work for had one 212 with fin another one without, both SCAS equipped. I never could tell any difference but some said it would maintain better dihedral stability in turns.
Yehh whatever, better have some real autopilots in the thing instead of Micky Mouse SCAS when flying hard IFR.

[Neerg rN]

Luxury! When I was a lad...

[Shawn Coyle]

The shark fin was required as an FAA official felt the machine had too much directional stability. How he managed to get that through as there is very little in the certification requirements about lateral directional stability is beyond me.
The issue was that with too much directional stability, the machine might be prone to negative spiral mode (i.e. it would roll into a turn or, put another way, require out of turn cyclic to maintain an angle of bank).
Rumor has it that when he retired, the shark fins could be removed... Hopefully someone will correct that if it's wrong.

[bellfest]

Luxury! When I was a lad...

...we used to fly 212's with no tail boom at all, (this is all in John Cleeses' accent by the way) our copilot, if we had one had to run along holding the skid straight until we had enough airspeed to keep straight then jump in before he was left behind:eek: . After a 40kt run on landing to the rig we would fly home, get beaten with razor wire:ouch: , forced to dring avtur and made to leave on the next sortie 1 hour before we got back and made to sleep in a wet paper bag in middle of the road:{

[Avnx EO]

You've all danced around it - but missed the real issue..... The 212 had a single thread AFCS. If that one system failed, you had nothing but the basic handling qualities of the airframe. The basic airframe did not provide sufficient inherent lateral stability to meet IFR handling requirements. Hence the big fin on the roof (It's for lateral stability - not yaw).

In the 412 the fin went away because they went to a redundant AFCS. Most other newer IFR machines out there have redundant systems - dual or better - so that a single failure still leaves you with SAS capability. You still have to have reasonable handling after a dual failure to "white knuckle" fly for 30 minutes. But the workload is allowed to be higher since it takes two failures to get there.

If the stability after a dual failure is not good enough, the Authorities drive you to a 3rd level of SAS. For example, I understand the EC-135 has a "limp home" SAS capability using some extra pitch and roll rate sensors that are plumbed into the actuators when both FCCs fail. It's not fully triplex (since it uses the same actuators) but it's close.

Hope that helps.

Avnx EO

[Neerg rN]

Sleep. We used to dream of having sleep. Our boss to used to strap us to the seats of our Bell 47's, glue our eyes open with loctite and make us fly without cyclics or radios or even a GPS. He sold the cyclics to raise money to buy stock whips to thrash us with and then made us navigate around the desert using maps and compasses. You tell young pilots of today this and they wont believe you.

[idle stop]

This used to be an old chestnut question for tps Selection Boards. Guess they'll be looking for a new question now!

[gadgetguru]

aye - they wont!

[Teton Rotor]

I realize that these posts are dated but we recently have taken responsibility for a 1977 212 that has the Dihedral Sail. In the Flight Safety training manual it states (as an addendum) "The dihedral sail, initially an integral part of the FFA IFR Package, is no longer needed. There appears to be some discussion that it actually flies better w/o the sail (understanding that this aircraft has a single channel stab system) any feedback from the field. I flew the UH-1N (granted a different stab system) which did not have the sail.

We cannot find any notification nor service bulletin that allows for the removal of the sail.

[Driptray]

If you contact your local Bell CSR he should be able to either provide the appropriate paperwork or get approval from Bell to remove this.

[Torquelimited]

TB 212-94-151 is the bulletin that allows the removal of fin P/N 212-030-498-001 installed on IFR configured aircraft.

Flew a lot of night and zero horizon crappy day ops in the basic 212 that were not configured with SCAS and although it was hands on there were no stability issues....did appreciate the force trim though.

[311kph]

Why would you take it off, it's not mandatory, is it?
What's the gain, not much weight save...
Besides, it looks cool...