Floats and ventral fins

[CaptainJon]

Just having gotten back from the International Seaplane Fly-In in Greenville, Maine, I am once again psyched about seaplane flying! (thanks again for the ride Perry) I have been holding off the purchase decision on a nice set of Edo 1400 floats that came off another BC12-D, for Tami T-Craft's restoration project.

I am not a rated SES pilot, have only flown T-Crafts on floats a few times, and know virtually nothing about their aerodynamics. My questions come down to the ventral fin. The 696 TC states in the accessory section under Edo Floats....
"(b) Model 92-1400 floats
Auxiliary fin (required on all model except BCS12D-85 and BCS12D-4-85)"

The plane that had the particular floats under consideration never had a ventral fin. Of all my other pictures of T-Crafts on floats, mostly Edo 1320's, only one showed a ventral fin.

Most of the time folks put C85's on their planes for decent performance on floats. The TC allows an exception for the BCS12D-85 and BCS12D-4-85? Is the ventral fin a power issue, CG issue, aerodynamic issue, or all of these? My project will have the Harer STC accomplished on it, making it the equivalent of a model 19 (IA9 TC). Are Edo 1400's the best choice for my project with the 1500 pound gross weight? What are everybody else's experiences out there?

Basically I'm looking for everything there is to know about T-Crafts and ventral fins with Edo floats. Please help educate me here.

Thanks,

Captain Jon

[Hank Jarrett]

Re: Floats and ventral fins

The ventral fin is to add additional yaw stability. The large lateral area of the floats moves the center of pressure around the vertical axis forward. Putting the ventral fin on makes your plane fly like a Taylorcraft on the rudders again instead of like a Fokker Triplane (not a Fokker Triplane in a fun way).
If the STC calls for it, you should put it on. I seem to remember it wasn't a complicated "bit of kit" and I think Forrest once mentioned he had one for sale once. He seems to have just about everything at his airport. If you buy one, how about tracing it so others can make one if they get floats.
Hank

Also, what ever happened to your web site? You had the best collection of Taylorcraft photos around. I used to love to just wander around in them.

[Robert Lees]

Re: Floats and ventral fins

Welcome back Jon.

Have a word with Rob Bradbury (if he doesn't chime in here first)...he's very knowledgeable about flying Tcraft on floats.

[CaptainJon]

Re: Floats and ventral fins

Hank and Rob:

Thanks for the wisdom. The aerodynamics make sense. Floats are rather large. I still wonder why so many T's don't have the fins. Need some input from our Alaska friends. As you said Hank, it doesn't appear complicated, the rear end bolting into the front clamp for the tailspring I suspect (saw that on an Aviat this weekend). How the front of the fin is attached, I don't know............. haven't seen the Edo installation drawings yet. Seems a lot of guys like to leave the tailspring on though to use as a handle moving the plane around............

As to the web site........... it's been moved from .info to .org (tcraft.org) but isn't all working yet. I'm working on some new stuff for it like search features, flash based slideshows, and video chat........ The chat currently works well between two or three parties right from the web page. You just have to set up a time or coordinate with your friends to be on the T-Chat page at the same time. Click on the flashing T-Chat plane (top left corner) and sign in with any "screen name" You can try it with a friend or two or we can try it together sometime. Eventually I'd like the page to show who's currently viewing, like this forum does, and let you have the option of requesting a T-Chat with another viewer. Back home in FL this winter I'll probably be up on the chat in the evenings while I'm working on the computer or perhaps I'll put up a "hangar cam" if I am working out there. I hope to get the whole webpage working again one of these days. It's just that retirement is so busy............ house to design and help build, kayak to paddle, grandkid(s) to visit (yes Rob, Kristie!)

Good to hear from you both. I did read Ray's discussion about ventral fins last night before I posted.

[Dano"T"]

Re: Floats and ventral fins

I notice virtually no difference in flight characteristics when I'm on floats or not on floats...I have a BC12D-85 Gilberti Conversion 1281 gross wheels....1351 gross floats...on Baumann 1500's....you only notice slightly more drag on final....even then barely noticable. You will not need a ventral fin, It will just get in your way! The only thing I ever really notice is my Cruise speed is 95 instead of 105

[Hank Jarrett]

Re: Floats and ventral fins

That is the kind of report that makes me wish my plane was flying. I really want to do an aerodynamic characterization of the Taylorcraft. I wonder if Taylor added the ventral fin and it wasn't really needed. Any idea where your CG is? If you have a forward CG that would add lateral stability. It would be interesting to see if the handling was different with he CG at the aft limit. I am NOT suggesting you do that test!!! I want to do it with instrumentation and sneak up on the limit measuring the rudder response and hinge moment. With a proper test plan, you will see the instability rise before you can feel it and before it gets dangerous. Playing at the aft CG limit can be a very dangerous area for flight testing!
Hank

[Dick Smith]

Re: Floats and ventral fins

I agree with Dano's comment. I wouldn't want a ventral fin sticking down where it was mounted on the older Taylorcrafts. It would be in the brush much of the time where I operate. I searched on this forum using "ventral fin" and read through a bunch of the comments. I pulled up a comment that answered my curiousity...something that Forrest said on the topic: "Re: Nose tank and ventral fin required:"

Quote: "For the rest of the tribe, Robert has a very unique airplane, I do believe I sent those drawings many moons ago. I will look for mine again too! The ventral attaches aft at the tail wheel bracket and forward at a cross tube. It was really only necessary for the pre war ships with the reduced fixed vertical surface aft of CG. ( fin) . Kept the ship from swapping ends on floats in the air. Known as yaw stability tests." Unquote

The portion of his comment regarding the "pre-war ships and reduced fixed vertical surface aft of CG." pretty well answered my question. There are a lot of Taylorcrafts on floats here in Alaska and I can't recall having ever seen one with the ventral fin. I do know Reeve Airmotive had a new, uncovered one in their parts inventory when they served as a dealership. My own plane doesn't require one and I've never sensed the need for "more fletching on the rear-end of the arrow". If Forrest has any further comment on the topic, it would certainly add to the discussion. I've included a few pictures that I found of some older planes sporting the ventral fins. Dick

[Hank Jarrett]

Re: Floats and ventral fins

The plane in the foreground is a 1945 and the other two are pre-war. The picture was taken sometime long enough after the war that at least two of the planes have the post war windshields. The 45 would have come from the factory with one but 28768 behind it would most certainly have been built with a 4 piece windshield and wind screen and in the picture it has been replaced with a post war one piece "blown" windscreen. That means it was long enough after the war to have had to have the glass replaced and they chose the more expensive option of the newer windshield.
With just that to go on I am guessing the picture was probably taken late 40s or early 50s. At that time I figure the factory would have told them they still needed the ventral fin.
Hank

By the way, for static stability you use the fin AND the rudder and the pre-war planes have MORE area total on the two than the post wars.

[mikeg]

Re: Floats and ventral fins

CAREFUL - spin recovery may be compromised without the additional fin area.
Mikeg

[Hank Jarrett]

Re: Floats and ventral fins

What really matters is what the written requirements are for floats. It doesn't even matter if the plane NEEDS the fin, if the paperwork requires it, you need to have it on there. This is one of those things that doesn't have to make sense, it's a requirement. What does the paperwork say?
Hank

Doesn't stop me from being curious about the QUANTIFIED loss of stability. But that is intellectual curiosity. If my tests PROVED the fin wasn't needed, I would still put it on till the FAA approved taking it off. The tests would be done while the plane was in a temporary "experimental" status. This is NOT the same status as the experimental homebuilts are in. It is for research and development.

[Dick Smith]

Re: Floats and ventral fins

Good comments...Luckily I fall within the TC's exception. I wouldn't encourage anyone to disregard legality. I'm just interested in why the exception permitted by the TC. I will wait to hear someone develop the line of thought. I just got off the phone with Chet Peek. Still digesting our conversation. Dick

[CaptainJon]

Re: Floats and ventral fins

All good comments guys...............

In talking with my local A&P/IA, he notes that virtually nobody has a fin on a Taylorcraft on floats today. Are they all installed with an exception to the type certificate, by STC or 337 perhaps. My pictures only show one fin, from Walter O'Conner's T-Craft fleet on the Connecticut River............. probably back in the 50's or 60's. I also see the same aircraft on floats in another picture with no fin............. wonder what happened?

Seems the consensus is that Edo 1320's are better at getting off the water, planning more easily than the 1400's. However, with a heavier airplane, full electrical system with a C85-12 and the Harer STC for 1500 pound gross my IA suggested that the 1400's would be a better match so as not to be "underfloated"........ any comments?

I have heard the requirement for displacement is 80% of gross per float. 80% X 1500=1200 so 1320's should be legal. Anybody seen an F19 on 1320's?

I am going to go inspect the 1400's tomorrow. Any ideas what they might be worth with all the T-Craft struts, aft clamp on fittings, etc. (2 rudders)?

[Dano"T"]

Re: Floats and ventral fins

Looks like the float bug "bit" Captn Jon....Itchy scratchy....it doesn't go away with neosporin or benedryl either The 1400's will do fine and there are some F19's with 1320's....also Chesepeak seaplanes has a BC12d-4-85 on 1320's.....they have a website http://chesapeakeseaplanes.com/

[CaptainJon]

Re: Floats and ventral fins

Thanks, Dano............ After a weekend of the Greenville Seaplane Fly-In and a ride with Perry, I AM scratching just thinking abut them......... Just about to head off to check out that pair of 1400's. Would like to know if they leak before I buy, but not quite sure how to do that........... put them in the lake....... fill them with water....... but it's raining today.....?

Just thought of something......................... would those 1400's be too heavy for Traci T-Craft with just an A65? Hate to have them just kicking around for a couple of summers waiting for Tami T-Craft's project to get done........... You are right! I've got the bug!

[Hank Jarrett]

Re: Floats and ventral fins

I don't think filling them with water is such a good idea. They are designed for the water to PUSH IN, not push out! Filling them with water might just blow the sides out.
Hank