STC Tailwheel 172 Conversion

[EZFlap]

Greetings from SoCal,

I have just finalized the paperwork and have taken over the old Ron Fravel STC, allowing early 172's to be converted to tailwheel, more or less yielding a "square tail 170C" or a "Cessna Model 171".

I'm looking to short-term borrow several 170B gear box parts and/or parts blueprints, so I can take measurements and research the manufacture of PMA parts for this conversion. The Fravel STC is currently "paper only" and I will want to offer a quality parts kit. I will be glad to offer offer some reasonable compensation for the "rental" of these parts, and they will be returned without damage.

I'm sincerely hoping that the members of this discussion group will be supportive of this, in the interest of making more taildraggers and taildragger pilots, and providing at least a "Second-best" equivalent aircraft option. Of course it can't ever have the classic look of a "real" round-tail 170, but the early 172 tailwheel conversion will offer essentially the same capability. I'm hoping your group will see this as a good way to create more International Cessna 170 Association members and participants in your events too.

I need the following 170B parts:

- Fwd. lower gear box bulkhead front reinforcement doublers p/n 0713495--11 and -12 (right and left)
- Inboard landing gear support bracket p/n 0713495-7 and -8 (right and left)
- Inboard landing gear attachment angle p/n 0713495-6 (only need one, identical L and R)
- Outboard landing gear support bracket p/n 0713495-3 or -4 (only need one, identical L and R)

I would appreciate contact from anyone with these parts, please contact me directly at info@ezflaphandle.com or 818-634-9762

Bill Berle
KWHP, Los Angeles

[Bruce Fenstermacher]

Bill I wish you good luck with this endeavor.

I'm curious what tailwheel bracket is used with the STC as I'm not familiar? If the same as the B model will you be looking for PMA parts suppliers for them. This are found cracked more on our 170s and I don't think the current supply of these will last for ever. Would be nice to have a fresh source.

[jlwild]

Bill,

Congratulations on your Cessna 172 taildragger STC effort. We have several members in the association with converted C-172's. Hopefully someone will contact you with a gearbox rental offer . Jim Wildharber

[EZFlap]

I'm afraid the Fravel tailwheel conversion uses its own tailwheel attach bracket. I believe it may be similar to the Bolen conversion, but I'm not absolutely sure. I'm told the early Fravel conversions used the 170/L-19 "alligator bracket" but because of the known cracking issues they switched over to a long wide strap that goes quite a ways forward, and is not angled upward like the row of rivets on the stock 170.

One of the first things I'm planning on doing is either increasing the thickness or width of these straps and beefing up the actual leaf spring attach mount, hopefully to get rid of the cracking problems once and for all. But I'm still on the near-vertical portion of the learning curve, and still have a lot to learn before I can speak with any authority on this.

I may be able to eventually offer this upgrade as an STC for the 170, because I will have already spent the time/money/aggravation getting it approved for the 172 conversion.

[53B]

Hi Bill,

I've done the Fravel conversion on my 172. While I can't really help with your original request, I would like to offer the suggestion of focusing on the tailwheel bracket first. The gear box parts are readily available. The tail wheel bracket is the hardest part of the conversion in my opinion and is difficult to fabricate for the typical mechanic. I think it would be to your benefit to start there.

Thanks for your efforts to keep this option avaiable.

[Jr.CubBuilder]

Go Bill! Nothing wrong with more tailwheel planes around.

[Bruce Fenstermacher]

Bill,

Hopefully we don't get to far off your original track but to clarify, here is a picture of the early 170 bracket and the later 170 bracket that looks like an alligator and is also used on the L-19.

Early 170 tail wheel bracket.png (18.43 KiB) Viewed 15031 times

Later 170 tail wheel bracket.png (13.95 KiB) Viewed 15031 times

The early bracket had a history of cracking. I'm not sure were it cracked but think it was the side plate attached to the fuselage. Thus the redesign by Cessna to spead the load and approval for it on all 170 models. The alligator bracket is the fix.

Now what we are seeing I think fairly often is cracking of the plate that spans the top of the later bracket. It cracks at the end tab that goes under the U bolt clamp at the spring exit. I'm now starting to hear of cracking of the later style bracket itself on the bottom end were the U-bolt clamp is located at the spring exit. My own is cracked in this area.

[EZFlap]

Hi Bill,

I've done the Fravel conversion on my 172. While I can't really help with your original request, I would like to offer the suggestion of focusing on the tailwheel bracket first. The gear box parts are readily available. The tail wheel bracket is the hardest part of the conversion in my opinion and is difficult to fabricate for the typical mechanic. I think it would be to your benefit to start there.

Thanks for your efforts to keep this option avaiable.

Thank you for the kind words. I agree the tail bracket is kinda funky, and would be hard to fabricate for an average Joe. There are indeed changes planned for this... I believe it originally was based on making the most possible use out of available 170B parts. Now, one or two key 170B parts are not available, so the "benefit" of the difficult fabricated mounting is gone, leaving only the pain-in-the-butt aspect.

Although the gear box parts are "available", and PPonk makes several very well-respected upgrade parts at reasonable prices, some of the other parts are getting prohibitively expensive if you buy them from Brand C. The inboard gear bracket (where the attach angle and PPonk beef up bolts on to) is well over $1000 new for each one. Buying retail Brand C parts, you can easily have $10-15K in parts alone. One of the key factors in my project is coming up with a product that is affordable, otherwise nobody will want it.

[Roesbery]

30 some years ago saw a cracked tail cone on a 52B with the early squared TW bracket. The crack was forward of the bracket itself, not the bracket that cracked.

[Bruce Fenstermacher]

30 some years ago saw a cracked tail cone on a 52B with the early squared TW bracket. The crack was forward of the bracket itself, not the bracket that cracked.

Thanks, as I said I wasn't sure were the early one cracked and apparently it may not have cracked at all but the design caused cracking elsewhere. And this info leads more credence to the alligator fix design that spreads the load differently.

[GAHorn]

The early steel bracket did indeed crack....and did so frequently and irrepairably.... It would "twist" at the aft end ( as if to condemn standing on a brake and pivoting the aircraft) ...and cracks would proliferate from that point. I've observed a half-dozen or more of the steel brackets themselves with severe cracking.
The only time I've seen the fuselage cracking is after severe abuse off improved surfaces.

The 170 brackets will not conform to the 172 tail cone and internal structure/longerons of the 172 are different (notice the difference in height of the skins on the sides), and that is why the Fravel and Bolen conversions cannot use 170 parts in that area. Neither can Fravel or Bolen tailwheel bracket mods be easily adapted to 170 aircraft so it's difficult to imagine how such a conversion would benefit 170 owners from a parts-availablity standpoint. (It's difficult to see in these pics but, the 170 has an "hourglass" or "coke bottle" shape, but the 172 has an entirely different "U" shape due to item 13 bulkhead for the rudder/stab-attach area.)

172

170B

EZ Flap, I'd think if you believed your customers would benefit by 170 Assoc'n membership... so would you...?? (and then you wouldn't appear to be violating our ad-rules either.)

[15A]

My 172 has the Bolin conversion. It has its own type of tailwheel mount. Long. Fuselage also has extra striffeners riveted inside the length of the fuselage from behind the back seat to the tail.
I won't be at the hangar until this week end. I'll post some pics afterwards.

[EZFlap]

I'm pretty sure that the 170 Association would see a win-win even if the Fravel parts (or whatever I have to change on them to make it simpler) will not be use-able on existing 170's. I'm definitely not a 170 expert or "good ol' boy" by any means. But I'm fairly confident that there are dozens of 172's that would convert to tailwheel if it was easier and less expensive than previously. Hopefully for all of us, even more than dozens ($$$$ $$$$)

Those new "171" owners will represent new members in the Association, for the same reason that the 180/185 club finally had to come to their senses recently and lower the drawbridge to allow converted straight tail 182's to become members.

Sorry to have run afoul of any advertising rules and edicts here... that was sincerely not my intention whether I was a member or not. My primary and overwhelming reason for starting this thread was to see if I could pay one of your members a small amount of money (or barter) for a short term loan of some key parts to help with this project. I'll keep this thread limited to that.

[avoight]

I have done the Fravel conversion on my old straight tail and found a few holes in the install. There are a lot of parts missing on the material list that you find are needed when you get deeper into the C-170 IPC. They are all available for the main gearbox area from the "C" store but yes, not cheap. Not to burst your bubble, but Dave Stoots has a more modern conversion available for both the 172 and the 175. I am contemplating "re-modifying" my aircraft with His STC to get away from the funky tail wheel bracket.