Dorsal Fin Attachment

How to keep the Cessna 170 flying and airworthy.

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GAHorn
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Dorsal Fin Attachment

Post by GAHorn »

The 170A introduced a more streamlined appearance… which has the additional benefit of somewhat improved directional control and spin-resistance…at the penalty of increased weather-vaning…. by the addition of a Dorsal Fin Assembly.

Some 170 owners have added that feature to their earlier fabric-winged model. (Needs a basis of approval but should be easily acceptable.)

The 170 B-model also has this Dorsal Fin Assembly. BUT THE B-MODEL has a different method of attachment and a slightly different SUPPORT (ribs and channel.)

A common method of ABUSE is to move the airplane around on the ground by grabbing that Dorsal Fin and giving it a SHOVE…. which can damage and/or break the small “mounting bracket” angles which connect the B-model Dorsal Fin to the fuselage.
Do NOT PUSH here.
Do NOT PUSH here.
If that “mounting bracket” (PN-0531112-4) needs replacement…. you are likely looking at an Owner Produced Part… made from .032 2024 Aluminum. It is rivetted to the lower rib PN-0531108, but is attached to the fuselage with AN526-1032R8 machine screws and AN365-1032 lok-nuts.

The A-Model is DIFFERENTLY-ATTACHED. It’s “channel” PN-0531110 (slightly different than the B-model 0531110-1) is attached with a AN366-1032 nutplate and a AN3-4A bolt. See the two screen-shots of the appropriate IPC illustrations.
A-Model Dorsal Attach
A-Model Dorsal Attach
B-Model Dorsal Attach
B-Model Dorsal Attach
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Poncho73
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Re: Dorsal Fin Attachment

Post by Poncho73 »

I wonder if either attachment option is applicable to my straight 170?
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GAHorn
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Re: Dorsal Fin Attachment

Post by GAHorn »

Poncho73 wrote:I wonder if either attachment option is applicable to my straight 170?
If you are planning on modifying your straight-170 you’ll likely source your parts from a salvaged airplane and that should guide you as to which method you employ.

(I can say that our Assoc’n does have one of the “rib, dorsal fin, lower, forward” PN-0531111 , common to either installation, in NOS conditon.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
Metal Master
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Re: Dorsal Fin Attachment

Post by Metal Master »

Note 609 from the 170 type certificate . (609) Model 170A dorsal fin (eligible on Model 170).
Regards,
Jim
A&P, IA, New owner C170A N1208D, Have rebuilt some 50 aircraft. So many airplanes, So little time!
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GAHorn
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Re: Dorsal Fin Attachment

Post by GAHorn »

Metal Master wrote:Note 609 from the 170 type certificate . (609) Model 170A dorsal fin (eligible on Model 170).
Regards,
Jim
Thanks for pointing that out, Jim. I don’t know which Revision included that note, but Rev 55 is the current version, and it specifies the 170-A Model method of attachment.
A-799_Rev_55.pdf
(80.8 KiB) Downloaded 157 times
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Poncho73
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Re: Dorsal Fin Attachment

Post by Poncho73 »

OK thanks. Looks like the “A” style attachment is the way forward.
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Poncho73
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Re: Dorsal Fin Attachment

Post by Poncho73 »

On that thought, does anyone have a line on getting a dorsal fin?
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dstates
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Re: Dorsal Fin Attachment

Post by dstates »

Poncho73 wrote:On that thought, does anyone have a line on getting a dorsal fin?
Try emailing global@globalparts.com. They have a wrecked 170A that might have a good dorsal fin (they are in British Columbia, Canada). My contact there was Lyndon.
N1235D - 1951 170A - SN: 20118
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Poncho73
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Re: Dorsal Fin Attachment

Post by Poncho73 »

OK thanks
hilltop170
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Re: Dorsal Fin Attachment

Post by hilltop170 »

I’ve checked a couple of the usual sources here in Alaska and no luck on finding a serviceable 170A vertical stab. I found a damaged one at Sutton Aircraft Salvage, 907-715-6998, that could be rebuilt but did not get a price. The top is crunched as most of the wrecks are nose-overs.

If you can’t find one, Gray Morris, M&M Aviation at Birchwood Airport, 907-688-3900, can make you a new one. It won’t be quick or cheap but it will be new and correct. I talked to Gray today and he said he is booked up for awhile but he would be glad to talk. Building mostly Cessna airframes, wings, and components is all he does. He works by the hour and doesn’t quote jobs but he works fast and does excellent work.

Good luck.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
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