Fuselage oil canning

[N3092A]

Does anybody know of approved data to install a stiffener inside on the cabin top in the section just aft of the rear baggage area bulkhead. I get a lot of oil canning from that area in flight and I thought I remembered a service bulletin about it years ago. Maybe it was for the 172. It would be from station 108 to 140. Probably the same bulb angle as the rest of the stiffeners on the cabin top.

Thanks

[GAHorn]

Is this on your Fleetwing Seabird?

(I'm searching for the info....but it might narrow things down a bit if I knew which model out of three 170's and the dozen or so 172's I was looking for.)

[GAHorn]

OK, Simon! I got it...a '53 or '54 170-B !

[flyguy]

OK, Simon! I got it...a '53 or '54 170-B !

N-number : N3092A
Aircraft Serial Number : 25736
Aircraft Manufacturer : CESSNA
Model : 170B
Engine Manufacturer : CONT MOTOR
Model : 0-300 SER
Aircraft Year : 1953

IT AIN'T THAT HARD GEORGE

[GAHorn]

OK, Simon! I got it...a '53 or '54 170-B !

N-number : N3092A
Aircraft Serial Number : 25736
Aircraft Manufacturer : CESSNA
Model : 170B
Engine Manufacturer : CONT MOTOR
Model : 0-300 SER
Aircraft Year : 1953

IT AIN'T THAT HARD GEORGE

Welcome to the real world FLYGUY! (You're only about 3 hours and 3 minutes too late! See the times of the msgs!)

N3092A... How do you know it's oil-canning in-flight? Is your rear baggage-wall removed and have you observed it? Or are you hearing it while taxying on the ground?

While taxying on the ground many metallic sounds will emanate from the rear of the aircraft, most of which is caused by the tailwheel and tw-springs and control cables which will "slap". Rudder cables are especially prone to this. (I insulated my baggage-wall aft-side with foil-backed foam deadener. I also added an upper wall behind the hat-shelf. Worked great!)

The flexing of the fuselage between sta. 108 and 140 is primarily resisted by the fuselage side-plates. Do you have any rivets which are "smoking" in those areas?

[gwillford]

My 170 skin has a tendancy to oil can a bit there when the aluminum is hot (sun). I cut a length of L shaped aluminum extrusion (yes hardware store) and epoxied it to the underneath side. No drilling or riveting thus no altering of the airframe and no paperwork. Worked great.

[wingnut]

Just some advice; if you are having problems with bulbed angles, canning skin, slapping cables, and smoking rivets, I wouldn't fly that plane on New Years Eve. You might have a few "smashed" bulkheads

[N3092A]

I'm sorry about the lack of specifics on the airplane. It's a 53 B model as mentioned. I am positive that it is the skin. I can go back there on the ground and make it do the same thing. It is especially noticeable when warmed by the sun. When I've sat in the back seat in flight, it sounds like it is doing it in response to air buffet/flow disruption in that area. I took all of the fiberglass insulation out years ago to prevent corrosion, so it is probably more noticeable than most of our airplanes. Now I have the airplane completely apart and would like to add some stiffeners, and wondered if any one knew of a legal way to do it.

Thanks

[GAHorn]

There are several legal ways to do it. You could add a stiffener (similar to those in the sta prior to 108) and probably log it as a minor alteration. (You may find it necessary to accomodate the ELT antenna commonly mounted in this bay.)

This might make the oil canning noise go away but it would be unlikely to add much real strength.

Look for evidence of overstress in the lower fuselage, belly and sides, and correct it. (Hard landings?)

By the way...I notice our airplanes are only 23 serials apart.

[wingnut]

Cessna has been putting some adhesive backed sound deadening/harmonic vibration dampening material in the newer airplanes. The PN# is P440032.

I know the 310's had a problem with the fuselage skin canning right where the wing leading edge meets the fuselage. In turbulence, the popping sound was pretty unnerving, especially at the wing root. This stuff would cure the problem on most of them.

I don't know how it's packaged; whether you get 9 one sq ft pieces, or 1 piece 3'x3'.
It would be legal, not even considered an alteration, easy to experiment with, etc.

Oh, and everything George said too. Inspect for damage. If this stuff doesn't help, you can bond an aluminum doubler on the inside, using Hysol 9309 or even PR1440B. After the doubler is fabricated, and surfaces cleaned, you'll want to apply the adhesive, place the doubler in position, temporary tape in position, lay some plastic between the doubler and get some dense foam rubber and plywood and a port-a-power to apply pressure while the adhesive cures. Just apply enough pressure to make good contact, careful not to distort the skin as viewed from the outside.

[minton]

Well, In reference to a minor repair. You'de be better off getting your advise from FAA "approved data". When you start installing rivets and extra structural materials you've crossed the line. Remember these aircraft fall under CAR-3 certification not the EAA.

I just checked out my '54 and it has two bulb angles set one on each side of center on the top skin. I'd reference the 170B parts book to see if they are required in all year models. If yours does'nt have those installed I'd be putting them in. But first give your A&P a call for assistance with advise, installation and the paperwork. A third down the center might require a field approval.

I did have a similar experience a while back and could see the area "oil can" while sitting in the three point attitude . It appeared just aft of the bulkhead. The suspect aircraft did have those angles installed at the time. Sometimes there is a beacon or strobe installed in that area which could weaken it. I would install a "U" shaped stiffener with 1/2 inch flange extending at least 2 inches outside of the outer circumference of the beacon. Use .040 2024-T3 with the proper radious bend the full length of that bay if such is installed. Any doulbers or angles must terminate 1/16-1/8 inch from the bulkheads. Be sure to cromate the underside and use appropriate size and rivet patterns and water seal the base of the beacon. And YES, Either way it would require the FAA's involvement unless you could find some model of beacon with a STC that addressed the installation in that specific area.

I found some info in the Cessna 100 series maintenance manual that somewhat addresses the subject Section 19 pg 27.

[N3092A]

Thanks for the replies guys. There isn't any evidence of stressed skins any where else. I think that maybe I will try some sound deadening material. George, I did notice that our airplanes are very close in serial numbers. Unfortunately, I think mine has had a bit of a harder life. It was delivered as a float plane and then spent some time on skis in the frozen north. I am trying to make it proud again though. Thanks for the help.

[n2582d]

I just checked out my '54 and it has two bulb angles set one on each side of center on the top skin. I'd reference the 170B parts book to see if they are required in all year models. If yours does'nt have those installed I'd be putting them in.

My 170B didn't have any stringers on the top surface of the skin between stations 108 and 140 like the forward two skins do on either side of the bulkhead at station 90. It only had two stiffners in the radius, #39 below. In looking at the parts catalog it appears that between stations 108 and 140 there are no stringers along the top of this skin (#40). Yet when looking at #39 "Stiffner--Aft section upper skin" it lists 3 as the required number. This would make me think that there should be one along the centerline of the top skin even though the rivet pattern for one is not shown. What am I missing here?

Upper Stringer.jpg (50.15 KiB) Viewed 11036 times

[GAHorn]

Item 39 is only as illustrated on my airplane....two of them...at each upper curved side.

[hilltop170]

That's your gross weight indicator. When that skin oil-cans, quit loading.