replacing aft upper skin on fuselage

[IWayman]

Hi,

I would like to replace the aft section upper skin (Fig. 23, #40 P/N 0512000-8) on my 170B due to an ugly patch of the old NDB(?) antenna.

Does anyone know if you can do it without bending the new skin prior to installation?
In other words, could I remove the old skin and build and install a new skin from a flat sheet without bending it to fit the curve? Just attach with clecos and rivet it on?

I see Yingling has replacement skins for $384.00, which might be the easier option.

I am going to install a baggage door too. I will contact Del-Air for the STC due to him being highly recommended by everyone here, but was curious if anyone had a nice photo of the work in progress for having done a baggage door.

Thanks,
Ian Wayman
#26032 N1888C

[bagarre]

I've never replaced that skin but, I couldn't imagine it coming out right without first putting the bend in it.
Will be interested in what others will say.
Also interested in the baggage door info as I'm starting that mod later this year on 95D.

[c170b53]

I don't have the IPC here in front of me, but I have replaced (I think) all of the upper skins aft of the upper skin with the window cut-outs. I've also replaced the lower skins except the skin immediately aft of the gear legs (which I now need to do due to a ground loop) and I've replaced the skin forward of the gear legs. I'm certainly no expert but its easy to spot a skin replacement especially if someone has attempted to do what you are considering. If you look at a skin in these areas from the inside you will see a small longitudinal bend that gives the skin some strength along the bottom rivet line. So you need to bend the skin to fit the frames and as well bend that small lip. If you don't make your bends well, well yes the skin will form around the frames but will bulge out along the two horizontal rivet lines between the frames.
Its easy to spot such a detail by simply looking down the rivet line from the nose to the tail.
Another thing to consider is how much pressure you use to re-rivet in the skin along the horizontal edges of the skin because the material of the older remaining skin will be squeezed out and then gather between the rivets if its now done with some finesse.
Like I said I'm no expert, but Del who frequents this forums is an expert and his shop does great work. I'm not saying that you can't do it, but in my mind sheet metal is an art form.
I can paint a house but there's more to painting, in a painting.

[blueldr]

Without a jig, I would be rather reluctant to pull off much skin. I don't think I'd want to depend on the rest of the skins to hold the necessary rigidity to maintain proper aerodynamic shape.

[n2582d]

I've wondered why Cessna lapped the side skin (#58) over the top skins. At each former there is a small gap for water to drain in. I thought it would be nice to slide the side skin under the top skins until I noticed this bend in the top skins that Jim referred to. Later C-172's have the top skins over the side skins so they must have got rid of the bend at the end of the top skins. What's your XP have Jim? Is there a stringer there or does Cessna make the bend in the side skin?

Fuselage.jpg

[mit]

I changed one. It is so much easier to just order a skin it fit prefect.

[cessna170bdriver]

Del can correct me if I'm wrong, but from the dull color the first and second skins back from the rear window on my airplane appear to be replacement skins. The shinier ones were fabricated from flat sheet. I have no idea if the OEM skins come pre-bent, or if Del bent (rolled?) the ones he fabricated. It would be interesting to find out.

IMG_0627.JPG

On the RV-7 those skins are flat sheet, and seem to lay down OK.

[c170b53]

Gosh Gary I'll have to have a look but your right the XP's top skins are over the middle skin.
My 79XP and I've been told by others that Cessna's of that era had shall we say, gaps in quality control. If there's one thing that's consistent, it's the inconstant riveting in the fuselage. One rivet will be correctly formed, next one is so overdriven it's amazing it does not pop on its own and the next rivet may have been fattened just enough to hold. Lots of Cherry max, bonded skins on the doors, just different stuff than what the 170 has.
I guess the flap position indication systems on Cessna's has me scratching my head; you know where your flaps are in a 170 by looking over your shoulder. Later 100 series had a position transmitter and gauge, the XP has a mechanical follow-up flap position indicator driven by a metal jacketed cable system off the flap bus cables.
Which system might work the best?
O.K. Maybe it's just me

[Metal Master]

[quote="IWayman"]Hi,

I would like to replace the aft section upper skin (Fig. 23, #40 P/N 0512000-8) on my 170B due to an ugly patch of the old NDB(?) antenna.

Does anyone know if you can do it without bending the new skin prior to installation?
In other words, could I remove the old skin and build and install a new skin from a flat sheet without bending it to fit the curve? Just attach with clecos and rivet it on?

I do not like using Cessna factory skins, Cessna has started where they have piloted the holes in the skin by de-burring them with a DA sander instead of using a deburring tool. Leaving the skin all scratched up. It is unlikely the new skin you want to replace would actually come rolled. They are thin enough that they take the curve without having to be rolled. Getting the roll accomplished smoothly without experience will actually make it fit worse than if you did not roll it.
The best way to make the new skin is to remove the old skin completely while supporting the fuselage in an appropriate support or jig. Unbend the old skin on a flat temporary table. Match drill the new skin using the old skin as a pattern. Do not cut the new skin using tin snips, it will stretch the edges. Trim the edges using a draw knife using the old skin as the pattern while the old skin is clecoed to it. After cutting the edges of the skin with a skin knife as I refer to it you can clean up the edges with a Vixen file. Bend the edges of the skin (the flanges on the edge that run fore and aft) after you have drilled it in a brake being careful to get the radius of the bend and the bend line the same as the original skin. The result will be a skin that fits the same as the original. It will also by the same token help rejig the fuselage naturally by using numerous clecos. Then carful riveting will result in a beautiful job.
This link sort of shows how to do this in pictures at the bottom of the link.
http://www.homebuiltairplanes.com/forum ... -skin.html
In the link I did roll the skin for the tail cone however it is a much tighter roll requiring it to be done. I have replace the subject skins on 172's before without rolling them.

[cessna170bdriver]

... I guess the flap position indication systems on Cessna's has me scratching my head; you know where your flaps are in a 170 by looking over your shoulder. Later 100 series had a position transmitter and gauge, the XP has a mechanical follow-up flap position indicator driven by a metal jacketed cable system off the flap bus cables.
Which system might work the best?
O.K. Maybe it's just me

The best flap indicator in the 170 is that big stick between the front seats.

[Bruce Fenstermacher]

... I guess the flap position indication systems on Cessna's has me scratching my head; you know where your flaps are in a 170 by looking over your shoulder. Later 100 series had a position transmitter and gauge, the XP has a mechanical follow-up flap position indicator driven by a metal jacketed cable system off the flap bus cables.
Which system might work the best?
O.K. Maybe it's just me

The best flap indicator in the 170 is that big stick between the front seats.

Cessna designed TWO flap indication methods. The head in the cockpit one is the flap handle. The head outside the cockpit method should be part of your scan left picking up the flap position in your peripheral vision, then scan right picking up and reaffirming the flap position in your right side periphery.

Of course an alternate to the head in the cockpit method is a temporary repositioning of the throttle hand from the throttle to the flap handle to approximate it's position. This last alternate method is the one I'd use most often.

[c170b53]

Cessna has started where they have piloted the holes in the skin by de-burring them with a DA sander instead of using a deburring tool.

I'm not sure Jim what the intent is with Cessna's process and the resulting finish you describe. I've got skins from them that are entirely treated that way and my 79 XP has the same thing but the reason I say I'm not sure at the reason is they have treated areas that have no rivets and left the same skin with the rivet areas smooth.
Another thing ...Humm

[Metal Master]

Cessna has started where they have piloted the holes in the skin by de-burring them with a DA sander instead of using a deburring tool.

I'm not sure Jim what the intent is with Cessna's process and the resulting finish you describe. I've got skins from them that are entirely treated that way and my 79 XP has the same thing but the reason I say I'm not sure at the reason is they have treated areas that have no rivets and left the same skin with the rivet areas smooth.
Another thing ...Humm

I do not know why Cessna does that except possibly as a labor time reducing measure. The Alclad coating is very thin and using a DA sander too debur skins compromises that Alclad layer. I figure in this day and age they would plan to prime the part, it seems their new airplanes are prepared that way. But if that is the case why not just use bare aluminum. But then they would have to change all of their drawings.The reason they pilot drill parts is that it helps in alignment of the new skin. I have found that often times their new skins hole pattern does not match the older parts ribs and bulkheads and I would rather fit them myself. I have found on occasion the Cessna part can not be used because of this. For me it saves time and $$$ to just make your own skins.
Jim

[n2582d]

If I recall correctly the late Harry Dellicker was able to order "unsanded" skins from Cessna for Steve Jacobson's 170A restoration.

[Metal Master]

If I recall correctly the late Harry Dellicker was able to order "unsanded" skins from Cessna for Steve Jacobson's 170A restoration.

As a mater of fact I have by asking for un-piloted parts from Cessna parts and working with our local Cessna service center have been able to order un-drilled skins. However it it is still cheaper, faster and the skins fit better if I make my own.