The International Cessna^® 170 Association

lowNslow wrote:I don't see why there is so much concern about drilling holes in the roof. If you hadn't noticed these aircraft come with LOTS of holes drilled in the roof, you just have to fill them up with something (rivet, bolt, etc,) and everything's fine.

I just don’t want holes above a U shaped piece of structure that would retain any water that leaked. Anywhere else the top skin could leak and I’d likely see a stain on my wool headliner, but I would never know if there is water in the carry through spar.

Doug’s concern has real validity... You’d be amazed at how nasty/corroded those hat-sections become over the years.

During restoration or anytime the wings are off it’s a good idea to use a brush on a stick and push/pull it thru the hollow spar carry-thru to clean it out, then inspect with a strong light. A chromate-soaked-rag pushed/pulled thru it is also a good idea before reassembly, IMO.

dstates wrote:

lowNslow wrote:I don't see why there is so much concern about drilling holes in the roof. If you hadn't noticed these aircraft come with LOTS of holes drilled in the roof, you just have to fill them up with something (rivet, bolt, etc,) and everything's fine.

I just don’t want holes above a U shaped piece of structure that would retain any water that leaked. Anywhere else the top skin could leak and I’d likely see a stain on my wool headliner, but I would never know if there is water in the carry through spar.

My understanding is that the holes required for the BAS retractor are forward of U channel not above it??

lowNslow wrote: My understanding is that the holes required for the BAS retractor are forward of U channel not above it??

Karl, BAS installation requires the one nut plate IN the rear spar carrythrough, and two screws through the roof just forward (or behind?) of that. The rub comes when the carrythrough doesn’t already have a nut plate installed, in which case the easiest way to get a nut plate in there is to drill a relatively large hole on the roof directly over the carrythrough through which the nut plate is installed. After installation, that hole needs to be sealed up somehow.

cessna170bdriver wrote:

lowNslow wrote: My understanding is that the holes required for the BAS retractor are forward of U channel not above it??

Karl, BAS installation requires the one nut plate IN the rear spar carrythrough, and two screws through the roof just forward (or behind?) of that. The rub comes when the carrythrough doesn’t already have a nut plate installed, in which case the easiest way to get a nut plate in there is to drill a relatively large hole on the roof directly over the carrythrough through which the nut plate is installed. After installation, that hole needs to be sealed up somehow.

I was referring to the holes for the extra structural screws. However having holes over the hat section with plugs wouldn't be so bad as you would have an easy way to check for corrosion with every annual without having to pull the wings and as mentioned you would also have easy access to corrosion proof the area.

I finished installing the nut plates this morning. I went with the 7/16 hole in the bottom of the carry through spar on the cabin centerline. Next time I go back to the hangar I’ll remember to bring my borescope and take a look inside the carry through spar.

I also got the holes drilled through the top skin and the front flange of the carry through spar for the top of the brackets. On the home stretch now for the shoulder belt install.

I’m making progress. The pilot shoulder belt is installed and I just need a few more minutes to finish the co-pilot belt. Question for you all, what do you recommend to keep my wool headliner cuts from fraying? I was thinking about putting some super glue along the cuts...
I also took advantage of the new hole in the carry through spar and used my cheap remote camera to take a look at the inside. You can see the nut plates i installed and he ones from the factory further outboard. Condition of the spar looks good to my eye. I may squirt a little ACF-50 up there just because I can.

Thanks for the pictures and dialogue. I'll be tackling this on my ragwing starting tomorrow.

Yeah,...Looks GOOD, Doug!

My seamstress-wife suggests “Bias-Tape” which is purposed for that sort of thing. You’d place it on both sides of the edge and then whip-stitch it by hand.

It’s probably over-kill tho’... When I installed my harness’s I just punched a hole and used a stainless fender-washer to prevent wear between the triangle-fitting and the fabric. I didn’t install the plastic cover, and now 21 years later it’s still in perfect condition.

(The MS-screw passes thru a steel bushing residing inside the washer so there’s no movement of the washer against the fabric or spar because the screw is tightened against that bushing making it immobile while still allowing the triangle-end to move. I’ll try to remember to post a pic...but while your install has a more finished appearance... the bushing/washer could be hidden behind it.)

Great pics.

Nice pictures Doug, which borescope/camera did you use to take them?

johneeb wrote:Nice pictures Doug, which borescope/camera did you use to take them?

Here is a very similar one on Amazon. I have an older version from the same company. You just use a portable battery for power and your phone or iPad as the screen. There is a dimmable light on the end. I would assume the newer ones would have better resolution.

Doug