'98C Gets a New Windshield

[cessna170bdriver]

Here's the details on how I located the template for drilling the four screw holes in the retaining channel at the front edge of the roof of the airplane. This will take a couple of posts, as we seem to be limited to 5 photos per post.

The Great Lakes Aero windshield comes with the holes predrilled and chamfered, and pre-marked for the location of the drill template:

Pre-Drilled Holes.JPG

It also comes with screws and elastomer bushings. The bushings are interference fit in the holes and the screws are loose in the bushings:

Screws and Bushings.JPG

The instructions tell you to Remove the protective paper from the double stick tape in the drill template and carefully locate the template on the top of the windshield and over the top of the upper channel, aligning the template with the marks on the windshield. However, on a trial run, due to the width of the line and the uneven radius on the edges of the template, I couldn't consistently get the holes in the template to line up with the holes in the winshield (which can't be seen with the windshield in place ):

Template on Factory Marks.JPG

My next idea was to replace the mark with blue masking tape, thinking the sharper edge would be easier to line up on. This worked better, but the uneven edge and radius on the as-received template prevented me from eyeballing the template in place close enough to suit me. After all, if I'm going to drill holes in my airplane, I want to them right on the first time .

Tape Marking Method.JPG

My next thought was to true up the edges of the template, but while I was at home doing that I looked down at the pile of trimmings from my Harmon Rocket project, and had an idea: Put the template in place with the screws, then tape some sheet metal coupons (thin plastic or or plywood would work as well) to the windshield to provide mechanical "stops" for the template in exactly the right postion. Of course, I put down a layer of tape to prevent scratching the windshield. The holes are much better aligned than is apparent in the picture, due the parallax involved in taking the photo too close.

Metal Stops Method.JPG

To Be Continued...

[cessna170bdriver]

Here's a shot of the whole rig in place on the airplane. Per the instructions, the windhield is in place along with the wing root fairings and bottom retainer strip in place to firmly fix it in position.

Template in Place on Airplane.JPG

Per the instructions, I only used the template (along with a #27 drill bit) to mark the holes. Removing the windshield before drilling also made access easier, as I could stand up in the cockpit and have the work right there in front of me. As you can see, there will be gobs of (technical term for "more than adequate" ) edge distance on the holes. The blue tape is for getting the windshield back in exactly the same lateral location on final install; there is a matching patch on the windshield.

Holes Marked.JPG

I haven't directly checked the final fit yet, but the screws are a drop-in fit in the template/windshield combo, and in the template/cabin roof combo, so I'm confident that all is well.

Template Fit After Drilling.JPG

It's handy having friends with the right tools; my AI brought this one over to make quick work of replacing the #5 rivets after removing the remnants of the windshield strap. As I mentioned earlier, these rivets were originally #4 (1/8"), but the holes were oversized during an earlier repair. The squeezer I'm using on the Rocket project tops out at #4; I have no idea what the capacity of this guy is. For a sense of scale check the standard-size air fitting on the right upper corner. It took one of us to hold the weight and pull the trigger, and the other to accurately place the dies.

BIG Rivet Squeezer.JPG

Here's the result.

Revets Set.JPG

That's all for now...

[wingnut]

Miles,
YOU would make an excellent sheetmetal man!!

[cessna170bdriver]

Miles,
YOU would make an excellent sheetmetal man!!

Thanks Del! Do you have any job openings? I do have over a thousand hours working on my Harmon Rocket II project. Very little comes pre-drilled, so I've had a bit of practice getting holes in the right place (without TOO many do-overs):

HRII Right Wing.jpg

I think I'm too slow to make a living at it though; it took me half the day Sunday to get those four holes for the windshield drilled and those two rivets set... When it comes time to put the baggage door in '98C, I'm going to throw the box-o-parts behind the back seat and fly them to Mena.

[cessna170bdriver]

For some reason, I woke up last Sunday morning with a bit more motivation than I've had the last month or so.

I was hoping to get the interior painting done before installing the windshield and panel, but so far I haven't found a color match that suits me, and it's getting too consistently cool to paint in my unheated hangar anyway. I've decided to get the windshield and panel done, so at least I can throw in a couple of seats and get '98C back in aviable condition pending finishing the interior. (Some of the locals think I ought to leave it in its current "bush" configuration.) Here's some photos of the final windshield install, completed over the last couple of weekends.

This first one is the butyl tape (Cessna sealant 579.6, aka Presstite) applied so as to seal the screw holes, the bottom of the outer retaining strip, and the top of the inner retaining strip. It looks like a bit of over kill but the squeeze-out isn't as much as you might think.

Final Install 1.jpg

This one shows the windshield in place (for the final time! ) and the position of the felt strip relative to the placement of the butyl tape. I didn't get a photo, but rest assured that felt is applied up the sides and across the top too.

Final Install 2.jpg

This one shows the placement of butyl tape along the top of the outer retaining strip. I installed the previous windshield in 1984 this way and it never once leaked, so I'm not messing with success.

Final Install 3.jpg

Here it is with all the screws in the retainer strip, and initial tightening of the screws. A final tightening with a hair dryer to aid in warming the sealant resulted in slightly more squeeze-out

Final Install 4.jpg

And with the squeeze-out (slightly larger than a golf-ball size when all rolled up) cleaned up. After sitting overnight, there was about another 1/32" of squeeze-out in a couple of places, but cleaned up easily. The sealant never "sets" so any additional squeeze-out will be easily dealt with.

Final Install 5.jpg

[Bill Hart]

Miles,

After reading this post several times, I am installing a windshield in my airplane this weekend, did you only use the felt in the sides and top or did you use sealant there as well?

I went with the LP Aero windshield and so far it has been no proplem with the install. Putting the retaining chanel was not an issue at all, but I had access to a pneumatic squeezer and had the job done quickly.

[Metal Master]

Karl,
After depopulating the instrument panel for the second time just to be able to reach the nuts to change the windshield, I started thinking about nutplates or rivnuts. I asked my AI which he would prefer, and he suggested type-B sheet metal screws and tinnerman nuts. As seldom as these fasteners have to come out, that might be an option worth considering, especially if I use some sort of adhesive when I put them back in. When I removed the nuts this time, not a single washer fell off, and I had to pick them all out of the putty that had squeezed through the holes on installation, so it may be that that would be enough to hold a flat tinnerman in place for next time. I'm still mulling it over.

Here is what I did with my lower retaining lip when I installed the new windshield. Instead of using riv-nuts or self locking nuts. I manufactured doubler plates to go under the instrument panel. These were match drilled to the existing holes. Each was about an inch wide and 5 to 6 inches long and formed to sit the cuvature of the skin panel. some were curved. I think there were 5 or 6 of them. I installed 8-32 nut plates to these plates which now could be held in place by hand while some one else (grand daughter) started the nuts outside the aircraft. I used a few stand alone nuts adjacent to the door posts as I recall, however they are easy to get to. This simplifies a lot of issues. It took a little time to make the plates however now they can easily be installed or removed at any time without removing anything else. God for bid it should ever need to be. I have done this same thing on a number of aircraft and every one has loved the idea. Especially when the owner was helping to install the windshield

[cessna170bdriver]

Miles,

After reading this post several times, I am installing a windshield in my airplane this weekend, did you only use the felt in the sides and top or did you use sealant there as well? ...

Bill,

Sorry for the late reply, I've been out of town and mostly offline for the past week.

I used sealant and felt around the bottom (see photos from my Nov. 7, 2010 post). Self-adhesive felt (came with the windshield) with no sealant up the sides and across the top.

[blueldr]

Whn I installed a new windshield in my '52 model, I used rivnuts in the fuselage. I consider it hhe easiest way. it worked just fine.