Archive for the ‘Empennage’ Category

Red beacon

Sunday, October 28th, 2012

I've been planning to put some kind of red flashing ground-recognition beacon on the airplane all along, and this weekend I finally got around to making it happen. For years I've been pondering exactly what kind of beacon I need and where to mount it – see here and here for details of previous plans that didn't get completed, plus thoughts on red beacons in general. What ended up working in my favor is the fact that, while I was trying to figure out what to do, the state of the art in LED technology has advanced to the point where it now makes more sense to use LEDs rather than xenon strobes or halogen flashers for this application.

The particular unit I picked is the Vertex LED lighthead by Whelen. These guys are known in aviation circles for making certified strobes and nav lights, but they make lots of automotive products too. This one is designed to work as a warning light for a cop car or other emergency vehicle, but it happens to also be the perfect size for an airplane too. Here's a photo I grabbed from the internet since I forgot to take a "before" shot prior to getting started:

I played with various mounting positions until I decided which one I liked best – it turned out to be the top of the tail, just like on your grandpa's Cessna. Then I got out the rudder cap and started cutting away at it with a unibit and Dremel tool.

The light will be held in place by two little pieces of scrap angle that will attach to the inside of the rudder cap.

A view from the bottom side. The beacon heatsink just fits into the widest point of the rudder cap.

That has the added advantage of putting the beacon about halfway back from the leading edge of the vertical stabilizer – farther back than on a Cessna – where the light shining directly forward will be blocked instead of getting into the cockpit and annoying me by glaring off the instrument panel.

The circuit board inside the beacon is flush with the top of the rudder cap. Now we just need to do something about the exposed shoulders of the heatsink sticking out into the breeze.

I covered the beacon with saran wrap and then laid up several plies of glass tape over it in a smooth shape:

It's a little late in the season to be doing fiberglass work – i.e. the temperature is a bit low in the garage – but for small projects you can cheat and use a heat lamp to get the resin to cure in a reasonable amount of time.

After sanding the initial layup, I installed the beacon again and followed up with a flox/cabosil mixture to build up the contour and give me a nice sharp edge around the opening for the lens.

I also laid up some flox inside the rudder cap to give the body of the beacon a nice solid shoulder to sit on, as well as thickening up the inside of the lens opening to avoid having a knife edge there.

After letting that cure and sanding it back down, the general shape of the "bump" for the beacon was basically done.

I applied one more coat of dry micro with a squeegee to fill in the low spots, then sanded it smooth.

A quick spray of primer dressed it right up. I'm quite happy with how the shape turned out. There are some small surface imperfections but I'll let the painter deal with those.

The beacon lens is very low profile. I still need to countersink the mounting holes in the sides, but that can wait until I get back the drawer full of #4 tinnerman washers I loaned out.

Now that it's all sanded smooth and blended in, the slight swell for the beacon is hardly noticeable:

What's that, you say you want to see my new rudder-mounted ground recognition beacon in operation? Very well:

It's hard to properly capture with the camera, but trust me, this thing is plenty bright.


Empennage fairing fitting

Sunday, August 24th, 2008

This morning I woke up early and flew a rental spamcan up to Falls City in Nebraska, taking advantage of the unseasonably cool (for August) morning to get a little daylight between me and the ground. Falls City has always held a certain special fascination for me; the first airplane I owned came with a Falls City Aero Service keychain, and though I never got around to making the short flight, I always wondered just what sort of a place it was. Turns out it's exactly like you'd think: a medium-sized runway, some old tin hangars, and a flock of agplanes. Nice morning though.

Later on, I got out the empennage fairing and spent some time cleaning it up. I used heat and pressure to reshape the areas that didn't fit so great – by clamping down a small section of fiberglass with wood blocks and duct tape, heating up the surrounding area with my heat gun, then letting it cool down, I iteratively got it to fit pretty well. Then I trimmed back the edges, countersunk the holes for tinnerman washers, and installed it with #6 screws to see how it looked.

Not bad really. I may have some additional shaping to do along the top edge, but that's all cosmetic. Overall, I'm pretty happy with how it turned out. There are some gaps of a 32nd or two here and there, but at Oshkosh this year I saw some that looked like they'd been put on with a hammer… quarter inch gaps, even. So, I think mine looks pretty good.

Since I was already sweaty and gross from cutting and sanding fiberglass, I decided to make it a trifecta by mowing the lawn and then going for a nine mile bike ride. Now it is, as they say in the old country, die Miller-Zeit.

Installed empennage for good

Saturday, January 26th, 2008

The tailwheel mount shares several bolts with the vertical stabilizer spar, so before you can put any substantial weight on the back wheel you have to install the vertical fin first. I've had the tail propped up on a pile of styrofoam insulation for a long time, but now it's time to get this thing standing on its own feet, or wheels as the case may be.

To provide the proper amount of vertical stabilizer offset, there is a single AN960-10 washer between the spar and the up-elevator stop, on the left side bolt only. This photo confirms that I did remember to install that pesky washer:

I torqued and marked all the bolts that attach the horizontal and vertical stabilizers:

I couldn't get a socket onto some of these, so I just tightened them using a wrench and German torque.

More bolts:

I couldn't get enough access to the nuts on these bolts to apply the orange torque seal goop, so I just marked the bolt heads to remind myself that I did actually torque the bolts.

The horizontal and vertical stabilizers are now mounted permanently, and the tailwheel is capable of supporting real weight. You can't really tell from this photo, but the tail is now resting on the tailwheel instead of sitting on a pile of foam.


Extended elevator stop

Saturday, April 14th, 2007

I wrote to Van's to ask their opinion of my elevator travel situation, and their reply was:

Matt,

You can either make a new elevator up stop or add a piece to the existing stop. The horns hitting the aft bulkhead is not a bad thing, but that will not happen when you fix the up stop.

Bruce Reynolds

Okay, I can do that. Since the existing elevator stop is already drilled for the bolts that attach the vertical stabilizer, I decided to leave it alone to avoid causing further problems. Instead, I created this little elevator stop extension out of some 1/8" angle:

It's riveted to the underside of the existing stop, using the existing three rivet holes through the stop and aft deck. It effectively moves the face of the stop forward about 3/32".

I also added three flush rivets to attach the other leg of the stop extension to the aft bulkhead. Probably overkill, but it makes me feel good.

Now to test the new elevator travel. Here's neutral:

Here's the new up position:

I now have 29.4 degrees of up elevator travel, which puts me in the allowable range of 25-30 degrees. I probably could have made my stop extension even a little bit longer, but as long as the elevator travel is within the okay zone I'm happy.

Canopy work aborted

Saturday, March 31st, 2007

After putting some protective tape over the end of the slider frame latch tube, I flipped the canopy over and laid the frame inside.

The goal is to get the frame aligned on the previously marked centerline, in the fore-aft location that results in the best fit along the center spine tube. Then you mark the location of the latch tube and drill a 5/8" hole. I got as far as marking the hole location, but the temperature didn't get up nearly as high as I thought it would, so I had to give up on drilling/trimming the canopy for another day. Bah.

In an effort to find something else to do, I dug up the subpanel pieces, dimpled the top rib flanges, and clecoed the whole works into the fuselage.

Then I deburred the forward top skin, which I hadn't yet bothered to do. I dimpled where I could reach along the edges, leaving the holes along the firewall undimpled for now – the cowling attach hinges still need to be match-drilled there, much further down the road. Then I packed up the skin and drove over to John's to use my DRDT to dimple the rest of the skin. Not a very efficient use of building time, but it felt like a good day to spend a couple hours driving.

Somewhere in there I did some more filler work on the left horizontal stabilizer tip fairing. I've had this clamp for at least ten years and I'm pretty sure this is the first time I've ever used it.

Also, I stopped at Lowe's and tried to buy a new belt sander, but they were out. Bah.