What have I gotten myself into!

Tuesday, August 25, 2015

Nose and nose gear - part 30

Hinge box (11.3 hrs)

One pretty common complaint heard in Long EZ circles is that of cold legs. A couple of reasons for this are the inability of the typical heat exchanger to send warm air from the rear mounted engine all the way up to the nose of the plane, and the air leak prone nose compartment.

Over the years builders have come up with all kind of creative solutions for this common issue. My approach would be to seal up as many holes as possible first, then worry about possible heating options.

Looking at the upside down nose of my Long EZ, one obvious source of unwanted high pressure air is the nose gear hinge area. The gaping holes left there look capable of delivering cold air right on the pilot’s legs.

"Dang, you can almost see the back-seater from here! "

My friend Beasley had a very interesting approach to sealing this area, by using a small forward-hinged spring-activated door in front of the hole.

The forward hinged door is able to slide on the strut cover as the gear leg moves

His approach was made possible by the omission of the foam wedge that went right in front of the nose gear hinge.

This foam piece is a faint attempt at closing one of the gaps

Since I had already installed it, I had no real good place for a hinge, and had to think of a different solution. One thing I couldn’t understand was the reason for the hole to begin with, so I thought about sealing it shut from the inside.

Grabbing some ever present scraps of foam around the EZ shop, I whittled them until they fit.

Getting the foam scraps to the right shape

Foam scraps closing the hinge hole

One other advantage of this modification, was the boxing on the fifth side of the forward space between NG30s, leaving a small enclosed space that could be handy to store a few tools, or a spare tube.

Foam scraps as seen from inside the nose compartment

I removed the foam pieces, glassed them on both sides, and tested them again.

Proceeding with the modification

After more fitting and sanding

I'm starting to like where this mod is going

At this point I reinstalled the nose gear, and finding no interferences anywhere, I went on to the installation phase.

Behind the microscope LED light, the Dremel is removing foam and micro for a flox corner joint.

Given the small confines, the Dremel was used extensively in this area.

Foam and micro were also removed on all four sides of the horizontal piece

Three sides were filled with flox, then the piece was inserted carefully in place

Same piece curing, as seen from inside the nose compartment.

The next day I added BID tapes just to secure this first piece, and make sure there would be no gaps for air to get through.

Small BID tapes

Sealing the horizontal piece

Same thing one day later

After flipping the fuselage right side up, I started working between the NG-30s.

Getting ready for a flox corner

Flox sandwich

To be cleaned up

Tying things together

Peel-ply over BID

In the morning, after a little cleanup.

No air is coming through here

My feet would have rested right next to the drafty hole

So, one might ask... What's the point of sealing the holes by the hinge when you can clearly see another gaping hole right behind it?

"Yeah... what about that hole!"

You would be talking about the hole through which the nose gear actuator operates.

Well, you've got to have that hole.

The good news is that the flange I added to the front of the entire nose strut will completely seal this area in flight when the nose gear is retracted. I might get a little indirect air for a couple of minutes on takeoffs and landings, but I can live with that.

I have more ideas on how to seal the remaining space between NG-30s in a way that will not impact the actuator mechanism and still be removable for maintenance, but we'll leave that for later down the road.

Nose gear hinge "box"

It's a tight squeeze in there now

Looking toward the right NG-8

I'm very happy how this mod turned out

The struts operates just fine, and the cold air shall remains outside.

Before and after

Sunday, August 16, 2015

Nose and nose gear - part 29

Nose bumper (12.2 hrs)

The Long EZ is certainly one very unconventional airplane, so much so in fact that the uninitiated often mistake which end is the front, and which is the back.

And how could one blame them! The Long parks with the nose resting on the ground (after retracting the front wheel), engine aiming to the heavens, while the canard could easily pass for tail feathers. One should be excused for thinking it is a taildragger, except when he notices that the seats are facing the “wrong” direction.

Talk about a conversation starter. You’ve got love Burt Rutan.

About the "nose on the ground" thing… something needed to be done about that. The plans' solution was to cut “a thick piece of rubber from an old truck tire” and attach it to the bottom of the nose with a fiberglass flange.

I suppose that would have worked just fine, but over the years I’ve seen plenty of more elegant solutions gracing the noses of many a Long EZ so, once again I decided to venture out on my own, designing a new bumper from scratch, and machining it on the CNC mill (if milling rubber was even possible).

I had two antithetic objectives in mind, on one hand I needed to make sure the design would be as aerodynamic as possible, on the other I needed to maximize its size in order to have enough surface to support the weight of the nose. Searching the internet for suitable profiles, I settled on a NACA 0050, for no other reason than it was fairly wide, symmetrical, and aerodynamic by design.

I ran a computer program that calculated two-hundred coordinates for the profile, and multiplied the results by a factor of 2.5. This way I could reproduce the chosen form within the lateral confines of a 3” (7.6 cm) hockey puck.

3" hockey pucks

The hockey puck idea is not new, as a matter of fact it is pretty common in Long EZ circles, but I wanted mine to be a proven aerodynamic design, and I wanted it to be easily removed and replaced, in case it wore out or I dreamed up a different design later on.

Importing the 200 coordinates in a CAD program was easy, then I spent some time figuring out how to make it removable, and here’s what I came up with…

The flared sides increase the surface in contact with the nose, and theoretically also reduce interference drag.

The actual rubber is smoother than the one these renderings depict

The two holes are counterbored to a depth of ½” (1.3 cm) to accept a washer and a stainless ¼-28 socket head cap screw.

To withstand the side loads of the profiling operation without moving, the puck had to be bolted down firmly, and this required drilling it, then counterboring the top holes. But holding the puck down with traditional clamps deformed it enough that the hole coordinates could no longer be assured.

To bypass this problem, I designed an aluminum fixture with a depression in it the same shape as the puck, but 0.003" (0.076 mm) smaller, that would hold the puck in a friction lock. This design would enable precision drilling and counterboring operations without deforming its shape, or allowing it to rotate in the fixture. After these initial steps, I could quickly, and reliably remove the puck and bolt it down for the profiling operations.

The fixture saved a tremendous amount of time that would have been spent setting up the clamps, and finding the puck's machine coordinates (multiplied by the number of pucks I decided to make). Gone was also the danger of a collision between cutting tools and clamps.

Aluminum fixture with puck and bumper

Machining rubber proved to be a bit of a challenge with a straight end-mill. Sharpness of the cutting tool was paramount, but even a brand new one left quite a mess in its wake.

I swear there is a partially made bumper in there... somewhere.

Had it not been for the sharp cutting ball-nose end-mill, this project would have been a bust.

Freezing the rubber in liquid nitrogen would have been helpful, but I had no such setup available. Luckily for me the ball-nose end-mill used for the finishing operation left a nearly flawless surface.

A little dusty, but 100% done.

Besides a lot of vacuuming, no further operations were necessary.

Since I had bought a pack of six, I made a few extra bumpers using the same G-code.

Before and after profiling

Making the bumper

The anchor plate to be embedded in the nose of the plane would need to be precisely made if the bolts were to engage the anchor's threads without distorting the bumper. I chose a spacing of 1.200” (3.05 cm) between holes.

I made the anchor out of a leftover piece of ⅛" (3.2 mm) thick aluminum bar, the same one I used for the nose gear doors.

First, I measured the exact thickness of the bar and the K1000-4 nut-plates. They came in at 0.126” (3.2 mm) and 0.042” (1.067 mm). I then put these values into the “Rivet chooser” Excel spreadsheet I made (available in the Downloads section of this blog). This gave me the dimensions I needed.

This spreadsheet has saved a lot of braincells from an untimely end

Using the “recommended hole edge distance” of 0.234” (5.94 mm), I scribed the outlines where the rivets should go.

Scribing the lines for the recommended hole edge distance

Lining up one of the nut-plate’s holes with the crosshair, I center-punched that and a second one 1.200” further down.

Bottom hole positions

Next, I drilled both holes with the #40 (2.49 mm) drill, as suggested by the spreadsheet, and inserted the rivets the spreadsheet chose automatically based on the thickness of the materials.

Holes drilled, and chamfered. Rivets acting as hinges to locate the top holes.

Because the scribed lines were parallel to each other, all I needed to do was to drill the two top holes on the line using the nut-plates as guides, to ensure the main holes of the nut-plates would end up exactly 1.200” apart.

Top holes identified

The entire process was quick, and worked flawlessly.

Test fitting the bumper with the anchor

The next challenge was to mount the anchor to the nose, below the fiberglass skin. Page A6 shows the bumper directly below the main nose round bulkhead (NG31).

No explanation for this location is given (perhaps location isn't critical)

Given the need to excavate foam and fiberglass in an area with very thin cross-section, I was able to only partially straddle the bulkhead with my anchor point.

Marking the cut lines

Cutting carefully

Separating glass from foam is not as easy as it looks

Removing bulkhead foam

Testing the fit

Foam and micro was removed below the edges of the remaining fiberglass

I decided to add some strength a bit later, by adding 5 plies of staggered BID to help spread the weight of the nose over a wider area culminating in the rubber bumper.

Meanwhile, I had to flox the anchor in.

Keeping the anchor top surface flush with the fiberglass

Hot-glueing threads to prevent flox from sticking to the bolts (it worked beautifully)

Anchor floxed

Flox dried and surface cleaned up

After sanding the glass dull, I applied the 5 plies of BID, and peel-plied over it. Unfortunately, I forgot to take a picture of the layup until after the peel-ply was laid.