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Monday, June 02, 2014

Nose and nose gear - part 8

Bulkheads (6.5 hrs)

I am glad I found this "gotcha" before glassing. 

The new issue I’ve been dealing with is that the distance between the nose gear pivot and the forward edges of NG-30 (nose main frame) came out 0.100” (2.5 mm) short. 

While it doesn’t sound like that big of a deal, the top of the nose gear leg ends up hitting the forward bulkhead by about 0.080” (2 mm).

The way the bulkhead should fit

Interference between bulkhead and top of gear leg

I’m not quite sure how that happened, perhaps too vigorous a sanding, whatever! What I decided to do is to create a slight depression into the bulkhead, in order to make room for the nose leg protrusion.

Depression outline

This time my hands were not as steady as they should have been with the router, and I really butchered the depression, but it doesn’t matter since it’s going to get sanded down, and radioused with micro. 

In the end the depression appeared to work well.

interference removed

Creating a smooth transition in the depression

From there, the usual sequence repeated for the rear face of this bulkhead.


Pure epoxy


What followed was a little trimming, and some sanding.


Scuffing up the surface

Changing gears for a moment...

It might just be my paranoia rearing up its ugly head, but one only has to google "fiberglass bird strike" to realize that birds hitting composite planes at 200 mph are going to do a lot of nasty damage.

Birds have the bad habit of folding their wings, and dropping like rocks, when they feel threatened by your presence (bow wave), so usually the ones you end up hitting are the ones slightly above you.

In the ‘90s, I once struck a bird at night over Dallas, TX at 170 kts. Luckily the windshield didn’t break, but the sound of the impact was so loud it made me think for a moment that the engine of the Bonanza had blown itself apart. It was a very scary night, especially since we had no idea what had happened until after landing (which we did right away).

I have had many more birds encounters since then, which always ended up badly for the poor creatures, and always caused damage of varying degrees.

One of my colleagues rejected a takeoff in a CRJ (regional jet) in Washington DC, after striking a large bird. The damage was extensive. The bird ripped the airplane slanted metal skin just below the windshield, and actually entered the cockpit, injuring one of the pilots. 

Why don’t bird strike ever happen at high altitudes? 

Because that's not where birds are! Birds are down low, and birds strikes always happen at relatively low altitudes (let's say 5'000 feet and below), and guess what? That’s where I will spend a lot of my time flying this thing.

But wait a minute! Wasn’t this blog post about nose bulkheads?

Oh yeah! Back to those...

Not everyone is going to share my concern (not that it matters), but I decided to add 1 layer of kevlar to both of my nose bulkheads, in an effort to reduce the chances of coming face to face with a bird (ask Fabio).

Top of bulkheads will be trimmed to fit a door

Kevlar covering most of the bulkhead except for the top

Peel-plied and curing

These brackets will eventually attach the small bulkhead to the big one

Once cured, I drilled two holes in the bulkhead, and used two nails to affix it to both NG-30s.

Drilling holes for nails

Nails holding bulkhead temporarily

I decided to attach the bulkhead permanently while the nose gear was installed, to make sure the proper NG-30 spacing was not disturbed. This meant that only the outer BID tapes could be installed at this time.

Wetting contact area with pure epoxy

Pure epoxy where BID tape will go

Flox on edge of NG-30

Nails and clamp holding bulkhead. Flox fillet applied to the outer sides of the juncture.

BID tape pre-preg applied to corner

Peel-ply on BID tape

Same thing, opposite side.

The next day I removed the nose gear, and added the BID tapes to the inner interface with the NG-30s.

"No, these are not my landing lights!"

More scuffing on the inner joints

Preparing BID tape pre-preg

Pure epoxy wipe

Right flox fillet

Left flox fillet

BID tapes ready

Centerline on pre-preg helps position the BID tape evenly

Plastic sheet backing being removed

Peel-ply applied to BID tape

The nose was left alone again to cure overnight.

Nose job completed

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