Step 11.6, ELT

At this phase of the project my attention is being divided between a number of different tasks which has the unfortunate effect of making the progress seems slower than it actually is.  Many of these tasks are fairly trivial and don't seem to warrant a separate blog post.  Nevertheless, if I don't post regularly, my reader assumes the worst.  I assure you, dear reader, that the project is in fact progressing nicely.  

That being said, I did incur a 5 day delay to my project when I recently traveled to Southern California hunting the elusive Gorn.  Those acquainted with Star Trek will understand what a problem the Gorn can be, and may well recognize the landscape where this epic duel took place.

Alas, I didn't spot any Gorn but it was fun to look.  By the way, the location should look familiar as it has been used in literally hundreds of movies and TV shows.  Vasquez Rocks is just east of Santa Clarita CA.

This posting concerns the ELT (Emergency Locator Transmitter).  There are currently two types of ELTs used in civilian aircraft.  They are specified by the frequency on which they transmit.  121.5MHz and 406MHz.  121.5 is the old frequency that is now being phased out.  The newer frequency is the 406MHz model.  My ELT has the capability to transmit on both, but at some point in the future no one will be listening to the 121.5MHz frequency.

The 406MHz ELT signal in addition to being a beacon that can be radio located, also carries GPS information which is relayed via satellite to the would be rescuers giving them an exact location.

The ELT must be mounted within the aircraft in a specific orientation so that the radio is automatically activated in the event of a crash.  There are several suitable locations, each having its own unique challenges. In the end, I selected a location in the tailcone.  In the photo below, the ELT is the orange box.  Below that is the mounting plate that it comes with.  To the right are the pieces of scrap aluminum that I collected to build a strong attachment to the aircraft.

So the basic idea is to mount the supplied plate to the J-stringers inside the tail cone just behind the rear baggage compartment bulkhead.  A couple to circles are cut out to lighten the mounting a bit.  On the forward and aft edges I've riveted on some light weight stiffeners. 

And here is the ELT in place.  This location is considered fairly survivable due to the proximity of major structural components.  Principally, the J-stringers and aft baggage bulkhead.  

The ELT's whip antenna is located under the rear canopy, just behind the roll bar.  Its not the best location for the antenna being so close to the roll bar, but it is fairly close to the ELT itself and the antenna should have a fairly unobstructed view of the sky through the canopy.  One problem to solve with this location was how to keep the metal antenna from touching the metal roll bar.  In addition, the whip antenna needs to bend over a bit to keep it from contacting the canopy.  My solution is a nylon standoff with a slot cut into the side to restrain the antenna.  The standoffs are held in place with nylon 8-32 screws driven in to the back side of the roll bar and retained using a self-clinching 8-32 nut.

Here's the top half of the ELT antenna.  Bonus:  In the background the interior side panel is being test fit.

Next time I move on to the canopy frame.

Step 11.5, Canopy latch

This week's task is to construct the canopy latch.  I'm using an aftermarket latch from JD Air that replaces the Van's latch handle with a flush mounted one.  How much this modification will increase my top speed is debatable, but I'm quite certain that it will be more effective than painting flames on the cowl or using a slanted font on my N number. I didn't think to take any photos of the latch mechanism itself, but here is Carol at work on the latch mounts which are the first step.

It seems that our dress code needs revising.

While Carol works on the mounts I am cutting a big slot into the fuselage side.  Here is the slot after the rough cut.  At this point I'm wondering if I can save the airplane.  I know that it will look better after I file it smooth.

The mounting angles and latch are riveted in place.

Then I discover that the handle can push inward slightly which is undesirable, and I think, preventable.  I cut a stop out of .032" aluminum sheet and riveted it in place at the end of the handle.  Compare to the photo above without the stop.  The tang is bent to stop the handle when it is flush with fuselage skin.

Next, the linkage is assembled.  Here is the overly complex mechanism.  The idea is that the canopy handle pushes back on the bell crank like arrangement that because of mechanical leverage increases the force applied to the canopy hold downs (top of picture). 

Here is the inside all together.

And now a view of the handle from the outside.  The button on the left presses in to release the handle which pops outward.  As the handle rotates outward the connecting rod moves rearward to release the canopy.

 This photo didn't expose properly.  Good thing I'm not paying for developing or flash cubes.  

So now I guess I should begin work on the canopy.