LHD-12F
Lift Duct

 



    And here's the lift duct.  The duct is made from 2 materials.  1/8" plywood makes the inner duct wall, and < 1 gal. of 2 part expanding Urethane foam is poured around the outside, encasing the ply in 2-3" of foam.  A mold made of 1" pink foam was used to contain the Urethane foam while it cured.  What I didn't get a picture of were the 2 5/8" plywood disks that the 1/8" ply was wrapped around to create the 26" dia. duct.  However, the process looked almost exactly like the lift duct in the UH-19P.  Click here to see it.  The slant behind the duct helps keep water from splashing up into the duct from waves while the craft is underway with or without lift.  The dark areas in the foam is wood filler used to fill small holes.  I laid down fiberglass on the foam around the duct to protect it from water and debris.

    I looked at the front of the duct and had to check on something.  To my amazement, the duct was exactly where it was in the CAD drawings I had made.  It cut through the front inner tack strip exactly where I wanted it to.  "Well, it should've," you say?  Yeah, but how often does something turn out exactly like it does on paper?  Haha, I just found it pretty amazing.

Hmm, I also just noticed that I cut out the nail in the tack strip that went into my thumb while installing the 3/4"X3/4" skirt attach strips.  I was using 2" nails, putting them in at an angle, or tow nailing.  As you may know, air nails sometimes curl back up after hitting something, or because they just feel like it.  That's exactly what happened to me.  I shot the nail in, about half way through the strip, it curled back up, right into my thumb, going either around or through the bone, and stopping at my nail (thumb nail).  Yeah, it hurt, but it could have been a lot worse.  The nail could have gone into the epoxy, then into my thumb :-(  The unfortunate thing about this was that I still had about 35 ft (1/8" ply and tack strip) of epoxied tack strip left to nail in.  Letting it cure without installing it would have been a big headache, so I changed the latex glove and finished the job.  OUCH!  The funny thing is, I pictured this happening just before firing the nail.  Tip of the day:  KEEP THOSE HANDS AWAY!

    The forward most lip of the duct has a small radius to help promote air into the duct.  The upper duct will get 2 layers of fiberglass on the foam, and the inside of the duct will either get a layer of epoxy, or 1 layer of fiberglass.  I added an access hole so that I could inspect the bow, and even perhaps ad some storage up there.

    In the next few days, I'll be installing the lift engine mounts and engine.  When I receive the lift fan, I'll install everything, then put the air splitter for the skirt in.  I want the splitter as close to the fan as possible which is why I'm waiting to install it until I have everything.

    As the Urethane foam expanded, it distorted my foam mold to the point of ugliness.  I've ripped off the foam nearest to the cockpit, and later, I will bend a piece of 1/2 foam around it for a more pleasing look.

    The lift engine mounts have are in the process of foaming in place.  This fills any gaps between the 1x4s and duct wall hole.  The 1X4s are 14" apart which allows enough clearance to drain the oil.

    Inside cockpit looking towards the duct.  I used duct tape to hold the foam from pouring out before expanding.

    Now the foam as set, and fiberglass has been laid down.  I used 3-4 layers which should be ample.  They're not going anywhere.  Later, I will wrap the mounts with fiberglass to help prevent cracks in the wood.

    Side view
 

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