Showplanes cowl ctd. [23.0 hours]

With the two outer cowl halves fitted, the next step is to fit the bottom cowl center support structure. This comes in two halves, that have to be trimmed to fit around the front gear leg/fairing. A long time ago I fitted nutplates to the bottom fuselage to hold the rear fairing, so it was fairly straightforward to make the slots necessary to allow the two halves to fit around the gear leg.

Then you fit the lower cowl, and match drill the support structure with the lower cowl. I am fitting eight skybolts, four each side of the gearleg, to fasten the lower cowl to this center support. I found that the support extended into the honeycomb’ed area of the lower cowl, which is no good since it is supposed to be flush against the solid part of the cowl, so I trimmed the nose of the structure and will close it in with a layup after I fit all of the skybolts. With that front section temporarily open, people now mistake it for some sort of air scoop!

Next I started on the intake plenums, which come as a kit from Showplanes. The lower third of each intake hole is used for induction air. Each intake plenum channels induction air down to a center combining section, which supports an air filter each side with drain holes for water, and mounts on the throttle body.

The right hand intake plenum actually intersects with the #1 cylinder head and #1 exhaust pipe, so it is necessary to trim the plenum and do layups to provide the necessary clearance. First though, the two intake plenums need to be trimmed and fitted to match the lower cowl intakes. The VAN’s front baffle ramps need to be cut out and new ones made to suit the Showplanes cowl. The support angles in front of #1 and #2 cylinders are used as a reference for locating the intake plenums, by means of a temporary metal bracket, clamping the plenums into place while epoxy’ing fiberglass supports in place.

I purchased this intake kit before Showplanes made one available for the SDS 80mm throttle body, so my center section had a 3.5″ hole in it. Once the intake positions were set up, I had to extend and reduce the throttle body connection to match. I protected the throttle body with masking tape, and coated the inlet connection point inside and out with PVA release. Then I used a balloon to bridge between the throttle and existing moulding, with everything supported in place, and wrapped several layers of fiberglass cloth to make the adapter cylinder. Once cured, I was able to pull the assembly straight off the throttle body and clean everything up. I decided I needed a bit more extension so I scuffed the outside surface, used packing tape around the throttle body, set it up vertically with the center moulding on the bottom, and applied another two layers of fiberglass. After this cured, I was able to make a nice straight cut in the end and a hose clamp applied enough pressure to the moulding to hold it securely onto the throttle body.

Next I finalized the cuts around #1 cylinder head, packed around the head to establish the required gap, and applied packing tape. I fiddled with the alignment of the entire assembly and decided I wanted to change the direction this plenum took so that I don’t have to modify the assembly to clear the alternator. So I cut around almost the entire section as well. With a balloon in place, I applied fiberglass cloth around the plenum cuts (allowing enough excess to be stretched into place), and carefully “smooshed” the plenum in place, which pushed the balloon inwards in the necessary places while establishing a smooth transition between the original shape and the modified sections.

Next job is to do the same around the #1 exhaust pipe. After that, I need to modify the left hand inlet plenum because of the A/C compressor, but that’s another story.

  • f49a
    f49a
    Center fairing protrudes too far
  • f49b
    f49b
    Trim line Showplanes front center fairing
  • f49c
    f49c
    Trimmed Showplanes front center fairing
  • f49d
    f49d
    Showplanes center fairings
  • f49e
    f49e
    Positioning Showplanes intake plenums
  • f49f
    f49f
    Positioning Showplanes intake plenums
  • f49g
    f49g
    Positioning Showplanes intake plenums
  • f49h
    f49h
    Essential equipment for fiberglass work
  • f49i
    f49i
    Setting up to extend intake plenum around throttle body
  • f49j
    f49j
    Completed intake section extension/reduction
  • f49k
    f49k
    Modifying right intake plenum
  • f49l
    f49l
    Ready for layup
  • f49m
    f49m
    Ready for layup
  • f49n
    f49n
    Right intake plenum layup
  • f49o
    f49o
    Right intake plenum layup to clear #1 cylinder head

 

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