Chapter 18 - Section 23

Cockpit Ventilation

 

Ventilation is certainly important for the Cozy flight quarter, especially in summer. I looked around for eyeball vents and I was surprised how expensive a good one costs! I decided to look some more and ran into Van's Aircraft web site. They have a pre-molded ventilation set consisting of 2 air vent scoops, 2 eyeball holders,  2 eyeball vents (plastic) and 4' of vent hose - all for $66. Sure beats me making the air vent scoops. So I placed an order the next day and it arrived few days later.

 

The kit came with installation instructions, the 3 pairs of parts (left) and 4' of vent hose. The eye ball vent is made by Whisperflo. Edges of the molded parts (white) are nice and smooth to minimize air turbulence when entering the air vent. The eyeball vent openings, however, are not tightly sealed. I can see gaps between the vent doors and the inside walls - air leaks, no doubt. After looking through the instruction manual, it actually has a section showing how to seal the air gaps with silicon rubber!

 

The only problem is that the air scoop looks larger than the plans scoop and is thinner. I gather if someone took time to make a molded assembly for the vent, they would have worked out all the bugs prior.

 

 

 

Cutting Out the Vent Opening

Today, I decided to mount the kit version of the air vent to the Cozy. To my disappointment, the air scoop is just a bit too big. The vent opening is 5 3/16" long while the plans' vent is 3". If I use the plans' vent position, the air scoop would have to butt against the instrument panel. On the other hand, if I move the vent opening forward, it will get pretty close to the trailing edge of the canard elevator. I decided to make my own air vent scoops per plan, but use the eyeball holders and the eyeball vents only.

 

Air Scoop

I traced the air scoop views from the plan and carved 2 foam blocks accordingly. I held them up on long nails, covered them with sealing tape (for mode release) and glassed with 2 plies of BID (left). After they cured, I popped them off and trimmed them per plan.

 

 

 

 

 

 

 

 

 

Cutting the Fuselage Sides

I took the measurement from the plan and cut out both the outside and inside of the fuselage. The only challenge in this task is to match up the inside scoop pattern to the outside one. Once I cut out the outside pattern, I used a very fine drill bit and drilled 4 small holes from each corner (of the outside pattern) straight through to establish the position of the outside pattern. The rest was straight forward. 

 

 

 

 

 

 

 

 

Forming the Transition Duct

I trial fit the air scoop onto the inside cavity - it fits well. However, the exit of the air scoop is so close to the forward face of the IP, there is hardly any room for transition from the rectangular shaped scoop to a round tube that connects to the eyeball vents, especially if the eyeball vents are mounted at the plans location. After much agony, I decided to stay with a rectangular/square shape per plan. Due to the location of my canopy locking mechanism, I decided to position the vent opening at the same level of the air scoop (4" below the longerons) and all the way against the fuselage sides. Due to the new eyeball vent location, I only need three (3) sides for the transition duct. I cut some scrap foam and fit them against the molded internal scoops.

 

 

 

 

 

Then I terminated the transition duct end to a 3"x3" opening. The opening can be a bit smaller, but I decided to give myself a little bit of tolerance, just in case I move the eyeball vent a bit. Shaping the foam was not difficult - it took me about 15 minutes.

 

 

 

 

 

 

 

 

 

I taped the foam (mold release), glassed with 2 plies of BID and trimmed after cure... I have not attached the transition duct nor drilled the hole for the eyeball vent at this time... just checking.

 

 

 

 

 

 

 

 

 

However, I drilled a small center hole (1/16") through the IP. I made a paper template the same size as the eyeball vent and trial fit with a stick pin. Its just below my canopy lock. If I forget to lock my canopy, the handle will be right in front of the air vent.

 

Note the latching handle is a bit 'over rotated'. This is per Wayne Hicks' design - a great safety feature.

 

 

 

 

 

 

 

It took me a while to find a correct hole saw (2 11/16" diameter) for a perfect fit. It is positioned right below my canopy locking handle. There is a little bit of interference between the handle and the eyeball vent, I just need to file down the handle a bit. I will correct that when I figure out the locking mechanism.

 

 

 

 

 

 

 

 

Here's a picture showing the relative position of the vent scoop and the eyeball vent. Its a straight shot...I have to glass the scoop and bolt down the eyeball vent next... 

Due to the tight space, I have to get 8 right angled (K3000) anchor nuts from Aircraft Spruce - just for this occasion.

 

 

 

 

 

 

 

 

Attaching the Air Scoop

I just cannot foresee making a smooth transition inside the air scoop using the plans approach per Fig. 84. I believe the intent for bending the outside skin inward is to provide a smooth air flow at the scoop inlet (minimize turbulence). However, trying to blend the rest of the skin to the inner surface of the air scoop would be a challenge. I decided to cut the outer skin off and form the transition with micro instead. First step was to flox the first part of my air scoop in place. Holding it in place was a bit of a challenge - until a couple of stir sticks from Starbucks and my hot glue gun came to the rescue.

 

 

 

 

 

 

Once cured, I put duct tape all around the air scoop. Then I applied thick micro along the forward and side edges of the scoop (to smooth out the air flow). The next day (after the micro cured), I sanded smooth the transition (forward) edge. Then I added 2 plies BID at the inside step (inside the air scoop) per plan.

 

 

 

 

 

 

 

 

Glassing in the Transition Duct

I added wet flox (mixed with a bit of 5-minute epoxy) to the bottom of the transition duct flanges and pressed it down in place - completing the air scoop/duct assembly. I also taped it down in place to cure. Once the 5-minute epoxy cures, I glassed all edges of the transition duct with 1 ply BID and peel-plied. The next day, I painfully filled all gaps inside the duct with flox and smoothed them out. 

 

 

Cleaning up the Duct

After all is cured, I filled the gaps around the duct with left over micro. After cure, I sanded it smooth.