Sunday, April 12, 2009

KR2S Exhaust Augmentors 01

Long time between posts, got distracted with other priorities. Back now.

Time for an update. At the end of the last post I had the top and sides of the cowl 80% complete but couldn't finish the bottom because I couldn't match the cowl up to the belly. The reason for this was I was going to extend the belly down ~60mm to incorporate augmentors and to better cater for the O-200 oil tank.

But first I needed to flip her over. I chose the rollover "D" as I was already on wheels and it seemed safer.

Flip over was easy with a few extra hands for safety. Roll her onto the drive, check for power lines then over she goes. You can just see a pair of trolley wheels to help roll it back into the garage.

This shot of the belly profile I want.

And this is what I achieved. But I've stepped forward to show this. Back to building it.

First I Extended the firewall bottom edge by the 60mm I needed. Note the fillet I built up to strengthen the corner (flox in this case).

Next I laid out 3 sheets of 20mm polyester foam to meet the profile I wanted. This technique is based on work Mark Langford had done before, modified slightly based on his learnings and other web research. I did away with NACA type walls as they added little in reverse. I will also close in the first 36" to make 2 true augmentor ducts 6.3" * 2.4" * 36" long. This gives me a 1:1 inlet to outlet area, more than enough. I've seen an RV4 with 2.7" in and 78% out with no cooling problems.

Here they are glued in and trimmed to size.

Next shape the ramp from new belly to aft fuselage.

1/2 hour of sanding and nearly done. Love converting foam into dust.

Shaping finished, side edges rounded, front edge cut back and hardened with a fillet of flox. This will help attach the layer of glass to come.
Laying out the cut lines for the augmentors. Don't need to bond the glass between the lines as I will be removing this foam.

One layer of glass to protect the foam.

then cut away the foam inside the augmentors. To help the removal of this foam I did not glue under this area.

The partially finished channels.

Here I have hardened the edges with flox for when I glass the inside of the duct. You can just see a fillet on the bottom corners, I decided these were not generous enough so later added to it with micro filler.
For the ducts I will be working with high temp VE. I needed an accurate means of measuring below the 1g my scales were capable of. came up with this balance lever which now gives me 1/4g accuracy.

1st step in finishing the augmentor ducts was to insulate with Fibrefrax. I carried this up the sides a way to add to the level of protection.
More soon.


colin said...

Dont know how long since you did the augmenters,but wouldn't the exhaust noise make the cockpit floor vibrate?and hot

Paul said...

Good question ... have not finished yet so I'll find this out when I do. Suspect not though because, the theory goes, that the exhaust nozzle finihes near the opening to the augmenter and the cool air it drags in both cools and muffles the exhaust. That's why they call them "Experimental" ;-)