KR2S Exhaust Augmentors 02

I apologise for the long time between posts, been busy.

When I left off last time I had built the two channels for the augmentors and lined them with fibrefrax.

Next I covered the fubrefrax with 2 layers of BID using high temp vinyl ester resin. This stuff stinks like crazy, need plenty of ventilation.
A little post cure to harden things up.

Now it's time to make sills to attach the cap to. I reused the chunk of foam I cut out of this slot and dropped the top surface a little to allow for the thickness of the cap and rounded the edges for a generous fillet. Packing tape allows easy release and ensures a smooth finish when I cut the foam out later.

FAILURE number ??? (too many to remember them all). You see I have been working almost exclusively with Epoxies but for this fillet I was using VE. I mixed VE with flox to make the 900mm long ledges but as they started to harden they started to shrink. Over the 900mm length a 2.5% shrink amounts to a shortening of the top edges by 25 to 30mm. This was enough to start bending the existing channel up out of it's bedding. The cracking noises as energy was pulling the edges away was quite alarming. S#!+ what do I do now....? I pulled out a grinder and cut out the semi-hard resin, I'll have to come up with a recovery plan. Had I known about this earlier I would have done 2" segments 2" apart, let them set then come back and do the other set of 2" segments. Oh well experimental category is for education.

Well I mixed up a batch of resin and bonded the channel back into place. Changed the plans to have the cap extend past and over the channel edges rather than inside it. This is a sheet of BID & VE I made up on a piece of glass. Nice and flat.

This is a shot up the augmentor with the cap bonded into place. I will come back later and fillet the joints once the aircraft is back on it's wheels.

This shows the transition from augmentor to the exit ramps.

Here I'm trying out my vacuum bagging rig. I'm making a wide sheet of Glass and will later cut it into strips and stack them together to make a sturdy strip to harden the front edge of the augmentors and for a place to attach piano hinge for the cowl.

Strips bonded together.

and bonded to the front lip. You wouldn't believe how tough this is now.

I've fared back from the lip and have started to attach the hinge. I will cover the whole lot later with a final couple of layers of glass to protect it from stone damage.

2 layers if glass and peelply

Trimmed, sanded and a couple of layers of epoxy primer. I will come back much later and do a little bit of filling and sanding but for now I just want to flip her back the right way up so I can start the final push for the finish line.

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.

KR2S Building the Fuselage

I have added this for continuity from the start. Much of this excellent work was done by the original owner, thanks for the fantastic start Gav.

(to view larger simply click on any of the images)