Will you be at Evans Head on 9/10 January? I am in the process of putting the 2 pac top coat of paint on my Sierra so won't be quite ready to fly in but I will be there to check out all the old, new, beautiful, ugly, slow, fast, quiet, noisy, large, small, cheap & expensive anything that flys.
It only needs 1 coat, is really hard, very chemical & corrosion resistant & has a better gloss finish IMHO. Most of the composite and aluminium A/C I know of around here are painted with a 2 pac paint. Wouldn't be any good on fabric.
I have been wondering why my red and silver sierra was at least 10kts faster. well I got a phone call from a owner who put a fairing on the under carriage who is getting another 10kts, then the penny dropped the silver sierra had the u/c fairing on it ( 148kts). I will be putting one on when we get back to the workshop.
I have made a fairing for the nosewheel leg mainly for aesthetics but it will also reduce drag. I looked at photos I have of your old red & silver Sierra & couldn't see any undercarriage fairing other than the main leg being shaped. I have a semi circular leading edge on the main leg & the brake line runs through a 6mm tube on the rear that I have glassed on so the trailing edge is faired somewhat. Do you mean putting a fairing right across the fuselage?
Gday Guys I did the mod to my Cheetah and definitely picked up 8 to 10 knots, at first I couldn't work out why I was doing 10 kts faster downwind in the cct. Over the next few days I did some test runs and sure enough she's much quicker and quieter as well, a definite improvement to performance since fitting the fairing.
The fairing was a simple $20 mod. Using a length of 50 and 50 aluminium angle (90 degree). I drilled a few holes in it and bolted one side to my workbench sandwiched between the bench and a piece of 90 x 75 timber and then used a block and hammer to gently tap the other flat surface till the 90 degree was more like 45 degrees. My main wheel spar sits 40cm from the bottom of the fuselage, so the intent was to just deflect the air that gets trapped in the pocket between the main wheel leg spar and the bottom of the fuselage. Because the spar flexes during taxiing and landing I needed to keep it away from contacting the spar.
I then cut the newly shaped piece of angle to the same width as the fuselage and using rivets and sikaflex attached it across the fuselage about 3cm in front of the main leg spar. To attach it I used 2 rivets at each end into the frame and 4 extras along the skin beneath the fuselage just to hold the sikaflex tight and add some strength.
Effectively it just diverts the air from the bottom of the fuselage around the wheel spar instead of that air getting caught up in the pocket between the fuselage and the spar.
While I was hoping for a tad of extra slip streaming, my main purpose was to stop the sheep poo and bugs getting stuck in between the fuselage and spar, sheep poo is damned hard to remove once its dry and mixed with some grasshopper guts and legs it sets like fiberglass.
I reckon the reduced cabin noise is due to the air just flowing across the bottom of the fuselage smoother and not causing turbulence in the air pocket between the fuselage and spar.
In terms of difficulty to carry out the mod and engineering prowess this is a very simple and cheap job which took about 2 hours, with a big return on investment in terms of performance, cabin noise and sheep poo removal, so I'm very pleased.
Thanks Russ, I'll certainly be doing something similar. I am painting my Sierra at present & removed the undercarriage & turned the fuselage over to paint the bottom & leg separately. When the leg is bolted to the fuselage underside it sits nice & snug against the bottom but as soon as the weight of the plane is put on it the natural flex creates the gap you mention.
What I did was a piece of 25-32th sheet 1200 x 300mm curved the front and back and fixed it to the leg. the rear is important then the front for drag. Also the fairing form the spat to the leg I had on the joey I am going to remold for the Cheetah /Sierra aircraft. This should hit the 150kts at s/l full power. There are many other mods that can be dont but just the simple ones with out making it to hard. Many of which would be under the cowl, which may surprise some. The fairings will be available very soon .
Bang on with that approach...bloody shocker. Normally 60-65kts but I was pushing 70. I still haven't got runway 36 at heck field down to a fine art. The hill/cemetery at the end of the runaway is deceptive!