Justin's Raven

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justin.schoeman
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Re: Justin's Raven

Postby justin.schoeman » Mon Sep 15, 2014 10:37 pm

Next was the exhaust. I was not 100% sure how to do this. Cutting those big holes out with a dremel was just not working, Neither was drilling out the 30 18mm holes in 1.6mm stainless steel for the tailpipe. That stuff is tough! Fortunately, someone mentioned that they had the holes burned through at an exhaust shop - so I thought I would have a look-see what a TIG could do. The tests on some scrap stainless looked perfect, so it was time to try on the real thing. 180A in one spot resulted in a nearly perfect hole of around 18mm in diameter. So for once I managed to put my best welding skill (burning holes through anything I try to weld) to use... A few minutes later, and all 30 holes were neatly burned through. A little work with a grinder cleaned them up and removed the slag. Unfortunately, I forgot to take pics of the tail pipe, so you will have to take my word for it! (I did learn an important lesson here though - when you crank up the amps on the welder, remember to set the helmet to shade 15! Doh!)

The muffler was easier, being of relatively thin steel. A steady hand and a low current, and I could cut out a fairly (round) hole...
rps20140915_202034_305.jpg
Repeat on the other side, and out to the air field for a trial fit. Perfect:
rps20140915_202149_912.jpg
Tack it in place with some epoxy, and then back home for welding:
rps20140915_202329_467.jpg
In the end (as usual for me, welding thin sheet to thick, I spent more time chasing and filling burn-throughs than actual welding. So in the end, I just tacked it (as above) and took it to Noise Boys for a full weld. Really wish I had just finished the job myself - the Noise Boys weld looks mechanically sound, but is ugly as sin. Fortunately no pictures...
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Re: Justin's Raven

Postby JvTonder » Mon Sep 15, 2014 10:45 pm

Baie nice Justin, een van die dae is jy in die lug!
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Re: Justin's Raven

Postby justin.schoeman » Mon Sep 15, 2014 10:48 pm

The last fairly time-consuming bit of work is the baffle to duct the standard Jabiru oil cooler to the cowl (which was intended for the oil cooler that Jabiru Australia uses). Here is a picture of the basic frame:
rps20140915_202242_813.jpg
Making the sides ended up more difficult than expected - so I just wrapped the whole thing in fibreglass. No finished pics, but it looks quite good, and fits perfectly.

And finally the finished product:
rps20140915_202512_581.jpg
Actually, not the finished product yet - the factory sent me the wrong prop bolts, so it is just tacked together for show. But SOON!

Hopefully get the new prop bolts this week, and do some test runs over the weekend. Inspection the week after, and away we go!
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Re: Justin's Raven

Postby t-bird » Tue Sep 16, 2014 2:04 pm

Very nice Justin.
Thanks for the updates.
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Re: Justin's Raven

Postby justin.schoeman » Mon Sep 22, 2014 10:47 am

Just told Giel that I think something is wrong with the engine. Started on the first blade, and settled straight into a silky smooth idle at 750rpm! Very un-Jabiru behaviour. Quite, and smooth a silk - can't wait to get it airborne!
rps20140921_193237.jpg
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Re: Justin's Raven

Postby justin.schoeman » Sat Oct 11, 2014 11:54 pm

AP inspection this morning, and all is perfect. CAA paperwork this week.

Software glitch on the Xtreme means I cannot swing the compass - hoping that MGL can help out this week, as this will be the last legal requirement for a test flight.
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Re: Justin's Raven

Postby t-bird » Sun Oct 12, 2014 8:54 am

Great !!!!!
How was the COG affected by the Jabiru engine and how much lighter is the plane ?
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Re: Justin's Raven

Postby justin.schoeman » Sun Oct 12, 2014 12:34 pm

t-bird wrote:Great !!!!!
How was the COG affected by the Jabiru engine and how much lighter is the plane ?
The entire exercise added 1.4kg to the aircraft. New empty weight is 284.5kg. CG is perfect now. Previously I was flirting with the rear limit 2 up. Now, full fuel, and I require a minimum of 62kg total in pilot+pax seats for the forward limit. Emty fuel, 90kg in each seat, and I can still put 30kg in the baggage compartment before reaching the rear limit. So basically, it is pretty much ideal.
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Re: Justin's Raven

Postby justin.schoeman » Mon Oct 20, 2014 11:48 am

First attempt at a test flight was on Saturday morning. The poor test pilot got a decent cardio workout when the EGT alarm went off soon after take off. He did the right thing, and did it tight circuit to land back again.

Unfortunately, for some reason, the Xtreme did not create a data file for the flight, so I have no real numbers on what went wrong. All I could really see were the high water marks on the CHT and EGT guages. CHTs were all green, but the #1 bank EGT was about 30F into the red (#2 bank was still green). EGT imbalance is a fairly common issue with the Zenith FWF kits. I tried one solution (that has worked for at least one other builder) of using a smooth, wide radius curved tube from the air box to the carb.

Without the data recordings, I have little to go on though, so not quite sure where to go from here.

Part of the problem may be that the test pilot did a partial throttle take off. With the jabi, this can result in an excessively lean mixture - so the solution may well be to just take off at full throttle.

Aside from that, there may well be another issue. The test pilot says that he was climbing out in the yellow arc (ASI) - meaning above 105KIAS - and this wasn't even at full throttle! There could well be an issue with exceeding Vne in level flight (a big no-no for issuing the final ATF) - so I may need to look into ways to slow it down a bit!

Take off video:
https://www.youtube.com/watch?v=vU4owyz9X-o
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Re: Justin's Raven

Postby avgas » Mon Oct 20, 2014 12:03 pm

Well done (^^) (^^)
Now the fun starts :wink:
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Re: Justin's Raven

Postby t-bird » Mon Oct 20, 2014 12:23 pm

Well done.
A lot easier to slow plane down than to speed her up.
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Re: Justin's Raven

Postby justin.schoeman » Sun Oct 26, 2014 9:54 pm

OK. Did some work, but Wx prevented further test flying.

1) put a vertical flow divider in the induction pipe
2) figured out how to get MGL Xtreme data recording working (turns out you need to switch recording off and back on, if you replace the SD card).

Did some brief engine runs. CHT limits preclude any extended full power runs, but got this plot:
temps.jpg
Can see the following:
1) always starts immediately and settles into a smooth idle at 730RPM.
2) EGTs are well balanced at low power and at full power. Seems to be some divergence at around 2000RPM - but no idea how they would settle with time.
3) Full throttle RPM just a hair shy of 3000.
4) MAP (in mb) - can see the induction restriction is quite bad, but apparently normal for Jabs.
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Re: Justin's Raven

Postby justin.schoeman » Mon Oct 27, 2014 11:10 am

And to top it off, MGL just sent a bugfix for the Xtreme, so hopefully the compass will also work correctly now.

Nearly there!
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Re: Justin's Raven

Postby justin.schoeman » Sun Nov 02, 2014 9:53 pm

Bah - another aborted test flight on Saturday when the oil pressure spiked (on the ground still). Stripped and cleaned the PRV - but no obvious issues found. Will do extensive ground testing next and see if I can replicate it :( .
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Re: Justin's Raven

Postby justin.schoeman » Fri Nov 21, 2014 10:43 am

Anybody else getting slightly peeved with this weather? Seems flyable weather and test pilot availability are a rare combinations :( .

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