Justin's Raven

Aircraft Projects Underway or Completed

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justin.schoeman
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Re: Justin's Raven

Postby justin.schoeman » Sat Aug 24, 2013 3:38 pm

AndyCAP wrote:Great news!!! Hope you get in the air today!

BTW so was the issue that your license had lapsed for more than 36 months?
METARs around Pretoria show 10G20 at the moment, so probably not going to happen today. Heading out in a few minutes to have a look-see.

My license had only lapsed for 3 months. But under the previous (pre 30 July 2013) CARs, it just reverted to an SPL once it expired - so I could keep on flying. But that fell away now, so I needed to renew my license before I could fly.
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Re: Justin's Raven

Postby justin.schoeman » Sat Aug 24, 2013 7:13 pm

Bah - I wimped out this afternoon. By the time I had the battery charged, refuelled and pre-flighted, it was already looking a little dark - so I decided to wait for tomorrow. Let's see how it goes then...
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Re: Justin's Raven

Postby justin.schoeman » Sun Aug 25, 2013 8:41 pm

My first (official) flight in my Raven:

http://www.youtube.com/watch?v=ateu6PZDZV0

Nasty crosswind (and turbulence behind the hangars), just to keep life interesting. Fortunately, the phone cradle fell off on downwind, so there is no recording of the landing...

A few issues to sort out. Most important is the throttle friction, which doesn't seem to hold well under partial throttle. Gave me a decent heart attack when I started writing some notes, and suddenly lost all power. Fortunately the throttle had just closed itself! Also, temps are not great. At a full throttle climb, #3 goes to 198C and #4 goes to 192C. Continuous limit is 190C and 5 minute climb is 215C. So the temps are OK, but climb is so anaemic, that you really need more than 5 minutes at full throttle. Down at 22" cruise max temp is around 180C, so that is fine.

In terms of the prop there seems to be headroom to up the RPM by about 10%, which should give decent climb performance, and around 100KIAS cruise. Well, at lease that is what I hope for ;) .
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Re: Justin's Raven

Postby t-bird » Sun Aug 25, 2013 11:44 pm

Well done Justin. You deserve many happy hours flying her after all the effort that you have put in.
justin.schoeman
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Re: Justin's Raven

Postby justin.schoeman » Sun Sep 08, 2013 10:13 pm

More testing this weekend, and I am starting to get to grips with things. Tried one baffle tweak on the #4 cylinder (hottest), and it made no difference. Tried another and now it maxes out at 177C in a continuous full power climb. Made the same tweaks to #4, and it is now hotter??? Will figure it out though. Very close to having no thermal restrictions on climb power.

Did the stall tests, and got a nasty surprise. It 'stalled' (mushed down gently) at 35kias - which should not be possible. It should stall at around 45 kias. But this gave me an idea of something else to look at - instrument errors.

Downloaded a GPS app for my phone, and set QNH so that GPS and altimeter agreed on the ground. At circuit height, altimeter said 5800', while GPS said 5950' - so my static is in a high pressure zone! Both altimeter and ASI under read. Did some upwind-downwind runs and GPS averages out at 105KTAS for a 22" cruise at 6000'. Much better than the indicated '80kts'... I am also climbing way too fast. Tested some slower climbs (not too slow yet!), and got up to 550fpm climb @ 7000' (close to 9000' DA).

So there is some pretty reasonable performance there - but I do need to get the instrument errors sorted so that I can start getting some real numbers.

Had a bit of a scare though on Saturday. When doing some climb tests, I suddenly realised that I was only getting 22.5" MAP at full throttle. Everything else seemed fine, but I decided to land, and check things out on the ground. Then just to complicate things, the break cable snapped on the landing roll, so I couldn't even do any ground runs. Removed the broken brake cable and went home very depressed, thinking that I had burnt a valve, or something...

Woke up Sunday morning, and I suddenly realised what I had done. Muttered a few choice swear words, and did some maths. I was testing at 7500' - max MAP available at that altitude is 23" - so everything was actually fine (DOH!).

Made up a new brake cable, using a piano wire rod this time, and everything seems fine today.

Looking forward to next weekend. Add some test ports to the static plumbing, and do some more tests. Hopefully show that this is actually a properly useful plane - not just a nice toy...
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Re: Justin's Raven

Postby AndyCAP » Tue Sep 10, 2013 6:44 pm

Hey justin it sounds really exciting. You have progressed from not knowing if you have enough power to where you are a test pilot :). Great to hear you are now getting some testing time as opposed to stripping the VW for the umpteenth time! Remember to enjoy the ride!
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AndyCAP
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Re: Justin's Raven

Postby AndyCAP » Sat Oct 05, 2013 9:45 am

Hey J are you flying so much you dont have time to post about it any more.....:)
justin.schoeman
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Re: Justin's Raven

Postby justin.schoeman » Sun Oct 06, 2013 9:02 pm

Had two weekends of crappy weather, and other commitments. But had a wonderful flight this afternoon. Have the static hooked up to the rear-most port now, and things look great. Altimeter and ASI both correlate with GPS now, so I think I have the static error licked. And with accurate airspeeds, I am now off and climbing in 400m. And VSI was pegged at 500fpm with a 7500' DA. Starting to look like a real aeroplane now.

Unfortunately, it will be the last flight for a while, as I have picked up a structural problem with the engine mount. Will do some research on options during the week.
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Re: Justin's Raven

Postby justin.schoeman » Sat Oct 12, 2013 10:14 pm

Turns out the engine mount problem was simpler than expected. On the advice of Carl Babst, I just added some reinforcing angles, and everything seems fine. We will see how it holds up over the next few flights.

Also added a symmetrical static port and finished the plumbing, then went to test everything out. My plane is no longer 'magical' - it stalls at 44kts (exactly as per the manual), instead of 35kts I measured before. Then flew some triangular courses to check ASI against the GPS. 80KIAS (88KTAS) comes out as 89KTS on the GPS, and 70KIAS (77KTAS) was 77 on the GPS. Altimeter also agrees perfectly with the GPS now.

Next are the climb tests. I am reliably getting 550fpm at 70kts now, but I need to do some proper clims at a range of speed, to properly peg Vy.

Let us see what happens tomorrow!
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Re: Justin's Raven

Postby ppakotze » Wed Oct 16, 2013 7:44 am

Hello Justin

How about a new youtube video of your take off now that you have made these fixes? The previous one it looked like you used a lot of runway and climbed very slowly?

Regards
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Re: Justin's Raven

Postby t-bird » Sat Nov 09, 2013 1:08 pm

Hi Justin
Are you still flying ?
justin.schoeman
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Re: Justin's Raven

Postby justin.schoeman » Mon Nov 18, 2013 10:08 pm

Seems I missed cross posting this one...

A sequence of bad weather, home maintenance and a minor 'flu has meant no more flying since the last post.

Spent some time studying the flight logs from the last flight, and doing some maths.

It seems that the engine produces around 51 thrust horsepower at 7000' (which normalises to 65hp at sea level). Assuming 85% propeller efficiency (which is extremely good for a trans sonic prop), this equates to 60 flywheel horsepower at 7000', or 76 flywheel horsepower at sea level.

Not quite what the book says (80hp), but better than what most people seem to suggest is possible for a VW.

If I get the prop to the sweet spot (3400RPM in cruise), I will have an extra 4hp available in the climb, which should push max sustained climb to 700fpm at the current weight, or 400fpm at MTOW.

Need to do the next two series of test flights (climb/glide and climb with alternate prop) before going back to Dr Prop though...
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Re: Justin's Raven

Postby justin.schoeman » Mon Nov 18, 2013 10:43 pm

Weekend weather has not really been playing along recently. Conditions were pretty bumpy, but I went up on Sunday afternoon anyway. Way too rough to get any usable readings, but who cares, I had a good flight!

Got one nasty fright when the engine started missing. Quick glance at the instruments showed the EGT creeping past 760C. Pushed the mixture to full rich, and all was peachy. Seems I need to add a friction mechanism for mixture too, as it seems to wander over long periods.

Also had trouble keeping the CHTs down. Temps were 35C+ at 6500', and #3 and #4 were hovering just over the yellow line. Had to run very rich to get it 'green' again. May need to tweak the baffles a bit more for summer flying.

The landing was also probably the most challenging I have faced in a long while. Directly into the setting sun, and thermic as hell. Fortunately the plane is very responsive, and I managed a safe (if rather inelegant) landing. Final round out and flare was done looking out the side window, as the final glare and strobe through the prop were just too disorienting to look straight ahead. Going to be a touch couple of weeks now, as the sun will be pretty much directly in line with 27 in the afternoons now, and the prevailing winds make 09 a no-no.

Some pics from the flip (first away flight BTW)...
20131117_170626_1.jpg
20131117_171535_1.jpg
justin.schoeman
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Re: Justin's Raven

Postby justin.schoeman » Mon Nov 25, 2013 11:39 am

There was some really good weather on Sunday afternoon, so I managed to get a good set of climb and dive tests in:
climb_dive.jpg
The good news is that the numbers were pretty good this time. Speeds stable within +/- 1kt for over 1 minute each time. Gave me some good numbers to work with. The bad news is that the resulting plots do not 'peak'. I started the low end of the tests at 55kts for a dive and 60kts for the climb (Vref is 57kts). So, best climb, and best glide speeds will be somewhere below Vref - but seeing as I will not climb/dive in those ranges, I will not even bother testing at those speeds.

Had a nasty scare doing the tests though. Was doing them in the circuit to have a 'safe' place to do them, as I would have to focus on the instruments a lot. Only to have a Pipestrel fly over about 300' above me - he flew straight through the circuit (below circuit altitude) without a single radio call. But I suppose I was primarily at fault here, as I was not maintaining a good lookout...

Best climb at 60kts (with the nose seemingly pointed straight at the sky) was 440fpm with nearly full tanks. Loading pax is still going to be marginal.

The long flat bit towards the end was a scenic cruise at 22" MAP (75% cruise) out to Bronkhorstspruit, and further East. Trues out at 89KTAS burning around 16l/h.
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Re: Justin's Raven

Postby Splinter » Tue Nov 26, 2013 4:15 pm

Was at Kitty Hawk on Sunday afternoon and saw a Pipestrel doing flips and shoot ups over the runway with a really young pilot as PIC. I assume it was his family and friends watching him the whole time and taking photos of his flying. Could be the same plane. The way he flew and the incident you described (obviously was not concentrating) I would not be surprized if it was the same plane.
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