Justin's Raven

[t-bird]

Well done Justin.

[Jean Crous]

Justin now you really have some interested readers..........wat gaan daai Volla motortjie maak Sounds as if it will perform better than the Jab motor?
Jean.

[justin.schoeman]

Justin now you really have some interested readers..........wat gaan daai Volla motortjie maak Sounds as if it will perform better than the Jab motor?
Jean.

It _shouldn't_ really perform better than the Jab... It could just be that it is too long since I flew the Jab, and can't remember how it accelerates. Or perhaps my pitch is wrong, and it will run out of steam very quickly. Or it really could perform better than the Jab .

Unfortunately, my geyser sprung a leak yesterday, so today has been dedicated to household maintenance.

Next weekend will be the W&B, and an extra engine run (I see the CAA wants 1 hour of documented engine runs for the PFA, but I only fully documented the break-in runs, which were 0.5 hours in total). Will also get Cyril to do some acceleration runs, and give his opinion...

Justin

[justin.schoeman]

A real mixed bag this weekend. I did the final half hour of engine runs as a trial 'test flight'. Full power for 5 minutes, followed by 25 minutes at 22" MAP. Engine behaved perfectly throughout. CHTs stabilised at max 200C. EGT was controllable from 640C up to around 740C (OK - this is more than the tuning manual recommends, so I do need to lean it a fraction more). The EGT split (left to right - I only have two probes), was 20C at full throttle, and around 10C at 22".

After this run, the engine was due for its 1 hour oil change. Once I got under the engine, I found evidence of an oil leak from the back of the engine. I knew I had a small leak from the oil strainer (I had assembled it without sealant, and was due to change the gaskets at this oil change anyway), so I hoped that it would just be oil blown up from there... Unfortunately another run on Sunday morning showed a dry oil strainer, but fresh oil on the back of the engine. So it is time for the engine to come off again... There are only two possibilities there, 1st is the cam plug (which would be VERY bad, as the engine must be split to replace it), and the second is the crank rear main seal, which I really hope is the problem. I did suspect there might be a problem there, as the engineering shop that remachined the flywheel center puck for an AD left some tool marks on the seal surface. I polished the surface, and then seated the oil seal slightly deeper to run on a clean section of the shaft, but this may not have been enough...

I also did the W&B, and got a seriously nasty shock. Final empty weight is 281kg, where I was expecting just under 260kg. It seems the basic empty weight Carl gave me was way off, because there is no way I have not accounted for 20kg of additional weight.

The CG was also waaaayyyy aft. Need 10kg right on the front of the engine if I want to fill both seats (without any baggage). It seems the biggest issue is the pilot arm. Zenith says it should be 650mm, but I measure it at 750mm. I am not sure how Zenith gets the pilot weight so far forward. I have been experimenting with various seat back configurations, and so far I have managed to move it ~35mm forward, and still reasonably comfortable. Need to try a slightly reclined position as well, and maybe get it a bit further forward. 35mm forward already reduces the ballast requirement to 3kg. A little more, and I won't need any ballast, and may even be able to take some baggage . With the rather hefty empty weight, even a little ballast is going to hurt...

[t-bird]

Hi Justin

This is real bad news. One thing I have learnt from this is it is not that easy to build an Airplane. I would have expected a forward Cg and not Aft with the vw engine.

[priester]

I also had to bolt 10kg to the front of my engine (Aerovee) to get the cg within limits.

[justin.schoeman]

I also had to bolt 10kg to the front of my engine (Aerovee) to get the cg within limits.

Yup - seems to be a big problem with the AeroVee conversion - it is just too light for the standard VW mounts!

[justin.schoeman]

Some picture of the finished plane, before I started stripping it ...

[justin.schoeman]

A truly wretched day today...

I was busy preparing the plane for Cyril's high speed taxi runs, but I picked up an on bug on the engine. I would run absolutely perfectly up until around 24" (2800RPM) and then suddenly start running rough, and the left bank EGTs would go down into the mid 500s. A little leaning would bring it up to the 600s, and smooth the engine, but this was obviously not ideal.

I was busy doing some engine runs, tweaking the carb orientation a little, but without any luck.

At the end of one run, I idled it at 1500RPM for a few minutes, to bring the CHTs below 160 for shutdown. It was running perfectly. Oil temp just over 70C, pressure 47PSI CHTs in the high 150s. Pulled it back to an idle - 800RPM, oil pressure 34PSI, running smoothly. And then the prop just stopped. At first I hoped, it had just cut out (fixed timing, and low idle could possibly explain a dead stop), but once I got out, I found the crank frozen solid.

Applying a little force got it to move, but the #4 main bearing (prop hub bearing) turned with the crank - so it seems this bearing has seized. And judging by the amount it has turned in the case, it will probably have graunched the bearing seat quite nicely (although I won't know until I strip it).

Up until now, I have been really chuffed with the VW. It was running better and better on each run (as it loosened up). Temperatures and pressure were fine. Oil a little cold, but CHTs were under control, and stable at 20"MAP, even with the smaller flight baffles.

I will start stripping it tomorrow, and hopefully get an idea what went wrong. But truth be told, I am very tired of building now, and may just opt to take out the checkbook, and get Jabiru to fit a 3300...

[JvTonder]

Shit Justin very sorry to hear sir! Remember that with flying/planes comes a lot "crap" one has to deal with but one's sorted you will enjoy it to the max. Sterkte mnr en byt vas!

[t-bird]

Hi Justin

Sorry to hear about your misfortune.
Would the Jabi engine solve the cg issues or increase the weigth needed ?

I hope you can sort out your problems and get into the air soon.

Regards

Callie

[justin.schoeman]

Just finished stripping the engine. Everything is good, except for the prop hub bearing, which is frozen solid. Unfortunately, the case is cracked, where the bearing dragged the dowel. Will also need to get the crank measured, and magnafluxed to see if it is still serviceable.

[JvTonder]

Sorry to hear!!!

[justin.schoeman]

Finally got to spend some time looking for the cause of the problem. Started checking all the oil journals, to make sure there were no obstructions. Then I had a look at the bearing itself, and noticed that there was no oil in the outlet holes. So I looked at the oil inlet...

First thought: huh - why isn't the oil feed drilled through? Second thought: (censored!!!) that is the dowel in hole. Yes, I had put the dowel in the oil feed . When trial fitting, I had marked the bearing, to make sure I lined it up properly, but when I cleaned up for final assembly, I smudged the marks, and didn't check them properly.

But that is one tough bearing. It ran 1.5 hours - most of that at 60+ hp - without a drop of oil (just the assembly lube), before it finally said 'I have had enough', and embraced SABC1s slogan 'Simunyene - we are one. Now the bearing won't budge on the hub. Wallying it with a hammer, while cooking it with a blow torch, and it just does not budge.

The manufacturer of the bearing is on the forum (not sure if he would mind his name being mentioned), and when he read about my problems, he immediately called, and offered advice, and support with rebuilding/replacing the engine - even when he did not know the cause. And when I called to tell him I found the cause, he said 'thanks' and 'the offer still stands'. What a gentleman!

[Jean Crous]

Hi Justin as i mentioned on "the other forum" , should it have been my fault, i certainly would not have wanted to hide. So no i dont mind being named .And as mentioned, the offer remains the same I truly hope you can get flying soon, a mishap like this is REALLY not welcome at this stage.
Regards
Jean.