Justin's Raven

[t-bird]

Very nice Justin !!
Can't wait for video of the maiden flight.

[justin.schoeman]

[JvTonder]

[AndyCAP]

Awesome stuff!! When is the maiden flight?

[Boet]

Congrats Justin, when u flying? Jus my ou, I salute you, for being the most patient guy that I know of! As daai bleddie Volla moeilikheid maak, ek sal vir jou n lekker groot hammer leen!

[justin.schoeman]

Thanks Boet. Will fly Thursday or Friday - weather permitting. So far the VW is behaving perfectly. Oom Joos was complaining about how long it took to warm the engine up for the blow bye test, and Cyril was exclaiming about how it 'buggered off' - so I think power and cooling will be OK. Reliability is the question now...

[Tailspin]

About Bladdy time Bro.

[t-bird]

Did she fly ?

[justin.schoeman]

Did she fly ?

Scheduling conflicts... Hopefully tomorrow at 9am.

[willemgreyling]

Hi Justin, I just read through this thread. Wow you sure have persistence and endurance
I hold thumbs for your first flight

Willem

[justin.schoeman]

No flying yet.

Test pilot did a couple of acceleration runs before declaring that it wasn't making the revs any more. I spent some time doing some more ground runs and tuning to discover the reasons. And there are a couple.

First, two things I changed since the last high speed taxi - secondary ignition timing, and adding more fuel. Both of these affected things in an unexpected way. I had set the mixture fractionally richer than optimal, under the assumption that you can always lean it manually - but you can't go more than full rich. Topping up the fuel raised the fuel head a bit, which increased fuel pressure a bit, and richened the mixture a bit. A little rich + a little more rich = too rich...

Also, the static timing of the secondary was not good. The manufacture recommends setting the timing statically (which I did), then tuning it from there by evaluating in-flight performance. Unfortunately, where I had it was causing a slight miss. I have now retarded it substantially, to use only as a backup ignition, until I have the other issues sorted out, and do the in-flight performance tests.

The final issue was the prop. It seems the prop is a little coarse - static RPM is 2950, but once you start building up some air speed, it DROPS to almost 2800. So the prop seems to be stalled in static runs, but unstalls (and loads up) as you build a little airspeed.

Anyway, after today's faffing I did some fast taxis (secondary retarded, and properly leaned). By the intersection, I was making 60kts @ 2950RPM, with both RPM and airspeed climbing steadily. So all looks good again.

Also discovered why the brake manufacturer says they are 'taxi brakes only'. After slowing down from a few 60kt taxi runs, they overheated, and lost effectiveness. Used up a lot of runway (laterally too, with some aggressive S turns), but managed to stop it before going farming. Need to keep that in mind before doing multiple high speed stops!

Next attempt tomorrow 9am...

[justin.schoeman]

High wind stopped this mornings attempt. Spent some time doing some high power tuning on the secondary ignition, and have that back in a sane state.

Mixture is another issue. Even although the fuel system parameters (min head and flow) are well within manufacturers spec, the mixture is still heavily dependant on fuel level. Will confirm with the test pilot that he is happy to fly like that (full rich results in fairly poor performance with high fuel level - you _must_ lean it for take-off). The only long-term fix for this is to fit a pressure regulator. But since the AeroVee makes no provision for a mechanical fuel pump, that means I need a secondary battery too. So the regulator installation requires quite an investment.

[t-bird]

Hi Justin

Could the Facet low presure fuel pump that is used in the Jabiru's not be your answer ?

[justin.schoeman]

Hi Justin

Could the Facet low presure fuel pump that is used in the Jabiru's not be your answer ?

Sort-of. You can use it together with a pressure regulator, but when the electricity stops, the engine stops. It is better to have some sort of backup too.

[t-bird]

Hi Justin

The Rotax 914 have only electric pumps, so pretty much the same setup.