Building the new Bushbaby SAFARI

[Wallaby]

Oupa-G, what's the weight now that you have the final legs? I see that there's an extra blade to fit under the main gear. Or is it going to fit above the main gear? Is that to make the gear a bit stiffer across the section under the fusealage?

[Oupa-G]

Wallaby the weight is more or less the same . That blade on top moves the springing movement to the legs and not to the part under the fuselage. The weight is not a lot extra I have not had the aircraft back on the scales because all the paperwork has gone to CAA and I now do not want to complicate matters. They already want a different type of logbook and different type of entries. I struggle to get my brain past this but the paper god's must now do their things and I'm not questioning the process. If they ask for papers they get it. Have just come back from Beaufort West had to sleep the night had a flat tyre and on a PC12 that is not an easy problem. It means jacks etc. from Cape Town so I had to sleep the night in Beaufort, and came home this morning. Thats all for now


Cheers Oupa-G

[KFA]

Heard via via that a profing flight is immanent

[Oupa-G]

Thanks KFA I have heard the same bird whistling I’m working in Upington and have no aeroplane to play with hence the bit of theory on a topic I have been longing to write on for a long time. The topic is

Cohesion and Adhesion

Anybody working with fluids and pipes must understand the concept of cohesion and adhesion. Let us define “cohesion” we are familiar with cohabitation or living together. It is the force that keeps similar molecules together if you take a water droplet in air the fact that the droplet is round is the effect of the cohesion forces. That is thus water in air. If we have a gas or air in a fluid and take for example your sodastream bottle then we again have air or CO2 bubbles these bubbles form because of the cohesion forces.

Now lets look at adhesion, take adhesive the concept of sticking objects together. Now when we combine these forces, we see how water droplets can stick to a leaf and we have a wonderful combination of cohesion and adhesion both working. I got a photo on the net from Wikipedia of a leaf with water droplets on it, it is a superb example. Now if you take these principles and put fuel inside a pipe and put an air bubble in it , and the right conditions then with adhesion and cohesion you have the making of an old fashioned air lock. More tomorrow on practical examples and how to fix it.


Cheers Oupa-G

[Oupa-G]

The saga of cohesion and adhesion continues. We will look at a more practical application of these principals. If you look at photo one, the air bubble and the siphon column of fuel is in equilibrium. The result is no flow and stagnation can occur and the result is fuel starvation. Something we do not like in aviation . We like the motion potion to flow freely. If there is the slightest possibility for stagnation of fuel flow a fuel pump should be added in line. Tail draggers are more prone especially the Bushbaby due to the way the fuel lines run and the rear pickup in the tank. So if you have a fuel installation look at it critically and visualize where can adhesion and cohesion with an air lock cause havoc and if there is any chance pump it away with the installation of an inline free flow pump, the action of the pump is just to start the siphon function . Once the flow is activated the siphon flow will continue without the pump action. This is the reason why the Bosvarkie has two inline pumps. I was not happy with the siphon characteristics of the design. I hope the readers of this site will have bubble free gravity fuel systems. Comments are welcome and readers opinions and experiences will enhance aviation safety. Remember 80% of engine stoppages are fuel related.

Cheers Oupa-G

[Oupa-G]

I should be home by Friday and hopefully the highly desired paper will be there. Then the important phase of the testing can begin and there will be plenty data to report. I'm keeping my fingers crossed.


Cheers Oupa-G












i

[Oupa-G]

I have now heard that CAA is asking who is going to test fly the Bosvark, that means it can fly. How ever I do not possess a test pilot rating so that will have to come. I will fill in forms till I get tired or they get tired. I am just waiting what next.
I thought having an ATP with 6500 hrs grown up on taildraggers would be sufficient but alas the answer is no! so please more papers and I will comply.

Cheers Oupa-G

[Boet]

Oupa, hoeveel bome moet nog omgekap raak vir NOG pampiere. Is jy ook al gatvol? Hoe lank moet ons nou nog wag?? Ek dink NIEMAND is beter gekalifiseer om die Bosvarkie te vlieg as die man wat sy enjin die beste verstaan nie. Test pilot gaan net jou errie opdinges.

[Oupa-G]

I did a very interesting test today . One of the 912S's on the DTA trike that we fuel injected has a Arplast prop on it and because the 912 turns in the opposite direction then the BMW I could use the pusher prop of the trike and put it on the Bosvarkie. The 912 has a reduction box of 2.43:1 and on that setup the static revs are 5400rpm with the BMW reduction of 3.2 :1 the theoretical equivalent revs are 7111rpm. When I test ran the engine with the Arplast prop the engine ran to the rev limiter of 7200rpm. Being the same prop with the same pitch I can make the statement that the BMW gives the same power as the 912S maybe even more. This was a very exciting test. The less exciting is that my Woodcomp prop cannot absorb the power the BM delivers luckily WoodComp makes other blades and I will talk to the people to-morrow. The problem is that when I set the variable prop so that the engine does not run away , the pitch is so course that the prop cavitates. But with careful testing we will get the correct prop engine airframe combination. Boet is sending me a De Necker wooden prop and I will test that as well. I will also do a pulling test. More tomorrow.

Cheers Oupa-G

[Oupa-G]

Today I documented the data we tuned on the Eboxi's and took a photo of the Arplast prop.The results of this test was given on the last posting.

This nose job did not improve the aesthetics of the Bosvarkie. To-morrow I'm getting the de Necker Prop for comparison. It will be interesting testing. I have to do all these things while I'm awaiting the paper results from CAA. Enjoy the picture

Cheers Oupa-G

[Boet]

Oupa, en hoe vliee hy met daai rooi prop??

[Oupa-G]

Boet jy weet mos ek kan nog nie vlieg nie wag nog vir die pampiere

Cheers Oupa-G

[Oupa-G]

I have made a copy of what I have written under technical and thought it would fit well in this blog on the Safari.

" We have spent a small fortune in time and money. Ystervark who designed the Eboxi is a top class electronic boffin. If I had to pay his professional time for the developmental costs it would have been prohibitive. The average microlight pilot would prefer to get something for free and is then happy to pay for the trial and error with a forced landing and the dangers that go with such an exercise. We have been busy with the BMW project now for more then 8 years. It is wonderful to see other projects like the Yaris etc being developed we accept all the initiative with open arms because it will bring the price of 2nd hand BMW engines down to a more realistic price and cross pollination is always healthy . Our engines now have full dual total redundancy on all critical parts. And now in the running of the Bosvark with various props it seems as if we are pushing out the same power as the benchmark 912S or maybe even slightly more. We are very pleased with this result. It also means the exhaust is working well and the comments from bystanders are that the noise emission is not loud at all. Over the weekend we will be running a P de Necker prop with the same diameter and pitch as for the 912S.This was just some info "


Cheers Oupa-G

[Oupa-G]

Today was a very special day. The very South African satellite was launched and Ystervark of Eboxi fame quietly mentioned that his software in the satellite was working well. It takes a different kind of thinking because they work in an environment where PVC evaporates and there is no ladder to quickly climb up there to go an fix something. We are proud of him because he is also a microlighter flying a trike. I also sometimes see parts of a new trike rotating in 3D on his screen. I think it is going to be powered by a BM and I also think it will be managed by the Eboxi system.
The other exciting thing is that I today fitted the Pieter de Necker prop, now Boet has been quietly breathing down my neck about this wooden plank and sometimes also not so quietly. Now I promised to do honest reporting and I was not happy with the performance of the variable pitch prop. I tried the Arplast the engine overpowered it and the prop must go back to its trike. So the wooden plank was test run and what a wonderful experience it was like a horse with a swarm of bees up its backside. The Bosvarkie wanted to get airborne on the taxiway. The BMW 1200GS is giving similar performance as brand X. We must now work on the reliability side which is hard to beat but something to strive for. The benchmark is set very high. Enjoy the pics.


Cheers Oupa-G

[Oupa-G]

Boet ek dink die spinner moet maar kom.

Cheers Oupa-G