Monday, 29 May 2017

Aerobatic Contest

On Saturday I competed in my first aerobatic competition.

I said many months ago I expected to finish last.

As it turns out I finished 8th from 14 who competed in the final judged sequence.

The conditions were challenging to say the least with a 30 knot crosswind straight across the display axis. Actually the judges were just being lazy as by all rights they should have moved to another position which was 90 degrees to the wind. This also made for some challenging conditions to land in with many people making go arounds and second attempts - myself included as the wind changed on my approach and I now had a tailwind component as well as the 30 knots of crosswind. I saw I was going to run out of runway and decided to go around and land in the other direction.

Another thing that was a curve ball was the sequence itself - which they had published in February when I first signed up for the comp and in the meantime they had changed to a different sequence - without telling anyone who had already signed up! So on the morning of the competition I had to delete two manoeuvres and add a brand new one to my sequence I had been practising for the last few months! The new manoeuvre was a Chandelle which I had never flown in the Twister before so had to learn that in the 10 mins practise I had in the morning before my first sequence flight in the box.

As you can see from the scores below I scored much higher in the morning sequence (not counted for points unfortunately) but was marked much more harshly by one of the judges in the afternoon (there were only 2 judges) despite me thinking that I actually flew better in the afternoon. 

I've just found out that I scored 1st from all those who flew in the morning sequence so that is some consolation. What a shame that did not count towards the final judged sequence points!

Anyway even in the afternoon sequence I beat 4 Extra 200's so that says something.

A quote from the BAeA website who did a write up on the event said:

"Although not really a contest, the leader in the scores after the first round was Andy McKee flying a lovely Silence Twister. Not a common aeroplane at our events but it was flown very well and presented beautifully. Lovely slow, crisp, deliberate aerobatics." 

All in all an excellent experience. I have not been put off and will enter another one - perhaps next year.

Chris Burkett was there in the afternoon and gave me some excellent advice and pointers - thanks Chris!

A cold front passed over with lightning, thunder and a rain shower before we got underway for the first practise sequence.

Weather had brightened up by the afternoon. The pilot in the red Pitts was the eventual winner.

Organisers Dave Farley and Nick Buckenham on the left with the 1st to 3rd placed competitors on the right.

My scores from the first practise sequence which turned out to be the best score from all the mornings entries - of which they were 15. One dropped out in the afternoon.

And the scores from the final Judged afternoon sequence. At least my positioning was better.
Final results.

Wednesday, 24 May 2017

Propeller Dynamic Balance

On Monday I visited Gloucester Airport to get a Dynamic Balance done on the propeller by RGV Aviation.

I had been meaning to do this since getting the full permit but what really motivated me was a vibration which I didn't seem to remember when I first flew it. I put this down to being more familiar and picky with the aircraft the more I flew it - but as you will discover below I was not imagining it after all.

The procedure starts with the top cowling coming off first then two sensors are attached. One is measuring the RPM very accurately and does so by 'seeing' a reflective piece of tape which has been applied to one prop back face. The other sensor measures the vibration in Inches Per Second - IPS. This is mounted to the front of the engine as close to the prop as possible.

The engine is then run up to full static RPM - in this case 2700rpm (with the top cowl off I get 100 more rpm out of the engine as the air is colder going into the air filter).

When full static is achieved the ACES unit is set to measure the vibration which only takes about 5 seconds or so.

The first reading was 1.26 IPS - which is BAD!

Typically they try to get the IPS down to 0.07 or less. Adam the mechanic said the worst they have ever had was 1.6 IPS so mine was quite bad and the ACES machine called for a 45 gram correction weight which is beyond the 30 gram limit.

Another more senior mechanic came out to look at it and suggested to take the prop off and turn it through 180 degrees before fitting it again on the backplate.

So we did that and lo and behold the next reading was only 0.15 - which is nearly a 10 fold reduction in vibration! 

I think I must have had the prop this way round when I first installed it - then at the 15hr service I must have put it on the other way. There is no right way as such - theoretically the prop should be the same either way but it must be heavier on one side and this just happens to cancel out the vibration or accentuate it depending on which way round it is fitted.

The next 4 runs were done after putting test weights where the ACES machine told us to. And when the 2nd to last run came up with an IPS of 0.02 Adam was satisfied that we had nailed it. The final weight was then fitted permanently to the backplate and it was just 3.4 grams of correction needed. A final reading after that showed it back up to 0.07 so work stopped there. 0.07 is the figure they work to and Adam explained that the final weight is tricky to get in the right place to retain the IPS we had previously.

Anyway the proof was in the test flight back home - turbine smooth now compared to before. 

My wallet is now £300 lighter but this was well worth doing and I would recommend it. Not only is everything subject to less vibration but it is also much more relaxing to fly when things are smoother.

This also explains why I lost the cowling screws on my France trip as the extra vibration must have worked them loose.

Adam fitting the sensors.

Vibration sensor mounted to the front of the engine.

Both sensors in place - the yellow sensor taped on the plenum is the RPM sensor.

The ACES machine displaying the first reading after switching the prop around. As you can see it calculates a 'solution'. Which is a weight and degrees from datum to fit it.

A protractor is then used to figure out where to place the correcting weights.

A test correcting weight using one of the spinner holes.

The 4 readings after switching the prop around.

The final correcting weight - just 3.4 grams - consisting of a screw with a small washer and nyloc on the other side. BTW this is where the ACES machine said to put the final weight - it calculates the position taking into account you are not putting it in the same place where the test weights were put.