A return to model building and flying. Part 19
A Brief Visit
In an all too brief visit of a few hours whilst passing through, I managed to show my Dutch friends Herbert and Erika Harritsen my model club flying field.
I even managed to get Herbert's almost new PAW 40 to run. Having never started a diesel of this size before I was curious. The natural tendency is to be very wary or frightened because it is a large capacity. In reality it is no more fearsome than a small capacity diesel. In fact the PAW 1.5 is probably bore likely to attack your fingers than anything else.
I have never owned a chicken finger or stick. Having been beating life into these beasts for most of my life, I have acquired a feel for what the bits of machinery are telling me when I flick them; anything that covers my finger seems to rob me of the feeling, especially the thick rubber finger stalls. What I have started to use is a an old leather glove. The leather is thin enough to give me feeling but stops the soreness that builds up due to constant friction if an engine is being particularly recalcitrant and a lot of flicking is required. The sad truth is, unless someone is prepared to take the odd wrap over the back of the fingers and occasional cut (if they are frightened of blood, they have no chance) a feel for diesels will never be gained. A lot of the finger biting that can be seen is often down to being timid with an engine, in the same way that kick starting an old motorcycle in a half hearted way could lead to a quick crack behind the ankle by a hard piece of metal. Once learned it can be a real pleasure to get one flick starts or know exactly what to do instinctively if it doesn't burst into life. Any way, I digress.
Starting the .40 which was no different from finding the settings on a smaller diesel. For anyone interested, the way I go about it is this. Close the needle valve back off the compression a full turn, prime through the venturi, and flick. If the there is no sign of life screw the compression in 1/4 of a turn at a time until it fires. It should give a one second burst not just a pop, if it doesn't increase the compression and try again until it does. It will probably kick back when you are near to this point, but only once; the next time it is flicked it should give a short run. The compression is now about right and within 1/4 of turn +/- of running. Leave the compression at that setting and open the the needle one turn, choke twice, and flick. Repeat this until the engine fires and runs, usually 2-3 turns open. The basic start settings have now been found. To explain the rest would take too long, but it's much easier too play with the settings once you have the confidence that you can start the thing.
I have digressed again haven't I?
The thing I noticed about the .40 was the enormous difference between two stroking and four stroking, diesels don't really four stroke, they develop a crackling misfire, At a four stroke it would loose around 80% of it's power, and vibrate like mad whilst sounding like a tractor. This can be quite disconcerting when you are holding a large model back at full chat trying to adjust the needle valve and it suddenly drops to a four stroke. The prop has a tendency to suddenly jump back towards your fingers.
In the brief time I had to try and find the settings on a new engine and get the thing airborn, it seemed that it had to be set in exactly the same way as it's smaller brothers, in other words like a small diesel, not a large glow. Which is useful to know. As diesels tend to take quite a while to run in, I have no way of knowing if this situation will change with time.
Now to the sad part. On take off the model left the ground and just seemed to keep climbing until it reached a very high upwind point then just lost line tension. The resulting dive and abrupt snap of the lines was enough to pull the leadouts off the bellcrank just before the model hit the ground. Whether this was due to the model, pilot error, or the fact that the circle is on top of hill with the prevailing wind blowing up it, we will never know. The wind is known to do peculiar things, and I have been caught out in a similar fashion myself on more than one occasion.
The damage was surprisingly light, with one wing panel sheared off at the side of the profile fuselage and the tailplane loose, certainly repairable. What was not, was the discovery that the crankshaft was bent. An even bigger shock occurred the next day when Herbert rang me after discovering the price of a replacement crankshaft, quoted at 40 UK Pounds + VAT. Having just looked at t he on-line price list this seems odd as you can see for yourself. Prices exclude VAT. Crankcase with bearings (40-60) £52.00 Crankshaft (40-60) £33.00. This is probably small change to some people, but to me it seems a little high. Myself, I would certainly be faced with the choice of abandoning it and looking for another complete engine for the price of the repair, but then I have been on the underside of the income curve for most of my life
The next day it all turned out better than feared, A visit to the PAW works revealed that the propdriver had somehow moved on it's mounting sleeve, the shaft was still true. Interestingly no one at PAW had seen this happen before. Resulting charge £12.00. So sighs of relief all round.
This month saw me stagger up to the field with a full complement of racers, mini goodyear, goodyear, and open. I feel a bit embarrassed calling them racers as going round on my own against the clock is not quite the same thing; however it does get the hardware sorted out, or not in the case of my plain bearing PAW 1.5 which seems to have a perverse mind of it's own when it comes to starting, and how far it will fly on a tank of fuel at any one given moment.
I actually managed to paint the Lil Quicky yellow, using some old car spray cans. Anyone following this saga will know that it is impractical to spray anything in my small flat. The only way I could do it was to stand in my front doorway and spray away from the entrance, as it is a narrow space shared by several flats, anyone walking by would get sprayed yellow along with the model. Fortunately this did not happen. It was very satisfying being able to spray finish again and very annoying that I can't do this all the time. A final coat of TufKote, YES! Hurrah! Ripmax finally have it in stock again, and I realised why I had liked it so much all those years ago. I also happily binned all the crap stuff that now passes for fuel proofer, now that I have the real stuff to replace it.
The MVVS was fired up in the Goodyear and is giving very little trouble, the mini pipe giving a very muted pleasant note. I had a big problem on my hands keeping it under control when flying, with a tendency to hunt up and down with the wind direction. The engine eventually started to harden up, and still running it in I decided to try my home made cutout. Not knowing how the model would react to the application of full down, however brief it might be, I climbed to a reasonable height. The cutout worked alright, a bit too well, suddenly! up wind and high. The resulting shallow uncontrolled stalled dive, resulted in an alloy undercarriage that looked like piece of modern sculpture.
Fortunately the undercarriage and a slightly out of shape mini pipe was the only casualty. The model is constructed like a brick out house, with the finest model shop, "That's all we have," hard balsa, so it's not surprising.
The models behaviour has me really puzzled. Everything is zero zero and aligned, the controls a free, the CG is where specified on the plan (although I have deep suspicions about a CG being on the leading edge of any model).
The only thing I can think of that may be causing this behaviour, is the weight. The engine is 'heavy,' so is the model. Not a good combination, but it should still fly in a more stable and controllable manner than it does; unless the forward CG is causing the model to fly at a high angle of attack, thus causing it to balloon as it flies into wind and vice versa. I had observed a nose up attitude, but could not decide if that was to do with the wind.
A test flight the following week proved that the weird characteristics where still there, and the brick like glide produced another bent undercarriage.
One thing I do seem to have managed to improve is the starting of all my engines, by doctoring commercial fuel. Diesel, by adding ether to take it nearer to the brew I developed myself many years ago, which strangely, is very close to what MVVS recommend. The Merco glow by adding Castor oil which also seems to have improved it's hot starting as well. Now I need some nitro to try and up the power a bit.
This month was also the Club Gala Day. It had been decided that for a change we would have a combat comp. Difficult with the small number of members we have, but just possible, even if most of us have difficulty keeping up with any kind of model a lot of the time.
As usual it turned into organised chaos, with people strangely reluctant to fly in the blustery wind which occasionally turned into heavy rain. Amid bad engine runs line tangles, broken models, and myself managing to stuff my model into the ground after idly throwing it round the sky waiting for the end of the bout; exactly on the whistle!. There was not one cut, and I managed to win by default on air time, so not so bad. One day I will get the hang of this combat lark. Strangely I didn't get as disorientated as I used to when I tried this at a much younger age. So there may be hope yet.
The following week saw me at the field again with a piece of lead on the tail of the Goodyear, a hammered strait U/C., and a slightly bigger wheel. The lead moved the CG to about 10% rearward of the L/E, which is more in keeping with where I think it should be.
Fully expecting another plummet to the ground type glide, I was almost caught by surprise at the controlled descent and gentle landing. So it looks like I was right, the LE position of the CG on the plan is not correct. Now I can concentrate on running in the engine, which is running at nowhere near it's potential performance yet.