Anson start technique…
The recommended starting technique and the one in the cards, of which you printed a copy, mentions what we used on our flight, as does the Anson 1 Pilot’s Notes. Subsequently, however, I have learned from our expert Shuttleworth engineer Toby Lee that we should simply put the mags on pre-start and leave them. If we fly single pilot of course we have to do this or we run out of hands, but before this I did not know it was normal practice.
The booster coil powered from the battery provides the high voltage spark at the trailing edge of the magneto distributor making the spark late in the cycle. So it’s not quite the same as ‘shower of sparks’ and I think the mag off start might be a hark back to the hand-crank to avoid an early spark and kickback. Peter Kosogorin Bsc(hons) FRAES I always enjoy and particularly enjoyed Dave Unwin’s account of flying the BAE Systems C19 Avro Anson. For the past six years I have been restoring to groundrunning condition an Armstrong Siddeley Cheetah Mk 17 engine and landing gear from two Avro C19 Ansons, G-AGPG and TX226 respectively. I hope the following answers the question raised by Dave Scott in December’s Airmail regarding the ignition system of the Cheetah engine.
Each engine has two magnetos, and each cylinder has two associated spark plugs. The port magneto supplies the ignition for the rear set of spark plugs and the starboard magneto supplies the front set of spark plugs. The firing order of the 7 cylinder radial engine is 1,3,5,7,2,4,6. The port and starboard magnetos are timed to normally fire nineteen degrees before TDC (top dead centre) and 21 degrees before TDC respectively. This timing difference ensures optimum firing and efficient combustion of the fuel/air charge in the cylinder. The timing angles are all related to crankshaft position.
The port magneto on each engine has an associated boost coil (induction trembler), used only on start up, which has its HT output connected, via a carbon brush, to the centre connection /pickup contact of the magneto distributor rotor arm. The port rotor arm has two contacts, one providing the normal ignition from the magneto to the distributor contacts, and a second one which is connected to the centre connection contact which distributes the ‘shower of sparks’ from the boost coil to the distributor contacts. The two rotor arm contacts are displaced by approximately thirty degrees, thus the timing of the ‘shower of sparks’ is retarded and the firing from the boost coil occurs at approximately eleven degrees after top dead centre, when the cylinder is on its down stroke, i.e. at the easiest point of starting. This timing position
ensures backfires do not occur on starting with potential damage to the engine.
In view of the above, the procedure is to initiate the starting sequence with the magnetos off and only the boost coil button is operated with the start button until the engine fires. Once the engine has fired the magnetos are switched on, the start button is released, and when steady running is achieved the boost coil is de-energised. This needs a quick reaction to bring in the magnetos quickly on first firing, as in my experience the engine will not run continuously on just the boost coil. See the Youtube video of my first post restoration start up when both the boost coil and magnetos were used simultaneously. This was the engine’s first run since it landed at Southend in 1971 and the engines were stopped. https://www.youtube. com/watch?v=eolmuosiwkc
At that time I had not mastered the technique of bringing in the magnetos in time.
A minor point re Dave’s article: the propeller blades are not metal, the propellers are Rotol R30/242/1 constantspeed variable pitch propellers and the blades are made from wood (Weybridge). This is indicated by the large yellow dot on the blade markings which confirms it is either Sitka Spruce or Douglas Fir. At the top of the yellow dot there is an R and an S inscribed, this indicates respectively the blade is covered in Rotoloid or Rayoid and the leading edge has a metallic sheath.
Thank you for an excellent magazine. As a non-pilot, retired nuclear engineer I find it interesting and entertaining, and enjoy the monthly challenge of the ‘How airbrained are you?’ questions. Dave Houghton by email … and appreciation The November issue of Pilot took my attention for its cover – as most copies do, in fact. But this one was special. The Avro Anson was, I have learned now, the 652A Type XIX Series 2 and G-AHKX in particular brought back many memories for me.
13 April 1961. My boss at Meridian Air Maps at Shoreham asked if I could fly Johnny Powers, our company pilot, up to Little Staughton to pick up our new plane – we were getting an Anson. The reason I could say yes was because I’d been fortunate enough to scratch together the funds required to learn to fly back in 1952. From that little trip in Auster G-AHHU, Johnny brought G-AHKX to Shoreham and by July ’61 I was aboard as nav/tracker. On 19 July ’71, now flown by Jackie Moggeridge, EX-ATA and one of the very few commercial lady pilots of her day, we set forth from Shoreham to Yeovilton, chosen by Jackie I think because of her past ferrying connections. I recall being presented to the duty officer of the day as one of “my boys”! After that trip, ’KX took me on many aerial survey jobs. However, in December ’61 I swapped companies to yet another Anson in the form of BKS Air Surveys and that is another story of another XIX, G-APHV. Long may these old ladies live on.
I apologise for my scrawl in this letter ( which was
handwritten) but anyone who had to find £90 for a PPL in 1952 is getting on a bit! Roger Ording Tribe, Ulverston