An­son start tech­nique…

Pilot - - AIRMAIL -

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. 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

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