Larkin from Canada has been in touch with us about an article that
appeared in the Aeromodeller section of June's Aviation Modeller
International. Dave disagrees with some of the comments made by
author John Stroud. If you have any comments to add please contact
us at email@example.com
received (here in Canada) my copy of the June edition of AMI.
Good issue but the article on 'Dealing With Diesels' contains
in my opinion, mostly misinformation. There used to be a myth
that diesels would not idle. But this was de-bunked by Bob Davis
when he started converting engines with decent throttles. To idle
properly, a diesel (or indeed any other engine) needs to have
the a decent carb and have suitable porting. Specifically the
cause of poor throttling on many diesels was not the fact that
they were diesels, but the fact that they used sub-piston induction.
They were engines converted from free flight or control line use.
diesels with variable mixture carbs like the Irvine 20D and 40D,
the PAW 40, 49 and 60 and the Webra 28 idle beautifully. The smaller
PAWs (down to 0.55cc/0.033 cu in)have a fairly simple carb (who
said crude?) but though this isn't very linear it still gives
a pretty good idle. However it is possible to misalign the spraybar
when adjusting the throttle arm position. This can adversely affect
the idle, but is easy to fix.
Stroud's statement that PAWs can only be idled down to half speed
is nonsense. It's not hard to get them all down to 3500 rpm.
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Masterson has been enterprising, and made his own carburettor for
his PAW 80.
I just saw your article about PAW diesel throttles, I have just
made a carb for my PAW 80 diesel (.049ci), used a OS 4a carb as
a patten (well they did copy all our best ideas!!) , & scaled
it down based on the size of the 80's intake made one & it
made another which is a little larger but same internal dim's
& it runs very sweetly esp as I have sealed the carb 100%!
(Without a perfect seal only 1/2 throttle is the min) almost too
slow to feel any airflow from the prop .If anyone wants a pic
email me firstname.lastname@example.org
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