I would just like to say how amazed I am at the diversity of the knowledge
that the people in this newsgroup have. Myself I fly Diesels, Glow (2 &
4-Stroke) and soon Petrol (Gas to those in the US). For reference I noticed
the discussing relating to large Diesel (that is Road Diesel) vehicles.
Over here in Britain Diesel power Cars are very common (about 23-25% of the
market) and these engines suffer nothing like the same narrow power bands.
Take for example the car driven by my father (the family car, one and only).
This is a Volkswagen Passat. The engine is a 110Hp Direct Inject 4-Stroke
3000rpm. This engine has a flat torque curve due to a variable geometry
turbo (to keep good boost all the time) and as a result out accelerates a
Golf GTi 125HP up a hill.
The answer to all our problems as far as models are concerned is larger
propellers. In order to swing a larger propeller we may not prop anywhere
near the max power output but we sure as hell will get a quieter models that
goes as well if not better. How should we achieve this? Well the easy
answer is to swing a larger prop. Over in the US I gather the 'ideal' prop
for a Thunder Tiger 42Gp is a 9.5x6 or 10x6. On my Thunder Tiger 42Gp I
fitted a cheap mini pipe to gain 1200rpm and a 12x6 propeller (balanced).
This combination gives 9900rpm and is very quiet. I have not had to shim
the head but I do not use Nitro so this to some extend compensates for the
increased loading. At present I am working on an idea of reduction gear for
an engine (only really practical on a big model I guess due to weight) to
increase torque. Combined with a Variable Pitch Propeller (such as those
which I believe are supplied by Gerrad in the US? & made by Syntec) this
should give an ideal combination of quietness and power. If you were to
step up to really big Petrol engines (yup Gas) such a 3W Powermaster 150iB2
diameter full size variable pitch propeller.
No what about strapping that 110Hp VW Diesel with reduction gear to the
front of a 1/3rd scale Spitfire or Racing Mustang?
By the way if anyone has a way of calculating torque output (lbs.ft) I would
be glad to know the equation.
Similarly one for Horsepower though I think the one I use is OK, giving the
same answers as a friend's copy of Barry Hobson's program ThrustHP.