>
> Hi! Richard
> I find myself a little bemused why the resistance to fitting a Manifold
> Pressure Gauge, apart from needing room on the panel? If you have a CS
> installation without the gauge you will have no indication as to how you
> are loading the engine, that is to say RPM is no longer an indication of
> power.
> So it becomes possible to run the engine at all RPM in a labouring
> condition not to be recommended for cruise configuration with respect to
> fuel consumption and engine well being. My MT CS prop. will hold the
> engine RPM at say 2,500 even with maximum MP at say 30 inches, where
> maximum recommended is about 22 inches. The rule of thumb is so called
> "squared"
> Which means 24" FOR 2,400 rpm ON A DIRECT DRIVE ENGINE. However I've
> managed to identify on the Jabiru 3300 that a lower MP with a slightly
> higher RPM gives a better fuel performance. (no snipes about fuel usage
> comparison with the Rotax thanks Duncan the scenario still applies)
> Problem without a MP Gauge is knowing the effect of the ambient and
> altitude changes and in pressure relative to engine performance.
>
> Regards
> Bob Harrison G-PTAG Europa Kit 337 MKI/Jabiru 3300
Hi
I do agree (and said so) that the MAP does allow that measure. However there
is NO requirement by Rotax or Airmaster for any restriction in the
combination of rpm and MAP. None whatsoever, certainly no requirement for
square.
I was spitting because I had finished the panel and everything was ready.
And Airmaster AND Rotax said that there was no requirement for the gauge.
I had to add the MAP to a sub-panel which destroyed the symmetry and lines
of the panel. I certainly wasn't going to re-design at that stage. [I am in
the process of re-designing now, with the MAP gauge in-panel, but it may not
see the light of day for some time as flying is more important than the
engineering now that it is running !]
My running norm is 5000/25.5 inches
I tried 4600/26 which gave the same speed but over 200 litres made no
difference to the fuel consumption. If anything it went up ! (that is
consistent with your information) but I don't want to run faster than 5000
so I am sticking with 5000/25.5 which gives around 120 knots at 16.2 litres
per hour. Oops I wasn't supposed to say that ! :-)
Richard
Richard F.W. Holder 01279 842804 (POTS)
Bell House, Bell Lane, 01279 842942 (fax)
Widford, Ware, Herts, 07860 367423 (mobile)
SG12 8SH email : richard.holder@avnet.co.uk
Europa Classic Tri-gear : G-OWWW, High Cross
PA-28-181 : Piper Archer : G-JANA, EGSG (Stapleford)
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