Engine Speed Governing

Soooo - the Brains Trust is stumped by this question?😈

After a huge 14 prop many months long research project set your ground adjustable prop to get 5600 - 5650 rpm WOT at your average altitude. This will give you a GOOD BALANCE for climb, cruise, fuel and eng. temps. Then you can cruise at your 5200 rpm. If you need a better climb prop then set it to get 5800 rpm, but you'll lose a bit of cruise speed and fuel. Most seem to cruise between 5K rpm and 5500 rpm with the average pilot around 5100 - 5300 rpm in cruise.

Someone who lives at sea level like Florida and never goes over 2K ' will have a different pitch setting vs someone who lives in Colorado at 7K' and always flies around at 10K+'.

Whatever you do DO NOT set the pitch so it gets under 5500 rpm WOT. Anything under 5500 at WOT is over pitched and you WILL lose out on climb, cruise, fuel and have higher engine temps. Plus this stresses the engine. In the older 1500 hr. engines doing something like this could cause such stress as to put a crack up on top of the crankcase. Some earlier LSA mfg's set WOT  at 5200 rpm. It was a bad idea.

If you have an in flight adjustable prop then make sure you don't set it up to get less than 5500 rpm either. You may want the take off rpm to 5800 for climb and then increased pitch for your cruise rpm.

Many seem to cruise at different rpms. Some cruise at 5K rpm and some cruise at 5500 rpm. Seems like many mfg's and owners kind of do their own thing.

To me the bottom line is to not stress out the engine and get the BEST ALL AROUND balance performance and since many have ground adjustable props and can't change the pitch in flight. Yes it would be wonderful if LSA in the US could all have a choice in using an in flight adjustable prop. Maybe MOSAIC will fix that. It's a wait and see.

Sean

While the engine has limits, like 5800 for 5 mins, the max continuous is max 5500.  This is misleading, sure you can fly it at that all day but you are going to burn a lot of fuel.  The range of just below peak torque on  your engine, generally not less than 4800 is appealing in that the fuel burn is very low.  This however puts you on a pressure climb to reach that 5252 torque peak.  The engine relaxes a bit from there up to 5500 (5800 with constant speed) to full power.  

In general full WOT should be determined by straight and level flight performance at your normal operational area/region.  As Roger noted the area where you fly most.  In engines before mid 2006 the crankcase stresses can lead to some cracking on engines operated with over pitched props that never allow the engine to "unload".  In simpler terms we referred to RPM in climb, now Rotax wants you to monitor inlet manifold pressures, MAP.  

In my opinion get the prop set as above.  With CS props fly it by throttling back some on the butterfly and put some pitch to get it to 5000 for a nice cruise with some fuel burn saving.  

Cheers

Roger/RW - thank you for your thoughts.

No offence gents but I think you miss the point of my question.

I am asking (admittedly a bit theoretical) if fuel consumption, specifically in a Bing carburettor, can be controlled by using the constant speed propeller (as a governor, which it is) to reduce/increase engine RPM, thereby influencing the manifold pressure (MAP).

By influencing the MAP the carburettor diaphragm, will move up/down, allowing more/less fuel to enter the engine.

I have picked wide open throttle (WOT) not as a goal but to minimise the variable of the butterfly valves influence on MAP.😈

Sean...in theory you could do that.  I just don't know if that is the best way.  

haven't we had this discussion before?

Cheers