Cruise RPM

My Eurostar is on a UK permit to fly and that is also placarded 4800rpm maximum. This is a limitation imposed by the local regulations to make them compliant with the standards required in the UK. 4800rpm on mine with a 3-bladed Woodcomp prop gives me about 100mph cruise.

If you're in the US and your aircraft is an S-LSA, it's probably placarded at 4,800 RPM to meet the 120 KCAS limitation for that sub-category of aircraft.

Hi Eric,

For airplanes:

We don't have variable pitch props here for SLSA and the huge majority use ground adjustable props and some fixed pitch. Any WOT rpm that is under 5500 is over pitched and has no redeeming qualities. You start to lose out on climb, cruise, fuel economy and higher engine temps. Here in the USA most of us set our WOT rpm to 5600 -5650 at our average altitude and then the average pilot tends to cruise around 5100 - 5300. Yes some cruise up around 5400 - 5500, but not many. For folks that need a better climb prop they may set the prop to get 5800 WOT.

When you have a ground adjustable prop you have to pick a pitch that works well for your aircraft and your specific flying areas. 

This all depends on things like aircraft type, where you fly, your average altitude you fly at, ect... 

For powered parachutes and some others they may be down in the 4K's.

p.s.

I learned a lot many years ago when I had 14 props sent from all different prop Mfg's and four identical planes. My research took months to do. We took off side by side and flew side by side to compare all the props in climb, cruise speed, ect...  This is where I learned that if you want an all around best prop pitch setup then the 5600 - 5650 AT YOUR AVERAGE ALTITUDE was a good balance between climb and cruise. If you needed a better climb prop then a little flatter to get that 5800 WOT rpm is good. Someone in Florida at sea level and never gets over 2K altitude will have a different pitch than someone that lives in Colorado and always flies around 10K - 11K. These second guys will have a flatter pitch to help achieve better HP and torque and not over stress and overload the engine.. We lose HP and torque the higher we go above sea level.

Back then too they didn't have the E-Prop so I never got to test it against the others, but it seems to be the leader of the pack right now. Maybe Mosaic will allow variable pitch on LSA. It's a wait and see.

All good Roger,

Your recommendations seem to be all about optimising conventional fixed pitch (ground adjust) prop Cruise rpm ie fly - land - make an adjustment -  fly again - repeat, until satisfactory WOT Cruise RPM archived.

BUT !

When FIRST setting your prop ie haven't flown yet/new diffrent prop, you must have an initial setting.

Dont know if Rotax has changed its recommendation however it was STATIC - WOT -  5200 rpm. STATIC meaning aircraft tied down.

This methodology will get the pilot started, with a good safe (for pilot & engine) setting. From this pitch, adjustments to optimise the aircraft performance, according to the pilots wishes, can be made.

NOTE: Using the 5200 RPM Static method, will require the pilot to use both throttle & aircraft angle of attack to control engine speed. 

The E-Prop is a completely diffrent story - best to go with the manufacture settings - have heard several stories where pilot used their own "logic" only to end up back where the manufacture said the prop should set.😈

Here in the UK most Rotax 912 engined aircraft have to be compliant with the operating limitations as laid down by one of either of the two flying associations:

1. Light Aircraft Association (LAA).

2. British Microlight Aircraft Assosiaction (BMAA).

Mine comes under the LAA and I have the following limitations:

1. Max weight - 480kg

2. Max engine RPM: 5800

3. Max continuous RPM: 4800

4. Max airspeed: 146 mph

5. Max airspeed flaps extended: 77 mph

It also lists the acceptable propeller types and specifies the pitch setting so there is no scope for adjusting it to obtain a higher WOT RPM.