The age-old engine question: 540 vs 390 vs 360 for 4-place

[Battson]

Yes, I measured mine from the datum with a plumb-bob and tape.

What caught my attention is my measurement is 4" further aft than the number in your spreadsheet, which made me wonder whether mine is too conservative.

Eric's is scratchbuilt so I could imagine some small variation there. I would have expected our kits to be an inch-perfect match.

[Enewton57]

Bob told me a good rule of thumb is to sit in the seat and measure to where your belly button is. He made a mark inside where the leading edge of the wing is so he always has a reference inside the cockpit to measure from. To do this, put the plane in the level flight attitude, drop a plumb bob line from the wing leading edge. Transfer the location to the inside of the cockpit and make a mark on the side wall. Now you have a reference mark to measure from anytime you load someone heavy inside and you want to figure CG. Eric Newton - Long Beach, MS http://mybearhawk.com

[Battson]

That is a great idea. Measuring on the day is certainly the most accurate.

[bearhawk2015]

You can realistically extend the motor mount out a fair amount for a 4 cyl engine. I talked to someone who did this to bring his cg forward, I believe it was like 4 inches.

I'll give the specs on my plane just to give an idea how mine worked out. I don't have the baggage door which I've read adds around 30lbs, I only lightly painted the fabric and left the aluminum bare, I lined the interior sides in .025 aluminum, have heavy 4pt seats belts at all seats, put the odysy battery on the engine side of the firewall, lightweight alternator and starter, home made simple exhaust, composite prop, J-series 540 which I believe is the lightest model, half sky light, full plexy doors (.080 thick), and my prop flange is around 59 or 60 inches (I can't remember the exact #). My empty wt is around 1370 and the empty wt cg is at 11.4, this is with 10qt of oil, back seat in, and unusable fuel in the tanks.

I recently took a trip with a aft cg and decided that I am going to limit my aft cg to 21", that's just for my comfort level, when I have the whole family with I really don't care for chasing the plane all over the place. The airplane flies fine at the aft cg but you will be busy and have to pay attention at all times.

I do wonder though that if the trim tab moved more in the same direction as the elevator so that it would get harder to push or pull the stick as you deflected it that it would feel more stable at aft cg.

[Battson]

I am surprised your CG isn't further forward considering all the lightweight solutions you're using. I suppose the composite prop has a big influence?

For comparison, my empty CG location is at 10.4", in the normal weighing configuration (oil, unusable fuel, equipment installed). Of course I have extra weight on the nose with a longer prop hub and fuel injection. My original empty weight was 1479, however the big tires have increased that somewhat.

[marcusofcotton]

Phil Johnson had his O-360 flying and then redid his motor mount to extend 10 (ten) inches and likes it. With my light engine/prop plans, and ideas to lighten the tail to compensate, it might be best for me to wait with engine mount construction until near the end.

Mark J

[Gerd Mannsperger]

One thing to consider is the O540 B4B5 is the most reliable aircraft engine ever build. On my last Maule I did run the engine 2 times to 2200 hours before overhauls and even on the second overhaule there were no surprises new bearings and cylinders and done. If you fly with someone in a 180 HP maule and throttle the 540 back to the same speed the fuel burn is almost exactly the same. If you bump the compression up and have the cylinders ported the altitude performance goes up dramatically and fuel consumption goes down.The extra speed of the 540 makes up for the extra fuel burn easily as well, so you can pick fuel burn and speed or save fuel and slow down. The B4B5 also is happy with good auto fuel. it just has to many great benefits to dismiss it
I would like to have Cato build me a 3 blade prop for the 540 just to try it out and if I do not like it go to the tried and trusted Constant speed McCauley 80"
prop. It is in the same league with the O540 for reliability. While the 4 cylinder Lycomings are good motors they have never traded me quite as good as the 540s the reasoning to me is they have to work much harder. Anyone who wants to look at something new and interesting the new UL power 520 later engine with 200 HP looks interesting A real Modern aircraft engine and a 6 cylinder with smooth power to boot. Definitely would need a longer engine mount with that one.

[tailwind]

A side note here. Phil did indeed have a 180 in his plane. It did fly well. Phil has since removed the 180 and installed a O 540. Since installing and flying the 540 he is now sold on the benefits of flying behind the 540. A 180 powered plane will perform very nicely but if you want the ultimate performance install the 540.

[Gerd Mannsperger]

One thing to consider is the O540 B4B5 is the most reliable aircraft engine ever build. On my last Maule I did run the engine 2 times to 2200 hours before overhauls and even on the second overhaule there were no surprises new bearings and cylinders and done. If you fly with someone in a 180 HP maule and throttle the 540 back to the same speed the fuel burn is almost exactly the same. If you bump the compression up and have the cylinders ported the altitude performance goes up dramatically and fuel consumption goes down.The extra speed of the 540 makes up for the extra fuel burn easily as well, so you can pick fuel burn and speed or save fuel and slow down. The B4B5 also is happy with good auto fuel. it just has to many great benefits to dismiss it
I would like to have Cato build me a 3 blade prop for the 540 just to try it out and if I do not like it go to the tried and trusted Constant speed McCauley 80"
prop. It is in the same league with the O540 for reliability. While the 4 cylinder Lycomings are good motors they have never traded me quite as good as the 540s the reasoning to me is they have to work much harder. Anyone who wants to look at something new and interesting the new UL power 520 later engine with 200 HP looks interesting A real Modern aircraft engine and a 6 cylinder with smooth power to boot. Definitely would need a longer engine mount with that one.