So my Hummelbird project is proceeding well, and I've had a Global 35HP 1/2 VW engine since before the project started. I've purchased a mag, carburetor and Prince P-tip propeller for it. I'm thinking about making the motor mounts soon. Should have a 105mph cruise at around 2 gallons per hour. All set, decision made, ready to proceed when...
A gentleman at my local EAA chapter gives me 2 MacCulloch 4318 O-100 drone engines - one rebuilt (still see the cross hatching on the cylinder walls), the other for parts. 4 cylinder 2 stroke, twice the power (72HP) as the 1/2 VW and 7 lbs. lighter. The engine is dead simple - there's so few parts, no valves at all, prop hub is attached, direct drive. There was a Hummelbird built with the same Riblett airfoil and wing tanks I'm using, but with this engine, economy cruise was 130mph at 4GPH, full throttle would exceed Vne (145) in level flight. It's been done before, so I'm not on the bleeding edge of experimentation with this formula. I'll have the fuel capacity for the extra fuel burn.
So now I'm faced with a choice. I'd like to hear some opinions.
1/2 VW Pros:
2 gallons per hour
Already have the prop and accessories
Well established conversion
Easy fueling
1/2 VW Cons:
105mph cruise maximum
Limited climb ability on hot days
McCulloch 4318 Pros:
Up to 145 mph cruise, 130mph economy
Short take offs, bat out of hell climb rate
7 lbs. lighter
Can sell the 1/2 VW and make money on the swap
McCulloch 4318 Cons:
4 gallons per hour economy cruise, 5-6 GPH fast cruise/climb
Mixing oil with fuel, or oil injector
Needs a carb and prop.
Feel free to add to the pros and cons of each.
A gentleman at my local EAA chapter gives me 2 MacCulloch 4318 O-100 drone engines - one rebuilt (still see the cross hatching on the cylinder walls), the other for parts. 4 cylinder 2 stroke, twice the power (72HP) as the 1/2 VW and 7 lbs. lighter. The engine is dead simple - there's so few parts, no valves at all, prop hub is attached, direct drive. There was a Hummelbird built with the same Riblett airfoil and wing tanks I'm using, but with this engine, economy cruise was 130mph at 4GPH, full throttle would exceed Vne (145) in level flight. It's been done before, so I'm not on the bleeding edge of experimentation with this formula. I'll have the fuel capacity for the extra fuel burn.
So now I'm faced with a choice. I'd like to hear some opinions.
1/2 VW Pros:
2 gallons per hour
Already have the prop and accessories
Well established conversion
Easy fueling
1/2 VW Cons:
105mph cruise maximum
Limited climb ability on hot days
McCulloch 4318 Pros:
Up to 145 mph cruise, 130mph economy
Short take offs, bat out of hell climb rate
7 lbs. lighter
Can sell the 1/2 VW and make money on the swap
McCulloch 4318 Cons:
4 gallons per hour economy cruise, 5-6 GPH fast cruise/climb
Mixing oil with fuel, or oil injector
Needs a carb and prop.
Feel free to add to the pros and cons of each.