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Engine conundrum for Hummelbird

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Engine for the Hummelbird (already have both)

  • Global 1/2 VW-35hp, 2 cylinider, 4 stroke

    Votes: 14 77.8%
  • McCulloch 4318-72hp, 4 cylinder, 2 stroke

    Votes: 3 16.7%
  • Global 1/2 VW-35hp, 2 cylinider, 4 stroke

    Votes: 15 83.3%
  • McCulloch 4318-72hp, 4 cylinder, 2 stroke

    Votes: 3 16.7%

  • Total voters
    18

12notes

Well-Known Member
Supporting Member
Joined
Aug 27, 2014
Messages
1,286
Location
Louisville, KY
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.
 
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