# 1/2 VW versus Briggs, Kohler, Generac V-Twins

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#### nheistand

##### Member
I see that the Generac and other V-Twin industrial engines are starting to show up on ultralight aircraft and powered paragliders. The great thing about these engines is the low cost, newer technology, and easy service/repair. They come with alternator, starter, and electronic ignition built in.

On the other hand, the 1/2 VW can be built with a magneto so no battery or alternator is needed so the weight can be kept down to 85lbs or so. Also the 1/2VW should be built with high performance parts like Mahle pistons, Scat Crank and Rods, etc. Everything in life is a trade-off. The cost for these engines will be about the same until you start putting extras on the 1/2VW like starter, alternator, etc. These parts can be very pricey. A nice 37hp 1/2VW with a magneto is $3400 without extras at Hummel Engines. However, I will build and sell a 37hp 1/2 VW for$2900 including prophub, magneto, exhaust, intake, and carb ready to go.

A stock 32hp Generac V-Twin is about $1700 without prop hub (including alternator and starter!:gig. Both the industrial V-Twins and the 1/2 VW are rated at 3600rpm. Since the industrial engine and the 1/2VW are so similar in performance, the direct drive prophub should work as well on the industrial engine as it does on the 1/2VW. Props will be limited to about 54in in both cases. It is relatively easy to design a belt reduction drive for the industrial engines so a longer prop can be used and more thrust will result. Now if I just had a low-cost redrive for the 1/2VW. What do ultralight builders think of these engines? #### Dana ##### Super Moderator Staff member If you can build a 37hp 85lb 4 stroke then why isn't it replacing 2-strokes in that class? -Dana "If you want to build a ship, then don't drum up men to gather wood, give orders, and divide the work. Rather, teach them to yearn for the far and endless sea." - Antoine de Saint-Exupéry #### nheistand ##### Member If you can build a 37hp 85lb 4 stroke then why isn't it replacing 2-strokes in that class? -Dana "If you want to build a ship, then don't drum up men to gather wood, give orders, and divide the work. Rather, teach them to yearn for the far and endless sea." - Antoine de Saint-Exupéry The short answer to your question is lack of marketing and availability. A usual, everyone wants more thrust for less money. And they want an engine that is light and has a proven track record in the air. Homebuilders love to do it themselves (why they are homebuilders). The biggest problem for Ultralight flyers is weight. The 85lbs is acceptable in that regard. The other problem is getting desired thrust for good climb and cruise speed. Without a redrive, the 1/2 VW will not come close to A Rotax 377 or 447 for thrust. These run a gearbox redrive to get 2.58:1. The optimum ratio for the 1/2 VW is about 1.6:1 where it could turn the same prop at the same prop rpm as the Rotax 377. If you fly ultralights, even the 377 Rotax is considered to be not as much power as you would like, however it does a good job on most one place true ultralights. So the 1/2 VW at 37hp will only "feel" right if it performs as well or better than the 377 Rotax. That could happen with a redrive on the 1/2 VW although there would be at least a 10lb weight penalty if not more. And the light half VW is hand prop only. Most of these ultraligters want electric start and a Rotax 447 to be really happpy. If they cannot afford the new Rotax, they find a used one. The Kawasaki 340 with a belt redrive does a good job for low cost. However, those who are fed up with mixing gas and oil, hard starting, and other 2-stroke problems, do tend to choose the 1/2 VW and it does do an adequate job with direct drive prop for aircraft like the MiniMax, the WeedHopper, and others. The V-Twin industrial engines will be showing up more and more. They are designed fairly strong for the construction industry and similar. But I suspect the 1/2 VW with Mahle pistons and Scat crank and rods is stronger and would be more popular if builders could get them off-the-shelf at a reasonable price and were even aware that they are available. Homebuilders tend to get into the mindset that they must build the engine as well as the aircraft. I believe that is a mistake where they try to cut a stock VW engine case, crank, and heads, and do various machine work operations to end up with an engine that does not have the performance upgrades or has other challenges. The Hummel 37hp 1/2VW is fair example, but even for$3400 you are getting a used engine case. I believe the winner is a new Mosler type engine case, Scat crank/rods, Mahle pistons, Slick magneto etc. for $2900 or so where it is very simple, and very strong and certainly adequate for single place ultralights. The machines fly okay with a 27hp single cylinder Rotax 277 with a gearbox, bit of vibration though. The 1/2 VW is much nicer IMHO. #### Dana ##### Super Moderator Staff member Well, the Cuyuna is 35HP and 85 lbs, while the 447 is 40HP and 85 lbs (with redrive and exhaust), so it's certainly in the ballpark. Both those engines have pull starters standard, which is all most ultralighters need. My friend has a 1/2 VW in his Minimax. He likes it, but says it vibrates a lot. I hear good things about the 1/3 Corvair, too. -Dana Cause of crash: Inadvertent contact with the ground. #### nheistand ##### Member Well, the Cuyuna is 35HP and 85 lbs, while the 447 is 40HP and 85 lbs (with redrive and exhaust), so it's certainly in the ballpark. Both those engines have pull starters standard, which is all most ultralighters need. My friend has a 1/2 VW in his Minimax. He likes it, but says it vibrates a lot. I hear good things about the 1/3 Corvair, too. -Dana Cause of crash: Inadvertent contact with the ground. The 1/2 VW crank requires balance weights on the crank throws to make up for the missing weight of the other two cylinders. I believe a true 1/2 VW counterweighted crank from SCAT will run smooth. Hummel Engines sells the counter weights that can be welded on a stock crank. Norm H #### erkki67 ##### Well-Known Member The old DAF 44 and 46 were nothing else then a 1/2 VW! The only drawback is that the engines are hard to find. Those guys living in the nederlands might be lucky to find these little gems at the srapyard. Bst rgds Erkki #### BigBen ##### Well-Known Member I see that the Generac and other V-Twin industrial engines are starting to show up on ultralight aircraft and powered paragliders. The great thing about these engines is the low cost, newer technology, and easy service/repair. They come with alternator, starter, and electronic ignition built in. On the other hand, the 1/2 VW can be built with a magneto so no battery or alternator is needed so the weight can be kept down to 85lbs or so. Also the 1/2VW should be built with high performance parts like Mahle pistons, Scat Crank and Rods, etc. Everything in life is a trade-off. The cost for these engines will be about the same until you start putting extras on the 1/2VW like starter, alternator, etc. These parts can be very pricey. A nice 37hp 1/2VW with a magneto is$3400 without extras at Hummel Engines. However, I will build and sell a 37hp 1/2 VW for $2900 including prophub, magneto, exhaust, intake, and carb ready to go. A stock 32hp Generac V-Twin is about$1700 without prop hub (including alternator and starter!:gig. Both the industrial V-Twins and the 1/2 VW are rated at 3600rpm. Since the industrial engine and the 1/2VW are so similar in performance, the direct drive prophub should work as well on the industrial engine as it does on the 1/2VW. Props will be limited to about 54in in both cases. It is relatively easy to design a belt reduction drive for the industrial engines so a longer prop can be used and more thrust will result.

Now if I just had a low-cost redrive for the 1/2VW. What do ultralight builders think of these engines?

How are you coming on the supplying of 1/2 VW for $2900??? #### AZSpyder ##### Member I think I am going to end up using a 1/2 VW myself. Hummel has them up to 45 HP. If the Hummel's numbers, and other suppliers HP for displacement too, are correct the bore/stroke I'm thinking about would be about 40. There are a lot flying but most have been with stock strokes at about 32 HP for half a 1835cc, or 918 cc. The 45 HP is at 1200 cc and seems to be about maxed out on heat extraction. So far no one has gotten a redrive to work on the 1/2 VW. I think only belt types have been attempted and the torsional shock eats them alive in minutes, but they are still trying. Maybe someday but it's been enough trouble that I wouldn't experiment myself. The 1/3 Corvair sounds interesting. The head looks very good for cooling. They seem to be about 32-35 HP and just under 900 cc. There is not the bolt in hot rod displacement available like the VW but some are adapting VW cylinders for some increase. Jerry #### Rod1 ##### Member In Europe the B & S engine is gaining popularity fast but I think the issue you will have is weight. The B & S engine is 51lb! Luciole.co.uk Rod1 #### litespeed ##### Well-Known Member Me I personally like the JCV 360 Its only 67lbs wet as a complete solution and has plenty of smooth power. It uses proven 4 valve heads and barrels with a aircraft specific bottom end and redrive. The B & S might be 51lb but then it still needs extras and no redrive, electric start, water cooled.............. Verner Motor, Czech Republic - Home page #### georgehreed ##### New Member Hey I see from an old post that you rebuild half-vw engines? If so, could you rebuild mine? It's fully modified, but has been sitting a while. I want it broken down and inspected, everything checked out - I'm putting it on my minimax and I want as much power out of it as I can. I want low rate of fuel burn and torque. Reply to georgehreed at gmail and I will send pics. I can ship it to you in about 2 weeks. Thanks, George I see that the Generac and other V-Twin industrial engines are starting to show up on ultralight aircraft and powered paragliders. The great thing about these engines is the low cost, newer technology, and easy service/repair. They come with alternator, starter, and electronic ignition built in. On the other hand, the 1/2 VW can be built with a magneto so no battery or alternator is needed so the weight can be kept down to 85lbs or so. Also the 1/2VW should be built with high performance parts like Mahle pistons, Scat Crank and Rods, etc. Everything in life is a trade-off. The cost for these engines will be about the same until you start putting extras on the 1/2VW like starter, alternator, etc. These parts can be very pricey. A nice 37hp 1/2VW with a magneto is$3400 without extras at Hummel Engines. However, I will build and sell a 37hp 1/2 VW for $2900 including prophub, magneto, exhaust, intake, and carb ready to go. A stock 32hp Generac V-Twin is about$1700 without prop hub (including alternator and starter!:gig. Both the industrial V-Twins and the 1/2 VW are rated at 3600rpm. Since the industrial engine and the 1/2VW are so similar in performance, the direct drive prophub should work as well on the industrial engine as it does on the 1/2VW. Props will be limited to about 54in in both cases. It is relatively easy to design a belt reduction drive for the industrial engines so a longer prop can be used and more thrust will result.

Now if I just had a low-cost redrive for the 1/2VW. What do ultralight builders think of these engines?

#### Armilite

##### Well-Known Member
I see that the Generac and other V-Twin industrial engines are starting to show up on ultralight aircraft and powered paragliders. The great thing about these engines is the low cost, newer technology, and easy service/repair. They come with alternator, starter, and electronic ignition built in.

On the other hand, the 1/2 VW can be built with a magneto so no battery or alternator is needed so the weight can be kept down to 85lbs or so. Also the 1/2VW should be built with high performance parts like Mahle pistons, Scat Crank and Rods, etc. Everything in life is a trade-off. The cost for these engines will be about the same until you start putting extras on the 1/2VW like starter, alternator, etc. These parts can be very pricey. A nice 37hp 1/2VW with a magneto is $3400 without extras at Hummel Engines. However, I will build and sell a 37hp 1/2 VW for$2900 including prophub, magneto, exhaust, intake, and carb ready to go.

A stock 32hp Generac V-Twin is about \$1700 without prop hub (including alternator and starter!:gig. Both the industrial V-Twins and the 1/2 VW are rated at 3600rpm. Since the industrial engine and the 1/2VW are so similar in performance, the direct drive prophub should work as well on the industrial engine as it does on the 1/2VW. Props will be limited to about 54in in both cases. It is relatively easy to design a belt reduction drive for the industrial engines so a longer prop can be used and more thrust will result.

Now if I just had a low-cost redrive for the 1/2VW. What do ultralight builders think of these engines?
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What is the 1/2 VW Spec's you talk of:
Bore & Stroke
Intake Valve Size
Exhuast Valve Size
Carb CFM
Compression
CAM Lift & Duration

Rich

#### Armilite

##### Well-Known Member
VW 2 Cylinder Big Bore 53hp 3500rpms.