Valley Engineering used to attend our annual fly in at K34 ( no longer held). They had the engine mounted on an in house developed ultralight but never flew it at the fly in. They had a very clever PRU that removed a lot of the big twin vibration, I'm not sure that it could be hand propped with the PRU in place so the electric start was required. Looked nice though.

for 125-130## you can actually go full VW if you absolutely strip it. Including the very heavy flywheel.

Seems as if there are a couple of noteworthy engine offerings on Barnstormers, a 447 w/box $1250 and a couple of 503s under $3K, obviously more info needed but if anyone is looking, you might want to check out Barnstormers.
Kim Brown New Hampshire

The 447 is tough, capable and what the miniMax was designed for. I would sooner spend $1250 on that than twice as much on a heavier 503 that will, at best have a marginally better ROC and a noticeably worse range.

+1 to what Tom said with one exception. The Mini Max was actually designed for the 277 at 28 hp. The 447 at 40 hp is a perfect match unless your goal is peak performance in climb, and speed.
A couple of years ago there was a 503 powered part 103 legal Mini Max for sale on Barnstormers. It was there for a long time, and I'm not sure if it ever sold. 5 gallons of fuel won't last long in a 503.  

If I were building a Himax today, I would seriously consider the Hirth F23.  50 hp, and 78 lbs including exhaust, electric start, and PSRU.

http://www.recpower.com/F-23%202%20cycle%2050hp.htm

Evolution Trikes are using both the following in their Part 103 (Rev) birds with good success.

Simonini Mini 3 and Polini Thor 250

http://www.simoniniusa.com/index.php?page=Engines&Engine=Mini-3

https://www.polinithor.com/en/polini-thor-250-thor-250-ds-2/

https://evolutiontrikes.com/rev/

I know the Avid/Kitfox folks have had very good success with the Simonini Victor 2 in their light sport birds.

Quoted from lake_harley

Here's the video(s) I think aeronaut was referring to.  https://www.youtube.com/watch?v=cj0hdymXfOg   and  https://www.youtube.com/watch?v=ppR5Boo7cn4

I had a 2A042 stripped and had a prop for it, but decided to go with a 277 on my MiniMAX. I ended up selling the '042 but still have some regrets about not using it. FWIW, you'll find various opinions about the HP potential of the '042, but I feel pretty comfortable about believing reports of them being about 24 HP in the real world. Spec rating is a LOT lower, but that was in very dismal military test conditions.

Lynn

The bore and stroke for this Teledyne 2A042 engine is 76x76mm and appears to fly the minimax very well in the video.

  It means that to get similiar results from a small 1/2 vw all you have to do is substitute a 76mm stroke crankshaft as the

  bore is quite large at 85.5mm . It seems to turn in the same RPM range too.

  I have been thinking since long why 1/2vw is not very popular in the minimax altough everyone says it is cheap to buy.

  I have concluded that the real reason why it is not being used is the COST rather than functionality.

  The cheapest smaller 1/2vw costs 3200 $ and the 92x78 1/2 vw engine is 3700$.

  When you can get a 447 for 1500 $ then a vw for 3700 doesnt seem rational .

   I once read an article about a uk minimax with 1/2 vw mosler MMCB which was a 92x78 engine and the test pilot did

   not mention any lack of power even though that minimax looked like a heavier streamlined version.

  
   KK

  

No, but it went bang. Like all the other ones did.  They only get airborne in order to break their crankshafts so we don't like them. We would like to. They sound nice and drink little.
But they go bang.

What goes bang, the vw engines?  I'm a bit of a noob in this, but I thought everyone liked them because they were reliable?

Quoted from tomshep

No, but it went bang. Like all the other ones did.  They only get airborne in order to break their crankshafts so we don't like them. We would like to. They sound nice and drink little.
But they go bang.

Does it mean that the 1/2vw engines are being used in ignorance and failure is inevitable?

I know there are issues with the hub/crank interface where the prop attaches on the fan pulley side of the engine.

The prop hub inner diameter where it fits on the nose of the crank is made 0015 to 003 smaller than the crank.The hub

is then heated and put on the crank.Once cool the hub shrinks and grips the crank, The key is only for alignment.

In theory this operation looks simple but 0015 is half or less then a human hair and very difficult to machine.

A loose hub is bound to crack the crankshaft which is already weak in this area.

Is there any other area where the crank breaks like in the corvair engine/


KK

Half Beetle engines in the UK bust their crankshafts. Every one fitted to a Max, (source John Hamer,) has broken yet we have a solid history of full engines converted with the same hubs and no problems.

.... The four cylinder engine firing strokes are spaced at 180 degrees and the two cylinder at 360.

Maybe that could be the reason for the crank breakages because everything else is the same.



KK

I don't think so. I think it is a matter of secondary balance. Flat twins built to be flat twins rev well and fast. Cut down fours seem not to.  I wonder how whole case twins fare?

I actually agree. More should be done to balance. Maybe a crank could be designed just for the application.

On any but the lowest horsepower 1/2 "VW" engines I believe you will find they use a custom crankshaft, not a cut down VW crankshaft.  Some of the lower horsepower ones used to have cut down cranks, but I don't know if they still do.

Tom

Quoted from tomshep

I don't think so. I think it is a matter of secondary balance. Flat twins built to be flat twins rev well and fast. Cut down fours seem not to.  I wonder how whole case twins fare?

E mailed John Hamer but the message bounced back.He's not there.Maybe out flying his minimax.

Did a simple read on secondary balance.Upgoing piston has more mass than downgoing one so an imbalance is introduced.

Looks relevant on the 447.

Doesnt seem  relevant to the opposed twin as the opposite piston is doing the same thing at any point in time.

There is imbalance due to the pistons being staggered which will swing the nose of the crankshaft alternately to the left

and then to the right.

It is easy to imagine a relatively loose hub able to move  breaking the keyway and the adjacent  part of  the

crank and to do that it probably doesnt need help from imbalance.

Any idea about location of the crank breaks on uk engines /?


  KK







KK

I think we'd need more information on what KK meant by one piston having more mass than the other.  There must be something that he has in mind, but of course the mass of the pistons is constant.  It can't change unless the size or material of the piston changes. A more detailed statement would be very helpful.

Tom

Mass/weight/acceleration/force are mutually confusing and I am not a science student . A piston is travelling

faster 90 degrees either side of TDC and slower 90 degrees either side of BDC so it has more force in the top half of the cycle

and less in the bottom half resulting in imbalance and seccondary vibration.


  KK

It doesn't matter because there has been plenty of work done on half VW motors over the years to know that if there was an easy answer it would have been found and there are lots of other engines to choose from so there is no point in choosing a pinless grenade.

Quoted from Greg Doe

A couple of years ago there was a 503 powered part 103 legal Mini Max for sale on Barnstormers. It was there for a long time, and I'm not sure if it ever sold. 5 gallons of fuel won't last long in a 503.  

Have to throw the BS flag on this one!

No 503 powered Minimax will ever meet Part 103 speed limits.

Radfordc, I'm just telling you what was listed. The airplane was in North Carolina, (Greensboro I believe). It might not meet the 62 mph max cruise restriction of Part 103, but nobody is checking. The seller listed it as Part 103 compliant. I was only pointing out that 5 gal. of fuel wouldn't last long. While I never heard of anyone flying an ultralight being checked for fuel capacity, that certainly would be a lot easier to check than whether someone is "speeding'.

Quoted from radfordc

Have to throw the BS flag on this one!

No 503 powered Minimax will ever meet Part 103 speed limits.

I used to fly a 503 ultralight and would get a good  1 & 1/4 hours out of the 5 gallons on board.  More than enough time for me anyway.  Ultralight after all.  Just going for a tool around the patch and take in the sights.

General rule of thumb for a piston/port 2 stroke is; HP being delivered (at the given time) divided by 10 = GPH

I think if I was to see a Radar Gun pointing at me, I'd just fly away.....

Just a note.
I was checking out a video about the Valley Engineering "Backyard Flyer". They were demonstrating one with "Tundra Tires" and a Hirth F-23. From what they said, the F-23 is 30 lbs lighter than the Big Twin (Generac), and has 10 more HP. So I'll be 18(ish) lbs lighter with the 2702.

https://www.youtube.com/watch?v=5cAikMeCbks

Quoted from LSaupe

General rule of thumb for a piston/port 2 stroke is; HP being delivered (at the given time) divided by 10 = GPH

For Air-cooled 4-strokes, Current HP÷12=GPH
(0.5 Lbs of fuel per HP Hour @ 6 lb/gallon)

So my 2-stroke should drink app. 3 gph @ 75% crz vs app. 2.5 gph with a 4-stroke of the same HP (on paper anyway).

The difference is that a four stroke can pull a coarser prop as it has more torque low down.

But a two stroke with reduction drive multiplies torque.

Quoted from beragoobruce

But a two stroke with reduction drive multiplies torque.

Even aviation 2-strokes have a peakier power delivery with much more power delivery at higher RPM than aviation 4-strokes. You'd think that would help because high propeller RPM needs a lot of power to turn it. But in my experience a four stroke (with or without gearbox) is a lot more tame. The throttle control acting more nicely as a thrust lever than with my 447 503 and particularly the 462 engine, which needed a lot of small throttle setting changes as air speed and attitude changes were made.

Don't care. I'll stick with 2-strokes for the foreseeable...

Quoted from tomshep

The difference is that a four stroke can pull a coarser prop as it has more torque low down.

As always....it depends.

I flew my Airbike with two different engines; 447 two stroke (40 hp, 2.58 reduction), and a big bore 1/2 VW four stroke (37 hp).  

The 447 typically ran at 5600 rpm (2200 prop rpm) in cruise turning a 64x32" prop and making about 56 mph.  Top speed was about 70 mph.

The 1/2 VW typically ran at 3400 rpm turning a 56x22" prop and making about 52 mph.  Top speed was about 60 mph.

The 447 performed much better than the 1/2 VW.  Fuel consumption was not much different between the engines.

There exist an 1/2 VW engine that was never cut in half, it had from the beginning only two cylinders, the DAF 44 or 66 engine.

As far as I know, they never had a crankshaft failure.