Perhaps I’m not searching in the right places, but I’ve found surprisingly little about operating VW aircraft engines. What I’m interested in is the sort of tips an owner should know in order to operate them safely. Whether they’re susceptible to shock cooling. How to tell if they’re happy/unhappy. What to check in a pre-flight. The answers to questions a person might not think to pose – if that makes any sense. For example, I’ve only just learned they stop windmilling very quickly and won’t restart in flight, which is the sort of thing that I might not have anticipated.
vwaircraftengines.com seems as if it may become a good place to start, but remains a bit sparse and more geared to builders.
Can anybody share any of their accumulated wisdom, or point me in the direction of some?
I’m building one, waiting for cylinder heads from Revmaster that should be here any day now. The thing is, ignition and fuel systems can be very different, all kinds of different things exist. Operation will be different because of this. The manual that came with the kit, is very much like any other engine. Change oil at regular intervals, check compression etc.
Otherwise there is only one thing that kills a VW, and that is over heating.
The people I knew who flew with VW engines in the past were continually fiddling with them, adjusting valves, swapping cylinder heads regularly, and worrying about about friction drive prop hubs, bolts clamping wood props coming loose, carburetors, ignition problems etc. I think in the here and now, it is possible by being very careful about parts selection and installation issues to build a reliable engine. It will still require a bit of fiddling.
VWs will restart in flight just fine if the starter is working and big enough, the battery has enough ummmph and the engine is functional. They will not start on their own, without an electric starter, because the small diameter wood propeller stops turning.
AFAIK there is a very big difference (as LeSving already wrote) between different aero-conversions of VW engines. For four decades, the “Limbach” converted VW beetle engines (over 6000 built!) were installed in almost every motorglider and in many homebuilts and VLAs around here. From what one hears (or doesn’t hear…) they seem to be almost trouble free and of course able to restart in flight otherwise no motorglider could use them.
it will still require a bit of fiddling.
I guess some fiddling is needed. But -prop hubs, wooden prop problems, carbs, ignition etc are not issues anymore. It will require fiddling to set it up, but once set. Cylinder heads, including valves, may be a problem, that’s way I got new ones from Revmaster (in the hope they are of better quality and workmanship than they ones I originally got). There are so many variables here that a VW in one airplane may be a very different engine altogether than the one in another airplane. Only the basic “core” is the same.
Limbachs and Sauers are generally as good as any other aero engine, but they are specialized, and experience with those may count for nothing in a more general VW view of things. But even a Limbach will not tolerate excessive cylinder heat, or it will crack. Revmaster too makes excellent engines.
At the same time, there is nothing a VW can do that a Rotax 912 cannot do better (and has done so for a couple of decades now), or a ULPower or Jabiru or d-motor, and now even the diesel Superior Gemini. In the end, there is no good reason to chose a VW unless you like a bit of fiddling, or have an aircraft designed for it. Also, there is something undeniably cool about an engine designed by Ferdinand Porsche 
I used to fly a Taylor Mono (a long time ago). The engine ran pretty well, but you do need to adjust the tappets regularly, usually at oil change time. I believe there are hydraulic lifter conversions available. Shock cooling never seemed a problem. I guess smaller engines are less prone to head cracking due to uneven cooling.
I had two forced landings; one due to a fuel system modification and the other due to throttle icing and an inadequate heat system. In both cases the propeller didn’t finally stop until I bought the speed back to 55 knots on final approach (that’s when your threshold aiming point disappears behind the nose).
Starting on a hot engine was painful, but probably much better with modern lightweight starters and electronic ignition.
Best thing was flying around on 2 galls/hr at a leisurely 80 knots.
Thanks all for the advice.
It’s somewhat reassuring to hear it’s unlikely to stop after any little blip. I’d fancied adding a mixture control in the longer term, but worried that I’d end-up needing to do a forced landing if ever I over-leaned.
At the same time, there is nothing a VW can do that a Rotax 912 cannot do better
There’s one very important thing: affordability.
There’s one very important thing: affordability.
Indeed. Except from Limbach of course.
The engine ran pretty well, but you do need to adjust the tappets regularly, usually at oil change time
Every 50h is stated in my manual, same as oil change. This is no different from ULPower that also has mechanical lifters. Even the Jabiru with hydraulic lifters needs to be checked every 100h and the heads torqued every 50h ! Fiddling vise nothing will beat a Rotax 912 I guess (except a turbine), but a VW is no worse than other similar simple designs ones it is set up properly. And you don’t need to set it up. Even today ready to run and tested engines can be bought from Limbach, Sauer, Revmaster and Hummel. Hummel will build any size from 30HP 1/2 VW to 85 HP 2.4 L.
