VW Engine?

[johnr9q@yahoo.com]

I'm not a very good reader so help me out here. In the following article:
http://bobhooversblog.blogspot.com/2...as-engine.html
Is Bob saying The VW engine is not reliable or that people that sell these engines overstate the horsepower or both? Or is he saying something else?

[gammaxy]

Your link didn't work. I assume you're trying to link to this article:
http://bobhooversblog.blogspot.com/2006 ... ngine.html

I'd like to mention that 80hp for a 2180cc engine at around 3300+ rpm isn't a ridiculous claim. Jabiru claims the same for the Jabiru 2200 with similar displacement: http://www.jabirupacific.com/specs/2200.htm. The Jabiru 3300 with 50% more displacement generates ~120hp at 3300rpm.

The prop speeds Bob Hoover is talking about are a lot lower than what we use. At the speeds of the Sonex, a smaller diameter, faster turning propeller are pretty efficient. Such a propeller wouldn't work so well on a draggier 80-100mph airframe, so a direct drive VW probably won't be as good a choice as an engine that develops 80hp at a lower rpm.

[lutorm]

The statements on cooling are interesting, though. Has anyone measured what pressure differential we get across the baffles in flight?

[John Monnett]

Bob Hover, rest his sole, was a self-appointed expert on VW aero conversions. To my knowledge, he never flew high performance "VW" aircraft and was one of the more negative individuals out there . He never (maybe if ever) published articles in Sport Aviation or any reputable magazine that supported homebuilt aircraft yet some still consider him relevant. I do not. VW based aero engines are "horses for courses". flying high drag, slow underpowered aircraft is quite a different proposition then flying fast, high performance (for their HP) clean aircraft. Sonex is among those that have a very broad performance envelope and can take advantage of higher RPM and small dia. props. They can also cool better because of the speed and air they are moving. The Monex was a perfect example, moving at speeds in access of 185, running 11:1 compression and full throttle for 500 miles. Should I make a list of others that have also proven that statement? Bob simply did not know what he was talking about relative to possible HP outputs of the type of configuration we use. He probably was right about airplanes like the "Goldbug".

[radfordc]

The statements on cooling are interesting, though. Has anyone measured what pressure differential we get across the baffles in flight?

The proof of the pudding is in the eating. Even if you don't measure the pressure delta you can still see the CHTs and know that the engine is cooling properly. Once past the break in period there really isn't any cooling problem with the Aerovee.

[radfordc]

I'm not a very good reader so help me out here. In the following article:
http://bobhooversblog.blogspot.com/2...as-engine.html
Is Bob saying The VW engine is not reliable or that people that sell these engines overstate the horsepower or both? Or is he saying something else?

A rule of thumb for determining how much HP an engine is producing is to measure fuel burn and calculate from that. A basic normally aspirated piston engine burns ~.5 lb of fuel per HP per hour (brake specific fuel consumption). https://en.wikipedia.org/wiki/Brake_spe ... onsumption

In cruise an Aerovee will burn about 5 gal/hr. Do the math... 5gal/hr x 6 lbs/gal = 30 lbs/hr; 30 lbs/hr divided by .5 lbs/hp/hr = 60 hp This is roughly the power being produced in cruise flight (~3200 rpm) by an Aerovee on a Sonex. Maximum power at full rpm (3500 rpm) will be approximately 80 hp.

[lutorm]

That is true, assuming the engine is actually operating at max power mixture.

Another way of looking at it is that a 2180cc engine at 3400 rpm with a volumetric efficiency of 90%, at a mixture of 13:1 and a BSFC of 0.5 comes out to 79hp. Now, 90% seems like a high VE for a 2-valve engine with sketchy intake design, I thought 80-85% might be more realistic. That brings it down to 70-74hp.

The ballpark numbers are right, but I think they could easily be off by 10% which is +-8hp...

[vigilant104]

In the event someone hasn't seen the Sonex-produced graph of an actual Aerovee on an actual calibrated dynamometer.

https://images.duckduckgo.com/iu/?u=http%3A%2F%2Fwww.aeroconversions.com%2Fimages%2Fproducts%2FHP-Torque_graph.jpg&f=1

There's nothing fantastic or unbelievable about it at all. As Chris points out, this output is in line with other air-cooled engines of similar displacement. Certified VW-derived aero engines by Limbach and Sauer also have similar claimed HP at similar displacements and RPM, and the certification authorities check these things out pretty closely.

For those interested in VW-derived aero engines, John Monnet's webinar on the development of the Aerovee https://www.sonexaircraft.com/eaa-webinar-series-supervee-to-aerovee-engine-history/ is definitely worth the time.