- Feb 13, 2010
- Fort Walton Beach, Florida, USA
I have communicated with the gentleman running the corvair on the rw20. He was not happy with the direct drive corvair as he converted it. He said with gearbox (2.03 to 1 SPG2) and a 73” prop it’s like a different airplane. Jumps of the ground like a helicopter. Faster then he was ready for, It climbed so steep and fast it made him uncomfortable so he backed off the ignition advance. I would not be surprised if it turned out that the draggy slow airplanes running corvairs are leaving a lot of power on the table by running the smaller direct drive prop.
Most of the 'canted' inline engines cant the redrive opposite from the engine lean, so that the prop centerline is 'above' the line of the cylinders. That moves some of the engine mass to the other side of the prop.How are people getging over the weight off to ond side when laying an inline 4 honda engine on its side. This is only reason i went subaru over a honda is honda wouldnt fit under cowling standing upright and leaned over is a lot of weight to the right .
This can work well, the slower prop RPM and longer prop also improving prop efficiency esp at low speeds.Not surprising at all. The engine can make more HP, and do it at lower BMEP, which can actually lower stresses on the engine in the bargain. Same effect with VW engines. There's a Kolb that flew with a DD VW and the owner said it was a dog. Then he installed a redrive and turned it into a useful a/c. I remember watching the little VW reduction drive 2 seat open cockpit Valley Engineering a/c (a few closeup pics here) at OSH back in the '90s. It outperformed everything else on the ultralite strip except the helicopters.
Wayne Clagg tried everything reasonable to let that engine make about 100hp at his airspeed. He attached "fat fins", adjusted the baffling, etc. He has (had?) a good blog that discussed this, and we've discussed it a bit here. Pops knows him well. Wayne took a very systematic approach and couldn't make it work. He likes the Rotax 912 he put in a lot.If you're actually using more power, cooling would obviously need to be increased, and there's a limit to how much heat can be rejected by VW heads. Did he increase air inlet/exit sizes? Install any kind of diffuser and/or flow directors to help with what little pressure recovery would be available, and get air flowing efficiently through the cylinders?
We agree. It is about asking too much from the engine, and, in the case of VWs, expecting that an engine run through a PSRU can produce more continuous HP than a direct drive. It cannot, because our limitiom isn't volumetrics, it is heat.... it isn't about the redrive. It's about wildly unreasonable expectations.
A lot of dreamers have ruined good VW engines and their airplanes trying to use a PSRU to get more HP. They might get more thrust (useful in itself), but the engine won't make more continuous HP reliably. Things could be very different with a liquid cooled engine with excess cooling capacity.The engine can make more HP, and do it at lower BMEP, which can actually lower stresses on the engine in the bargain. Same effect with VW engines.
That is a logical starting point if there's no history of other successful installations in aircraft. Once there's some experience, obviously, there's more to base things on.Expecting more HP, continuously, than the 'stock' HP of a car engine, is the 1st sign of a conversion attempt doomed to failure.