The best critique of the PFM is here:
http://www.seqair.com/Other/PFM/PorschePFM.html
An excerpt:
Quote:
The one absolutely horrible design feature is the fan cooling system. While it only uses a couple of horsepower to drive the fan, it totally destroys the exit velocity of the air. In normal installations, the engine acts as a radiator and the heat expansion of the air drives it out of the engine compartment. This thrust keeps the cooling drag to a minimum. One engineer estimates that the Porsche Mooney is losing 12-15 knots from the fan cooling.
Porsche claims that the engine is efficient, but this is statistical mumbo-jumbo. At best economy, Mooney's Lycoming and Continental engines are more efficient, but brake specific fuel consumption does not account for the extra drag of the cooling system and the bulbous cowling. These steal power from the installation. The faster the airplane, the greater the net power loss. The extra weight steals from the payload. What counts is moving payload efficiently. Watch the CAFE 400 for a true measure of the engine's efficiency.
It is now well understood that listening to customers and understanding their needs, desires and problems is of critical importance to the success of any commercial venture. In a Kendo blow of incompetence, arrogance and stupidity, Porsche did not talk to the major light aircraft companies before designing the engine. It's often been said that Porsche has forgotten more about engine design than aviation engine manufacturers ever knew. Porsche mistook a compliment for the truth and never bothered to find out the few things that Lycoming and Continental did know.
Had they asked, they would never have designed the silly three-point engine mounting system with one of the pickup points on top of the propeller gearbox. This makes for an awkward and complex engine mount, which on most singles also picks up the nose gear. It is difficult enough to design a tubular steel structure which will reach over the engine, but you must also provide some means of removing the engine. In the Mooney installation, the engine is trapped between the nose gear and the complex tubular structure which reaches out over the engine. You tilt the engine nose down and then take it straight forward. You can't use a block-and-tackle hoist, but Porsche has a special gizmo designed for that purpose.
Had they asked, Porsche would also have discovered the addiction to four engine mounting points-one more than you need to fly. If you lose one of the Porsche mounts, the engine is going to go bye-bye. (I have a friend who actually broke two of the four mounts on his Baron. On that airplane, the mounts are all on the bottom, so the engine continued to sit on the totally-cracked-through castings.)
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Seriously now, the biggest problem with this engine is that it used a cooling fan, and I dont' mean the big one up front! (The prop is a fan to keep the pilot cool-- if you don't believe me, turn it off in flight and see how much he sweats)
Here's a photo. See the flange where the prop mounts?
Now see the fan at the other end? WTF?
What were these guys thinking, were they taking a page out of the BMW 801 playbook?
Hmm. . . something a little familiar about that fan. . . did these guys all study from the same engineering texts or what?
