I'm kind of new to CL, very new to bigger planes, so it's not obvious to me why this is the best of the breed. For instance I think I've only seen one or two plans/kits that specify a .75 size engine: Paul Walker's Impact and a derivative of that: The Paladin. The largest model I've seen in person was a Strega, 60" span / 742 sq in and that big ol' plane only uses a 51-60. Are there other designs to fit this monster? What are they?
Someone please post some of the top reasons why anyone would want to spend $500 on this enormous engine.
OY! The definitive model using a PA75 is 625 square inches (David Fitzgerald's Thundergazer) and 64 ounces. The prop used (Eather 13-4.25 3-blade (flat back)) is also usable on the PA and RO-Jett 61s, and maybe the PA51 in a stretch.
You don't need a larger engine to "get more power" or to fly a larger airplanes. Almost all the engines used in stunt from a piped 40 to a piped 91 (which has been tried) put out around the same horsepower on average, and almost all of them have reasonably close to the same response in the maneuvers in terms of HP increase.
Why you might want a PA75 is that the ease of getting the kind of response required to fly almost any airplane. It is easier to get the right response and more reliable than most (almost all) of those engines that went before it. Sure, you *could* get an absolutely astonishing amount of power out of it, but a 625 square inch 64 ounce airplane needs no more power to fly around at 5.4 second laps than it did in 1980 with a ST46. What you want is *control*, and why the PA75 is better than almost all of what came before it is that you can pretty easily get exactly the response you want. David's PA75 setup uses a prop that could easily be swung by a PA51 and for sure works fine on a RO-Jett 61 (since I have run the same type of Eather 13-4.25 on mine, no problems aside from slight trim degradation).
The 75 can be set up to idle around in a constant 4-stroke all day long and provide sufficient power. This definitively solves the problem most people have with smaller engines (whether they know it is a problem or not) - excessive power change during a 4-2 break. The other alternative is to run it across the break and use compression ratio, nitro, and venturi adjustments to get an acceptably small power boost when it goes from 4 to 2. Do this on lesser engines and you tend to lose enough power than you are trading off overall power VS reduction in break. The 75 can be adjusted to the point that you gain *no* power at all at a break, and still have enough overall to fly the airplane with authority. Even with a 61, that's a much trickier proposition, you can do it, but it' a much more careful balancing act.
I don't fly the 75, so I have no stake in it at all, but that's the reason.
Getting more power or swinging bigger props hasn't been an issue for stunt planes since about 1988, they ALL have enough power in terms of raw HP, from a 36 to 91 and you don't want or need large props to get better performance. What you want is to be able to control it in all conditions, and the PA75 is about the best of the breed in those terms.
Brett
Topic: NEW ** PA 75 New run Orders will Stay open (Read 9667 times)
