---------------------------------------------------------- TeamGrumman-List Digest Archive --- Total Messages Posted Sun 12/19/04: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:06 PM - Re: Two Questions (n4zd@juno.com) 2. 10:38 PM - Re: Two Questions (WILLIAM KELLY) ________________________________ Message 1 _____________________________________ Time: 04:06:48 PM PST US From: "n4zd@juno.com" Subject: Re: TeamGrumman-List: Two Questions --> TeamGrumman-List message posted by: "n4zd@juno.com" > ---------- There is an AA1C here at Fox with an O320. > It's not that fast. The AA-1C was never meant to be fast. Blame the fat, flat-bottom wing airfoil and poor choice of prop (fixed) pitch as used with both low and higher hp engines. > A good Traveler with HC piston will out run it. A real Yankee with the small O-235 will outrun any Traveler; again blame the wing airfoil. Downside is the fat & flat wings all =climb= more rapidly than the real Yankee, ya takes yer choice but ya never gets it all. We =can= have it all with a variable pitch propeller, but no one has gotten Approval for that so we do not have it on our usual list of choices. > For the money, get a Cheetah and take out the back seats. No, save the extra purchase money to buy less gas more often for a =real= Yankee. > ... if a plenum for engine cooling is so efficient, why don't > manufacturers (other than older Mooneys) use them, ... They do and did. The only question is whether the plenum is made in one "box" a la Mooney, or out of 213 pieces with rubber strips so the top cowl becomes part of the assembly. > A properly designed baffle system does not need a plenum. KISS That baffle system =IS= a plenum. Keeping It Simple Stupid would favor the Mooney's simple box over the complex (and heavier) assembly of rubber strips... and most fabricators of those rubber strips are incompetent to address that assembly --- witness the continued problems, and the fact that the Factory did not assemble it correctly either. Look for miter corners and you'll seldom see them --- the incompetent fabricators neither know how nor why to use a miter. However, I agree --- a well made baffling system ( whether simple per Mooney, Lo Firsty, and myself, or complicated using rubber strips weighing 3 pounds to avoid 12 ounces of sheet metal ) will work fine. a r t Winston-Salem, NC ... Juno Gift Certificates Give the gift of Internet access this holiday season. http://www.juno.com/give ________________________________ Message 2 _____________________________________ Time: 10:38:49 PM PST US From: "WILLIAM KELLY" Subject: Re: TeamGrumman-List: Two Questions --> TeamGrumman-List message posted by: "WILLIAM KELLY" >> There is an AA1C here at Fox with an O320. >> It's not that fast. I think the AA1C referred to is mine. The stock aerodynamics of the airplane limit the additional speed an O-320 can provide. Remember, at the high end of the speed range, the primary type of drag holding the airplane back is parasite drag (skin friction and pressure drag), as opposed to induced drag which decreases the faster you go. Opposing parasite drag is the component of power called parasite power. Since parasite power varies as the cube of velocity, it works out that I need every bit of the 35 additional horsepower my O-320 provides to have a top speed just 10 knots faster. To travel 20 knots faster, I would need about 185 hp, unless I somehow lessened the parasite drag of the airplane. AA1X owners recognize that much improved climb rate is the real benefit of the O-320, since an airplane's climb rate is related purely to the amount of excess power you have at any given weight. By installing the O-320 you have essentially doubled the excess power over the O-235, and therefore doubled your climb rate. This can be proven by working backwards through the rate of climb equation where: ROC = 33,000[(Pa-Pr)/W] So, if a stock AA1X with a 115 hp O-235 climbs at 660 fpm at 1600 lbs, then the "Pr" ends up being 83hp at normal climb speed. If we then plug this Pr value back into the equation, but use 150hp for the Pa value, the new ROC with an O-320 is now over 1300 fpm. Because of this added climb capability, I routinely cruise at 10,000 to 13,000 feet to take advantage of tailwinds and reduced fuel consumption, plus having more clearance between me and the mountains. Bill Kelly AA1C 39065 Lancaster, CA