Today's Message Index:
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1. 04:06 PM - Re: Two Questions (n4zd@juno.com)
2. 10:38 PM - Re: Two Questions (WILLIAM KELLY)
Message 1
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| Subject: | Re: Two Questions |
--> TeamGrumman-List message posted by: "n4zd@juno.com" <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. <sheesh>
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
...
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Message 2
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| Subject: | Re: Two Questions |
--> TeamGrumman-List message posted by: "WILLIAM KELLY" <v1rotate@verizon.net>
>> 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
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