Narrowing it down... Comanche?

Douglas Paterson wrote:
: 3. Maintenance. The Pathfinder wins here, hand's down. Both planes
: utilize the Lycoming O-540, but the Pathfinder's is de-tuned to 235
: horses. The Comanche's is pushed a bit harder, running at 250 horses.
: We burn a bit less fuel, and the engine (should, in a perfect world) last
: a bit longer.
:

: Not sure I buy this--but I am NOT an expert on engines (and obviously still
: learning airplanes). My thought is, the engine is "pushed" however far the
: operator pushes it--if a Comanche 250 is only run at 94% of power (max) and
: cruise at 70.5%, wouldn't that be the equivalent "pushing" and burn the same
: gas as running the Pathfinder at 100% and 75%? Not that I'm suggesting that
: technique would be used, just that it seems like it's more a case of having
: more "available" power than a case of "pushing." Unless 235 is the max that
: engine "should" be used for?

The "detuning" of the PA28-235 Jay mentions is in the compression ratio. The
PA24-250 runs at 8.5:1, vs. 7.0:1 for the 235. That alone makes for hotter cylinders
and higher octane requirements. I don't know if autogas is in your decision-making
process, but the PA24 is definately out for that.

All that said, what you say is correct from my way of thinking. Just because
you have the horses doesn't mean you need to use them all the time. If you run a -250
at 55% rather than a -180 at 75%, it'll definately be happier for it. You don't even
lose a whole lot of speed and you often gain quite a few percentage points in fuel
economy.

: Excellent point. Is there any commonality between Comanche and other, more
: current Piper products? As for knowledge-base for working on them, is the
: Comanche so different as to erase Cherokee experience??

Tire size and the overhead crank for the elevator trim is about all I can
think of that might be common between the two. They're completely different
airframes.

: Agreed (and, of course, apparently any Comanche I get will likely have 90
: gal tanks anyway).

: I've asked on the Comanche boards, but I'll repeat it he anyone have
: climbout figures for the Comanche (or other models for comparison) at
: 10,000' DA (a common DA in the summer here, I'm told)?

That issue right there limits your decision more than most of the other things
you mentioned. At least the Hershey-bar PA-28s tend to blow goats at high DA. The
taper-wings are allegedly a bet better. If you're not willing to sacrifice
significant load or runway flexibility, the PA-24-180 is definately out, as would be
any PA-28 less than 235 that isn't turbocharged. I seem to recall climb rate in a
friend's PA24-250 that was mid-range loaded (40 gallons on-board, 2-people, and 50 lbs
baggage) was about 400fpm at 12k. Only one datapoint I know, but a *takeoff* at such
DA's would burn up a helluvalotta runway loaded.

: However, this is the heart of the matter: bang-for-the-buck. So long as
: I'm not shelling out a lot of bucks on bang I don't need/want/use, I want to
: maximize that (duh!). Look at it this way: from what I've read (and your
: discussion), I can do everything in a 260C you can do in your 235, for about
: the same operating cost--or, I can push it up and use those extra 25 horses
: when called for (and pay for the privelege). Do I have that about right?

... so long as you're willing to do a lot of the work on the PA24, you may
have comparible operating costs. The annuals are a fair bit more involved on them, as
are some of the recurring AD's

-Cory



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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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