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If a subject continues to expose new information or concepts that could be
educational to others on the list, it seems good to keep it going. John
and
I shouldn't be having all the fun, though.
When knowledgable sources of different opinions debate as to whether a cup
(8 oz.) is half empty or half full, there remains the single reality of 4
oz. present. Positive or negative perspective in a survival situation can
make a life and death difference, so perspective IS important.
When knowledgable sources of different opinions debate as to whether the
cup
is 3/4 full or 3/4 empty, it is necessary to learn whether each position
is
25% off the single reality or one is the whole 50% "off the mark". Half
of
being smart is knowing what you're DUMB at!
Objective debate is good. Copper wire was invented when two lawyers
argued
over a penny, and I see no losers here. Participants and observers all
learn, and that's why we subscribe to this list. This time there's a
bonus.
If you're patient, I'm going to publicly eat some well-deserved crow.
Overall, John and I ARE in substantial agreement. Where we aren't, most
is
presumptive differences. His "...is that we're going to stay legal and
respect the redline". (That's the only possible professional position.)
For me, the FAA is part of Uncle Sam. He's our uncle...not our dad! So I
can (and do) exceed the posted speed limit on occasion, survive, and sleep
well at night. That doesn't mean I recommend everyone do this. In the
mirror I don't see Captain Kirk. I'll watch HIM go where no man has gone
before. Me, I'll tiptoe out on "unapproved" ice only when data heavier
than
me satisfies me it's acceptably safe to do so.
> In a message dated 2/14/03 4:44:09 PM Eastern Standard Time,
> [EMAIL PROTECTED] writes:
>
>> The
>> Continental power curve for the C-90/O-200 mechanicals of the STC
engine
>> show it putting out 85 hp at 2395 (or so) rpm. When it reaches 2575
rpm, I
>> see around 97 hp. If 85 hp will maintain that rpm and speed, then 97
hp
>> will allow that engine to rev past peak cam power output to whatever
rpm
>> available power can maintain (but not increase further).
>>
>on 2/15/03 11:00 AM, [EMAIL PROTECTED] at [EMAIL PROTECTED] wrote:
>
> I'm not sure where these numbers come from. Two things come to mind,
though.
> First, at 2575 an O200 is rated about 80 hp...
>
which is understandable, given a cam designed for sustained operation at
100
hp and a prop of size and pitch for the prop load and hp to meet at
approximately 2750 rpm and 100 hp. My figure was (misread) from the C-90
S.L. performance curve p. 29, Continental Operator's Manual X30012 ('80),
so
hp should have been 94. DUMB...
>
> ...and secondly, the whole packckage has to be taken into consideration,
including especially the carburetor and prop. The C85 carb is sized for
the
smaller displacement, and 2575 rpm.
>
Ouch! John, you're 100% right...I goofed in forgetting an important
factor.
>>
>> The STC engine has a C-85 cam with peak power and torque
characteristics
>> optimized for 2575 rpm. The C-90 has a cam with peak power and torque
>> characteristics optimized for its maximum continuous hp of 90 at only
2475
>> rpm. So the STC engine should be capable of producing more power than
even
>> the C90 curve shows from 2475 rpm up!
My carburetor venturi goof (above) made the last sentence above wrong.
The
rest remains consistent with Continental's C-90 data.
>>
>> I also don't think you're "legal" at 2575 rpm.
>
> According to the paperwork, you are. Nothing else matters :~)
>
I defer to the expert that has (seen) the paperwork as to what's in it!
>>
>> The moment you allow this powerplant/prop combination to exceed 2395
rpm,
your C-85 produces more than rated hp
>
> Not necessarily. RPM alone does not determine power. Manifold pressure
has
> to be considered. Again, in a fixed pitch world, it's hard to quanitfy.
As
> preveiously alluded to, the C85 produces 85 hp at 2575 rpm and about
28.92"
> MAP To produce 85 or more HP at lower RPM you'd need more MAP. That
ain't
> gonna happen unless you have ram air or a turbo, or something like that.
You
> do, however, have more compression and displacement with the modified
engine,
> so you can produce some more power, or the same power at lower rpm.
Exactly
> how much is not obvious, but the C90 information is more applicable than
the
> O200. The C90 makes about 93 hp at 2575. There is no reason to think
the
> C85 can make any more than that. Remember, we're already on the back
side of
> the MAP curve.
>
If "...more compression and displacement with the modified engine...
produce... more power, or the same power at lower rpm..., (and) the C90
information is... applicable...", you're over 85 hp in any scenario
likely.
>>
>>- the FAA regards that as a no-no.
>
> Don't ask, don't tell. Actually, I recall the requirement is "within
10% of
> rated power". 85 + 8.5 is 93.5, so we're still good to go.
>
GREAT!!! Could I have the authoritative reference?
>
>(and the) C90 makes about 93 hp at 2575."
>
94 hp, 93.5 hp, 93 hp...close enough for government work.
>>
>> C-85 power and rpm limitations are as unreasonable and arbitrary today
as
>> the ones for the C-75 were in yesteryear. We already know mechanicals
with
>> longer stroke (and higher stress) of substantially identical material
and
>> production process are FAA APPROVED for sustained 2750 rpm (O-200).
Static
>> limits merely give the FAA a measurable parameter of
(in)efficiency...to
>> make sure that new Cessna 172 with 160 hp (you earlier used as an
example)
>> can't go as fast as a 172 SP...different redline and prop AS APPROVED.
>
> Actually, static RPM limits are performance evaluators, not operating
> limitations. Checking the static RPM should be part of your regular
> condition evaluation process. An aircraft that cannot meet the lower
limit
> either has too much prop, and won't be able to meet takeoff performance
> charts, or has a weak engine. An aircraft that exceeds the upper limit
> probably has too little prop pitch and will be difficult to keep below
> redline in cruise. Obviously the first condition is more problematic
than
> the second.
You're right-as applicable to the coupe, this seems more important than
the
(un)likelihood that an aircraft would be (successfully) ground checked by
the FAA for compliance. I'll plead lack of oxygen up on my soap box :~).
> Oh, yeah, pilot limited static rpm is a meaningless. The
> aircraft must meet the static RPM limits in the TCDS at full throttle
or,
> technically, it is unairworthy (and practically it will not perform as
> expected). Remember this the next time you are inspecting veins in tree
> leaves from above or run short of fuel 1/2 hour before you expect to...
>
but "According to the paperwork, you are (legal). Nothing else matters"
!!!
>>
>> Once again, the pilot with the STC engine has choices. He can exceed
the
>> "paper" (and unrealistic) C-85 redline (with complete mechanical
safety) as
>> far toward the O-200's maximum APPROVED sustained rpm of 2750
>
> Not if he retains the prop and carb from the C85. There is no prop that
> meets the static limits that'll spin that fast anywhere other than a
dive.
> Regardless, he's still limited legally by the redline. Anything else
voids
> your insurance policy.
>
We each assumed "existing" carb and prop. There's yet another constraint.
The STC engine can't rev like the C-90 and O-200 because they have higher
valve spring pressures that delay valve float as rpm increases. So yes, I
now see why it's unlikely this STC C-85/prop could exceed the 2575
redline.
An insuror would clearly have the burden of proof to void prior coverage
on
an (approved) STC installation when a static rpm increase results (but
policy terms and conditions vary a lot).
Regards,
William R. Bayne
<____|(o)|____>
(copyright 2002)
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