Percent power altitude

Anyone tell me at what altitude I get 75% and 65% power respctively
(with full throttle, normally aspirated).

You don't have a POH?

On 10/21/2006 10:33 AM, Doug wrote the following:
Anyone tell me at what altitude I get 75% and 65% power respctively
(with full throttle, normally aspirated).

Mitty wrote
You don't have a POH?

You know, he might not even have an airplane. He just asked
a question and expected an answer, not a wise crack.

No POH required, answer is not aircraft specific, see:

http://www.kellyaerospace.com/articl...bocharging.pdf

Bob Moore

Possibly Cessna and Piper have not seen your chart. I have several POHs he

An Arrow PA28R-201 POH shows 75% power, full throttle, at 6,000 feet/2400 RPM
and 7,500/2700 RPM. 65% power at about 9,800/2400 and 12,000/2700. (IO-360/200
Lyc.)

A Cessna 182T (T-model, not T for turbo) POH has tables that are a little harder
to read than the Arrow's graphs, but the highest % power they show at 8,000 feet
is 74% and at 12,000 feet 64%. (IO-540/230 Lyc.)

A carburated Cherokee Six/260 shows 75% power, full throttle, at 8,300 feet and
65% power at 11,200 feet. Engine RPM is not stated. (O-540/260 Lyc.)

I also have a tiny and very complicated power chart from Lycoming for the O-540
but I am too lazy to figure it out.

I am no fluid dynamicist (and may be about to prove it), but my dim
understanding is that the Reynolds number has a major effect on fluid flow and
in its calculation there is a density term. Certainly the mixture velocities at
various points in each different intake system would be different. Velocity is
also a term in the Reynolds number calculation. So (leaping) it does not
surprise me that intake systems with different geometries would perform at least
slightly differently at different altitudes. Exhaust systems, too, I'd guess.

Possibly I should have been more diplomatic in how I suggested that the OP
needed a POH but that still seems to me to be the case.

On 10/21/2006 12:46 PM, Bob Moore wrote the following:
Mitty wrote
You don't have a POH?

You know, he might not even have an airplane. He just asked
a question and expected an answer, not a wise crack.

No POH required, answer is not aircraft specific, see:

http://www.kellyaerospace.com/articl...bocharging.pdf

Bob Moore

Doug wrote
Anyone tell me at what altitude I get 75% and 65% power respctively
(with full throttle, normally aspirated).

See the graph at:

http://www.kellyaerospace.com/articl...bocharging.pdf

Bob Moore

In article .com,
"Doug" wrote:

Anyone tell me at what altitude I get 75% and 65% power respctively
(with full throttle, normally aspirated).

Depends on the engine, depends on the OAT (density altitude).

john smith wrote
Depends on the engine, depends on the OAT (density altitude).

Not on the engine as long as it's "normally aspirated' as
specified in the OP.

Bob Moore

5 and 7 thousand
"Doug" wrote in message
oups.com...
| Anyone tell me at what altitude I get 75% and 65% power
respctively
| (with full throttle, normally aspirated).
|

Jim Macklin wrote
5 and 7 thousand

Running on (faulty) memory again, Jim?

How about 7,500' and about 12,500', ISA of course.

See my previous replies to this thread for a real chart
answer.

The formula answer is:

bhp at altitude equals bhp at sea level times the quantity
(density ratio minus the quantity(1 minus density ratio divided by 7.55))

Works out to 76% at 7,500' and 64% at 12,500', or thereabouts.


Bad information is worse than no information at all.

Bob Moore

In article ,
Bob Moore wrote:

The formula answer is:

bhp at altitude equals bhp at sea level times the quantity
(density ratio minus the quantity(1 minus density ratio divided by 7.55))

Works out to 76% at 7,500' and 64% at 12,500', or thereabouts.

OK, I'm confused. Full throttle, 64%, is 12,500' for any engine?
How come my cherokee 140 couldn't even get to 12,500'?
What am I overlooking?

--
Bob Noel
Looking for a sig the
lawyers will hate