Percent power altitude

Bob Noel wrote

Bob Moore wrote:
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?

:-) The wing, of course. :-)

Bob Moore

Bob Moore wrote:
Bob Noel wrote

Bob Moore wrote:
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?

:-) The wing, of course. :-)

Bob Moore

Perhaps you need to pedal faster?

(*chortle*)

Leaning and density altitude (performance altitude).



"Bob Noel" wrote in
message
...
| 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
|

Bob Noel wrote:

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?


Because 64% of whatever HP you have isn't enough to get you there/
hold you there.

I've got 300HP in an airframe designed for 185. At 65% HP I'm
doing better than they can do with WOT at sea level.

Yes, after age 60, my recall gets muddy.


"Bob Moore" wrote in message
. 122...
| 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

Jim Macklin wrote
Yes, after age 60, my recall gets muddy.

Hmmmm....at 71, I must have missed that stage. :-)

Bob

Note, I did say MY recall. I sleep like a baby now. Go to
bed, wake up every hour or two, cry and go to the bathroom.

I my defense, I'm not perfect.



"Bob Moore" wrote in message
. 122...
| Jim Macklin wrote
| Yes, after age 60, my recall gets muddy.
|
| Hmmmm....at 71, I must have missed that stage. :-)
|
| Bob
|

As a first approximation, it should be the same for any normally
aspirated engine (and yes it would be based on DENSITY altitude). The
engine develops 100% HP only at sealevel. As the altitude goes up what
changes? The density of the air decreases and in response the fuel
delivered decreases (from both the carb delivering less fuel and the
pilot leaning the mixture). This is the same for all the normally
aspirated engines.

Now at somewhere around 65-70% power it becomes impossible to get
excess EGTs and CHTs due to overleaning the engine. So run the engine
at that altitude and lean for max rpm and note the EGT. This is
guaranteed to be a safe EGT! Now use this EGT for leaning at ALL
altitudes. Thus you have found 100 or so degrees rich of peak without
ever having to run the engine at peak (which is too hot and hazardous
in itself).

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

"Doug" wrote in message
oups.com...
altitudes. Thus you have found 100 or so degrees rich of peak without
ever having to run the engine at peak (which is too hot and hazardous
in itself).

What makes you think that?

Karl
"Curator" N185KG
Gami ser# 19

Doug,

Thus you have found 100 or so degrees rich of peak without
ever having to run the engine at peak (which is too hot and hazardous
in itself).


Come again? That part in parenthesis is completely wrong.

--
Thomas Borchert (EDDH)