O-360 takeoff power fuel flow question

argon39 wrote:
: In fact, the presenting problem is that I have not been solidly below
: 400?F. The hottest peak CHT just after takeoff on a standard day would
: be more like 430?F, and the coolest about 40?F. On really hot days I
: have seen even higher values, albeit for only a short time. I think I
: have solved this problem at this years's annual by installing a fairing
: around the big gap between the PowerFlow exhaust pipe (much smaller
: than the standard Cessna exhaust). With the fairing installed, peak
: CHTs just after takeoff are now between 400?F and 37?F as a result
: of better airflow inside the cowling.

What type of CHT probes? If they're the spark-plug type, then you're still
pretty much fine. They tend to read 50-75 degrees hotter than the "official" locating
of the cylinder well lug type.

The other indirect reading of fuel flow will be the EGT. How much lower than
high-power cruise peak is it on full-rich takeoff? In my O-360-A3A Cherokee, I read
1600-1650 peak EGT in cruise, but 1400 on full-rich takeoff. In fact, during a long
climb I'll lean to that 1400 as I gain altitude. From what I've read, with 200-250
degrees between the two, I should be more than fine... might want to check yours

: Regarding design limits, I do appreciate that Deakin was referring to
: bigger engines. But I still wonder what a limit for the O-360 might be
: as a result of adding the tuned exhaust.

Probably not getting more than 5-10hp out of it. Although, with the
scavanging effect of a tuned exhaust, the max fuel flow could certainly require that
additional 5-10hp's worth. Making more power takes more fuel.

Of course, all that assumes the tuned exhaust actually works... ;-)

: One step at a time, let's check the prop governor and maybe the
: wide-open mixture.

... and EGT. It's the best way (short of a wideband O2 sensor, etc) to
determine the *actual* mixture of the engine on takeoff.

-Cory

--

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

Thanks, Cory

(Apologies for the delay, spent last week on jury duty.)

What type of CHT probes?

Bayonet-style, not the spark plug type.


The other indirect reading of fuel flow will be the EGT. How much lower =
than
high-power cruise peak is it on full-rich takeoff?

Less than the 200=B0 you mention. Peak EGTs while leaning are perhaps
200=B0 above climb-out EGTs, but I have been advised to run 125=B0 rich
of peak by my mechanic. At 50=B0 lean of peak the exhaust pipe has a
light grey appearance that suggests a too-lean mixture.


Probably not getting more than 5-10hp out of it. Of course, all that assu=
mes
the tuned exhaust actually works... ;-)

Well, all I can say is that I noticed the difference after installing
it. But to be fair, it wasn't a very scientific experiment because I
also installed an O-360 and a c/s prop at the same time. Those three
items conspire together to make it a real hot rod, among elderly C-172s
at least. Too bad the aerodynamics resemble that of a 1978 Volvo 240DL.

: The other indirect reading of fuel flow will be the EGT. How much lower than
: high-power cruise peak is it on full-rich takeoff?

: Less than the 200?? you mention. Peak EGTs while leaning are perhaps
: 200?? above climb-out EGTs, but I have been advised to run 125?? rich
: of peak by my mechanic. At 50?? lean of peak the exhaust pipe has a
: light grey appearance that suggests a too-lean mixture.

One universal truth in aviation seems to be that there are more untruths than
can be counted. Lots of old-wives-tales, especially regarding leaning. Reading
Deakin's articles on AvWeb should be required reading. Bottom line is that the engine
cannot be harmed with the mixture knob at 65% (or 70%) power so long as CHT doesn't
get too hot. Light grey exhaust pipe to me indicates a correct mixture where there's
not an abundance of either fuel or air, and the lead is being scavanged nicely. 125
rich is burning a lot of extra fuel, depositing lots of carbon on the pistons, valves,
and valve guides.

: Probably not getting more than 5-10hp out of it. Of course, all that assumes
: the tuned exhaust actually works... ;-)

: Well, all I can say is that I noticed the difference after installing
: it. But to be fair, it wasn't a very scientific experiment because I
: also installed an O-360 and a c/s prop at the same time. Those three
: items conspire together to make it a real hot rod, among elderly C-172s
: at least. Too bad the aerodynamics resemble that of a 1978 Volvo 240DL.

That's a whole 'nother kettle of fish. The CS will let you actually *make*
rated HP at sea level. Putting a CS prop on a fixed-gear bird will not get you any
appreciable speed. It might give you a bit better economy if you can run it
over-squared. The only thing it buys you is takeoff/climb performance, and unlikely
to have increased your legal gross weight any.

-Cory

--

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

Putting a CS prop on a fixed-gear bird will not get you any
appreciable speed.

The only thing it buys you is takeoff/climb performance, and unlikely
to have increased your legal gross weight any.

I never said that the prop did either of these things. What did change
things was putting a 180hp O-360 in the place of a 150hp O-320. The
extra 19hp at 65% power does in fact make it go faster. And the new
legal gross weight per the STC is now 2500.

argon39 wrote:

: Putting a CS prop on a fixed-gear bird will not get you any
: appreciable speed.

: The only thing it buys you is takeoff/climb performance, and unlikely
: to have increased your legal gross weight any.

: I never said that the prop did either of these things. What did change
: things was putting a 180hp O-360 in the place of a 150hp O-320. The
: extra 19hp at 65% power does in fact make it go faster. And the new
: legal gross weight per the STC is now 2500.

I wasn't disparaging your decision, just making a point. Lots of people bolt bigger engines on thinking that
it will make a plane go a lot faster. Actually, it's more or less the cube root of the ratio of horsepower.

My plane originally had a 150hp O-320, but it's been upgraded to a 180 O-360. I find that it helps with
load/climb/takeoff, but primarily it lets me cruise at the same speed at a lower percentage power and be kinder to the
engine and burn the same fuel. For me, the 2 gph difference between 60% and 75% and it's 5 kt difference in speed
isn't really worth the fuel burn.

Cool that you got a gross weight increase. Mine notsomuch.

-Cory

--

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

On 1 Aug 2005 15:48:13 -0700, "argon39" wrote:


Putting a CS prop on a fixed-gear bird will not get you any
appreciable speed.

The only thing it buys you is takeoff/climb performance, and unlikely
to have increased your legal gross weight any.

I never said that the prop did either of these things. What did change
things was putting a 180hp O-360 in the place of a 150hp O-320. The
extra 19hp at 65% power does in fact make it go faster. And the new
legal gross weight per the STC is now 2500.


I fly a CAP C172P that has also been upgraded with the O-360 180HP
engine. But ours stuck with a fixed-pitch prop. On our 172, it
brought our gross up to 2550. I wonder why the difference???


Chuck
PA28-180

Chuck wrote:

I fly a CAP C172P that has also been upgraded with the O-360 180HP
engine. But ours stuck with a fixed-pitch prop. On our 172, it
brought our gross up to 2550. I wonder why the difference???

Chuck

In this conversion, the prop and prop governor are a bit heavier than a
fixed-pitch prop, so that extra weight may account for part of the
difference.

A second potential factor is that in this conversion (STC by Del-Air of
Porterville CA), the STC holder wanted to have full use of flaps (40
degrees) instead of the 30 degree restriction characteristic of other
conversions. My understanding is that FAA certification required that
the aircraft be able to climb at gross weight with full flaps deployed.
Those extra 50 pounds may have been significant in meeting that
specification.

The aircraft used for certification flight was loaded up with fuel and
sandbags and did indeed climb with full flaps on a hot day at
Porterville (442 MSL) to the satisfaction of the FAA inspector.

You have a later model. My F model does not get a GW increase. I tried
to to find anyone with data to support a GW increase on pre 68 models.

Regards, Ross
C-172F 180HP
KSWI


argon39 wrote:
Putting a CS prop on a fixed-gear bird will not get you any
appreciable speed.


The only thing it buys you is takeoff/climb performance, and unlikely
to have increased your legal gross weight any.


I never said that the prop did either of these things. What did change
things was putting a 180hp O-360 in the place of a 150hp O-320. The
extra 19hp at 65% power does in fact make it go faster. And the new
legal gross weight per the STC is now 2500.