Engine power question???

J.Kahn wrote:

It forces you to use a certain minimum prop pitch to avoid overspeeding
it in flight.

An O-320 makes 120 hp at 2300 rpm and 26". At wide open throttle at SL
and 2250 it is probably around 130 hp. Add a couple thousand feet and
125 hp at the start of the roll sounds about right.

Any fixed pitch airplane is the same. A 150 with a stock O200 doesn't
have 100 hp available while static either, probably more like 80-85. So
all things being equal you still have 50% more power available than stock.

You know, we ALL really ought to go get another hour in a 150 every once
in a while.

When I was in high school, the 150 was IT! WoW!

But I flew one a couple of years ago and the prevelant thought was,
"What happened? This used to be FUN".




With all the old wives' tales about running constant speed engines
"oversquare" (rpm below mp) it's amusing to note that fixed pitch
aircraft are way oversquare all through their takeoff and climb phase
until they're going fast enough.

John

wrote:
It IS simple. You are not getting 100% horsepower at takeoff. You
are inventing the need for the constant speed prop. Great example
is the 180hp Tiger with a cruise prop!

Now, I want to learn something from this...

Why is it that maximum static RPM is independent of altitude?

Horsepower drops with altitude. But static RPM does not. Horsepower
is related to the cube of RPM for a fixed pitch prop IIRC. Why is it
that static RPM stays constant?

Good thing, actually, or a fixed pitch prop would be practically
useless.

Bill Hale



For a given engine, the drop in static HP with altitude corresponds to
the drop in air density (and therefore air resistance) with altitude.

Air Density affects both factors equally.

J.Kahn wrote:


With all the old wives' tales about running constant speed engines
"oversquare" (rpm below mp) it's amusing to note that fixed pitch
aircraft are way oversquare all through their takeoff and climb phase
until they're going fast enough.

John

But without that manifold pressure gauge on a fixed pitch prop, us
knuckledraggers are blissfully unaware of that fact. I did see at 152
with a MP gauge once.. nice "feature".

Dave

OK, I guess I can buy into that one, but I'm still confused a bit. If
one is limiting it (the O-320) to a given RPM that gives 100 HP out,
wouldn't that same RPM give less than 100 HP at high density altitude
just as an O-200 would?

Scott


Stuart & Kathryn Fields wrote:
Scott: It is simple. An 0320 is said to be a 150hp engine at 59 degrees,
sea level, short exhaust stacks and a certain humidity. At Rioduoso (sp?)
NM on a hot day the density altitude will make you wish that you had put an
0540 on there even if you have to limit it to 100 hp cause you ain't going
to get 100hp out of the 0320 with a Cessna Exhaust and intake system at a
high density altitude.

Stu Fields
Experimental Helo magazine
"Scott" wrote in message
.. .

So why would a guy "upgrade" to an O-320 and limit it to 100 HP? What's
the "gain" ???

Scott

Orval Fairbairn wrote:



The placarding probably relates to the STC, which "limits you to 100 hp",
for certification purposes.

It is easier to get an STC for a higher power engine if you "limit, via
placards, the max power" to that called out in the original type
certificate.

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)




--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

On Oct 10, 7:14 am, Scott wrote:
OK, I guess I can buy into that one, but I'm still confused a bit. If
one is limiting it (the O-320) to a given RPM that gives 100 HP out,
wouldn't that same RPM give less than 100 HP at high density altitude
just as an O-200 would?

Scott

They're not deliberately limiting it to 100 hp. The fixed-pitch
prop does that on any airplane. Your O-320 will make any O-200 look
sick. You need to fly a 150 with the O-200, and you won't complain
anymore. A 150 with the O-200 on takeoff won't generate anywhere near
100 hp. In fact, I have my suspicions that it never did, even at 2750
RPM. We had those engines in a couple of 150s, and I flew an Aircoupe
with a C-90, 10 less hp than the O-200, and it took off much shorter,
climbed and cruised much faster than the 150. It generated that 90 hp
at a lower RPM, which means that less hp was lost to drag. The
airplane weighed only 150 lb less than the 150.
A guy in the US did some testing on a 150. He did a static
thrust test, full RPM with the airplane pulling on a hefty spring
scale. Got around 230 lb, IIRC. Then he took that O-200 out and put in
a 100 hp Subaru conversion and did the static test again and got
almost 300 lb. That wasn't with a lower-pitched prop, either; the
airplane cruised as well as before at a similar RPM. Makes one wonder
about hp claims.

Dan

cavelamb himself wrote:
J.Kahn wrote:

It forces you to use a certain minimum prop pitch to avoid
overspeeding it in flight.

An O-320 makes 120 hp at 2300 rpm and 26". At wide open throttle at
SL and 2250 it is probably around 130 hp. Add a couple thousand feet
and 125 hp at the start of the roll sounds about right.

Any fixed pitch airplane is the same. A 150 with a stock O200 doesn't
have 100 hp available while static either, probably more like 80-85.
So all things being equal you still have 50% more power available than
stock.

You know, we ALL really ought to go get another hour in a 150 every once
in a while.

When I was in high school, the 150 was IT! WoW!

But I flew one a couple of years ago and the prevelant thought was,
"What happened? This used to be FUN".




With all the old wives' tales about running constant speed engines
"oversquare" (rpm below mp) it's amusing to note that fixed pitch
aircraft are way oversquare all through their takeoff and climb phase
until they're going fast enough.

John

Actually, I'm starting to look for a 150 to play around with and for the
kids to learn in next spring. They fly about as well as most
airplanes, with a really good useful load for that size. The 150 does a
lot of things reasonably well and are becoming dirt cheap as the big
flight schools unload them. Where else can you get a 600 lb useful
load, electrics, really powerful fowler flaps, etc all for 20k.
Everybody else hates them, but I like the '64/65 straight tails. If
you block out the front half of the airplane in a picture, it looks like
an A-26.

Apparently aileron gap seals make the ailerons much lighter and
snappier, probably the biggest complaint in handling.

John

On Oct 10, 5:10 pm, "J.Kahn" wrote:
cavelamb himself wrote:
J.Kahn wrote:

It forces you to use a certain minimum prop pitch to avoid
overspeeding it in flight.

An O-320 makes 120 hp at 2300 rpm and 26". At wide open throttle at
SL and 2250 it is probably around 130 hp. Add a couple thousand feet
and 125 hp at the start of the roll sounds about right.

Any fixed pitch airplane is the same. A 150 with a stock O200 doesn't
have 100 hp available while static either, probably more like 80-85.
So all things being equal you still have 50% more power available than
stock.

You know, we ALL really ought to go get another hour in a 150 every once
in a while.

When I was in high school, the 150 was IT! WoW!

But I flew one a couple of years ago and the prevelant thought was,
"What happened? This used to be FUN".

With all the old wives' tales about running constant speed engines
"oversquare" (rpm below mp) it's amusing to note that fixed pitch
aircraft are way oversquare all through their takeoff and climb phase
until they're going fast enough.

John

Actually, I'm starting to look for a 150 to play around with and for the
kids to learn in next spring. They fly about as well as most
airplanes, with a really good useful load for that size. The 150 does a
lot of things reasonably well and are becoming dirt cheap as the big
flight schools unload them. Where else can you get a 600 lb useful
load, electrics, really powerful fowler flaps, etc all for 20k.
Everybody else hates them, but I like the '64/65 straight tails. If
you block out the front half of the airplane in a picture, it looks like
an A-26.

Apparently aileron gap seals make the ailerons much lighter and
snappier, probably the biggest complaint in handling.

John

We're at 3000' ASL here. We found the 150 to be underpowered
and really tight inside, and the O-200 would usually give top end
problems by mid-life. There were days in the summer (30°C/85°F, 5000'
DA) when the dumb thing would climb at under 200 FPM and take all day
to reach circuit altitude. They might be OK near sea level.
The older straight tails, or at least the ones without the
back window, were lighter and faster. Not many of them around now. The
150's flaps are awesome, and the rudder has enough authority to deal
with strong crosswinds, better than the 172. And it'll spin readily,
something the 172 is really reluctant to do.

Dan

wrote in message
ups.com...
On Oct 10, 7:14 am, Scott wrote:
OK, I guess I can buy into that one, but I'm still confused a bit. If
one is limiting it (the O-320) to a given RPM that gives 100 HP out,
wouldn't that same RPM give less than 100 HP at high density altitude
just as an O-200 would?

Scott

They're not deliberately limiting it to 100 hp. The fixed-pitch
prop does that on any airplane. Your O-320 will make any O-200 look
sick. You need to fly a 150 with the O-200, and you won't complain
anymore. A 150 with the O-200 on takeoff won't generate anywhere near
100 hp. In fact, I have my suspicions that it never did, even at 2750
RPM. We had those engines in a couple of 150s, and I flew an Aircoupe
with a C-90, 10 less hp than the O-200, and it took off much shorter,
climbed and cruised much faster than the 150. It generated that 90 hp
at a lower RPM, which means that less hp was lost to drag. The
airplane weighed only 150 lb less than the 150.
A guy in the US did some testing on a 150. He did a static
thrust test, full RPM with the airplane pulling on a hefty spring
scale. Got around 230 lb, IIRC. Then he took that O-200 out and put in
a 100 hp Subaru conversion and did the static test again and got
almost 300 lb. That wasn't with a lower-pitched prop, either; the
airplane cruised as well as before at a similar RPM. Makes one wonder
about hp claims.

Dan

Don't confuse thrust with HP unless you're using the exact same prop and
prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust
because of gearing, disc area, etc? But, that thrust is only effective in a
narrow (vertical) speed range. The same engine, combined with an RV-style
cruise prop, would only generate (WAG coming) 250 lbs of static thrust.

HP claims on certified engines were +/- 5% back in the day when most "100
hp" 0-200's were built, meaning that a "bad" engine generated 95 HP when it
was built.

KB

wrote:
On Oct 10, 5:10 pm, "J.Kahn" wrote:

cavelamb himself wrote:

J.Kahn wrote:

It forces you to use a certain minimum prop pitch to avoid
overspeeding it in flight.

An O-320 makes 120 hp at 2300 rpm and 26". At wide open throttle at
SL and 2250 it is probably around 130 hp. Add a couple thousand feet
and 125 hp at the start of the roll sounds about right.

Any fixed pitch airplane is the same. A 150 with a stock O200 doesn't
have 100 hp available while static either, probably more like 80-85.
So all things being equal you still have 50% more power available than
stock.

You know, we ALL really ought to go get another hour in a 150 every once
in a while.

When I was in high school, the 150 was IT! WoW!

But I flew one a couple of years ago and the prevelant thought was,
"What happened? This used to be FUN".

With all the old wives' tales about running constant speed engines
"oversquare" (rpm below mp) it's amusing to note that fixed pitch
aircraft are way oversquare all through their takeoff and climb phase
until they're going fast enough.

John

Actually, I'm starting to look for a 150 to play around with and for the
kids to learn in next spring. They fly about as well as most
airplanes, with a really good useful load for that size. The 150 does a
lot of things reasonably well and are becoming dirt cheap as the big
flight schools unload them. Where else can you get a 600 lb useful
load, electrics, really powerful fowler flaps, etc all for 20k.
Everybody else hates them, but I like the '64/65 straight tails. If
you block out the front half of the airplane in a picture, it looks like
an A-26.

Apparently aileron gap seals make the ailerons much lighter and
snappier, probably the biggest complaint in handling.

John


We're at 3000' ASL here. We found the 150 to be underpowered
and really tight inside, and the O-200 would usually give top end
problems by mid-life. There were days in the summer (30°C/85°F, 5000'
DA) when the dumb thing would climb at under 200 FPM and take all day
to reach circuit altitude. They might be OK near sea level.
The older straight tails, or at least the ones without the
back window, were lighter and faster. Not many of them around now. The
150's flaps are awesome, and the rudder has enough authority to deal
with strong crosswinds, better than the 172. And it'll spin readily,
something the 172 is really reluctant to do.

Dan


Well, that's all right, I guess.
But it's sure no 65 HP Taylorcraft.
(Which gets off shorter, climbs better and is (no ****) faster!)

Richard

On Oct 10, 9:17 pm, "Kyle Boatright" wrote:


Don't confuse thrust with HP unless you're using the exact same prop and
prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust
because of gearing, disc area, etc? But, that thrust is only effective in a
narrow (vertical) speed range. The same engine, combined with an RV-style
cruise prop, would only generate (WAG coming) 250 lbs of static thrust.

That Soob had the same diameter of prop and ran at the
same RPM. I'm aware of the diameter/RPM/pitch effects, and that's why
the results were so startling to me. The 150s performance was much
better with the Soob, confirming its output. So either the Soob
produced more power than claimed, or the O-200 was really sick. Yet
the guy said that the O-200 was OK and the 150's performance with it
was typical.

Dan