Cherokee 180 prop RPM

I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
the standard cruise prop for a PA28-180.

The POH indicates that 2700 RPM should only be able to be achieved
through 7000ft DA.

I am able to hit redline (2700 RPM) in level flight up to 11500 feet
density altitude. POH indicates that it should achieve about 2550.

It has operated this way as long as I can remember (several years) so
it is not a new phenomena.

So what could cause this? Prop pitch, poorly calibrated tach? Any
others? My plane has all of the K2U speed mods, so the reduced drag
probably plays a role.

I am able to achieve close to 150mph true airspeed at max cruise,
while the POH indicates 140mph for book. This makes me think the prop
RPM indications might be accurate.

Appreciate your thoughts.

Thanks,
Nathan

3 things to check. First, the on-ground static wide open runup rpm given by
the manufacture (and most before takeoff checklists) and done at every
annual should confirm correct pitch of the prop/ or condition of the engine
if not enough rpm is achieved. Secondly, when this static runup is done,
check the prop rpm with a prop tach to confirm that your engine tach is
giving you correct information. Just about any model airplane shop or
supplier can sell you or your mechanic one of these and they are fairly
accurate. More accurate than most 20 year old mechanical engine tachometers
for as low as $25 and can be done from the pilot's seat facing into the sun.
Thirdly, check the actual blade length and pitch per the TCD sheet for the
prop and aircraft using a prop protractor. All things to make you say,
"Hmmm".
"Nathan Young" wrote in message
...
I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
the standard cruise prop for a PA28-180.

The POH indicates that 2700 RPM should only be able to be achieved
through 7000ft DA.

I am able to hit redline (2700 RPM) in level flight up to 11500 feet
density altitude. POH indicates that it should achieve about 2550.

It has operated this way as long as I can remember (several years) so
it is not a new phenomena.

So what could cause this? Prop pitch, poorly calibrated tach? Any
others? My plane has all of the K2U speed mods, so the reduced drag
probably plays a role.

I am able to achieve close to 150mph true airspeed at max cruise,
while the POH indicates 140mph for book. This makes me think the prop
RPM indications might be accurate.

Appreciate your thoughts.

Thanks,
Nathan

In my case a low static RPM was caused by the mechanical tach reading about
60 RPM too low at most power settings. A simple in-cockpit check with a $40
hand-held optical tach revealed the amount of error.

--
Best Regards,
Mike
http://photoshow.comcast.net/mikenoel
"Nathan Young" wrote in message
...
I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
the standard cruise prop for a PA28-180.

The POH indicates that 2700 RPM should only be able to be achieved
through 7000ft DA.

I am able to hit redline (2700 RPM) in level flight up to 11500 feet
density altitude. POH indicates that it should achieve about 2550.

It has operated this way as long as I can remember (several years) so
it is not a new phenomena.

So what could cause this? Prop pitch, poorly calibrated tach? Any
others? My plane has all of the K2U speed mods, so the reduced drag
probably plays a role.

I am able to achieve close to 150mph true airspeed at max cruise,
while the POH indicates 140mph for book. This makes me think the prop
RPM indications might be accurate.

Appreciate your thoughts.

Thanks,
Nathan

If I were you, I wouldn't be complaining too much... Those are better
numbers than I'm able to muster (but I don't have too many speed mods either). The
2700 RPM only at or above 7000' DA is pretty much what I get (my POH doesn't actually
say that, though).

Nathan Young wrote:
: I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
: the standard cruise prop for a PA28-180.

The TCDS on at -180 require *exactly* 76" prop... cannot be smaller due to
vibration problems. If it's been trimmed at "overhaul," you could be slipping more
and spinning higher because of it.

: The POH indicates that 2700 RPM should only be able to be achieved
: through 7000ft DA.

Like I said... probably about what I get, but above 7000' DA, you can barely
make 75% anyway. Pretty thin operating envelope.

: I am able to hit redline (2700 RPM) in level flight up to 11500 feet
: density altitude. POH indicates that it should achieve about 2550.

Things get kinda wonky up high like that. Just from my observations, DA
doesn't seem to be the whole story. I certainly wouldn't be relying on the maximum
RPM at a high altitude like that to be accurate. Way too many other variables to
count on it.

: It has operated this way as long as I can remember (several years) so
: it is not a new phenomena.

: So what could cause this? Prop pitch, poorly calibrated tach? Any
: others? My plane has all of the K2U speed mods, so the reduced drag
: probably plays a role.

Yeah, it would. As others have mentioned you should check the static runup
and tach calibration.

: I am able to achieve close to 150mph true airspeed at max cruise,
: while the POH indicates 140mph for book. This makes me think the prop
: RPM indications might be accurate.

I would think that all of your speed mods might buy you 5 kts over book, but
it sure sounds like your prop is under-pitched. If you make higher than TCDS static
runup, it would also imply that. The only other good way I can think of to check is
to see your fuel burn. I was able to detect a 50rpm low indication in my tach by
comparing the fuel burn numbers to the book values. After putting a strobe on it to
cal, it was verified.

: Appreciate your thoughts.

Which speed mods do you have?

-Cory

--

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

I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
the standard cruise prop for a PA28-180.

The POH indicates that 2700 RPM should only be able to be achieved
through 7000ft DA.

I am able to hit redline (2700 RPM) in level flight up to 11500 feet
density altitude. POH indicates that it should achieve about 2550.

It has operated this way as long as I can remember (several years) so
it is not a new phenomena.

So what could cause this? Prop pitch, poorly calibrated tach? Any
others? My plane has all of the K2U speed mods, so the reduced drag
probably plays a role.

I am able to achieve close to 150mph true airspeed at max cruise,
while the POH indicates 140mph for book. This makes me think the prop
RPM indications might be accurate.


You can check your tach for free with a portable computer and this program
http://www.tunelab-world.com/rpmsound.html

On Thu, 13 Apr 2006 17:00:32 +0000 (UTC),
wrote:

Which speed mods do you have?

Aileron & flap seals
stabilator seals
flap track fairings
wing root fairing
landing gear/brake assembly fairing
wingtips with landing lights

There is definitely some speed increase, which is nice. However, in
my opinion the best value(s) are the wingtip landing lights followed
by the improved pitch/roll authority with the aileron and stabilator
seals.

-Nathan

On Thu, 13 Apr 2006 19:51:47 GMT, "Mark" wrote:

I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
the standard cruise prop for a PA28-180.

The POH indicates that 2700 RPM should only be able to be achieved
through 7000ft DA.

I am able to hit redline (2700 RPM) in level flight up to 11500 feet
density altitude. POH indicates that it should achieve about 2550.

It has operated this way as long as I can remember (several years) so
it is not a new phenomena.

So what could cause this? Prop pitch, poorly calibrated tach? Any
others? My plane has all of the K2U speed mods, so the reduced drag
probably plays a role.

I am able to achieve close to 150mph true airspeed at max cruise,
while the POH indicates 140mph for book. This makes me think the prop
RPM indications might be accurate.


You can check your tach for free with a portable computer and this program
http://www.tunelab-world.com/rpmsound.html

Cool thanks. I run a tablet PC in the plane, so that is an an easy
one to try.

-Nathan

: Aileron & flap seals
My duct-tape experience indicates that flap seals yield +1-2mph. Aileron no speed,
but slightly increased roll response.

: stabilator seals
Don't know about those

: flap track fairings
Or those

: wing root fairing
Seems like they might help

: landing gear/brake assembly fairing
Allegedly provide big benefit... +5mph or so. We're working on getting a field
approval for our PA-28-180 to use Warrior fairings.

: wingtips with landing lights

: There is definitely some speed increase, which is nice. However, in
: my opinion the best value(s) are the wingtip landing lights followed
: by the improved pitch/roll authority with the aileron and stabilator
: seals.

Not that you even *asked* for another opinion, but I have been amazed at the
different the AMR&D VG's make on slow-speed response. Dropped power-on stall by 15mph
lightly loaded (60mph down to 45mph IAS dirty). Power-off stall by 5-10mph depending
on load. Climb increased, and significantly decreased power-off glide decent rate.
Had to re-learn how to land. Imperceptible cruise speed change. Slight increase in
cross-wind landing liability due to the wings flying more/slower, but the same control
surfaces.

-Cory


--

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

On Fri, 14 Apr 2006 13:06:55 +0000 (UTC),
wrote:

: landing gear/brake assembly fairing
Allegedly provide big benefit... +5mph or so. We're working on getting a field
approval for our PA-28-180 to use Warrior fairings.

This is true.

I take the fairings and wheel pants off occasionally to clean up the
brake fluid/dust (that gets everywhere) and to check on the status of
the brakes.

If I fly without the wheelpants, I notice a few mph difference, and
the plane floats less on landing.

-Nathan

If your tach is accurate, my thought is does it ever go over redline?






Nathan Young wrote:
I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
the standard cruise prop for a PA28-180.

The POH indicates that 2700 RPM should only be able to be achieved
through 7000ft DA.

I am able to hit redline (2700 RPM) in level flight up to 11500 feet
density altitude. POH indicates that it should achieve about 2550.

It has operated this way as long as I can remember (several years) so
it is not a new phenomena.

So what could cause this? Prop pitch, poorly calibrated tach? Any
others? My plane has all of the K2U speed mods, so the reduced drag
probably plays a role.

I am able to achieve close to 150mph true airspeed at max cruise,
while the POH indicates 140mph for book. This makes me think the prop
RPM indications might be accurate.

Appreciate your thoughts.

Thanks,
Nathan