Prop performance in clouds question

On Mar 4, 10:33 am, Bertie the Bunyip wrote:
" wrote in news:77bb7a2a-6285-4bb2-
:



On Mar 4, 10:03 am, " wrote:
On Mar 4, 8:58 am, " wrote:

The marginal reduction in BHP performance is offset by the marginal
increased TAS, n'est pas?

Dan

Do I understand you to be saying TAS would increase after entering
IMC???

Allen

If the air density has decreased due to increased humidity (clouds),
there will be offset between to reduction in BHP efficiency and the
increased TAS (due to reduced profile drag)....

Maybe, but the water on your wings is going to cost you quite a lot.

Bertie

Not every cloud will produce water on the wings, though?

If it does, that's right -- there's an additional drag due to liquid
water coursing over the airframe.

If not, then ...?

" wrote in
:

On Mar 4, 10:33 am, Bertie the Bunyip wrote:
" wrote in
news:77bb7a2a-6285-4bb2-
:



On Mar 4, 10:03 am, " wrote:
On Mar 4, 8:58 am, " wrote:

The marginal reduction in BHP performance is offset by the
marginal increased TAS, n'est pas?

Dan

Do I understand you to be saying TAS would increase after entering
IMC???

Allen

If the air density has decreased due to increased humidity
(clouds), there will be offset between to reduction in BHP
efficiency and the increased TAS (due to reduced profile drag)....

Maybe, but the water on your wings is going to cost you quite a lot.

Bertie

Not every cloud will produce water on the wings, though?

True.

If it does, that's right -- there's an additional drag due to liquid
water coursing over the airframe.

If not, then ...?

Dunno. I remember flying in actual rain and losing quite a lot of
performance in things like Navajos. Most noticable difference is the
fuel consumption. I don't think any performance loss will be significant
unless there's water running over the airframe, though. Just thought i'd
interject that bit about the water


Bertie

On Mar 4, 11:36 am, Bertie the Bunyip wrote:

If it does, that's right -- there's an additional drag due to liquid
water coursing over the airframe.

If not, then ...?

Dunno. I remember flying in actual rain and losing quite a lot of
performance in things like Navajos. Most noticable difference is the
fuel consumption. I don't think any performance loss will be significant
unless there's water running over the airframe, though. Just thought i'd
interject that bit about the water

Bertie


I suppose the reduction in BHP performance would be due to water
ingestion, reducing the combustible mixture?

IIRC, some high performance engines used water injection to boost HP.

Dan

" wrote in news:2069ba74-10bc-4280-
:

On Mar 4, 11:36 am, Bertie the Bunyip wrote:

If it does, that's right -- there's an additional drag due to liquid
water coursing over the airframe.

If not, then ...?

Dunno. I remember flying in actual rain and losing quite a lot of
performance in things like Navajos. Most noticable difference is the
fuel consumption. I don't think any performance loss will be significant
unless there's water running over the airframe, though. Just thought i'd
interject that bit about the water

Bertie


I suppose the reduction in BHP performance would be due to water
ingestion, reducing the combustible mixture?

IIRC, some high performance engines used water injection to boost HP.

I've flown one jet that does tht, but I was talking about reducion in
performance overall. It's to do with drag from the water on the aiframe.

Bertie

On Mar 4, 12:27 pm, Bertie the Bunyip wrote:

I suppose the reduction in BHP performance would be due to water
ingestion, reducing the combustible mixture?

IIRC, some high performance engines used water injection to boost HP.

I've flown one jet that does tht, but I was talking about reducion in
performance overall. It's to do with drag from the water on the aiframe.

Bertie

So I suppose we can assume a marginal decrease in BHP due to reduced
engine efficiency and a marginal increase in TAS due to decreased air
density in clouds that don't cause water to stream along the airframe.

Ok..whew.

On Mar 2, 6:37*pm, "Kyle Boatright" wrote:
I suspect the moisture in the air made your engine deliver less power,
therefore fewer RPM...

I have a very hard time believing the RPM changed. That would be
pretty dramatic. I would guess that the difference is the camera
opening to allow more light in in the reduced light environment of the
inner cloud.

-Robert, CFII (who knows little about photography)

On Mar 4, 2:31 pm, "Robert M. Gary" wrote:
On Mar 2, 6:37 pm, "Kyle Boatright" wrote:

I suspect the moisture in the air made your engine deliver less power,
therefore fewer RPM...

I have a very hard time believing the RPM changed. That would be
pretty dramatic. I would guess that the difference is the camera
opening to allow more light in in the reduced light environment of the
inner cloud.

-Robert, CFII (who knows little about photography)

If there were actually an RPM change that was visible every time we
passed through clouds, we'd certainly have to address that in
instrument training.

I've never seen such an indication in either a constant speed, fixed
pitch, or controllable pitch (ie, electric prop).

Your theory sounds like the most plausible explanation for the OPs
observation.



Dan

On Mar 4, 3:49*pm, " wrote:

If there were actually an RPM change that was visible every time we
passed through clouds, we'd certainly have to address that in
instrument training.

I've never seen such an indication in either a constant speed, fixed
pitch, or controllable pitch (ie, electric prop).

I think that's the problem, it's not visible on the analogue gauges,
nor in sound level, only digitally.

It does make more sense to me, now that I have posted the density
content of a cloud, showing less O2, that it is possible (I don't know
for sure) that the engine output **could be** reduced from less oxygen
being available.

The meteorologist figured based on the strobing, and 30 frames per
second on the camera, and 2300 prop rpm, that while in the cloud, the
rpms dropped by about 24 rpms in the cloud.

So, just maybe we do need to lean **a touch** more while IMC????

24 RPM isn't much and like I have been saying, while in flight, never
saw any changes in the gauges, no change in sound, air was smooth so
no change in pitch, but is our antiquated equipment sensitive enough
to detect a 24 rpm change?

I'm not so sure we would notice it without digital equipment.

When I get my plane out of the shop in about a month, I plan to
explore this more.

Allen

On Mar 6, 11:01 am, " wrote:
On Mar 4, 3:49 pm, " wrote:

If there were actually an RPM change that was visible every time we
passed through clouds, we'd certainly have to address that in
instrument training.

I've never seen such an indication in either a constant speed, fixed
pitch, or controllable pitch (ie, electric prop).

I think that's the problem, it's not visible on the analogue gauges,
nor in sound level, only digitally.

It does make more sense to me, now that I have posted the density
content of a cloud, showing less O2, that it is possible (I don't know
for sure) that the engine output **could be** reduced from less oxygen
being available.

The meteorologist figured based on the strobing, and 30 frames per
second on the camera, and 2300 prop rpm, that while in the cloud, the
rpms dropped by about 24 rpms in the cloud.

So, just maybe we do need to lean **a touch** more while IMC????

24 RPM isn't much and like I have been saying, while in flight, never
saw any changes in the gauges, no change in sound, air was smooth so
no change in pitch, but is our antiquated equipment sensitive enough
to detect a 24 rpm change?

I'm not so sure we would notice it without digital equipment.

When I get my plane out of the shop in about a month, I plan to
explore this more.

Allen

The A36 has a digital RPM readout --in and out of the clouds today --
no change in MP or RPM.

Dan