Stupid hp to thrust question

In article , RobertR237 says...

Depends on rather you answer the question as written or read more into it.
Answering the question directly as written the answer is both would produce
exactly the same thrust. If the question however asked which was capable of
producing more thrust, the answer changes.

Ahh so he says as the bulb lights and the dawn arises ...Now I see :-)

Chuck (I'm sliding on the ice) S

In article , "Mark"
wrote:

Does a prop turning at 2300 rpm on a 150hp motor produce more thrust than a
prop spinning 2300 rpm on a 100 hp motor ?




Insufficient data!

Constant speed prop?
Manifold pressure?
Zero wind?
Same atmospheric conditions?

In article
, Orval
Fairbairn writes:


Does a prop turning at 2300 rpm on a 150hp motor produce more thrust than a
prop spinning 2300 rpm on a 100 hp motor ?




Insufficient data!

Constant speed prop?
Manifold pressure?
Zero wind?
Same atmospheric conditions?



Where do you get insufficient data? Question does not indicate a different
prop turning on the two engines. "A" prop indicates the same prop used on two
different hp engines turning at the exact same RPM with no indicated
differences. The resulting thrust will be the same.


Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)

osite (RobertR237) wrote:

Where do you get insufficient data? Question does not indicate a different
prop turning on the two engines. "A" prop indicates the same prop used on two
different hp engines turning at the exact same RPM with no indicated
differences.

No, the query was ambiguous both semantically and in its technical
context. Evidence of the query's ambiguity is right in this thread,
where reasonable people took its meaning differently. Orval was
correct, "Insufficient data."

David O -- http://www.AirplaneZone.com

Where do you get insufficient data? Question does not indicate a different
prop turning on the two engines. "A" prop indicates the same prop used on two
different hp engines turning at the exact same RPM with no indicated
differences.

No, the query was ambiguous both semantically and in its technical
context. Evidence of the query's ambiguity is right in this thread,
where reasonable people took its meaning differently. Orval was
correct, "Insufficient data."

David O --
+++++++++++++++++++++++++++++++++++++++

Where the hell is the poster of the original question?
Has he left town after all this scientific
and not so scientific commotion?

If not...
Maybe, he will rephrase his question so 'we' can
settle this once and for all and move on to solving
the rest of the world's less pressing problems. g

Barnyard BOb - with a mouse in his pocket

In article , RR Urban
writes:


Where the hell is the poster of the original question?
Has he left town after all this scientific
and not so scientific commotion?

If not...
Maybe, he will rephrase his question so 'we' can
settle this once and for all and move on to solving
the rest of the world's less pressing problems. g

Barnyard BOb - with a mouse in his pocket



What and end all this fun. ;-)


Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)

RR Urban wrote:

Where the hell is the poster of the original question?
Has he left town after all this scientific
and not so scientific commotion?

I expect that "Mark" ) is sitting back enjoying the show.
BTW, of those who attempted to answer his question, yours was the best
IMHO -- it was concise, to the point, and included reasonably
sufficient conditions (identical props, test stand).

David O -- http://www.AriplaneZone.com

[Ron throws his oar in]

On Thu, 4 Dec 2003 20:24:00 -0500, "Mark" wrote:

Does a prop turning at 2300 rpm on a 150hp motor produce more thrust than a
prop spinning 2300 rpm on a 100 hp motor ?

Assuming the engines are mounted on a ground test stand, and the propellers
are "normal" (no paddlewheels, etc.):

If the props are identical fixed pitch propellers, the same thrust is
produced. Both engines are producing the same power.

If the engines are NOT producing the same power, it is because their
throttle positions and the propellers. Either may produce more thrust,
depending on the combination of the two parameters. For instance, the 150
HP engine could have controllable-pitch prop at flat pitch....it might turn
2300 with the throttle barely cracked.

If both engines are producing their rated horsepower, the 150 HP engine
produces more thrust. Its propeller must move more air in order to absorb
the higher power at the same RPM.

Ron Wanttaja

Ron Wanttaja wrote in message . ..
[Ron throws his oar in]

On Thu, 4 Dec 2003 20:24:00 -0500, "Mark" wrote:

Does a prop turning at 2300 rpm on a 150hp motor produce more thrust than a
prop spinning 2300 rpm on a 100 hp motor ?

Assuming the engines are mounted on a ground test stand, and the propellers
are "normal" (no paddlewheels, etc.):

If the props are identical fixed pitch propellers, the same thrust is
produced. Both engines are producing the same power.

If the engines are NOT producing the same power, it is because their
throttle positions and the propellers. Either may produce more thrust,
depending on the combination of the two parameters. For instance, the 150
HP engine could have controllable-pitch prop at flat pitch....it might turn
2300 with the throttle barely cracked.

If both engines are producing their rated horsepower, the 150 HP engine
produces more thrust. Its propeller must move more air in order to absorb
the higher power at the same RPM.

Ron Wanttaja


Typical static thrust for the engines in light airplanes is around
three pounds per horsepower, IIRC. This figure will vary somewhat with
prop efficiency and rated RPM. A lower rated RPM for a given HP will
produce more thrust, as less of the energy is lost to prop blade drag.
An example of this is the Thielert Centurion diesel now STCd for
the Cessna 172 N and P models, among others. It produces 135 Hp at
2300 instead of the 160 at 2700 from the Lyc it replaces, yet the
performance doesn't suffer at all. Drag is about 28% less on 16% less
power. These are my rough calculations and I'm open to correction. Try
http://www.centurion-engines.com/
Turning an engine much faster to increase HP has been a standard
trick of both auto manufacturers and aircraft engine makers, but so
much of the increased HP just goes into making more noise, especially
when driving a prop.

Dan

In article , Dan Thomas says...

Turning an engine much faster to increase HP has been a standard
trick of both auto manufacturers and aircraft engine makers, but so
much of the increased HP just goes into making more noise, especially
when driving a prop.

Unless you have a redrive installed so as to be able to use the additional hp.

Chuck S